Dynamic Compression Ratios... and blown engines

[06Speed6]

Originally Posted by FreeFlyFreak This is from the Cobb ATR help file: "Table values are the degrees of timing advance (shown in camshaft degrees) the VVT system will attempt to target. Higher values mean more intake camshaft advance, lower values mean less advance. You cannot retard (use a value less than zero) the intake camshafts." The max value I see in any table is 30* Maye we are talking at cross purposes here, 30* from what?? Im guessing 30* from the unadvanced position, whatever that is, but it could be relative to something else. You are saying 18*, but 18* from what?, maybe we are talking the same thing really? EDIT: I missed your post #31 ,so I dunno then??!!

There is part of the VVT that can go 30*, but at its narrowest point which is the point you have to measure from, its 18* of total advance from the original 104 LSA position.

Originally Posted by superskaterxes after talking to john from PTP the stock LSA is 103 or 104.

Nice work.

Originally Posted by superskaterxes also your not going to be able to see a full 18 deg just because of the physical limitations of the VVT. also 18 deg is ALOT of overlap and you might even run into piston interference or start touching the exhaust valves.

Its got 18* of physical movement at its narrowest point, apparently there is no interference.

Originally Posted by FreeFlyFreak So if I read that right....... at 18psi we would be better off zeroing that table out!!?? "Staying below 8.25 DCR is probably best for trouble free motoring" : for reference linky: Dynamic CR Am I reading it right??? Beuller? Beuller? My brain hurts. I need booze......... it helps me think more clearly. How are you guys calculating these numbers.

Boost Compression Ratio Calculator

Yeah I read that article among others, they all seem to say the same thing.

The 18psi has little to nothing to do with the dynamic compression ratio, if you change 18psi to 1psi you will notice that there is no difference in dynamic or static compression ratio, only in boost compression ratio which is boost pressure in bar * dynamic compression ratio + some constant probably.

[djuosnteisn]

To show a more tangible side of this VVT discussion, here is a log i took which prompted me to start messing with the VVT tables. In this log 5500rpm was all 10's




Here is my latest VVT table, simply smoothed the 5500 rpm to 7's.



You can see a damn significant bump up in the maf g/s, which usually corresponds pretty close to actual hp.

[Lex]

Boost does not change DCR since by definition DCR calculates a change in volume - just like static CR calculates a change in volume of the cylinder as the piston moves from BDC to TDC.

Boosted CR simply relates the resulting compression if there is a pressure differential from atmospheric. At sealevel absolute atm pressure is 14.7psi. When RUNNING 14.7psi of boost, you double the amount of pressure inside the cylinder. So now your boosted DCR is double what your non boosted DCR is. So boosted DCR is DCR * ((boost pressure on your gauge +14.7)/ 14.7psi)

[superskaterxes]

i just took this log and as you can see the MAF g/s HIGHLY correlates to the VVT and i seem to be hitting target VVT* pretty well.



also this is copied out of the ATR tuning guide.

VVT Intake Cam Adv. VVT stands for Variable Valve timing and is a variable camshaft phasing control technology used by Mazda. Hydraulic oil pressure is used to advance the intake camshaft timing in an effort to optimize power through the entire engine speed and load range. Table Description - This table represent the amount of intake camshaft advance represented in camshaft degrees. The table is referenced by Engine Speed on the x-axis and by Calculated Engine Load on the yaxis. Table values are the degrees of timing advance (shown in camshaft degrees) the VVT system will attempt to target. Higher values mean more intake camshaft advance, lower values mean less advance. You cannot retard (use a value less than zero) the intake camshafts. The system is closed loop and will make attempts to compensate for differences in oil pressure, temperature, oil viscosity, etc. As the system is hydraulically controlled by engine oil, changes may not instantaneously occur. Tuning Tips - Tuning these tables takes patience and the ability to accurately quantify if changes are resulting in improvements or not. Depending on your level of modification, there are appreciable gains to be made through VVT intake camshaft advance tuning. For most cars that are not very heavily modified, the gains will be focused at low to mid-range Engine Speed across all Engine Loads. Partial throttle (ie: not full load, WOT) gains can be significant as well, provided you have the equipment (load bearing dyno) capable of accurately quantifying any gains from these changes. It is ultimately your responsibility to understand in more precise details about what setting work best for your hardware combination. This is part of the job of tuning. Keep in mind that the engine is an air pump and functions as a system of all it's parts. Changes in your VVT intake camshaft advance can result in changes in your measured A/F Ratio, fuel consumption, optimal ignition advance, boost control, etc. Precautions and Warnings 1) If you data log slightly different VVT intake camshaft advance from what you've tuned for in the table, this is typically normal. However if your data logs show large disparities between the commanded VVT intake camshaft advance shown in this table and what you are data logging, this potentially means you have a mechanical issue with the hydraulic oil pressure control system. 2) The system has safe guards to prevent valve-to-piston interference ONLY when using stock pistons designed for the cylinder heads used and stock valvetrain including stock camshafts. If you are using after market pistons or camshafts, you are advised to contact the supplier as to the safe amount of VVT intake camshaft advance you may run. 3) If you increase the VVT intake camshaft advance values and the VVT data you are logging does not increase, this may mean you have reached a designed mechanical limitation. The camshaft advancing mechanism may simply not be able to increase intake camshaft phasing beyond a mechanically limited point by design.

[FreeFlyFreak]

Originally Posted by 06Speed6 The 18psi has little to nothing to do with the dynamic compression ratio, if you change 18psi to 1psi you will notice that there is no difference in dynamic or static compression ratio, only in boost compression ratio which is boost pressure in bar * dynamic compression ratio + some constant probably.

Originally Posted by Lex Boost does not change DCR since by definition DCR calculates a change in volume - just like static CR calculates a change in volume of the cylinder as the piston moves from BDC to TDC. Boosted CR simply relates the resulting compression if there is a pressure differential from atmospheric. At sealevel absolute atm pressure is 14.7psi. When RUNNING 14.7psi of boost, you double the amount of pressure inside the cylinder. So now your boosted DCR is double what your non boosted DCR is. So boosted DCR is DCR * ((boost pressure on your gauge +14.7)/ 14.7psi)

OK, I got that now, it is obvious once you point it out.
But surely what matters knock wise is the the boosted DCR........
Wouldnt boosted DCR be more related to knock than just DCR??
What part of the puzzle am I missing here?

[Lex]

To add - having such a high DCR once again brings us to the fact that this engine is efficient - and built to be very close to peak efficiency in the low RPMs. More boost in the lower RPM is not what it needs. That's for longevity.

Knock marks on the top of pistons aren't there so this makes me think DI is letting us get away with a higher DCR.

Now, let me be the devil's advocate and suppose that with such a high DCR, an injector, let's say, remains open during the entire compression stroke. Remember that if this was a port injected engine, the fuel would simply spray on the back of the valve and the engine would "bog" at the next stroke. Our injector being inside the combustion chamber however sprays inside the bore with all 1700psi of pressure behind it. How much do these injectors flow? I can tell you how quickly that compression ratio goes through the roof and the rod goes through the block.

Anyone consider the failure rate of the injectors? How about after some wear, deposits, and high heat exposure? I know even dealers blamed injectors for blowing motors. I can assure you there is enough fuel there to sink an engine and like 06speed6 mentioned, we'd see no marks in any other piston that any liquid was ingested.

Sorry for the off topic but DCR talk had me thinking and this would explain why cars let go so randomly.

Originally Posted by FreeFlyFreak OK got that now, it is obvious once you point it out. But surely what matters knock wise is the the boosted DCR........ Wouldnt boosted DCR be more related to knock than just DCR?? What part of the puzle am I missing here?

Yes, with boost, you increase the potential for knock because pressure is increased as is temperature and the density of the mixture. Ultimately a lower DCR will let you run more boost before knocking. It's all a game of tradeoffs.

[FreeFlyFreak]

Originally Posted by Lex Anyone consider the failure rate of the injectors? How about after some wear, deposits, and high heat exposure? I know even dealers blamed injectors for blowing motors. I can assure you there is enough fuel there to sink an engine and like 06speed6 mentioned, we'd see no marks in any other piston that any liquid was ingested. Sorry for the off topic but DCR talk had me thinking and this would explain why cars let go so randomly.

Injector failure is as good a reason as any, in fact better than most, if you ask me.
Precisely because of the glaring lack of piston damage in almost all rod failures.
Injector failure fits the evidence, or lack thereof, better than most theories that get thrown around.

I have yet to see the part throttle knock people talk about.
I get the 183-187* Coolant knock, which I attribute to the sensor hearing the thermostat cracking open.
I get occasional throttle lift knock, not worried about it.
And I get WOT knock in 4-5th from 4000-5700 rpm where the sensor goes deaf, the rpm varies depending on AFR and load aggressiveness of the map.
The only way I can get rid of that knock (so far) is to butcher the map, by getting rid of a lot of load, less than OTS, some parts less than stock, OR add a little xylene or Torco to my California 91 Octane piss water, in which case I can get rid of WOT knock totally, and run much much higher load maps.
This VVT may be a way that I can increase MAF and load without getting knock because I am decreasing DCR.... maybe.
But it will have to wait because my tank is full of octane boosted fuel.

[djuosnteisn]

Originally Posted by Lex Boost does not change DCR since by definition DCR calculates a change in volume - just like static CR calculates a change in volume of the cylinder as the piston moves from BDC to TDC.

Not sure if this was directed to my posted data log or not, but all i was showing was the drastic increase in maf g/s related to the VVT table.




So if less advance lowers and broadens the torque curve, i'm thinking with breathing mods on this car, it makes sense to expand this low value region into the higher load points on the table. Lower compression at the points of peak torque (esp at our extremely low rpm) should be mandatory.

06speed6, thanks for pretty much explaining the whole theory behind this VVT stuff. It makes much much much more sense now.

[FreeFlyFreak]

Originally Posted by djuosnteisn Not sure if this was directed to my posted data log or not, but all i was showing was the drastic increase in maf g/s related to the VVT table. So if less advance lowers and broadens the torque curve, i'm thinking with breathing mods on this car, it makes sense to expand this low value region into the higher load points on the table. Lower compression at the points of peak torque (esp at our extremely low rpm) should be mandatory. 06speed6, thanks for pretty much explaining the whole theory behind this VVT stuff. It makes much much much more sense now.

Lex's post was for me.

That is a pretty impressive top end increase using just a few degrees of VVT.
Is there a reason you then backed it off at 5500 from 10 to 7? You said that log was 5500 @ 10, but then your current table is 5500 @ 7..... Knock or anything?

[fjames]

OP, you should edit your first post to correct backward numbers.

I changed mine a long time ago, just based on logic. Intake valve advance=increase in dynamic compression, so it increases efficiency which means better mileage, lower emissions and more torque. It only works at low rpm because the breathing restriction is a negative at higher piston speeds. I figured the factory would push it as far as they could, so I backed it off to make room for ~30% boost increase. Recently I backed it off even more, just because.

Oh, I've logged 20+ deg for what it's worth.

Below is the old one I ran for months and the new one I've had for a few weeks. You can't help wondering about all the PT pops relating to this to some degree (I made a pun!) but it would probably be just one of many contributing factors. Unless maybe the mechanism itself was malfunctioning, if that's even possible.

Old



New

[FreeFlyFreak]

^^^^^^^^^^^^^^^^^^^^ That makes sense logically.

But........... how do you reconcile that with djuosnteisn's jump in MAF at 5500rpm when he advanced the VVT to 10 at that point?
After all it is MAF that matters, not boost pressure, MAF is the air that is getting through to the cylinder.
To be devils advocate, it is possible your (fjames's) increased boost pressure could be because less air is getting to the cylinder because of the retarded valve timing, therefore building more pressure in the Manifold...... not saying it is, just being contrary because that is how I learn ;-):
See more post after the image.




I see no reason to retard the valve timing unless you are getting knock.
I am getting knock on CA91 fuel and may try this attack as nothing else has worked.
But for now I am having much more fun and 0 knock using Torco accelerator. LOL

[fjames]

I haven't gotten there yet I've been concentrating on the peak load areas. I found his chart very interesting - I've been studying my logs a lot lately, and there's definitely a relationship between load and vvt as they both tail off, but I don't know if it's coincidental or causal. I'm happy with mine up to 4500, but I'll be looking at what to do from 5K-6K.

Even though you can't compare cars, no way of knowing what the cam grind is, when I was researching all this I found a reference to the early Porsche system. The guy said it was an on/off setup with 25 deg advance (intake) from just off idle to almost 6K. The car probably didn't have much more than another 1000 rpm to redline lol. I've been assuming all along that the obvious drop-off in load as you pass 4.5K or thereabouts was just the way it is, turbo efficiency, flow characteristics and whatever. But if you could get a little more load for the same boost with a few degrees of valve timing, that would be sweet.

I've got my power induced KR and my boost spike pretty well licked though, I thought I was almost done. If my last changes do what I expect, I will be done, so exploring high rpm vvt will be a new story for me - I have to get my head around starting a new path.

[ljudgeii]

Not sure if I can help, but thanks to Christian I was able to see a change that was made in my PROTune map, and oddly enough the VVT was changed. to this

Code:
0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	4.00	0.00	0.00	0.00
0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	4.00	0.00	0.00	0.00
0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	4.00	0.00	0.00	0.00
0.00	0.00	0.00	0.00	0.00	0.00	0.00	5.00	5.00	5.00	4.00	0.00	0.00	0.00
0.00	5.00	5.00	5.00	0.00	0.00	0.00	10.00	10.00	10.00	4.00	0.00	0.00	0.00
0.00	10.00	10.00	10.00	11.00	12.00	13.00	14.00	12.00	10.00	4.00	0.00	0.00	0.00
0.00	15.00	15.00	15.00	15.00	15.00	15.00	15.00	12.00	10.00	4.00	0.00	0.00	0.00
0.00	15.00	20.00	20.00	20.00	20.00	20.00	20.00	20.00	20.00	4.00	0.00	0.00	0.00
0.00	20.00	20.00	20.00	20.00	20.00	20.00	20.00	20.00	20.00	4.00	0.00	0.00	0.00
0.00	20.00	20.00	20.00	20.00	20.00	20.00	20.00	20.00	20.00	4.00	0.00	0.00	0.00
0.00	25.00	25.00	25.00	25.00	25.00	20.00	20.00	20.00	20.00	4.00	0.00	0.00	0.00
0.00	25.00	25.00	25.00	25.00	25.00	20.00	20.00	20.00	20.00	4.00	0.00	0.00	0.00
0.00	30.00	30.00	30.00	30.00	30.00	20.00	20.00	20.00	20.00	4.00	0.00	0.00	0.00
0.00	30.00	30.00	30.00	30.00	30.00	20.00	20.00	20.00	20.00	4.00	0.00	0.00	0.00
0.00	30.00	30.00	30.00	30.00	30.00	20.00	20.00	20.00	20.00	4.00	0.00	0.00	0.00
0.00	30.00	30.00	30.00	30.00	30.00	20.00	20.00	20.00	15.00	4.00	0.00	0.00	0.00
0.00	30.00	30.00	30.00	30.00	30.00	20.00	20.00	20.00	15.00	4.00	0.00	0.00	0.00
0.00	30.00	30.00	30.00	30.00	30.00	20.00	18.00	18.00	15.00	4.00	0.00	0.00	0.00
0.00	30.00	30.00	30.00	30.00	30.00	20.00	18.00	18.00	15.00	4.00	0.00	0.00	0.00
0.00	30.00	30.00	30.00	30.00	30.00	20.00	18.00	18.00	15.00	4.00	0.00	0.00	0.00
0.00	30.00	30.00	30.00	30.00	30.00	20.00	18.00	18.00	10.00	4.00	0.00	0.00	0.00
0.00	30.00	30.00	30.00	30.00	30.00	20.00	18.00	18.00	10.00	4.00	0.00	0.00	0.00
0.00	30.00	30.00	30.00	30.00	30.00	20.00	18.00	18.00	10.00	4.00	0.00	0.00	0.00
0.00	30.00	30.00	30.00	30.00	30.00	20.00	18.00	18.00	10.00	4.00	0.00	0.00	0.00
0.00	30.00	30.00	30.00	30.00	30.00	20.00	18.00	18.00	10.00	4.00	0.00	0.00	0.00
0.00	30.00	30.00	30.00	30.00	30.00	20.00	18.00	18.00	10.00	4.00	0.00	0.00	0.00
0.00	30.00	30.00	30.00	30.00	30.00	20.00	18.00	18.00	10.00	4.00	0.00	0.00	0.00
0.00	30.00	30.00	30.00	30.00	30.00	20.00	18.00	18.00	10.00	4.00	0.00	0.00	0.00
0.00	30.00	30.00	30.00	30.00	30.00	20.00	18.00	18.00	10.00	4.00	0.00	0.00	0.00
0.00	30.00	30.00	30.00	30.00	30.00	20.00	18.00	18.00	10.00	4.00	0.00	0.00	0.00
0.00	30.00	30.00	30.00	30.00	30.00	20.00	18.00	18.00	10.00	4.00	0.00	0.00	0.00
0.00	30.00	30.00	30.00	30.00	30.00	20.00	18.00	18.00	10.00	4.00	0.00	0.00	0.00

I have no Idea why these changes were made so don't ask me all I can tell you is the mods I had for the Map and what I wanted done to it:
Mods
COBB SRI
GHL CBE
Corksport DP
CP-e HPFP
TURBOXS FMIC
DNP Exhaust Mani
TURBOSMART BOV
DO Stg2 MI
Denso ITV22 plugs

I wanted Boost targets of
1st = 10-12
2nd = 12-14
3rd = 20-22psi
4th = 20-22psi
5th = 20-22psi
6th = 20-22psi

[fjames]

Just a quick note, too tired to think it through, but i found a few old logs of ots maps and one of my old ones that would have had the ots vvt mapping, that had load and/or MAF logged. Basically it looks like the trend off in load is virtually identical to my current maps. MAF is all over the place - higher with less boost, lower with higher load, I can't find a correlation. Of course weather was much colder when I was doing that logging.

In case it wasn't obvious I guess I should say I tune by load. If I raise boost and load doesn't increase, then I assume it didn't do anything useful. I've been concentrating on the 5-6K region for he last few weeks, trying to figure a way to get some power there which is why the idea of playing with vvt up there caught my attention. So far, what I've found is less is more as far as boost - there's just nothing to be done for it.

Still, I'm intrigued enough to probably check it out. One of my rules for life is never do something because someone else says it's a good idea, I have to find a way that it fits in my head first. I've found it a good way to keep from making mistakes that get you lost.

Edit: Don't forget that djuosnteisn has a gt30, so who knows how his findings relate to the stocker. It's also interesting that right at the factory wall (6K) is where the stock vvt goes positive again, after zeroing at 5.5.

[06Speed6]

I wonder if zeroing the chart past 3k rpm would let the turbo breathe better, that would be a more logical test for wot responce.

First post is edited and revised, go back and read it.

[Fobio]

there's gold in them there posts...

[djuosnteisn]

Originally Posted by FreeFlyFreak That is a pretty impressive top end increase using just a few degrees of VVT. Is there a reason you then backed it off at 5500 from 10 to 7? You said that log was 5500 @ 10, but then your current table is 5500 @ 7..... Knock or anything?

Originally Posted by FreeFlyFreak ... how do you reconcile that with djuosnteisn's jump in MAF at 5500rpm when he advanced the VVT to 10 at that point?

free fly, i backed it off at 5500 to 7 cause the point in my log where the maf jumped seemed to correlate with the drop from 10 to 4 degrees.

IMO (and i haven't had a chance to test it much more lately), lower values in the higher rpms is the best, and results in higher maf.

I think some zeros in my map would be very interesting, and i'll test on it this weekend. I also think that since i'm using a BT that's happily efficient at the high rpm / high boost area, it would be a legitimate study of the VVT effects, cause there would be no issues with turbo efficiency or anything like that.

[FreeFlyFreak]

Its funny how it all ties in to what some guys have been saying for a while..........
Drive it like a Grandma.....
Or Drive it like you stole it.....
And you wont blow.

But drive it normal and boom.

[itzl0l]

lmao

[06Speed6]

lol thats funny, but also probably true.

[Lex]

Another representation of cylinder pressure as DCR is increased (intake valve closes sooner ABDC)

So if the problem was overloading the rods, then we should just set that VVT to a lower number in the "BOOM" zone at the expense of torque. It would have a similar effect to running lower boost at lower RPMs.

But is the rod overloading simply through combustion pressure really the issue here?

06speed6 - how much cylinder pressure do you think you'd need (read boost) before you think we'll start disrupting the ability to deliver enough fuel - especially on a weaker pump? At 25psi we're at at 215psi compression pressure. Combustion pressure shown in the diagram below is much higher of course.

[itzl0l]

Originally Posted by Lex 06speed6 - how much cylinder pressure do you think you'd need (read boost) before you think we'll start disrupting the ability to deliver enough fuel - especially on a weaker pump? At 25psi we're at at 215psi compression pressure. Combustion pressure shown in the diagram below is much higher of course.

Ever wonder if the ECU is trying to supply so much fuel (due to high dcr + us running much richer than most DI cars) if the ecu maybe just kinda says fuck it and keeps the injector open the whole cycle instead of kind of pulsing...maybe fuel then begins to puddle or the injector sticks.

I've been bugged for a while on why we run so much richer then all the other DI cars....maybe we see pt knock and try to bandaid it with more fuel and its actually making things worse

[Lex]

Originally Posted by itzl0l Ever wonder if the ECU is trying to supply so much fuel (due to high dcr + us running much richer than most DI cars) if the ecu maybe just kinda says fuck it and keeps the injector open the whole cycle instead of kind of pulsing...maybe fuel then begins to puddle or the injector sticks. I've been bugged for a while on why we run so much richer then all the other DI cars....maybe we see pt knock and try to bandaid it with more fuel and its actually making things worse

Nothing is done without purpose. Mazda did not by chance have the car run so rich. Whether it's to protect the emissions equipment or the motor itself. Also note how much richer the car runs if it encounters knock on top of it pulling timing. That's another clue.

[FreeFlyFreak]

Originally Posted by Lex Also note how much richer the car runs if it encounters knock on top of it pulling timing. That's another clue.

Something to note.
I knock at high rpms using cali 91.
I can move my knock rpm range at will by varying the AFR.
Too rich is just as bad as too lean from what I have experienced with my car.
First thing I tried was richening it up, that map knocked worse than anything else I tried.
Leaning it out helped, but only to a point.

Right now I am running a little torco. It is the only way so far that I have been able to get rid of all my knock with this CA91 oct. other than butchering the load to less than OTS.
Im basically going to make a boosted octane map, tuning out knock with the 91 was next to impossible.
I'll try the 91 again when I have finished this map, I am hoping that vvt table will help me out there, lower those numbers over 4K (all my knock is over 4k usually 4.5-5.5), it is the only thing I havent tried.

[06Speed6]

Originally Posted by Lex Another representation of cylinder pressure as DCR is increased (intake valve closes sooner ABDC) So if the problem was overloading the rods, then we should just set that VVT to a lower number in the "BOOM" zone at the expense of torque. It would have a similar effect to running lower boost at lower RPMs. But is the rod overloading simply through combustion pressure really the issue here? 06speed6 - how much cylinder pressure do you think you'd need (read boost) before you think we'll start disrupting the ability to deliver enough fuel - especially on a weaker pump? At 25psi we're at at 215psi compression pressure. Combustion pressure shown in the diagram below is much higher of course.

That chart is probably accurate, 1.5 is about 220psi. It isnt stated, like 75% of the charts and diagrams they attach to their patents, but the scale of the chart is mpa. It would make their patents alot easier to read if they listed what unit of measurement they were using and the number of units of said measurement. Some of them are worthless lines with no reference.

I am assuming you are talking about net injection pressure. I believe John @ PTP and some others have stated that around 1000psi of cylinder pressure the injector seals begin to fail, so I assume that most of us are running less than 1000psi. Now how they know all this is beyond me because I have the formula that some Harvard prof calculated to find the cyl pressure but ill be damned if I am ever going to have enough information to ever come close to working it. It is *very* complicated to find the peak pressure.

If fuel delivery and proper atomization are related to the differential in pressure between the rail and the cylinder, then I would look at our idle parameters for a clue as to what minimum pressure is needed. If we assume 180psi compression and injection at the top of the compression stroke, then we can take our 400psi of fuel pressure and subtract 180psi which gives us ~220psi of fuel pressure differential.

Now, if the injection event occurs at BDC where we have only atmospheric pressure then we would need to have ~400psi of fuel pressure.

But lets not forget, if the injection event occurs BBDC on the intake stroke when we have a vacuum condition in the cylinder then we would need >400psi of fuel pressure.

For the sake of argument, im going to throw out there that the injector opens about 40* BBDC and it does not inject at all on the compression stroke, which is contrary to what 95% of the people on here think. If thats the case, then we would need >400psi of net rail pressure to properly inject and atomize the fuel. Also note that boost isnt much of a factor because the cylinder will always be in a vacuum condition on the intake stroke regardless of how much boost is in the manifold.

Now back to the rods and peak cylinder pressure, I bet we can ghetto calculate a number...

If 8.2:1 DCR @ 1 atmosphere = 180psi cyl pressure then 180/8.2=21.95

And at 25psi our DCR is 23.17:1 then 23.17*21.95=508.6psi of cyl pressure @ 25psi of boost pressure. Thats quite a bit and the combustion process hasnt even started yet.

And to make it better...

If we take the area of a 3.445" piston which is 9.32113sq" * 508.6psi = 4694.121lbs of force on the crown of the piston @ TDC pre combustion @ 25psi boost pressure.

Note that you can subtract 1000+lbs of that due to the crankstaft trying to slow the velocity of the rod/piston as it nears TDC. Thats why 2 cycle engines are superior to 4 cycle engines for high rpm use when both engines use the same rod/piston.

Also note that in simple form engine torque is directly related to cylinder pressure so on a dyno graph the point of highest torque is also the point of highest cyl pressure regardless of other operating parameters.

[superskaterxes]

i dont think cylinder pressure has anything to do with rods breaking. is whoosh can make 386 awhp on a GT 35 on stock block/tune then there must be another reason people are blowing on stock turbo @ 300whp.


btw how many people have blown with a BT and stock block? last i checked not many

[Laloosh]

Originally Posted by Lex Nothing is done without purpose. Mazda did not by chance have the car run so rich. Whether it's to protect the emissions equipment or the motor itself. Also note how much richer the car runs if it encounters knock on top of it pulling timing. That's another clue.

do you even know why cars run rich when they knock? Hopefully you realize that timing and fuel are related, more time will run learner, less timing will run richer. This is not a clue, this is common sense

Originally Posted by FreeFlyFreak Something to note. I knock at high rpms using cali 91. I can move my knock rpm range at will by varying the AFR. Too rich is just as bad as too lean from what I have experienced with my car. First thing I tried was richening it up, that map knocked worse than anything else I tried. Leaning it out helped, but only to a point. Right now I am running a little torco. It is the only way so far that I have been able to get rid of all my knock with this CA91 oct. other than butchering the load to less than OTS. Im basically going to make a boosted octane map, tuning out knock with the 91 was next to impossible. I'll try the 91 again when I have finished this map, I am hoping that vvt table will help me out there, lower those numbers over 4K (all my knock is over 4k usually 4.5-5.5), it is the only thing I havent tried.

Did you check fuel pressure while you richened it up? You were probably exceeding fuel pump limits

Originally Posted by superskaterxes i dont think cylinder pressure has anything to do with rods breaking. is whoosh can make 386 awhp on a GT 35 on stock block/tune then there must be another reason people are blowing on stock turbo @ 300whp. btw how many people have blown with a BT and stock block? last i checked not many

quoting rons number is getting old. It dynoed once, at the power level. How many blew up with bigger turbos.....im gonna go and guess 80 percent.

[superskaterxes]

Originally Posted by Laloosh How many blew up with bigger turbos.....im gonna go and guess 80 percent.

id be willing to bet less then 15% of blown motors had BT on them. just look at blown resource thread

[Laloosh]

Originally Posted by superskaterxes id be willing to bet less then 15% of blown motors had BT on them. just look at blown resource thread

your math skills are off today. You asked how many BT blew up right. So if you have 10 BT owners im saying 8 of them blew up. Your saying....im not sure what your saying because that isnt the question you asked.

[FreeFlyFreak]

Originally Posted by Laloosh Did you check fuel pressure while you richened it up? You were probably exceeding fuel pump limits

Fuel pressure was good. 1600-1700

[superskaterxes]

Originally Posted by Laloosh your math skills are off today. You asked how many BT blew up right. So if you have 10 BT owners im saying 8 of them blew up. Your saying....im not sure what your saying because that isnt the question you asked.

im saying out of 10 stock motors that blew, 2 of them had BT's

[bf360]

Originally Posted by Laloosh do you even know why cars run rich when they knock? Hopefully you realize that timing and fuel are related, more time will run learner, less timing will run richer. This is not a clue, this is common sense Did you check fuel pressure while you richened it up? You were probably exceeding fuel pump limits quoting rons number is getting old. It dynoed once, at the power level. How many blew up with bigger turbos.....im gonna go and guess 80 percent.

the last part is funny, i remember when u were convinced that a gt35r is safer than the stock turbo, which i still believe is true.

Of all the big turbos, besides the ones that blew because of a wg line, how many have blown up?

[Lex]

Originally Posted by Laloosh do you even know why cars run rich when they knock? Hopefully you realize that timing and fuel are related, more time will run learner, less timing will run richer. This is not a clue, this is common sense

Looshie, looshie, the car commands more fuel when knock is encountered along with lowering timing.

In less kind words ... bitch, please.

[Laloosh]

Originally Posted by superskaterxes im saying out of 10 stock motors that blew, 2 of them had BT's

because out of 10 stock motors maybe only 2 even go big turbo. Once again your looking at this wrong

Originally Posted by Lex Looshie, looshie, the car commands more fuel when knock is encountered along with lowering timing. In less kind words ... bitch, please.

once again, stating baby facts. Why dont you post something that isnt common sense already. Show me a log of commanded af ratios during a knock event. Id like to see just how much difference knock causes as apposed to getting rich by timing alone

Originally Posted by bf360 the last part is funny, i remember when u were convinced that a gt35r is safer than the stock turbo, which i still believe is true. Of all the big turbos, besides the ones that blew because of a wg line, how many have blown up?

I stil think a BT is safer, however its gotta be bigget then a gt30. Of all the stock turbos, how many blew up? Alot, people blow everyday and it stays off the boards. How many blew up WOT, a couple blew wot back in the day. I remember a memember called ms6mike or somethign like that. Blew at 5500rpm floored. You fools are all impressed that not to many blew wot.....were under 350 whp people, that not power, that baby shit that any motor now a days could take.

[06Speed6]

Laloosh, we are talking about the effect of the dynamic compression ratio on knock. Extra fuel wont save you from knock caused by high compression.

We are asssuming correct a/f for this discussion.

If you had come in and said something about octane, you would have proved yourself usefull, but as it stands you can take your a/f ratios and gtfo of my non As MSF Turns thread.

[djuosnteisn]

I was reading a bit more about VVT last night in one of my books, and it mentioned about how DOHC were great in the old days cause you could just tweak and fine tune the LSA while on a dyno. We're pretty spoiled with ecu control over it.

It mentioned that a wider LSA is more beneficial in the higher rpms with small turbos that are real restrictive with exh mani pressure >> intake boost pressure. But with upgraded bigger turbos and better exh manis, up to about 5% gains can be had by reducing the LSA slightly (creating a bit more over lap) by roughly 3-6 degrees.

With atr, i'd imagine that higher numbers correspond to more cam advance (and thus more overlap), and that would explain why the values fall to 4's and 0's towards redline with the k04. But with BT's i think these number could be increased a couple degrees to find the new sweet spot. Can someone confirm my logic? Higher VVT values = more overlap (less lobe separation angle)?

[papajohn026]

lots of nerdery in here. keep it up

[06Speed6]

Originally Posted by djuosnteisn I was reading a bit more about VVT last night in one of my books, and it mentioned about how DOHC were great in the old days cause you could just tweak and fine tune the LSA while on a dyno. We're pretty spoiled with ecu control over it. It mentioned that a wider LSA is more beneficial in the higher rpms with small turbos that are real restrictive with exh mani pressure >> intake boost pressure. But with upgraded bigger turbos and better exh manis, up to about 5% gains can be had by reducing the LSA slightly (creating a bit more over lap) by roughly 3-6 degrees. With atr, i'd imagine that higher numbers correspond to more cam advance (and thus more overlap), and that would explain why the values fall to 4's and 0's towards redline with the k04. But with BT's i think these number could be increased a couple degrees to find the new sweet spot. Can someone confirm my logic? Higher VVT values = more overlap (less lobe separation angle)?

Higher VVT valves = more LSA = less overlap.

[djuosnteisn]

Technical Specs & Information


I was going off this diagram, and the thinking that since the exh valve "leads" the int valve, advancing the intake valve would create more overlap.

Also, since more overlap increases lower rpm torque, that would explain why our current VVT table has higher numbers in the lower rpms and lower numbers near redline (less overlap better in higher rpm turbo applications).

I agree more LSA = less overlap, I just don't think this correlates with higher cam advance (higher VVT values).

If i'm just being incredibly stupid, i'm sorry, but it just doesn't make sense that the stock map would have less overlap and low rpms (pushing power to higher rpms) and more overlap at high rpms (pushing power to low rpms).

[phantom3]

Originally Posted by 06Speed6 Higher VVT valves = more LSA = less overlap.

Originally Posted by djuosnteisn Technical Specs & Information I was going off this diagram, and the thinking that since the exh valve "leads" the int valve, advancing the intake valve would create more overlap. Also, since more overlap increases lower rpm torque, that would explain why our current VVT table has higher numbers in the lower rpms and lower numbers near redline (less overlap better in higher rpm turbo applications). I agree more LSA = less overlap, I just don't think this correlates with higher cam advance (higher VVT values). If i'm just being incredibly stupid, i'm sorry, but it just doesn't make sense that the stock map would have less overlap and low rpms (pushing power to higher rpms) and more overlap at high rpms (pushing power to low rpms).

Think of it this way. when you advance it your not advancing it ahead if it current position, your advancing it in the combustion cycle (Read: making it happen sooner "Advanced").

More LSA "Lobe separation angle" = the angle between the lobes.
If you increase the "Angle" you are moving the lobes further apart giving them less overlap.
Less overlap means a higher VVT Value or "retarding the cam"

EDIT: I re-read you post, and now I'm confused too... mayby THAT'S WHY WE'RE NOT MAKING POWER!