compression ratio

[Boosted_One]

Going to a .060 over JE

 

What do you guys think of the compression ratio? I had 8:1's in and I I am leaning towards 7:1 now.

 

My head was milled twice and the block was decked once so far.

 

Thanks

[JasonC]

Rough calculations (slightly educated guess. LOL) says that with the machine work you have had done those 8-1 were more like 9.5-1 or better. That milling adds up quick. Could have been your demise. Just my .02 cents.

[DUTCHGPS]

Hi Jason,

 

If you still have got the block apart this would be a perfect time to do some measuring.

Using a burette, measure the amount of cc's in the combustion chamber and the amount in the "bowl" of the piston while the piston is in the block and at TDC.

Find the last used head gasket, measure it's "compressed thickness", convert that to cc's, add all the cc's together.

Do the basic calc's on "swept volume" using your stroke and rebored bore.

It's actually the only way to find out the true (static/mechanical) compression ratio.

 

Kind Regards,

 

DUTCHGPS

 

'88 Starion 4G54

'82 Starion 4G63

 

P.s. : If you find CR to be in the region of around 9:1 I'd say about 15 psi to be the very max of the 4G54 assuming a VERY good intercooler and absolutely correct A/F ratios 12.5:1 or even richer mixes.

[Lizzord30]

Even tho spool up may not be quite as well i would go with 7:1, mainly becuse of the turbo you are running, to get it in its efficency range you need too run righer boost then 8:1 will alow. You got a turbo that can do the work so dont try to use comrpression to do it for you.

[Tim_C.]

8:1 pistons are plenty low for compression. 7:1 just doesn't have the power for around town driving. You say "milled twice", and "decked once". It was only for making them true, correct? You only lose .020 doing that on the head, and less usually on the block, unless you did it to gain compression. Then it is enough to be concerned about. Besides, 8.2:1 is a good ratio still. No way that is over 8.5:1 even if you need to mill again.

Compression was not the problem! We all know that. Fuel quality at over 15 PSI boost was the problem. You still can't run 91-93 octane at over 14 PSI boost even with 7:1.

The air fuel readings were low too. It just needed better fuel, and more of it. Nothing to do with compression. Well, it had to do with compression, but that is not why things went wrong. Not having it set-up right, bad gas, not enough fuel, timing way off, is why. Plus the motor was being winged at a lot higher RPM than it wanted to make power at. Inefficiency heats stuff up in a hurry.

I'm not saying it was wrong to have done the testing that way. A man has to do what he needs to, in order to learn. That's what it's all about. I'll say that I know Mike K. knows more about what he's doing than I do, so if I had his set-up, it probably would not have made it to the Dyno!

I do know one thing. 8:1-8.5:1 is not a problem compression for these cars even without MPI. Let alone having the means to handle it with MPI.

All we found out here, is that it doesn't end at MPI. MPI in itself isn't some big cure-all for our fueling needs to handle high boost.

I would not give up on getting it right by making it harder to ruin things. 7:1 will have 500 RPM more lag, & no off boost power even with MPI.

Our engines are flowing a lot more volume than any other turbo 4. The fuel line really isn't big enough for the cubes. No, go 8:1 & learn from your set-up, and just make the needed improvements. I think you will go into this one with all the bases covered. Going 7:1 means you think you can't cover the bases. You can, and reliably.

 

Tim C.

[Lizzord30]

8:1 pistons are plenty low for compression. 7:1 just doesn't have the power for around town driving.

 

I would not give up on getting it right by making it harder to ruin things. 7:1 will have 500 RPM more lag.

All we found out here, is that it doesn't end at MPI. MPI in itself isn't some big cure-all for our fueling needs to handle high boost.

Some ppls power demands are diff some ppl are happy having tracktion problems in 3rd with street tires other want that with drag radials and yet others want it with wrinkl walls . I know my 7:1 (or lower) has great spool up, get full boost by 3k. But with my turbo it doesnt make big power till 4-4.5k boost doesnt change but when the rpms get their it just takes off. (this may have something to do with my cam, stock which i am changing to 284H). It may have 500 RPM more lage but it doesnt matter at all if the turbo doesnt do anything till 4.5k. Who knows it may be diff with 20g but on mine the spool up isnt an issue. The issue is beeing able to run enof boost to get it to where the turbo shines.

But if i was you i would find the accutaly compression of your engine with the milling and stuff you have had.

And about your last comment very true the car is not one mod you need others to go good with it or it wont be fast at all.

[Tim_C.]

Some ppls power demands are diff some ppl are happy having tracktion problems in 3rd with street tires other want that with drag radials and yet others want it with wrinkl walls . I know my 7:1 (or lower) has great spool up, get full boost by 3k. But with my turbo it doesnt make big power till 4-4.5k boost doesnt change but when the rpms get their it just takes off. (this may have something to do with my cam, stock which i am changing to 284H). It may have 500 RPM more lage but it doesnt matter at all if the turbo doesnt do anything till 4.5k. Who knows it may be diff with 20g but on mine the spool up isnt an issue. The issue is beeing able to run enof boost to get it to where the turbo shines.

But if i was you i would find the accutaly compression of your engine with the milling and stuff you have had.

And about your last comment very true the car is not one mod you need others to go good with it or it wont be fast at all.

 

Yeah, the turbo staying in its hi-efficiency range is the #1 concern for power. I guess it matters what turbo you run and what you want, but I really hate driving a 7:1 car around. It just doesn't get it for me, so it's my opinion from my perspective. I always, always wish it had more off the line. I live at 6,000' altitude, so I have less air to deal with, & probably a big factor to why I don't like 7:1. It just doen't get it up here. So, I forgot that 7:1 runs much better down low.

Tim C.

[chiplee]

Sorry Tim but I have a bit of an issue with your views on compression there.  You may be correct that 8:1 is fine but it's this statement that I have to say something about, "Compression was not the problem! We all know that. Fuel quality at over 15 PSI boost was the problem. You still can't run 91-93 octane at over 14 PSI boost even with 7:1."  Call it a difference of opinion but, no offense, it's really not a matter of opinion.  I think I went into this somewhere else here but it applies directly to what we're talking about so here's another one of my cut and paste jobs.  I don't mean to be contradictory but we need to get all of these facts straight, or we'll never stop blowing motors.   I for one am completely enthralled in all the recent discussion and hope that we all come away from it more knowledgable than before.  I think we all owe Mike a fee (how's $50?) for the lessons we're learning from his misfortune:

 

"Higher static compression creates more power throughout the rpm band, but it'll lower your maximum allowed boost before the onset of detonation. Boost is worth way more power than compression, because boost raises your compression and your total air flow at the same time. With the down side of, when you're not on the boost, you have slightly less power.

 

Effective Compression Ratio = static compression ratio x (1 + boost/14.7)^1/2

 

For a car running 8.5:1 pistons and 18psi(~max on pump gas)

8.5 x (1 + 18/14.7)^1/2 = 12.67 ECR

 

If you run 9.0:1 pistons and want to maintain the same 12.67 ECR (~max on pump gas), you'll have to lower your boost to: 14.4psi

[(12.67/ 9.0)^2 - 1] x 14.7 = 14.4 psi

 

So you have to run 3.6 psi less boost to maybe pick up a tinny bit of bottom end. Or to take it even further for 9.5:1 you can only run 11.4psi. I'll tell you right now that the difference between 11.4psi and 18psi is huge. And at some point (12.67:1 in this case) you can run no boost and be maxed out on ECR for pump gas. And how fast is a N/A car with 12.67:1 compression, ask the Honda boys running 15's.

 

Of course you get to a point where you don't want to go the other way too much ether. A 6.0:1 car isn't too much fun on the street, but it can run 50.8 psi boost on pump gas. But the kind of turbo that could support that much boost would never spool up. You have to find what's right for you, but 8.5:1 is what most of the DSM guys like. My friend just built a motor for his DSM with 9.0:1 JE's and he is quite upset to find that he's getting lots of knock running 16psi. While lately in the cold weather, I've been running 20psi (8.5:1) on pump gas w/o any knock. And I drove his car and the difference in bottom end grunt isn't even noticeable. And his top end performance is sad compared to mine." End quote. It is also more involved than simply plug numbers into a calculator like this one

 

http://www.rbracing-rsr.com/compression.htm

 

Continued:

[chiplee]

I guess we don't have quench engines but this stuff is still very interesting,  Quench is commonly refered to as "artificial octane" which helps to understand its purpose.

 

"Since it is the close collision between the piston and the cylinder head that reduces the prospect of detonation, never add a shim or head gasket to lower compression on a quench head engine. If you have 10:1 with a proper quench and then add an extra .040" gasket to give 9.5:1 and .080" quench, you will create more ping at 9.5:1 than you had at 10:1--The quench distance is the compressed thickness of the head gasket plus the deck height, (the distance your piston is down in the bore)--The suitable way to lower the compression is to use a dish piston. Dish (reverse combustion chamber), pistons are designed for maximum quench, (sometimes called squish), area. Having part of the combustion chamber in the piston improves the shape of the chamber and flame travel. High performance motors will see some detonation, which leads to preignition. Detonation occurs at five to ten degrees after top-dead-center. Preignition occurs before top-dead-center. Detonation damages your engine with impact loads and excessive heat. The excessive heat part of detonation is what causes preignition. Overheated combustion chamber parts start acting as glow plugs. Preignition induces extremely rapid combustion and welding temperatures melt down is only seconds away!"

 

"'Compression Ratio' as a term sounds very descriptive. However, compression ratio by itself is like torque without RPM or tire diameter without a tread width. Compression ratio is only useful when other factors accompany it. Compression pressure is what the engine actually sees. High compression pressure increases the tendency toward detonation, while low compression pressure reduces performance and economy. Compression pressure varies in an engine every time the throttle is moved. Valve size, engine RPM, cylinder head, manifold and cam design, carburetor size, altitude, fuel, engine and air temperature and compression ratio all combine to determine compression pressure. Supercharging and turbo-charging can drastically alter compression pressures.

 

The goal of most performance engine designs is to utilize the highest possible compression pressure without causing detonation or a detonation related failure. A full understanding of the interrelationship between compression ratio, compression pressure, and detonation is essential if engine performance is to be optimized. Understanding compression pressure is especially important to the engine builder that builds to a rule book that specifies a fixed compression ratio. The rule book engine may be restricted to a 9:1 ratio but is usually not restricted to a specific compression pressure. Optimized air flow and cam timing can make a 9:1 ratio but is usually not restricted to a specific compression pressure. Optimized air flow and cam timing can make a 9:1 engine act like a 10:1 engine. Restrictor plate or limited size carburetor engines can often run compression ratios impractical for unlimited engines. A 15:1 engine breathing through a restrictor plate may see less compression pressure than an 11:1 unrestricted engine. The restrictor plate reduces the air to the cylinder and limits the compression pressure and lowers the octane requirements of the engine significantly.

 

At one time compression pressure above a true 8:1 was considered impractical. The heat of compression, plus residual cylinder head and piston heat, initiated detonation when 8:1 was exceeded. Some of the 60's 11:1 factory compression ratio engines were 11:1 in ratio but only 8:1 in compression pressure. The pressure was reduced by closing the intake valve late. The late closing, long duration intake caused the engine to back pump the air/fuel mix into the intake manifold at speeds below 4500 RPM. The long intake duration prevented excess compression up to 4500 RPM and improved high RPM operation. Above 4500 RPM detonation was not a serious problem because the air/fuel mix entering the cylinder was in a high state of activity and the high RPM limited cylinder pressure due to the short time available for cylinder filling."

 

 

This is me again: ok that all leads me to believe that 7:1 or even 7.5:1 pistons would be a reasonable way to build a little longevity into our motors and even some margin for error where none seems to exist currently.

[Tim_C.]

That's what I mean. Going lower changes the direction from what performs better and lasts 60,000 miles or so, to less performance with no garantee of life? Sure, there is a bigger margin for error, but that's what EGT, AF, Boost, Oil Pressure, Fuel Pressure, Coolant Temperature gauges are for. Anyone running serious boost needs all those gauges to be sure there is no error when they crank up the boost.

9:1 is too high for our big cube, long stroke engine.

7:1 isn't acceptable for the vast majority of people.

7.5? Maybe, but then why doesn't TEP, EIP, BTSG, Frank, CNM, and everybody posting big numbers, run anything less than 8:1?

All I know is that the best improvement my car got was going to 8:1. The margin of error perspective should be left to the guys with TBI. Even then, 8:1 is far better. The TBI cars are harder to get set-up right than MPI, but they can go 8:1 and last plenty long enough.

I think people are way too boost happy, and crank it without the needed precautions for any turbo engine. We aren't doing our homework enough when we crank the boost and aren't set-up for it. That's what happens. It's too easy to get a big honken turbo on there and just crank it up. That's why I only went with a 17C. I would be too tempted to crank up a 20G & watch the parts fly. I still need an EGT, but I already know I don't have the fuel even for 10PSI with my volume, so I need an AIC, or bigger secondary, or the RRFPR. The right combo of those things will get me there to run 16-18 PSI on race gas. I will have more power than I'll ever use with that.

You can't put as big a camshaft in a 7:1 motor either. So, your top end will drop off sooner. Unless you want a real dog off the line that's worse than stock. with 7:1, you might as well get water/alcohol injection, an intercooler sprayer, an MSD 7 series, and maybe even Nitrous! Ha Ha!

No, I think you can get 7:1 to perform too, so it really does matter what you're after. Nobody with 7:1 has ever put up any numbers that are too impressive?  

Tim C.

[chiplee]

Yeah but lately I've just been reading about so many rebuilds, it makes me wonder.   It's making me think there could be something inherently wrong with the piston aspect of our approach to building the 2.6.  Again, I feel like a detective leaving no stone unturned so I'm not arguing, just discussing.  Opinions about rebuilds move like water.  They ebb and flow with the tide that is this BBS for the most part.  Opinions are also developed based on just what you said, EIP, BTSG, CNM, TEP.  These are often considered "companies" with a huge background in performance automotive tuning which I guess a couple of them are, but at least one was just "a guy"  Would we know if those motors were still running or had blown like ours?  I've heard of several TEP stage III engines with piston damage.  What made mitsu use 7:1? and why are we the only ones who increase static compression when we intend to increase boost pressure and total airflow.  I'm looking for an article i saved about stroke, compression and cam choice but can't find it.  That's obviously not the only engineering change we all make but it's one of the ones that most directly effects compression pressures and resistance to knock.  Like I said, 8:1 may very well be just right but I'm not as confident as I used to be that TEP and EIP aren't marketing parts in the name of performance with a hidden agenda that revolves around speeding up engine wear.  I mean it's the perfect business to be in, you can do whatever you want to an engine, build it as tight or loose as you want and then say "well of course there's no warranty on a performance engine"  I don't know, I'm just curious.  I'd like to see some numerical representation of the whole thing including requred octane for said effective compression and airflow charts for 7:1 at 15psi and 8:1 at 15psi with no other variables and EGT comparisons and it'll never happen but if you had never heard of those companies or this board how would you deside what pistons to use?

[chiplee]

Here we go, good stuff http://www.e30m3performance.com/myths/more.../comp_ratio.htm  covers basics on page one and is more applicable to this discusion on page two.

argues for your case in some ways Tim.

[chiplee]

Hi Jason,

 

If you still have got the block apart this would be a perfect time to do some measuring.

Using a burette, measure the amount of cc's in the combustion chamber and the amount in the "bowl" of the piston while the piston is in the block and at TDC.

Find the last used head gasket, measure it's "compressed thickness", convert that to cc's, add all the cc's together.

Do the basic calc's on "swept volume" using your stroke and rebored bore.

It's actually the only way to find out the true (static/mechanical) compression ratio.

 

Kind Regards,

 

DUTCHGPS

 

'88 Starion 4G54

'82 Starion 4G63

 

P.s. : If you find CR to be in the region of around 9:1 I'd say about 15 psi to be the very max of the 4G54 assuming a VERY good intercooler and absolutely correct A/F ratios 12.5:1 or even richer mixes.

 

here's a calculator for this to make it a little easier, maybe.   :

http://www.rosspistons.com/CR%20Calculator.htm

[Boosted_One]

This info off of SDS along with your opinions here got me thinking....

 

Fuel Octane vs. HP

 

03/13/98

 

In turbocharged engines there is a fine balancing act when it comes to making a lot of power on low octane fuel. In most cases, ignition timing must be retarded as the boost pressure rises above a critical point and finally there reaches a further point where the engine simply loses power. If the timing was not retarded with increasing boost, destructive preignition or detonation would occur. Normal combustion is characterized by smooth, even burning of the fuel/air mixture. Detonation is characterized by rapid, uncontrolled temperature and pressure rises more closely akin to an explosion. It's effects are similar to taking a hammer to the top of your pistons.

 

Most engines make maximum power when peak cylinder pressures are obtained with the crankshaft around 15 degrees after TDC. Experimentation with increasing boost and decreasing timing basically alters where and how much force is produced on the crankshaft. Severely retarded timing causes high exhaust gas temperatures which can lead to preignition and exhaust valve and turbo damage.

 

We have a hypothetical engine. It's a 2.0L, 4 valve per cylinder, 4 cylinder type with a 9.0 to 1 compression ratio and it's turbocharged. On the dyno, the motor puts out 200hp at 4psi boost with the timing at the stock setting of 35 degrees on 92 octane pump gas with an air/fuel ratio of 14 to 1. We retard the timing to 30 degrees and can now run 7psi and make 225hp before detonation occurs. Now we richen the mixture to 12 to 1 AFR and find we can get 8psi and 235 hp before detonation occurs. The last thing we can consider is to lower the compression ratio to 7 to1. Back on the dyno, we can now run 10psi with 33 degrees of timing with an AFR of 12 to 1 and we get 270 hp on the best pull.

 

We decide to do a test with our 9 to 1 compression ratio using some 118 octane leaded race gas. The best pull is 490 hp with 35 degrees of timing at 21 psi. On the 7 to 1 engine, we manage 560 hp with 35 degrees of timing at 25psi. To get totally stupid, we fit some larger injectors and remap the EFI system for126 octane methanol. At 30psi we get 700hp with 35 degrees of timing!

 

While all of these figures are hypothetical, they are very representative of the gains to be had using high octane fuel. Simply by changing fuel we took the 7 to 1 engine from 270 to 700 hp.

 

From all of the changes made, we can deduce the effect certain changes on hp;

 

Retarding the ignition timing allows slightly more boost to be run and gain of 12.5%.

 

Richening the mixture allows slightly more boost to be run for a small hp gain however, past about 11.5 to 1 AFR most engines will start to lose power and even encounter rich misfire.

 

Lowering the compression ratio allows more boost to be run with less retard for a substantial hp gain.

 

Increasing the octane rating of the fuel has a massive effect on maximum obtainable hp.

 

We have seen that there are limits on what can be done running pump gas on an engine with a relatively high compression ratio. High compression engines are therefore poor candidates for high boost pressures on pump fuel. On high octane fuels, the compression ratio becomes relatively unimportant. Ultimate hp levels on high octane fuel are mainly determined by the physical strength of the engine. This was clearly demonstrated in the turbo Formula 1 era of a decade ago where 1.5L engines were producing up to 1100 hp at 60psi on a witches brew of aromatics. Most fully prepared street engines of this displacement would have trouble producing half of this power for a short time, even with many racing parts fitted.

 

Most factory turbocharged engines rely on a mix of relatively low compression ratios, mild boost and a dose of ignition retard under boost to avoid detonation. Power outputs on these engines are not stellar but these motors can usually be seriously thrashed without damage. Trying to exceed the factory outputs by any appreciable margins without higher octane fuel usually results in some type of engine failure. Remember, the factory spent many millions engineering a reasonable compromise in power, emissions, fuel economy and reliability for the readily available pump fuel. Despite what many people think, they probably don't know as much about this topic as the engineers do.

 

One last method of increasing power on turbo engines running on low octane fuel is water injection. This method was evaluated scientifically by H. Ricardo in the 1930s on a dyno and showed considerable promise. He was able to double power output on the same fuel with the aid of water injection.

 

First widespread use of water injection was in WW2 on supercharged and turbocharged aircraft engines for takeoff and emergency power increases. The water was usually mixed with 50% methanol and enough was on hand for 10-20 minutes use. Water/methanol injection was widely used on the mighty turbocompound engines of the '50s and '60s before the advent of the jet engine. In the automotive world, it was used in the '70s and '80s when turbos suddenly became cool again and where EFI and computer controlled ignitions were still a bit crude. Some Formula 1 teams experimented with water injection for qualifying with success until banned.

 

My personal experience with water injection is considerable. I had several turbo cars fitted with it. One 2.2 liter Celica with a Rajay turbo, Weber carb and no intercooler or internal engine mods ran 13.3 at 103 on street rubber on pump gas back in 1987. This was accomplished at 15psi. With the water injection switched off, I could only run about 5 psi before the engine started to ping. I think you might see water injection controlled by microchips, catch on again in the coming years on aftermarket street turbo installations. It works.

 

R.F.

[kev]

In all honesty I think the 7:1 CR is capable of the most horsepower.   However your everyday driving will suffer tremendously in my mind.   You have to think about what you want here.  Do you want a car that will give super high hp numbers on the dyno and great times at the track or do you want a street rocket that will blow away almost anything on the roads and highways but still pull pretty nice at the track?   I myself go for the street rocket.   I need that low rpm kick just as much as I need the massive pull at 4000 rpms.   I am not willing to sacrifice this cars drivability over a bit extra pull and an extra 20hp.  Thus I think I will stick with the 8:1 CR.  Chad noted that even with his mega To4 turbo, he still has about the stock pull on the very low end with the 8:1 CR pistons and lightened internals.    Any less in CR, you will have less lower rpm power then the car was stock!  

 

So in all, I will stick with 8:1, Magna MPI, and 10-15psi.   When we figure out what is keeping your curves from increasing past 4000rpm, that car should pull 250-275 rwhp at only 10psi.   I will be very happy if I could get my car to that point.  

[heefner]

Tim you didn't define "impressive numbers" on 7:1 so I don't know if 300rwhp (@ 24psi @ sea) levelqualifies or not but I'm running close to 7:1 on 93 octane and when I first had my engine tuned thats what I got.    I can turn up the boost on the street and not have to worry about detonation or anything else.  BillTSG said he runs 110 octane in his car all the time.  I'm not sure what his CR is but who wants to $5+ / gallon to ensure saftey.  I will dig up my dyno sheet and try to get it scaned so that I can post it.  As far as losing streetability with 7:1 I can't speak for the anyone else but I can say I'm happy with mine.  Maybe I wouldn't be if I had driven a quest with 8:1, who knows.  WIth this CR I reach full boost (25 psi) before 3k and I can lug around in 5th at 40mph and not have to down shift.  

[Ray_R]

man, i hope after all this we can get some kind of chart going to help everyone pick a set up for there car and what to use pending on what kind of turbo, exhaust,cam,EFI ect...

[88BlueTSiquest]

It seems Liz and Mike really need the power up high. My question would be, is there a non-stroked crankshaft available for the 2.6l, to maybe lower it to a 2.3l. Then with the slightly less rotating mass, and the shorter stroke, you can maybe achieve rpm's in excess of 7000 safely. The only draw back there would be the limitations of the valve train, and whatever reason there is for the 4k rpm drop off in power. Also, since the turbo is a load device, wouldn't the 2.3l be working harder, and possibly start turning the bigger turbo's at a lower RPM?

 

I'd almost think we'd need to figure out what exactly the DSM crowd is doing, we know that the 2.0l is capable of much higher rev's then our engine, and a good majority of those guys are running hapily in the 12's in the 1/4. I'd really feel that our engine's displacement can get us up to those numbers too, and be streetable, if we can only get the engine's ability to rev up there.

 

 

Chip,

 

You are the copy/paste King  ;D But it's some extremely valuable information  

[chiplee]

Yeah you know it seems like people read it more if it's pasted into a reply than if I just copy the link.  Not sure why but I think most of the info is just vital to taking a motor where most of us want to take them.  I've been going at it all wrong in alot of ways and have been more than happy to do some of the leg work it will take to straighten some things out.  

 

Mike I'd never read that at the SDS site, but that's almost all I needed to hear to  make my decision about the pistons.  I'll obviously continue with this motor 'till it blows up but the next one will be getting at least 7.5:1 and a solid evaluation of actual static compression via that calculator above.  I would support your decision to use 7:1 in a heartbeat.

[Boosted_One]

It seems Liz and Mike really need the power up high. My question would be, is there a non-stroked crankshaft available for the 2.6l, to maybe lower it to a 2.3l. Then with the slightly less rotating mass, and the shorter stroke, you can maybe achieve rpm's in excess of 7000 safely. The only draw back there would be the limitations of the valve train, and whatever reason there is for the 4k rpm drop off in power. Also, since the turbo is a load device, wouldn't the 2.3l be working harder, and possibly start turning the bigger turbo's at a lower RPM?

 

I'd almost think we'd need to figure out what exactly the DSM crowd is doing, we know that the 2.0l is capable of much higher rev's then our engine, and a good majority of those guys are running hapily in the 12's in the 1/4. I'd really feel that our engine's displacement can get us up to those numbers too, and be streetable, if we can only get the engine's ability to rev up there.

 

 

Chip,

 

You are the copy/paste King  ;D But it's some extremely valuable information  

 

 

I am seriously considering destroking it a bit to a 2.4L.

 

Chip sure is good on his homework. It's efforts like that that bring success.

[chiplee]

my motives are primarily selfish I assure you,  

[Joel]

Well, Funny thing is I've read all these articles (and many more) that Chip is posting over 2 years ago. Not trying to prove that I am older and wiser, or if I really know anything at all... But I happen to agree with Tim C.

 

I do not believe Mike's motor was blown by detonation (even the machinist told him he was running to much timing). That would not have been very adjustable by adding leaded gas, as leaded gasoline won't cool it down much more than unleaded. Octane rating has little to do with heat (although lead does help cool it down a tad).

 

If you research all the "fast" DSM's, for instance, they all usually run 8.5:1 from the 2g motor in their 1g block and 1g big rods. Reason: 7.8:1 on 2.0L won't spool a FP green or FP red without a bottle attached. Likewise, these "street cars" just wont pull around on a large turbo real easy.

 

I think, personally Mike, you would be heading the wrong way going to 7.0:1. You are attempting to change your entire setup it seems, and you have no idea if it's going to work. Make small changes.... Or wait until some of the rest of us catch up and see what we do... I state that as I realize were not all made of money (like myself), so maybe we need to take turns figuring it all out. I don't see how 7:1 compression will fix anything to do with your drop off at 4k, and if it continued to climb at 15psi past 4k, you would be in the 300-340HP range!! Thats better than a DSM and they have 500-1000rpm more revs (sometimes more if they raise it). I think concentrating on making the power you want doesn't need to be done by more boost. We have a big motor, we only need so much assitance from boost. To much is a bad thing, low or high compression.

 

So if you switch to 7.0:1, you'll have slightly less hp per lb of boost, but your power will still drop off at 4k.

 

Not only that, but when you bore over .060, a 7:1 piston will likely be closer to 7.5:1, so you'd have to measure everything and have custom 1 off pistons made.

 

Irregardless of all that, if you read those articles more and more, static compression is a number that is almost useless... dynamic compression is adjustable by boost, cam, and the like. Even an exhaust system has effects on that.

 

Joel

[Shelby]

while makeing for a LOT of  reading  these  couple of threads  are very intersting , some of the best stuff we've  had on here in yr's

that said i got a question,  what if this  drop off in power has nothing to do with what we're talking about,   what  is the diff is  Mike's first  dyno run and this  one

what  is the same

we can  asume it's  got nothing to do  with the the intake cause  every thing is diff

aslo  on the first run  the dist was stock  right , and on the  last run it was control'd by  the SDS, so  at a glance i'd  say it wasn't the  timeing altho the engine was damage'd due to  heat , timeing or what have you, that still don't explain the 4500rpm  wall he ran into

 

where was the cam  timeing on the first run and the last,  was any thing change'd in the cam , lets  say the  cam is running late and it stop'd the power at  higher rpms  from being made, even with more fuel and boost , is it the same cam ,  has the  cam  timeing  been check'd as per  the cam spec sheet ?? any changes in the  cam .. etc from the first run and the last ?

 

now how about the  exhaust system, several questions about the  exhaust houseing  being a bottle neck  and limeting the  max out put, well we got  several guys  claiming  strong  pull right up to  7 k, so whats the story  here is or is not the exhaust houseing a  restrictor to max power in higher rpm's ,

now is there some thing in  Mike exhaust system thats  limiting the amount  of air  flow thru it , cause this  engine  starts out   like a rocket  makeing power and  just stops ,  way short of  what most guys are  claiming to be running theres to , is there some thing else   in the  set tup that  is not  being adress's that should be , theres thing  i am also real interst'd in find ing out befor i  bolt this 20g  and mpi intake on ,   right now i have  no problem  pulling right thru the  4500 on up to 6 k real strong, i  know that  not  with a  dyno run  but   you can feel the power   building  right thru it

could he have a  inner  wall on the exhaust houseing  seperateing and  blocking some of the  flow,  i say this  cause  my old 83  12a   melt'd the  exhaust  houseing walls and they  nearly flow'd out of shape  actually burning a hole in two  places thru the houseing

 

just question s  knock um down chew  um up and throw them away , but there is some thing odd here  other then the  damage done to the pistons

[MidNiteRide89]

Does anybody here know of a way to get Tony Waldrop's thoughts on this? He isn't running a MPI, but is one of the foremost experts on our engines, he has also stroked his motor to 3 liters.

 

I agree with Shelby, this is some fantastic info/discussion!

[Shelby]

right Marc and we have a tool  that   has never  been avaliable to  guys befor in history a computor forum  thanks to  ryddlers  money and time , it's kind of like haveing a 500  man pit  crew , we  would have love'd one of these back in the 60's when it was  basicly every man for him self  , to learn by trial and error, and if some one did  tell you something it was hard to trust them cause no one  gives out infor  to alow them selves to be  beaten  any thing that work'd was a closely guard'd secret