i have seen a couple discussion on this board and others about the saftey of running a sc/turbo at 10.3:1 compression. i was wondering (as many people have mentioned) if it would be necessary to drop the compression to say 8.5:1 so you could safely run a decent amount of boost. also, iwhat about the effectiveness/need for a higher flowing plenum when using fi?

 

I would drop it, most cars that are Turbo charge from the factory are anywhere from 7:1 to 8.5:1 they most know something.

 

the compression is not the issue, it's the fueling.........if you run lean normally aspirated the car will blow up also.......if the compression was too high to run boost then the Smithtown Nissan car would have blown up long ago since they're running a 225-shot of nitrous........they have it fueled properly, thats why it still runs

 

I'm no expert on cars, but think just dumping more fuel in is a quick fix. I may be wrong though, the Procharger is relatively new, I'm still waiting for long term results on these cars before I make a decision. I agree with Barrybell in that most factory cars are at a much lower compression ratio, and they are looking to sell a car that has long term reliability. Don't get me wrong, I'm all for boosting, but I think the margin for error is VERY small running boost at such a high compression. I'd like a little more "grey area" between a fast car and a broken car.

 

I couldn't agree more...as of right now building up a VQ is a waste of money, Until we know the limits of the stock internals.

TUNING IS EVERYTHING

 

Compression Ratio does matter. Fuel delivery does matter. Ignition Timming does matter, Fuel octane does matter. Point being not just compression ratios. But the combo of all those factors, plus many more!

But 10.3 is NOT the end of the world!

N20 Car Compression Ratio should NOT be compared to FI CR's Since that N20 LOVES compression! And is not a fair comparo in anymeans of the word.

It's not like just because it has 10.3 it will get hurt with FI. You have to have a good Tune, and moderation in mind when it comes to boost levels. With that in mind, then it can last a long long time.

Think about this... There are plenty of Z06 Corvettes 10.5:1 CR, at 7psi of boost blower or turbo that are VERY durable and happy. (Plus make over 500 RWHP with a good tune)

I understand that this is NOT an apples to apples comparsion. BUT, the Corvettes have cast pistons, and junk rods, and still can make decent power with FI, with high compression.

I would post more on this matter, but I don't feel anyone would listen anyway

EA

 

Some of us are listening. We (this forum) need more input from knowledgable sources, not just opinions. I mean no offense to those who have posted their ideas & know-how so far on this subject.

 

Some people are listening........what would you say the appropriate safe A/F ratio would be on a car thats 10.3:1 compression, with an ATI S/C?.......i think it should be richer than normal FI on NA engines, because our ECM changes its fuel maps........the FMU and ECM aren't talking to each other, so the FMU never knows that ECM might be going lean for some reason......if its richer than the usual 12.5:1 that tuners shoot for, then it could compensate for the ECM going lean on occasion..........am i way off on this assumption?

 

I don't think you have to worry about the ECM leaning out at WOT. The WOT fuel maps are burned into the ECM if I'm not mistaken so they never change. Partial throttle fuel maps are the ones that change.

 

My major concern is changes that it will make when going from one climate to the next.......i drive an awful lot in various elevations

 

I have a ATI Procharger on my LS1 Fbody, I live at sea level and taken it up the mountains of WV and never had a problem. It is fun passing people on a mountain at the speed limit while they crawl up it.

 

Does the ECU on LS1's vary fuel maps and timing like the Z's?

 

You can run any amount of boost on a high compression engine, but you have to know what your doing. With high compression engines it require less boost to receive more HP compared to an engine with a lower compression ratio, but tuning is way harder. The most difficult part with using boost on high compression engines will be the tuning. You should get this professionally done with someone that knows how tune high performance engines.

Many factors will determine how much boost you will be able to run on a high compression engine safely on pump gasoline. Octane, timing, heat are all part of the variables. I have seen some people run 15 psi on a 14:1 setup safely, but as you can imagine it was not pump gasoline and it was well tuned.

If you are serious about producing a lot of HP you may want to lower the compression ratio. This will make the tuning process less of a headache. The lower the compression ratio the better it is on a force induction engine. Engine builders prefer the compression ratio in the 8:1-9:5:1 range. You will be able to run more boost safely, tuning will be less of a headache, and end HP should be a lot higher. So it's recommended that you use lower compression ratio for a force induction engine, but not needed if properly done right.

The bottom line is, if you are going to run FI on a stock bottom end with pump gasoline on a high compression engine, then lower boost levels are recommended. And the key for it to run flawlessly will be a good engine tuner.

 

I will post a bit more later, on this matter for those that are intrested. Even some on the LS1 and the 350Z and what happens under WOT conditions.

I will say this. LS1 Cars love hovering around 12.0-12.2 AF with FI. Though the 350Z's that I have been around that are FI, love fuel. They are safer, and make more power being fatter then a "normal" FI motor. The ones I have done for friends have benifited being in the lower 11:0 ish Range. Remember that is only while you are under load, with boost. These cars retain a rock soild 14.7ish when normal driving, and idleing. (FJO wideband ready)

My only wish is that I had the ability to "get into" a 350Z computer. I am chomping at the bit to be a part of one being turned up. Low comp, big boost, big fuel system, computer tuning. Daddy like, daddy like.

I think by the time all the waiting around is done. I will have to advise my friend to just by a Stand alone, and we will do it with that. Is anyone out there running a Stand Alone on a 350Z yet? (Halltech, Autronic,AEM,FAST,DFI, SDS?...anyone?)

EA

 

I dont think there is any stand alone system. When I talked to AEM about the EMS they said it does not look like they will be doing this for another 8 months or so.

 

Not sure, but I know LS1 has two timing maps incase it gets a bad tank of gas, it goes to the low octane map. The second map has lower timing to save the engine.

I would love to have the control over the stock computer in the wife's Z as I do in the Fbody PCM. I won't think twice about putting a blower on it. But just playing with fuel I don't get a warm fuzzy about putting 7 or 8 lbs of boost to it.

 

It is about time someone else recognized the need for some common sense with this topic. Geez.

 

Yes, good tuning will always be the key. However I wouldn't say you could run "any" amount of boost on a high com engine. Where you run into a problem is the higher compression causing higher heat. High heat equal detonation. This is what will ultimately limit your HP. The power gained from being able to raise the boost alot makes the power lost from lower compression look like a drop in the bucket. Well maybe not that much but you get the idea.