Guest bastaad525 Posted October 22, 2002 Share Posted October 22, 2002 Okay.. I run a relatively high CR (10.3:1) L28 bored to 2.9 liters. One thing I had always wondered about is why you never hear people talk about adding a turbo onto this type of setup, as opposed to just going out and buying a whole turbo motor. I know cost is probably the main factor, as turbo motors can be found for pretty cheap sometimes. But other than that, I know a few people have said to me that it would be impossible to run a turbo on a high CR motor on pump gas. However, since then I read an article, I believe in Sport Compact Car magazine, where they did a project car out of a Toyota Matrix (or it may have been a ford focus??) that had a 10.?:1 motor, that they added a turbo to. Of course they didn't boost it THAT much.. I think it was like 8psi? But that 8psi made a HUGE leap in performance for the car. And they did the intercooler and all that... and succesfully got the car to run on pump gas. I believe they MAY have used an aftermarket EFI system also. ANYWAYS!!! Why wouldn't this be possible/feasible to do with a high CR L28? I mean... most people that go turbo with a Z and go for serious performance end up getting things like intercoolers and programmable EFI systems.... could not these things be put together with a 10:1 CR motor, and be made to run safely? And what about STOCK non turbo L28's?? in the 8 or 9 to one CR range? How hard would it be to take a non turbo motor and put a turbo on it? Quote Link to comment Share on other sites More sharing options...
Cody 82 ZXT Posted October 22, 2002 Share Posted October 22, 2002 First off anything can be done with enough money. That said yes, you could run 10.? to 1 and get away with it if you have all the right parts to help support it. Such as very good intercooler, and engine managment system. Every little piece will have to be right for the system to work reliabley for any real period of time. It is much easier to lower the compression and make more power with the added boost you are able to run. Yes, you will sacrifice some off boost response and what would be total power given the same boost levels but, it can be done easier and with less money. I think most people try to limit compression ratio to 9 to 1 on a turbo car. Even that may be a little high for the L motors. The stock 7.4 is really to low for a performance car to have but, it was the early 80's and Nissan had to answer to warranty claims and things like that. If you are wanting to turbo a Non turbo car you can do it but, you will have to limit the amount of boost you run and make sure the tune is right. I used to drive one and didn't go over 10 psi. Eventually the car got wrecked so I bought a factory turbo car the next time. Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted October 22, 2002 Share Posted October 22, 2002 You can do that, but with that high a compression ratio, you need to have a very good engine management set-up, big injectors, and a good intercooler. I look at it this way. A point of compression is worth approx 4 percent more power, a psi of boost is worth approx 7 percent more power. Quote Link to comment Share on other sites More sharing options...
Mikelly Posted October 22, 2002 Share Posted October 22, 2002 ...And based on LockJaws figures, and what you would likely be able to run on that high compression motor (Likely only 6PSI, 8 would be a real stretch), would it be worth it to only make LESS than 50 more HP??? Were talking a pretty sophisticated engine management system AND an expensive innercooler, as well as the turbo and plumbing... Mike:D Quote Link to comment Share on other sites More sharing options...
blueovalz Posted October 22, 2002 Share Posted October 22, 2002 Can this also be looked at from the point of view of what the boost itself is adding to "assist" the piston movement on the intake stroke? With the lower CR/higher boost model, the piston is being assisted (pushed) in it's downward movement more so than on the higher CR/lower boost model. Quote Link to comment Share on other sites More sharing options...
Guest Zcarsmakemyheadhurt Posted October 22, 2002 Share Posted October 22, 2002 I see where your coming from with the hi compression and boost and you may be able to boost it, but with lots of retard in the timing and lots of exhaust gas temp and if you get a lower compression motor you may be able to boost the hell out of it with better result from all the fuel and ignition upgrade required with the hi compression set up. The other thing you haven't taken into consideration with the Matrix is the design of the cylinder head DOHC 4 valve per cylinder and a very smoth hi flow intake and exhaust. Engine design makes a big difference when your talking about compression and those engines are state of the art. Good luck Alex C Quote Link to comment Share on other sites More sharing options...
Mudge Posted October 22, 2002 Share Posted October 22, 2002 Originally posted by bastaad525:I believe they MAY have used an aftermarket EFI system also. If your going to add $1000-$2500 to your project you may as well start out with the purpose built motor. If the pistons are hypereutectic (cast), then it is even less suitable for boost and is likely to be nuked at some point, especially for those of us with crappy CA gas. Quote Link to comment Share on other sites More sharing options...
Mudge Posted October 22, 2002 Share Posted October 22, 2002 Low compression + higher boost = more peak power High compression + lower boost = lower peak HP People have been putting 8psi (intercooled) on 10.5:1 engines, but again you are waiting for the day that the thing blows up. Again it sucks that you end up pulling so much timing your giving away power anyway, so with all that hassle I would just do it half way right the first time Quote Link to comment Share on other sites More sharing options...
johnc Posted October 22, 2002 Share Posted October 22, 2002 Heat, heat, heat. If you can cool the intake charge and the combustion chamber down then running boost on a high cr engine is subject to the same cylinder pressure limitations as running boost on a low cr engine. Ideally you should be able to hit the same cylinder pressure numbers with either setup. Unfortunately, this cooling is done mostly with fuel so, as said above, precise fuel management and high octane fuels are key. In addition you can add oil jets to the undersides of the piston, intercoolers, piston and combustion chamber coatings, etc. I tend to look at engines as either pressuruzed or unpressurized. Some auto manufacturers have built very successful high cr pressurized engines, but none of us have those kinds of resources. Quote Link to comment Share on other sites More sharing options...
pparaska Posted October 22, 2002 Share Posted October 22, 2002 John, while reading your post, I was wondering - does the pressurization of the intake charge aid in fuel/air mixing? Anybody remember Smokey Yunick's Hot Air Engine? I typically believed most of what he wrote, but I always felt his power gains were really from the small boost he was making, not the "homogenization" of the intake charge, as he claimed. Woah, pretty far afield. Sorry Quote Link to comment Share on other sites More sharing options...
katman Posted October 22, 2002 Share Posted October 22, 2002 Originally posted by johnc:Ideally you should be able to hit the same cylinder pressure numbers with either setup. Which brings up a point. A large combustion chamber (low CR) boosted to the same pressure as a small combustion chamber (high CR) contains more fuel/air and hence more power. The desire for a high static CR motor is for off boost driveability, me thinks. Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted October 22, 2002 Share Posted October 22, 2002 Yeah off boost driveability is one thing. Alex is on the money when he talks about lots of timing retard amd high egt's. Size your turbo properly, have good engine management and run lots of advance and pull it out when the boost hits, and a lower compression engine will run great. Seems to me you are limiting yourself with a higher compression engine. More boost = more hp, and you make way more hp with boost than with compression. In a modern engine that is DOHC with a pentroof combustion chamber, you have more lattitude, but with our head designs, you are sort of limited. I should be careful here or I will get another P90 N42 debate going. Clearly, the design of the combustion chamber lets people with these cars get away with doing what they are doing. Personally, I think they are stupid, and their stuff will be blown up and we will get to read about it when they do a feature story on how to build a bullet proof matrix engine. Seriously, there is no free lunch when it comes to turbo's and compression. If you have really good engine management, run 8.5 to 1, otherwise, run a little lower. Better to be safe and a little sluggish til the boost hits, then reckless, responsive , and blown up soon thereafter. That is IMO. Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted October 22, 2002 Share Posted October 22, 2002 If the pistons are hypereutectic (cast), then it is even less suitable for boost and is likely to be nuked at some point HUH? WHAT? Damn, someone should have told me this before I started using them and running 26+ psi of boost. I guess I just do not care for such generic statements. Any piston is susceptible to being nuked if you try and run high boost with junk pump gas, have an inadequate fuel system or the engine is not properly tuned. Quote Link to comment Share on other sites More sharing options...
johnc Posted October 22, 2002 Share Posted October 22, 2002 > John, while reading your post, I was wondering - > does the pressurization of the intake charge > aid in fuel/air mixing? Don't know. Quote Link to comment Share on other sites More sharing options...
johnc Posted October 22, 2002 Share Posted October 22, 2002 > A large combustion chamber (low CR) boosted to > the same pressure as a small combustion chamber > (high CR) contains more fuel/air and hence more > power. That would be true if you were measuring cylinder pressures just before combustion. In my post earlier I was implicitly referring to max cylinder pressures after combustion (usually about 30 degrees ATDC) which, if they are equal, then you will be producing identical power (assuming identical rpms.) But, that's one of those "all things being equal" arguments that has no basis in reality. Quote Link to comment Share on other sites More sharing options...
Mudge Posted October 23, 2002 Share Posted October 23, 2002 Originally posted by Scottie-GNZ: quote: If the pistons are hypereutectic (cast), then it is even less suitable for boost and is likely to be nuked at some point HUH? WHAT? Damn, someone should have told me this before I started using them and running 26+ psi of boost. I guess I just do not care for such generic statements. Any piston is susceptible to being nuked if you try and run high boost with junk pump gas, have an inadequate fuel system or the engine is not properly tuned. Your the first I've heard of them, are they coated at all? I am not as familiar with aftermarket hypers being used non NA as I am with stock, LT1 more specifically, and they will not take the abuse for long, even running rich on race gas. I know a guy now in the 9s, but was making about 650 crank HP on a stock bottom LT1 until he lost a rod and about 3 pistons. Obviously the LT1 is not the best example being built for NA compression wise. I've heard good thing about KB pistons, but again your the first I've heard of with large PSI on hypers, since hardly anyone trusts that route. Quote Link to comment Share on other sites More sharing options...
TimZ Posted October 23, 2002 Share Posted October 23, 2002 Originally posted by johnc:> A large combustion chamber (low CR) boosted to > the same pressure as a small combustion chamber > (high CR) contains more fuel/air and hence more > power. That would be true if you were measuring cylinder pressures just before combustion. No, it wouldn't. The amount of fuel/air in the combustion chamber is dependent on the swept volume of the cylinder and the manifold pressure, not the combustion chamber volume. It just doesn't get compressed as much with the larger chamber. (John - I'm guessing that you misread the original statement) Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted October 23, 2002 Share Posted October 23, 2002 I am using federal Mogul hypers and they have been in the engine since Dec '00 with about 140-150 passes on them. I do not run at the track w/o race gas and use the best components to prevent detonation. Most important of all is how carefully you tune and monitor. I basically tune the engine to run as hard as it can w/o detonation. For my setup, that is 26psi boost with the EGT registering about 1600* through the traps. Sounds frightening, but again, the key is no detonation. Quote Link to comment Share on other sites More sharing options...
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