Nate1647545505 Posted November 24, 2003 Report Share Posted November 24, 2003 Welcome back to another one of my posts, Just wondering what the general boost limits of an intercooled car with a compression ratio of 9:1 is on 93 pump gas, drivetrain and engine fully forged. Im worried that to low of a compression rate will cause the motor to be dog slow in spool up, and to high will not let me use full use of the turbo at highway speeds. Do you supra owners that run in upwards of 20-23psi use race gas everytime you switch to a "race" setting on your boost controllers? Any light on the subject would be greatly appreciated. Quote Link to comment Share on other sites More sharing options...
Crash1647545504 Posted November 24, 2003 Report Share Posted November 24, 2003 im not 100 percent sure but just from what i have seen usualy 9.5:1 cars will take only around 10 psi give or take, so i would guestamate som place around 15 or 16 again not sure just a guestamate from what i have seen around Ben Quote Link to comment Share on other sites More sharing options...
Guest mudbutt Posted November 25, 2003 Report Share Posted November 25, 2003 Im sure brett will chim in with better explanations. But here goes me... I went over the timing/octane/compression/boost thing for over a year. Pulling my hair out. There are other factors you have to think about, like chamber design and air temp/efficency. One car may ping at 10psi on 9:1 and another may take 15+ both on 93. I have found that a proper sized turbo and timing set at optimum will be more important than compression for spool. My advice, if you are trying to determine what cr to run would be to figure out how much boost you want to run then go from there. Start with a proper turbo for your app (compressor maps are your friend) then find out what other people are experiencing on similar motors. Water injection is another option, but IMO not to be used as a bandaid. Timing can be retarded, but you also lose power here and it becomes a real bad thing, causing high egts after awhile. Many people also like to just keep throwing fuel at the problem, this isnt a great idea either IMO. I will give you my setup for example... 7m-gte 8.4:1 stock compression. I was leaning toward going to 9.2:1 n/a pistions to reduce lag, but the tiny gain in response wasnt worth the loss of top end. I decided on a Garrett ballistic turbo due to the fact that it is one of the most modern designs from the wheels to the dueal ball bearing chra. I'll be running a gt3040. After research in timing, octane, and knock, I came up with a general idea of how I will do my fuel. low boost ~12psi 94 octane, mid boost ~18psi 94 and mild water, high boost ~26psi 110 and water. This "solution" is quite general and I wont have spacifics determined untill I start tuning. The goal is to make as much power as possible with proper timing and only have to run race gas when I am on high boost.......waiting on release of ems. Hope all of my ramblings helped atleast somewhat. Joel Quote Link to comment Share on other sites More sharing options...
Nate1647545505 Posted November 27, 2003 Author Report Share Posted November 27, 2003 Thanks for the information. I'm still reviewing current turbo cars. I have hit a bottle neck since i want to run around 100 shot of nitrous and water/alch injection. Correct me if I'm wrong, but the owner of the 12psi M3 was running with an A/F of 11:1. What is the safest ratio you can run without melting anything? I thought it was 12:1 was the "stoic", but i may need to review. I just want to get all the ideas I can. Thanks still! Quote Link to comment Share on other sites More sharing options...
Razorback Posted November 27, 2003 Report Share Posted November 27, 2003 9:1 compression is very safe for boost. When you start to get to 10:1 and above, then you start pushing it a little bit. 9:1, with a good tune, and intercooler will be able to take well into the teens with regard to boost, and should be able to do it on premium pump gas. Quote Link to comment Share on other sites More sharing options...
Guest mudbutt Posted November 28, 2003 Report Share Posted November 28, 2003 Originally posted by Nathan P: Thanks for the information. I'm still reviewing current turbo cars. I have hit a bottle neck since i want to run around 100 shot of nitrous and water/alch injection. Correct me if I'm wrong, but the owner of the 12psi M3 was running with an A/F of 11:1. What is the safest ratio you can run without melting anything? I thought it was 12:1 was the "stoic", but i may need to review. I just want to get all the ideas I can. Thanks still! 11:1 is a tad on the ritch side, but it isnt terrible at all and is safe. If you are wanting the 500hp you clamed in the other thread. Id think going a tad lower than 9:1 compression would be a good idea. 8.5 seems to be a decent point on many cars, though as I said before it will varry. Joel Quote Link to comment Share on other sites More sharing options...
slow4now Posted November 28, 2003 Report Share Posted November 28, 2003 Many race cars run what we consider high compression ratio with boost on top of it (but they generally don't have to last very long). High compression ratios allow for a smaller window for tuning error. I personally don't see what you are trying to accomplish with high compression + boost + nitrous.....? The short answer boosting a motor of 9:1 CR with aluminum heads is perfectly safe, as long as it's tuned properly and you run good gas (93-94 octane). Maybe I missed some other threads, but if you can give us a better idea of what you have to work with and what your goals are we can help you better. Not all motors run the same with the same setup. Quote Link to comment Share on other sites More sharing options...
Nate1647545505 Posted December 1, 2003 Author Report Share Posted December 1, 2003 Originally posted by Nathan P: S52 with ODBI Conversion. Full port and polished head, 1mm bigger exhaust, and intake valves, dual spring with titanium retainers, custom ground cams with stock duration with additional lift. Plannng to run Pauter rods pushing JE pistons with Total Seal rings. I will expand on the setup later tonight... Quote Link to comment Share on other sites More sharing options...
desperado Posted December 4, 2003 Report Share Posted December 4, 2003 Got to remember that runnin it rich, will put that unburnt fuel in the exhaust, and your EGT can get rather high. Quote Link to comment Share on other sites More sharing options...
iwishiwascool Posted December 4, 2003 Report Share Posted December 4, 2003 Originally posted by Desperado: Got to remember that runnin it rich, will put that unburnt fuel in the exhaust, and your EGT can get rather high. um... thats not right. Running rich will cause lower EGTs. A leaner condtion (an oxygen rich combustion is much hotter than a fuel rich one), or the ECU pulling timing will create higher EGTs. Quote Link to comment Share on other sites More sharing options...
Guest mudbutt Posted December 7, 2003 Report Share Posted December 7, 2003 fuel burning in the turbo will cause high egts. I can recall a messed up injector and glowing turbo that proved this. Running rich is a bandaid. Run the right gas for your boost, run water, do something. On a boosted car a low cr ~8:1 is not going to kill your low end or give you terrible throttle response. The motor, boost, and octane should determine your cr not your desire for marginal low end torque. Quote Link to comment Share on other sites More sharing options...
Berto Posted December 7, 2003 Report Share Posted December 7, 2003 Originally posted by I brake for more trends than CR: 11:1 is a tad on the ritch side, but it isnt terrible at all and is safe. If you are wanting the 500hp you clamed in the other thread. Id think going a tad lower than 9:1 compression would be a good idea. 8.5 seems to be a decent point on many cars, though as I said before it will varry. Joel +1 on the 11:1 ratio i'm going to run that wheneve ri tune my rx-7 just as a safety blanket against detonation and maybe boost creep on a higher gear pull. like ricky said higher compression basically just makes the tuning window much smaller. boost that bitch, make sure u have fuel. Quote Link to comment Share on other sites More sharing options...
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