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Compression ratio is at 10.5 to 1, and boosts hp from 130 to 155hp. I plan on getting a Rippmods supercharger later on, so is this compression ration too high? or all right?
I don't know what the compression ratio has to be under for FI, but I can tell you that all of the FI Toyota engines that are out there are under 9:1 (not counting turbodeisels of course). Most are in the low to mid eights. Including the 3S-GTEs.
Obviously, it would appear that you can have high compression, or high boost, but not both. Thus, I would consider chosing one or the other.
A stock 5S-FE is probably somewhere in the neighborhood of 9.5:1, so you'd obviously get more of a benefit from lowering the compression ratio and going with the SC.
High compression such as 10.5:1 and boost are possible BUT it takes amazing tuning. Professional drag cars use both high compression and boost for higher HP, but they run race fuel, methanol, alchy injection and so forth, and don't have to worry about emisisons. Basically the issue you get with high compression engines is pre-detonation. Add boost onto that then you are addng more likelyhood that you will have predetonation, hence y you should use higher octane gas. The higher CR is creating more heat and the gas is more likely to predetonate.
With that being said, it is possible but beware that you are going to really have that fine-tuned, and will be paying alot for gas. I think the stock ratio of 9.5:1 or even 9:1 is a good compromise for both good CR and ability for boost. Most high boost cars run on 8:1 CR, but that is also one of the reasons y they have alot of lag. A higher CR helps eliminate some of that lag.
If you're car has 135hp at 9:5 CR without FI and then you go to 8.5 CR and boost your car, while your turbo is spooling up you'll be running on less than the 135hp you had to begin with, untill the turbo reaches good boost of course Now with a supercharger you don't have to worry about lag since its belt driven and not by exhaust gases.
So there are benefits and drawbacks of High CR, you just have to figure out which way you want to tackle it. Ok i've rambled on for a but now, hope this helps and didn't confuse you!
Luis
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I need some more people with actual experiance to let me know what compression ratio to use. Wraith, got any advice?
Anyone who has rebuilt an engine, esp. a 5sfe and put induction on it what compression ratio did you use?
Keep in mind, the max boost I'll use is 9-10 PSI, so fairly low boost. Also, I have no problem using super premium fuel. Just worried about performance and engine life.
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Last edited by Gen3cruiser; 03-12-2004 at 01:03 PM.
Ok, first off...I have rebuilt the 5S-FE purposely for turbo charging it. So I think I meet your requirements.
Now, as Luis already pointed out, the stock setup is indeed 9.5:1. The first time I requilt, I dropped the CR to 8.5:1. This was useless. Here's why;
- you loose power off the line. Until the turbo kicks in, you have very little
- my overall power went down (99hp at the wheels pre-turbo, to 104 at the wheels running 8.5:1 and 5psi boost)
When I did this rebuild, I used a set of JE forged pistons. The machine shop that bored my blck screwed up and my pistons were ruined in less than 1 year. $600 down the drain. So I said, what the hell...the second reuild was on a new block bored 0.020 over (.5mm) and Toyota cast pistons...back to 9.5:1 CR. That was over 1 year ago and I'm now running 8psi boost...and very happy.
What Luis said is exactly correct. If you keep the CR up and run boost, there will be problems with detonation. But Toyota engines have knock sensors. These detect the knocking and cause the ECU to retard timing...and you loose power to the wheels.
So far, the ECU is not reatarding the timing at all while I've been on the dyno...and the knock sensor is new!
Personally, I would keep it at 9.5...based on my personal findings. I think 10.5 is too high for our engines. Toyota engineered it to run 9.5. If you raise it and add boost, I think you're asking for problems.
Meisner... very much correct on the 9.5:1 on low boost... But I would run a 8.8:1 with the stock head gasket and run boost no higher than 17psi on it because of stock head bolts and head gasket...
Originally posted by luisitol
Basically the issue you get with high compression engines is pre-detonation. Add boost onto that then you are addng more likelyhood that you will have predetonation, hence y you should use higher octane gas. The higher CR is creating more heat and the gas is more likely to predetonate.
You mean preignition
Anyways, go higher than 9.5:1 CR or go home. For a small displacement 4-cylinder, you want good compression for low-mid RPM power. If you go too low of compression, you will have to compensate with more boost. Chances are that you won't get much boost with a 4-cyl at low RPM, whether it's a turbo or a centrifugal S/C.
I will be running 10.5:1 in my 1MZ-FE -- keeping my stock compression. I am a tuner myself, so I am willing to do more tuning with a reward of more power and torque everywhere
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Originally posted by da_horse so would you reccommend JE Forged Pistons or not Meisner? i've thought about them but unsure...
Personally I wouldn't do forged pistons again. Stock cast pistons seem to work fine at 8psi boost. If I ever have to pull the engine to rebuild it again, I am using hypereutectic cast pistons next.
Forged pistons are too loose when the engine is cold...damn loud. This is the reason companies like Mercedes started using hypereutectic on stock engines. They grow as much as cast aluminum, but are stronger due to the higher silicone content.
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Now with a supercharger you don't have to worry about lag since its belt driven and not by exhaust gases. 
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