Hey guys, some of my 300zxtt friends are debating spool up vs. compression. Some say high will spool faster some say low, both having diffrent theroy to back it up. SO i was wondering if any of you had 11:1 and went to 9:1 but kept everything else exactly the same as far as your turbo set up. Post up what your spool time used to be vs what it is now. If you have dyno sheets that would be great but if not just the info will be fine.

 

Simple answer, Higher Compression = Higher exhaust pressure = quicker spool time. But that is the simple answer. I am sure there will be plenty here that will tell you about proper exhaust manifold design will help match the pulses to give faster spool up, etc. etc. But that is in the design of the kit (if you are buying a kit) If you are just talking lowering the compression ratio with flat tops vs. standard high compression NA pistons, then what I first said will hold true. Downside is higher compression limits the total amount of boost you can run, thereby limiting the maximum horsepower you may make.

Would love for others to join in on this as I would like to here any other information on maximum boost you can run on which octanes and other things related to high compression vs. lower compression for tubro setups.

 

I believe Mase is planning on just blowing an f20 just to see what boost levels stock internals can take... I want to say the bottom end is limited to around 750hp... rods start to fail beyond that, IIRC. I also think the stock head gasket tends to let go over 10 psi with our high compression (assuming pump gas).

John

 

I would think so too but after reading some of the post, science and thermal dynamacs got brought in. Here is one of the post(edited a little by me).

The gases are being brought up to higher pressures at the time of ignition which ultimately leads to higher combustion temperatures - definately agree on that one. This is actually a more sound reaon behind why the higher compression engine produces more power than the same engine with a lower CR. The fact that there is a specific amount of energy available within a fixed amount of fuel and air being reacted. If a higher compression engine makes more power from that given amount of energy, there will be less energy left over in the exhaust. Hence, the reason we see the high CR engine producing laggier spoolup rates.

 

very interesting

 

 

They will spool the same, however the higher compression motor will make more power off boost so it will feel like it spools sooner.

http://www.evans-tuning.com/comp2.html

Tim

 

Thanks tim. thats exactly what i needed.

 

I went from 8psi on stock CR to 16psi at 9:1 and the spool is the same with only noticable difference between shifts as for a nanosecond you feel the boost dropping, but not like in a Supra or similar. However you have to take into account that 16psi takes longer than 8psi to build up. You will not feel the difference if that calms you down.