4g64 questions/compression ratio questions
4g64 questions/compression ratio questions
I am looking at a few diff routes, thinking about going with a engine that was recently built. Receipts included. The guy thinks the compression ratio is around 9.0-1. I will be running e85 and running a fp black and BF272 cams. I know typically e85 with my set up people run 10.0-1. My question is how much power will I be sacrificing by running the 9.0-1 instead of 10.0-1?
Another question is, is the complete swap as easy as I have read? I know the timing belt/water pump issues. Which I will be running a map adapter, and using adjustable cams.
The car is tracked only a few times a year, and only driven as a weekend warrior.
Another question is, is the complete swap as easy as I have read? I know the timing belt/water pump issues. Which I will be running a map adapter, and using adjustable cams.
The car is tracked only a few times a year, and only driven as a weekend warrior.
9:1 and here is why.
10:1 feels snappy on the street, should (and I use this loosely) make an addition 4% power for a given boost level as long as timing doesnt change, help keep bigger cams a little more civil.
BUT
On 93 (and you can imagine 92 or less out west) you still get limited to the amount of boost you can run before the timing has to drop to make the best use of the boost you want to run. Let's take Derek's boost level as a hypothetical example.
Derek runs a large turbo and 26psi on a 10:1 2.3 on 93 octane. At this boost level we are both convinced his car is knock free and as he indicated it made 560whp in VDR. We up the boost but now we have to start pulling timing at the same level to keep knock at bay so we get to the point where we make more torque but timing is so low it doesnt really make that much more power.
I have seen logs (not Derek btw) of 10:1 motors trying to run 29psi of boost on 93. Timing is 7-8* at 8,000. I know my car at 29psi is going to be 12-13* on 92 at the same boost level, same turbo but a 9:1 motor. I also happen to know that 1* of timing is normally 10whp. A few pieces of math based on my car at that level-
650whp at 29psi and 12*
vs the same car but 10:1 and 7-8*
650 - 45whp (4 or 5* less so let's split and say 45) = 605
605 (if it was 9:1) * 1.04 (+4% for a 10:1) = 629.2 at the same boost level with lower timing
So you look at it and say its only 21whp...why loose even 21whp though right? In addition lower timing elevates EGT and makes the risk of a misfires even greater. If its on E85 this is a non issue but what if E85 goes away and you get stuck running 93? Then you need racegas or meth injection to get the timing back, drop EGT, get reliability, etc.
Our cars have run just as fast as 9:1 and 55psi as they do at 10.5:1 or 11.5:1 and 55psi.
10:1 feels snappy on the street, should (and I use this loosely) make an addition 4% power for a given boost level as long as timing doesnt change, help keep bigger cams a little more civil.
BUT
On 93 (and you can imagine 92 or less out west) you still get limited to the amount of boost you can run before the timing has to drop to make the best use of the boost you want to run. Let's take Derek's boost level as a hypothetical example.
Derek runs a large turbo and 26psi on a 10:1 2.3 on 93 octane. At this boost level we are both convinced his car is knock free and as he indicated it made 560whp in VDR. We up the boost but now we have to start pulling timing at the same level to keep knock at bay so we get to the point where we make more torque but timing is so low it doesnt really make that much more power.
I have seen logs (not Derek btw) of 10:1 motors trying to run 29psi of boost on 93. Timing is 7-8* at 8,000. I know my car at 29psi is going to be 12-13* on 92 at the same boost level, same turbo but a 9:1 motor. I also happen to know that 1* of timing is normally 10whp. A few pieces of math based on my car at that level-
650whp at 29psi and 12*
vs the same car but 10:1 and 7-8*
650 - 45whp (4 or 5* less so let's split and say 45) = 605
605 (if it was 9:1) * 1.04 (+4% for a 10:1) = 629.2 at the same boost level with lower timing
So you look at it and say its only 21whp...why loose even 21whp though right? In addition lower timing elevates EGT and makes the risk of a misfires even greater. If its on E85 this is a non issue but what if E85 goes away and you get stuck running 93? Then you need racegas or meth injection to get the timing back, drop EGT, get reliability, etc.
Our cars have run just as fast as 9:1 and 55psi as they do at 10.5:1 or 11.5:1 and 55psi.
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