With force induced engines, what do you get out of lowering your compression?

 

slower spool, shitty low end. Oh yea, and more margin for error when tuning, so if you cant get your tuuning done the right way on a dyno, I would suggest lowering compression. I lowered my compression and have been kicking myself eversince....

 

I thought it was better for tuning, less errors. Anyone else have any thoughts on this?

 

Easier to tune and less risk of detonation. If you lower your comp go with a slightly larger bore and the difference in your bottom end power will not be as noticeable.

 

with lower compression you will yield less hp per psi.
lower compression is easier to tune due to the larger margine for error. If you have high compression you need to have better tuning (which is always good). Imo lowering the comression is counter productive afterall boost raises the compression of an engine.
For a street set-up i wouldn't run lower then 9.5:1 compression (if you have a choice) unless you have lower compression then that stock (i.e sohc d15 have 9.2:1 compression)

 

Im going to run 9:1 on a b16 with stage 2 revhard. Anyone else with opinions on this subject?

 

How much boost do you plan to run? Are yo building the engine or just lowering the compression via head gasket?

 

I am getting srp pistons, eagle rods. I am planning to run 7-9 psi so far. Tuning via Hondata, but don't know what size rc injectors to get. It's a daily driver, but I want to be able to kick some *** with it. What do you guys think?

 

Go with 9.5:1 or higher compression and run about 12psi. You will need a 3 bar map sensor to run more then 11psi I beleive. You should be able to pull some nice numbers with that se-up. 550cc injectors should provide enough fuel for that set-up. Or you can go to rc's website and put in your needs/wants and it will give the size of injector that you will need for that amount of power

 

I already ordered the 9:1 srp pistons.

 

everyone seems to be saying that you lower comp just so you can run a shitty tune but the other reason is that we don't & cannot run race gas on the daily.

or am I missing something

For example if your static C:R is 11:1 & you put a turbo on that, there is no amount of tuning that is gonna let you overcome the shortfalls of pump gas.
But
if your running 8.8:1 you can run it rich and crank the boost and make more power.
this may make for a shitty daily driver but you will turn in higher MPH at the track.
This is always how I thought things worked.
I'm not neccisarily saying i'm 100% right on this so someone who tunes and does truely know please respond to this post.


paging Corky Bell.


[Modified by T-sohctec, 3:08 AM 3/7/2003]

 

With higher compression you could always pull some timing to compensate. Or you could just run less boost when on pump gas. Either way it'll be easier to drive on the street, right? Sorry I'm learning too, and that's my take on it.

 

well, here's my take*

all the guys who are running really high HP on the dyno use forged pistons between 9:1 and 9.5:1.

All the guys who chose to stay at stock compression or go higher....well I don't see them at all posting their numbers...now having said that, I have not ran my car on a chassis dyno yet, so not sure what I am going to see...but all the pros, including my mechanic tell me to go low comp.... Top Fuel Mie cars (the 400 to 500whp) CTRs and ITRs lower their compression..not trying to start anything..its just food for thought

 

why are u getting pistons and rods if your only going to run 7-9psi?

im running 7-9 on a stock b16 and when i go to the track ill be running 10-12 on 93-94 octain gas. my only mods will be exhaust, GS-R cams, vafc for fuel, dsm 450cc injectors and the MSD BTM for timming retarted 1 degree per psi. im shooting for 275 whp on a stock b16. so if your going to run lower comp pistons and rods run aout 14-16psi and enjoy your investment in piston and rods and with hondata you can run atleast 10psi daily on pump gas. because i may end up doing that on a stock block with only the vafc 450 injectors and the MSD Btm

 

 

that's a good point, anyone who is putting down say 500hp is using low comp pistons. all of those aforementioned cars probably had plenty of DYNO/TUNE TIME yet they still go for low comp. therse more to lowering your comp than being able to run a shitty management.

here is another point. when you raise your boost it's not the same thing as raising static compression. When you boost you are putting more cold air, and more importantly cold fuel into the chamber. Not just more tightly compressing a given volume of air but you are effectually adding displacement to your engine, more fuel & air to burn.

I think thats why it's better to have a low comp FI motor.

anyone know better?

 

Sorry, this is kind of long!!

Well, this is the reason I am lowering my compression to 9:1. My car got stolen back in October. It was running well. When the cops found it and it was at the shop, it wouldn't start. I had the engine torn apart and found three broken pistons and rings. I told my insurance company that they should fix it because it was running before the theft. They denied it. I hired a lawyer to fight it. My insurance company had said that the engine blew due to detonation. The proof was that there was carbon build up behind two of the rings and one did not. Supposedly, if the rings just blew recently, there wouldn't be carbon build up behind it. After about a month, I won the case and they are fixing it to stock. So instead of fixing it to stock, I am putting extra $$$ in and decided to get 9:1 srp pistons and eagle rods. Upon inspection of my engine bay, I found that my deltagate was connected on the top and the side, which I think made my car spike to 12 psi? The deltagate is supposed to be only 7-9 psi. You think it detonated because the wastegate was connected wrong and I was boosting 12 psi. I read that it should be connected only on the side and the top was for a boost controller.



[Modified by Autobot_Killer, 6:05 PM 3/7/2003]

 

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