centri blower guys HELP me out with compression!!!!

ADRENLN

ADRENLN

Active Member
Apr 16, 2003
2,342
3
49
NJ
#1
guys i need help to figure out what compression to run on a built engine!

i know some of you are stock engines but i need the higher hp applications.

im going to run about 12-15 psi with intercooler hopefully around 500rwhp.

thing is my mechanic/tuner says he would like the engine to be 8.5:1

the engine builder is saying that he dont usually build engines that low compression for cenrti blowers at my psi. i guess he perfers 9.2:1

WHICH WAY IS BEST! i need to hurry this up because im getting a deal on the block but the guy needs to know soon.

what are you higher hp blower guys running for compression on your built engines?

BTW this is for pump gas!
 
#4
hotmustang thanks. ive posted this on every site to see what guys are running.

seems like alot more are saying 9.2:1 is fine and 8.5 would be to low and make the car sluggish down low.:shrug:

also saying 8.5 is old school thinking. my tuner is old school used to race the 5.0's . i dont know what the heck to do.

i dont want the engine to be dangerous or pushing the limit. i figure he could just richen it up or lower the timeing to make it safe. :shrug:

however, i dont want to spent all this money and have a sluggish car down low. that is where im driving most of the time. :nonono:
 
#5
8.5 is too low on a daily driver with a centri. If all you were seeing was track time it would be ok, but for the street it will be a dog down low. You can always lower boost, fatten the mxture, or pull a little timing to make up for a little extra compression. You can't do anything to make up for not enough compression.
 
#6
hi, i build with my friend a 2000 stock components with 15 pounds the only thing i did was polished the combustion chamber and shaved the little montain next to the intake valve, ARP studs and stock gaskets back again and no isues it has a vortech, 42 pounders, cobra 2003 dual pumps, boost cooler,270 cams, springs (comp cams) the rest of the engine stock and he's going LT headers and bigger catback and the car is tuned with a predator custom tune by diablosport(willie figueroa) this car has arround 500RWHP
 
#8
ADRENLN said:
hotmustang thanks. ive posted this on every site to see what guys are running.

seems like alot more are saying 9.2:1 is fine and 8.5 would be to low and make the car sluggish down low.:shrug:

also saying 8.5 is old school thinking. my tuner is old school used to race the 5.0's . i dont know what the heck to do.

i dont want the engine to be dangerous or pushing the limit. i figure he could just richen it up or lower the timeing to make it safe. :shrug:

however, i dont want to spent all this money and have a sluggish car down low. that is where im driving most of the time. :nonono:
Click to expand...


I don't think you will loose that much bottom end before the blower kicks in going with a lower compression.. The reason I think to go lower is that gives you more room to play with it should you change your mind latter on and add more boost. Sure it won't be quite as snappy down low but it would be nice to be able to add more boost latter on.. Just run some shorter gears like 4.10's if you don't have them yet.

Any build I have been involved in I always advise people to overbuild on the bottom end and leave room to add more boost.this was they can add power safly later on because the chances are you will want more at somepoint.
 
#10
well, i guess thats the question. will i be ok running the 2.9 pully on 9.2 compression. i just assume that the 2.9 pully will give me around 15psi.


i know this varies but round about the 2.9 pully = what? for boost.

also what is the stock compression on a gt and on an 03 cobra?

thanks guys.
 
#12
ADRENLN said:
well, i guess thats the question. will i be ok running the 2.9 pully on 9.2 compression. i just assume that the 2.9 pully will give me around 15psi.


i know this varies but round about the 2.9 pully = what? for boost.

also what is the stock compression on a gt and on an 03 cobra?

thanks guys.
Click to expand...

Stock compression on a GT is 9.3/9.4:1. Stock compression on a Cobra I think is 8.5:1, but don't quote me on it because i'm not quite sure :)
 
#13
Since its a Centri i'd run closer to stock C/R...if you were doing a Roots/Twin screw/Turbo then the 8.5 C/R would be better. If i was running a Centri i would just install 17cc forged pistons. They will be perfect with 15lbs of boost. 03 Cobras run @ 8.0-8.5 but thats needed with the Roots blower and high boost.
 
#14
03-04 cobras see I believe 8.5 PSI from the factory and have 8.5-1 compression. I mean, I honestly dont think you could feel the difference between 8.5 and 9.2.

All you tuner has to do is add more timing <2000RPM and on top of that with a brand new built block that has better sealing, the car should feel exactly like it does now at least.
8.5 = less heat than 9.2. Ill take reliability, and more longevity vs more lowend power that you will never even tell is gone :shrug: .
 
#15
hotmustang331 said:
03-04 cobras see I believe 8.5 PSI from the factory and have 8.5-1 compression. I mean, I honestly dont think you could feel the difference between 8.5 and 9.2.
Click to expand...

yes.


i would go 9.2, but would prefer 9.0. higher compression is more efficient, so you will get a little better gas mileage than at 8.5. also, like others have said, there will be a little more low end power. you'll need it when it takes until 3000rpm just to start hitting boost. now with higher compression comes the increased risk of detonation but really, that risk is offset by the heat of a roots when compared to a roots/8.5 setup. as long as you are tuned properly, you'll be fine. just for reference, the turbocharged Mazda3 and Mazda6 run 9.4:1 and the Saleen S7 twin turbo runs an amazing 11.0:1, but with low boost.
 
#16
I dont know, its what I would do....but he can do whatever he wants.

15PSI is going to make some heat, even with an IC. And like SVT says EVERYONE will get greedy and want more later on....I wouldnt want to limit myself for a bit more power right now.

But eh, thats my opinion...im the type of guy that always plays it safe....well almost always :D .
 
#18
thanks guys, these are great replies. i can choose either way, i just dont know which one i want.

if i was sure there wasnt going to be much lowend missing, i would go with the 8.5. i want it reliable and to last long but i dont want a slug until 300rpm either.

most of the time i shift at 3000 so if the 8.5 turns me into a slug im gonna be pissed.

the other thing to take into consideration here is im doing a stroker! so vt was telling me that 21cc pistons would make it 9.2. is this right? they will get me the proper pistons to lower it if i want 8.5.

will the stroker engine tq make up for the 8.5 compression do you think?

i do want to get what my tuner feels comfortable tuning but i cant let it be a turd under 3000. what do you think.
 
#19
i am going with 8.5cr on my forged block with my vortech and i am also looking for 15psi and about 500rwhp

i also have 4.10's in the car so the 8.5 will not kill me and to me its like having a high ceiling of safty

reliability first // hp second is my thing
 
You must log in or register to reply here.

Similar threads

from6to8
Progress Thread Progress Thread- From6to8's 95 GT/Saleen Supercharged 331 install
Replies
24
Views
712
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
from6to8
from6to8
X
VE Table Not Dialed? Send Me Your Datalog.
Replies
49
Views
1K
Digital Self-tuning Forum
X-cam34
X
from6to8
Progress Thread Progress Thread- From6to8's 1994 Cobra Supercharger install
Replies
420
Views
8K
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
from6to8
from6to8
J
Help Figuring Motor Choice(Possible future turbo)?
Replies
13
Views
466
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
Jarhead67
J
3
Eight inches is enough for me...
Replies
5
Views
499
1974 - 1978 Mustang II Talk & Tech
Bullitt347
Bullitt347
Top Bottom
Back
Forums
Menu