Raising Compression

TYTILIDIE

TYTILIDIE

METH HEAD
I remember seeing that we are like 8:1 compression ratio? I was reading on a local racing forum this morning that there are guy s with stangs and what have you that are stock with 280hp and theyre throwing S/C's on them and running like 8 psi and getting 480hp. So I guess it seems to me like theyre getting these #'s with such low boost becasue their comp ratios are already higher. So would it be beneficial to do this with our trucks or is running 25 psi the way to go? Ive had people with turbo/ S/C camaros, Civics, Mustangs etc be pretty fast on low boost levels but they all had one thing in common, they were at a N/A compratio. Anyway, thought it might be a good way to make more power without having to get a gi-normous turbo. What does anyone think?
 
gjp

gjp

another post whore
Re: Raising Compression

1st I think our trucks are 8.35:1
2nd if they are running 8psi on a 4.6l or 4.9l and think they are getting 480hp then I have a bridge for sale for them to buy. I was running 12psi on roush built engine and could only get 405 to the wheels. that was on a 9.5:1 compression I think.
I would guess rasing our compression would cause more knock and detonation. You would need alky and a great tune.
 
kessler

kessler

New member
Re: Raising Compression

The whole deal with Raising compression on a boosted motor goes something like this.

1. If you raise Compression on a boosted motor then it takes less boost to get the same amount of HP then with a lower Compression motor, But you have to look at it this way. if you raise the compression on it then if you want to run more boost then you have a very high risk of getting Knock, Unless you run a Higher Octane fuel all the time.

For Example i had a Talon that was a AWD Turbo a couple of years ago know most people will run a Max or 9.0-1 on these motors i had pistons made by ROSS for 10.0-1 and just ran less boost its a quicker responce in power but when i turned the Boost up i had to run Race Gas ALL THE TIME.
I had a friend who had the Same mods and was running less compression with the same amount of boost i was and i put down 63 more HP then he did on the Dyno. But also keep in mind that i was no longer able to run as much boost as he was due to Cylinder pressure, But i had Quicker spool up time and better responce on the street. So it all depends on how your driving your truck and how deap your pockets are for what Compression you want to go to.

IMO
 
dgoodhue

dgoodhue

BuSTeD 4.3
Re: Raising Compression

Denny Raab runs 10.0:1 CR.

If I had some balls, I would think about running ~9.5:1 with my new motor. The big advantage of running higher CR is that you don't need to run as much boost. It also would help with the NA performance and I think it would also help turbo spool up. From what I have read our stock intakes have air flow distribution issues starting at 22 psi and starts to hinder performance at 25+ psi (ie little performance issues). In additon it could put the turbo (inturn less stress on the intercooler cooling capacity) at a better efficiency range. This is one of the reasons Denny is still able to run the stock upper IC.
 
TYTILIDIE

TYTILIDIE

METH HEAD
Re: Raising Compression

Interesting, I may give this some serious thought on my next build. Would anyone say its safe to say that our head design would interfere with this?
 
James Thomas

James Thomas

"NO CLASS"
Re: Raising Compression

I will be runing 9.5 on the project "RICE CKR" Ty engine. I been building blower engines all my life and someone made the comment above about right at 400 on a Roush Mustang with 12 psi.? Man there are other issues at work there cause that's real low output. Talk to Nolan, he has experience with this and he will tell you that a higher C.R. is the way to go on our engines and that "only the Dyno knows!".

_____________
James
 
kessler

kessler

New member
Re: Raising Compression

Like i said before its all about the tune and about Cylinder Pressure, Thats the biggest. Yes less boost with the same results are nice but you just have to make sure that the fuel and tune is right on the money. Ive done it in the past with other cars and theres allot of ups and downs with it. How ever since my motor just got done being rebuilt i only went to 9.0-1 on my build and i think that that will be fine for just a weekend cruiser with a once in a blue moon trip to the track.
 
gjp

gjp

another post whore
Re: Raising Compression

car came stock with 360. I was putting 320 to the wheels. After hours of tunning and a diferent pulley and a few other things we got 405 to the wheels. According to the dyno. If you are saying I should have had more then I will go back and ask for my money back. It was tuned for 91 octane and a DD. Even the 405 was way to much for the car.
 
0260IN3

0260IN3

Engine Builder
Re: Raising Compression

We have been raising the compression on our turbo engines and have seen good results but the static compression and the dynamic compression (cam event timing) must be considered as well.
 
TYTILIDIE

TYTILIDIE

METH HEAD
Re: Raising Compression

I wonder if bumping up to 9.0:1 with just maybe some eagles would be a decent build? Does anyone think that that increase in comp would be horribly tough on the rotating assembly? Almost seems like free power in a way. I know when I did my Vette's motor back in 00, It came stock with 8.5:1. Gotta love it right? So when I did my rebuild everything was stock except the cam and pistins(to make higher comp). I ended going to 9.5:1. I have to say, it made a huuuge difference. I nkow this was N/A but can imagine the gains with a turbo.
Now even though you get less heat in the IC, you get more in the motor itself now right? I remember having to upgrade radiators and having a helper fan in the front on my Vette.
As far as cams go, I imagine a new cam would be in order correct? Upping comp like that on a stock cam would be kinda lame or am I wrong? If you would need a cam on a build like that and wanted to run 10-20 psi, what kinda grind would be needed?
 
James Thomas

James Thomas

"NO CLASS"
Re: Raising Compression

gjp said:
car came stock with 360. I was putting 320 to the wheels. After hours of tunning and a diferent pulley and a few other things we got 405 to the wheels. According to the dyno. If you are saying I should have had more then I will go back and ask for my money back. It was tuned for 91 octane and a DD. Even the 405 was way to much for the car.
Click to expand...

Hard to say because each "set up" will act different even with the same parts combo but it does sound "mildly detuned" to be a safe DD for 91 octane. I'm not sure about "hours" of tuning but after weeks - months of tweaking we pulled 445 - 453 and then started adding water injection (no alky, just water) etc. and got it up to 487 on what I consider to be a street tune. There is more there, just gotta find it is all.


_____________
James
 
canadian

canadian

sy in progress
Re: Raising Compression

Raising compression can be done on a turbo motor, you just have to select your cam properly to work with it. The right cam can bleed cylinder pressure when necessary and make sure you don't detonate too easily.
 
gkrcr882

gkrcr882

SyTyless......for now!
Re: Raising Compression

All this talk of high-compression, low boost is inspiring me. Anyone out there think that it would be possible to run 3-4# with 10:1 compression on a 4-bolt main engine? Aluminum Vortec heads w/ 58cc combustion chambers.
 
0260IN3

0260IN3

Engine Builder
Re: Raising Compression

gkrcr882 said:
All this talk of high-compression, low boost is inspiring me. Anyone out there think that it would be possible to run 3-4# with 10:1 compression on a 4-bolt main engine? Aluminum Vortec heads w/ 58cc combustion chambers.
Click to expand...

We tune LS1's with over 10:1 with 6-8 psi all the time on pump gas and they work awesome. Remember.............you can run higher cylinder pressure (compression / boost) with aluminum heads because they disapate heat faster than cast iron. Typically a 10:1 motor with aluminum heads is like a 9.25:1 motor with steel heads (approx .75:1 ratio effective drop)
 
gkrcr882

gkrcr882

SyTyless......for now!
Re: Raising Compression

Awesome. I was hoping to be able to run in the 5-7 psi range on 93 octane without going too crazy. Only thing is, I've heard that the stock pistons in the ZZ4 motors are pretty fragile when it comes to forced induction applications.:(
 
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