9.0 compression

[BMFB]

so, i've been looking around for pistons and the idea of running a little bit higher of a compression ratio has come up in my thoughts, my reasons being price. it seems i can get a set of forged pistons for a good price at the 9.0 range, any lower and prices start to double. A little about my truck, im running code 59, and i can change my boost pressures with no prob, the motor is going to be close to a stock rebuild, but with a scat crank and arp bolts in everything. i know guys say you can run the new vortechs and those have ratios closer to 9.4, but i was just wondering, is 9.0 on the brink of safety?

 

[qbnkiller]

Re: 9.0 compression

With good tuning...no problems!

 

[dgoodhue]

Re: 9.0 compression

so, i've been looking around for pistons and the idea of running a little bit higher of a compression ratio has come up in my thoughts, my reasons being price. it seems i can get a set of forged pistons for a good price at the 9.0 range, any lower and prices start to double. A little about my truck, im running code 59, and i can change my boost pressures with no prob, the motor is going to be close to a stock rebuild, but with a scat crank and arp bolts in everything. i know guys say you can run the new vortechs and those have ratios closer to 9.4, but i was just wondering, is 9.0 on the brink of safety?

I personally think 9.0:1 CR is good idea if you can tune for it. It helps reduces lag and should be better at part throttle in vacuum and it allow lower the boosts levels. Lower boost levels is better for those of us running stock intakes. The higher boost levels really accentuate the intake manifold air distribution issues.

 

[It's just a six]

Re: 9.0 compression

I think 9: is fine for your purpose.

My Wifes Stock Audi has 10:1 w/a turbo I believe.

I am just sorta guessing here,but I have not heard too much about the stock intake manifold having air distribution problems & cylinders/pistons buring up because of this.

I have heard about it on the Buick GN's & T-Types & there is a plate (RJ something?)that helps out w/this problem.

But when you look & the Buick intakes,they do not look as good of a design as the stock Sy/Ty manifolds. :2cents:


I think the Stock intakes are a fairly good design,othere than where they position the TB.

 

[BMFB]

Re: 9.0 compression

I was looking specifically at a set of kieth blacks icon forged pistons, i don't see to many other people rock'n those though...

 

[leroy]

Re: 9.0 compression

I think 9.0 is fine with the correct tuning. Talk to your machine shop about getting the proper quench/squish. The proper squish can minimize detonation and improve combustion.

Jim

 

[turbodig]

Re: 9.0 compression

The CR isn't going to be an issue with proper quench.

Whether or not the piston is suitable for a high-heat boost application depends on the piston being selected, and I'd be more concerned about that vs. anything else.

 

[TYTILIDIE]

Re: 9.0 compression

Please expand on squish/quench. Never heard these terms used before.

 

[Six-is-Enough]

Re: 9.0 compression

With good tuning...no problems!

X2 and the high CR would be great with a stock/ stockish small turbo in keeping it in its effecency range.:2cents:

 

[turbodig]

Re: 9.0 compression

Please expand on squish/quench. Never heard these terms used before.

Nutshell version - the distance from the top of the piston at TDC to the quench pad (flat surface) on the head.
How far the piston sits down in the hole and the head gasket thickness are the primary things that determine this.

You could write a book on the effects of squish/quench distance/chamber shape. Google around, you'll find lots of references.

 

[turbodig]

Re: 9.0 compression

I am just sorta guessing here,but I have not heard too much about the stock intake manifold having air distribution problems & cylinders/pistons buring up because of this.

There's actually lots of problems. In fact, I suspect many motor failures occur because of the imbalance.
The more boost you run, the worse the imbalance gets.

 

[It's just a six]

Re: 9.0 compression

There's actually lots of problems. In fact, I suspect many motor failures occur because of the imbalance.
The more boost you run, the worse the imbalance gets.

Where is this info?

Are these stock engines & detonating?

Built engines having more of a problem?

Never seen a thread about the intakes causing cylinders running too lean or too rich.

Link please.

Not getting after you Dig,just curious myself.

Are guys running individual EGT probes & data logging on each cylinder to know which cylinder/s are the problems?

 

[MRKING]

Re: 9.0 compression

I recall Gerber talking about it before , look at some of his past threads .

 

[It's just a six]

Re: 9.0 compression

Please expand on squish/quench. Never heard these terms used before.

On the GM LS engines the piston actually sticks out of the top of the block having a positive deck height.

That's part of the reason how the high compression engines (LS series) can run pump gas,they have a close distance of the piston to the cyl head surface,the closer the better quench,but,,, there are minimum distances you need to know.

 

[Try Me]

Re: 9.0 compression

There's actually lots of problems. In fact, I suspect many motor failures occur because of the imbalance.
The more boost you run, the worse the imbalance gets.

I think that was why my v6 kept popping head gaskets on the back two cylinders. I know ive read multiple things on here in the past about the poor distribution of the stock intake.