Compression ratio questions

[88-383]

Do you guys think 10.1 is to high for a K5? The enfine is built 355 with aluminum heads, full blueprinting and balance. I don't mind having to use high octane fuel, but i don't want it to blow up either.

Kelvin

 

[Hogback Fabrication]

With aluminum heads I think 10:1 would be just fine, but you will have to use premium fuel.

 

[dyeager535]

What kind of heads besides aluminum?

I think one rule of thumb states you can go a full point on compression with the same gas.

I'm running 9.2:1 with 87, you probably can with AL heads @ 10:1 if they've got a good chamber.

 

[gauder]

Especially okay if you can use small cc combustion chambers and flat-tops to achieve 10:1.

 

[RootBreaker]

stupid question.... how do you determine your compression ratio????

 

[SUBFAN]

Measure everything....

http://www.projectpontiac.com/ppsite/content/view/16/30/

and use a calculater like this one....

 

[1985_K5_Silverado]

Oops, the previous poster already dealt with what I was going to post.

 

[88-383]

I'm using the 195cc Trick Flow CNC heads on this engine. Normally I would've had the block zero decked, but some reason this time I didn't. Would you guys say it'd be ok even towing?

KM

 

[dyeager535]

Are these the Kenny Duttweiler models? I can't find the 195's on TFR's site, but I do see some 23* Kenny Duttweiler ones there.

Looks like fast burn inspired chambers on the 175 non-Duttweiler models, so if the Duttweilers follow suit and are also fast burn, I would *suspect* (experience may prove otherwise) that you would be fine with 87 octane at that compression ratio.

 

[RootBreaker]

Measure everything....

http://www.projectpontiac.com/ppsite/content/view/16/30/

and use a calculater like this one....

thanks.. now if I only knew all those values

 

[RootBreaker]

thanks.. now if I only knew all those values

yeah i dont know what im doing.. i came up with a 1.43 : 1 ratio!!!

she should purr like a kitten

 

[88-383]

Are these the Kenny Duttweiler models? I can't find the 195's on TFR's site, but I do see some 23* Kenny Duttweiler ones there.

Yup 195's you can see them here. Being able to run 87 octane would be a real bonus. I just wanted a sanity check because I don't want a pinging engine.
http://www.trickflow.com/product/chevycylinderheads/23degree/pr_23degree.asp

 

[dyeager535]

What are your combustion chambers like? That's key to what kind of compression numbers you can expect to get away with, and that sight doesn't show on your 195's that I could find.

If you are worried about it pinging on even super unleaded, I wouldn't worry at all. (just in case it does with 87 or 89)

 

[MTMike]

The 195 is the intake runner volume, not the combustion chamber volume - more than likely your CC volume is either 64 or 70. They can be had in may other cc volumes depending on the mfr, but AFIAK 64 & 70 are the more common ones for small block Chevys.

I'm running the Vortec heads on mine, and though I don't know the cc volume, they come in either 64 or 70. If it's got 64ci I'm pushing 10.48:1 (which sounds about right because it pings like a Diesel on anything less than 91 octane), or if it's got 70 I'm running 9.84:1.

Mike

 

[dyeager535]

Yeah, I understand the CC volume vs. runner volume, it's just that the sight doesn't show a pic of the combustion chamber design.

The other heads pictures do have the fast burn (used in the Vortecs) chamber design, so that was where I was going with it..10:1, AL heads, and a fast burn chamber *should* be pretty easy on the fuel.

 

[tarussell]

Don't forget about cam timing playing a role in different motors that are being compared with the same C/R ratio's . What works in one engine might not work as well in another .
Tom