i need to order a set of piston to complete my base engine
i have choice of 8.1 ,8.8 ,9.5 anl lot of more
what is the best comp.ratio for my setting
plan to run around 800-850hp@+/-20lbs
i have an aftermarket ``man o war``block strocker 347
victor intake
victor alu head 60cc 2.05/1.6
twin turbo (no sure witch)see other post
custom cam that i will order soon from crane or comp.
My guest is 8.8 (or around 8.7-8.75 with thick cometic gasket)
any help will be apreciate,thanks

 

My new setup is 8.5:1 while my old setup was 8.25:1.

 

8.5 cr is a nice compromise for that setup.

 

Is this going to be a race car, street car, or both?

 

8.5:1 = turd. Especially on the street. That's a fair amount of cylinder head for that stroke, now compound that with low compression and it will be a turd. You can easily have a 9.5:1 engine and accomplish your goal.

Take the time to CC everything! If you don't odds are that your 9.5:1 pistons are actually alot less. You must know the area above the ring, the valve relief, etc. If you don't measure everything you are going to get less than good results. Invest the time.

 

Depending on what you plan on doing with this thing(race,street) compressions up to 10.5 r good if you want to make some serious power. Sounds like the block will hold it ,but if your going to go this high with the cr you might look into a billett crank,rods ect...

 

week end drive with ocasionaly 1/8 track
i want to leave on pump gaz 94 octane

 

For car living its life on the street and light 1/8th mile racing I would go as high compression as I could but still keep it pump gas safe.

 

sory for my bad english
what you mean by ````turd``

 

9.5.1CR sounds like what you may want too look for.

Hope this helps

 

Turd= fecal mater,poop,shit, that brown stuff that comes out of your butt while you are going to the bathroom. What he mean't by saying it will be a turd is that with lower compression it will be slower and less responsive until the turbo gets into boost.

 

lol...thanks ok i see now what you mean
i'm french canadian and i'm not to good with english
thanks to all of you

 

My 408 has 8.5ish : 1. N/A at the moment. I wouldn't call it a turd at all. Losing traction in third rolling on the gas untuned seems pretty healthy to me.

Half a point isn't the end of the world, maybe 15hp down on a 9.5:1 setup.

4cylinder 7.8:1 turbo car, now that's a turd.

 

It amazes me how many people think this deal is simply a number. Doesn't anyone look at the head cross section, the displacement and the stroke.

 

Please explain. Does't 9.5.1 mean 9.5.1 no matter how its acheived

 

i went with 8:8 from 9:8

More boost

 

I think Don is refering to the fact that not many people account for the area around the pistons down to the top ring. This area can easily add up to a few cc's and chang ethe compression ratio a fair amount. If you just look at head cc, chamber size, gasket info and piston cc, it does not give you a true compression ratio number. You need to put a piston a cylinder in at fill it up with fluid, and verify the actual cc of everything.




Mark

 

You will gain more power running boost over compression, but if you run higher octane racing fuel you can get away with high compression and lots of boost and make great power. For a pump gas car for street/strip action I would recommend more compression and less boost for quicker spool ups and better off throttle responce.

 

a 500 CID motor can probably get away with less compression compared to a 300 CID motor because of the giant torque difference, without suffering as much sluggishness down low.

 

That's part of what he was saying in the 2nd half his first post, but in the first half of his first post, and the 2nd post, he's talking more about the difference between engine builders and engine assemblers. Everything effects everything else, a short stroke motor with a big head is going to need more compression to get the pop and get it up on the pipe than one the other way around....for example.