Estimated Compression?

[Caleb]

I'm thinking about boosting my engine and need to drop the compression. Its currently 10:1 with flat-top pistons and 64cc heads. If I got 76cc heads, what would it drop it down to roughly? Just a good round guess would be fine.

[LT1Dan]

I don't know what your head gasket thickness is but this calculator says roughly 9.5:1 with what info I gathered from your sig...

http://www.csgnetwork.com/compcalc.html

*EDIT: The numbers that come up when you click the link are NOT what I entered. They are just the default numbers.

[Caleb]

Its just a standard gasket, but my bro came up with some different numbers, roughly 8.8 with 76cc running a compression ratio calculator and pulling some specs from other like products. I'll keep looking around. I bought the engine from Sperry's as a short block and I remember them saying it was 10:1 with a 64 cc head...so well see.

[LT1Dan]

I'm not a pro by any means. I just used the standard 350 numbers when I ran it. I very easily could have messed up on one of them. Good luck with it though. We need more GM muscle around here. haha

[69gt4speed]

hey don't change it yet, you need to run my 2011 first. I get around 9.5 also.

[Caleb]

This is gonna be for my other project car Rob :-)

[Scott]

You need to know your bore, stroke, piston dome/dish volume, piston to deck clearance, gasket compressed thickness, and combustion chamber volume. Then its easy to use a calculator!

[Caleb]

Yep, I've learned all that in the past couple of days :-) I love the internet. Haha.

[sparkles]

Also, what's the bore of your headgasket. Most likely, this is your specs:
4.030 cylinder bore
3.48 stroke
.020-.040 gasket thickness
4.060 gasket bore

[AutoMods]

or run e85 or meth injection and leave the compression high . my motor is stock 10:1, i've ran 11psi through it on pump gas with meth injection

then you have a nice high compression motor off boost and no knock on boost

[Caleb]

Gonna work on it this spring getting the body straight and save money for piecing out the engine and components. Been looking at some high flow heads and so forth, trying to find a good balance. Not really into running Meth injection or anything like that, I'd prefer just running pump gas on this build. A lot of people prefer low compression high boost to make safe power and that's what I'm going for.

Looking at some AFR Heads with 210cc intake and 75cc's. And looking at running dished forged pistons/rods/crank to get the compression ratio around 8.25:1 with a .026 thick gasket. The issues that I'm down to now for choosing is the cam for the centrifugal supercharger. From what I've read, you need decent lobe separation 112-114 preferred and decent/mid-ranged intake/exhaust duration @ .50 (with the exhaust higher than the intake for boost) and a really decent lift depending on the RPM range ran.

Granted this is a Summit Cam, but it looks like its about in the ball-park range of what I'm looking for:

http://www.summitracing.com/parts/SUM-K1105/

Idk, what do you guys think? I know theres some name brands out there, but I'm looking for something fun and streetable.

And if I were to do anything to my current engine in my firebird, I would get new heads and a return fuel pressure regulator to help stabilize my fuel issue if its not properly running.

[Deimos]

try yellowbullet alot of steals over there

[sparkles]

When I was picking out a cam, I downloaded Comp's software and went from there. It's free. You just plug in all the specs of your engine, car, bolt ons, blower, etc. It'll spit out a few different suggestions and give you complete specs of all their cams for the type of driving you will be doing. It'll also give you estimated horsepower levels.

http://www.compcams.com/downloads/register.asp

Download that and go from there.

[Caleb]

Thanks man, I'll check it out :-)

[Ninesecsnake]

Stay 10:1 and run E85, with compression that low the car will be no fun on the street it will be a dog down low.

[Caleb]

Is E85 the same shit as the 93 Ethanol Octane @ Road Ranger? Or does it specifically have to say E85?

[AutoMods]

no that stuff at road ranger is probably 10% ethanol or less. google is your best friend, you have a lot of reading to do on e85. but its great stuff and your lucky to have it close to you in the midwest. some people in other states drive hours to get it and drag it home in a barrel. marion has it , north liberty , iowa city , coralville have e85 stations.

http://graphics8.nytimes.com/images/blogs/greeninc/e85pump.jpg

also meth injection is cheap and effective, a $3 gallon of meth will last you through probably 2 full tanks of gas.

[AutoMods]

wow that cam and lifters on summit is cheap. must be because sbc parts are so common.

i wouldn't be afraid of summit brand, they usually rebrand other big name reputable brands out there and their stuff is usually good.

summit is in it deep with trick flow. in fact when you call trick flow you get summit reps, not sure why that is but a lot of summit branded filters I've noticed are trick flow. summit fittings are usually goodridge brand.

[Scott]

First of all before you order anything or make a decision I would be sure about what you have now so you know what the compression is. IMO

[Drifte]

So let us know when you determine your current compression. Id leave the motor itself alone if everything is good, and throw the blower on. water/alcohol/methanol injection is cheap and super easy for a knock deterrent. Oh, and I have found Caseys 91 octane NON ethanol gets me about 2mpg better but dont recall if it helped with knock.

[69gt4speed]

You could always go down and buy some turbo blue gas and mix it in or use straight w a carb. A lil expensive but wouldn't have to do much else. It's like 108 110 oct.

[slow ride]

Man e85 is nice, but the fuel consistency can be all over the place if you buy it at the pump and with a blow through setup it's not like you will have nock sensors, etc to help protect you. If you are splitting hairs with stuff it would be best to measure everything having to deal with SCR and not just guess using standard numbers.

[krustindumm]

or run e85 or meth injection and leave the compression high . my motor is stock 10:1, i've ran 11psi through it on pump gas with meth injection

then you have a nice high compression motor off boost and no knock on boost

Werd, E85 ftmfw.