How hard is it to switch out a crank, cam and lower compression?

Pokageek · Oct 11, 2008

If I wanted to throw boost at my car, I would have to go forged crank, and lower compression. I am at 10:45:1 right now. How do you lower it? Is it a lot of work changing out a crank?

final5-0 · Oct 11, 2008

Hey Keith

I remember a thread where Don 95Vert was talking about using boost
with high compression

He pointed out the obvious

You would not want to go crazy with the amount of boost

I remember him using examples of factory cars ( IIRC, it was GM )
with high values of compression and running around 6 lbs of boost

Just something to think about ... I know it made me think about it

Grady

revhead347 · Oct 11, 2008

Realistically you have to take the whole engine apart to lower the compression. It has to do with the pistons more than anything. You can lower it by running larger combustion chamber heads, or by running head shims, which is a bad idea. Either one will make very little difference. Realistically you're going to have to pull the engine and put pistons in with a huge dish. While you're doing that you can put a shorter stroke crankshaft in there which will make it easier to lower compression.

Kurt

Pokageek · Oct 11, 2008

Thanks guys. Maybe I will just be happy with what I have..or throw nitrous at it lol.

revhead347 · Oct 11, 2008

Nitrous is my friend. So much easier. And nothing compares with the torque.

Kurt

Pokageek · Oct 11, 2008

I am going to ask Rick_91GT as well. he built my engine. If I had an automated bottle opener I might be more ok with nitrous. I have to find out exactly how much HP and TQ my crank will handle. I think it is roughly 650 total HP and not sure TQ...thats roughly 525rwhp I think.. I am already putting out close to 450rwtq IIRC..that doesn't leave me much room though. If I am hitting 525rwhp I will be hitting prolly...560rwtq..I dont want to blow it up.

ga94gt · Oct 11, 2008

You can run boost with that compression heck look at all the lsx's cars running 10.5:1 with boost and the new z06 10.5:1 with a blower.

Just make sure the tune is spot on and you have enough fuel because what it really comes down to is keeping it from detenation. I had friend run 10.5:1 with 9lbs from an s-trim

revhead347 · Oct 11, 2008

ga94gt said:
You can run boost with that compression heck look at all the lsx's cars running 10.5:1 with boost and the new z06 10.5:1 with a blower.

LSX cars have a smaller bore, better combustion chamber design, and an aluminum block. Most of those blowers only put out like 6lbs of boost too. It's a totally different setup. It's totally different from a stroked Ford motor.

Kurt

revhead347 · Oct 11, 2008

Pokageek said:
If I had an automated bottle opener I might be more ok with nitrous.

I think a 414 would make all the power and torque you can handle on the street N/A. I would reserve the bottle for the track, where an auto bottle opener really isn't necessary.

Kurt

Pokageek · Oct 11, 2008

It does...I've got 2 friends who bought cobra's and are tricking them out.

1slow95 · Oct 11, 2008

I've done some research on this subject over the summer. I even had a thread here about a while back. You might be able to run 4-6 pounds with pump fuel and an awesome tune. You could definitely do it with race fuel. I did some math, and 5# on my engine should get me close to 580-600rwhp. Unfortunately I haven't won the lottery yet, so no sc for me.

To answer your original question, you basically need to replace all the internals in the engine. Dished pistons and maybe a shorter stroke crank are needed to lower compression. The cam also affects compression. If you're running a semi wild n/a cam, you probably wouldn't have a problem with boost right now, but you won't make near as much power as you would with a blower cam.

Look up Parchisi (sp?) on here. He has a blown 408 IIRC.

revhead347 · Oct 12, 2008

If you are running a blower, you're going to need a low overlap cam, which is going to raise compression.

Kurt

parchisi · Oct 12, 2008

I'm running about 8 lbs of boost with a 10:1 compression ratio and I have run into some problems with blown headgaskets and "blowed up" pistons. After the most recent catastrophe I finally went with some head studs rather than bolts and some of those fel-pro 1011 lockwire headgaskets, got the timing right, and it seems to be reliable now. With your higher compression, it may be tougher. If you have the time and money, I'd definitely say go ahead and swap in some pistons with a good amount of dish. Otherwise, nitrous loves high compression!

revhead347 · Oct 12, 2008

Nitrous works well with compression somewhere in the middle. It's all relative to the fuel and stuff. Generally speaking you can run higher compression with an N/A setup than you can with a nitrous setup.

Kurt

parchisi · Oct 12, 2008

Yeah, I've only read somewhere that nitrous is good for high compression, since you have first hand experience, we'll go with what you say.

Pokageek · Oct 12, 2008

I think if I went blower..I would just sell my shortblock and buy another one made for it. Then I could make my money back. When you guys say shorter stroke, are you saying go 383c.i. or something?

Also, after calculating it, I think I could go 100 shot just fine. On my smaller 302 it netted 60rwhp and 70rwtq. I would prolly want to stop there for safety to keep me under 650 whp. I rather not go nitrous though.

How hard is it to switch out a crank, cam and lower compression?

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