Hi... just installed a new valve train, so I also installed a tachometer so I could break in the new cam at the correct RPM. Just wondering where I should put my little red shift indicator needle... and where redline would be on my engine.

Top end all new all stock, except the new cam is an RV cam.
Bottom end is all new all stock.

Thanks all

 

Here's a little bit of math, but keep in mind you'll probably run into valve-float before you reach the RPM derived below. The idea here is that, as a general rule of thumb, piston acceleration in feet per second per second should be kept below 100,000, and that beyond that point, the lower half is likely to come apart. But it's just a general guideline.

There's probably a better way to get at this answer, but the way I do it is to plug in my guess at a redline RPM, see what the answer is, then adjust my guess accordingly until the answer's around 100,000 piston acceleration.

Here's what you need:

RodLengthToStrokeRatio = RodLength / Stroke

Piston Acceleration = (Redline RPM)^2 * Stroke * (1+(1/(2*RodLengthToStrokeRatio)))/2189

Here's an example for my 390:

1.72 = 6.488 / 3.78

97132 = (6600)^2 * 3.78 * (1+(1/(2*1.72)))/2189

So, theoretically, I can pull 6,600 RPM and get 97,132 piston acceleration in f/s/s. Personally, I won't go above around 5,500 RPM. But that's me, and this is a "big block" or "medium block" or however people like to classify a 390.

I'm sure someone more knowledgeable about engine builds will give some good advice soon, and maybe some insight particular to your 302. I just tinker. Cheers.

 

Wow my high school teacher was right, I did use this after I graduated... she didn't tell me it would take 10 years.

This is what I got...

Stock 302
Stroke=3" Rod=5.09"

100,000=(x)^2*3*(1+(1/(2*(5.090/3))))/2,189
100,000=(x)^2*3*(1+(1/(2*1.696)))/2,189
100,000=(x)^2*3*(1+(1/3.392))/2,189
100,000=(x)^2*3*(1+0.2948)/2,189
100,000=(x)^2*3*1.2948/2,189

Let X=7,500

F/S/S=7,500^2*3*1.2948/2,189
F/S/S=56,250,000*3*1.2948/2,189
F/S/S=168,750,000*1.2948/2,189
F/S/S=218,497,500/2,189
F/S/S=218,497,500/2,189
F/S/S=99,816

So everything on the bottom end will fly apart at 7,600 RPM

Thanks Zerfetzen for the formula, my head hurts I am going to bed now.

 

I know some people turn alot more with a 302 but I keep mine under 5,500.

I thought I have heard people say the stock rods and crank will let go at 6,200? Not sure though.

 

Interesting. I never got my 400 over 3000rpm. And the new 466 that's in it now is set at 5000rpm.

 

Yea, I doubt I ever get it over 5,000 under load I just wanted to know.

Any one know at what RPM max HP is with a RV cam on a stock 302?

 

If your RV cam was Comp Cams, they have a program you can download for free that estimates a lot of things about your engine, including peak horsepower at a given RPM.

If I remember correctly, the old 302's were great motors, but the stock rods were a weak point. If that's true, then they're not up to the task of 100,000 f/s/s. Are your rods new and aftermarket, new OEM, or reconditioned?

 

The cam is an Eagle Racing brand RV cam... stand by and I will go get the specs and post.

Rods are new aftermarket. They are high carbon.

 

It sounds like your bottom end can handle the equation then for sure. The Comp Cams free download is called Cam Quest. While it has only Comp Cams in there for you to pick, you can either pick a cam that has close specs to get an idea, or I wouldn't be surprised if you can enter your own Eagle cam specs. If you use Cam Quest, let us know what it gives you. I've done a few engine builds, and to the credit of Comp Cams, it's been pretty accurate for me, but I've never focused on the peak RPM for HP though. Cheers.