Opinions on 400 build: 4" crank 434 or 4.25" crank 461
 

When you boil everything down to the syrup and A/B two different cid motors using the same heads you find that hp produced is independent of cid.

That said a 4.00" stroke motor will hold onto peak hp numbers longer due to less friction an also will rev faster which is a big plus in the acceleration game.

A 4.00" stroke motor tuned well will still make you enough torque to annilate your rear tires at will at most any rpm.

I would take full advantage of having Aluminum heads and get your compression up to 10.5 minimum .

I understand the idea of something different. I have my share of 461's. I went with the 433 RA IV in my '70. 4 inch stroke forged SCAT crank etc... I love it. Recently had to change the reproduction RA IV intake manifold with a real deal RA IV intake. The repro wasn't lining up properly and had two major vacuum leaks. The real RA IV intake lines up so much better. My mechanic thinks the intake cost me 10 to 15 HP when the engine was dyno'd. It was a pure bottleneck. Cam is a Butler grind (see below). Compression is a tick above 10:1.

https://www.youtube.com/watch?v=AXveB8zehOw

Also upgraded the lifters to the new Comp Cam Evolution. Very quiet as opposed to what you hear in the video.

Used exhaust manifolds with the 2.45 inch outlet. Figured the HP was 460 before the intake change now I would say it is 470-475.

That’s a beautiful ride, Napster! What idle RPM and have you ran it at the track ?

What length pushrods did you end up with with those lifters/ helping a buddy build a RAIV head 455 using them.

Do you have a dyno sheet that you can post?

Stan

If the car is being autocrossed, I would absolutely go with the 4" stroke. You'll be able to manage off corner acceleration a bit easier without the grunt the added stroke is going to give you at lower RPM's. Greater RPM potential will help you as well.

Thank you. Idles between 750 to 800RPM. Never raced. I don't trust myself with the stick. Might miss a shift and lose the engine. If it was automatic I might try it.

Use this as a guide. My mechanic started with 8.75 inch push rod and didn't like it. Ended up with 9.00 inch push rod with chrome molly 80 thousandth's (SP) wall. Rocker arms are rollers @ 1.65:1 ratio.

Hope this help especially with all the variables involved.

Stan,

This is what I have written down and the numbers are uncorrected. I guess the corrected numbers are 460 HP and 545 TQ before the intake change. Figure the HP went up 10 to 15 with the new real deal RA IV Intake.

The owner of the dyno my mechanic uses is a real Richard. That is why the numbers are uncorrected.

Thanks. I was just having a discussion with someone over on Yellow Bullet who only likes looking at uncorrected number .

Stan

Thanks it gives me a starting point. I have a couple of different adjustables we are going to use when we mock it up in the next week or two. I told him to get the rockers he is going to use also as even same ratio different brands affects that a bunch.

I think my Comp HR-"S" ended up 8.75.

I have a 4.00 stroke 400 block build planned -decision is do i use my RAIVs or soem Speedmasters.

Correct, the heads are cast Iron #614's. The heads are stock and not ported. Numbers I have read in books is 230 or 240 CFM. I remember reading in Rocky's book, Nunzi Romano, saw some of the 614's flow 250CFM. The heads on this engine have not been bench flowed under my ownership.

I have a 4.00 stroke 400 block build planned -decision is do i use my RAIVs or soem Speedmasters.[/QUOTE]

I would use the RAIV's. A 428 RAIV should have happened in 1969 and the LS1 Ram Air Super Duty would have been nice to see in 1970. Even a 1970 455 with a RAIV top end would work as well. Hemi who? What is an LS6?

If John D. was still Division Manager in '69 &'70 I think one of the versions above had a chance to come to Market.

At best on a calibrated bench stock RA4 heads flow 230 cfm @ .600”.
At .500” lift they flow about 225 cfm which is enough intake flow to make a potential 57.5 Hp per cylinder, or 463 hp.

That should get you 550 to 600 hp if all is good in your parts selection.

Is that 325 cfm taking place at only .600” ?

Yes around 600 lift