[Cliff R]

We did a 428 build for a stick shift GTO a few years back with 3.73 gears.

KRE 74cc aluminum "D" port heads unported. Oliver rods, Ross pistons, custom ground Comp HR cam with 236/242/110 specs, iron intake, late model Pontiac q-jet.

It made 497hp/540 tq on the dyno, peak hp at 5800rpm's and peak tq at 4200rpm's. The 540 torque number rivals similar 455 builds with plenty of top end power to go with it. It also made over 500ft lbs torque across most of the load/speed range, showing how good the 4" stroke engine combination really is.

This engine was 434cid and built on a 67 block with an Arma-Steel crank in it. It still lives fine today, nearly 10 years later, and the owner absolutely loves that engine, and zero issues on pump fuel as well.....Cliff

[Will]

Cliff - that's a great combo! Care to speculate on what treating those heads to something like Dave B's 295 cfm cnc porting would do to the power numbers, all else being the same?

Was the intake ported or stock? If stock how about porting the intake and heads?

[Dick Boneske]

Call Butler with your questions. He is very helpful and will give you the "right stuff" for as reasonable a price as anyone. He's been there, done that, and won't lead you astray.

Our 455 with 87 cc round port Edlebrocks, Ross pistons, Lunati hydraulic roller, PRW rockers, and Butler's 467 stroker kit using Eagle rods runs like a tiger. We ended up at about 10.5:1 compression.

The only unconventional thing with our setup is the aluminum '66 Tripower setup that's ported extensively to match the E-heads. It required welding added material to the port are of the manifold to allow porting large enough intakes.

[Cliff R]

"Cliff - that's a great combo! Care to speculate on what treating those heads to something like Dave B's 295 cfm cnc porting would do to the power numbers, all else being the same?

Was the intake ported or stock? If stock how about porting the intake and heads?"

The KRE heads received a port match and very minor clean up I the bowls, I didn't remove a teaspoon full of material from them, just helped out some with port alignment to the seats and gently opened them up to a stock intake gasket size.

They were obviously PLENTY of head to easily make 500hp from 434cid with a relatively small cam in it.

I'm not sure what head porting would have done to the combination without more camshaft. Apprx 260cfm up to 295 is significant, and we know that with 455cid under those heads the end result is 550hp/600tq without too much effort.

We used three different intakes on the dyno. My own iron intake which is NOT ported in the runners, just cleaned up nicely, but is modded under the carb to make the plenum areas the same apprx size/shape as the Edelbrock RPM, and I added material and a second bolt pattern to it for Holley style square flange carburetors.

The second intake we tested was an HO "re-pop" done in similar fashion.

The last intake tested was a port matched and nicely cleaned up RPM.

The HO intake made 487hp, the RPM made 491hp, and the iron intake made 497hp on back to back pulls with no other changes......Cliff

[Will]

Originally Posted by Cliff R

...

I'm not sure what head porting would have done to the combination without more camshaft. Apprx 260cfm up to 295 is significant, and we know that with 455cid under those heads the end result is 550hp/600tq without too much effort.
......Cliff

Cliff, thanks for your thoughts.

Given that a smaller engine will make just as much horsepower as a bigger one, just at a higher RPM and with less peak torque, it's probably safe to say that the 295 cfm heads on a 4" stroke motor would be capable of delivering close to that same 550hp number using the same cam, intake, exhaust, etc., it would just be at a correspondingly higher RPM and have slightly worse idle quality.

How big of a cam is needed to reach those 550/600 power figures with a 455 combo?

[Cliff R]

Of course we'd be guessing on the cam, but for the 4" stroke and rpm range required to make that power, it will need to be a big one. I also kept our custom grind on a 110LSA, which no one seemed to notice. For the 4.21 and longer strokes we've found they like 112-114LSA. For the 428 with the 4" arm, 110LSA proved to be a good place to be, but it took 236/242@ .050" to get the power on par with 455 builds we've done using 230-240@ .050" cams.

I'm certain if we would have used a smaller 230@ .050" cam in our 428 build, we would have left quite a bit of power on the table. So I kicked the SCR up to 10.6 to 1 and went to a slightly larger camshaft and pulled the LSA down to 110. It was a gamble at that time, but proved to be a very good move when we got that engine up on the dyno.

I didn't use "ported" KRE heads for a reason, as I wanted to compare the 434's dyno numbers with what we had obtained with the three previous 455 builds we did with KRE heads and a bit less compression (10.4).

What happens here, is that as you reduce CID and go larger with the cam, it can help to pull the LSA down some, to pull peak power down and tighten up the power (torque) curve a bit. Doing this degrades idle quality, so we opted for 74cc chambers to get the SCR up some.

We were nicely rewarded with peak HP at 5800rpm's, and a strong/broad/flat torque curve similar to what we see from the longer stroke engines in about the same rpm range.......Cliff

[Will]

Cliff, thanks again for your input. I think I confused the issue a little with my previous post though.

What I really want to know is what heads and cam did you use to achieve the 550hp/600lbs figures with a 455?