[louis1]

My 71 455 h.o Formula dynoed at 335 hp to the rear wheels, factory rating is to the flywheel. Only slight mods are Pype exhaust, Cliff Ruggle carb tweak, MSD ignition, slight cam upgrade. What do you figure is my flywheel hp?
thanks,

[njsteve]

Since you said "at the flywheel" I assume it's a manual trans car. Usually the parasitic loss through the clutch, trans, and rear differential is between 15-18 percent on a manual car, 20 percent for an automatic.

Where's a fifth grader when you need one? I'm no math wiz but I would guess 390 at the flywheel

[louis1]

Yes it's a 4 speed, thanks for input, the car really kicks butt, I'm really happy with the performance.

[1971455HO]

Did you get a print out when you had your car dyno'd? That would be nice to see, if you could post it. Were you at 5500-5800 rpm? Our cars were rated at 335 @4800. I suspect they made a tad more up a little higher. But I can't prove it. I don't know where they begin to drop off and it's useless to push harder. Just grab another gear.

That sounds great. I hope to get mine dyno'd some day. Heck, I just hope to get it finished. I've done a few simple things. I had the heads cut years ago to 105, Comp Cams RA IV , port matched. Nothing special to the carb.

If I had all to do again. I would buy a set of good forged rods. That's just good insurance. I'm not too worried about ever hurting the crank. Everybody I've ever talked to said they had never had a stock crank failure in a 455 Pontiac. There's a lot of meat there. Being an over square engine has you living at a 5500 red line with stock parts. Nice to hear you got 335 at the tires.

[louis1]

Hi, I got the print out but not able to post it, its about 5200 rpm. With heads cut and ram air IV cam you should do pretty good. Thanks for suggestion about forged rods if/when I rebuild.

[njsteve]

I went with the forged rods in my 72 455 HO to go along with the .040 forged pistons installed in a prior owner's rebuild. I also replaced the crank with an Eagle crank (the original was previously cut and still needed another cut).

It's good insurance. I figured if the original 455HO could last 114,000 miles with those rods and crank with a four-speed behind it, it was time to give it an upgrade.

[Formulabruce]

I put Forged rods in mine, SCAT, what a mistake. They balanced out after some work, but little did we know the big end, the holes were not exactly "round" due to the machine making them before the rods were cut for the caps. ( can you say "jet" china machine tools?)
Took engine apart for the oil leak, found the rod bearings getting destroyed, had to have them resized.. and balanced again. Im sure the original rods would have been fine for me with an automatic.
This is why EAGLE now says that their cranks are machined "IN THE USA on USA made equipment" on the BOX

[weranc55]

Originally Posted by louis1

Hi, I got the print out but not able to post it, its about 5200 rpm. With heads cut and ram air IV cam you should do pretty good. Thanks for suggestion about forged rods if/when I rebuild.

The shop that built that motor is very good. I would not be worried about it at all. To bad my buddy that sold you the car never sent out the carb to get it to run right. The car was kind of a pig when he had it. Congrats on the good HP #'s

[LeighP]

SCAT.....I've seen SCAT pushrods that bent when hand turning the engine (nothing wrong other than cr@ppy pushrods), SCAT rocker arms that galled on their balls inside of 30 minutes of running, a SCAT crank that broke in two while cruising at 50mph (no real load).....all in people's cars that thought that SCAT parts were a good bargain.

I wouldn't even let SCAT parts sit on a shelf in my garage....no way I'd trust them in an engine.....just my opinion.

[Formulabruce]

Originally Posted by LeighP

SCAT.....I've seen SCAT pushrods that bent when hand turning the engine (nothing wrong other than cr@ppy pushrods), SCAT rocker arms that galled on their balls inside of 30 minutes of running, a SCAT crank that broke in two while cruising at 50mph (no real load).....all in people's cars that thought that SCAT parts were a good bargain.

I wouldn't even let SCAT parts sit on a shelf in my garage....no way I'd trust them in an engine.....just my opinion.

Well said!!

[louis1]

Originally Posted by weranc55

The shop that built that motor is very good. I would not be worried about it at all. To bad my buddy that sold you the car never sent out the carb to get it to run right. The car was kind of a pig when he had it. Congrats on the good HP #'s

Thanks Chuck, yes I'm really happy with car's performance, only problem I'm having is it won't start if engine is hot, I have to put a mini starter in there. I was wondering if the car would make more h.p. with a true dual exhaust as opposed to the Pypes sytem it's got on there now, anyone knows?