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Pontiac 455 HP estimate

14K views 5 replies 5 participants last post by  AutoGear 
#1 ·
I'm also building a 455

I was wondering what my Horse Power would be on my 1971 HO 455 Pontiac. I've heard it would be less than the factory, (330). I can't belive that. I have a 278 duration cam and lifters from Edelbrock, Edelbrock Perfomer manifold (spread Bore), it's bored 30 over with a Edelbrock 1411 750 Electric Carb. Roller rocker arms, Edelbrock 110 fuel pump, with a HEI dizzy. TH 400 Trans rebuilt with a B&M 2500 stall and B&M shift kit. The engine had 70000 original miles on it. My guy that did the machine work says at least 425 HP, 495 torque. Another guy that build engins says I went backward in horsepower, SMH.....everything I've read says 425 is a realistic number. I even got the billet pullies and an electric fan.... :confused:
 

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#2 ·
billonwheels said:
I was wondering what my Horse Power would be on my 1971 HO 455 Pontiac. I've heard it would be less than the factory, (330). I can't belive that. I have a 278 duration cam and lifters from Edelbrock, Edelbrock Perfomer manifold (spread Bore), it's bored 30 over with a Edelbrock 1411 750 Electric Carb. Roller rocker arms, Edelbrock 110 fuel pump, with a HEI dizzy. TH 400 Trans rebuilt with a B&M 2500 stall and B&M shift kit. The engine had 70000 original miles on it. My guy that did the machine work says at least 425 HP, 495 torque. Another guy that build engins says I went backward in horsepower, SMH.....everything I've read says 425 is a realistic number. I even got the billet pullies and an electric fan.... :confused:
It depends on how much work (if any) was done to the D-ports on the engine now. If it had the original heads it might be making more power than the estimated 425 hp and 495 ft/lb.

It should be a strong running combo, though. Easy 12's. If you take it to the track or if you've already been, the mph and weight will give you a good estimate of the hp.

I would be a little concerned the TC stall might be higher than 2500 if that estimate was based on a 350 SBC like many converters are. Hopefully the actual stall speed is at or below the torque peak.
 
#4 ·
A '71 455HO has "round port" heads. Large chamber, though.

We recently built one ('71 455HO) for a man in Mass. He dynoed it just Monday (chassis, '69 GTO). Heads were ported to 250 CFM @ .600 (int). Comp solid roller 236/242 @ .050, .620 lift. Torker II, AED 850HO, Super Comps.

With 93 octane, it made 407 RWHP and 435 RWTQ. That "converts" to about 480-500 GBHP and 540 or so lb. ft.

I doubt you're making more than 400 -420 HP with that Edelbrock cam ("generi-grind"). But you ARE probably making 500 lb. ft.

Dave took his car to the track a couple weeks back (same car). It went 12.32 @ 111 (best ET) and 12.45 @ 114 (best MPH). 60' times were in the toilet, as he had "street" tires (1.9-2.0). 3,810 lbs. with him in it (weighed on the track scales). With good traction, easily an 11 second car.

FWIW

Jim
 
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