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Old 04-01-2009, 03:14 PM
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real horsepower rating for 400 pontiac

I just purchased a 1976 pontiac 400 w/ t400 tranny. It needs to be gone thru but it was running a few years ago (according to the seller.....). It is one of those 185 hp rated motor. I know that rating is at the transmission with everything including the osterizer running. Does anyone know what the hp is figured the way they did before those ratings came out? THanks

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Old 04-01-2009, 04:42 PM
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From HERE.

"How horsepower is measured depends upon circumstances and history. Back before 1972 American manufacturers used SAE Gross horsepower to rate the output of their engines. To measure horsepower they mounted an engine on a test stand and hooked it up to a dynamometer (more on that later, too). It is important to note that the engines, as tested, had no accessories attached. Power was measured at the bare flywheel and the amount was, by definition, gross horsepower.

"In 1972, American manufacturers phased in SAE Net horsepower. This is the standard on which current American ratings are based. This rating is measured at the flywheel, on an engine dyno, but the engine is tested with all accessories installed, including a full exhaust system, all pumps, the alternator, the starter, and emissions controls. Both SAE net and SAE gross horsepower test procedures are documented in Society of Automotive Engineers standard J1349."

Note: Because the test equipment used back in the "old days" to measure gross horsepower is different from today's setup, it is impossible to provide an absolute conversion from one to the other. A rule of thumb, however, is to assume that SAE Net is about 80% of SAE Gross.
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Old 04-01-2009, 05:03 PM
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should be around 230 hp. don't be discouraged though, you can see 350hp with just a cam, intake, headers, and carb.
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Old 04-01-2009, 05:42 PM
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Quote:
Originally Posted by roknroy
should be around 230 hp. don't be discouraged though, you can see 350hp with just a cam, intake, headers, and carb.
Thats a fact!

And, if you're on a tight budget, skip the intake and carb for now, and just get a cam kit, headers and a good, free flowing exhaust.

This assumes you can tune a Q-Jet. And you will need to adjust the timing curve of the distributor, but that's been covered here and elsewhere dozens and dozens of times. Engine tuning 101 type stuff.
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Old 04-01-2009, 05:54 PM
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Hey Cobalt and Roknroy, It has been a few years since I built my poncho motors. Had 64 Goat, 62 catalina (not a sd) w/ 421 69 firebird etc. When I looked at the engine codes I thought there was a mistake on the hp rating. After looking into it a bit more I discovered where and how that rating came to be. 230 seems about right. And yes a cam, intake and headers is in the cards. Any ideas on combination's would help. This has the 6x (8) heads on it. I used to use a sig erson 500h with alumn. mani and doug headers. Tried holleys on top but found dual quads with two afb's to be the best for that goat. That probably tells you how long its been!
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Old 04-01-2009, 06:23 PM
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6x heads flow decent. are you going to change the pistons? if not, what is your compression ratio. 500h is too big, unless your going to do alot, (hi compression, 10 inch converter, 3.73 gears, etc. what car are you putting this in?
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Old 04-02-2009, 09:36 AM
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roknroy thanks again for your insight. the motor is going into a 48 ford f1 pu. The 500h was what I ran in my gto and I am not building this one like that! I am going for a very streetable and dependable ride. I want to have it sound healthy but I would like to run pump gas. Its just a putter. I dont want to have to run anything special in the tranny either. No stall convertor etc. The rearend I have right now is a 2:56 posi 8.5 10 bolt. I dont kow yet if I will stay with that tall a gear. I got a good deal on it and if the carrier is good I can always space the ring and run 3:08's if needed. Any thoughts??? Thanks again for your help. I have been building bikes for the last little while and these mid 70s motors with the low compression etc. are a new beast. Got a little homework to do!
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Old 04-02-2009, 11:39 AM
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there's plenty of help at this website, your in good hands. you can get a nice sounding, great performing cam with the stock converter, and gear. i would like to see you put the 3.08 gears in. the cam i would use is comp cams 270 magnum, part number 51-233-4. 1800-5000rpm. this cam is the most you should use with the stock converter. since you have 400 cu in, it will have plenty of off-idle power. put it in straight up (cam is ground with 4 degrees of advance). please, please, change the valve springs and retainers! alot of people don't think they need to. i've ridden in cars with stock springs on performance cams, and some wouldn't pull past 4000rpm. new springs fixed the problem
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Old 04-02-2009, 02:59 PM
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that is what I'm looking for. I am with you 100% on the springs and retainers. I dont understand not doing it at all! I have found a R n P with a 3:08 ratio. It is what I want to run in it. Again with the learning curve, I found out after I bought the rear end that the 8.5's use two different carriers depending on ratios. It was easier back in the day! lol Your help has been greatly appreciated.
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