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71' 4 bolt 350 4bbl.

15K views 9 replies 6 participants last post by  HellCamino8 
#1 ·
Hello, I am wondering how much horsepower my motor is making in the eyes of you all. It's a 1971 Chevy 350 4 bolt main 4 barrel, this stock motor made 270 horses. It's been bored .30 over, we've added ( Me and My dad ) New Summit Racing Heads with the 2.02 intake, a new edelbrock aluminum air gap intake, A 600cfm Edelbrock 4 bbl electric Choke Carb, an edelbrock cam ( Not sure which one ) , flowmaster dual exhaust. It was set at either a 9.2-1 or 9.4 compression ratio when it was rebuilt 4 years ago. Can anyone give me an estimate of what power it might be making? Thank you! Oh also, this is in a 1978 el camino. :)
 
#4 ·
okay lets see here, in 1971 the GM chevrolet 350 could be had in 3 different hp options: 245hp/350tq, 270hp/360tq which are both hyd lifter motors with 8.5:1 CR, there was also a 330hp/275tq option that still used solid lifters and had 9:1 CR.

assuming that you have the 270hp/360tq engine, you added and updated version of a set of double hump heads, so you wont have any incrediable gains there. then you added a higher rise, larger runner intake which will free up a little air going into the cylinders, regardless what Vinnie says the 600cfm carb is not choking this engine as a 600cfm carb can turn a mild 350 to 5500RPM without any problems. then you mention flow-masters (i dont care for them but i'm sure they flow a little better than the factory mufflers. you gained about 0.8-1.0:1 on your compression ratio which is likely good for about 5-7% gain. the heads I know flow about 10% better than the factory heads, and the intake is flowing around 20% more than the factory intake. the big question would now be did you put headers on it, if not how is this added amount of air that is getting into the cylinders getting out.

based what i would guess the cam you put in there would be around 210-220° @ .050 and roughly .440-.450" lift.
without headers you are likely making in the 290-315hp range with roughly around 350-370tq, but if you added a set of headers you would likely be in the 310-330hp range with roughly around similar tq numbers.
 
#6 ·
there would be around 210-220° @ .050 and roughly .440-.450" lift.
without headers you are likely making in the 290-315hp range with roughly around 350-370tq, but if you added a set of headers you would likely be in the 310-330hp range with roughly around similar tq numbers.
And here's where it gets fun. I think that 270 hp was a "net" rating, whereas 1970 and earlier used a "gross" rating as well as higher compression. Gross ratings are what we get on a dyno with no alternator, fan, mufflers, air cleaner, etc. And gross ratings are what we hear about in the hot rod world. So maybe that 270 net horsepower would have been 350 gross. Who knows?

So, depending on the cam's torque curve and ignition advance curve, I'd guess his 355 is making 280-300 net with the same air cleaner, fan, exhaust system, etc. as the original car used. Gross rating might be more like 330-350.

And, yes, 600 CFM is not an issue, although an Edelbrock 1405 carb will probably make more power than a 1406. (The difference is more than choke and jetting.)
 
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#9 ·
I agree with f-bird!:thumbup:



Hellcamino 8: you could pay a few bucks and put it on a rear wheel dino or engine dino! and get an exact figure for the conditions the day of the dino run! Your rating out of a book is averaged on the differences on a few engines tested of the exact same build at the factory!!! You can dino 20 engines all built and blueprinted exactly the same and get 20 different h.p. ratings + or - from the rating listed because of small differences in tolerances heat transfer, flow differences, even spark plug and plug wire resistance can reduce or increase hp, efficiency of rings,ETC and factory built engines had wide variations of tolerances and still passed inspection! Cams ground at Gm could have 200 run through a machine before tooling was changed so the first cam would be dead on perfect with a very tight tolerance and the last cam at the outer range of the limit of acceptability! If you happened to get all the close tolerance parts in one engine coming down the line you had what we old guys called a street freak because the hp it produced was exceptional! If you got one at the outer ranges you got a slug! Estimating hp off of aftermarket parts that were added is like spitting at a fly the odds are your way off!!!

If You put your foot in it and it brings a smile to your face:D be happy, If your disappointed:( trouble shoot it or redo it!

Jester
 
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