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Old 05-17-2013, 04:40 PM
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how to calculate horsepower

i have a 68 350 olds engine im getting built here's the specs

cam 274/286 duration .520.523 lift
valve springs to match cam
stainless steel valves (non w-31)
#5 heads shaved ported hardened valve seats
comp cams steel roller tip 1.6 ratio rocker kit 3/8 stud and pushrods
stock connecting rods with arp bolts
stock crank
.030 over with probe flat top forged pistons with two valve reliefs
edelbrock performer rpm intake
high volume aluminum water pump
trans dapt crank water pump and alternator aluminum pulleys
no power steering
flowtech headers 1 3/4 primary tubes 3 inch collectors
70's 350 olds hei distributor
160 degree thermostat
800 cfm edelbrock carb
tci streetfighter automatic trans with 2500 rpm stall converter

car 1980 trans am 3:73 gears full posi

just want to know how to calculate hp or if anyone has a rough suggestion would be nice and should i stick with the 800 cfm carb or drop to a 750
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Old 05-17-2013, 06:01 PM
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Quote:
Originally Posted by oldslover View Post
i have a 68 350 olds engine im getting built here's the specs

cam 274/286 duration .520.523 lift
valve springs to match cam
stainless steel valves (non w-31)
#5 heads shaved ported hardened valve seats
comp cams steel roller tip 1.6 ratio rocker kit 3/8 stud and pushrods
stock connecting rods with arp bolts
stock crank
.030 over with probe flat top forged pistons with two valve reliefs
edelbrock performer rpm intake
high volume aluminum water pump
trans dapt crank water pump and alternator aluminum pulleys
no power steering
flowtech headers 1 3/4 primary tubes 3 inch collectors
70's 350 olds hei distributor
160 degree thermostat
800 cfm edelbrock carb
tci streetfighter automatic trans with 2500 rpm stall converter

car 1980 trans am 3:73 gears full posi

just want to know how to calculate hp or if anyone has a rough suggestion would be nice and should i stick with the 800 cfm carb or drop to a 750
Why do people build motors like this with stock rods using better bolts?

Usually it's the rod that craps out not the bolts, not that they don't, but there are a lot more failure modes going on with rods than the bolts. Typical are fractures in the upper outside beam just under pin boss due to twisting moments induced by the piston. Failure of the cap to keep dimension, this pinches at the mating surface pulling the lower bearing shell into the journal which wipes the lube off, toasted, spun bearing quckly follows. This probably relates in no small way to the very common to see shank fracture just above the big end. To keep this under control not only requires good bolts but a damn strong cap with top notch machining of the interface by someone that understands these loads and how they deform the cap. The average rod rebuilder most likely ain't that guy. The OEM Olds rod is well know for its cap deformation in high output engines. The connecting rods are the higest loaded part in the engine and the most destructive when they let go. All that pretty stuff you put in and on the engine is just a few hundred pounds of scrap metal after a rod lets go.

Bogie
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Old 05-17-2013, 10:31 PM
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to answer your question about guesstimating HP:
start with varified head flow numbers(most important part)
supporting combination of parts,ie carb/manifold/cam/exhaust/piston configuration&deck height,
consider the care and attention to details(blue printing)

start with head flow numbers,roughly,,, double the intake flow number to get a possible horse power potential,,,
IE; the heads flow 250 cfm on the intake side,you could make 500 ,,,ish hp
ideally the exhaust side of the head flow numbers should be as close to 80% of the intake flow numbers as possible
the combination must match.

If your heads flow 250 CFM but your cam is unable to give the engine enough lift and duration to allow the heads to flow the full amount,then the HP figure will be lower,

If the carb is too small or the efi doesnt flow enough air,,,same result

If the exhaust system is to small or restrictive,,,
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Old 05-17-2013, 10:54 PM
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If it was well assembled and tuned you may get close to 450hp, provided everything is dialed in. If its not dialed in perfectly 400hp would be a closer guess.
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Old 05-17-2013, 11:17 PM
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unfortuneatley what AP says is true

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Originally Posted by ap72 View Post
If it was well assembled and tuned you may get close to 450hp, provided everything is dialed in. If its not dialed in perfectly 400hp would be a closer guess.

I would expect over 500 HP but its a lot of effort to get a good build and spend little money.

Horses are expensive,how many would you like to purchase???
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Old 05-18-2013, 06:52 AM
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500hp out of 350ci is pretty hard, those heads would need a damn good port job and he'd need really high compression. That carb is hard to get perfectly tuned as well. Easy carb to get close, hard carb to get perfect.
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Old 05-18-2013, 07:20 AM
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before this thread gets too confusing and you think that your engine is very high out put,,,

I would think your parts list and lack of details would indicate a 300 horse power engine,,,maybe?
your question was how to figure hp? no head flow numbers=no idea
stock HEI= engine loses power starting at 4,500 rpm
flat tappet hydraulic cam=limited rpm and flow
800 cfm carb=adequate
other high performance parts/machine work,not listed???
aluminum pulleys and water pump=nice looking,(no hp added)
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Old 05-18-2013, 03:33 PM
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The only flow I can find for the heads is on the Stan Weiss site, max flow 234/148 @0.600" lift. Max flow 222/144 @0.500" lift, or about the same flow as 350 Chevy L31 Vortec heads. Don't expect any miracles.

Last edited by techinspector1; 05-18-2013 at 03:41 PM.
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Old 05-18-2013, 04:19 PM
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To answer the question how to calculate horsepower would be torque X rpm divided by 5250, but to make it easier, go to one or the weight to et or weight to mph calculators, like on the Wallace Racing site.
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