five7kid

iTrader: (14)

Jan '03 issue of Hot Rod Magazine has an article "10 Ways to Estimate Your Engine's Power", page 38. They rate the methods from 0-5, with 5 being as accurate as an engine dyno.

Method #3 is "Quarter-Mile Top Speed (MPH)", with an Accuracy Factor of 4.5 (for reference, a G-Tech Meter is given an AF of 4, DD2000 3). The formula is:
hp = (mph/234)^3 x weight
for rear-wheel horsepower. Supposed to work fairly well for under-4000 lb cars running 9's to 16's in the quarter.

I was curious if anyone has actual dyno pulls and 1/4 mile runs to compare. Using the formula, my Camaro comes out to about 250 HP at sea level (using the NHRA elevation conversion factor), and the '57 at 330 HP based on the Topeka performance. The Camaro doesn't surprise me too much based on DD2000, but the 396 does (haven't tried to estimate the 396 with DD2000).

Also, this doesn't take aerodynamics into account at all. I'm fairly certain the Camaro is a little better in that regard than the '57...

'87FAKE-IROC-Z

They seem a little high to me. Going by that my '88 which runs 105 and weighs about 3600 puts 325 to the wheels.
And my '92 which run 95 and weighs 3710 is putting 248 to the wheels.
I know the '92 isn't making that kind of power, probobly closer to 248 at the crank. The '88......well its so out of tune I don't know, I hope its making more than 325 at the crank, but I wouldn't put money on it making that at the weels.
here is a calculator that seems to do that for you, I get very close results to this.
http://www.gordon-glasgow.org/hpcalc.html

five7kid

iTrader: (14)

That one puts me at 325 (406 crank) and 235 (295 crank), respectively. Still fairly close. The Camaro is probably affected more by your calculator because gearing (and tranny shifting) is affecting my ET, which is slow compared to MPH.

I assume you haven't had yours on a dyno, either. Funny, the HRM article considers the MPH more accurate than (some) chassis dynos...

P.S.: The "325" number is interesting for the 396, since that was its factory gross flywheel HP rating.

AlkyIROC

The NHRA conversion factory doesn't take into account for density altitude unless you use the higher altitude as the correction factor. My local track is around 3350 feet above sea level but the density altitude is usually at 5000 feet. If you use the NHRA factor for 3350 feet then the conversion is inaccurate against the currect weather conditions.

My HP calculations are from 1/4 mile MPH in relation to weather conditions calculated from dyno conversion formulas. Theoretically if I ever get on a dyno, it should be very close to the numbers I come up with.

The dyno will tell you exactly how much HP is at the rear wheels at sea level on a perfect day but can't tell you how fast you can run a 1/4 mile since aerodynamics can't be calculated.

The MPH method will give you an accurate enough calculation and will give the HP in relation to current weather conditions plus any other factor that will affect the car going down the track.

My calculated HP is 505. That's what a dyno should tell me. My HP based on a time slip MPH is only around 420. That shows how much HP I give up by racing at altitude. Going to a lower altitude track, the car is much quicker because it will make more HP. If I ever go to Mission BC which is at 24 feet elevation, on a good day the density altitude can be below sea level. My engine could produce over 505 HP then.

five7kid

iTrader: (14)

Completely understood. The Camaro has only been run at 5800' Bandimere, and the best density altitude was in the 8000' range. I used the NHRA 5800' correction for that vehicle. It would never run the number at sea level, or with gears, in its current condition, since there's no 2-3 shift at WOT (it tachs out in 2nd at the stripe at Bandimere).

The density altitude when the '57 ran those "best" numbers was around 900' at a 700' elevation track. NHRA doesn't correct for under 1200'. FWIW, the best 5800' run the '57 made, with DA of around 8000', corrected to 13.54, so the real-life "sea level" run was 0.1 sec better than theoretical based on the high-altitude run, corrected only for elevation.

I understand dynos correct their results to sea level, based on DA at the time of the pull, anyway. I understand why: The calculated HP for my Bandimere runs raw data, using either method, is too depressing to put in print.

Question still remains: Anyone have both dyno and 1/4 mile numbers?

SSC

5.7, kinda off/on topic but what heads are you using in the 57? I'm building a 402 for my truck similar to your 396 except I'M using a stealth manifold, but I'll be if its got less power then the 355.

Edit: Ive got an old Dyno sheet from the truck and time slips but I havent been able to find them recently but I'll scan em if I do find them.

five7kid

iTrader: (14)

They're the stock '66 396 325 hp heads. 98cc chambers, 260cc intake runners, 2.065/1.72 valves. I had the covers off in late August to check against data a fellow racer had accumulated, and I remember those numbers. But, I forget the casting #'s - I think 702, though.

They have hardened exhaust seats & valves, bronze guides, 502 take-off springs & retainers. Otherwise, untouched. I plan on the DIY porting job this winter, also hope to swing Pro Flow valves & better springs. Dreams include Stealth, solid cam, higher stall - perhaps if Santa is really good to me this year...

As-is, it's a good second faster than the 355/TH350, dished piston, 882 heads, mild upgrade cam, headers, iron manifold q-jet that was previously in the car (calculates to 230 hp elevation-corrected by both of the above methods ).

MdFormula350

cool calculator...

NJ SPEEDER

i usually use www.prestage.com they have all kinds of calculators adn rference stuff on there.

later
tim

five7kid

iTrader: (14)

Hmmm, that calculator gave me --- 330 HP!

I suspect the first one is the same formula that HRM suggests.

JAY87GTA

Haven't done the calculator on my car, but did it on a friends %.0 running a 100 shot. Calculated 420HP by the MPH and I believe 440 by the ET. He runs 11.50's at 120-121. Had it on the dyno a few weeks ago and it made 413 at the wheels. So I guess it's fairly close.