Trying to figure out some Chebby performance today. 119 through the traps x 3. Calculators call it 447 hp, is that crank or wheel?


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- 70 Fastback Mustang, 489 cid FE, TKO-600 5 speed, 3.70 9 inch, EFI in progress!
- 71 F100 shortbed 4x4, 397 cid FE, headers, Street Dominator, 280H, 4 speed

There is some disagreement on this subject. I've always been pretty convinced that it is rear wheel HP, but lots of people disagree. One thing for sure, though, is that those calculators are an estimate at best, and they can be high or low depending on whether or not the car is really dialed in at the track.

Jay Brown
1969 R Code Mach 1, Drag Week 2005 Winner BB/NA with 511" FE(10.60s @ 129), Drag Week 2007 Runner Up BB/PA with 490" Supercharged FE (9.35 @ 151)
1964 Ford Galaxie, Drag Week 2009 Winner Modified NA with 585" SOHC (9.50s @ 143)
1968 Shelby GT 500 Convertible, 492" 667 HP FE
2005 Ford GT, 2006 Drag Week Winner, 12.0 Daily Driver
1969 Ford Galaxie XL, 460 (Ho Hum....)

According to my trusty Moroso "Power Speed Calculator", 119 MPH with 447 HP would give a race weight of about 3450 lbs. (If the car was a good working combination, that should be approx 11.1 ET). As for Flywheel vs rear wheel HP, I say flywheel, based on my admittidly few personal experiances. My Fairmonts 428 made 518 flywheel HP on my buddys Super Flow 901 engine dyno. According to the Moroso calculator, it should run about a 10.3 @129 MPH with that power and 3100 lbs, it has actually gone 10.0`s @132 MPH, but then it`s a 4 speed, maybe the calculator is based on automatics sucking up some power. On my buddy with the dyno`s own cars, his 66 Chevelle Super Stock 396 made 665 HP, and at 3550 lbs, ran a best of 9.77 @ 136MPH, his current D/S 68 Z/28 302 made just a tick over 400 HP, and at 3150 lbs, has ran 10.97 @120 MPH. Maybe his dyno is either a bit stingier (or honest) than some, especially the California car magazine dynos used. You know, the ones where a stock 5.0 Mustang engine can make 400+ HP with just a head swap on a junkyard engine, yet only run high 12`s at the strip.

428 powered Fairmont drag car, Best ET:10.03@132.11MPH, best 60 ft: 1.29
59 Meteor 2 dr. sedan 332, Ford O Matic
74 F350 ramp truck 390 4speed

I read that article. I guess that's how you sell mags, huh? Please your sponsor and the kids now all think they have a bunch of horse power! I recon they think it's OK for tv and newspapers, it's OK for them. Might as well be one of those trash mags on celebrities! I would rather keep my integrity and sleep better.

We all know there'er some Happy dyno's out there - and maybe even a few operators that for one reason or another come up with optimistic results. But, as in the PHR contests; a few years back, they gave the figures for engines that were dynoed on the East coast, west coast and mid west. Seems like the east coast and midwest numbers were low compared to the west coast. But once the ran the finals (I think they were a WestTech, in LA at that time), the number jumped.

Better air, magic? Who knows, but once they were all being matched on the same dyno - a lot of the differences evaporated.

Best explaination - you don't race dynos, you race cars. That covers the whole spectrum of variables; aero, to track conditions, to correction factors and everything in between.

RWHP seems to make sense, but like Werby said, if its really the average hp between shift point and recovery, I could buy that too.

Its a 440 inch Rat. 13:1, 260/270 solid roller, 4.30 gear, ported rectangular port iron heads flowing about 360 if I remember right, 1050 Dominator, ported Team G intake.

I'd figure it'd make more than 550 FWHP, but it's never been on the pump, and I can't verify much on the build except what his receipt says.


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- 70 Fastback Mustang, 489 cid FE, TKO-600 5 speed, 3.70 9 inch, EFI in progress!
- 71 F100 shortbed 4x4, 397 cid FE, headers, Street Dominator, 280H, 4 speed

....an 11.50 1/4 mile converts to about a 7.40 1/8th mile. My 347 guy was originally running a 306ci SBF with a little bit of spray. He could run a 7.38. This was with a Tremec TKO 500 and a 4.30 gear with a 3400 lb car with driver.

In this case, I would imagine that the horsepower estimate given by the calculator may be flywheel horsepower.

Wasn't this a stroked 396? If you lost 15% to the tires, that's only 525hp. What were the ET's? Does it need more gear?

LOT's aint right, LOL, first time out, line lock problems, driver error, chassis setup changes. B

ut all the runs got a pretty solid top end charge and both 119 mph traps were had the shift light come on in the traps

Ran 11.57, 11.57, 11.87, with a lot of body roll on each

Trap speed was 114, then took a little timing out, ran 119 for 3 other runs.

67 Chevelle, caged, other than that pretty much street ready, 440 inch solid roller, Super T-10, 4.33 geared. Owner says that he weighed it with him in it at 3400

There is a lot more ET in the car, when I get the videos loaded you guys can take a look, it needs some suspension work, the body is all over the place going down the track. Drives straight, but body roll, and nose and tail moving all over.




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- 70 Fastback Mustang, 489 cid FE, TKO-600 5 speed, 3.70 9 inch, EFI in progress!
- 71 F100 shortbed 4x4, 397 cid FE, headers, Street Dominator, 280H, 4 speed

That's all the info that is in the trap speed - the average RWHP, not net at flywheel or gross at flywheel, that info is not in the trap speed.

And from trap speed, you cannot even get peak RWHP, all you get directly is some average of RWHP at the bottom of the shift and RWHP at the top of the shift, since those matter about equally.

From there I think a lot of those calculators nudge up the average RWHP from the trap speed up to a guess at peak RWHP, and then some of them try to convert that to net NHP or gross GHP at the flywheel.

And in the process, they have to guess whether you have an auto or a stick, and whether you shift gently like me, with gear-changing times measured in "seconds", or like Rory and some others, with gear-changing times measured in microseconds.

The correlations are useful because they are so quick, but you can see why so many numbers are needed for the Gonkulator, all that stuff eats power and matters.

Once the trap speeds are much over 100mph, wind matters quite a bit (even a gentle headwind like 3-4mph which is just walking speed) and aero of the car, you can't just use weight any more. A slick 1994-2004 Stang will mph quite a bit quicker than a brick-like 67-70 Stang coupe just due to the aero but a single equation calculator cant account for that.

The car runs strong, just need to get the chassis worked out and then get the driver some additional time in the seat.

4 runs, launching at 4000, shift light at 6200 (slow reacting drive had to move it early LOL) and the only casualty was a single glass fuse.

Not a bad first time out for him


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- 70 Fastback Mustang, 489 cid FE, TKO-600 5 speed, 3.70 9 inch, EFI in progress!
- 71 F100 shortbed 4x4, 397 cid FE, headers, Street Dominator, 280H, 4 speed

I belive the slide calculators are figured on a manual trans with no slipage. You have to figure converter slipage rate for auto trans and also a clutchless trans will out run the numbers so you have to figure a little less hp when figuring et. don't think it effects mph on the clutchless.

Jeff Colvert
Jeff Colvert Racing CNC Cyl.Heads
2009 NHRA national record holder 9.48@140.53
69 Mustang SS/G first in the 9's
68 GT500KR 2330

Doubt that it`s near 550 RWHP. His car is 300 lbs heavier than mine, both 4 speeds, but he has more cubes, compression, cam, heads and carburation, yet he traps 13 MPH less than me. With all that stuff, assuming it`s setup half ways close, it should be a whole lot quicker AND faster. Is he shifting that Chevelle like a dump truck? That would explain a lot. Is he racing at high altitude? Somethings out of whack.

428 powered Fairmont drag car, Best ET:10.03@132.11MPH, best 60 ft: 1.29
59 Meteor 2 dr. sedan 332, Ford O Matic
74 F350 ramp truck 390 4speed

Want to thank all the folks for the comments about going into the 8s. I have had a lot of experience with a Dyno Jet and sometimes the power you get does not add up. I ran our car on a dyno jet and only got 694 RWHP.Converter did have a torn fin on the pump side which we had fixed and thought might have an effect on dyno. readings. Car ran 8.80 at strip. Moroso slide rule says car makes 770 HP. at 8.80 at 153 mph..We did run car at a local eigth mile strip where times were 5.64 at 125 mph..A chart that Jay Brown backposted a while back said the car would run the 8.80s at 154 mph.. I'm sure old FE makes more ponies than that. I have run a lot of Mustang Cobras on a Dyno Jet, most with a chip, underdrive pullies put out more than 400 RWHP ponies. Our old 513 FE which only put out 600 RWHP and the best it ever ran was 9.05 at 150 mph.. I don't think that there is any crystal ball that can predict hp vs drag racing times. I only know that cars generally go slower than you think they should.