How does frictional drive line loss factor in here? Trying to make an accurate guess with my own combo. My 416 is 500 flywheel HP on the dot. Car is probably 3,100-3,200 with driver.

My current guess is 11.00.

Not easy to say, on average I think its around 10% loss from FW to RW dependent on drivetrain, some calcs say its as much as 17% loss. I never really took notice of rwhp, fwhp is the key as nobody can accurately say how much every particular car will lose.

A true 500fwhp in 3200lbs at the track would be =
60 Foot E.T. : 1.50 ******
1/8 Mile E.T. : 6.82
1/8 Mile Trap Speed : 99.61
1/4 Mile E.T. : 10.81
1/4 Mile Trap Speed : 124

500hp on a dyno won't of course be 500hp on the track as you know so if we say 470 on the day depending on conditions/tune etc. its>
60 Foot E.T. : 1.53 *****
1/8 Mile E.T. : 6.97
1/8 Mile Trap Speed : 97.58
1/4 Mile E.T. : 11.04
1/4 Mile Trap Speed : 121
so your guess is pretty good...however these numbers are from Wallace who base things at 0 altitude I believe?...they were almost spot on for all my calcs on my cars which ran at Santa Pod which is 0.

Thanks for the reply. I guess the only way to measure driveline loss somewhat accurately is to go from engine dyno to chassis dyno and see what the difference would be, all things otherwise being equal. Other than that, ET/MPH is the most accurate on any given day.

I agree with the actual HP varying from day to day and even from minute to minute. Here in NY/NJ area we are pretty close to sea level. The best days for DA are in the fall, so that's when the records are set at Maple Grove in PA. Between June and September, it's usually 85+ with pavement melting humidity.

I am hoping to be in the 10s with my combo but am a little skeptical for now. I know one guy who has a similar if not milder combo than me who has been 10.60s. I think he weighs a little less but not much.

Other than that, ET/MPH is the most accurate on any given day.


Not so much ET as thats just an indication of how good your chassis is but it will show up deficiencies there, mph/weight is the key to hp....However when it gets to something like a Stocker, we have 1 running here..a legal '69 Camaro A/SAA the calcs can go way out of synch....

3500lbs/700hp
60 Foot E.T. : 1.38
1/8 Mile E.T. : 6.28
1/8 Mile Trap Speed : 108.15
1/4 Mile E.T. : 9.96
1/4 Mile Trap Speed : 135

He has actually run 9.90@133 with a 1.28 60ft.

The Moroso slide rule shows 500hp/3200bs as 10.50@126.5.
7% loss is 465hp, which shows 10.71@123.6.
10% loss is 450hp, which shows 10.81@122.2.

If it really weighs 3200, and won't go at least 122 at a NJ track in the spring/fall...... Either there is something really wrong with the set-up, or the dyno numbers are happy(or a little of both).

My friends Stocker shows 530hp on the Moroso slide rule(in good air), and the motor is under 500hp. In some really good air it'll show 540hp. In the middle of the summer it'll show 490hp(east coast tracks).
At the Vegas nhra fall race in 2015 it showed 460hp.

The quality of the air you run in makes a big difference.

I always thought the Moroso slide rule was based on RWHP?

Last time I weighed the car it was 3,060 without driver and a full tank of gas. Since then I've taken maybe 50-60 lbs out and will be taking more out soon with a 'glass hood. I weigh 187.

Engine was dynoed at Merkel's here in LI. I don't remember what the DA was that day but it was clear and not terribly humid. The operator used a psychrometer.

I got all excited when I saw it flash to 520+ hp on the screen but with the correction it said 500.2 on the printout. I thought it would be a little more. It was fairly consistent in that range though so I don't think it was a fluke. There wasn't much in the way of tuning.

You actually commented on it when I posted the results. 416 dyno day.

Right, and that is correctable. I too use the Moroso Calc. for comparison purposes. Seems accurate and levels the playing field. If you correct the MPH to std conditions, and plug that into the Moroso Calc, it will be close to the gross corrected from a not-too-happy engine dyno. The several percent that it is if off is usually and reasonably explained considering net verses gross. The closer your engine sitting in the car looks like your engine sitting on the dyno the smaller the difference.

RMCHRGR,
Forgive me, I should know this, but is the Duster strictly a drag car, or will concessions be made for street use, as in converter and gear?

I bring this up, because, like my Valiant for example, I have a 4800 stall speed and a 3.89 gear with a 30 tall tire, hardly ideal for an engine that made peak HP at 6600 rpm. At high altitude tracks or on high DA days, it really struggles to get up on the converter. The stout torque curve is fairly forgiving, luckily, especially since I tend to short shift (old, 906 hyd cam bb guy) but I'm sure the engine would run closer to it's potential with a 5700 stall and 4.30 gears.

Billy, this is a 100% street car. Pump gas, full interior, current tags and inspection, yada yada. Just had a 6 point CM roll bar installed two weeks ago though so I guess you could say it is creeping towards more of a dedicated race car. Trying to avoid that though.

Got a new converter when I built the motor, a Dynamic 9 1/2" that theoretically will stall at 4,000 rpm. I gave them all the specs. They said it will act like a normal converter on the street...

4.10 gear, 28" drag radials. 904 FMVB, standard gear set. 6 (count 'em) clutch discs in the drum.

On the dyno, the motor made best power around 6,000-6,200 rpm then started to drop after that. I figure I will shift it at 6,500-6,600.

Well.......my friends motor, which I have had on the dyno at least 25 times through the years, makes a little less than 500 std corrected hp(hp corrected to 29.92 baro, 60deg, 0 humidity), and even in pretty hot, humid, summer air, at the east coast tracks it will run enough speed to show 500hp on the Moroso slide rule.

I'm pretty sure his car isn't so good it would also make 500rwhp........ so, from my perspective......it's engine hp.

Here's another one.....

572 Indy motor......made 920 on the engine dyno, 778 rwhp on the chassis dyno(glide with a 5600 converter).
Car went 8.33@165 at 2700lbs.

How do those numbers work out?

You're correct. Guess I have been operating under a misconception for a long time!

Just for sh*ts and giggles, I plugged both FW and RWHP numbers into the Wallace Racing 1/4 mile stats calculator which I believe is based off the Moroso slide rule.

With 920 HP @ 2,700 lbs it spit out 8.34 @ 162.05. Pretty close.

With 778 HP @ 2,700 lbs it says 8.82 @ 153.24.

Guess I could have a 10 second car after all. Plugging my 500/3,200lb numbers in to the weight/HP calc. says 10.81. If you use the 3rd calculator down which is ET/weight it says 10.50 @ 3200 = 546 HP.

Since yours is a "street" car, I'd say a realistic number to shoot for is 10-12% "observed" loss.
In other words, see what the calculators show for 440-450hp(for your 500 std corrected hp).

Just the fact that your converter is probably 1000 less stall than what it would be if it were a race only application is going to impact the results, and what the calculators show for power.

My friends motor is under 500hp, and the car weighs 3450, and has gone 10.60's and 126mph at a few different tracks in decent air.

It is possible to beat what the calculators show for power, and most Stockers and Super Stockers that run in that one second under the index area are doing it........by a fair amount.

Another one that I'm sure of the data on........ 3650lbs, 470hp, 11.19@119+

On this one, the ET(514hp)looks way better than the MPH(478hp),mostly because the converter is too loose and the motor is driving through it in high gear, but the car still leaves pretty good with it(1.50 60').

My Valiant had a 389, ported J head 296/557MP cam, 4.30 gears, and a TA 5000 stall. It was a good little 10.90-11.10 (10.89-121.6 best) bracket car with my fat butt in it. Went a 10.73-123 with my skinny buddy driving.

I converted it to a street car, added a passenger seat, extra fans, switched to 3.89 gears, and the 4500 stall. I now had a nice 11.30-11.40 (11.27-117.2 best) street car! No changes to the engine at all.

I think RMCHRGR's Duster will run 11.35 at 118 or so, and he'll have to work from there, and I say so without impugning his dyno sheet in any way.

My point: It's real easy to take an engine off of a 40,000 dollar dyno, strap it into a 15,000 dollar car and figure out how to go slower than the dyno numbers showed it had potential to run.

I never had a dyno sheet on my 440 in my Challenger, but in the 6 years and 759 passes that I put on it, at tracks all over the west, it ran from 9.96-134 to 10.47-125, and the initial dyno numbers would still be the same regardless of which pass you compared it to.

This is what I get touchy (fair or not) about. If you feel a speed/weight/HP slide rule or online calculator gives you a fair amount of information to discredit a dyno, an engine builder, or a dyno data sheet, you are doing the equivalent of someone using a crescent wrench as a hammer.

(This is the place where I would normally couch this statement with some qualifiers, and try to soften the tone, but I think I'll just let you kick me around for a while...)

Fast,
920 to 772, normal drop from crank to wheels? Not rhetorical, I'm not sure if you feel that is acceptable or not.

Billy are you saying we race cars not Dynos?

God I hope so.

One liners are not my thing...

I prefer to say it four or five paragraphs...I should've been a preacher.

That's kind of how I look at RWHP, not as an actual number but more of a reflection of whatever driveline % loss you choose to use. So maybe I wasn't operating under a total misconception.

As my rule of thumb, I use 15%. So 85% of 500 is 425. Using that number, Wallace says I will go 11.42 @ 118.38 which is closer to what Billy was saying.

Case in point, 778 is 84.5% of 920. Go figure.

I believe the car should be a little better than 11.40s which is why I said 11.00 at first. Could it go 10.80? Maybe but again, I won't hold my breath.

Again, my buddy went 10.60s (not sure what mph) with a milder combo and a little less weight. (His car is pretty much gutted). He even had a throttle stop for some reason.

Billy, 15-20% loss from the engine dyno I run to the chsssis dyno that car was tested on is pretty typical.

I think part of problem with trying to interpolate the numbers between the two, at least in this case is, they aren't using the same correction factor.
Most engine dynos are using the "standard" correction factor, and many of the chassis dynos use the "SAE" correction factor, which means they are correcting to different weather conditions, with the SAE correction being the poorer of the two, so the numbers are lower.

So, the 920 fwhp was standard corrected hp, and the 778 rwhp was SAE corrected hp.

I can't recall if there is a humidity factor in the SAE correction or not, but iirc, the temp is 77deg, and the baro is 29.38, whereas the Standard correction uses 60deg and 29.92 baro, and zero humidity.

I'm a big believer in dyno testing, and feel it's the best way to sort out and evaluate an engine combo.

However, I would never tell someone to take the numbers as "gospel".

There should be an acknowledgement that dyno numbers can be pretty different from one facility to another.
On my own motor, 60+hp spread between two different dynos.