Chassis dyno of stock 1968 Charger R/T (440/727)

[DAMatt]

Took the car to a chassis dyno yesterday, haven't seen a dyno showing what rwhp a stock hp 440 makes. Took a couple of videos of the runs, here's one of them:



262.7hp @5108rpm & 477Nm @ 3277rpm (that's 351lbft). If you take into acount a 25% drivetrain loss, that would translate to 350hp & 468lbft.

Ignore the estimated engine hp & torque, the rwhp is the one you can rely on, and calculate torque from, as I did above.

I did a few followup tests:
-carb hat & filter off, but keep the base: 268.3hp @ 4588rpm
-same as above but hood open: 276.5hp @ 5142rpm

So what do you think about the numbers? Do they line up with the common wisdom?

 

[AR67GTX]

I’ve heard many times that the 440/375 was optimistically rated and 355 - 365HP at the crank was more accurate. If your engine is in good condition and tune and the assumption of driveline losses is close, then it would seem to support that. However, that never seemed to square with how strong they ran back in the day. Maybe it was always all about the torque.

 

[66 Sat]

Wow, lovely car, interesting how much horsepower is gained with the cooler air with the hood up.

 

[RemCharger]

#'s make sense.
Way back I made 325 with a warmed up 383- and before that I'd estimated 425 fwhp.
Also, the factory did not dyno engines in cars with all the crap on them and the lights on lol

Iirc it was 22hp for every 50F. ( or was it 70)

 

[INTMD8]

I'm not familiar with that dyno but I think the numbers look good. Car looks great too

Appears to lose valve control at 6k so I would keep it below there.

 

[BSB67]

Those are good numbers.

Different types of chassis dynos will also give different results. Who's the manufacturer?

 

[BSB67]

Appears to lose valve control at 6k so I would keep it below there.

You are probably right, but the 440 cast iron intake and and the factory cam cannot go over about 5800 no matter what you do, from my experiance.

Retard the cam, and put a 6 pack on it, everything else the same, it behaves a bit differently.

 

[DanielSlocum]

how is it that drivetrain loss is a percentage of max output? why would the drivetrain loss ever increase because the engine is making more power? anyone???

 

[AR67GTX]

They don’t - at least not in linear fashion. That’s the big fallacy in using a correction factor for converting chassis dyno HP. Might be 25% on a 383, 20% on a 440 and 30% on a 318. Who knows, it’s all guess work. As HP and torque increase there is more loading/friction/heat in the gear trains/ fluid couplings that contribute to the loss but it’s not close to a uniform or linear ratio to HP.

 

[66 Sat]

I've questioned this before as a blanket % loss makes no sense.

Got a 300hp engine @ 25% loss you are at 225hp at the wheels - 75hp loss

Rebuild engine with upgraded cam, intake and exhaust, carb, pistons, heads etc to 500hp @ 25% loss you are at 375hp at the wheels - 125hp loss

No change to transmission, fan, alternator, power steering etc and all those efficiencies you built into your upgraded engine and it's losing an extra 50hp in drivetrain losses? Makes no sense.

AR67GTX is correct, it's a mystery area.

 

[BSB67]

Probably not linear, but don’t forget the additional hp it takes to accelerate all of those things. accelerating the same mass faster will take more hp. My combined tire/wheel weight is over 200 lbs. it will take noticeably more power to accelerate 200 lbs faster

 

[Nirvana]

This is an easy read to help you understand drivetrain power loss.

Drivetrain Power Loss - The 15% "Rule"- Modified Magazine

 

[33 IMP]

To be honest, that's a bit better than I predicted (to myself) when I saw the thread title.
I figured a 375hp 440 for about 300 net (real) horsepower, and a 20% drivetrain loss, so I came up with 240 to the wheels.

 

[BSB67]

Mopar called the 440 315 actual hp

 

[33 IMP]

Imo, drivetrain loss depends on what kind and type of trans, and which rearend is used.
Basically, the beefier the components, the more drivetrain loss. C6 ford trans, and nine inch ford rears are notorious for eating hp. Probably three times the drivetrain loss of a slant six/manual 3 sp. Turbo 400s and 727s are supposed to be better than a C6, but every Mopar racer knows a 904 will eat less power. So do powerglides. Ford guys try to make C4s live for the same reason.
Racers know that 9" ford eats power, (acute hypoid angle) but the put up with it for the strength. A Dana eats less power than a 9, but there is the weight thing, and gear changes are a nightmare compared to a ford, and the ford has way more ratio choices.
So, I guess if you want sufficient durability for your power level, drivetrain power loss is gonna be part of it.

 

[33 IMP]

If I remember right......
Dave McLellan engine dyno'ed his Stage One 455 Buick engine before putting it in his car.
He then chassis dyno'ed it, with A/C compressor, water pump, alternator etc. Installed, exhaust hooked up, driving thru a turbo 400, two piece driveshaft, and a twelve bolt rear. Any guesses?






He lost over 35%.

 

[DAMatt]

I think I have to give additional details.

I also knew from old literature that the '68-'71 hp440 was realisticaly rated at 305-315hp.

I have the RV2 factory compressor on the engine, but the clutch was not engaged - so it was just idling the A/C/ clutch pulley. Does that rob hp as compared to a non A/C car?

I did not turn on the headlights, just the parking & position lights. Forgot that each amperage request eats a little hp, but I think the headlights are the major contributor.

I was a bit sneaky, and oil was to minimum, 10w30 Amsoil premium protection (zinc). 40 and a little psi, perhaps would be a good idea to go 10w40.

Have a fluidampr instead of the factory piece, pertronix 2 instead of points, and an AVS2 800cfm carb.

Except that, factory 178 manifold, unported 906 heads with stock valves, stock rocker arms, six pack pistons & .039 gasket (so 9.5:1 I guess). Also Accurate Exhaust 2.5" downpipe into 2.25" piping. The non-sport, factory-like kinked mufflers.

I asked the operator to only go 6000rpm, so maybe he was in the process of lifting off the throttle for the last 200rpm. That would also explain the big lean-out you can see on the graph, from 11 and a bit to more than 13. On a 10 speed you never have to go past peak, because the gears have it so that you are always at the perfect rpm, but on the wide spacing of our 3spds, you strangely have to go 1000rpm + past peak for optimum acceleration. the wider the gear spacing, the more you have to go past peak. After doing the math, it is about a 6000 shift point from 1st to 2nd (2.54-1.54), but ~5500 from 2nd to 3rd (1.54 to 1)

 

[BSB67]

Good stuff. Sounds like you did a nice job of recreating “stock”.

Thanks for posting

 

[33 IMP]

Alternator drag for a few lights, and an unengaged a/c compressor is negligible hp loss. Certainly less than five, I would guess less than two. And killer ignition is worth nothing on an engine that has good functioning stock stuff that is not stressed by high horsepower/high compression/high rpm.
Oh, and for reference, I believe the 375bp rating was at UNDER 5000 rpm.

 

[AR67GTX]

Mopar called the 440 315 actual hp

View attachment 1503885

Is that reflective of the change from gross HP ratings (pre 1971) to net HP ratings (71 to current) ?