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

[BSB67]

No. They are intended to reflect true gross flywheel. It does not say it explicitly, but when you play around with their numbers and formula, it becomes apparent.

 

[lewtot184]

having played with a chassis dyno with my '69 r/t i believe true horsepower loss with a stock converter, exhaust, and gear is about 21%. chrysler says the net horsepower for a 440 tops out at about 330hp; that's about 260 or so at the tire. i believe these numbers to be fairly accurate. my stock 440 won't run 5000rpm. in fact about 4600rpm is all it wants and that's the rpm the factory rated peak power. mine would go flat at around 4300rpm on the dyno and that's with a 6pak (stock converter, gear, exhaust; peak power was 327hp).

 

[BSB67]

No. They are intended to reflect true gross flywheel. It does not say it explicitly, but when you play around with their numbers and formula, it becomes apparent.

Upon further consideration, it makes sense that they are likely net hp numbers.

 

[BSB67]

having played with a chassis dyno with my '69 r/t i believe true horsepower loss with a stock converter, exhaust, and gear is about 21%. chrysler says the net horsepower for a 440 tops out at about 330hp; that's about 260 or so at the tire. i believe these numbers to be fairly accurate. my stock 440 won't run 5000rpm. in fact about 4600rpm is all it wants and that's the rpm the factory rated peak power. mine would go flat at around 4300rpm on the dyno and that's with a 6pak (stock converter, gear, exhaust; peak power was 327hp).

Lew, do you still have your old R/Ts chassis dyno numbers and corresponding track numbers? I seem to recall you measured 290 at the wheels, but that 4000lb beast was trapping at 105 mph. Do you remember?

My Charger’s fwhp verses rwhp show 21% drivetrain loss too, despite the notable hp difference between our cars

 

[33 IMP]

I have used 20% as a ballpark figure for years, knowing full well that its a generalization/guess. (for an auto trans car anyway). I'm kinda surprised that Wallace uses 10% considering all the formulas he has available.
I figure my drivetrain loss for two of mine is about the same, despite fairly huge difference in drivetrain.
1. Small block, powerglide,5500 converter, 4" shaft, 9"ford with a spool, and 14x32s.
2. Big block, 727, 4800 converter, stock shaft, 8 3/4 with a dapco locker, and 10.5 slicks.
Timeslips for both say around 400 whp, so I'm guessing 500 net at the crank.

 

[PRHeads]

The only one I can think of off the top of my head......

14:1 572 Drag engine:
-918 stp corrected hp on the engine dyno(SF-901)
-778 sae corrected hp at the wheels(Dyno Jet)

Went 8.33@165 at 2750lbs, which shows 930hp on the Moroso power speed calculator.
The car has a P/G transmission.

 

[PRHeads]

I thought of another one......
This was in like 2003/2004....

NHRA stock eliminator 400 Pontiac:
460 stp corrected hp at the crank(SF-901)
410 sae corrected hp at the wheels(Dyno Jet)

Car was the first NHRA stocker GTO to get into the 10’s.......10.97@122 at 3600lbs.
The car used a Jerico 4 speed transmission

The Moroso power speed calculator shows about 500hp

 

[RemCharger]

So a 100 hp loss seems to be an average
On lower hp cars anyway

 

[lewtot184]

Lew, do you still have your old R/Ts chassis dyno numbers and corresponding track numbers? I seem to recall you measured 290 at the wheels, but that 4000lb beast was trapping at 105 mph. Do you remember?

My Charger’s fwhp verses rwhp show 21% drivetrain loss too, despite the notable hp difference between our cars

327 at the tire, 107.92 trap speed, 4060lbs, 3.23 gear, stock converter. unfortunately i never worked with the combo because et's were frustrating. later found that some of the e.t. issue was me using the wrong distributor. the 289hp thing was my first trip to the dyno. i was looking for some answers as to why some things weren't working well. believe i had a head gasket give up and maybe some fuel issues. like a dummy i never kept notes back then like i do now so maybe some dog chasing the tail thing,...?
when i first bought the car and rebuilt the engine stock, complete original factory exhaust, 3.23, stock tranny, 4000+lbs it ran 14.01/99mph. probably 255-260 at the tire. i may have been able to improve on that a little with better driving technique and a better awareness of the engines true power curve. when i was playing with the 6pak stuff i always shifted around 5200rpm and the dyno sheet showed the engine dead at that rpm and going flat around 4300rpm.

 

[Nxcoupe]

A dyno is easily fooled. I have guys all the time come use mine and they have a big stall speed converter and that messes with the dyno's calculation. It always shows less hp and torque. I warn them before hand and tell them a dyno is not for a number, it's for a base to see if your changes make more power over the base as the OP did. Excellent use of a dyno. Chasing a number is a waste if time and money. You can go to 10 different dynos and get 10 different peak numbers.
On to driveline losses, they are real and over the years I've come up with my 'rule of thumb', but there is a way to actually calculate them. I need to dig out my manual or call dynojet, but it's got to do with running the engine up to peak rpm in gear, letting off and then clicking the pendant, sampling the 'run' as the engine decels, which will record the power in an inverse slope. This tells you driveline losses. I'll get the specifics when I have a minute to find it or call them.

 

[lewtot184]

an interesting read is the september '70 popular hot rodding issue with a '70 6pak chassis dyno/drag strip test. i don't know how many times I've read that article. good info for somebody doing stock or near stock stuff.

 

[Nxcoupe]

an interesting read is the september '70 popular hot rodding issue with a '70 6pak chassis dyno/drag strip test. i don't know how many times I've read that article. good info for somebody doing stock or near stock stuff.

Got a link or post pics of article?

 

[lewtot184]

no link. tried to take some photos from the article. i might have to get a 10yr old how to do it,..lol!

 

[33 IMP]

Either hot rod or carcraft did a local chassis dyno crawl thru five chassis dynos, with a stone stock blown Shelby mustang. Around 600 (rated) crank horsepower. (I don't remember if it was an auto or six speed)
Chassis horsepower results varied from one dyno to another by MORE than a hundred horsepower!

 

[BSB67]

Either hot rod or carcraft did a local chassis dyno crawl thru five chassis dynos, with a stone stock blown Shelby mustang. Around 600 (rated) crank horsepower. (I don't remember if it was an auto or six speed)
Chassis horsepower results varied from one dyno to another by MORE than a hundred horsepower!

They are tuning devices. I don’t get very excited about someone’s chassis or engine dyno data. The real equalizer for me is a time slip and atmospheric data.

 

[33 IMP]

They are tuning devices. I don’t get very excited about someone’s chassis or engine dyno data. The real equalizer for me is a time slip and atmospheric data.

Agree. Knowing how easy it is to "fudge" results to make the customer happy, I tend to discount most instances of huge numbers. E.t. slip is the determining factor, but how much of a race setup the car is, is definitely a factor.
Racer A may really have 700 hp, but if it's in a 4000 lb car with a 2800 converter and 3.23 gears, and T/A radials, he's gonna get smoked by Racer B, with 3200 lbs, 5000 converter, and an honest 500 hp.

 

[BSB67]

Agree. Knowing how easy it is to "fudge" results to make the customer happy, I tend to discount most instances of huge numbers. E.t. slip is the determining factor, but how much of a race setup the car is, is definitely a factor.
Racer A may really have 700 hp, but if it's in a 4000 lb car with a 2800 converter and 3.23 gears, and T/A radials, he's gonna get smoked by Racer B, with 3200 lbs, 5000 converter, and an honest 500 hp.

Sure.

My reference to “time slip’ verses et was purposeful. Mph generally neutralizes differences in suspensions. I did fail to mention race weight though.

 

[33 IMP]

Sure.

My reference to “time slip’ verses et was purposeful. Mph generally neutralizes differences in suspensions. I did fail to mention race weight though.

Again, agree. Mph is a much better determinate of horsepower, E.T. a better indicator of how well a drag car is set up.