numbers from chassis dyno vs. engine dyno

General engine tech -- Drag Racing to Circle Track

Moderator: Team

hotrodhp
Member
Member
Posts: 98
Joined: Sun Mar 02, 2008 9:15 pm
Location:

numbers from chassis dyno vs. engine dyno

Post by hotrodhp »

today i took my 383 to the chassis dyno. the best pull i had was 447hp@6600rpm an 403 ft.lbs @ 5700rpm. my ? is what is the general rule of thumb as far as % hp lost thru the drivetrain goes when dealing with the chassis dyno vs. an engine dyno - knowing that there is no exact number or %. maybe 15 or 20%. just wonderin what it Might do on the engine dyno.. thanks
Jason G
Pro
Pro
Posts: 228
Joined: Mon Feb 21, 2005 8:56 pm
Location: TX

Re: numbers from chassis dyno vs. engine dyno

Post by Jason G »

hotrodhp wrote:today i took my 383 to the chassis dyno. the best pull i had was 447hp@6600rpm an 403 ft.lbs @ 5700rpm. my ? is what is the general rule of thumb as far as % hp lost thru the drivetrain goes when dealing with the chassis dyno vs. an engine dyno - knowing that there is no exact number or %. maybe 15 or 20%. just wonderin what it Might do on the engine dyno.. thanks
hotrodHP,

There are a lot of factors that come into play and you can't really compare from one chassis dyno to another, but......

The first iteration of my engine was 672 HP @ 6300 RPM on what I believe to be a reasonable SF-901 engine dyno. I installed the engine in the car with an 8" converter (4400 flash), TH350, 3.5" steel driveshaft, 12-bolt w/posi and 27x9 tires DOT slicks. It put down 548 RWHP @ 6400 RPM.

The only changes were adding 3.5" exhaust, 3" mufflers, and an alternator. Everything else was as it was run on the engine dyno.

Jason G.
David Redszus
Guru
Guru
Posts: 9633
Joined: Tue Nov 27, 2007 9:27 am
Location: Chicago
Contact:

Re: numbers from chassis dyno vs. engine dyno

Post by David Redszus »

- knowing that there is no exact number or %. maybe 15 or 20%. just wonderin what it Might do on the engine dyno.. thanks
That is pretty close.
andyf
Guru
Guru
Posts: 1387
Joined: Tue Oct 05, 2004 12:55 pm
Location: Oregon
Contact:

Post by andyf »

The last time I did some back to back testing we had 550 hp on the engine dyno and 475 rwhp on the chassis dyno. So that is a drop of 14%. That was with a manual transmission, 3.54 gear ratio and radial tires.
Andy F.
AR Engineering
1989TransAm
Guru
Guru
Posts: 15481
Joined: Thu Feb 15, 2007 8:43 pm
Location: Cypress, California

Post by 1989TransAm »

A couple of weeks ago I got to witness an engine dyno and then a chasis dyno with the same motor, the same facility and the same brand of dyno's.

The motor made 525hp on the engine dyno. The motor was then installed in the car and made 425 horsepower on the chasis dyno. The transmission was a built 200-4R and non lock up converter. The car was a 1972 Corvette.
Last edited by 1989TransAm on Tue Dec 09, 2008 12:49 pm, edited 1 time in total.
hotrodhp
Member
Member
Posts: 98
Joined: Sun Mar 02, 2008 9:15 pm
Location:

Post by hotrodhp »

thanks alot for the info!!
maxracesoftware
Vendor
Posts: 3625
Joined: Sat Feb 14, 2004 4:04 pm
Location: Abbeville, LA
Contact:

Re: numbers from chassis dyno vs. engine dyno

Post by maxracesoftware »

hotrodhp wrote:today i took my 383 to the chassis dyno. the best pull i had was 447hp@6600rpm an 403 ft.lbs @ 5700rpm. my ? is what is the general rule of thumb as far as % hp lost thru the drivetrain goes when dealing with the chassis dyno vs. an engine dyno - knowing that there is no exact number or %. maybe 15 or 20%. just wonderin what it Might do on the engine dyno.. thanks
i just talked with a Guy who builds 1 Cyl 4-Valve and 5-Valve ATV Drag engines
77.0 HP @ 10,500 w/27.391cid on Engine Dyno
67.0 to 69.0 HP on Chassis Dyno

this is a 4-Wheel ATV...its around 10% Loss on Chassis Dyno

for Cars basically, its somewhere between 18.0 to 22.0 % Loss on Chassis Dyno

i've seen up to 22 % Loss on 800 HP Engines
going to Chassis Dyno, some of the loss due to tire distortion
on the Rollers as to how much force you need to tie-down the tires
to the rollers, and what tire compound as to how much its trying to grow
MaxRace Software
PipeMax and ET_Analyst for DragRacers
https://www.maxracesoftwares.com
User avatar
MadBill
Guru
Guru
Posts: 15024
Joined: Tue Nov 15, 2005 10:41 am
Location: The Great White North

Post by MadBill »

A lot of people screw up on the conversion from chassis to engine power. Assuming a 20% loss, you do not multiply the chassis figure by 1.20, you divide it by 0.80.

e.g.; 500 HP engine dyno with 20% loss = 400 CHP x 1.20 = 480 BHP, Wrong!
400/0.80 = 500 HP. Correct!
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.
revolutionary
Guru
Guru
Posts: 1393
Joined: Wed Feb 20, 2008 10:43 pm
Location: Colleyville, TX

Post by revolutionary »

Similar numbers here. We ran an engine on a SF901 and made 622 then on a Mustang Chassis dyno through a TH400 and 9inch made 518 for a loss of 17%
Daryl

Revolutionary Performance and Machine
hotrodhp
Member
Member
Posts: 98
Joined: Sun Mar 02, 2008 9:15 pm
Location:

Post by hotrodhp »

great info. the test was done on a dynojet 224 LC. its a 69 camaro with a 4 speed an 9' ford with 4:30 ratio- 275/60-15 radial tires. thanks!!
W. Tripp
Expert
Expert
Posts: 574
Joined: Thu Apr 10, 2008 8:28 pm
Location: Birmingham, AL, USA
Contact:

Post by W. Tripp »

hotrodhp wrote:great info. the test was done on a dynojet 224 LC. its a 69 camaro with a 4 speed an 9' ford with 4:30 ratio- 275/60-15 radial tires. thanks!!
FWIW- the 9 inch Ford tends to take a couple more percent to drive than the 8.8" Ford or 12 bolt Chevy, mostly due to the outward pinion location from centerline.

Also, transaxels tend to be a bit more efficient than normal trans/diff combinations.
EthylCat
Pro
Pro
Posts: 232
Joined: Wed Jul 12, 2006 12:02 pm
Location: Midwest
Contact:

dyno

Post by EthylCat »

My two experiences showed more loss than most of you guys.

1. 435 hp 383 on DTS Powermark into mid 80's El Camino. Put 300 to the tire on Mustang 1100se same day, same building. TH350 trans and 9 inch rear.

2. 495 hp 460 on the same Powermark became 325 hp to the tire on the same chassis dyno.
69 Mustang w/ C6 and 9inch.
GOSFAST
Expert
Expert
Posts: 604
Joined: Tue Jan 08, 2008 7:09 am
Location: Long Island

HP-Flywheel vs. Rear Wheels

Post by GOSFAST »

According to the "Vette Doctors" here on Long Island you can use a 16%/18% factor and be right on the money!

We've had the opportunity to confirm about 4 builds recently with the dyno HP and then with the chassis dyno!

The guys at the "Vette Doctors" were correct, 16%/18%.

The last one I recall was 676 on the dyno and 575 at the tires!

Thanks, Gary in N.Y.
1989TransAm
Guru
Guru
Posts: 15481
Joined: Thu Feb 15, 2007 8:43 pm
Location: Cypress, California

Post by 1989TransAm »

GOFAST, are those numbers with manual or automatic transmissions?
Duner
New Member
New Member
Posts: 22
Joined: Wed Dec 03, 2008 10:09 pm
Location:

Post by Duner »

So would an automatic putting down 625 at the rear wheels be about 750 at the flywheel then?
Post Reply