Chassis dyno numbers—

[Skelly]

I am looking at putting my car on a chassis dyno system that hooks up to the rear hubs. Has anyone had any experience with these systems and what power numbers do you see. We have access to a dyno but no Hubs. Any help would be great.
thanks
sean

[alangbaker]

I am looking at putting my car on a chassis dyno system that hooks up to the rear hubs. Has anyone had any experience with these systems and what power numbers do you see. We have access to a dyno but no Hubs. Any help would be great.

I dyno'ed my RF89 on a dyno of that type; a Dynapack. The operator had adapters that fit my 3.75" 4 bolt hubs.

[Skelly]

What HP did you see at the wheels? The dyno we are using is also a Dynapack
Thanks
Sean

[alangbaker]

What HP did you see at the wheels? The dyno we are using is also a Dynapack

I can't find the sheet anymore...

All the record-keeping is my worst thing in racing.

[Dee]

You will see roughly 18% less at the wheels than you would see on an engine dyno

[lowside67]

Based on what? I would think that the Hewland gear box is very efficient at transmitting power and given how little stuff is in the driveline that the loss would be a lot lower.

-Mark

[alangbaker]

You will see roughly 18% less at the wheels than you would see on an engine dyno

Based on what? I would think that the Hewland gear box is very efficient at transmitting power and given how little stuff is in the driveline that the loss would be a lot lower.

-Mark

I've got to agree with Mark here.

18% sounds WAY too high for a driveline with straight-cut gears.

I would think closer to 5% would be accurate.

[Dee]

I have Hewland in a super vee and a staffs in a rt41 on a floor dyno 18% loss at the ground

[alangbaker]

I have Hewland in a super vee and a staffs in a rt41 on a floor dyno 18% loss at the ground

I'm sorry, but I have severe reservations about that.

While it might represent the numbers you see on two different dynos, I don't see any way that 18% of the power can be lost in a straight cut box and the diff.

[stonebridge20]

I have Hewland in a super vee and a staffs in a rt41 on a floor dyno 18% loss at the ground

You may want to think about REM-ISF processing your gearbox guts.

Just sayin.

[TimH]

I'm sorry, but I have severe reservations about that.
While it might represent the numbers you see on two different dynos, I don't see any way that 18% of the power can be lost in a straight cut box and the diff.

"on the ground" may also mean some loss between the tires and the rollers.

[mark elder]

So here are some real figues for F1600. Calibrated dynos (both same make, same shop), air corrected etc, if 115 on dyno, 96 at wheels the next day. Equals about 17% loss. Done this many times, always the same loss. Never over 98 at wheels ever.

[t walgamuth]

The loss of the ring and pinion is significant. Straight cut gears are more efficient but they still take power to turn. Each transformation of energy takes some away.

18% sounds pretty good to me.

[Jon Jeffords]

If possible, try to conduct your tests at a repeatable/consistant engine oil temp and transaxle oil temp. The actual viscosities of these two fluids during the tests can have a surprising affect on parasitic losses in the powertrain. This may be overkill for a majority of the SCCA racer's test objectives, but it should be a consideration none the less.

[JLind]

Honda and Ford Dyno graphs


https://www.f1600canada.com/en/honda...rd-dyno-tests/


Sent from my iPhone using Tapatalk

[recaryob]

My personal experience between the engine dyno results I get from my engine builder and the chassis dyno results I have personally seen with a couple of different engines and two different cars (two different transaxles one mk9 and one ld200), match pretty closely with what Mark is explaining above. I was a bit surprised as well.

[Raceworks]

The problem with chassis dynos is that they're rarely climate controlled and results can vary widely. Just a little bit of tire slip can throw the numbers way off. Plus the various styles give varying results. You're going to see different numbers with a portable unit that the tires roll on versus the types that bolt to the hubs versus the types with the big rollers buried in the ground.

You only get reliable numbers with the same dyno under the same conditions (temperature, humdity, etc). This is why the best comparative numbers you get are water-block dynos that are climate controlled.

Chassis dynos are best for measuring relative changes from tuning changes or relatively simple bolt ons (like changing a header or air filter). The only way you're going to find out if your engine is "good" is to have a "known good" engine do a pull either the same day or they have record of that car under similar conditions.

[David Ferguson]

Sean,

I have a Dynapack Hub dyno, and have made (and have) many adapters for centerlock wheels. If I don't have something that fits, I can make it.

I am currently in New Zealand and planning to visit Dynapack on Thursday!

[mark elder]

Sean,

I have a Dynapack Hub dyno, and have made (and have) many adapters for centerlock wheels. If I don't have something that fits, I can make it.

I am currently in New Zealand and planning to visit Dynapack on Thursday!

Dynapack are very clever people. They also made a simulator for 'humans' who were the grinders for the Americas Cup Yachting. NZ is a country obsessed with yachting....

David, any chance you will be in Christchurch (New Zealand) in 10 days? There is a good race meeting on including some FF1600 racing (plus classics etc etc). Look up "Wigram Revival Meeting". I sort of live in Christchurch. Both my boys are racing there that weekend.

Mark


Vintage Car Club

[David Ferguson]

I was in Christchurch the past few days, we are currently headed north, and I won't be back (this trip) to the South Island. But thank you for the offer to visit.