Chassis dyno horsepower

[bigjoe1]

The reason for my inquiry is this. A friend had his car dyno tuned on a chassis dyno. They got a 40 HP increase --before and after.- He runs his car at a local 1/8 mile track, and it is very consistent- The 40 HP increase only improved his times my three to four hundredths, and the MPH barely changed too. That seemed very small to me- This is a street driver 547 BB Chevy that is making 600 HP at the tire.




JOE SHERMAN RACING

[andyf]

There is a lot of potential testing error when using a chassis dyno. Tire slip and clutch or convertor slip are two big areas that you don't have on engine dyno. Plus you have all of the regular errors that can happen with an engine dyno with calibration errors, weather station issues, sensor failure, fuel system problems, cooling system issues, etc.

I've found that a chassis dyno is a great place to do some transient testing and tuning as well as dialing in the cruise circuit on the carb and things like that. I don't think I'd spend too much time measuring peak power on a chassis dyno. If you took a car to 5 different chassis dynos and plotted the results you would most likely see something that looks like my target practice targets. One point over here, one over there, etc.

[Orr89rocz]

most cars i've seen that base line a pull on the dyno, then get tuning while on the dyno and find hp all over the curve, it will pick up at the track. If it doesnt then i would look at shift points, converter, etc. something during acceleration may be holding it back. Oil windage/drain back issues in g force environment vs static dyno pull?

Other thing is i noticed most of the time the basic dynojet stuff doesnt load motor as hard as the track. So a gain in hp on dyno at a giving airfuel value and timing may still require adjustment at the track. Especially on boosted cars


Last car i dynoed in different gears for sake of the thread op, i did a pull in .70 od by accident on a 700r4 trans lol. Then dyno'd again in 1:1 3rd. Made slightly less torque in 1:1 but was a different day same dyno so hard to tell. Hp was within 5 or so. 270 whp 350 sbc street deal

[cgarb]

Joe, I assume your friend paid to have his car tuned. If you go there and pay for a tune, you expect to gain something. Maybe they showed more of a gain somehow to justify their work. I've never had a car or engine of mine on a dyno, but I'm sure it possible to manipulate the numbers to show a gain. If it don't compute on the track...that's all that matters to me.

[turboivo]

Lower, due to more traction loss in a lower gear, (more Torque, easier to turn the tyres if not correctly strapped).

Good point ...

Higher, due to the Inertial losses of the wheels having less effect in a lower gear (more Torque).

Here you're trying to break the laws of physics.

This 1:1 rubbish that people always talk about is crap, the gear box ratio is merely one of 3 ratio's that the Torque/Power has to go thru before it is measured by a chassis dyno.

In fourth gear, no power is transmitted through gears in a Muncie and similar transmissions. FWD transmissions are different and your statement would be correct.

Really low powered cars suffer the most when using say 3rd against 4th, you might get 45kw in 4th and 55kw in 3rd, using the same ramp rate. Use a slower ramp rate in 4th and you might get close to the 55kw in 3rd. "

The Mustang is an inertia dyno ... ramp rate is determined by the torque applied to the rolls.

Also this thread:
http://www.ls1.com.au/forum/showthread. ... ue+chassis

Has no basis in engineering ... try this one instead ... http://www.engineersedge.com/motors/sol ... uation.htm

I guess you just don't read my post and the link info correctly. You could try again.

[Truckedup]

My land speed racing bike has spent as much time on the chassis dyno as the track.... The dyno is a tuning tool, not a bragging rights tool and it work pretty well for me...I get the carbs and pipes sorted out and on the track it's damn close to maximum performance but not perfect....I use a Superflow dynamometer ..It's a dual purpose machine with both eddy current and inertia capabilities...For tuning bikes the inertia feature seems to work well... The Dynojet is an inertia machine know for giving optimistic power readings compared to an eddy current...
Someone mentioned Mustang being an inertia, the one I've seen and used were eddy current...

[bigjoe1]

Another interesting point. On my own stuff, we always get a boost in performance when I get more power, however, I have tuned up other peoples engines, and their cars actually ran the same or SLOWER . The only thing I can think off is that the newer ( more power ) caused a slight loss of traction, resulting in a slower E T at the track. This is not always the case, but it has happened.




JOE SHERMAN RACING

[DaveMcLain]

A few years ago a friend of mine took his drag racing truck to a chassis dyno. A local diesel specialty shop was having a dyno day and the guy invited him to bring his truck. We had run the engine on my dyno previously and it made 870 horsepower(557 Ford with A460 heads). When they put it on the chassis dyno they got 870 horsepower! This was in a '64 Ford pickup with a Powerglide, a 4.86 gear and a set of 33 inch drag slicks. He did three runs and they were all within a couple of horsepower so it seemed to be pretty repeatable we just always wondered if the numbers were supposed to be what the engine made or what was put down to the rear tires.... Who knows but I would have thought that with a 5000 converter, that gearing and those tires that it would have lost at least 50HP during an acceleration run from 5000 to 7200rpm..

[Orr89rocz]

A few years ago a friend of mine took his drag racing truck to a chassis dyno. A local diesel specialty shop was having a dyno day and the guy invited him to bring his truck. We had run the engine on my dyno previously and it made 870 horsepower(557 Ford with A460 heads). When they put it on the chassis dyno they got 870 horsepower! This was in a '64 Ford pickup with a Powerglide, a 4.86 gear and a set of 33 inch drag slicks. He did three runs and they were all within a couple of horsepower so it seemed to be pretty repeatable we just always wondered if the numbers were supposed to be what the engine made or what was put down to the rear tires.... Who knows but I would have thought that with a 5000 converter, that gearing and those tires that it would have lost at least 50HP during an acceleration run from 5000 to 7200rpm..

Yeah something is wrong there. Theres always drivetrain loss.

[statsystems]

Another interesting point. On my own stuff, we always get a boost in performance when I get more power, however, I have tuned up other peoples engines, and their cars actually ran the same or SLOWER . The only thing I can think off is that the newer ( more power ) caused a slight loss of traction, resulting in a slower E T at the track. This is not always the case, but it has happened.




JOE SHERMAN RACING

Yup. And I've de tuned some cars at the track to make the go faster. Some guys never learn chassis and power go hand in hand.

[F-BIRD'88]

A few years ago a friend of mine took his drag racing truck to a chassis dyno. A local diesel specialty shop was having a dyno day and the guy invited him to bring his truck. We had run the engine on my dyno previously and it made 870 horsepower(557 Ford with A460 heads). When they put it on the chassis dyno they got 870 horsepower! This was in a '64 Ford pickup with a Powerglide, a 4.86 gear and a set of 33 inch drag slicks. He did three runs and they were all within a couple of horsepower so it seemed to be pretty repeatable we just always wondered if the numbers were supposed to be what the engine made or what was put down to the rear tires.... Who knows but I would have thought that with a 5000 converter, that gearing and those tires that it would have lost at least 50HP during an acceleration run from 5000 to 7200rpm..

The numbers from the chassis dyno are after correction. "corrected horsepower"

and probabily over corrected. Look a the raw uncorrected power numbers that the test actually did BEFORE any correction is added by the dyno software.

[MadBill]

..I guess you just don't read my post and the link info correctly. You could try again.

Or not. I read the quote you posted and came to the same conclusions as 4sfed: Your guy is just plain WRONG on at least a couple of points:

"Higher, due to the Inertial losses of the wheels having less effect in a lower gear (more Torque)." No, the inertia losses are higher, leaving the reported power lower because the acceleration rate of the drivetrain components is greater in a lower (higher numerical) gear.

"This 1:1 rubbish that people always talk about is crap, the gear box ratio is merely one of 3 ratio's that the Torque/Power has to go thru before it is measured by a chassis dyno. People tend to forget about the Diff Ratio and the Tyre to roller Ratio, so there is no be all to end all gear that has to be used." Also wrong, because the power lost to heat through a gear pair is largely related to the contact forces which in turn depend on the power being transmitted. A gear pair spinning free generates much less heat and most manual transmissions have one direct drive gear that eliminated a loaded gear pair.

[digger]

..I guess you just don't read my post and the link info correctly. You could try again.

Or not. I read the quote you posted and came to the same conclusions as 4sfed: Your guy is just plain WRONG on at least a couple of points:

"Higher, due to the Inertial losses of the wheels having less effect in a lower gear (more Torque)." No, the inertia losses are higher, leaving the reported power lower because the acceleration rate of the drivetrain components is greater in a lower (higher numerical) gear.

some chassis dynos run at a certain ramp rate (e.g. 15mph/s) so the angular acceleration of the wheel and tyre is the same regardless of the gearing
so the torque lost in accelerating the wheel/tyre (mass moment of inertia x angular acceleration) are the same regardless of gear but in a higher the gear the rpm is higher therefore power losses are higher in a higher gear.

obviously in the real world when you make inertia changes e.g. flywheel or whatever on a vehicle driven the "gains" are felt more in a lower gear. so chassis dynos get fooled by inertia changes when you dont have the engine and drivetrain accelerated at the rate it does on the actual vehicle which of course depends on the gear etc

[user-23911]

Build your own dyno.
Calibrate it yourself.

Then you can print out whatever numbers you want to and you get the ultimate bragging rights.


I prefer road tuning with a datalogger.
You can tune for the best acceleration , you can do whatever you want to and it will always be correct.


As far as numbers go, say you made a 40HP increase in max number?
Well so what?
It's only at one specific RPM point which you only hit once in each gear.

There's always losses in the lower revs associated with gains in the upper revs.
Nobody ever talks about those and most people wouldn't have a clue because most dyno runs start too high up in the RPM range.
Why do they start too high up in the RPM range?
Because most water brakes can't hold torque in the lower RPMs.
What about eddy current brakes?
Same?

[AMXstocker1]

i don't think your going to see a 40hp spike at a single rpm# on a NA big block chevy, and a car with a 5000 stall and 4.88 gears probably only operates in maybe a 2-3000 rpm band maybe narrower there are alot of drag cars that don't seem more than 1000 rpm swing going down the track so as long your improvement is in that range your probably ok. i would probably guess theres something fishy about the dyno #s or the car is now spinning a bit and needs chassis adjustment or if you did move up the power band for the gain you might have the wrong converter, powerglides are very converter sensitive.