BHP Figures.

[Big T]

Not sure if this is the right forum but hope someone can help me out with my query.

I had my car dyno'd a little while ago but the device used was not the normal rolling road facility but a device called a DYNAPACK which measures the power at the hub and not the wheels or flywheel.

I know there's an approximate calculation that can be done to work out Wheel BHP to Flywheel BHP and vice versa but is there a similar calculation for working it from the hubs to wheel or flywheel BHP??

I know there's many variables when measuring true horsepower so it can never be exact, just interested to see how much BHP my 360 roughly has without paying for some more sessions. I didn't pay for this session so I haven't wasted any money if this device is not very good.

Any help would be great.

T.

[adrianr]

This is the remove-wheels-and-bolt-on job? If so it will be measuring power at wheels but without any tyre friction losses.

Calculating egine power from power at wheels is all fudge factors and bar talk....the most reliable method is based on a "coast down" measurement. You do your power run, then knock it out of gear and let the drivetrain freewheel back to rest, still connected to the dyno, then add that measurement to your recorded power to get what the engine is actually delivering.

Would have thought your dyno operator would have done that? It's pretty much standard practice.

AdrianR



>> Edited by adrianr on Thursday 4th November 14:04

[kevinday]

For bigger engines I suggest the following formula will give you a rough answer:

Losses through drivetrain will be in the order of:

10 bhp +10%

Therefore 350 at the wheels would be around 400 at the crank.

To work it the other way add 10 to the wheels figure then add 1/9th of the figure.

[andys2]

Just out of interest what were the results?

[stevieturbo]

no matter what way flywheel HP is calculated it is only approximate.

The Dynapack is a cool bit of kit.

[Big T]

Thanks for all the comments chaps...Andy, the result was 358.1 at the axle, twice...I take it that this is most probably very good if Kevins formula is correct...that would make approx 405 odd BHP...now that is excellent cos I've been told recently that the usual 360 only puts out about 380...

The reason I'm asking all this is I'm considering on doing a few performance enhancements...

T.

[chuntington101]

the best solution is to use the same type of dyno each time. then you will get a "percentage inprovment". this is more useful than trying to back track and calculate crank power. and at the end of the day who cares? its not like you gona let thta t**t in the pub who says he's got more than yours drive the thing anyway!
a couple of points for the people who insist on atempting to calc crank figures (and i have no problems with, each to thier own). you need to measusre the efficency of the drive train that you have. so a mesured power (like a dynod engine) need to be used to get the losses. then just a case of doin the maths. but at the end of the day, a figure at the wheals is the actual amount of power and torque that the road will feel! :-)

thanks Chris.

[steve_D]

Big T said:

.....The reason I'm asking all this is I'm considering on doing a few performance enhancements...

If you have a number of changes/mods to make then returns to the dyno will become expensive.

One of these G-tech Pro <a href="eBay Item #7931695039 could save you a lot of £££.

It works by measuring exceleration over time and only needs the exact weight of your car to work out everything. Torque, BHP, 0-60, 1/4 mile etc.
Guys in the states say it is very accurate.

Steve

>> Edited by steve_D on Friday 5th November 14:51

>> Edited by steve_D on Friday 5th November 14:52

[Big T]

Thanks Steve, looks a really good piece of kit...I noticed this in a post on the VMAX forum too so must be worth the money.

I will order one of these today.

T.

[atom290]

You could always take the engine out and put it on a proper dyno??

sorry i'll get my coat now!

[scuffham]

adrianr said:

This is the remove-wheels-and-bolt-on job? If so it will be measuring power at wheels but without any tyre friction losses. Calculating egine power from power at wheels is all fudge factors and bar talk....the most reliable method is based on a "coast down" measurement. You do your power run, then knock it out of gear and let the drivetrain freewheel back to rest, still connected to the dyno, then add that measurement to your recorded power to get what the engine is actually delivering. Would have thought your dyno operator would have done that? It's pretty much standard practice. AdrianR

Can't do that with a dynapak, they have almost no inertia in the pods, so if you dip the clutch, it will stop.

very hard to come up with a figure for losses as all you are looking at is the box/FD grear losses + whatever the hub/CV/Tripod take.

with gearboxes this really depends on the design, what oil is in them, which gear is used, how hot they are, etc etc.

what this comes down to is that every 'type' will have it's own losses.



>> Edited by scuffham on Monday 8th November 09:38