Wheel BHP to Flywheel BHP...

[TVR Beaver]

Okay... Just been set up by Mark Adams at TVR Power and have come away quite pleased... The car is a lot more responsive and pulls much better up to the red line... I can spin my wheels in 2nd again so the torque also has increased.... But they have a Dynojet unit that gives results at the wheels and not the Fly... I got 262 BHP and 300 Lb/Ft.. so is there any accurate way of converting this to flywheel numbers so I can make a comparison?
I got 280 BHP at the growl and 325 Torque on their set up but it was overfueling badly... This is now sorted by Mark and has made a huge diferance (Many thanks Mark!!).. Just wondered if anyone had been on Powers rollers and the Crazey Horse ones (or North London Dyno or something).. as they are now and can estimate the corection needed?....
I know it means nothing!.... but would just like to see

[JR]

TVR Beaver said:

is there any accurate way of converting this to flywheel numbers

No, but people usually settle for adding 20%. If your numbers are for a 500 that sounds like a very healthy engine.

[dbv8]

I reckon you have gained over 30bhp.... so 310+

[V8 GRF]

Looks like you had a good day there John, a bit more successful than last time. Sorry I couldn't join you

[blueg33]

When my Tuscan was at TVR Power in May they showed 314 bhp at the wheels and Dom said that equated to 362/3 at the fly. I make that a loss of about 15.5%. This is also in line with AJEC racing figure for transmission loss when it went on their RR in Jan.

[JR]

blueg33 said:

When my Tuscan was at TVR Power in May they showed 314 bhp at the wheels and Dom said that equated to 362/3 at the fly. I make that a loss of about 15.5%. This is also in line with AJEC racing figure for transmission loss when it went on their RR in Jan.

Just for clarity that's the equivalent of adding about 18.5%. Others do generally add more than TVR Power but it's all nominal.

[blueg33]

JR said:

Just for clarity that's the equivalent of adding about 18.5%. Others do generally add more than TVR Power but it's all nominal.

314 + 15.5% = 362.67 This is what I said

314 + 18.5% = 372.09 This is what JR said

362-18.5% = 295 This what JR could have meant but is still wrong

362-15.5% = 305 This what JR could have meant but is still wrong

So I think JR is wrong, or am I missing something and the maths fail is mine?

Edited by blueg33 on Wednesday 24th August 15:20

[JR]

blueg33 said:

JR said:

Just for clarity that's the equivalent of adding about 18.5%. Others do generally add more than TVR Power but it's all nominal.

314 + 15.5% = 362.67 This is (NOT) what I said

314 + 18.5% = 372.09 This is what JR said

362-18.5% = 295 This what JR could have meant but is still wrong

362-15.5% = 305 This what JR could have meant but is still wrong

So I think JR is wrong, or am I missing something and the maths fail is mine?

My word! Yes, you are missing the fact that I meant that a 15.5% loss is the eqivalent of adding about 18.5% to the at the wheels figures. I didn't mention any bhp figures because your maths is astray. Originally you said a 15.5% loss and as you point out 362.5 x 0.845 = 306. We didn't know whether your 15.5% loss was correct and the 362.5 was wrong or whether the 362.5 was correct and you meant a 13.2% loss. Either way you were and still are wrong. Happy to help.

[blueg33]

JR said:

My word! Yes, you are missing the fact that I meant that a 15.5% loss is the eqivalent of adding about 18.5% to the at the wheels figures. I didn't mention any bhp figures because your maths is astray. Originally you said a 15.5% loss and as you point out 362.5 x 0.845 = 306. We didn't know whether your 15.5% loss was correct and the 362.5 was wrong or whether the 362.5 was correct and you meant a 13.2% loss. Either way you were and still are wrong. Happy to help.

Ta! I am having one of those days

[TVR Beaver]

Thanks for the answers... but did I read somewhere that Dynojet tend to be on the top side?.. not that I'm trying to undermine my excellent results at all

Yes David... a much better carry on... done and dusted in 2 hours of roller time and 2 1/2 hours of Marks time.. result!! and solid as a rock!! Sorry you could not come.. I'm sure it would have been a posative outcome for us both.... I'm well pleased.

[LordGrover]

Didn't Power do a 'before' run too? I assume little has changed between Growl and that run, so you should be able to gauge the difference there.

[TVR Beaver]

LordGrover said:

Didn't Power do a 'before' run too? I assume little has changed between Growl and that run, so you should be able to gauge the difference there.

No.. but the Growl do it on a twin roller set up.. in 3rd gear and give Flywheels numbers....
Powers is a single roller in 4th and wheel numbers??..... if you use 21% as I've been told it works out at 317 BHP.. yahoo... .. but is this possable...

[LordGrover]

If you call Gary he'll give you the RWHP - very accommodating chaps are North London Dynos.

Edited by LordGrover on Wednesday 24th August 16:31

[dbv8]

You also have to remember that Griffiths allow for twice the transmission losses of Chimaeras so flywheel figures can be artificially inflated in the pub or on dedicated forums.

Griffiths also suffer from a greater loss of traction at the drag strips due to huge torque which explains their poor ETs.

[blueg33]

TVR Beaver said:

No.. but the Growl do it on a twin roller set up.. in 3rd gear and give Flywheels numbers....
Powers is a single roller in 4th and wheel numbers??..... if you use 21% as I've been told it works out at 317 BHP.. yahoo... .. but is this possable...

AJEC use a dynojet but I am sure its both wheels, and do the run in 3rd gear. They gave virtually the same figures as Power.

In fact I know its both wheels as their RR also does 4x4's in which they specialise

[TVR Beaver]

blueg33 said:

AJEC use a dynojet but I am sure its both wheels, and do the run in 3rd gear. They gave virtually the same figures as Power.

In fact I know its both wheels as their RR also does 4x4's in which they specialise

When I say single roller.. I mean both rear wheel on top of a single roller... and not in a V between a front and rear roller... if you get what I'm saying...

[blueg33]

TVR Beaver said:

When I say single roller.. I mean both rear wheel on top of a single roller... and not in a V between a front and rear roller... if you get what I'm saying...

Ah I see what you mean. Does the single roller method make a difference? Less friction is my guess.

Personally I find rolling roads scary things, strapped down cars doing 80-90 mph with just a bit of webbing keeping them in place

[TVR Beaver]

Well.. it has been sugested that on a twin roller.. one roller does the BHP (front) and the other the torque?... however, they tend to climb up the front roller loosing traction with the rear so can in fact give a higher Torque reading than is actualy the case?? du-no if it's true, but sounds plausable??

[steve-V8s]

[quote=TVR Beaver]Well.. it has been sugested that on a twin roller.. one roller does the BHP (front) and the other the torque?... quote]

The only thing dynos measure is torque. BHP is calculated from the torque. The formula being Torque x RPM / 5252. Which is why the torque and power lines should always cross at 5252 RPM.

Some RR operators do a coast down test at the end of a power run where the car is knocked out of gear and allowed to coast to a stop so the RR can make a stab at the transmission losses. The technique is considered slightly inaccurate but at least gives another figure to argue about.

If it helps I have a plot from when the Griff was fairly standard which shows 258 BHP at the wheels and a calculated transmission loss of 43. More recently with a rather different state of tune and different RR I have a chart that shows 308 at the wheels and a calculated loss of 49 BHP so I guess on that basiss 15% is not far off.

[jcpgasoline]

I thought that losses drive train losses were about 15%, so power at the fly is roughly power at the wheels divided by 0.85