Converting THOR dyno figures

I was wondering if we had enough info. to make some tentative conversion factors for the Thor dyno. set up.

As I understand it, the Thor dyno measures power at the hub (RHHP), whereas most other rolling roads measure it at the wheel (RWHP). Manufacturers usually quote figures at the crank (crank BHP).

So it would be useful to have some conversion factor for Thor. I had a search on here, but couldn't find many people with either stock cars or who had run the car on rwhp dynos.

Step forward Bobbeh. His car was measured at Thor at 306rhhp. He's also had it dyno'ed on another rolling road at 265rwhp. His only mods - in both cases I think - are his exhaust. This suggests that rhhp x 0.866 = rwhp.

Wipeout has a completely stock UK manual. The figure I've usually seen cited for crank bhp is 326. On the Thor dyno day, his rhhp was 293. This suggests that to get from rhhp to crank bhp, multiply by 1.11.

OK, trying this out on some BBS member's 6 speed cars, it would mean:

Bobbeh (UK, exhaust, no decat) = 339 crank bhp

MFS (Exhaust, decat, hybrids, uprated fuel) = 347rhhp, 385 crank hp, 300 rwhp

Mark Ayling (exhaust, decat, FMIC, uprated fuelling, more?) = 381 rhhp, 422 crank hp, 330 rwhp

Obviously, this is all a bit flimsy because it's only based on one or two vehicles, but the crank figures produced for bobbeh (14bhp over stock due to exhaust) seem reasonable. Oh yes, Millhouse has similar to Bobbeh and his comes out with virtually identical figures...in a j-spec auto.

Anyway, hoping tech heavyweights will wade in and throw some light on this.

Regards,

Cliff

Oh yeah,

also if you look at the power figures from Thor and rank them from high to low, there's an excellent correlation (by eye anyway) with boost levels, regardless of the level of mods.

Good work dude, I had been wondering about this myself for a while!

I'm not too sure if what your saying is particularly accurate.

Converting from rhhp to rwhp is dependant on wheel radius, some cars have 16's some 17's others have 18's or 19's, which means rhhp compared from one car to another with different size rims will produce different rwhp.

Converting from crank hp to rhhp or rwhp is also a little bit more difficult again, because you basically have losses involved in the transmission from the effort of turning gears etc., however this isn't a straight percentage drop from the crank power. Think of it like this:

If I increase the horsepower of my car from say 300 bhp to 900 bhp, the losses from the transmission wouldn't multiply by 3 times, they would pretty much stay the same. (Not exactly the same but by no means 3 times as much)

Why would it take more effort to turn the same gear ratio?

The best way to look at this is to find out what the stock crank bhp is of the 2JZ GTE and then dyno someone's stock car at THOR to get rhhp and then dyno it again on a RR to get RWHP. Then repeat the RR stint with different sized wheels to get other %age differences from the rhhp.

For my GT-FOUR, I vaguely remeber having about 247BHP at the flywheel and 200 ish BHP est at the wheels. Now that's a 4wd transmission so obviously it won't be as much as for the supra.

So basically RWHP=(Crank hp-transmission losses/100)*(100-%delta from rwhp/rhhp).

This is one of the reasons why on a RR the operator will calibrate the RR to say 3000 RPM on the tacho of your car. That way the RR knows the total ratio from the gear to the wheels.

I would like to say I hope that's made things clearer but probably hasnt at all.

Sorry:(

Originally posted by TLicense

Converting from rhhp to rwhp is dependant on wheel radius, some cars have 16's some 17's others have 18's or 19's, which means rhhp compared from one car to another with different size rims will produce different rwhp.

I know what you're getting at but that's not exactly correct. You could have 14" wheels on that weigh a ton and you'd lose more bhp than if you had ultra-light 18" wheels. The wheel radius makes no difference, it's the rotational mass.

Calculating the crank HP from hub horsepower should be more acurate than calculating it from the wheel horse power as there's less variables.

Roy's figures seem about right to me.

edit: I should have said that total radius would make a difference but when you change wheel sizes you also change tyre sizes to keep the radius the same, so this would be negligible.

Your right I'm getting confused between the power produced and acceleration. I'm a twat.

I also agree that currently Roy's figures do look about right however, as I was saying, (well OK not saying but trying to say) it's only down to the relatively small %age hp increases that we currently have record of. I'm not sure if it'll hold up against a massive performance increase of the likes they have over in the states (also bearing in mind they measure HP differently again).

If its going to be of any use to you guys i am planning to goto Thor and the end of next week to get a dyno plot of my completely standard 6sp manual Supra RZ-S.

I want a dyno readout of my standard jspec supra before i start modding it

Originally posted by TLicense

I'm not too sure if what your saying is particularly accurate.

 

If I increase the horsepower of my car from say 300 bhp to 900 bhp, the losses from the transmission wouldn't multiply by 3 times, they would pretty much stay the same. (Not exactly the same but by no means 3 times as much)

Why would it take more effort to turn the same gear ratio?

 

Ah ha, I wondered if it could be that easy - obviously not.

I've seen people use a figure of 18% loss from crank bhp to rwhp for a manual and 25% for an auto. In fact, on one thread, some folks were using this formula and applying it to the rhhp figures - resulting in very high crank figures.

I haven't seen any suggestion before that the % loss diminishes with increasing engine power -not that I'm challenging this, just never come across it before. It therefore never occurred to me that the relationship could be anything other than straight-line.

Oh, BTW,

For my GT-FOUR, I vaguely remeber having about 247BHP at the wheels and 200 ish BHP est at the flywheel. Now that's a 4wd transmission so obviously it won't be as much as for the supra.

Is there a mistake in here? Genuine question - not trying to be a smart arse! If there isn't, I'm really lost!

Thanks for the input,

Cliff

Who is this Roy character? If that's 'Big Roy' (as in 'enormous, proper bodybuilder Roy') you're confusing me with then I'm flattered!

Cliff

How about - 200bhp at the crank and 247bhp at the wheels? That's the kind of drivetrain I'd like

-Ian

Originally posted by Tannhauser

Who is this Roy character? If that's 'Big Roy' (as in 'enormous, proper bodybuilder Roy') you're confusing me with then I'm flattered!

 

 

Cliff

er, yeah sorry, just saw the avatar and thought, bodybuilder, er Roy. Sorry

Originally posted by Tannhauser

Is there a mistake in here? Genuine question - not trying to be a smart arse! If there isn't, I'm really lost!

No that's about right (I think unless I've had a typo and read the same typo twice without noticing it)

Basically all the gubbins required to turn 4 wheels is a bigger drain on the horsepower produced by the engine than the gubbins to turn two.

Remember power is a form of energy, turning a gear uses energy to overcome friction and energy sapping by products. The more gears and energy sapping stuff you have between the engine and the wheels the bigger the total loss.

However start off with a bigger amount of energy and it still uses approximately the same amount of energy to turn all the gears and stuff, hence why the drivetrain loss is not just a straight %age of the crank hp.

Hope that's right.

Originally posted by TLicense

No that's about right (I think unless I've had a typo and read the same typo twice without noticing it)

 

Basically all the gubbins required to turn 4 wheels is a bigger drain on the horsepower produced by the engine than the gubbins to turn two.

 

Remember power is a form of energy, turning a gear uses energy to overcome friction and energy sapping by products. The more gears and energy sapping stuff you have between the engine and the wheels the bigger the total loss.

However start off with a bigger amount of energy and it still uses approximately the same amount of energy to turn all the gears and stuff, hence why the drivetrain loss is not just a straight %age of the crank hp.

 

Hope that's right.

Quite clearly I did do a typo and am still a twat. I've ammended my previous statement about RWHP being greater than Engine horsepower.

Hang on.......

Sorry,

Will post my comment later when i have it sorted

Originally posted by Tannhauser

Step forward Bobbeh. His car was measured at Thor at 306rhhp. He's also had it dyno'ed on another rolling road at 265rwhp. His only mods - in both cases I think - are his exhaust. This suggests that rhhp x 0.866 = rwhp.

Sorry fella. The 265 rwhp figure was on a totally stock car (same as Wipeouts). The guys at G-Force advised of 18% loss for a manual so that worked out at 323 bhp (fly) which is about right.

Thors = Veilside Exhaust and BOV (still stock boost etc)

Originally posted by Bobbeh

Sorry fella. The 265 rwhp figure was on a totally stock car (same as Wipeouts). The guys at G-Force advised of 18% loss for a manual so that worked out at 323 bhp (fly) which is about right.

 

Thors = Veilside Exhaust and BOV (still stock boost etc)

Oh, bugger.

OK, but wipeout’s figures should still hold. So the very approximate conversion of rhhp x 1.11 = crank bhp still holds (bearing in mind Tony’s comments)

However, I was using a figure for Bobbeh’s rwhp that was too low, so the conversion factor of 0.866 is incorrect (needs to be slightly higher, but we can only guess how much so).

you would sooner go by thors numbers as it seems to be more accurate.where rolling roads tend to give out all sorts of readings. some places dyno cars different ways. been to a lot of well lane dyno days as its local. lots of big power cars spin on rollers, so you end up having people sat in boot to get power down. lots of the rover boys had 3 and 4 people stood on front end. i could not see point, if you cant get power down on rollers surely it will be same on roads. at well lane dont think they like dynoing autos.

harvey with the scooby estate made 585 bhp at well lane on his scooby estate, but there were 5 rather large people inside the car to get power down. you would not have 5 people in when you racing it. i know you get 4 or 5 people in a supra it kills the performance.

before you say you cant get 5 people in a supra you can.

michele l got 504 bhp at well lane in his uk spec. and macanny has been to a few different places getting dyno numbers. seems like the dyno at thors seems to be a benchmark to compare. i like to see what cars do over 1/4 to see how you compare for power the black stuff never lies as they say. it sounds like the americans and they are dyno queens looking for high numbers all the time.

would like to get mine on thors machine just out of been curious.

still good to see what people making

nicked off scooby site of last weeks cars well a few of them

******************

was a new record for well lane turbo centre today with harveys result of 585bhp! congrats!

some other interesting results from todays 200+ club event:

grant parker mk1 golf turbo 4wd 425bhp , 360 ft/lb

dave young R32 GTR 445bhp 390ft/lb

andy nicholls Rover 220 turbo hatchback 374bhp 280 ft/lb

dave naxton GTO3000 364bhp 330ft/lb

Doug Scriven Escort cowsorth estate 340bhp

martin metcalfe wrx 320bhp 290 ft/lb

andy robinson rover coupe turbo 320bhp 260ft/lb

mark perkins Celica gt4 305bhp

lovely cold day for the turbos!

chris m

The dyno results I got at THOR were very interesting... I've got a JSpec Auto with a new CW SMIC, FCD, Decat and Hiper. I got 367hp at the hubs running 1.2bar boost I've had a conversation with Terry S about the conversion factor because I cannot believe that my car with those mods would make that type of power. I would have expected something around 325hp.

Not that I'm complaining though

Originally posted by Bobbeh

Sorry fella. The 265 rwhp figure was on a totally stock car (same as Wipeouts). The guys at G-Force advised of 18% loss for a manual so that worked out at 323 bhp (fly) which is about right.

 

Thors = Veilside Exhaust and BOV (still stock boost etc)

your sure about that stock boost? The Veilside exhaust should have given an extra 1psi or so as the toyota system is quite restrictive compared to the aftermarket units.

JB

Originally posted by Patrick_Devlin

The dyno results I got at THOR were very interesting... I've got a JSpec Auto with a new CW SMIC, FCD, Decat and Hiper. I got 367hp at the hubs running 1.2bar boost I've had a conversation with Terry S about the conversion factor because I cannot believe that my car with those mods would make that type of power. I would have expected something around 325hp.

 

Not that I'm complaining though

Good figures, could be alot to do with the new CW SMIC, does THOR dyno monitor your inlet temp, if so what did it look like?

I bet CW would love to use these figures as an advert for his new IC They did measure a temp somewhere!!! Here's the graph.

Originally posted by Patrick_Devlin

I bet CW would love to use these figures as an advert for his new IC They did measure a temp somewhere!!! Here's the graph.

Does anyone know what the two lines mean, has the temp been taken in two different places?

Thats the two dyno runs that were made on the car. Cant remember which one came first though! I guess the one showing lower temps....

the dyno runs go in order of the colour dots on the left of the results sheet

red, green, blue

Ahh i see, really need someone a bit more technical to look these over.

The top shows a an increase in temp with both turbos online, I am guessing that this is because the amount of airflow has doubled.

The bottom one start to climb in the same way but then drops off, not sure why that is.

What was the power figure for both runs?