Dyno Numbers, FWHP/RWHP/RHHP

[Guest kenblockseal]

Do you mind me asking your launching technique Jamie? And what tyres you were running at 630bhp.

[JamieP]

Do you mind me asking your launching technique Jamie? And what tyres you were running at 630bhp.

 

Never had much of a technique Ken, was on 275/50/15 BFG drag radials.

 

[Guest kenblockseal]

Cracking video cheers. hopefully the mapping goes ok tomorrow i will be running MT ET Streets on sunday in 16s, But im also going to take my Bogarts with ET Drags and try a few non qualifying passes.

[JamieP]

Cheers and good luck, agree with TDR on the project thread, get some pictures up.

[Neil-NA]

Never had much of a technique Ken, was on 275/50/15 BFG drag radials.

 

 

Wow

 

As you seem to be the launch master you can help me on sat try and get my P1ss poor NA off the line

[scoooby slayer]

this stuff always interests me, i have this chart from rob at rips racing

 

 

forget et just look at terminal, i managed 134 mph 2 weeks ago at pod at 1750kg is about 740 whp.

[Wez]

this stuff always interests me, i have this chart from rob at rips racing

forget et just look at terminal, i managed 134 mph 2 weeks ago at pod at 1750kg is about 740 whp.

 

How does that represent any car, surely gearing, tires, suspension and driver ability affect these result

[Wez]

As you seem to be the launch master you can help me on sat try and get my P1ss poor NA off the line

 

Have you tried putting it on starting blocks

[scoooby slayer]

How does that represent any car, surely gearing, tires, suspension and driver ability affect these result

 

a quick launch will majorly affect the time but the speed only comes with hp

[Wez]

a quick launch will majorly affect the time but the speed only comes with hp

 

And I guess the aero dynamics and gearing of a particular car have no affect then, learn something new everyday

[Chris Wilson]

I could not be bothered with the hassle tbh mate.

 

 

 

That will be good to see.

 

Then you will NEVER know, TBH. Real, properly calibrated, properly compensated for air temp and pressure, etcetera, engine dyno cell figures are often poles apart from rolling road figures. Hub dynos with accurate loss and compensation figures *SHOULD* be close. Sam at TDI is very good, as is their set up, but the really accurate figures come from manufacturer / high end engine dyno cells with total control. Flash figures from a quick dyno "pull" are both flattering and misleading. You need a sustained 20 second plus peak power hold to have anything meaningful, power and reliability wise, IMHO.

Edited October 12, 2011 by Chris Wilson (see edit history)

[Chris Wilson]

One of the best, most honest and accurate articles on dynos I have read, from a retired and incredibly honest and knowledgeable independent expert on engine tuning in the UK:

 

http://www.pumaracing.co.uk/POWER3.htm

[scoooby slayer]

And I guess the aero dynamics and gearing of a particular car have no affect then, learn something new everyday

 

aero dynamics have very little affect until the speeds get up higher than 100 mph.

[Guest kenblockseal]

Good luck with the car tomorrow and let us know how you get on, whats the spec? what dyno are you going on?

 

Jamie.

 

I never managed to get it mapped, The compression was down on a cylinder, So Ryan never got to work his magic on it, Though he did come to view a R35 GTR i was thinking of buying with me that turned out to be down on oil pressure, So thank god for that.

 

But im back at the dyno at lunchtime today, Ryans mapping it remotely, ive switched the engines over and ready to go again, Making this USSC will be the death of me as ive had 3 hours sleep in 2 days.

[tDR]

But im back at the dyno at lunchtime today, Ryans mapping it remotely, ive switched the engines over and ready to go again, Making this USSC will be the death of me as ive had 3 hours sleep in 2 days.

 

Good luck for today Kenny - you deserve a break Supra reliability wise!

 

You get that spiggot bearing then?

 

Cheers,

 

Brian.

[JamieP]

Making this USSC will be the death of me as ive had 3 hours sleep in 2 days.

 

Madman, cant knock your dedication, how did you get on today kenny?

[Guest kenblockseal]

Bad jamie.

 

Couldnt get the car mapped by ryan due to the dyno i was usings internet connection problems.

 

I had to draft in another mapper i use for our Evo track cars to throw something together for me, the intake temp sensor wasnt functioning correctly so he couldnt do a full on map.

 

I had [email protected] bar as the engine i fitted on friday was completely stock, we never transfered a thing over except turbo kit and inlet manifold.

 

We painted the car and corrected all the bodywork all through the night untill 5am this morning, then i was up at half 6 to go racing.

 

Got to crail, weather was decent, decided to give it a go on the ET Drags, ( i got Tdr to take a picture of these after 2 runs to show this forum members realy howbad crails surface is, Im sur ehe will post it soon ) , Got to stage and the starter noticed my HKS BOV had worked lose i suspect it was when we refitted the front bumper during the night. so Had to bodge it up as the retaining circlip was missing.

 

Back into the queue and got to the start, done my burnout , Staged lights whent green, Wheel spin in first, then tankslappered, then 2nd and tank slappered, then 3rd and same again, got traction in 4th and ran a 12.8

 

Second run, i gave my mate who helps me with the car drive with TDR as a passenger, He got a decent start but sturggled with wheelspin, and went from 3rd gear to 6th gear and ran a 13.2

 

At this point one of the Crail staff aproached me and told me they were throwing me out of USSC for running full on slicks, So i changed to my ET Streets, Which were more grippy in crails surface, Got into the queue and the big ends went as i sat waiting, I was gutted to say the least.

 

 

Back to the drawing board, are you still selling youre forged bottom end mate?

[JamieP]

Blimey, bad luck mate, it looks like my spare engine is sold now, if it falls through i will let you know.

[Guest kenblockseal]

Yeah no bother, Car had potential today just my first time launching a manual hard and couldnt get the hook up right in the 1 run i got, a bit of practise and id have mastered it, Its a pitty running a RWD Car at Crail it really is a loosing battle due to the surface the amount of debris and pot holes on the surface are frightening.

 

Im still deciding which way to go with the car, but if the engine falls through i could be intrested mate cheers.

[tDR]

Be good to see you stick with it an get it perfected over the winter for next season Kenny! Understandable if you decide you've had enough an sell it in bits.

 

Tyre pic of ET slicks from Crail thread showing debris from the crappy surface:

 

[captainchaos]

was talking to Jurgen about this thread when I was over XO/JM on Saturday and found some info from the church automotive testing site who run 2 sets of dynapack:

 

here is a extract :

 

As power increases for a given combo, the difference will grow due to the change in acceleration rate on the Dynojet (assuming the same gear is used for all tests). As the acceleration rate goes up, the total torque required to accelerate the wheels and tires will go up (remember, the torque calculation is MoI * acceleration - twice the acceleration rate requires twice the torque). But on the Dynapack the acceleration rate is kept the same (or at least should be), so losses remain largely the same. Furthermore, both dynos are subject to inertial losses accelerating the flywheel, transmission, etc. and the faster acceleration rate as hp climbs will show increasing losses on the fixed load Dynojet.

 

This is why we recommend people use a rough percentage adjustment to estimate flywheel hp on the Dynojet versus a rough fixed adjustment on the Dynapack. In our experience, a manual transmission FWD car will lose 20-25 hp to the hubs on the Dynapack. A RWD car will lose 25-30 hp and an AWD car about 35-40 hp (the FWD case has been verified on an engine dyno). In contrast, losses on the Dynojet will be in the 12-14% range for FWD and 14-16% for RWD (opinions vary).

 

http://home.earthlink.net/~spchurch/index.html

[scoooby slayer]

One of the best, most honest and accurate articles on dynos I have read, from a retired and incredibly honest and knowledgeable independent expert on engine tuning in the UK:

 

http://www.pumaracing.co.uk/POWER3.htm

 

interesting read that and states roughly just add about 9% to hub power for engine power, which would seem relevant to tdis anyways as rototest themselvesd also say average of around 9%.

 

i made 758 latest on tdis and trapped 134 mph on a far from perfect run with no burnout on nittos, so add 9% will be 830 crank hp which should be about right considering my weight and trap speed.

 

jamie when you consider you are in the 10s with 2.2 60fts over 150 mph that in itself proves how quick your car is, if your 1700kg total your 152 mph proves your at least 1000 whp which will always be abit less than hub power, and irreleivant to what anyone says when you get the launch right and get a 1.6 sec 60 foot you will be gaining more speed than ever before so be trapping even higher, and also be straight in the 9s.

[JamieP]

Yeah could be about right, Dan said to add about 10% himself.

[garethr]

There was a question earlier in the thread about "PS" vs "BHP".

PS (Pferdestärke) is the DIN calculation, as opposed to the SAE calculation, and 1 PS = 0.98632 BHP

 

 

 

One of the best, most honest and accurate articles on dynos I have read, from a retired and incredibly honest and knowledgeable independent expert on engine tuning in the UK:

http://www.pumaracing.co.uk/POWER3.htm

 

 

http://www.emeraldm3d.com/rolling-road

 

Written by Dave Walker. He has slightly different views about calculated flywheel figures, in that they have proved accurate when he's been able to compare them with engine dyno numbers (although he's talking about a Sun rolling road dyno that "measures a maximum of 330bhp at the wheels up to a speed of 160mph").

What he has to say about single vs twin roller is interesting, though.

 

 

More modern rolling roads tend to have one very big single roller and you park the car on top of that roller. The main reason for this system is so that you get less tyre distortion with a single large diameter roller. With an older system using twin rollers, you get more rolling losses because you have two contact points, not one. Car manufacturers like Mercedes who make powerful engines and very heavy cars will only allow their dealers to have single roller dynos to limit the tyre loading – it’s a safety issue.

Several factors prevent you from getting exactly the same result in every gear. First off a lower gear means more torque at the wheels and hence a little more tyre slippage than when you run in a higher gear. The run also takes less time, so the engine accelerates faster and gives you more of a "flash" reading. Our Sun Ram 12 rolling road allows us to alter the acceleration rate so that we can adjust it for different power outputs. The software in our system uses the road speed, measured by the rear roller, to obtain engine rpm in order to scale the power curve. We take an rpm reading at 60mph and the software works out the revs at any given road speed from there. What this doesn’t take into account is tyre growth. As the revs increase the centrifugal force makes the tyre grow – which alters the gearing slightly, putting the rpm out by a tiny amount. When you take all these "fudge factors" into account, it’s a wonder the rolling road is as accurate as it is, but it can be accurate, and more importantly, repeatable.

With careful setting up of the acceleration rate to match the engine power, and accurate setting of the engine rpm, (dashboard tachometers are often out), you can get a meaningful number from a rolling road. I know that when trying to improve the engine in the 'Red Shed' our rolling road is depressingly accurate enough to give the same power curve time after time – despite my best efforts to increase the power output! I always call our final figures "simulated" flywheel figures but they are close enough to engine dynamometers judging by the comparisons we have available. Ken Snailham at Q.E.D recorded 218bhp on his dyno and the same engine showed 220bhp on our rollers. We've had similarly close results to the Lotus Service Centre dyno and J.E. Engineering’s dyno. We also see close to factory-quoted power outputs on most standard cars that we have run in the past.

 

 

Hub Dynos

A big problem with rolling roads is tyre grip. As power outputs reach the levels where you question the sanity of the engine builder it gets harder and harder to put the power down. On a rolling road you usually have more grip than you do on the road or track but I leave problems like that up to the driver – the throttle tends to work both ways after all. The answer would appear to be to eliminate the tyre from the picture. A hub dyno bolts directly to the drive shafts so there is no slip at all. This, on the face of it, would appear to be the answer to all our problems, but you still come back to the question of what you are measuring. By removing the tyres from the picture you get much lower rolling losses but not enough inertia in the system to measure any sort of run down. For setting up it’s probably the perfect answer but not much use for comparing one engine to another as you can’t get back to what the engine is making at the flywheel.

Edited October 23, 2011 by garethr (see edit history)

[JamieP]

Just been reading a thread on pistonheads about a TVR, on TVR powers dynojet dyno the car made 362 RWHP, same car on SRR put down 363 FWHP a short while after..