150BHP at Flywheel

[Geoff Davies]

TR6 pi 150BHP at the fly wheel, what does this drop down to at the wheels. I think I have assumed 15% but dont know if this is correct.Also depending who you talk to the 150BHP at the fly wheel is more like 140, is this correct?

 

Thanks

Geoff

[IanR]

Hi,

Sadly the oft reported 150bhp was a bit ambitious on Triumph's behalf. But is easily obtainable with moderate tuning.

Losses on rolling roads are oft quored as 15%

[IanR]

Hi,

Sadly the oft reported 150bhp was a bit ambitious on Triumph's behalf. But is easily obtainable with moderate tuning.

Losses on rolling roads are oft quored as 15%

 

Whoops that was not finished ... however some, including me, believe the losses are greater... Has your rolling road been calibrated .. a lot are not...

[JohnC]

Alec's spot on. While interesting over a pint, 'absolute' power on the dyno is much less valuable than relative power comparisons to see what a tweak has done, and to do tuning under load.

 

I'f you're interested in a rather opinionated (but informative) view on dynos, go here, and read through the technical articles.

 

Cheers,

John

[wheeler]

Hi Guys

 

What happens to the lost bhp? Taking 18% losses gives 27 bhp for a 150 engine which equates to approx. 36kW. Is this amount of power dissipated as heat in the transmission and tyres? With the car jacked up and in neutral you can easily turn the rear wheels by hand - a few Watts of power. Surely if 36kW is lost something would melt or are my physics wrong? Simple explanation please, 45 years since 'O' level physics!!!!

 

Bill

[Tom Fremont]

Hi Guys

 

What happens to the lost bhp? Taking 18% losses gives 27 bhp for a 150 engine which equates to approx. 36kW. Is this amount of power dissipated as heat in the transmission and tyres? With the car jacked up and in neutral you can easily turn the rear wheels by hand - a few Watts of power. Surely if 36kW is lost something would melt or are my physics wrong? Simple explanation please, 45 years since 'O' level physics!!!!

 

Bill

 

Bill,

 

A bit fresher on the physics ( 20 years +/- since, in my case ) so here goes:

 

27 bhp equates to 20 KW - the conversion is 746W/HP

 

Power is ( torque x rpm )/constant, so the losses are proportional to rpm. The resistance felt by hand is multiplied by the rpm at speed, so significant.

 

Finally, the losses are almost entirely expressed as heat and are given off at speed thanks to convection cooling on the diff and gearbox housings mostly.

 

You raise a good point about overheating: are fans employed on rolling roads? If not I too would expect unusually high temps to be realized after some time.

 

I would like to see a comparison of losses using GL80/90W vs. SAE30W in the gearbox I have a hunch that much of the loss goes to lubricant churning...

[Geoff Davies]

Hi Geoff,

 

The '150 bhp' (SAE rating) CP engine was more like 135 at best in the real world, and that was on a good day, as opposed to the more-or-less genuine 125 bhp DIN of the later PI engines.

 

Transmission losses on the IRS cars are probably averaging more like 18%, condition of the running gear obviously has some modest bearing on this.

 

'Absolute' figures from any rolling road are of relatively academic value, and need not necessarily mean much (if anything)in comparison with figures from any other rolling road. It's an aid to setting-up, as in correctly tuning the engine to maximise performance, nothing more than that. In any case, torque can be as significant as power, if not more so.

 

Cheers,

 

Alec

 

Hi Alec, so if I have this right 135BHP at the flywheel losses say 18% = 110 - 112bhp at the wheels (depending on the rolling road). An engine rebuilt to a genuine 150bhp at the flywheel will give around 124bhp at the wheels?

 

Thanks

Geoff

[TIMS]

Guys

 

Ah!! so is this thread showing the lack of engineering knowledge of the Top Gear team when they put the 500BHP Mustang on a rolling road, only got 425BHP at the wheels and then proceeded to imply that Ford are telling porkies in the description? Wheras infact there is only a 15% drop between flywheel and back wheels which is well within the tollerances you have suggested.

 

As ever, the forum is a learning curve.

 

Regards

 

Tim

[JohnC]

...they also used 'coastdown losses' to calculate the flywheel BHP for the £10k mid-engined supercars. Probably not ignorance on the part of Clarkson et al, but more a case of simplifying for Joe Punter. The joys of television.

John

[Red 6]

theres an article in this months track and race cars or whatever its called, its the one with the chequered flag cover that looks like the old car and car conversions and explains losses and how the rr arrives at the figurea and more importantly why rr's give different figures for the same car.

 

Sorry about the waffle there i cant lay my hands on the article!

 

Now what was the question?

[mwoollam]

I recently had my TR5 PI on the rolling road to tune out a mixture problem, I was disappointed to find BHP of 113 at the fly / 88 at the wheels (max power @ 4500rpm) post tuning

 

I expect this is DIN, has anyone else had rolling road printouts? I knew the 150bhp was a bit pie in the sky, but has anyone had similar results? I guess it varies from each rolling road, I used Aldon Automotive in Dudley. (227 quid and they worked on it all day, bargain in my eyes)

[JohnC]

Two points Alec made above:

1. The absolute reading is much less important than before/after. What improvement did you see?

2. Torque is often much more important than power. What improvement in torque did you get? What rpm gives max torque? How much of that do you have at 4000rpm? 4500rpm? 5000rpm?

 

You don't say how you got flywheel bhp - I assume you didn't remove the engine & put it on a test rig! I'd just stick with rear wheel readings, then you won't get into a debate about what % losses to assume. Having said that, using the formula quoted on the site I linked to above, working backwards from Alec's 135bhp the '150bhp' cars should deliver around 109bhp at the wheels, so there is probably quite a bit still to come from your car, regardless of how well calibrated the dyno was. There may be an error of 10bhp+ from calibration and even tyre pressures, but 20bhp is less likely.

 

I'll be interested to your answers to 2....

 

Regards,

John

[67_gt6]

So too can a decent fuel system cleaner, mixed at twice the recommended doseage and with Shell V Max - a whole can of cleaner to 5 gallons of petrol and then boot it hard for 100 miles.

 

The net result can be quite surprising !! Gone from clogged to clog-it.

 

I've often been tempted by this Alec but put off by fears of losing compression by maybe removing too much carbon from the rings - is that a possibility?

 

Andy

[rpurchon]

i went to the international last year and was hanging around the rolling road.

a dutch chap with a gt6 got 150 from his car but he wasnt happy .

tr5 owner got 124 from his car and he wasnt happy.

and so on with only a few smiling owners.

i will put my car on this year if they are there. pay my £15.

i will have some tissues ready because i might not be happy?

richard

[Guest Wyn]

Seems to me that someone with half a brain should set up a rolling road that tells fibs i.e. adding 15% on to the actual readings. Everyone would be happy but no more power in the car in reality. As Alec said, it's the ability to tune up the car properly that is the great benefit of the rolling road. I've been twice in the last three years, an hour's drive there and an hour back. The drive home both times are the greatest drives I've had. First time, set up the webers properly and had 20% more torque, more bhp too but I would not want more of that and lose the torque. Second time was last summer after fitting a new cam etc, again, webers re-set and a huge difference in performance. I believe that perhaps different rollers show different figures, all that matters is how it feels to me to drive. I think we all put too much emphasis on bhp at flywheel. Thats my view, I'm sure some would disagree.

I drive a Golf 2.0GT TDI, a real flyer in my view. When I bought it first, so many men who are kind of car enthusiasts enquired 'have you chipped it? and they couldn't understand why not. How much power is enough I ask you.

 

Wyn

[JohnC]

Seems to me that someone with half a brain should set up a rolling road that tells fibs i.e. adding 15% on to the actual readings.

Quite. Mind you, an accurate dyno could well drum up tuning business later on, if the punters were comparing their results with manufacturers' or road test results from the 60s & 70s!

 

If you're a devious operator, make sure the tyres are a little soft for the 'pre tuning' run, and a little hard after 'tuning'. A bit of spanner & screwdriver waving, looking knowingly at the dyno screen, judicious criticism of lesser mortals who have 'messed' with the car before, and Hey Presto! - another 5bhp for the cost of a little air (hot and compressed).

 

That's why absolute figures are so unreliable. Unless you are certain everything is the same between different sessions/dynos/operators, the experimental error wipes out any meaningful comparisons. Most modern dynos have calibration software that attempts to correct for things like atmospheric pressure, temperature and humidity, but I've not seen one yet that checks tyre pressure & condition (although the one I use does at least have a tyre pressure input for record-keeping). I've even found that the calculated gearing (i.e. rpm vs 'roadspeed') on my car varied 3% between sessions. Not much, but the tyres & pressures were the same between sessions.

 

I'd love to know the range of results for untuned cars put on the dyno at the International. 80bhp - 105bhp at the wheels?

 

Cheers,

John

[heckler]

I recently had my TR5 PI on the rolling road to tune out a mixture problem, I was disappointed to find BHP of 113 at the fly / 88 at the wheels (max power @ 4500rpm) post tuning

 

I expect this is DIN, has anyone else had rolling road printouts? I knew the 150bhp was a bit pie in the sky, but has anyone had similar results? I guess it varies from each rolling road, I used Aldon Automotive in Dudley. (227 quid and they worked on it all day, bargain in my eyes)

just out of interest my 6 standard bar triple 40 webbers. rolling road print out states engine output 139.5 bhp, wheel output 101.0bhp max power at 4970 rpm. max torque at 63mph or 3050rpm = 1631bf-ft

cheers chris

[JohnC]

just out of interest my 6 standard bar triple 40 webbers. rolling road print out states engine output 139.5 bhp, wheel output 101.0bhp max power at 4970 rpm. max torque at 63mph or 3050rpm = 1631bf-ft

cheers chris

Wow! You must have some seriously thick oil in there (or the handbrake on) to get a loss of over 27% between flywheel and wheels Seriously though, it would be more interesting to know how much improvement you managed to get after a session on a dyno with a skilled Weber (I assume you have Webers, not three racing drivers, under your bonnet) artiste. Who did your setup? If he wasn't an expert, then you may have several horses just dying to get out. Tom?

 

FWIW if your dyno happened, by an amazing coincidence, to be operating under exactly the same conditions as the one at the Triumph factory 'back in the day', then you're probably getting almost exactly the output of the later '125bhp' engines - 101bhp at the wheels is more likely to be 125bhp at the flywheel than 139... By way of spurious comparison, I get anything from 108bhp-113bhp at the wheels from my 6, with a dog's breakfast of TT1200 manifold (the nasty one) and a wild cam (but no head mods). The variation depends, I think, on whether I had one or two coffees before taking the car in, whether it's a high tide, and whether the Spice Girls have got back together or not (just to show that valueless trivia makes its way to Oz via BBC podcasts...). It may also depend on small variations in tyre pressure and condition, valve clearance, timing and humidity. But I prefer voodoo.

 

If you're interested in understanding more about dyno testing and what it can & can't do, check out the website I linked to earlier in the thread.

 

Cheers,

John

[Roger H]

The Puma Racing article that John refers to is excellent.

 

Here is another link which adds fuel to the debate (don't ya hate puns!!) and while it is written by a BMW associated business, explains very well the reasons that dyno's cannot be trusted.

 

It also appears to have a realistic opinion of the realities of 'performance chips' in modern vehicles.

 

http://dinancars.com/whitepapersFile.asp?ID=9

[Tom Fremont]

Here's an idea:

 

Since it seems HP ratings at the flywheel are all derived indirectly and hence subject to error, perhaps considerable in magnitude, why not put a strain gage on the prop shaft just aft of the gearbox and take a read there? At least that would eliminate the rear U-joint, differential, half-shafts, wheel bearings and tyres from the calculation.

 

Otherwise, FWIW Darryl at Racetorations told me he's never seen a stock P.I. 5 or 6 give more than 130 at the flywheel. It's good to find a specialist who disdains exaggeration of performance ratings

[Andy Moltu]

Otherwise, FWIW Darryl at Racetorations told me he's never seen a stock P.I. 5 or 6 give more than 130 at the flywheel. It's good to find a specialist who disdains exaggeration of performance ratings

 

Without implying anything improper we should remember it's not in the interest of someone in the tuning game to big up the standard car's performance!

 

How often have totally standard TR engines been run on an engine dyno since the launch of the cars?

The powers quoted for the CP & CR cars by Triumph were measured at the flywheel - literally. Most TR engines that get put on the dyno do so on the rolling road and the flywheel power is an estimate from the coasting power losses. Given the error margins must be pretty high and for that matter the calibration of the rolling road is another uncertain factor.

 

The original BHP figures were done to SAE and latterly DIN standards which are more strict about the ambient temperatures, pressures, attachment of engine ancillaries and the calibration of the dyno than is relevant to a rolling road.

 

Rolling roads are best used to compare the effect of engine tuning and adjustment on the same car - does changing one thing or other give more power or not.

You can't really use rolling roads to compare the power of one spec of engine against another that is on a different rolling road.

[Iain Rollo]

Rolling roads are best used to compare the effect of engine tuning and adjustment on the same car - does changing one thing or other give more power or not.

You can't really use rolling roads to compare the power of one spec of engine against another that is on a different rolling road.

 

Whilst agreeing with all the above I think it has to be said that those of us that are working on, or, as in my case having worked on for us mods to engines. What else can be used to give some sort of comparative measure of progress or otherwise?

 

I agree that while results from one set of rollers to the next can be wildly different I find it hard to believe that most of us who are serious about the direction our mods are going don't take time to find out whether the equipment we are relying on is calibrated and operated to acceptable standards. Surely only with the homework comes some degree of faith in the results.

 

Before I decided to have my rebuild done I went to have a tuning/health check done on my 6. This was just before I set off to Germany in it for an extended business trip. Which just happened to include 3 weekends at the Nurburgring and even 45p a mile of exe's because the car was over 2ltrs.

 

Anyway after a session on the rollers with an engine that had 100,000 miles on it, the PI removed and a set of 40's of uncertain provenance and a GT6 manifold with worn bushes on the throttle spindles. We thought we ended up with 138 flywheel BHP and it running as well as could be expected.

 

Of course the trouble with that particular trip was that after it I started to think about how much more fun it would have been in a really hot TR6.......... Which led on to a greater problem, the complete rebuild of the 6. Once the new engine was built it was sent to the same guy to put on his engine break to be run in and have the ignition mapping done. I'd decided to have Omex ignition fitted but not the matching EFI. Mostly because I just love the sound of 3 Webbers sucking away and I kind of think they fit with the period and they definitely do not cause any performance disadvantage!

 

On a later run on the rollers this time we had almost identical results to the engine brake. I have to say that on both road and track I'm very happy with the results. On 'A' roads I can get past whatever and surprise more than a few hot hatch pilots.

 

So check out the kit your going to use don't be obsessed by the numbers because the real result is felt through the seat of your pants on the open road.

 

Iain.

[marvmul]

It's logical that after fitting a mapped ignition, the maximum torque and maximum bhp have not improved, because a standard ignition will be tuned in a way that the advance is right for achieving that max bhp and torque, but the ignition advance will be off the ideal value at other rpm's and especially at all 'transitional' conditions : you will feel that a mapped ignition is performing better, but it will not show in the max bhp figure.

 

It's strange that the rebuild of the engine has brought no performance improvement : or your engine was still strong after

100 000 miles, or the rebuild could have been better done? Did you use the chance to rise the CR?

What cylinderhead is fitted?

 

Btw, was the mapping and rolling road work done at Bömanns near the Nürburgring? He is competent and the bhp figures are not flattered.

[jemgee]

I see reference to the RR dyno at malvern was £15 - is this correct? If it shows you are down on power compared to other stock engines can any tuning be done at Malvern?

[mwoollam]

Two points Alec made above:

1. The absolute reading is much less important than before/after. What improvement did you see?

2. Torque is often much more important than power. What improvement in torque did you get? What rpm gives max torque? How much of that do you have at 4000rpm? 4500rpm? 5000rpm?

 

You don't say how you got flywheel bhp - I assume you didn't remove the engine & put it on a test rig! I'd just stick with rear wheel readings, then you won't get into a debate about what % losses to assume. Having said that, using the formula quoted on the site I linked to above, working backwards from Alec's 135bhp the '150bhp' cars should deliver around 109bhp at the wheels, so there is probably quite a bit still to come from your car, regardless of how well calibrated the dyno was. There may be an error of 10bhp+ from calibration and even tyre pressures, but 20bhp is less likely.

 

I'll be interested to your answers to 2....

 

Regards,

John

 

Hi John,

 

1. Improvement of 8bhp, but on closer examination, i'm suspicious of the graph, i.e the before run plots stop at about 4300rpm without showing a drop off in power, whereas the after run the power drops off at 4400 and plots cease at 4700rpm. A few data points deleted methinks? printout states maximum power of 88bhp @ 4424rpm

 

have attached picture of the graph, not sure how much you can make out, so here goes....massive improvement in power on graph at 1200 rpm, thats noticable from driving the car, pulling away improved significantly, then no improvement until 2500rpm when the final run's power curve improves by a couple of bhp per 1000rpm

 

2. Torque pretty similar up to 2500 rpm (not including a big increase at the 1200rpm mark)

maximum torque seems to be at 3000 rpm, tailing off on a flat curve

3000 rpm - 154 lbft

3500rpm - 150 lbft

4000 rpm - 140 lbft

4500 rpm - 130 lbft

5000 rpm - no reading

 

the graph also gives a green line for fly power, but this is just estimated as you say.

 

Overall I'm happy with the cars performance, especially on a before / after comparision. I'm definately not on a hunt for big bhp numbers. I was just surprised at the large discrepancy between the 150bhp figure and what i actually got. It made me read more on the subject, and made me even more curious when I read max power was supposed to be at 5500 rpm

 

however the same source quotes max torque as 164 lbft @ 3500rpm, which is a lot closer to my readings. The engine has been rebuilt, and only has 1500 miles on it so far, and none of that has been above 4000 rpm. oil was changed 1000 mile ago.

 

the whole point of taking it to the rolling road was to sort out the fact that it was running weak, and thus getting a bit too hot ( eventually blowing a head gasket) I checked the plug tips since the tune up and they're a lovely biscuit brown colour, not the white colour prior to tuning, so im satisfied they have sorted that out. I just need to do a run and see what the fuel consumption is. Prior to tune up I was getting 20mpg. What's typical for you guys?

 

i'll shut up now!

 

thanks

 

Mark