Standard (Almost) Chim 400 dyno curve.
Discussion
I thought this was a pretty reasonable run, however I'm surprised by the transmission loss on the at wheels readings. I say standard (Almost) because all I've changed is the chip in the ECU to a Mark Adams tornado plus I've modernised the ignition system, coil rotor arm, all that gubbins.
Edited by Danattheopticians on Friday 25th November 14:01
Agreed. They obviously measure power/torque at the wheels, the rest is estimation by the machine and operator. The at the wheels figure looks about right to me for a 4 litre. For comparison my Griff 500 made 233bhp and 239bhp at the wheels on two different, but the same make of rolling road, both giving an estimated 300bhp at the engine.
The actual figure also depends on which make of rolling road. Others have reported that Powers Performance at the wheel figures equate to Surrey Rolling engine estimate figures for instance.
The actual figure also depends on which make of rolling road. Others have reported that Powers Performance at the wheel figures equate to Surrey Rolling engine estimate figures for instance.
Englishman said:
Agreed. They obviously measure power/torque at the wheels, the rest is estimation by the machine and operator. The at the wheels figure looks about right to me for a 4 litre. For comparison my Griff 500 made 233bhp and 239bhp at the wheels on two different, but the same make of rolling road, both giving an estimated 300bhp at the engine.
I'd tend to agree with the above, my at the wheel figures are almost exactly the same as yours, actually a gnats cock more on petrol a an even smaller gnats cock less on LPG, but whos measuring a gnats cock for heavens sake?I tend to add 18% to the "at the wheels" figure which usually checks out well.
The questions you should be asking yourself are:
- Does the car drive nicely?
- Does it still get down the road rapidly making lovely noises?
- Does it make me smile?
Back to the performance thing it's also worth keeping in mind a Chimaera is 1060kg, even my gas powered oddity sits at 1100kg making it a very light car by modern standards, so even if you're sat around the 240hp mark it's a lot more than the numbers look in the real world, then there's the torque which is the same deal as HP only more so because even a 4.0 litre makes a lot of torque for the car's weight compared with most heavy weight modern stuff.
We're not up there with the big boys but try not to let that get you down, actually if you study your BHP per litre you are doing just fine. The most important thing in all this is to enjoy your TVR, have fun and don't stress over the numbers, because for the most part all numbers are is a way to show your mates you've got a bigger cock.
I'm very happy with mine, are you happy with yours?
Danattheopticians said:
I am actually happy with the car and it's performance. I thought it would be just over 200 at wheels. But the guy said the car was very healthy. The graphs are good and both line are smooth. He said fuelling was absolutely spot on. So I'm not disappointed just a little surprised.
the last time mine was on the rollers it was a stage 3. 4ltr running standard edu. it made 204 at the wheels and 261 corrected at the flywheel so a 21% loss or there a bouts 
Discopotatoes said:
the last time mine was on the rollers it was a stage 3. 4ltr running standard edu. it made 204 at the wheels and 261 corrected at the flywheel so a 21% loss or there a bouts
Not sure how you got 261hp from that Rich 
204whp X 1.21 (Your 21%) = 246.84hp at the crank
I've always used 18%, which (using your 204whp example) would look like this:
204whp X 1.18 (My 18%) = 240.72hp at the crank
The truth is using a percentage may not be the best way to make the calculation, drive-train losses will vary from car to car, an extreme example would be a Chimaera will have a lot less drive-train losses than Range Rover.
A better way to make the calculation would be to establish the typical drive-train losses of every vehicle you're measuring, Lloyd Specialist Developments have a very accurate hub dyno that is carefully calibrated to record genuine figure at the hubs, bolting the dyno directly to the vehicle's hubs eliminates the common inaccuracies associated with a traditional rolling road, IE traction and frictional losses.
You wont get an inflated ego boosting figure from the Lloyds hub dyno but you will get an accurate one, the team at LSD have completed a lot of calculations across a large sample of Chimaeras to establish a genuine drive-train loss figure. LSD claim the typical drive-train losses of a Chimaera is 45bhp at peak, so using the LSD fixed Chimaera peak drive-train loss figure of 45hp your 204whp figure now becomes 249hp at the crank.
Now lets take our three crank HP figures and find the average:
246.84 + 240.72 + 249.00 = 736.56 / 3 = 245.52
Of course all of these calculations only exist because we demand to know our crank output figure and it's impractical to remove our engines to measure it. It's always nice to quote a larger number but mostly we need that "at the crank" figure as a comparison because all manufacturers measure their engine outputs on an engine dyno, which is really the only properly scientific way to measure engine output.
Everything outside of a proper dyno cell is going to be subject to error, a hub dyno has to be better than a traditional rolling road but on both you're still making some very unscientific calculations to get to that crank output figure, the only real way to know the truth would be to pull the engine from the car and bolt it to a properly calibrated engine dyno.
Now consider no two dynos of any type will give you the same figure, even two dynos of the same make & model could give different figures, less honest dyno operators knowing their market is guys who want big numbers may also choose to calibrate their dyno on the optimistic side to send their customers away with a smile and a big number. Add to this elevation, atmospheric and temperature changes and in the end it all becomes a bit meaningless.
The truth is a dyno is actually a sophisticated tuning tool not a means of generating bragging rights numbers, try to forget those peak numbers for a minute, spend some time on a good dyno recording how small ignition timing changes alter the torque output of your engine within a specific load site and you'll soon start to understand the real value in strapping your car to a dyno.
You could never do this on the road, a dyno proves with no argument what's really happening as you advance or retard your timing, playing with the fuelling will have an effect too, ignition and fuelling are linked but it's the small adjustments you make to ignition timing that will always deliver the biggest gains or losses. Now move onto the next load site and repeat.... repeat, repeat, repeat moving from load site to load site until you've covered every conceivable RPM/Load scenario finding peak torque at every point.
When you've finished the complete process you've built yourself the perfect dyno map where the engine is proven to deliver it's maximum potential efficiency always no matter how you're driving or the demands you're making on your engine. But it doesnt stop there, because a dyno can never fully replicate every situation you're engine will encounter in the real world you now need to spend some time on the road smoothing out any undesirable anomalies within your almost perfect dyno map.
This finding of peak torque at every rpm/load site is of course what a dyno is for, using it just to find the final ultimate peak figure at WOT is a bit like the teenage boy using a ruler to only measure how many inches he can muster at peak excitement, so it's important to understand & acknowledge the peak figures we see quoted on these pages are just one specific figure under one specific condition that you'll actually very rarely visit for very brief moments unless you're regularly using your Chimaera on the track. The one final all out peak figure tells you little or nothing about the way the engine truly performs and behaves across it's full operating range on the road. Way more interesting is to record and improve what the engine is actually delivering under significantly more common conditions like driving through town on a light throttle between 1500 - 1800rmp, or under medium to heavy load from 2500 - 3500rpm... a condition typical of overtaking.
The real source of interest for me are all the complex and highly variable load conditions that reside between idle and peak RPM, because these are the very conditions you actually experience when driving your car and reveal the true efficiency of your engine under real world driving conditions. In my personal opinion we should all try to be a bit smarter than simply discussing our peak output figures, lets be honest here it's a very one dimensional reference point that will quickly become largely irrelevant when you jump in your Chimaera and take it out on the road.
At the wheels figures is the best comparison. As above says using various % to kinda guess crank output isn't the way forward. Tvr factory figures are mostly if not all not achievable with standard fit engines. The best total output figure to compare is a Range Rover fitted with the Buick lump not the BMW or jaguar lump.
Rated at max 190bhp this Buick engine can pull a 2.5ton brick up to a limited 112mph which is good going I think
A TVR at less than half that weight and with better aerodynamics will make better use of the Buick power and torque. A good combination
Rated at max 190bhp this Buick engine can pull a 2.5ton brick up to a limited 112mph which is good going I think
A TVR at less than half that weight and with better aerodynamics will make better use of the Buick power and torque. A good combination
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