Discussion
quote:Depends where you get it measured and how. Different rolling roads get wildly different answers, and there are lots of correction factors that can be applied to change the results even further. I understand the HC is basically the standard engine with a high lift cam. Heads and induction are unchanged. The standard 4.0 cat typically puts out a little under 200 bhp and I'd guess at around 215/220 for the HC, with more top end than standard but perhaps less low-down torque. You would need to remap the fuelling as well. A 'Mark Adams' rechip adds around 10 bhp to a completely standard engine but the difference feels a lot greater than this number suggests, the throttle response improves enormously. For comparision when I had the old 4.0 engine (as fitted to Chimaeras) with Stage III heads, hybrid cam, modified manifold, trumpets, plenum and throttle body it went up from 200 to nearly 240 bhp. The extra power was all at the top end, with these mods it would pull better at 6000 rpm than the old engine would at 5000. But this setup lost all the bottom end torque so it was much less tractable. Obviously these mods are far more extreme than a simple cam change which is basically what the HC spec is. Peter Humphries (and a green V8S)
Chaps Does anyone have any accurate bhp figures from a 4.0HC engine. It supposeed to have approx. 275bhp from the factory, but does anyone realy know? and does a rechip improve output much? what was changed from the standard 4.0 to make it a HC ?
Monaco,
Figures for the engine at the flywheel (DIN) on a dyno and don't include the transmission losses you get when recording the numbers at the back wheels on a rolling road. I suspect as well that the factory are very careful in selecting the engine that gets tested -- +- 10% variation between vehicles not at all unusual. Mark Adams is a well known ECU re-mapper of Rover V8s. Don't use one of his products myself but you hear many good things about him. My Wedge has a Stage III head, hot cam, light flywheel, high compression pistons, balanced crank, revised ECU etc. Like Peter my engine is very strong at the top end (from 3250-6000 it pulls like a Nascar racer) but relatively mild mannered lower down. NCK who did the mods about 10 years ago claimed over 240PS from 3.5 litres which might be optimistic but it certainly feels as quick overall as a 4.5 Chimp I had a spin in last year.
Rob
quote:All the numbers I gave were flywheel figures, measured at the back wheel but with the transmission losses factored in. They should be directly comparable to the factory figures. There are lots of ways for a manufacturer to make their engine look good on the dyno. The measurement is supposed to be taken under very specific conditions (temperature, humidity etc) and if the actual conditions are different you are allowed to apply a correction factor. This is the main reason that dyno numbers don't always correlate - because the results were corrected to different 'standard' conditions. Some places don't correct at all and just give you the actual BHP your engine put out on that day. Go in next week when the weather is cooler and you might get a higher reading. Similarly there is a margin of error for the dyno which is determined by the peak power the dyno can handle. Use a bigger dyno and the margin of error is bigger. Calibrate it carefully before hand and the error all works in your favour. And so on and so forth. There are all sorts of tricks that can be played and readings that are 'optimistic' by 25% are easy to produce. That's before you get into questions of how standard was the engine they tested, and was anybody leaning on the dyno at the time. The nice thing about TVRs is that the engines are all immensely torquey. You may not get the 320 bhp that they claim, but there is so much mid-range torque that the real-world performance is still better than many cars that really do produce that sort of power. BTW Mark Adams' number is in Sprint under Helplines, or you can book a session with him through Tower View. Peter Humphries (and a green V8S)
Monaco, Figures for the engine at the flywheel (DIN) on a dyno and don't include the transmission losses you get when recording the numbers at the back wheels on a rolling road. I suspect as well that the factory are very careful in selecting the engine that gets tested -- +- 10% variation between vehicles not at all unusual. Mark Adams is a well known ECU re-mapper of Rover V8s. Don't use one of his products myself but you hear many good things about him. My Wedge has a Stage III head, hot cam, light flywheel, high compression pistons, balanced crank, revised ECU etc. Like Peter my engine is very strong at the top end (from 3250-6000 it pulls like a Nascar racer) but relatively mild mannered lower down. NCK who did the mods about 10 years ago claimed over 240PS from 3.5 litres which might be optimistic but it certainly feels as quick overall as a 4.5 Chimp I had a spin in last year. Rob
If everything else about Mark Adams is as good as his telephone manner, then it'll be very good indeed.
I phoned him a week or two ago about his chipping and rolling road work. In the end I decided not to proceed with anything yet, given that I still have warranty on a car that seems to be a little too keen on the dealers at the moment.
However, that didn't stop it turning into a half hour phone call, plus he may have recommended the right people to fix my BMW autobox!
Trouble was... he told me about the 5.2l V8 developments conversion. Damn damn damn damn... (What do you mean "the 500's fast enough already?" )
Edited by Marshy on Wednesday 14th March 15:16
Edited by Marshy on Wednesday 14th March 15:16 
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