how much hp is to much in a westfield
Discussion
Depends on weight and torque, amongst other things; 'Sevens' can vary in weight between circa 370 kilos and circa 750 kilos, so you're better off thinking in terms of BHP/tonne.
Personally, I'd say that around 350bhp/tonne is the sensible limit for road use, given current chassis and tyre technology... anything much more than that is pointless willy-waving, 99% of the time.
Personally, I'd say that around 350bhp/tonne is the sensible limit for road use, given current chassis and tyre technology... anything much more than that is pointless willy-waving, 99% of the time.
Edited by Sam_68 on Sunday 1st January 12:01
really depends on what you want to with the car....
i had 270 bhp V8 in mine and it handled brillantly, if you beefed up the chassis then more power would not be a problem, the beauty of sevenesque cars is you can pretty much do anything with them from a bike engine to a V8. 500bhp per tonne is fine if the rest of the package is upto the job imo
i had 270 bhp V8 in mine and it handled brillantly, if you beefed up the chassis then more power would not be a problem, the beauty of sevenesque cars is you can pretty much do anything with them from a bike engine to a V8. 500bhp per tonne is fine if the rest of the package is upto the job imo
Gulf LS3 said:
500bhp per tonne is fine if the rest of the package is upto the job imo
The problem is that with the current state of the art (and the typical quality of public road surfaces in the UK), the tyres and more particularly the dampers will not be up to the job for this sort of power:weight ratio for road use.The big limitation with 'Sevens' is that, being relatively lightweight, they have an unfavourable ratio of sprung:unsprung weight. As a result, whatever the quality of the rest of the package, the damping has got to be absolutely spot-on to avoid unacceptable variations to the loads at the four tyre contact patches. Even the very best current dampers will struggle to consistently deliver the power to the tarmac at power:weight ratios above 300-350bhp/tonne, so you end up driving everywhere with feathered throttle, unable to fully use the power you have at your disposal.
The effects vary according to the insatallation, though: a Seven that delivers a very high power:weight ratio by means of low weight (like my own Westfield) will suffer more from the effects of sprung:unsprung weight ratio than a much heavier car (say a 750 kilo V8 engined machine). On the other hand whilst the ultimate grip and traction of the lighter car might be worse, it can be a lot more manageable and predictable than the V8 engined car, due to the more benign torque delivery of a smaller, higher-revving engine and the quicker chassis reactions, so the two things tend to cancel each other out.
Obviously, on the very smooth tarmac of some race circuits, the problem of damping and sprung:unsprung weight ratio is less of an issue, so somewhat higher power:weight ratios can be exploited... but if you're looking at primarily track use - and you want to go as fast as possible - then the 'Seven' is an anachronism, anyway; there are much faster ways to go around a circuit.
I have a sylva striker with a 2ltr zetec blacktop engine.Last time on the rollers it put out 174 bhp.My car weighs in at 520kgs so the power to weight ratio is somewhere around 330ish bhp per tonne.The car way out performs my abilities,but very drivable and forgiving. Questions you should ask yourself is how good a driver am i? If i buy a cossie turbo kitcar,how long will it take me to wrap it around the nearest tree?!!
The other factor is power delivery. Low torque high bhp na engines, with good linear deliery, suit the character of the car - more so than turbo orv8 motors IMO.
I had about 400/tonne in my westy and it was still usable on the road - although it was a little too frenetic at times.
I'd say 300 is the sweet spot for a fun benign road car.
I had about 400/tonne in my westy and it was still usable on the road - although it was a little too frenetic at times.
I'd say 300 is the sweet spot for a fun benign road car.
alfasteve said:
You have never too much HP its your driving skills that is the limiting factor on how much is too much.
rhinochopig said:
The other factor is power delivery. Low torque high bhp na engines, with good linear delivery, suit the character of the car.
...But both these posts are actually telling you the same thing: Of course the car is manageable if you are able to predictably not use all the available power, and you'll only be using all the available power when the right hand pedal is pushed fully to the floor and the engine is at peak power revs. Provided you can modulate the throttle so that the engine only metes out as much power as the chassis can cope with, you'll be fine. 
There are two schools of thought, here:
- One is that it's always better to have unlimited power, no matter that you are never (or very infrequently) able to use it.
- The other is that, if you can't use it, it's dead weight and it's slowing you down and blunting the car's reactions (and we're not just talking engine weight: the chassis, cooling system, brakes and transmission all need beefing up to cope with the 'worst case' power available).
Colin Chapman said:
To add speed, just add lightness
I reckon that if you think you need more power than the chassis (and by chassis, I mean tyres and dampers, really) can deploy, then you're missing the point completely: 'Sevens' are all about minimalism and razor-sharp reactions, so if you want a cumbersome fire-breathing monster, you'd be better off with something that's designed to be a cack-handed sledgehammer (a Cobra or Ultima will probably serve your needs better).But each to their own... it all boils down to engineering ethics and perception of the car's raison d'etre.
Edited by Sam_68 on Monday 2nd January 17:07
v8will said:
Porkie's westy is mental. he has spent alot of time, effort and money getting it right though. also there are a few turbo bike engined cars out there! I've got a Cosworth Turbo in my Fisher Fury and I would definately agree with Sam about it being impossible to use on the road at full power.
It will wheelspin in 4th on cold tyres and the way it catches the cambers in the road and takes off on poor road surfaces means that I drive it at around 8/10th maximum and I never use all the revs.
However on the track it is a bautiful thing to use and its great having around 450bhp per ton
It will wheelspin in 4th on cold tyres and the way it catches the cambers in the road and takes off on poor road surfaces means that I drive it at around 8/10th maximum and I never use all the revs.
However on the track it is a bautiful thing to use and its great having around 450bhp per ton
Too much power is a problem only when driven. A mate of mine built a Westfield with a Chevy V8 and as much power as you would want along with enough torque to pull a house down, it was fine as he drove it sensibly. I also had a mate with a Cosworth powered one with in excess of 460bhp, he went off the road twice in that when the turbo spooled up.
Mine has 200bhp and it I can never use full throttle for more than a few seconds as it is ballistic. It makes me smile whne people ask on the Westfield site what they should buy and everyone starts saying you need 250bhp at least, and yet when I take people out to show them what a mere 200 is like they always come back saying 150bhp is enough.
Steve Hole from TKC magazine always says his favorite Chaterham is one with a crossflow of aroud 130bhp, as you have to work it on the road to get the best out of it. On the track is a different story but the limiting factors will always be tyres and talent.
Mine has 200bhp and it I can never use full throttle for more than a few seconds as it is ballistic. It makes me smile whne people ask on the Westfield site what they should buy and everyone starts saying you need 250bhp at least, and yet when I take people out to show them what a mere 200 is like they always come back saying 150bhp is enough.
Steve Hole from TKC magazine always says his favorite Chaterham is one with a crossflow of aroud 130bhp, as you have to work it on the road to get the best out of it. On the track is a different story but the limiting factors will always be tyres and talent.
The biggest problem with big power CEC's is the big torque figures, i think this causes a lot of the problems with traction.
A turbo BEC will be a lot easier to drive and use in my opinion as they don't make massive torque like the car engines do.
eg my Mac Worx has a ZX10R engine with gt3076 turbo making 297bhp/139lbft @wheels and on a dry road surface (with warm R888 tyres) I can use full throttle through all the gears and not get wheelspin or dragged all over the road, with cold R888 tyres it will wheelspin in first, but then grip from second gear onwards.
A turbo BEC will be a lot easier to drive and use in my opinion as they don't make massive torque like the car engines do.
eg my Mac Worx has a ZX10R engine with gt3076 turbo making 297bhp/139lbft @wheels and on a dry road surface (with warm R888 tyres) I can use full throttle through all the gears and not get wheelspin or dragged all over the road, with cold R888 tyres it will wheelspin in first, but then grip from second gear onwards.
rhinochopig said:
Low torque high bhp na engines, with good linear delivery, suit the character of the car.
Red16 said:
The biggest problem with big power CEC's is the big torque figures, i think this causes a lot of the problems with traction.
This is a perfectly correct and valid point, but since it's obviously becoming a common theme, maybe we need to look at understanding why this is the case?Torque and power are interrelated, and can effectively be stepped up or down by means of gearing.
What really matters is the thrust at the tyre contact patches, which in turn is directly related to the torque at the rear hubs and the diameter of the wheels. You can get exactly the same thrust at the tyre contact patch from a high rpm/low torque engine as you can with a low rpm/high torque engine, by means of appropriate gearing.
It's absolutely true that low torque/high RPM engines are much more manageable and predictable in lightweight cars, but that's because it's easier to modulate the thrust at the tyre contact patch, since it takes a much bigger change in engine RPM to deliver the same change in tyre thrust (after gearing), compared to a high torque/low rpm engine.
In other words: high revving engines are easier to drive because it's easier to ensure that you don't deploy too much of their power.
It comes back to the same basic point: too much power (actually, too much thrust at the tyre contact patches, if we're being pedantic) is unusable.
...And there's a good technical argument for saying that too much power is not merely pointless, it's counter-productive: it makes the car trickier to drive than it need be, and it means you're getting into a vicious circle of extra weight in the form of additional torsional stiffness, bigger brakes, bigger cooling system, often heavier engine and ancillaries, beefier transmission, etc. to try and cope with it reliably.
The 'Chapman principle' (actually, just basic good engineering) says that eveything should be in balance; there's no point in having huge brakes, or huge power, if the chassis isn't up to using them. Equally, therre's no point in having a superb chassis, with super-dooper trick dampers and sticky tyres, then giving it an asthmatic old 84bhp Crossflow that can't deliver enough power to fully use their capabilities.
The thing is that at the moment the limiting factor isn't engine power, it's tyres and damping; you can easily build an engine that will provide a much higher power:weight ratio than current 'Seven' chassis technology can use, so the difficult bit is constraining the natural male insecurity of worrying about whether you're better endowed than the competition, and concentrating instead on good, logical engineering.
Am I correct in saying a road going superbike has about 700bhp per tonne (excluding rider). If so then a car with similar performance is no problem.
But if the question is "how much power can I have, and still boot the throttle every where?" Then I would say 300 bhp/tonne is a serious amount, but only in the summer.
But if the question is "how much power can I have, and still boot the throttle every where?" Then I would say 300 bhp/tonne is a serious amount, but only in the summer.
Am I correct in saying a road going superbike has about 700bhp per tonne (excluding rider). If so then a car with similar performance is no problem.
But if the question is "how much power can I have, and still boot the throttle every where?" Then I would say 300 bhp/tonne is a serious amount, but only in the summer.
But if the question is "how much power can I have, and still boot the throttle every where?" Then I would say 300 bhp/tonne is a serious amount, but only in the summer.
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