Power: Bike engine vs. car engine
Discussion
Hi,
I'm new to the kit car game but looking to buy a second hand MK Indy or MNR but I'm wandering what the difference in power-to-weight is between the bike engined cars (r1 or fireblade derivatives) and the higher powered car engined varieties.
I know the BECs are considerably lighter but how much difference does that make when they don't produce as much power?
I'm looking at either a Vauxhall XE 2lt version (approx 200bhp) vs. a 125bhp fireblade engine. I know the Vx engine will probably loose quite a bit of that power at the flywheel but I'm not sure how much. I understand bike engines don't loose much power from engine to the driven wheels. These factors make it difficult to compare the two.
Anyone got experience of these 2 setups and which would offer the better/stronger performance? Or how many bhp in a car engine do you need to keep up with a fireblade? The car will be used for about 60% road use and 40% track use.
Thanks for any help..
I'm new to the kit car game but looking to buy a second hand MK Indy or MNR but I'm wandering what the difference in power-to-weight is between the bike engined cars (r1 or fireblade derivatives) and the higher powered car engined varieties.
I know the BECs are considerably lighter but how much difference does that make when they don't produce as much power?
I'm looking at either a Vauxhall XE 2lt version (approx 200bhp) vs. a 125bhp fireblade engine. I know the Vx engine will probably loose quite a bit of that power at the flywheel but I'm not sure how much. I understand bike engines don't loose much power from engine to the driven wheels. These factors make it difficult to compare the two.
Anyone got experience of these 2 setups and which would offer the better/stronger performance? Or how many bhp in a car engine do you need to keep up with a fireblade? The car will be used for about 60% road use and 40% track use.
Thanks for any help..
Another 'can of worms' question!
There's no clear answer to this one: each type has it's protagonists, some of whom can be obsessively evangelical!
As a rough guide (even individual cars of the same make and model vary):
If you say a Vauxhall engined Seven will weigh around 575 kilos and a Fireblade engined Seven will weigh around 420 kilos.
Allowing for a 75kg driver and 25kg of fuel in both cases, the Vauxhall engined car will give about 296bhp/ton (with much better torque), laden, the 'Blade engined car will give about 240bhp/ton, laden.
BUT, the 'Blade engined car will have much shorter, closer gearing (6 closely stacked, sequential gears, and you'll be bouncing off the limiter with the engine screaming at 12K revs at maybe 115mph, whereas the 5th top in the Vauxhall might be geared for cruising and give a theoretical top speed of 150+ mph at about 2/3rds of the 'Blade's revs), so if you keep it in the right gear, in the right part of the powerband, you'll be able to make very rapid progress.
What this means in practice is that the Vauxhall will give much 'stronger' (more accessible and more relaxed) performance on the road; you will be able to overtake by simply pulling out and flooring it, rather than having to prepare by changing down two gears, and you won't have to concentrate on being in the right gear quite so much, or drive everywhere with the engine screaming at big revs to make progress on the twisty bits. On the road, the sequential gearbox can be as much of a pain as a benefit (they're pretty clunky in slow traffic) and you can't make as much benefit from the low weight (what you gain from the reduced inertia, you lose skipping about on the ruts and the potholes!).
On the track, you're not worried about 'relaxed' performance, so the 'Blade will gain an edge, because of the lighter weight (better cornering and braking, if set-up properly) and may well be able to lap a circuit as fast as the Vauxhall car, despite the lower power:weight ratio. The lack of inertia and the sequential geabox is very nice, on track, too, in terms of feel and sensitivity. Both would be pretty quick, though: to be honest, it would be as much down to driver skill anyway and you do need to remember that track days are non-competitive, so the last fraction of a second on lap time isn't really that important either way.
Personally, I tend toward the car engined camp - I'd only want a BEC (particularly a 'Blade engined one) if it was pretty much exclusively for track use - but there'll be someone from the bike engined church along shortly to say that they're the best thing since sliced bread and superior to a car engine in every way!
The sensible advice is that you really need to have a decent drive in both types before you decide.
There's no clear answer to this one: each type has it's protagonists, some of whom can be obsessively evangelical!
As a rough guide (even individual cars of the same make and model vary):
If you say a Vauxhall engined Seven will weigh around 575 kilos and a Fireblade engined Seven will weigh around 420 kilos.
Allowing for a 75kg driver and 25kg of fuel in both cases, the Vauxhall engined car will give about 296bhp/ton (with much better torque), laden, the 'Blade engined car will give about 240bhp/ton, laden.
BUT, the 'Blade engined car will have much shorter, closer gearing (6 closely stacked, sequential gears, and you'll be bouncing off the limiter with the engine screaming at 12K revs at maybe 115mph, whereas the 5th top in the Vauxhall might be geared for cruising and give a theoretical top speed of 150+ mph at about 2/3rds of the 'Blade's revs), so if you keep it in the right gear, in the right part of the powerband, you'll be able to make very rapid progress.
What this means in practice is that the Vauxhall will give much 'stronger' (more accessible and more relaxed) performance on the road; you will be able to overtake by simply pulling out and flooring it, rather than having to prepare by changing down two gears, and you won't have to concentrate on being in the right gear quite so much, or drive everywhere with the engine screaming at big revs to make progress on the twisty bits. On the road, the sequential gearbox can be as much of a pain as a benefit (they're pretty clunky in slow traffic) and you can't make as much benefit from the low weight (what you gain from the reduced inertia, you lose skipping about on the ruts and the potholes!).
On the track, you're not worried about 'relaxed' performance, so the 'Blade will gain an edge, because of the lighter weight (better cornering and braking, if set-up properly) and may well be able to lap a circuit as fast as the Vauxhall car, despite the lower power:weight ratio. The lack of inertia and the sequential geabox is very nice, on track, too, in terms of feel and sensitivity. Both would be pretty quick, though: to be honest, it would be as much down to driver skill anyway and you do need to remember that track days are non-competitive, so the last fraction of a second on lap time isn't really that important either way.
Personally, I tend toward the car engined camp - I'd only want a BEC (particularly a 'Blade engined one) if it was pretty much exclusively for track use - but there'll be someone from the bike engined church along shortly to say that they're the best thing since sliced bread and superior to a car engine in every way!
The sensible advice is that you really need to have a decent drive in both types before you decide.
Edited by Sam_68 on Saturday 11th April 10:12
I use my BEC exclusively on the road. But then I live out in the sticks, and as such have no real requirement for docile town driving or good manners in traffic. If I lived in central London, my car would be as much use as a chocolate fire-guard. My car is pretty brisk up to the legal limits, but beyond that a car engined 7 would start to gain on me and above 100 it will probably beat me. However, speeds above 80-90 or so don't really matter to me. Oh, my car's geared for 125, which I'm told is enough for most circuits in the UK.
I built a Fury R1 for mainly road use. It's a bit mad when compared to my other cars but I wouldn't have it any other way. It's a motorbike with four wheels and not really a car with a motorbike engine. It's way quicker than my Lotus Elise was on the straights and in the corners. It's more extreme, more involving to drive and simply much more fun. On road and track, I still don't have a need for something faster. Two years on, the limiting factor is still me and not the car.
In my case, it's a third car and I drive it for fun only and not to go anywhere in particular. I also live in rural Suffolk so traffic is not really an issue. If you actually have to get to places then I suggest something more practical is in order. If you just want fun, then it's seriously hard to beat something that is not compromised by a large lump of metal in the engine bay :-)
In my case, it's a third car and I drive it for fun only and not to go anywhere in particular. I also live in rural Suffolk so traffic is not really an issue. If you actually have to get to places then I suggest something more practical is in order. If you just want fun, then it's seriously hard to beat something that is not compromised by a large lump of metal in the engine bay :-)
Although I will be doing various track days throughout the year I live in London so it sounds like getting in and out could be a pain in a BEC. I would also like to drive to the Ring sometime, which obviously involves some long distance driving..
Relating to the original power question:
On the CEC front, is the Pinto best to avoid if I'm after something a bit more potent? There's several nice Pinto MK Indy's in the classifieds but research tells me that the Vauxhall engine (or maybe zetec) is likely to be the better option.
Relating to the original power question:
On the CEC front, is the Pinto best to avoid if I'm after something a bit more potent? There's several nice Pinto MK Indy's in the classifieds but research tells me that the Vauxhall engine (or maybe zetec) is likely to be the better option.
To be honest, the Pinto would be right at the bottom of my list as an engine for a Seven. It's really quite a heavy engine and it doesn't make that much power.
Even for its generation it wouldn't have been the best choice (Crossflow, Fiat /Lancia Twincam or Lotus Twin Cam were better). If you can afford something more modern (Vauxhall Twin Cam, Toyota Twin Cam of Ford Zetec), then that's definitely the way to go.
The Rover K-series is ideally suited to Sevens, too - it's very light, but can be tuned for 175bhp very easily, so it is a good compromise between the bike engined cars and the heavier car engines - but with the exception of Caterham and a few Sylvas, you won't often come across it because of the cost of the inline conversion parts.
Even for its generation it wouldn't have been the best choice (Crossflow, Fiat /Lancia Twincam or Lotus Twin Cam were better). If you can afford something more modern (Vauxhall Twin Cam, Toyota Twin Cam of Ford Zetec), then that's definitely the way to go.
The Rover K-series is ideally suited to Sevens, too - it's very light, but can be tuned for 175bhp very easily, so it is a good compromise between the bike engined cars and the heavier car engines - but with the exception of Caterham and a few Sylvas, you won't often come across it because of the cost of the inline conversion parts.
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