BEC v CEC

[JeffC]

I would be more concerned that it isnt dry sumped  

the orange one with all the bits on would be my choice at £10k its for nowt    

[Bean]

But without doubt my choice has to be this

buy me

Gotta agree with you, if I was on the market for a bike engined Westie I'd definitely have a look at it

[ChrisG]

Chris, I am only comparing a 1.3L Busa 7 against a 200bhp car engined 7 both with exact same spec.

Lets look at the figures: So Jeff's 1.3 Busa has a PTW ratio of 343bhp. The same spec car but with a 200bhp VX weigh circa 550kg has a PTW ratio of 363bhp, so without even considering the difference in torque figures which assists you very nicely from standing starts and accelerating out of hairpin type corners, the 200bhp VX has to be quicker which answers the question of this thread  I am not taking in to consideration, driving styles, tyres, suspension setup, transmissions, I am basing my comments on two very similar spec cars but with differing engines. And the calculation cannot lie

How come, a 7 type car with 200bhp -175lb ft of torque pull away quicker from hairpin type corners and start lines quicker than a lower powered 1.1 kwaker or 1.3 Busa bike engine car such as a Radical, is it because the Radical driver is dog poo, or the Radical weighs too much, no grip or could it be something to do with Torque

Oh dear  

[conibear]

Interestingly I reckon my Busa had better drive out of corners than my mates 208BHP VX. We were runing the same tyres. I would get a better drive out of the bends he would then reel me in slightly at around 80-90mph.

If I was in front though I could use better braking etc to pull a gap.

But I do have to say though even with the standard 175bhp I have never been trounced down a straight by any 7 type car.

Baz, your almost certainly taking more speed through the corner thus exiting the corner at a higher speed than your mate, which is very probable as your car is lighter and in theory have more grip

[ChrisG]

Could it not simply be that due to the BEC being a lot lower geared, its weeny engine torque output is magnified to a greater degree and thus the torque levels at the wheels are similar which allows it to accelerate just as quickly as the CEC?

[conibear]

This would be an interesting comparison. Chris have you got the calculation to establish the torque level at the wheels Or perhaps you can advise on mine.

I got a 2.3 ratio 1st gear with a final drive 4.09, circumference of wheel is 1780mm and the overall torque is 206lb/feet, car weighs 530kg. Do you need any other info. Tyres are irrelevant aren't they as we are trying to do a comparison, but if you need to know mine are 9.5" wide

[steve_m]

Is it time for bed yet        

[ChrisG]

A bit of deja vu here as IIRC I posted something similar a few months back, but anyway

I guess you can assume wheel sizes are the same because that's not BEC / CEC specific, the rest is a simple multiplication up through the ratios to find it, ie

206lbft x 2.3 x 4.09 to give torque at the output shaft = 1937lbft

or a car with say 210bhp / 170lbft (realistic?) with the same gearing would give 1599lbft

In comparison a stock busa would be something like:

100lbft x 2.613 x 1.596 x 3.62 = 1509lbft

The 1.596 is the primary reduction ratio (the ratio between the crank RPM and the clutch / gearbox input RPM) which doesnt exist on car engines as the clutch is directly driven off the crank.

Therefore a (60kg+ lighter) busa gives almost as much peak wheel torque in 1st gear as a Vx with 170lbft. This will vary a bit in the other gears though, so a comparison in the upper gears would be more representative of realworld acceleration on track etc. You'd also need to look at the torque figures across the whole rev range to accurately assess it, which obviously would be rather tedious!

Its generally a lot simpler (and fairly realistic) to simply look at power / weight as a good indicator of overall acceleration before drag kicks in, assuming the two cars being compared have reasonable gearing to allow them to reach a similar speed, in the case of a Westie say ~130mph.

[conibear]

You can assume wheel sizes are the same because that's not BEC / CEC specific, the rest is a simple multiplication up through the ratios to find it, ie

206lbft x 2.3 x 4.09 to give torque at the output shaft = 1937lbft

or a car with say 210bhp / 170lbft (realistic?) with the same gearing would give 1599llft

In comparison a stock busa would be something like:

100lbft x 2.613 x 1.596 x 3.62 = 1509lbft

The 1.596 is the primary reduction ratio (the ratio between the crank RPM and the clutch / gearbox input RPM) which doesnt exist on car engines the clutch is directly driven off the crank.

Therefore a (60kg+ lighter) busa gives almost as much peak wheel torque in 1st gear as a Vx with 170lbft. This will vary in the other gears though, so a comparison in the upper gears would be more representative of realworld acceleration on track etc. You'd also need to look at the torque figures across the whole rev range to accurately assess it, which obviously would be rather tedious!

Its generally a lot simpler (and fairly realistic) to simply look at power / weight as a good indicator of overall acceleration before drag kicks in, assuming the two cars being compared have reasonable gearing to allow them to reach a similar speed, in the case of a Westie say ~130mph.

Thanks for this, it is very useful  

Although tedious no-one can argue with figures, not even me

It does go to prove again though which ever calculation you use, the 1.3L Busa will not be able to accelerate as quick as a 200bhp VX as the two cars with similar spec will not have a 60kg in weight difference will they  

[ChrisG]

It does go to prove again though which ever calculation you use, the 1.3L Busa will not be able to accelerate as quick as a 200bhp VX as the two cars with similar spec will not have a 60kg in weight difference will they  

Err does it? LOL

For starters even if the above advantage was consistent across the revs in each gear (which it wont be), thats only a ~6% advantage for the CEC. 6% of 550kgs is only 30kgs, yet there's likely to be at least twice that in weight difference so "torque at the wheels per ton" (made up term!) is higher on the busa car than the Vx which would suggest otherwise.

As I said thats only a comparison in 1st gear anyway, and if you haven't got a CR box in the Vx thats well matched to the engine you're unlikely to have any advantage over the busa's wheel torque figures most of the time at a given road speed, and could well be less.

We also won't go into how much time between gearchanges the busa gains because of the sequential against H Pattern gearbox

Either way though we're talking small percentage difference, some favouring the BEC, some favouring the CEC so their performance would be very evenly matched (as reinforced by most other people's experiences).

[conibear]

Chris, as I keep writing we need to compare 'similar spec cars' thats not colour, tyres, gel coat but the same. So there is no need to mention gearboxes, all the figures you keep stating are in favour of a CEC, so just say it you know you want to  

Lighter cars will have an advantage cornering, which will assist them initially accelerating out from.

My mates 2l VX caged SEIW weighs in at 545kg with fuel and his spec will be very very similar to a car such as JeffC, these Megabusa's are not as light as we all think it would seem.

Maybe you should come to a race day where BEC race against CEC, witness the starts and acceleration out of corners and discuss with race drivers, because generally racers are at 100% which cannot be compared to a trackday, which we have all done and all patted ourselves on the back at how quick our cars are and how good a driver I am  

Anyway, Mr Seer I think has got a good response to his question

[Bazzer]

Chris, as I keep writing we need to compare 'similar spec cars' thats not colour, tyres, gel coat but the same. So there is no need to mention gearboxes, all the figures you keep stating are in favour of a CEC, so just say it you know you want to  

Lighter cars will have an advantage cornering, which will assist them initially accelerating out from.

My mates 2l VX caged SEIW weighs in at 545kg with fuel and his spec will be very very similar to a car such as JeffC, these Megabusa's are not as light as we all think it would seem.

Maybe you should come to a race day where BEC race against CEC, witness the starts and acceleration out of corners and discuss with race drivers, because generally racers are at 100% which cannot be compared to a trackday, which we have all done and all patted ourselves on the back at how quick our cars are and how good a driver I am  

Anyway, Mr Seer I think has got a good response to his question

My busa after SVA the turbo was 480Kgs with half a tank of fuel.

How do RGB race series lap times compare to yours conibear  ?

Bazzer

[conibear]

In my race series they don't Bazzer, also my car is not 200bhp or a VX so not a comparison. Bazzer, lap times is not what I have commented on, just acceleration

Edited: SVA weighbridge's are never accurate as been discussed to death on here in the past. I used to think my car weighed b****r all (according to suspension specialist) then it got weighed properly on three different devices, all of these three devices showed it was 45kg heavier than I thought

[ChrisG]

Of course there's a need to mention gearboxes unless you can get unlimited choice of ratios for each, because you certainly cant use the same gearbox on both! If you want to compare a sequential boxed Vx with a Busa thats fine, but then you get into the realms of one install costing 2 or 3 times more than the other, in which case is it really like for like in affordability terms?

The best way to guage the true weight difference though would be to know the weight of the engines and gearboxes, IIRC a busa weighs about 85kgs including its gearbox......

If you're talking racing, what laptimes would a 200bhp Vx Westie do around Cadwell for example?

cheers

Chris

[ChrisG]

...or if we're talking straight line acceleration, what standing quarters can a 200bhp Vx do?