Dumb questions

[Kitcat]

Is the big advantage of BEC's the reduction in engine & transmission weight? If so, what is the weight savings?

 

Also, is the vehicle chain driven, like a motorcycle?

[R1 Seven]

The weight savings...at least 200 lbs. My R1 engine/tranny was weighed at shipping (incl. wiring and radiator) and came in at 148 lbs. The lighest car engine/tranny combos come in around 350 lbs from what I have seen. Maybe there are some that are lighter. It is not uncommon for BEC sevens to come in at 900 lbs (minimalist autocross cars).

 

Typically BEC sevens are shaft driven. Where the sprocket would normally go for the chain, an adapter gets bolted on there that mates up to a driveshaft. The driveshaft has to be a two-piece unit due to the length back to the rear end, but it is a tried and true method.

 

Here is a pic of my installation for clarity.

 

http://www.project-seven.goof.com/images/DSCN2151.JPG

 

HTH

[slngsht]

kitkat, in addition to the engine/tranny savings (well, because of it), BEC's can run with lighter brake rotors (rotating weight) and other components as well. So the net result is a little more than just the lighter engine/tranny.

[Kitcat]

Thanks! As we all know, lightness is a good thing. Relatively stock Caterham SVs weigh about 1450, quite a bump up from 900-1000 lbs. Of course Classics are a bit less & deleting all of that unnecessary luxury equipment helps too (heater, windscreen, spare tire, roof, etc.).

[R1 Seven]

FWIW My car is a little heavy for a BEC...it tips the scales at 1138. A lot of that extra is the full cage and some strengthening in the frame. Since I will be mixing it up with tin tops on a regular basis I gladly took those penalties in the name of safety.

 

Lightness it a good thing for sure. IMO although they are not for everyone, the BEC concept fits a seven perfectly. If Colin were building cars today...they would be something like that.

[scannon]

As another data point, I weighed my '04 SV with the Miata turbo engine and transmission today. Came in at 1371 lb with spare wheel and tire, jack and tire iron, full weather equipment and 4 gallons of fuel. About what I expected, more than I would have wanted.

[andrew7]

I agree with what Jeff said. Mine is around 1050 lbs. When I got my engine I could have pick it up about 125 lbs. (engine and FI only) For racing their cheap and fast, between $1000-$2000 My 2005 R1 has 170hp close to 14000 rpm. I've never ridden in a Lotus 7 and have only seen 2 old ones so I can't compare. BEC's are hard-core and very violent. Tap the thottle and it goes to 5000rpm. The clutch engagement is 1" full lockup to free and throttle has a little more travel . A sudden big bump has caused me to punch the gas and accelerate. I came back yesterday from a 50 mile ride with my ears ringing. I drove back country roads 35-55mph and my engine was turning 5000-7000 the whole time. I am changing gears tuesday, hopefully. Even with paddle shifters, shifts are clunky at a slower pace but smooth out when driven agressively. My dad and I have had several conversations about putting a car engine in just for a smooth drive. I'm going to keep it like it is and treat it like a side by side motorcycle, take it out on nice days, wind blowing and engine whinning. I'll take anyone who wants to for a cruiser ride at the 777 rally to understand a BEC but no power/dragon rides.

 

Jeff, no one told me I had to have a 2 pc driveshaft. I have 1 long one and it works. Should I get my hacksaw and make it into 2 pcs?

[R1 Seven]

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Jeff, no one told me I had to have a 2 pc driveshaft. I have 1 long one and it works. Should I get my hacksaw and make it into 2 pcs?

 

Holy cow! It must be a good one...

 

The reasons that I was given for the 2-piece...1) A driveshaft that long is going to whip and be hard to balance. 2) It keeps some of the load off of the output shaft on the transmission.

 

You are the first person that I have seen with a single...congrats!

[andrew7]

My driveshaft is shorter than the T'bird it came from. It was precision balanced but only because the bike engine revs so fast. If I had a car engine I would have cut and welded it up myself. Our engines are putting out 140-180hp at the crank, I have a hard time believing the output shaft bearings would not handle the stress.

 

Love your videos, I understand your gearing problem. I have one myself. I had 3.08s but could barely pull out. I put 4:10s in because I figured I'd never hit 120mph but with the close ratio tranny the engine screams everywhere. I'm going to put the 3.08s back in with lighter and smaller 13" tires. I'm hoping between the two and driving experience it will be OK. Otherwise I'll have to order 3.55s. I don't want to have to pretend to be an F1 driver every time I pull out, although I wouldn't mine one of those umbrella girls at every stop light.

[R1 Seven]

Yep...you would think that the output shaft could handle the duties...that was just the "convention" that I aways saw and read from the UK boys.

 

The 3.08 with the shorter tires might be a good compromise. Silly question but have you used the BEC gear calculator spreadsheet yet? You can put all your data in and play with the numbers to see what will happen before you buy anything... http://www.gamlin.adsl24.co.uk/Images/bike_ratios.xls

 

L8er...

[ptrxly]

The Hayabusa motor/gearbox combination is heavy for a bikemotor at 180# but with my SR7 weighing in at 1010# the 180HP pushes it along just fine. I could keep up with just about anything at Mosport's Driver Development track last weekend despite short shifting at 9,000rpm. The faster cars had race rubber and way more skillfull drivers.

Peter

[Al N.]

As a car engined owner, I'll say that bike-engined cars are bad ass. I think they are the closest one can get to driving a formula car on the street, in terms of revs and sonic impact.

[andrew7]

I haven't used that spreadsheet, Yamaha manual and a calc.

Pete, the engine has more than enough power for anyone but the drive ability on the street is what I wanted to be clear about.

 

I have a 2-stroke MX bike I converted for woods riding, regearing didn't help. The power was WFO acclerating or dying, no in between. The flywheel looked like a service bell, I added a 10 ounce flywheel weight and it totally transformed the engine power delivery. The lack of flywheel weight on the R1 engine makes it harder to drive on street conditions. A FZ1 motor might be better for the street with a 40% heavier flywheel. The ratios of bike trannys are very close which doen's help. If you gear for pulling out, your 6 gear cruise could be 7000 rpm. That's where I'm at now, the diff is draining as I type. 3.08's are going back in. If I were in Texas no problem but with Pa. hills starting out on a hill is a good possiblity.

 

I think a BEC 7 is a great track car but difficult to live with as a street car. Consider carefully how YOU are going to use the car.

Al refered to F1 cars, how drivable on the street are they, no starter and reverse, overheating when driven slow. I feel my car is closer to a Formula car than a Mustang and might be the ultimate sleeper. A British vintage car with a Indy soundtrack.

 

[Birkin42]

When I looked closely at Deman's car, I would say the primary reason they are running a 2 piece drive shaft is to keep the tunnel narrow while allowing the connection to the engine to be as far to the right as possible to centralize the engine.

 

I did look closely at a BEC, a Deman in specific, before I decided I wanted to the car engine route. I spent the better part of a decade road racing motorcycles and know the thrill of their engines. These engines have to be one of the best bargains going in terms of technology and performance per dollar and weight. I also know that these engines, as good as they are, are designed specifically to power a motorcycle and not a car. They typically have a very tall first gear (my last street bike was a Honda RC30 with an 80 mph first gear!), and their clutches and gearboxes are not overly robust. A motorcycle has a high CofG, short wheelbase and low weight. This all adds up to the bike not being able to use all it's performance in lower gears and not putting too much load into things. You can easily fry the clutch in 1 launch in a race if you abused it. Also the lubrication system is not designed for the G loading a car can generate while turning. To some degree you can modify things to improve it, but you are still working around its fundamental design.

 

I wanted a car that I could comfortably cruise with my wife as well at take to a track day or autocross for fun. That's a big spread that requires some compromise. I choose the car engine route since that made more sense to me, but I can easily justify going the other way. In fact, I can see myself building a BEC some time in the future, though that will need approval from the minister of war and finance, my wife.

 

I think the suggestion to look for an engine like a FZ1 is a good idea. They will give you almost the same power with a better torque curve and a wider ratio transmission. You might be able to get the gear set out of a FZ1 and put it into an R1, but I'm not sure it would bolt right in. Not cheap either. I would think sport tourer, or big bore top speed bikes like the Busa or ZX14 are better then the 1000cc race oriented bikes as a donor for a BEC.

 

Both are great options but likely one is more right for a given person and their desires.

 

[andrew7]

:hurray: It worked. The 3.08 with the lighter smaller tires was the right combination. I could drive through town in third and on th highway 55mph was about 5500rpm. 1500rpm less than before, alot smoother too. The violent acceleration seems tamed down but I didn't push it much.

 

I agree with birkin42, "Both are great options but likely one is more right for a given person and their desires." I think the bikes internals are weaker but I'm not the type to sit and do multiple burnouts or drag passes. If I wanted a racer only like Jeff's then I would try to improve certain areas that could be potential problems later.

 

My passenger seat is 1" narrower than the drivers which is difficult to see. The tunnel is wider than normal to permit the drive shaft to run at an angle from the right side toward center with out the tunnel looking offset and goofy.

[tajordan]

It was precision balanced but only because the bike engine revs so fast. If I had a car engine I would have cut and welded it up myself.

 

Am I missing something? With a given differential ratio, and a given speed, the driveshaft is turning at the same speed, regardless of engine. Just because a motorcycle engine revs to 14,000 RPM, the output shaft speed is the same. In some cases that I've seen, a BEC will have a lower top speed than a car-engined-car (due to the transmission gearing and a high diff ratio), so the driveshaft actually turns slower.

 

I opted for a two piece shaft to keep the tunnel as narrow as possible. A one piece shaft would have worked (for 1/3 the cost!), but would have been a larger diameter, and would have started migrating into the right side of the car from the differential forward.

 

Also, with it spinning so close to my leg, I wanted a little more assurance that it was done correctly.

[andrew7]

I agree Jordan you made a good point. I was concerned an out of balence driveshaft would cause an output shaft failure and "thought" the bike engine would spin the driveshaft up faster than a car engine. I now believe ALL driveshafts should be professionally balenced for safety.

[R1 Seven]

FWIW - I calculated that my maximum speed for the driveshaft is somewhere around 6500 rpm.

[ottocycle]

Hello all,

Just to add my 2 cents worth. I too have a 1 piece driveshft. I have yet to drive the car at speed (only up and down driveway to check clutch action and leaks etc.) but hope to be able to put it on the street in a few weeks. I did things a little differently in that I have a rear weight bias (my thinking was better traction under power and weight would transfer under hard braking), so my driveshaft may be a little shorter than others. My question is this: Is there a way of determining whether a driveshaft problem is length related or pinion angle related. Mine was professionally balanced and built using new UJ's.

 

-Dermot.

Hayabusa/Fury.

[BobDrye]

You need to do a little research on drive shafts and critical speed. There are many web sites with calculators.

The critical speed of a spinning shaft is described as the lowest speed which excites the shaft at it's natural frequency of vibration. This will cause the shaft to bend under the stress of vibration coupled with the centrifugal forces due to the rotation. In english, this means the shaft will vibrate very badly and possibly take a permanent bend (if not destroy the car in the process) as the critical speed is exceeded.