engine and drivetrain Bore question plus other issues

[bmw02rally]

I just stripped my engine due to an exhaust valve breaking, the rotor arm snapped on a rally which also melted a plug on the same cylinder. Its a 121 spec tii engine which I don't know the origin of. I suspected it wasn't standard as after sticking 40 dcoe's on it and a very mild cam 284 I think, It made 150bhp on the rollers. The pistons are bath tub type and have 89.490mm stamped on them so seeing as they should be 89.00mm standard. What cc am I running???

Also there seems to be alot of rolled metal in the sump which suggests something is touching. The only marks I can see are where the Big end caps of the con rods get close to the bores when turning the crank. What could cause this??

By the way pics from rally can be found at

http://www.edpphoto.com/fatalbert%2081-93.HTML/index.htm

Regards

Mark

[schwarz75]

If you don't have a longer stroke crankshaft, then the increase in displacement isn't anything significant - you still have approx. a 2,000cc engine. In all likelihood, your engine has been overbored once by less then 0.020"/ 0.5mm. Many machine shops want to take this much off the cylinder bores. If your engine has a longer stroke then either the pistons have a different pin location than that of stock pistons, and/or shorter rods than stock rods. Maybe someone can provide the pin location and rod length for a stock engine. Regardless, that was a lot of HP to the rear wheels.

[TobyB]

Actually,

if you have a good exhaust system and the car is jetted right,

150 is pretty believable- I make that with a mild cam and 40's as well.

Yes, your pistons are second overbore- and that's not enough to really

change the c/r much. Bathtubs are nice.

What do you spin to? breaking a valve is... unusual.

t

[bmw02rally]

150 at the wheels!!! I wish. No that's at the flywheel......

Thanks for the replies guys!!!

Bearing in mind lack of cash, what would do think would be the minimum to change and renew to put it back together?

I was thinking new gaskets, big end shells, obviously the valves, cylinder head bolts and a new competition headgasket.....what else?

I rev to about 5800rpm, no point in buzzing it any more as it peaks out at 5750.

Regards

Mark

[Guest Anonymous]

how did you get 150 to the wheels on a stock tii setup? You said you were running a 284 cam and have one-over bathtubs? Did you put jet fuel in there or something?

I would think that 100 to the wheels with that setup would be optimistic...

[bmw02rally]

You are correct, just below 100 brake at the wheels. I thought that was crap but they said a getrag dogleg box and LSD equals lots of transmission loss.

[TobyB]

hmmm- with 150 at the crank, I'd expect 120- 130 at the wheels.

That's about what I see. Much more loss than that means that something has to be on FIRE under that car! One or the other of your dyno operators is a bit optimistic/pessimistic!

You should actually see power through 6500- I'm up to 36mm chokes, and I pull strongly to 7400. But I don't have a cam card- my lift's 10mm at the valves, duration unknown.

Check your valve springs while you're in there- stock is 70 on the seat, 170 at lift, and isn't enough for over 6800. Ireland's 'race' springs are 90/230 and seem to work just fine to 7400.

Where in Wales? I was at Bangor for a while...

t

[bmw02rally]

Toby,

Cardiff, South Wales.

7400rpm!! I assume you have the bottom end balanced?

What can safely be rev'd on a stock bottom end?

[Guest Anonymous]

I had mine bored out to approx. 90.2, gives me like an extra 40cc's, so no big gain there. Also, the bottom end on these babies is almost bulletproof stock, but the valvetrain breaks somewhere around 7200. 6400 is stock redline, and seems like a good place to stop. 30% loss on the dyno is not good, should be somewhere 15-20%. Or the dyno guy is bad at math.