BDR rev limit

[paul_w]

Looking for some advice on the rev limit for an unmodified 1700 BDR, as reading this useful article there is a note that Cosworth stated a rev limit of 6200, I seem to remember that there was a note in the contemporary owners manual that crossflow and Cosworth cars weren't suitable for sustained revs above 6750, and peak power was quoted at 6500 by Caterham.

Given peak torque isn't until 5500, and the engine loves to rev, these limits seem pretty low, especially as if you read any crossflow tuning guides the stock crank and rods are supposed to be good for 7500-8000rpm before you need to switch to steel.

Any BDR people know why Cosworth's limit was so low, and can advise on a safe limit? I'm interested as I'm going to recommission my father's car in the coming months and fit mapped ignition. I know it's been the far side of 7000 in his hands and survived but keen to get input on not blowing it up!

[Roger King]

Personally, I'd limit a std BDR to 7000rpm, but that would be if the crankshaft had been tufftrided and best material bearings, etc fitted.

Unless you're racing, I'd limit even a tweaked version to 7200rpm, bearing in mind that it has a standard crank and rods, flywheel, etc. For competition use we have taken them to 7500rpm, but I assume you want it to last.

A steel bottom end is a different proposition, but will cost.

[anthonym]

I would always defer to Roger above; who also kind enough to muse about a few pics of my engine with the sump removed recently.

My 1987 owner built BDR isn't rev limited or if it is I have never found it. I apply 7,000 as my max gear change revs - which is also max in the rev counter so that's easy; would not want to bend the needle :-)

Anthony - Tazio prolly has an interesting vie  

[Tazio]

My now gone BDR was rebuilt by John Wilcox, we replaced the standard crank with a Scat crank, and i was told not to go above 7200 rpm, but in all honesty it seemed pointless as the extra performance from the last 500 revs didn't  add anything to the experience.

Alan

[anthonym]

That's very nice to know thanks

[paul_w]

Many thanks all. The engine is as built by Langford and Peck and at 30k miles. I don't know how they prepped the cranks so will keep it to the 6750 advised by Caterham.

If even a Scat crank is limited at 7200 I'm not sure why Burton and others would state a stock crank is good for 8000rpm - maybe in Burton's case they figure they'll sell you more parts if you blow it up!

Guess I'll have to start saving for a rebuild with steel bits in the future if I really want it to wail...