Anyone know what RPM valve float sets in?

[mole42]

Well, it follows on from questions that I was thinking about - has anyone done desmodromic valves for the Stag? Probably not worth it, since the bottom end would give up long before the valve train did.... Has anyone built a 32-valve Stag engine?

So, what RPM are the standard springs good for? We always used to put stronger valve springs in the 970 Mini Cooper engine I ralied in the '70s to stop valve float, but I've not heard it needed on a Stag.

[DJT]

There were rumours of attempts to fit the TV8 with 16-valve heads like the Sprint 4-cylinder. Even that a couple of engines were built, but none survive. As the Sprint head wouldn't fit the LH bank without changes to the casting, and a completely new head would have to be made for the RH bank, the tooling costs would have been unaffordable for a company struggling to get by. And with the reliability problems with the standard TV8 and Sprint engines (as built at the time), putting together a reliable 32-valve engine would have been a real challenge.

[GDPR]

Valve float, simply put, is when the spring fails to close the valve before the cam comes round again and is dependent on the mass of the valve train - it is called the critical velocity of the spring.

The Mini, being OHV, has not just the valve but a rocker, pushrod and a tappet (follower) to overcome by just the spring with not just a lot of mass, but a lot of friction too. To achieve high revs, a strong spring is needed but that has drawbacks with higher valve train loading and a need to make it stronger without making parts heavier...

The Stag being OHC has a very light valve train having just a lightweight bucket, and is probably good for 8500rpm on a good standard spring although I don't have an official figure.

[wilf]

I suspect the inadequacies of the inlet manifolding would call a halt to rpms well before valve float ensued, lol.

The Stag TV8 is a remarkably high revving engine for its time, really, all down to being SOHC as Kryten says.

But you can, relatively (!) easily build USA smallblocks that will rev to 8000+, and they are ancient old pushrod things.

[Guest]

I reckon the valve float would occur just before the cam chains broke or it buffed a rod!!!Dont think I will try it out though!
Tony

[stag8manod]

Would not Tony Hart be the man to ask.
Cheers Ian A

[pagan]

A 32-valve Stag engine?
would be nice but no chance.

A Stag motor with a Desmo head.... ?? why, stop valve bounce... ?

If Honda ( and the others) can build a production motorcycle 250cc 4 cylinder mota that is reliable to 18,000 rpm with DOHC..
Why try to use a Desmo system.

Allan

[tonyh]

On both the Modsport engine and the 70's production racing engines I used standard valve springs and standard Renold timing chains, the Modsport engine produced about 280bhp and was safe to 7,500rpm and occasionally used 8,000rpm, standard pistons are good up to about 7,500rpm then the tops fall off, forged pistons are good for over 8,000rpm, the 70's production engine produced just under 200bhp with standard carbs and inlet manifold, with the restrictions of the carbs and manifold the power band was between 4,500 and 6,250rpm.

Tony.

[StagManiac]

I'd love to see some video of the Modsports Stag. Do you have any, Tony? Does anyone else know of any?

Paul

[mole42]

Try this: https://www.youtube.com/watch?v=DqeX3puUTxQ

And part 2: https://www.youtube.com/watch?v=W9AjbUF_GEo

[pagan]

Try this: https://www.youtube.com/watch?v=DqeX3puUTxQ

With wood dash too.

[tonyh]

Unfortunately there is no video of the Modsport Stag that I know of, there are photos in my profile and several video clips of the 70's production Stag on youtube.

Tony.