Exhaust valves

[smotorboy]

Hello All,

Are the 500 exhaust valves larger than the 350 exhaust valves ???

Robert in California

['It must be a .....']

Hello Robert, yes 500 exhaust valves are larger.
From memory I think they are 26mm, I can measure an old pair tomorrow.
In the late 80's you could get stainless oversize 350 valves which were still slightly smaller than the 500 valves, but I can't recall if both inlet and exhaust stainless valves were available.
Also 501 engines have bigger valves than the 500's.
As usual lots of possibilities.
Have fun, Ian

[smotorboy]

Oh, Thank You Thank You Ian,,,

This could be the fix I need on the LSR supercharged 350 Morini,,,,

I spent all last year trying in vain to squeeze more HP from the motor, but it seems the motor is "choked" and nothing I did helped.

Over the winter, I put in a lot of effort in calculating what Cam profile would work well with the Supercharger and provide a lot more breathing duration on the exhaust events to "un-choke" the motor some significant amount.

My engine computer simulation software predicts a 4.5 HP gain,,, I'll test that in May at the first race event,,,, The Morini should be north of 120 mph with the new cam,, We'll see.

The cam will do all it can, however the real issue is the stock exhaust valve area. With the power up from 32 hp at the flywheel to 51 hp at the flywheel, the amount of exhaust product is up accordingly and has the motor "chocked". Those tiny valves can only handle so much.

I'm looking into fitting larger exhaust valves, even if it means down-sizing the Intake valves as the cam might not do all that is needed…The Supercharger will handle the smaller Inlet valves no problem.

Any info on this will go a long way toward taking the speed titles from the Ameracchi powered bikes…. I'm sure us Morini riders would really like this to happen…

The oversize 350 valves might just do the trick…

I'm excited over this prospect...

Robert in California
The Baron Race team

[EVguru]

Bengy Straw used to fit 500 heads on 350 bores by notching the top of the liner.

[smotorboy]

That is an idea that needs looking into !

Thanks !!!

Robert

['It must be a .....']

Hi Robert, I measured the 500 exhaust valve heads which are as I thought, 26mm.
I don't know the size of the larger stainless 350 exhaust valves (supplied by Benjy Straw's WeeVee) and I can't measure them as they are still in my 500 engine but they were close to the standard 500 valve diameter (25mm?).
Should be quite easy to go with 500 exhaust valves in 350 heads if you take that route.

Have fun, Ian in Wales

PS 500 inlet valves are 32mm

[smotorboy]

Thank again Ian,,, your info is a huge help on this...

I'll contact NLH and get some 500 valves to work with,,,I have a couple of tatty head that can be used to trial fit things,,,

I worked through the area numbers and going up to a valve seat with a 20mm ID will increase the breathing area almost 20%...

A huge gain,,,, as much as the new camshaft might give,,,

Both improvement might enable the little 350 to get to the milestone 3hp per cubic inch without increasing the rpm one bit !

No easy feat,

Robert in California

['It must be a .....']

Hi Robert, just thought that 501 valves are larger again but I don't know by how much.
Have fun, regards Ian

[norbert]

501 valves will definetly be too large! Their centers are more seperated than in the 350 an 500 heads (and therefore their axle of the rockers is a bit longer). They separated the valves a bit more because of the well known problem with the cracks between the seats (very unusual with 350 motors, but very usual with the 501).

I think it should be possible to use 500 heads with 350 barrels. Never did it, but heard about that

norbert

[SupermotoDave]

If it was that easy everyone would have done it by now. Remember that as the valve gets bigger it gets nearer the cylinder wall and thus gets more shrouded which starts to negate the perceived gains.This is far more of a problem than with a more conventional Hemi style valve layout even with modern narrow valve angles. When tuning the 350 the benefit of the 2mm overbore to 64mm was believed to rely as much on the reduction in valve shrouding as it did the extra 20 odd cc.
The flow rate and Cam timings printed in ATG339 may prove instructive, along with the 3D porting models. Despite the tongue in cheek nature of the remainder of the article these represent actual data from recent testing.
I have a set of Weevee tuned 500 heads for my 350, these have a reduced size exhaust valve? (it's a long time since I looked) to enable them to fit on the 350 bore.

David

[smotorboy]

Hmmmm,

So many new possibilities,,,,

64mm bores with the stroke shortened to 54 mm would keep me in the 350 class...

This could go a long way to help the breathing and parts are available....

I'll run the numbers and see what is what...

Thanks Guys

Robert in California

[SupermotoDave]

250 crank and 500 pistons has been done before, 325cc?

David