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He doesn't need a CNC machine to do that part though.
Just good old machining skills.

ringo wrote: ↑

05 Nov 2017, 00:36

He doesn't need a CNC machine to do that part though.
Just good old machining skills.

I've seen many an impressive manual machined part for sure.
But I'm a CNC guy myself. Most of the stuff I'm involved in would be impossible on a manual machine

On topic - I've always wanted to make a pneumatic valve setup on a street car. Maybe someday when I have the time this thread will motivate me.

There are very good reasons why there's no pneumatic valves in road cars yet.

Seals wear fast, they need a pneumatic bottle and/or a compressor, the oil purge system is a black art, valve rotation is very poor and highish lift, large included angle valves can drop and lock when pressure is lost (as in when the car has sat for a while).

Ah yeah and calculating the required pressure is another pain - too high and the they eat up more power than a spring, too low and they float.

ringo wrote: ↑

05 Nov 2017, 00:36

He doesn't need a CNC machine to do that part though.
Just good old machining skills.

I started machining about 20yrs ago on a lathe and mill with about 3mm backlash that turned out parts accurate to 3 thou so a cnc these days is just a nice commodity to have

Brian,

Mudflap wrote: ↑

06 Nov 2017, 23:31

There are very good reasons why there's no pneumatic valves in road cars yet.

Seals wear fast, they need a pneumatic bottle and/or a compressor, the oil purge system is a black art, valve rotation is very poor and highish lift, large included angle valves can drop and lock when pressure is lost (as in when the car has sat for a while).

Ah yeah and calculating the required pressure is another pain - too high and the they eat up more power than a spring, too low and they float.

The seal problem is solvable using available parts. Pneumatic bottle / Tank is obvious.
As far as the rest - if I ever did pursue such a project I would develop the valvetrain using FEA and then test on a Spintron. But that's a big if, I doubt I'll ever have the time to be honest.

Besides when I say "street car" I'm not talking about a vehicle that lasts 250,000 miles I'm talking about one of my project cars that typically see less than 10,000 miles between rebuilds.

The benefits would be pretty marginal - even on high revving (>12,000 rpm) engines.

gruntguru wrote: ↑

08 Nov 2017, 23:41

The benefits would be pretty marginal - even on high revving (>12,000 rpm) engines.

I don't think I would say the benefits are marginal... not when getting beyond 12,000 rpm with conventional valves can be very difficult to keep the valve under control.

Just saying - on a race engine 5% is a worthwhile benefit, for the street you just get a 5% bigger engine.

I think if the valvetrain is starting to be one of your concerns then you will have crossed many hurdles before that point with other parts and spent a LOT of cash prior. Do/Don't some of the bike engines run springs upto 14k?

Brian,

Yeah it' really one of those projects that I'd like to do for the sake of doing it.

On any existing street car engine that I would likely use the stroke length will limit things more than likely.

Brian.G wrote: ↑

09 Nov 2017, 15:55

I think if the valvetrain is starting to be one of your concerns then you will have crossed many hurdles before that point with other parts and spent a LOT of cash prior. Do/Don't some of the bike engines run springs upto 14k?
Brian,

and beyond - I know Yamaha R6 was turning 17k years ago. Pretty small/light valves though.

Part of the reason engines like the R6 can achieve such a high rev limit is because of the very short stroke - around 42mm.
The other reason is the valves themselves are so small. This means the inertia being moved is a lot lower but more importantly the valve lift is physically a lot lower.
There is a magic sweet spot for valve lift as a percentage of valve diameter. Because of this the smaller the valve the smaller the lift and the easier the job of the valve spring. Apples vs Oranges so to speak.

Then the answer is obvious weld 4 bike engines together on a custom crank and use valve springs.

godlameroso wrote: ↑

11 Nov 2017, 04:56

Then the answer is obvious weld 4 bike engines together on a custom crank and use valve springs.

Haha genius.
Of course you can already buy a V8 that is done using 2 motorcycle 4 cylinders and a custom crank and crankcase.

godlameroso wrote: ↑

11 Nov 2017, 04:56

Then the answer is obvious weld 4 bike engines together on a custom crank and use valve springs.

Save you the hassle, here's one that was made earlier:

https://www.youtube.com/watch?v=66CKSzyKZno

(Yes, that's 4 x R6 engines on a common crank)