500 valves in a 350 Head

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500 valves in a 350 Head

Postby fastharry » 17 Mar 2018 12:52

Can anyone shed any light on what it takes to put 500 valves into a 350 head. Do i need new seats? or can the standard seats be cut to suit ? And are the gains measurable? Bearing in mind i have a 375cc conversion fitted.
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Re: 500 valves in a 350 Head

Postby 72degrees » 17 Mar 2018 14:34

I've not heard of that being done (which doesn't mean it hasn't). Are the valve stem diameters and lengths the same? I know some people have put 500 heads on 350 (or '375') cylinders by relieving the top of the cylinder to accommodate the bigger valves and greater distance between them?

The 250 and 350 use the same head casting so you can in theory use 350 valves in a 250 head by changing the seats. I'm not sure if that would work for 500 valve seats in a 350 as the castings (and therefore presumably ports) are different.

Paging Harrymuffin.
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Re: 500 valves in a 350 Head

Postby 'It must be a .....' » 17 Mar 2018 19:35

Hi, back in the late 80's when I needed them there were no valves available for 500's, so I fitted oversize 350 valves which I got from WeeVee.
The stem lengths and diameters are the same and the heads of the larger 350 valves (racing!) were only slightly smaller than the standard 500 valves and fine with the standard 500 valve seats.
Sorry don't recall the diameters and they are still in the 500 engine.
It all depends on the diameter of the 350 valve seats, but you could take them out as far as you dare and if you need to alter the 500 valves to suit?

Hope this helps? Good luck
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Re: 500 valves in a 350 Head

Postby fastharry » 17 Mar 2018 21:36

Im thinking of this as a stop gap until the 507 engine is ready, so i do not really want the expense of buying 500 heads, but try and improve the breathing of the 350 heads, I guess i should put up a wanted add to see what kind of price they might be, and i will look out for those oversize 350 valves, thanks for the replies chaps.
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Re: 500 valves in a 350 Head

Postby smotorboy » 21 Mar 2018 16:43

I've put 500 exhaust valves in a pair of 350 heads and am seeing significantly better flow on the exhaust side of things....I'm still doing "touch up port grinding" so final flow bench numbers are not available just yet.....

My examination of 350 heads is that the intake valves are fine as to flow and size....it is the exhaust that need help,,, beside there is no room to increase the intake valve diameter and notching the cylinder tops to reduce valve shrouding can reduce overall all air flow as per some flow bench tests I did.....

Robert in California
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Re: 500 valves in a 350 Head

Postby huub » 22 Mar 2018 15:29

interesting!
i remember Benjy Straw saying the biggest issue he found tuning a 350 is getting the exhaust gasses out of the cylinder fast enough , your results seem to point in the same direction.
did you change the valve seat? by how much did you open up the exhaust port?
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Re: 500 valves in a 350 Head

Postby smotorboy » 22 Mar 2018 17:18

OH I agree 100% with the exhaust flow .....

Yes, you need to change the seat and open the port to match the seat....My machine shop used their own seat as they had a seat cutter that didn't match with the 500 oem seat and I lost at least a mm of throat diameter... you should have better luck in the UK getting the proper 500 seat installed...

My throat diameter is up from 18.5mm stock to 20.5mm now....

My bike was stuck in the 115 to 116 mph range no matter what supercharger boost level was used... Then I had the Exhaust cam lobes built up and reground to yield faster and longer exhaust valve events....

Bing ! speed jumped up to 121 mph with no other changes.

My hope is that the larger Exhaust valves will help get to something over 125 mph and displace the New Zealand Moto Guzzi that has posted a 124 mph run and is currently the fastest gasoline pushrod 350 bike .

Best I have done is 123 mph with the small exhaust valves....
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Re: 500 valves in a 350 Head

Postby huub » 22 Mar 2018 20:49

nice work, should be interesting to see the results!
kudos to those guzzi guys , for getting that speed out of a engine that is even less likely to be tuned.....
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Re: 500 valves in a 350 Head

Postby huub » 22 Mar 2018 20:49

sorry , double post...
Last edited by huub on 23 Mar 2018 07:35, edited 1 time in total.
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Re: 500 valves in a 350 Head

Postby MickeyMoto » 22 Mar 2018 21:41

I've seen a Yamaha 5 valve head. How the hell did you manage to get 500 valves in a Morini head?

I'll get my coat...
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Re: 500 valves in a 350 Head

Postby smotorboy » 25 Mar 2018 15:17

Hello Lads,

Here are photos of :

OEM valves within a stock 62mm bore

O/S exh valve and standard Intake valve in a 62mm bore

Notching the top edge of a cylinder bore in an attempt to "unshroud' the valve edge somewhat for better low lift flow...

Enjoy,

Robert in California

Dang !,,,,,, Sorry Boys ,, the board attachment quota has been reached
Attachments
OEM valves-s.jpg
OEM valves-s.jpg (102.27 KiB) Viewed 817 times
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Re: 500 valves in a 350 Head

Postby smotorboy » 26 Mar 2018 19:35

OS EXH Val.JPG
OS EXH Val.JPG (387.22 KiB) Viewed 767 times


notched-s.jpg
notched-s.jpg (60.83 KiB) Viewed 767 times
[attachment=1]
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Re: 500 valves in a 350 Head

Postby fastharry » 30 Mar 2018 08:19

Great info chaps. It would interesting to see where the gains are in the power band and flow figures, i have to weigh up if its worth the extra work and costs, for a usable gain, as i am usually in 3rd gear racing round 350 mtr speedway tracks, with short bursts of acceleration .
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Re: 500 valves in a 350 Head

Postby harrymuffin » 30 Mar 2018 19:00

I would be interested to know how the gas flow was assessed on the exhaust port. Was it assessed the same way as the inlet port is done with the head mounted on plate with a plenum chamber beneath and a vacuum created with manometers or equivalent or was it assessed by pressurising the head in the Morini case on top of a cylinder to a representative value in the range of 4 - 7 bar as would be the case in a live engine at the moment the exhaust valve opens? If the gas flow was reversed then the results would be different to the gas going out and under residual pressure. If the exhaust valve is increased in size the the gas speed would be lower effecting the pressure or vacuum in the cylinder and lessening the scavenging effect the escaping exhaust gasses induce on the incoming charge, which with heron heads, more so than with pent roof combustion chambers, is more sensitive. If supercharging then this would not be too much of a problem, as the supercharged gases entering the combustion chamber should have a scavenging effect, but with natural breathing then this could be detrimental, and unless you can create a pressure with volume of air and maintain it, in the combustion chamber on the test rig, then any results would be problematic.
A long time ago (70s), a tuner reckoned that bigger exhaust valve was the answer to cylinder filling and volumetric efficiency, back to back tests from standard did shew improvements on the dynamometer, but when compared to an engine fitted with bigger inlets was inferior for the effort involved. His improvements was explained because of any work dome on the inlet port at the time of modification. He was not heard of again.
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Re: 500 valves in a 350 Head

Postby smotorboy » 31 Mar 2018 15:08

Airflow thru the exhaust was done with the flow going in reverse of normal and flowing in the correct direction at a pressure equivalent of 28" of H2O....

Note: flow is much higher in the normal flow direction than in reverse due to all the "edges" in the flow path tripping the flow...Think the way singles on a roof keep water from going under then.

Measuring flow at normal cylinder operating pressure is only done in University and industry research labs as far as I know....

Flow bench testing give relative flow results as in that a "a" style port can flow more or less than a "b" style port.

My analysis of Morini valves and ports is that the "larger" than normal Intake valve and the "smaller" than normal exhaust valve were and are the best setup for the stock 350 engine series power levels.

Modified engines that create a lot more gas volume that has to pass thru the small exhaust valve/port in diminishing time intervals( as RPM gets higher and higher) have a problem .....

Usually, effort on the intake side yields more power gains than an equal effort on the exhaust side of flow improvement.

This maxim assumes that the ratio of intake valve size to the exhaust valve size falls in the 70% to 80% range....The Morini motor does not.....

Robert in California
Red Baron Race Team
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