Big valves, realy huge !

howardsmed

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This thread wont be of interest to many, but as I ( with my two other compatriots) have designed a set of valves for big racing engines, I thought I may as well tell everyone.
BIG engines, i.e. 840 and 880cc, start to run out of breath at high rpm even with the biggest easily obtainable valves out there. So I have designed a set of 45mm inlet valves ( +4mm oversize). They will be stainless steel, made by G&S as usual. will have 7mm stems which will require new collets and top collars. and new guides, however a well known USA bike manufacturer make parts i can use for very little £££ which is a massive bonus. We will also be using a Beehive valve spring set

will be ready for spring sometime
 
RD springs are far too heavy spring pressure for street use. The guy that owns Megacycle cams, Jim Dour, his wife brother owns RD, which is why they suggest using them. I had eight sets, I wouldn't buy another lot.

The springs that Rick sells I sourced from an American seller, they work well in our race bike, we don't bother with titanium top collars a complete waste of money. Our 750 revs to 8300rpm. They install at 85lbs seated and 180lbs on the nose, what cam are you using a 3.5 ?

Using all the "best " bits will not make the best engine, we use a lot of cheaper parts where expensive won't make any difference
 
That’s good to know, cheers Howard! I also have a set of the valves you designed.

I plan on using one of your billet steel cams in 250-30 profile.

Daniel.
 
Hi

We will get the new inlet valves cut in, then flow bench test the head, to ascertain what size increase ( if any) needs to be made. The velocity in an exhaust is much higher than the inlet, and its very hot and supersonic, so the parameters by which you measure cold gas speed are changed. My view has always been to change one thing, measure, assimilate, then assess what needs to be done. The cam we are using has an early opening figure which gives enormous blow-down, we might not need to change the exhaust at all. The camshaft we use is a dual pattern design, but not the traditional dual pattern type where the inlet has more timing than the exhaust, it is the other way around. All the high performance Harley and Buell engines have a similar design, as its harder to get the gas out than get it in. I took my design cue from this.

We are designing a short stroke 750 at present, with the big bore of the 880 and a short stroke which will allow the engine to rev safely to 10,000rpm. if we can achieve the target BMEP we want, there is the potential for 90+ hp rear wheel.

How's the drag racing going ?
 
Been struggling with 250 40 cam so I've given up gone back to my old cam of unknown make with inlet duration 266 exhaust 285, with 2mm over XV valves, for next year, only low lift compared to other cams but still seems to work well.
 
if the head stops flowing at say 0.440 lift ( stock head gives up at under 0.400) then having a cam with more lift wont make it run any better.
in an ideal situation, and one obviously that the manufacturers avail them selves off, the head flow matches the cam properly.

The cams duration (for a given lobe centre angle) will change the closing point of the inlet valve, which is THE most important part of the whole 4 stroke cycle
The later the inlet valve closes the higher up the rpm scale the power will be.
it is wholly possible to have this event occurring too late.
it is wholly possible to have too much CFM for a particular sized cylinder.
the trick ( which the manufacturers know well) is getting it all to work in harmony

is that 266 and 285 degrees at 1.00m lift with no tappet clearance ?

the + 2mm oversize XV valves work well, but when the seats are cut you must open up the seat ID to the correct %, if not you wont get any more flow ( or not much better)
 
They line bored the seat as well when they did it,

It's not a standard head even the chamber is perfectly smooth

Cam was measured as per megacycle
 
that is a lot of exhaust duration, the dual pattern cams in designed and used by Buell are usually 5-10 degrees more exhaust than inlet.

if those are really accurate figures you have a bit of a problem

the inlet lobe centre line is 111 degrees, whilst the exhaust is 97.5 degrees. for a total lobe separation of 104.25 degrees, the inlet is far too retarded, the most we run is 104 degrees. the later the inlet closes the higher the rpm at which the engine will want to try and make max power. However to do this everything must again be in harmony
from what we do and what Megacycle show as lobe centre figures I would suggest that you need to advance the inlet timing by around 7.25 degrees.
that would bring your inlet closing figure back to 58.75 degrees
The later inlet closing is bleeding off compression at all rpm.( well not 10.000 rpm )

the exhaust also needs to open earlier on a race engine, getting the timing right will give you more blow down and less sensitivity to the exhaust
the overlap is 67 degrees that alone is big figure, more than any of our race engines, and also more than my 1250 Buell

I think the cam maybe a Sig Erson grind
 
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Not sure what it is the only clue as to identity is a c and what looks like a partial j or maybe u next to it but very faint, then just what I assume is date stamps, whilst everything might be wrong with it, it does seem to work, though probably starts to run out of steam at around 8500 revs, as I've said before also has very rounded lobes compared to the 250 40 which has a very sharp opening and closing,
 
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Yes xs650 valves, theres someone in Germany selling new pattern ones on ebay at a very good price compared to other valves available
 
Smedspeed sell one piece stainless steel valves, they are specifically made to enhance the stock port size. On OEM seat cuts the seat diameter to seat ID ratio is a bit high. the valve address this problem by being +1mm inlet and from memory +0.8mm exhaust.
made in the UK by G&S valves
 
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Not sure what it is the only clue as to identity is a c and what looks like a partial j or maybe u next to it but very faint, then just what I assume is date stamps, whilst everything might be wrong with it, it does seem to work, though probably starts to run out of steam at around 8500 revs, as I've said before also has very rounded lobes compared to the 250 40 which has a very sharp opening and closing,

We ran a megacycle 40, in fact the same I copied digitally from your profile. it produced no more power or torque than our existing race cam, and the valve spring pressure has to be much higher to cope with the wild ramps. That does not mean its not a good cam, it just didn't work for us.
As a general rule, use the mildest cam that will get the job done, just like carburettors too, use the smallest that will do what you expect, the only exception is compression, use a lot !!!
 
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