8 valve head conversion
- Thread starter lcgtr
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This was discussed here just recently. Can't remember the thread title though.
Was mentioned that Norvil is still selling off 8 valve pistons - only for one side though (they are not symmetrical ?).
The performance gain in a longstroke pushrod engine with a low rev limit is not going to be startling, however ?? And designing out the strong low rev torque of a Commando engine is not going to win too many friends either ?
Was mentioned that Norvil is still selling off 8 valve pistons - only for one side though (they are not symmetrical ?).
The performance gain in a longstroke pushrod engine with a low rev limit is not going to be startling, however ?? And designing out the strong low rev torque of a Commando engine is not going to win too many friends either ?
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lcgtr said:
You should probably chat with comnoz and fullauto about just how easy it is...
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without overhead cams to suit,this would be pointless, infact allmost 30's design...Rudge :?:lcgtr said:
swooshdave said:
Hahahahahahaha.
Thanks, I needed a good laugh. I might get my money back one day. However, I did go for best quality so I suppose somebody could go to China, have them design something made out of coke cans that sort of looked like a Norton head, almost fitted after extensive modification and didn't work all that well but hey, it'd be cheap.
Seriously, the Norton head design is pretty good. Narrow (ish) valve angles, flat top pistons and great porting (in Fullauto heads anyway, thanks Jim) and there would be absolutely no advantage in going to four valves. Compared to the domed pistons and wide valve angles of the Triumph twins, it's no wonder that Commandos chew them up and spit them out power and torque wise. It's interesting that Kenny Cummings uses standard valve sizes and is making excellent power compared to other much modified heads out there. Any modification that moves the power up the rev range on a Commando is an absolute waste (in my opinion) for a road bike. The beauty of the Commando is the way it makes power from virtually no revs, especially with a Fullauto Technologies head. The ports in my heads were developed over many years by Jim Comstock and I got the design dirt cheap, which i shall try to rectify by giving Jim stuff in the future. Like, he's getting a couple of raw head castings from the next batch to see what he can do with them.
Talk about cheap development costs. For me anyway. Thanks Jim! The Weslake/Nourish 8 valve conversions available for Triumph twins have never set the world on fire and I've never heard of any great claims as to their worth, just the ads to say they are available. And they should provide a much better power boost than a similar conversion to a Norton. I'm no expert on the matter but I've always been under the impression that the less ignition advance you have to run, then the more efficient the combustion chamber design. Compare the Norton head to some pretty fancy runners and you may get a surprise.
Someone correct me if I'm wrong. Please.
Talk about cheap development costs. For me anyway. Thanks Jim! The Weslake/Nourish 8 valve conversions available for Triumph twins have never set the world on fire and I've never heard of any great claims as to their worth, just the ads to say they are available. And they should provide a much better power boost than a similar conversion to a Norton. I'm no expert on the matter but I've always been under the impression that the less ignition advance you have to run, then the more efficient the combustion chamber design. Compare the Norton head to some pretty fancy runners and you may get a surprise.
Someone correct me if I'm wrong. Please.
The 4 valve head was developed by Piper Engineering in the UK. It didn't make any more power than a stock motor and when the project was shelved, Les Emery and Pete Lovell had another look at it. Turned out the valve springs where far too strong and absorbing too much power and stressing the valve train. Anyway, Lovell managed to get it to work in the end but the killer is - it looks bloody awful! Imagine a finned bread box with a square tin cap.
If you want a go fast head then get a Full Auto or see Steve Maney.
Mick
If you want a go fast head then get a Full Auto or see Steve Maney.
Mick
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lcgtr said:
Twin spark would have nothing to do with modern sparkplugs. The benefit of twin spark is seen in large bore engine where the flame front has a long way to travel. In a small bore engine such as a Norton the benefit would be very small. The Norton chamber has very good burn characteristics as can be seen by the small amount of spark advance needed.
However I do recall reading of someone who has tried it on a Norton. It would be a difficult task given the poor access to the inside half of the chamber. Jim
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Yes sir, generally seems so, BUT and I mean it in capitols, I lost a bunch of Norton ego to Tim's Turnip that so blazed past the Nortons, Kenny included - Kennny did not even mention it = because it so out classed the rest of the field I can only assume its head mods made it a whole nother class that the best Nortons couldn't touch to compete against. I quizzed forum some seasons ago on this but no one offered a reason for such advantage over the good Norton head flow.
A good 2 valve head that creates swirl more than tumbles mix as most 4 valves do can out power 4 valves on same engine in the rpm levels it can flow similar to 4 valve. A staggered intake opening, or different size intakes 4 valve can match or beat 2 valve even off idle. Smaller port size helps the speed of intake filling.
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hobot said:
I'm sure Tim would love to log back in here and tell us all about his secrets. Are you sure that wasn't before Kenny had his new toys (Full Auto and Jim's stuff)?
Not only that but have a look at the mods to the Triumph. They're listed somewhere. Extensive and expensive. Hear what Kenny says about his motor. There's nothing special about it. Anyone can go out, buy the bits and pieces and get Jim to put the motor together and away you go.
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Tim left the field behind 1/10-1/4 mile by 3rd or 4th turn with Kenny and two others neck and neck fender to fender down the longest straight, with Kenny lossing a placer d'/t the common missed shift set back, in Oct, 2010 at Barbers, which is last race of the season, so I think Kenny had Jim pistons and lower crank
BF, so likely Fullauto head also by then.
A tiny hi velocity flow can't make as much power as more total flow even if slower flowing. This is what I've gleaned from the head posts on Fullauto so far, great up to the maxed out rpm, which is not what matters in turns or in public use.
If someone knows what was so different in Tim's top end, please educate me.
I've had details expanded of what is wrong with Turnip factory heads, but not what's possible to work around and still look like factory outside.
BF, so likely Fullauto head also by then.
A tiny hi velocity flow can't make as much power as more total flow even if slower flowing. This is what I've gleaned from the head posts on Fullauto so far, great up to the maxed out rpm, which is not what matters in turns or in public use.
If someone knows what was so different in Tim's top end, please educate me.
I've had details expanded of what is wrong with Turnip factory heads, but not what's possible to work around and still look like factory outside.
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If someone knows what was so different in Tim's top end, please educate me.
I already did. You didn't pay any attention. It is called engine development.
Small high velocity ports can make more power than big ports- even at high rpm's. Especially on an undersquare engine.
Better check up on modern engine design. Jim
I already did. You didn't pay any attention. It is called engine development.
Small high velocity ports can make more power than big ports- even at high rpm's. Especially on an undersquare engine.
Better check up on modern engine design. Jim
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