Making the Commando faster

acotrel · Apr 4, 2014

I've been wondering if anyone has made a four valve head for a commando ?
What does this mean ? :

http://www.xplorer.co.za/articles/bmep.htm

http://hpwizard.com/bmep.html

myjota · Apr 4, 2014

Classic bike mag june 1988 had an article about norvil 8 valve head.

pete.v · Apr 4, 2014

Aren't they dangerous enough?

brxpb · Apr 4, 2014

Do you mean 8 valve, I've already got a 4 valve head :roll:, I seem to remember adverts for 8v heads in the UK in the late 80's early 90's, I can't remember who made them but if my minds eye still serves me correct they were ugly as hell.

Hobot · Apr 4, 2014

Westlake Norton heads were called 8 valves though they made 4 valve per jug for many engines. Otherwise simple as rocket science to take off mass while adding more thrust on a biplane like craft.

john robert bould · Apr 5, 2014

Nitro?

Chris · Apr 5, 2014

Hi Acrotel

If you do a search on this site you will find details of the Piper head that was stillborn. Pete Lovell developed it in the 80s & it seemed to be good. However not good enough for people to cough up the money for? Les (fairspares) recons they were for sale but I am not sure if any were sold.

Chris

Reggie · Apr 5, 2014

An article was posted here about Norvils 8 valve head by Ken (Icrken). Scroll down to the second article.

valve-head-conversion-t9137-45.html

Hobot · Apr 5, 2014

I've got one in the works that could run on methanol and nitromethane with boost but only in special events through I'd have to try it out in public. Comnoz has one in the works that may be turbocharged which can make higher boost than a Drouin if he wanted to for street use. Stripping mass off sure helps the acceleration up to some speed though vintage craft are straight line tire traction limited or then wheelie limited too. The most powerful Norton engines to date were the essentially stock ones in TC Hogslayer on nitro ~150 hp each w/o boost, though the Gulf Norton ones might be close.

Matt Spencer · Apr 19, 2014

" 've been wondering if anyone has made a four valve head for a commando ? " NO , But . . .

COSWORTH ( Manufactured ) WRX Sabaru cyl head , :lol: its a start ? ? maybe 86 x 86 or 84 x 90 or 85 x 65.8 if its a 1500 ( halfs 750 of course ) others are 2l or 1L if ' We ' bufricate them , and make one or two bits . :lol: :cry:

http://www.ebay.com/itm/SUBARU-IMPREZA- ... 1339314841 appears the exhausts there arnt symetrical , though intake might be something like that .

lcrken · Apr 19, 2014

Matt Spencer said:
" 've been wondering if anyone has made a four valve head for a commando ? " NO , But . . .

COSWORTH ( Manufactured ) WRX Sabaru cyl head , :lol: its a start ? ? maybe 86 x 86 or 84 x 90 or 85 x 65.8 if its a 1500 ( halfs 750 of course ) others are 2l or 1L if ' We ' bufricate them , and make one or two bits . :lol: :cry:

http://www.ebay.com/itm/SUBARU-IMPREZA- ... 1339314841 appears the exhausts there arnt symetrical , though intake might be something like that .

But where are the pushrods?

Ken

phil yates · Apr 19, 2014

pete.v said:
Aren't they dangerous enough?

With you on one?
"Bloody deadly" would be a better description!!

Hobot · Apr 19, 2014

Duh Ken what do ya think the spaces around the chamber wall are for.

There is another type of cam drive besides chains and gears, a small gear driven crank shaft deep inside engine that pumps the push rods connected to it in pairs like a bicycler's legs to turn the over head cam like another crankshaft. Playing one of Kenny Cummings dyno runs would be appropriate here but darn it its tough on my nerves to be around a topping out Norton engine, ugh.

Matt Spencer · Apr 20, 2014

" But where are the pushrods "

Id think someone could get out the disc grinder :shock: carve of most of it leaving the deck & skull ,
knock up some fins , and weld on starting from the bottom up . So No Trouble :lol: to chuck a few pillars on to pick up rocker shafts .

But Id think 4 valveing it pretty much a pointless exercise . Maybe intresting to do a comparison to vavle circumferance area when open though . :?

could be worthwhile on a 10.000 rpm 500 , if you had to much time on youre hands .

Matt Spencer · Apr 20, 2014

Bad Penny , Ive Foundit Ive Foundit .

acotrel · Apr 20, 2014

I would have thought a 4 valve head was only necessary for a short stroke high revving motor. However Jawa speedway motors are all 4 valve these days, and when they first did it in the 70s there was about a 10% gain in power. A friend of mine had a Rickman 650 Triumph racer with the Weslake head, and he said he didn't get much gain over the standard Bonneville head. I would have though that if his 650 was turning out 55 BHP, he would have felt an extra 5 BHP.
Thanks for the pic of the Subaru head Matt, it is food for thought. It might be possible to build a water cooled commando motor with a chain or belt up the side. I wonder what the spacing is on the two combustion chambers ?

Hobot · Apr 20, 2014

Reading this Woods article left by archivist Matt Spencer inspired me to plug in the P!! data in online hp vs E.T. calculators.
http://i184.photobucket.com/albums/x93/ ... 3155b6.jpg

P!! ~250 lb, race pilot 167 lb. I was 15 lb lighter but w/o a flat drag slick so smoking habit made me slower. Seller told me its history and best time.
http://www.wallaceracing.com/et-hp-mph.php
HP is 82.42 computed from your vehicle weight of 417 pounds and ET of 10,49 seconds.

Nater_Potater · Apr 20, 2014

acotrel said:
I would have thought a 4 valve head was only necessary for a short stroke high revving motor.

I think that's the usual assumption, since they're normally optimized to take advantage of the inherent high-flow capabilities afforded by the four-valve design. But, just like a two-stroke, that doesn't have to be the case. One of the numerous cool things that a four-valve allows is the ability to have much more aggressive opening and closing ramps on the cam lobes. This can make the valve action much more "digital" like, since the valves are much lighter, and, in doing so, spend more time fully open. If you combine that with a "milder" cam duration, you get better low- and mid-range without compromising top-end horsepower, since the two valves can flow more air than a single valve, and spend more time in the open position for a given cam duration.
I had an '84 Yamaha YZ550 that would pull high gear around town @1500 rpm, and wind clear out to 10,000 rpm at over 100 mph. Trust me; no exaggeration!
I'd add a picture, but wouldn't want to soil these hallowed pages with a Nipper bike.

Nathan

davamb · Apr 20, 2014

I seem to recall some Bentleys having 4-valve heads and they certainly weren't high-revving motors.

Hobot · Apr 20, 2014

2V once had some advantage in lower rpm for a time d/t swirling in a hemi thickened TDC charge instead of 4v tumble stopping with flattened roof until 4V began staggering openings &/or different size valves. Laser sintered metal printing pretty matured now so anything possible if starting from scratch. Otherwise just have to make do with two.

Making the Commando faster

acotrel

myjota

pete.v

brxpb

Hobot

john robert bould

Chris

Reggie

Hobot

Matt Spencer

lcrken

phil yates

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Nater_Potater

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