commando camshafts

acotrel · Sep 4, 2012

I haven't yet seen anyone on this forum claim they've had success with a 2 into 1 exhaust ? Many years ago I fitted one to my triumph to get a bit of sanity into the proceedings, and I finally started to get decent lap times. I'd lost 1500 revs off the top of the range, but at least it gave some mid-range power, and stopped going sideways if it dropped off the cam in a corner, and I slipped the clutch to ge t it pulling again. I found I had to cut the collector until there was absolutely no restriction. Then the bike regained most of it's top end. With my Seeley, I use a tail pie with a crossectional area the same as the two header pipe. The motor spins up extremely quickly, and I'm sure that it is still undergeared. First gear is the limitting factor with the old gearbox. If I increase the overall gearing, it staggers off the start, and needs massive clutch slip.
The timings I am using result from advancing the standard cam 15 degrees :
Inlet opens 65 btdc
inlet closes 59 abdc
exhaust opens 97 bbdc
exhaust closes 27 atdc

I believe I would achieve the same inlet open and exhast open by advancing the combat cam 6 degrees, and the timings would be longer, and the overlap bigger. I found years ago that it is better to keep the exhaust opening later than 85 bbdc, or the noise usually gets louder and the bike goes slower. With the back pressure the early exhaust opening doesn't seem to matter. The 2 into one pipe changes the physics considerably, and I am still wondering if anyone has really conquered them. I find it difficult to play with this - on a triumph you have separate cams for inlet and exhaust - it is a bit easier.

pete.v · Sep 4, 2012

Here's one for ya.

http://www.ebay.com/itm/0611-069576-6S- ... ts&vxp=mtr

Bernhard · Sep 5, 2012

acotrel said:
I haven't yet seen anyone on this forum claim they've had success with a 2 into 1 exhaust ? Many years ago I fitted one to my triumph to get a bit of sanity into the proceedings, and I finally started to get decent lap times. I'd lost 1500 revs off the top of the range, but at least it gave some mid-range power, and stopped going sideways if it dropped off the cam in a corner, and I slipped the clutch to ge t it pulling again. I found I had to cut the collector until there was absolutely no restriction. Then the bike regained most of it's top end. With my Seeley, I use a tail pie with a crossectional area the same as the two header pipe. The motor spins up extremely quickly, and I'm sure that it is still undergeared. First gear is the limitting factor with the old gearbox. If I increase the overall gearing, it staggers off the start, and needs massive clutch slip.
The timings I am using result from advancing the standard cam 15 degrees :

re; "First gear is the limitting factor with the old gearbox. If I increase the overall gearing, it staggers off the start, and needs massive clutch slip."

You might want to try a semi close ratio gearbox, you can convert a standard g/box just by changing, I think, three gearbox cogs.
Oh, silly me I have reread this and I am referring to a Norton gearbox, so, if you have a Triumph……………………

comnoz · Sep 5, 2012

I have had to advance the cam with some 2 into 1 exhausts to get them to work but I don't think that is the best way to make them work. No proof- but I think it is only covering up a bad match. 2 into 1 systems still don't make much sense to me and I have trouble tuning them.

I will have to say that Kenny Cummings bike is now making real power with a Maney 2 into 1 and straight up cam timing. I suspect part of the reason it is working so well is the large anti-reversion ledge in the exhaust port. Jim

acotrel · Sep 5, 2012

What is an 'anti-reversion wedge' ? I'm amazed that mine worls as well as it does. Old Australian saying ' arse beats class', or I will interpret for you guys - 'ass beats class' !

lcrken · Sep 5, 2012

Some years back I switched from a twin megaphone system on my featherbed/Commando racer to a Maney 2-into-1. I'd quit racing myself by then, but both the riders I had at the time said it gave noticeably more drive out of the corners, and they preferred it for most of the tracks. I never dynoed it with that pipe, but I'm pretty sure it makes a little less top end than the megas. But on most tracks the better mid-range is more valuable than a few hp at redline. For Daytona, I'd probably go back to the twin megas. I used an Axtell cam timed to it's normal spec.

It did have a bit of anti-reversion effect, because the exhaust ports were smaller than the inside diameter of the 1.625" pipes I use. Maybe, as Jim speculated, that could play a part.

Ken

comnoz · Sep 5, 2012

acotrel said:
What is an 'anti-reversion wedge' ? I'm amazed that mine worls as well as it does. Old Australian saying ' arse beats class', or I will interpret for you guys - 'ass beats class' !

The antireversion ledge refers to the fact that the exhaust port floor is 7mm higher than the bottom of the pipe. It stops the slower moving gas that clings to the floor of the pipe from affecting the mixture at overlap. Jim

acotrel · Sep 5, 2012

Where did that bit of technology come from ? Is it used on racing cars with extractors ?

comnoz · Sep 5, 2012

acotrel said:
Where did that bit of technology come from ? Is it used on racing cars with extractors ?

It is used on cars and bikes both. Not too sure where the idea came from but Mondello used to promote the idea when I was going to classes there in the late 70's.

I do know it works wonders if you have an engine with megaphones that will not pull through the midrange. Jim

Hobot · Sep 5, 2012

Ok so how big a deal is it to do this ant-reverstion D shape port mod on a Combat CHO head? If'n it was a Harley we could just stick in anti-reversion cones.

comnoz · Sep 5, 2012

hobot said:
Ok so how big a deal is it to do this ant-reverstion D shape port mod on a Combat CHO head? If'n it was a Harley we could just stick in anti-reversion cones.

I used to do them with a cast aluminum shoe that I bolted to the bottom of the port. I have quit doing them now that the Fullauto head is available. It is built in.

It required many hours to fit the inserts. Too many hours at the porting bench was turning me into a hunchback. Jim

J.A.W. · Sep 5, 2012

Anyone ever seen a Norton cam that is splined together & so allows changes to relative in/ex timing events?

Matt Spencer · Sep 5, 2012

The Dreaded term " TWO STAGE Cam " doesnt seem to appear ? the olde ' comes on at X rpm ' effect Vs ' seamless from zero revs .

Tri Y headers ( pipes ) are typical Rally type , good midrange / tourque availability / throttle reponce . As per the 2 into 1 , or siamesed .

4 into 1 ( bear with it ) or FULL LENGTH headers , tend to enhance the output at maximum / upper rpm's .IF suited here , the responce in the lower rpm range may be abscent .

Generally the more volume in a Ex. system , the less the restriction , or the better the silenceing per flow capeability .

The nasty little narrow pipes get the mid range responce and drive out of the corners and save reving it like snot and demanding intense concentration like a H2 ring ding .

comnoz · Sep 5, 2012

J.A.W. said:
Anyone ever seen a Norton cam that is splined together & so allows changes to relative in/ex timing events?

I have heard that some were built but I have never seen one. I have seen pictures of one for a Yamaha. Jim

worntorn · Sep 5, 2012

acotrel said:
Where did that bit of technology come from ? Is it used on racing cars with extractors ?

Pontiac first used it on their very successful 6cylinder stock car race engines in the early 50s.
It was used here and there over the years but mostly forgotten about. Very recently the latest version of the high performance GM LS engine, now at the LS9, has gone to a D exhuast port.

My Terry Prince Vincent race heads for the 1360 motor use a D exhaust port. Ill see if I can find a photo and post it.

Glen

SteveA · Sep 6, 2012

Alan,

Steve Maney has sold a huge number of his 2 into 1s and most who have them seem to reckon they are the best they have used!

It is the most popular exhaust on Nortons racing in the UK! He is often out of stock an dsays it is his most popular line, even if it aint the cheapest thing out there and needs you to carve huge lumps out of your fairing! They do work.

SteveA · Sep 6, 2012

comnoz said:
SteveA said:

comnoz said:

There is absolutely nothing wrong with the stock grind cam. It is well suited for the RPM range of a Norton longstroke motor. Many roadraces have been won with the stock grind cam.

I would be willing to bet that more performance cam installations end up loosing power under the curve than gain it. [power under the curve is what you want for roadrace or street- well maybe not at Daytona] Jim

Click to expand...

JIm, I was not criticising the stock cam, I rode a season using one, in a stock 750 fastback and I reckon it was a good start package. My logical progression to an ex Thruxton cam came with the package I bought. More recently I have ridden with a PW cam and liked that an dthink it was balanced to rest of the engine too.

Could not agree more that cam alone does not give the return some expect but surely at some stage you need to move it on? When do you feel that comes?

Click to expand...

The first consideration in going to a cam with more timing is the fact that it will narrow the powerband. You can certainly make more power with a race cam in a narrow RPM range but to take advantage of the power you will need closer transmission ratios. You also have to consider how a narrower powerband is going to affect your launch if you have a tall first gear.

You will also need a considerable increase in compression ratio to go with the PW3 cam.

If you have those two covered you would be in good shape but you may be better off to spend the money on the head instead of the cam and gearbox. A bit of port work with oversized intake valves will net a larger power gain without narrowing the powerband. Jim

Jim, I am building a short stroke, initially with a stock head (hopefully Fullauto later), but I need to get the bike running rather than delaying a couple more years to save for all the best bits and end up being to old to ride it! Anyhow, I am considering PW3 or JS's similar grind with his lightweight valve train. bear in mund that today I have no cam, and new ones are all similarly priced, and I expect this motor to rev hard.

The issue will be getting enough compression. Personally I don't want to go too high and I want to run pump fuel, UK 99RON. I have JS 77mm high comp flat top pistons an short stroke long rods. I reckon I will need to skim the head as well toget enough compression in a short stroke.

Initially there will be very little port work, just enough to make standard size valves work better, no real sense investing too much in first build when I hope for a Fullauto later. Exhaust may be Maney or similar, but I always prefered a separate pipe set up way back when so we will see. What would be 'enough' compression?

As for gearbox, short term I don't have enough funds for a TTi 6 speed, or the UK import tax! for one. Cheapest box for me would be a 4 speed close ratio made into an old case I have, one of these worked well enough with my high output 850 way back when, but that was push starts and the Quaife 5 speeds about were the same ratio 2 to 4 as my 1 to 4, and back then somebody broke a Quaife box at every race I went to whilst my 4 speed just worked.

So I could end up with close ratio 4 speed behind a short stroke, at least to start with. I know that is not ideal, but of course to start with I ain't going to be coming off the front row, so losing a little at the start or giving the clutch a hard time won't worry me that much.

comnoz · Sep 6, 2012

Pump gas will be the limiting factor. I am not real sure how your fuel compares to what is available over here but I would think 10-1 will be about the limit. With race fuel I would go 10.5 or 11 to 1. Jim

SteveA · Sep 6, 2012

comnoz said:
Pump gas will be the limiting factor. I am not real sure how your fuel compares to what is available over here but I would think 10-1 will be about the limit. With race fuel I would go 10.5 or 11 to 1. Jim

Up to 10.5 was what I was looking for, so fits well for me. Our gas is OK for that, especially if you seek out certain brands. My 850 ran between 10.25 and 10.5 in the '70s and I could push start it, some ran as high as 11 then, today a lot of guys here are running higher compression, but dosing with Avgas.

I think most likely first build is mild porting on stock head, standard valves, 10.25 to 10.5 compression, JS 1st stage cam and valve train and see where we go.

That gearbox is still a conundrum. Budget says 4 speed, but logic says minimum 5 speed with Short Stroke.....fit and forget says TTi 6 Speed.....

acotrel · Sep 6, 2012

Steve,
I think I have been silly with my old 4 speed CR box. I never really got my head around the gearing difficulties. If I'd used a standard commando first gear and slghtly increased the overall gearing, the 'stagger' would have moved up towards second gear, and I probably would never have felt it. Once the bike is mobile, even a high second gear would be the lowest gear I would use. The 4 speed box was always OK, but getting good starts was always a problem. I've only ever raced it against the really good guys three times. I got one good start and was under them on turn two at Winton when I popped a fuel line, and stopped. However it demonstrated the potential of my bike to me, so I will have another go at them next year with the 6 speeder. I am too old to do the antics required to make up 150 yards lost at the start to a gaggle of 1100cc CB750 Hondas. These days, I want a nice quick start, and the rest is then normal quick road racing - easy.
Back in the days when I was racing my Triumph, it was always push starts, and I always blitzed them off the start. The rest was much harder , they always got past me down the longer straights. The reality is that I couldn't start a race that way these day so the clutch start is better, but it gives the gearing problem. If you end up with a second gear which is too high, it simply means you roll a bit further in the slowest corners. If you need power to steer the bike, it could be present a difficulty.

commando camshafts

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