PW3 Cam timing

Status
Not open for further replies.
It is very interesting reading about the cam timings. I have done a lot of fiddling with Triumphs with different cams. I have made alterations and felt the differences they made.

What I would like to know is if the PW 3 cam will produce more power(at higher engine speeds) than the standard cams in an engine with only 8.5 or 9 to 1 pistons? Is it suitable for this use. My friend has a 750 with a PW3 cam and 9:1 pistons. It doesn't seem to be any faster than my 850, which is pretty much standard except it has only a single 38 mm carb which should make it slower. I always thought the reason his bike was slow was because the PW3 was really meant to go with 10 or 10.5 :1 pistons.

Do you think my friend has his cam timing wrong? If his bike should be faster we could just look down the exhaust port with the pistons at TDC to see if he has the timing in the right ballpark. Maybe we will be able to see that his exhaust is open more than the intake and so he just needs to make some adjustments.

It may be also a problem of fuel flow. I know he has huge main jets. It may be the the float needles are not passing enough gas to keep up at the higher speeds.
 
tricatcent said:
It may be also a problem of fuel flow. I know he has huge main jets. It may be the the float needles are not passing enough gas to keep up at the higher speeds.

If his fuel taps are acting as main jets, he should be able to feel it when he opens the throttle at higher rpms - nothing much would happen, acceleration wise.
If ride like that too much, the motor could well get hot and start to melt pistons, so not a good idea...
 
By installing an aggressive cam with a static ratio at 9:1 whose intake closes at 56 degrees after bottom dead center, the corrected compression ratio declines to 7.6:1. This corrected compression ratio barely has enough compression to light the load, much less do it in an efficient manner. A motorcycle with a low corrected compression ratio like this would likely not even be able to pull 5th gear. Not only that but, in 5th, this bike wouldn’t accelerate, nor could it maintain its speed. In addition, the bike would continue to slow until it began to misfire and experience other running abnormalities.
more
http://www.hildrethperformance.com/arti ... ssion.html

http://www.badasscars.com/index.cfm/pag ... /prd68.htm
 
tricatcent, I agree with some of your points. The 38mm carb would be a draw back unless is was a flatside type which has been shown to many that they have better metering and atomization characteristics than round slide types.

gripper says "I'm running standard CR with a +0.020" re-bore Hepolite (Taiwanese) pistons and pea-shooter exhaust"
The +0.020 rebore won't matter much and the peashooters are relative and may or may not be optimal, but the standard CR? I think that is a real issue.

It is rather common knowledge that the 2s will not live to it's design without raised compression. I think that slapping a PW3 in a stock motor without a supporting cast of enhancement is just going to sit there and sleep unless awakened by a 10 to 1 compression ratio to start with. Boosting the carbs to feed the demand is the other real thing to consider.

I do not know what pistons to use other than stock, which was the norm for all combats, but some head work should seriously be considered, at least shave .040 off the head and set the cylinders to the deck. I feel this above all will have the most effect on the PW3. You can also get a .021 head gasket from JS. This will give you a 1/2 point or so.

I think that putting in this great cam into a stock setup and not doing anything else will make any efforts toward cam timing a moot point.
 
acotrel said:
My only way of knowing whether a change has been beneficial, is by riding the bike and noting its acceleration out of corners, and whether it is easier and faster to ride. As you say - 'seat of the pants', however it is the moment of truth. Rationalising gearing for the commando, I find problematic.

Acotrel, I didn't intend to knock 'seat of the pants" testing. It's not uncommon for a particular setup to make really good top end horsepower, but be a pita to ride. I like dyno testing because it gives you precise, repeatable, quantifiable information about the effect of modifications. At the end of the day, you still have to be able to ride the bike. I've chosen setups with less top end power for my race bikes if they give better results. A good example of that is exhaust systems. Two separate pipes of the right dimensions will make the maximum top end power, but might not give the quickest lap times. For years I used a standard Axtell exhaust design with two pipes and megas, because it made the best top end power and a reasonable power band. After I became friends with Steve Maney, I tried his unequal length 2-into-1 high exhaust on my featherbed/Commando race bike. I was no longer riding the bike by then, but my friends who were racing it preferred it over the megas everywhere except the really long tracks, like Daytona. They thought the increased mid-range drive more than made up for some top end loss. We won a lot of AHRMA races with that setup. A good case for 'seat-of-the-pants" testing.

Ken
 
" IThe only thing I can think of is that because the exhaust lift is as high as the inlet lift, is that it lets a lot more gas out keeping the compression down."
" Hence the need to advance. "

for the pulase scavengeing / ramchargeing , the ex closeing time can become critical . like everything else . :lol: :lol: :lol:

However , with the correct head set up ( mine was a accidental combination , not as requested BUT conforming to a few
theorys then current , for maximiseing Charge Density ) The Measured C.R. was 8.7 : 1 .
The effective ratio , Chamber Filling taken into account , in comparison to a ' non pulse effect ' engine ,
would be significantly higher .

Significant too was / is the unobstructed intake / manifolds . With coustom carb - head intakes for ther Mk IIs .
Where the change in contour / radius is continuous & progressive .

Haveing the bottom / floor a significant differance in length to the top / ceiling , as per std. cast manifolds isnt a recipie
for uninterupted / unobstructed charge progress .
 
You can see on this picture here , these ones arnt kinky . :P

PW3 Cam timing


also the fact that Jet / valve head dimension ( as well as valve / throat Dimn. )
can have significant effects in combination with said scavengeing / intake pulses .

Stright Through Mufflers can also be essential for ' Race Spec ' opperation .
Yes Sir . Perfectly Stock . They made them this way . All Factory Parts . ! :D
 
Years ago I went through an exercise of changing exhaust valve liming, and changing the exhaust pipe on my short stroke Triumph. I found that opening the exhaust valve before 85 BBDC, the bike was louder and went slower. Also using any sort of megaphone on it except in combination with a two into one pipe, made it impossible to ride fast. The two into one pipe knocked 1500 RPM off the top (max power down to 9,500 RPM), however I got much better lap times due to the improved mid-range. The tail pipe diameter of the two into one was critical, any back pressure really slowed the bike. With this PW3 cam, I'd be checking the exhaust valve opening point, to see if it looked reasonable. If the motor has become louder and slower, there is a reason for it.
 
Interesting report Alan, Ms Peel was just so so with 2-1-mega with all the plates of a supertrap in so very heavy on end of muffler, that put just cover plate on after blowing almost 2" hole in it by shot gun, oh LALA, purple orange jets of flame would shoot out over a foot after that and I was able to develop hobby telling sports ridders I'd tag along till bored. In my meger experience on a few types of engines not much happened good with many major changes until tweaking this or that a little bit then suddenly wowee wonderful.
 
You might believe that the profile of the exhaust cam is relatively unimportant. The 1959 Bonneville triumph used an E3134 Race cam on the inlet, and the E3275 Tiger 110 cam on the exhaust. It was possible to use the race cams on both inlet and exhaust, and the bike would become a blur. The unit construction 650s used the T110 profile ehaust, but because it had the extension for the points, it was not possible to substitute an E3134. There was a cam available which had the same profile, but a different part number. When we were kids , we imported that cam and used it in a 1963 Bonneville with really great results. In later years Triumph used BSA profile cams in their 750s, and my mate has used them in racing his 650 Triton. He recently decided to go back to using two E3134 race cams. The commando engine doesn't present the opportunity to easily make those sorts of changes to the cam timing, however I've often wondered what the big Nourish Weslake engine would be like to race. The Commando engine is great even with the limitations on changing cam timings.
 
'After I became friends with Steve Maney, I tried his unequal length 2-into-1 high exhaust on my featherbed/Commando race bike. I was no longer riding the bike by then, but my friends who were racing it preferred it over the megas everywhere except the really long tracks, like Daytona. They thought the increased mid-range drive more than made up for some top end loss. We won a lot of AHRMA races with that setup. A good case for 'seat-of-the-pants" testing.'

I love this comment. When I think of riding my bike, even at Phillip Island, I get a sinking feeling. If it did a big number on itself two thirds of the way down the main straight ...OOPS ! Daytona ? - the mind boggles. The infield might require some ridability, however I think the rest would be all top end, and I wouldn't like to go there with a commando engine. I know what is inside it.
 
Rohan, About metering your mixture using the fuel taps. The fuel taps are immensely bigger than the main jets. The way to get any bike going fast is to get the carburation as lean as possible everywhere. Just before the motor destroys itself, is the fastest the bike will ever go with its current mechanical configuration. In tuning two strokes, it is normal to lean off and keep the black ring on the porcelain, down inside the plugs. The fast guys go way beyond that. Four strokes respond in the same way, however if you take note of how often you ride for long distances on full throttle, you will find that the needle and needle jet setting are usually more important than the size of the mains. If the mains are too big the bike can be minimally slower. If they are too lean you will start burning things in the head. One thing that people don't realise about using methanol in two strokes is that the main jet is sometimes required to be the same size as the needle jet. Then the metering is on the tip of the needle, and fitting bigger mains has no effect. The answer is to recess the needle jet, so that the tip of the needle is in the recess at full throttle. (Then the metering point at 3/4 throttle is at a different height). Doing this stuff with a two stroke can get very expensive, very quickly. With a four stroke, it is not so bad - if the motor coughs you know it is too lean, with a two stroke, it can cough a crankshaft , detonate, burn pistons and seize immediately.
 
The generally recommended way to (safely !) tune a bike is to get the jets too big, and then work down until it runs right.
Burning or blowing up motors in the process is the idiots way of doing it ?

Blocked or partially blocked fuel taps quite commonly function as the main jet size.
Not recommended. !
Alcohol burners and folks who suddenly turn the wicks up beware.
Always use 2 taps if you think the fuel flow may be inadequate, until you get home and clean em out...
 
I 2 second Rohan wisdom on possible leaness on full buggey after a time. I ran into boggy downy climbing Mt's WOT with only one tap open on Peel. There is an Amal mod to cut slot in side of float needle passage for direct flow to the bowl w/o restriction at top exit pass needle. BSA found this one out. BSA shows up in a lot of speed development and part tolerance like crank BF but just don't get much credit.
 
Rohan, the first thing anybody should do when tuning a bike is to check the fuel flow to the bowl, and make sure the tank breather is clear. Alcohol kitted carburettors usually have very big needle and seat assemblies. What flows through that must be much geater than the main jet ever flows. I say t o you again, the fastest your bike will ever go without modifying the mechanics is when carburation is at the point when the motor is minimally away from selfdestruction. With my brother's alcohol fuelled H2 and H1 Kawasakis, he has to be extremely careful when he tries to get more speed by leaning off the mixture. Lowering the needles one notch in the carbs gives instant disaster. The other thing that is interesting is that with t he H2, it popped a plug lead out, and cracked a head. However the thing is that to win races consistently those bikes must be run that lean. With my own 850 commando motor, I ordered two 34mm MK2 Amals with the alcohol kit. When it arrived it had X needles, and 0.120 inch needle jets and the mains were about 800 Amal. I immediately changed those three things. I made two new needle jets from brass hex at 0.117 inch using number drills, and fitted two 6DP6 mikuni petrol needles , and also 670 Amal mains. I know from experience what is needed for alcohol in a fourstroke twin of moderate capacity, and as supplied the carbs were ridiculously rich. When I first rode the bike on alcohol, I lowered the needles until the motor coughed, I then raised them one notch. The motor cleared and accelerated cleanly and very fast out of corners. The carburation is perfect at all throttle openings. I've been riding the bike with the 670 mains and never done a plug chop, however the plugs look OK. It doesn't really matter if the mains are a bit rich, it is the mid to 3/4 throttle opening situation which is critical. Even on a race circuit you only hold the throttle wide open on the straights. What happens around the twisty stuff and out of corners can be more important. It should be noted that changing the ignition timing can give similar effects to changing jetting. That is why an extremely good ignition system is essential on a two stroke. With my 850, I always run 34 degrees advance on methanol.
I would never try to road race an H2 Kawasaki on methanol, however the T250 Suzuki was great when I used it in that.
It sometimes helps to put a spot of paint on the twist grip at 3/4 throttle opening. You cannot look at it while you are riding , however while the bike is stationary you can get used to feeling where it is, that is the point where the needle and needle jet must be correct . The rest is usually relatively unimportant.
 
Even on a race circuit you only hold the throttle wide open on the straights.

this is exactly what I love to hear about the reason there's several race bunch up starts along a track by solid mounted light hi powered elite cycles on hot race rubber, hehe...
 
Hobot, with my 850 commando, when I was using the 4 speed CR box you could gear for the clutch start and the twisty bits, or you could gear for the straights. I always reconciled myself to the fact that the very fast bikes would pass me at the ends of the straights. My main jets are probably still too rich, but that is pretty irrelevant. When I race my bike it is all about outriding guys in the tight stuff and out of corners . What you lose on the swings, you pick up on the roundabouts. And besides, the faster you are going at the end of the straights , the more careful you have to be under brakes .
 
Yes Sir Alan deep down everyone's most challenging thing to respect the most is getting around the tough spots the fastest safest. Two things can happen on essentially WOT while leaned the rear lets go to lose acceleration and line of aim or hooks up a sideways wheelie accelerating even sharper. I love sex as any one, but nothing gets me off like the G's a great motorcycle can deliver, even if pilot just so so. I know you got innate sense to really ride the tires off likes of Ms Peel so maybe can meet up at a track day to share her like the Eskimos' did their wives.

I've got to modify the Lake injector needle so paying attention to your clues as usual.
 
Hobot, I would not dare to attempt to ride a fast commando on the dirt, I have not got the head for it. My experience has been that if the rear tyre moves sideways 1mm, I was on the deck. I now ride with modern tyres and go nowhere near using them to their fullest extent. I stay upright , quick, decisive and supersmooth.
 
Naw Alan it'd be love at first slide on real honest to God's Earth, as tire can dig in a good bit so there's always some good resistance to keep from just fly\ing out from under and pretty much stops slide with power let offs, easy as pie as long and not very rough rutted but washboards not much an issue. THE Gravel is sort of similar to pavement of dirt skip drift slide - except once started its take like twice to 3x as long for any resistance to save ya. If I didn't have to ride it I sure wouldn't and each ride usually gives me a scream or leaves me crying while barely making it around a sloped bend as careful as I can and wondering why I risk this at all.

Back to cam power bands I'm kind of hoping Peels long one dulls its repose below 2500 so I can cross THE Grit Shit w/o spinning out. The above crying part begins with hanging off and any extra throttle to make head way mostly just slips further down side slope and if stopped may not get started again w/o rolling back down to get a run back up, which bring tears of fear as gotta be going fast enough to mostly coast up with some mild help by engine. Cdo's like most Brit bikes are pretty decent off pavement.
 
Status
Not open for further replies.
Back
Top