Topic: PISTONS (970cc? 1000cc?)

[Retro Rocket]

Thanks MRieck, next question, if i have 2 different cams how difficult is it to change them over, can i just slacken the tensioner off and slip one out.?

Mick

[MCRider]

Thanks MRieck, next question, if i have 2 different cams how difficult is it to change them over, can i just slacken the tensioner off and slip one out.?

Mick

Pardon me for butting in, 

On the bench, remove all rockers, the cam bumps (cams) are too big to pass otherwise. Still pretty easy job though.

In the bike, remove the engine. Unless you have one of Gordon's frame rail kits.

[Retro Rocket]

Thanks MCRider, i have one of Gordons kits on the way.....

Mick

[voxonda]

I have just installed the frame kit, it is a beaut! No more lifting that big chunk of metal to just replace a coverseal!

[Jerry Rxman Griffin aka MuthaF'er]

Thanks for bringing this up Jerry... . Being mainly for street use i want this engine to be a torque monster, you know, wheel spin under hard acceleration in the lower gears, power stands, that kinda grunt,{and i thought i had grown up.... } So any suggestions would be most welcomed.

Mick

I go with a cam that has good lift and shorter duration for torque. The sooner you close the valves the better your compression which will increase torque. The 125-65 is a very good cam. If you want even more power the 125-75. It is also a very good cam and is what I run in my 915.

Hey Mike, please explain how this works. With what you've said I'm picturing a long duration cam keeping the valves open longer while the piston is traveling upward. The valves close right at the moment the piston hits TDC and you do not get that "pent up anger" like when the valves close earlier. However in my feeble mind this theory would not create as much compression as a short duration cam that closes valves earlier thus creating the compression earlier. OR does allowing the valves to remain open longer still allow the same volume of air into the cylinders somehow. OR are we saying that compression is starting to build as the piston is moving downward before it's upstroke and a short duration cam just begins this a little sooner. Enquiring minds want to know. Also once you're done with this will you explain the theory of relativity?     

[Terry in Australia]

Well I don't really understand camshaft theory as well as Mike, but the theory of relativity is pretty simple:

"First, it's not an entirely original concept: Galileo used a kind of relativity to explain why we're not all swept off the earth as it rotates. Imagine a moving ship, he said; within that ship, everything functions as though you're on dry land (or, if you're worried about wave motion, try a train). Einstein's observation was that the passage of time, which everyone had always simply assumed is constant and immutable, is not: it's the speed of light that is. "Now Galileo would start to get unhappy there," says Sir Roger Penrose, author of The Road to Reality: A Complete Guide to the Laws of the Universe, "because you'd think if you're moving along almost with the speed of light, the light should seem to be going more slowly. Why does it seem to be going at the same speed, no matter how fast you move? It seems like a paradox at first."

The theory of relativity was revolutionary because it showed how the speed at which time happens is mutable; that space and time are not discrete entities: time and space and motion (ie, movement through space) collapse into a fourth dimension, in which all act on each other. It is impossible to say "now" without saying "here" and "how fast".

Or, to put it another way, imagine you have a twin. You stay on earth, your twin goes into space on a fast rocket ship for 10 years; when they come back, they're a couple of years younger than you are. It even works with aeroplanes: circle the earth, flying low; when you return to your starting point, your watch will be slightly behind. "If you were actually moving at the speed of light (which you couldn't do, but suppose you could)," says Penrose, "your watch would stop altogether." It's a rather more expensive method of age-defiance than Crème de la Mer, but then again, it has the advantage of being a physical law of the universe."

Over to you, with the hard question Mike!

[MRieck]

 Higher lift/shorter duration cams allow good cylinder fill (if the ports can accommodate) without excessive valve overlap caused by long duration cam(s). Long duration cams increase valve overlap which cause a loss of intake charge and kills compression. If you are running a ton of compression or doing long, extended WFO throttle positions (Bonneville etc) extra duration is OK.
  If you close the valves earlier before TDC you will increase compression. Long duration cams hold the valves open longer which bleeds off pressure on the compression stroke. This is the reason why stock cams often produce good torque at lower RPMs (actually throughout the rev band) then a lot of aftermarket pieces. Performance Bikes just did an article in which they reduced both lift (a little) and duration (more so) from some ZX-9 cams and improved the torque quite a bit.
  Relativity pertains to the assumption I will get something out of something....if not, it's not relative to me.

[MJL]

Higher lift/shorter duration cams allow good cylinder fill (if the ports can accommodate) without excessive valve overlap caused by long duration cam(s). Long duration cams increase valve overlap which cause a loss of intake charge and kills compression. If you are running a ton of compression or doing long, extended WFO throttle positions (Bonneville etc) extra duration is OK.
  If you close the valves earlier before TDC you will increase compression. Long duration cams hold the valves open longer which bleeds off pressure on the compression strokeduring lower rpms. This is the reason why stock cams often produce good torque at lower RPMs (actually throughout the rev band) then a lot of aftermarket pieces. Performance Bikes just did an article in which they reduced both lift (a little) and duration (more so) from some ZX-9 cams and improved the torque quite a bit.
  Relativity pertains to the assumption I will get something out of something....if not, it's not relative to me.

Longer duration cams bleed off pressure at lower rpms, so in a way they are good for higher compression motors. At higher rpms their is still moving into the cylinder even as the piston is moving up, (inertia) so the longer duration helps to create more compression, as well as fill the cylinders with extra air and fuel.


I have a spare 750 motor in my garage. For $775 (pistons & sleeves) I am interested, but I need to come up with $1000 to finish paying for my new F4 before I buy parts for a new project.  Give me a couple weeks.



Not as big an issue as the valves and cam, but I'd suspect the ignition should be upgraded, also.

[paulages]

Thanks for bringing this up Jerry... . Being mainly for street use i want this engine to be a torque monster, you know, wheel spin under hard acceleration in the lower gears, power stands, that kinda grunt,{and i thought i had grown up.... } So any suggestions would be most welcomed.

Mick

I go with a cam that has good lift and shorter duration for torque. The sooner you close the valves the better your compression which will increase torque. The 125-65 is a very good cam. If you want even more power the 125-75. It is also a very good cam and is what I run in my 915.

Hey Mike, please explain how this works. With what you've said I'm picturing a long duration cam keeping the valves open longer while the piston is traveling upward. The valves close right at the moment the piston hits TDC and you do not get that "pent up anger" like when the valves close earlier. However in my feeble mind this theory would not create as much compression as a short duration cam that closes valves earlier thus creating the compression earlier. OR does allowing the valves to remain open longer still allow the same volume of air into the cylinders somehow. OR are we saying that compression is starting to build as the piston is moving downward before it's upstroke and a short duration cam just begins this a little sooner. Enquiring minds want to know. Also once you're done with this will you explain the theory of relativity?     

hey jerry- just to add to what mike said, the characteristics of the port and flow and cam timing are critical here as well. ideally, this pressure "bleed off" portion as the valve is closing and the piston is traveling back upward will be timed exactly right as well. the A/F mixture is in motion coming into the cylinder at high speeds as the piston reaches BDC. for a short time as the piston begins traveling back upward, the intake velocity continues to bring the charge into the cylinder, thus increasing the CR a bit (as the cylinder volume is actually decreasing). leave that valve open too long, and you begin to get reversion (charge flowing backwards as the valve is closing) and a loss of CR. if you're tuning specifically for 9-11K RPM for a racetrack or whatnot (and maybe not if it's a tight track), you might be able to time a longer duration cam/port  to exactly that sweet spot of perfect volumetric efficiency where you getmore charge in and keep a good CR. with two cams, you can sync this process with the exhaust a little better, but the SOHC makes it a little harder to tweak.

simply put: higher lift (rather than duration) gets more charge in there at more rev ranges.

[Terry in Australia]

simply put: higher lift (rather than duration) gets more charge in there at more rev ranges.

At the expense of low, to mid range torque, which in most riding conditions is much more desirable than absolute top speed.

Over here in Oz, Toyota have a crappy V6 Camry that they advertise as "The most powerful V6 in Australia", as it produces a couple of BHP more than the much bigger, under-stressed Ford or GM (Holden) 6 cylinder cars, but the truth behind the advertising snake oil, is that down low, the Toyota has one of the most gutless engines on the market.

This is why a big torquey twin (Harley or BMW, for instance) will kick an R1 or a GSXR1000 in a stoplight drag race, for the first 50 yards or so. My old BMW R100RS would just about whoop any bike off the lights to the legal speed limit, and if they wanted to break the law to beat me, I let 'em!

[MRieck]

simply put: higher lift (rather than duration) gets more charge in there at more rev ranges.

At the expense of low, to mid range torque, which in most riding conditions is much more desirable than absolute top speed.

No...the opposite is true. Longer duration at low RPMs increases overlap which reduces compression on the compression stroke. It also increases reversion and decreases fuel milage aqs intake charge goes out the exhaust valve on the overlap. This was mentioned by others. This overlap problem goes away at higher RPM's. More compression equals more torque in general. If you want/need more cylinder fill you need more charge which can be accomplished by higher lift/shorter duration, long duration/moderate/high lift or turbo/supercharging. You need an efficent port for the high lift/short duration cam. The long duration will fill a less efficent port more efficently. HD and other twins develop torque in different ways like stroke and cams. I'd say if you want a big bottom end/midrange on a CB stroke it 5mm, increase the static compression and put small cams in it

[Sam Green Racing]

If ya want torque, nitrous it. 

Sam.

[MRieck]

If ya want torque, nitrous it. 

Sam.

Yes....I forgot that one BUT it is basically more charge.

[samoto-honda 1000]

More torque?


Put a supercharger!

(I'm serious. I love that blowers on bikes)

I am working on a blower Triton but maybe I will fit also on a Four.

There are no substitutes for cubic inches is a fact , but supercharging + overboring could be better.

Fabrizio

[Terry in Australia]

simply put: higher lift (rather than duration) gets more charge in there at more rev ranges.

At the expense of low, to mid range torque, which in most riding conditions is much more desirable than absolute top speed.

No...the opposite is true.

Sorry Mike, you've lost me mate, you're saying that a high lift race cam (my Megacycle 125/75, for example) will give me more torque at low to mid range RPM?

That doesn't sound right, especially since the increased overlap will actually reduce compression down low? How does that work? Man, the theory of relativity is FAR simpler than cam theory...........

[Retro Rocket]

The more i read, the more confused i get... ...

Mick

[MRieck]

simply put: higher lift (rather than duration) gets more charge in there at more rev ranges.

At the expense of low, to mid range torque, which in most riding conditions is much more desirable than absolute top speed.

No...the opposite is true.

Sorry Mike, you've lost me mate, you're saying that a high lift race cam (my Megacycle 125/75, for example) will give me more torque at low to mid range RPM?

That doesn't sound right, especially since the increased overlap will actually reduce compression down low? How does that work? Man, the theory of relativity is FAR simpler than cam theory...........

Terry....in a relatively stock engine (or one with some porting) if you want more torque (in general) stick with lower lift, shorter duration cam (stock or close to). Like you said....it closes the valves earlier and produces higher compression on the compression stroke. Now if you bump up the compression ratio, increase the bore and or stroke, get more charge via 125-75/porting etc you will ultimately produce more torque. My bike makes something like 60lbs which is way more than stock and it makes more torque (then a stock CB) everywhere.
  Sam mentioned nitrous. I'm sure you've seen dyno charts with nitrous used. The torque goes through the roof (and sometimes the crap goes into your pants) when it is used.

[754]

My bike had way more torque than most 4 cylinders..

836cc 10.5:1
stock ports, valves with good valvejob
RC 315 cam, and Webers.
turbo pipe (woith SMALL primaries)

If you think that 77/78 carbs with accel pumps work nice, these are a lot better in the response dept.

[MRieck]

Back to the kits......Jerry ( and some others) are getting antsy Jay. Any word there big guy?

[kos]

AS Rob Muzzy says, when asked about camshafts by Kevin Cameron of Cycle World (& old, defunct Cycle magazine)
I don't know of many advances in cam designs over the past 35 years, but an engine does not make much power when valves are open.

We made the most torque and HP with lifts at over .407" and shortest duration posible in our CR762cc Daytona racers.

KOS

ps: you guys understand who Rob Muzzy is don't you?

[MRieck]

 The ramp speeds get up there with the high lift /short duration but I have had very good luck with power and torque output with that combo.

[Jerry Rxman Griffin aka MuthaF'er]

AS Rob Muzzy says, when asked about camshafts by Kevin Cameron of Cycle World (& old, defunct Cycle magazine)
I don't know of many advances in cam designs over the past 35 years, but an engine does not make much power when valves are open.

We made the most torque and HP with lifts at over .407" and shortest duration posible in our CR762cc Daytona racers.

KOS

ps: you guys understand who Rob Muzzy is don't you?

Mike Mc,

What kind of HP numbers have you been able to achieve with those 762 M3 racers?  In your opinion am I correct in thinking that once you achieve near maximum lift based on piston/valve clearance then a further increase in cc's will then require an increase in duration to properly fill the cylinders? In your opinion is there a point of diminishing returns with these 736cc engines as far as size goes taking into account the design and availabilty of necessary parts to do so? What would your ideal size engine be for maximum HP and relative reliability? Are you going to do a 1000 along with us?

[Retro Rocket]

What would your ideal size engine be for maximum HP and relative reliability?

And that there is the question.......anyone have the answer?

Mick

[MCRider]

What would your ideal size engine be for maximum HP and relative reliability?

And that there is the question.......anyone have the answer?

Mick

Headwork first: Valves.
Without rods?  836cc mild compression and cam, carbs iffy.
With rods?  888cc choose your weapons.  You'll never miss the extra cc's. Room for overbores.

JMHO

[Retro Rocket]

Hi MC, i have an engine with RC crank and rods and ported head, bigger valves, {ex drag bike from the early eighties in perfect condition}  and was looking at Jays 970 cc pistons, with 1000cc size {OD} sleeves this leaves me room to rebore if needed but its the reliability thing that has me a little concerned. I am just after heaps of torque for the street so high revs aren't really a concern. What are your thoughts?

Mick