If the cam duration is the same as stock you will lose no compression. But if the cams have a greater, more agressive duration and therefore more overlap of the intake and exhaust valve opening sequence, you could end up with the phenomenon Mickey speaks of. Some of the intake charge will blow out the exhaust valves at low RPM, giving the effect of losing compression. Higher compression pistons would make up for some of the loss. I would think that a cam ground for the 650 would have only a small increase in duration considering most people would still want good power at lower RPM ranges.

 

You will likely need heavier valve springs with a new cam, too.

 

Nova,
How do you come to this conclusion about higher compression piston and heavier springs on valves. The only time you need heavier springs is when your rpm is greater than the spring can respond to opening and closeing. Regardless the shape piston the timeing is the same its the cam that alows for more fuel to get into the head not the piston. Over lap on a lower compression piston is extremely minimal the only problem that will arise is when the rpm is greater than what the springs can handle. With our CDI there is no way we can even reach that point as the rev limiter is set at what some people may have 7200 rpm. If we reach 9000 rpm then and only then will there be a certain amount of over lap up untill then there is no concern. Because we have an auto clutch it is almost physicaly impossible to over-rev the engine more yet with our elustrious cdi there is no hope in he** will this ever happen. Your worries are minimal to say the least, people have been doing this type of modd for years with no adverse affect!!!!!!!

If the duration were to be kept open longer then yes there would be some overlap then a high compression piston would come into play but they would go hand in hand, cam with piston as jets to muffler modd. Would you need springs for the valves they might help somewhat but not with our lovely cdi. PBR has been selling cams for some time originally designed by TC racing for the 650 with Autoclutch these cams would not work well with a standard trany machine. These are my thoughts you will have to make your own decisions.

 

The need for heavier springs isn't related to the higher compression pistons or higher RPM's, which we can't reach anyway. The way Four Stroke Tech explained the need for heavier springs is that their cams are ramped more abruptly during the opening and closing sequence, thus having the effect of physically bouncing the valve off the face of the cam lob during opening and bouncing the valve off the valve seat during closing, if using the weaker stock valves. And you're right, if an aftermarket cam only has a minimal increase in duration, you won't lose on the bottom end. The Four Stroke Tech cams must have enough of a duration increase to cause a bottom end loss, as they do recommend the cams, springs and pistons as a package, so as to counteract that loss.

 

Sorry, Alltoys. I guess I didn't hear that only from Mickey, I heard it from you too.
Posted - Sat November 23, 2002 10:20 PM



Hello Scott

When the lobes on the cams are more radical than stock, the springs will have to be stiffer as the speed at which they open and close are more pronounced. In other words the valves will have open and close faster than they would at stock configuration for the same rpm and greater. The lobes are not egg shaped now they are more square so the edge on two sides will be sharper making the valve open faster at a point and close faster at the opposite point therefore needing a stronger spring so you don't valve float.

Mickey does that explain the need for stronger springs or am I talking for the heck for the heck of it? Would I need heavier springs for the intake and exhaust or just the exhaust itself? Again thankyou for your help!

-------------------------
Got that ball grabbin head snappin kind of horsepower.
(Defination of Speed in Greek) SPEEDAMUS MAXIMUS RAPPIDUS CATCHME IFYOU CANUS
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for what it's worth..

in my Royal Star, stock rpm is 5800, single valve springs, shim & bucket design, dohc, v-4, with the Dyna 3K cdi box, it says..with stock valve springs, do not exceed 6500 rpm, or valves will float, or 7500 on a venture, this is becuase the venture, and the Vmax have dual valve springs, inner and outer.. when springs are replaced rpm limit can go to maximum of the cdi, or 8K, stock rpm on a v max is well over 10K, so this is not a problem. If I wanted more performance out of the royal, I'd put the dual valve springs in, and venture intake cams, leave stock exhaust.. for max performance, I'd go with the v max cams..but the bottom end would suffer a little..so the venture would be my best bet.. the profile of the exhaust is almost the same, so it would not have to be changed for good results..

I agree that single valve springs are only good to a certain rpm, then they float, heavier ones would help when the rpm is allowed to go up..as far as more radical cams, that open quicker, but duration is similar to stock, I would venture that the heavier springs would'nt hurt, but probally would'nt give that much of a benefit, unless they were part of a package that included the cams, springs, & cdi..then I'd want them, as the rpm was increased.. as far as if I was selling this stuff, I'd want the customers to buy it, as it would help with the longevity of it..

now, my thoughts are from the motorcycle area, and this is a auto clutch quad, so your milage may vary, and all the other typical disclaimers will apply..

as far as the cheap horsepower, I'd go with pipe, airbox mods, jets, cdi, then cams...as the other gives good results for the $$ & time invested in it.. the horsepower will come from the rpm..but it needs to breathe as well..

 

I have all the mods including the cams, Big Gun exhaust and so on. When I installed the cams I did notice a slight difference but not enuf to justify spending the $$$$ to do it. When the CDI finally is released I'm hoping the combination of the cams and the cdi will work together and really kick some azz.

 

I had a test run today with my new cams they are more radical than PBR's witch are also the same as the ones now sold by Web Cams. I also had my Super Charger working so it is official I have it working the combination cams and blower is stagering. Before cams I had 76hp after cams 84hp they are a difinate benefit behind a blower.

Prairiewrench,
Did you get my PM, e-mail etc.

 

Scott,
Had I taken more time to read your post I would have realized we were talking the same stuff. Same thing but different LOL.