Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.

Messages - TIMINATOR

Pages: [1]
Engine Mechanical / Electrical / Re: XM 278 Cam Question?
« on: June 14, 2015, 05:12:32 PM »
If you use a hydraulic roller in a boat, rev kits are a good idea, they allow a lower spring pressure at the valve and make up the difference by pushing on the lifter body itself. The lesser spring pressure against the plunger reduces the amount of lifter bleed down and power loss, but the loss is still there. We prefer to only run solid rollers in boats because of the oil aeration allows the lifter to partially collapse at higher RPM or at any longer distance running, dropping the available HP. The solid roller setup is usually cheaper in the long run, than the hydraulic roller, especially if the rev kit cost and extra installation labor is figured in.
In a 21 Daytona with a 572 Chevy (268@.050/ .690 lift) in back to back testing the solid roller was 9 MPH faster. In a 25 Daytona blower motor 565" deal (264@.050/.668 lift) there was 11 MPH difference. These were both pretty hefty hyd rollers, and with a smaller hyd roller there would be less difference, but why use a smaller roller if your spending the money anyway?
    If you read and believe "magazine Horsepower" (you shouldn't), keep in mind that they are reading dyno Horsepower. Dyno HP is usually "corrected" to sea level air pressure (29.92"hg) and 68 degrees air temp. These conditions are rarely ever encountered at the lake, especially in summer. Dynos don't move, they sit there, they are not "going bow high" on the launch, trimmed out (also bow high) and throwing all of the oil up against the bottom of the crank and whipping it into a 'milkshake", nor are they going over waves and boat wakes, also throwing the oil against the crank. Oil against the crank slows the crank, rods and pistons sapping HP, aerating and heating the oil also. Hot oil is thinner and bleeds past the lifters plunger quicker, aerated oil is thinner and does the same thing. Any time the plunger bleeds down, it reduces the lift and duration of the cam.
Don't think aeration affects your hydraulic cam?  Buy a milkshake at your favorite "burger barn." See how full it is, don't drink any and let it sit for a half hour. See how full its not, the difference was air. Keep in mind that the "shake maker" probably only turns 1500 rpm and is 1 1/2" diameter, your crank goes 5000 rpm + and is 6" diameter. On the dyno we could make more HP by running a 10 quart pan with 6 or 7 quarts in it, all dyno operators know that, even with a windage tray.
Can't afford a roller cam? Use a solid cam and high lift rocker arms, that will help. No more lifter bleed down.
Olds motors have one of the worst  oiling systems known to modern engines, if you run a hydraulic cam, there is about 20+ HP to be gained by doing all of the correct oiling mods during rebuild, more if  you run a big cam, or just run a solid. 
Sorry about "jacking" the thread, but its good info....     TIMINATOR

Pages: [1]

Website Security Test
Powered by EzPortal

Website Security Test