The engine shop was a bit disappointed with me though. The ship mentioned they had done up hundreds and hundreds of the M-blocks in the 80’s and early 90’s and they could safely hit 500-600hp and 500-600+ torque with the engine.
I wanted a nice street drivable car, not something to take to the strip, so I said it must have a decent idle and be reliable if I am driving my family around. I won’t mind the noise from the heads and dual exhaust, that just gives it character.
It will be weeks before they finish the rest of the restoration so I am still worried the cam might cause the idle to be a bit too rough? Anyone know about this?
The cam is comp 270H (270, 224, .519, 110). I don’t understand exactly what that means, particularly the 224 at .050. I also remember this was their second choice cam – their first choice was unavailable. It was comp XE262H (262/270, 218/224, .513/.520 ,110) They said I would not notice very much difference between the two cams. Also not sure what numbers have the biggest impact on idle, or what is smooth or not.
Thanks for any input
Well the first two refer to duration.
And the .519 refers to valve lift
It has 270, degrees intake duration 224,degrees exhaust duration
And it has .519 inch intake valve lift and .519 inch exhaust valve lift
And the 110 refers to centerline
Duration refers to how long the valve is opened to relation to crankshaft rotation. This open valve time period is expressed in degrees of crankshaft so. A cam specification 224 degrees duration simply means the cam holds the valve open for
22.4 degrees of crankshaft rotation
More duration is helpful for high RPM. And low duration is better for low RPM.
With high duration The extra degrees of open valve time at high RPM gives the air flow a little more time to get in/out of the cylinder in spite of the pistons stroke. However at low RPM more duration can cause less power because the valves well be open at the wrong time in relation to the Piston’s stroke. Because the engine is running slower “the crank shaft is running slower” is making the valves stay open longer causing the combustion chamber to fill up with to much gas “ causing miss combustion” and then the exhaust valves are open to long causing fumes and air to escape the cylinder “causing miss combustion” at low RPM.
Low duration does just the opposite at low rpm it is perfect for making horse power and torque but at high RPM the valves are not open long/wide enough causing it to suffocate the cylinders at high RPM
Valve Lift refers to how Wide the valve is open
If valves are not open wide enough, they will cause the restriction for the air trying to enter/escape the cylinders. However opening the valve past a certain point well not increase the flow to/from the cylinders as the heads can only flow so much
Valve lift is measured in thousandths of an inch and you got .519 “just over half an inch”
Separation refers to the spacing between the intake lobe and the exhaust lobe on the cam shaft this separation is expressed in degrees on the camshaft “Not the crankshaft” so a 110 lobe separation means the intake and exhaust lobes are 110 degrees apart from each other on the camshaft
Separation just like center line is another way to tie the duration to the crankshafts rotation and end with valve events this spec is a little more complication though, because it is in the cam shaft degrees and the crankshaft rotates two degrees for each one degree of cam rotation also if the cam has been either advanced or retarded, the valves events well be different.
But with the right cams it is impossible to make more horse power at low rpm then at high rpm “with the right camshaft” but at higher rpm you start to lose torque "you have to give to take"
Your engine should run pretty smooth with that camshaft
Me personally I like the rough sound of a bigger camshaft
<font size=-1>[ This Message was edited by: ixtlan on 7/25/05 12:07pm ]</font>