We race 3/8 mile asphalt.Porting is allowed,but we are limited to cam lift and stock exhaust manifolds.For all practical purposes,carburetion is wide open. We are pretty comfortable with our exhaust manifold as it aproximates a good shorty header in dimensions.The cam rule leaves us at .3 lift/ dia. ratio on the intake valves,which Pipemax says are already big enough.( even though they are only 46% of the bore size).It recommends way more lift than I can have.What is the best workaround to get enough flow?
This is a 4 cyl class so the intake tract size and shape is pretty open.I'm thinking straighter,smallish, super efficient ports with higher than average velocity together with a little more duration in the cam(probably going up to around 266@.050).We have been using the 5500-7500 rpm range with success.
Another alternative would be bigger intake valves I suppose. Has anyone experimented with Thicker headed,contoured TI valve heads to help create a better teardrop shape to help pull the cone around a bigger valve?
I fall somewhere between a "A Man With A Plan" and a "Dummy With A Dream" but I'm smart enough to listen to sound advice.Thanks in advance.
Cam Lift Rule
Moderator: Team
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rmcomprandy
What kind of head?
The tighter pattern you want around the valve head is influenced a bunch by the bowl and valve job. I think you can get there without having to use an exotic shaped valve (which also sounds heavy)
And, what's your lift in inches
In general, more duration with more valve (if the port can support it, and it doesn't screw up your ring package) can equal more RPM more power, and more broken parts
The tighter pattern you want around the valve head is influenced a bunch by the bowl and valve job. I think you can get there without having to use an exotic shaped valve (which also sounds heavy)
And, what's your lift in inches
In general, more duration with more valve (if the port can support it, and it doesn't screw up your ring package) can equal more RPM more power, and more broken parts
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Mark Workman
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- Location: Missouri
There are gains to be found in valve shape, obviously. To develop a shape, I buy used Ti valves of a (way) larger diameter than I need, then cut them down on a lathe. This increases the margin to give more material to work with. With a little ingenuity, you can even change the back angle and radius.
I don't have any personal experience with these, so I do not know how hard they are on parts, but you could possibly have a cam ground that will throw the lifter off of the nose for increased lift(and duration). Comp Cams calls them their "Launcher Series".
I don't have any personal experience with these, so I do not know how hard they are on parts, but you could possibly have a cam ground that will throw the lifter off of the nose for increased lift(and duration). Comp Cams calls them their "Launcher Series".
I assume the 4 cylinder is OHC 2V. The key will be in the camshaft. You will need the quickest steepest lobes possible, the maximum area within your allowed lift. An early opening exhaust valve will help blow down the cylinder thru those manifolds. More exhaust duration than intake. Make the maximum allowable modifications to the exhaust manifolds and any that are semi allowable.
I don't have any personal experience with these, so I do not know how hard they are on parts, but you could possibly have a cam ground that will throw the lifter off of the nose for increased lift(and duration). Comp Cams calls them their "Launcher Series".
We found a bad "fuss point" last year at 8000 when we tried spinning faster for end of the season shennanigans and bent a valve.
I can imagine how easy it would be to break stuff if you PLAN on floating the valves over the nose.However,I suspect if it's done right it's less harmful than bouncing off the seat at closing time.
Are roundy round guys using these cams or is this pretty much a drag race part?