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Old 09-24-2012, 06:41 PM
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I measure how far the valve lifts off the seat, in several ways at the rocker tip or at the valve face or wherever convenient particular to the build and eng. design and model

As an example: I guess everyone measures a flat head V8 or L Head valve lift at the stem with a dial indicator during assembly with the heads off ! I do it at the face of the valve as I turn the engine over its easier

to those that are interested I'll post this unuseful info to some people and useful to some others:

Mouse motor naturally aspirated as an example.

Dual grind cam:
on a cam with extended exhaust timing 1.6 ratio rockers on the exhaust are detrimental to performance like a cam with 2 durations and lifts the larger on the exhaust lobe stay with the 1.5s, but on the intake the 1.6s may help power.

But on a straight ground cam same duration and lift on exhaust and intake! The 1.6 ratio rocker may help a lot on the exhaust valves not the intakes! The 1.6 rocker when opening The smaller exhaust valve will open a little more at full lift increasing the off seat gap (making it larger) so the crank isn't pushing as hard on the rod and piston to push the spent exhaust out of the smaller gap between the valve and seat thus relieving back pressure creating a little more torque, Thats a simple explanation. With open headers scavenging the increase is greater like at the drag strip!!! On the street with restrictive exhaust it will probably show no gains at all!!

With high compression engines the intake charge as the piston goes down creates a lot less drag but when the charge ignites it expands and the higher the compression the more it expands and more heat is created and more expansion, so the crank works harder on the exhaust stroke to push the hot expanded gases out, then the intake stroke pulling a cool charge in. It also helps get a cleaner intake charge in because the cylinder has been evacuated of spent gases more effectively!!

Dont just throw on larger ratio rockers on any cam grinds, you may actually kill power!!! YOU HAVE TO TEST!! Many cam company's sell adjustable rockers one rocker can be used for 1.5 or 1.6 ratios by a simple adjustment. run a few passes with 1.5s on all valves, then put the 1.6 ratio on your intakes (you can buy 8 rockers and put them on the intakes or buy a whole set or borrow some) run a few pass's and see if it runs stronger. then put the 1.5s back on the intakes and the 1.6s on the exhaust run a few pass's and see if its running stronger! or all 1.6s on all valves but Ive never had to do that.

Its a lot of work and its better to use a dino and easier but expensive.

You can have cams ground to the specs you need to do the same thing but how many cams would you go through before you found the right one!!!! for your set up! That's why company's came out with cheep different ratio rockers as an alternative.

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