Cam help?

[TheEnemy]

From what I have read the intake is usually the one you want to increase.

[Christ]

Originally Posted by TheEnemy

From what I have read the intake is usually the one you want to increase.

Please exemplify this statement?

(Show me what you've read, so that I can read it and come to my own conclusions.)

[TheEnemy]

Cylinder Head Porting Basics - Popular Hot Rodding Magazine

Apparently the intake valve causes more restriction than the exhaust valve, which is why the intake valve is larger.

They had a few articles besides this one, but that was where I started.

I don't think it will change much at the low end, but it might some.

[DonR]

Let Summit Racing be your friend. Normally on cams they list an RPM range. You obviously want a lower range. Typically these type of cams are referred to as RV cams. Below is a link to a Comp cam part at Summit. Crower makes good cams for AMC straight 6's so I imagine they do good work for Fords as well.

COMP Cams CL66-236-4 - COMP Cams High Energy Cam and Lifter Kits - Overview - SummitRacing.com

Rocker arms won't affect the duration the valve is open, just lift. If you're making a hot rod the larger lift is desirable. I don't know about in a low RPM rig.

Don

[micondie]

If you check the specs from Comp Cam you see that the lift and duration are the same for the intake & the exhaust. With modern CNC technology there would be no problem grinding them differently if there was an advantage to do so which leads me to conclude there would be no advantage to just changing the intake rocker. although considering the ease of changing them I personally would try just the intakes first and document the results before changing the exhaust rockers. Perhaps if fuel economy is the main goal, not increasing low end power which is Comp Cam's goal, this approach might show some gains.

[Christ]

Originally Posted by micondie

If you check the specs from Comp Cam you see that the lift and duration are the same for the intake & the exhaust. With modern CNC technology there would be no problem grinding them differently if there was an advantage to do so which leads me to conclude there would be no advantage to just changing the intake rocker. although considering the ease of changing them I personally would try just the intakes first and document the results before changing the exhaust rockers. Perhaps if fuel economy is the main goal, not increasing low end power which is Comp Cam's goal, this approach might show some gains.

I'm not sure if I can do that with the EFI head, but w/ the carb'd head, I think I can. They changed the rocker design in the '85+ models to pedestal mount, instead of stud mount, so I'd either need machining work or a special bedplate to mount them on, and that's not something I want to do twice!

However, Comp's RV (low end torque/gas mileage) cam claims improved gas mileage as well as increased low-end torque, so once I can find the OE specs for the cam (I'll have to keep searching, haven't found it yet.), I'll compare the rocker increase to Comp's low-end cam, and see how they compare.

Maybe the rocker increase will get me something in a close approximation to the RV cam for less than half the price/work, which is the ultimate goal, for me anyway.

I would suggest that I build one of the carb'd heads I have laying around for the purpose, and just change it when I need a new head gasket, but that's not likely to happen any time soon... the I6's can go more than 300k between rebuilds, and then it's just rings and bearings/seals, usually.