Rocker Arm question

[bigcarguy]

Do our trucks (307 in mine) have 1.5 ratio rocker arms? I've read in numerous magazines how if you replace 1.5s with either 1.6s or 1.7s that you'll get some extra lift. I'm thinking of putting a mild cam in the truck eventually so I wouldn't want to risk any valve-to-piston crunches. I'll probably put roller rockers in the truck anyway but was thinking of going with a higher ratio. Anyone do this?

[my new 72]

The stock ratio is 1.5. If you go too high with a ratio you can have problems with push rod clearance. Most head builders recommend no higher than 1.6. For you application, the higher ratio is more trouble than it's worth. Get a bigger cam to achieve the same affect. You won't have any problems with geometry if you do.

[Blue68]

Going with roller rockers of 1.5 ratio would probably gain you a dozen or more ponies alone. And a cam swap will do even more. ONLY you need to keep in mind a few things. The 307 was one of the first smog engines GM built. It's a great little engine and will run forever. But the displacement and ratio is limiting on making power. Essentially this is a stroked 283. So it makes good torque but isn't able to make much in the HP realm. The stroking reduced emissions.

You may find that a "mild" cam on a 350 turns radical when installed in a 307 due to the decrease in displacement.

Your heads may be a limiting factor as well with small valves.

By no means should any of this discourage you. Hot rodding is powering up what you've got. I would have loved to do some of these modifications to my 307 just out of curiosity more than anything else. GM never made a HO 307 and look though I might, I never found a hot rodded one. Lots of pumped up 305's out there (but it has a larger bore) making 300 hp and over 300 lb/ft of torque.

[bigcarguy]

Well, I'd absolutely love to put all this stuff on a 350, but like you said, you gotta fix up what you got. I had a 77 Camaro with a 305 that I did alot to. It didn't make 300hp, but it was enough to shut all the Honda guys up. So what would be a good cam for a 307? I want it to be mild cause I'm trying to be somewhat concious of gas mileage, but I'm willing to give up a couple mpg for some good power. I may eventually move to a larger engine, but for now I'll just have to see what I can get out of the ol 307.

[Blue68]

To be honest, I'd do what I did. Call some of the cam folks. You can contact Comp Cams @ 1-800-999-0853 or send them an email outlining all the infor needed on http://www.compcams.com/information/...on/default.asp I did both. Or call someone like Sallee-Chevrolet (www.sallee-chevrolet.com) who sells a lot of their cams and has experience selling and running them. Do both and compare the answers.

You may find prowling around the compcams.com catalog useful if you have broadband connection. I'm running a roller cam so we'd be talking apples to oranges but it is a Comp Cams Extreme 4x4 X4260HR. Something similar with flat tappet might be any of the Extreme 4x4 flat tappet cams. Kind of depends on where you want to make power. (The 4x4 cams are on p78-79).

Main thing to be concerned about is valve to piston clearance. That's where talking to the professionals is very important unless you intend to pull your heads and measure it yourself. You will probably need new springs as well.