Hey guys, been a while...

I'm starting to compile some more parts to add some more power to my 85 T/A. I was looking for some input on rockers, from what I have found 1.52 ratio would be good for my cam Comp 12-600-4 Thumpr cam, my question is: Roller tip or full roller? Also, with the stock spec springs, would I be ok running 1.52s with that cam or should I change the springs too? If so, any input on what springs to run?

Thanks!

Cam specs can be found here: http://www.summitracing.com/parts/cca-12-600-4

The heads are stock, some very mild porting was done when it was built, but nothing extreme for sure. Running an Edelbrock Performer intake manifold, soon to switch to an air gap, with a Edelbrock 1406 carb, and shorty headers. Stock compression ratio.

 

Roller tip rockers will be fine as you wont be running a lot of spring pressure with a flat tappet. No need to spend some hard core $$$ on ultra pro mags or something. Stock springs wont work with those sorts of grinds, so you will need to upgrade. Since you will be using a flat tappet, you'll want to limit the open spring pressure to no more than 250 lbs to ensure reasonable life out of the cam and lifters. Are your spring seats still the stock diameter? Did you measure how much lift the heads could handle when you built them originally? Answers to those questions will help with the spring selection.

Id also use GM performance parts lifters with any flat tappet you buy. They have hardened spun-welded heels that make them more durable than the aftermarket lifters from my experience. Also dont forget the ZDDP additive (ZDDPlus) with each oil change since modern oils dont have near enough ZDDP for older flat tappet cams.

You may want to look at another grind. With a stockish motor, that cam will just make lots of noise at idle. The tight LSA and overlap of a thumper will kill the cylinder pressure on a low compression 305 since they are ment to lope a lot. Probably something like an XE262 or similar will work much better.

 

I should clarify, this motor is already built and running. Lol

It runs really well, and makes great power. I have to ask my brother about the springs for sure but I'm almost sure they're stock spec. The lifters are the Comp lifters that came with the cam I posted above. The spring seats should be stock as well. I'll confirm that.

But assuming they are stock springs what should I look into to run that cam with 1.52s?

I will also verify what kind of work was done to the heads. I believe they were just stock heads from another carb'd 305 when he got them and built the motor years ago.

Thanks for your input.

 

Just confirmed the springs and rockers are stock, the seats are stock, but the heads were cleaned up and had new valves and seals installed with some mild valve work done at the machine shop when the cleaned the heads up.

 

I'm thinking that springs/rockers might not be worth it on this particular build for me at this point. Thanks for the help though.

 

One good reason to get springs is to avoid valve float at higher RPMs. What RPM does the engine shift at? If its being shifted at 4500 RPM, your leaving a lot of power on the table with a cam, but the stock springs will still provide sufficient control of the valve train, not to mention longer lobe and lifter life. On the other hand, if its going up to 5500-6000, then springs will be a must if you dont want valve float or broken springs. Isky Cams makes stock replacement springs that are a good upgrade that will fit your heads. Those with some magnum rockers will probably cost <$300.