Inliners International Forums General Discussion Hi Performance gmc 302

I just got a gmc 302. I want to build it up some. I was thinking of the 5 two intake and running 3 holley 94's on it.(just something about multi carbs!) Who sales the lump ports for the heads. How much can you safely plane the head. And I have been told to use sbchevy valves. I have read to use the 248 crank and punch it .100 over But what rod and pistons do you use? Or is there a rod and piston combo for the stock crank maybe even to offset grind the crank? Would like to have lighter pistons for more RPM. What and who's cam would you sagest for a mostly weekend only street truck?

This is going in a 53 GMC pickup.
Thanks

And I also forgot will my 228 flywheel fit this 302 crank?

The great strength of the GMC 302 is low- and mid-range torque. For "a mostly weekend only street truck" you will probably be happier with the stock 4-inch stroke. You can safely bore the cylinders to 4.125 for 320 cid. Patrick Dykes sells "Venolia" pistons for the 302 in a range of sizes. They are probably the best choice for a street-driven truck. Ross and Arias sell racing pistons for the 302.

Patrick Dykes sells a Howard cam (228 @ .050) ground by Donnie Johansen on your core. You could also consult with Tom Langdon, who recommends a "dual pattern" grind that some people have apparently used successfully.

Chevrolet V8 valves (1.94 intake, 1.6 exhaust) can be installed in the 302 head. i am not aware of anyone running lump ports in a 302 head on the street. For a street-driven truck, two or three Holley-Webers or a single four-barrel carburetor should offer more than adequate performance and throttle response.

You should consider using a Chevolet V8 flywheel and clutch with a Saginaw or Muncie four-speed and a later differential. Your crank flange can be modified to accept the later flywheel.

There are several discussions of all these issues in the archives of this forum.

God's Peace to you.

d
Inliner #1450

Thanks Don.
So do you just have to drill the new bolt pattern in the end of the crank? I got 3 saginaw 4 speeds the 3.50:1, 3.11:1, and 2.54:1 first gears which would be the better one for a pickup? I have a 8.5 ten bolt posi with 3.23:1 or was it 3.08:1 that I think I will put in it. I might change the gears but I want to be able to drive it on the street so nothing more than a 3.42:1 gear. How would a t-5 hold up to a torque monster 302?

Yes, your machine shop can drill the crank flange to mount the V8 flywheel.

With a 3.08 differential you would be wise to use the 3.11 low gear, which gives you the 2.2 second. If you plan to haul loads or pull a trailer with that combination, then the 3.50 might be a better choice. You might also think of adding an overdrive from a Saginaw three-speed to your 2.54 transmission, which would allow you to run a 4.11 or lower differential with a higher ratio available for cruising on the highway. See

http://www.chevytrucks.org/tech/overdrive.htm

i have no knowledge of what kind of abuse the T-5 can absorb, but i hope soon to find out what the Saginaw's capacity may be.

In my '52 Chevrolet two-door we have a 3.11 Saginaw four-speed with an overdrive conversion and 4.88 posi differential. In overdrive the final ratio should be 3.42. For most purposes i plan to use the 2.2 second as the "low" gear, duplicating the old "close-ratio" three speed. (This vehicle is not a "daily driver" . . . especially on $3.00 gasoline.) At some point, after we have seen what this machine can do, we may install a 3.36 differential and use the 3.11 low gear. That might be a good combination for you in your truck.

God's Peace to you.

d
Inliner #1450

I think I read on here that with a 12-volt ring gear that you have to us a 12-volt starter so can I replace the ring gear with a six volt ring gear on the starter or can I replace the gear on the starter? I want to keep the original bell housing and the push peddle on the floor starter. And do I need to get a 168 tooth or 153 tooth v-8 flywheel?