Inliners International Forums General Discussion Hi Performance GMC Cams, Carbs and Intakes

Well I know I posted a question about 248s a while ago but things are a little closer now and I would like some clearification.

1. I see these NOS gmc 302 cams on ebay and else where. Are these cams bigger than a 248? Would this make a good "RV" type cam in a 248? What are the GMC Stock cam Specs?

2. Though it is just a 248 I plan on at least 2 1bbls. What 2 carbs should I be looking for? I have 1 rochester (46 chevy 216) and 1 zenth (stock carb) and was looking for some glass bowled holleys which is the easiest for adjustment and parts?

3. From above I said I wanted a 2X1 or bigger intake. Will the McGurk one work or do I need to look for one like was on ebay the other day? Suggestions?

4.I know it is a small engine and small head but how small? Do I need to move to a 270H head? I would just like decent power for highway cruising and riding around. The 248 runs great and was rebuilt not long ago, hard to get excided about dropping in a 302 right away. I have a BBC camaro to go fast with just would like to not be eattin buy geos at the stop light.

5. Finally what are the stock specs on a 248? Compression, bore and stroke? What Over bore will it take if I NEED more power?

Thanks you guys are great!

Dear John;

The way to get more power W/O spending a bundle is to go to the 302" engine. There must be dozens in the 'mid-west' etc.

Patrick's will have info. on speed equipment and the Public Library has Motors Manuals with all the internal specs.

Doing it this way gets the most (vehicle improvement) for the $.

Good luck.

A NOS 302 camshaft is not a "performance grind," unless perchance it comes from Howard, Herbert, Iskenderian, McGurk, or some other manufacturer of speed equipment. i had a NOS 302 cam reground by Donnie Johansen to the Howard specs, and the change in its physical appearance was quite remarkable. You can "see the difference."

A stock 302 made peak power at 3,400 rpm, and peak torque at 1,600 rpm. If you plan to haul bricks or pull stumps with your truck, you will do well to find a stock 302. There is, as we used to say, "no substitute for cubic inches" where that kind of power is needed. Your rebuilt 248 could benefit from more carburetion, compression, and improved "breathing"--bearing in mind that gasoline will only become more expensive, not less. The most useful improvements you can make may be a higher (lower numerical) rear end ratio and larger tires that will allow quieter and more economical operation at a higher "cruising speed."

God's Peace to you.

d
Inliner #1450

I understand big power comes with more cubes, I have a 427 in my camaro. For right now I was just hoping to get a little more out of what I had and add a bit of nostalgic speed parts to help set it apart from every other truck. I am not looking for a trailer puller or a drag racer just to hot rod it a bit and make it neater to open the hood. Compression a cam swap and some better air in and out should help any engine I just need a little direction on what parts work the best. I am looking for a 302 but maybe just to hold down the shop floor for a while. The engine is just rebuilt like in still on the 2nd oil change. I would just like to use what I have for a while since it is in good working order at least the short block. Kinda like the kid with a 305 in his car it may never be a 350 but, with some work it can still be made to run and if he ever does get the 350 he can swap the parts that are the same and be ahead of the game. I do thank you for your information because I am pretty much in the dark on this earlier stuff.

Oh and the only reason I wondered about the 302 cam was because if a it peaked at 3400 in a 302, 50 cubes smaller may get a 4000 rpm peak on a 248. I think this would be about right in a heavy truck. Plus $50 would be pretty cheap. Just a idea. Oh one more thing is Though it is a 3/4 ton my grand father and I swapped in a 1/2 ton front and a 3.55 posi car rear axle so it doesn't spin to hard to go 60-65.

You have, then, with the 3.55 posi, already done the best thing you could do for your 248 GMC. Before pursuing a dual manifold, you might try one of Tom Langdon's progressive two-throat Holley-Webers on an adapter with your stock intake manifold. You could split the exhaust manifold or, if you want to spend the money, buy or make a set of headers; either would help the engine breathe. Tom Langdon also sells a "mini-HEI" ignition for the GMC--no more points, and a hot spark all through the range.

A dual intake manifold for the GMC, such as an Ellis or McGurk, did not come from the factory with heat. In Nebraska summers, that won't matter much, but in winter you will need heat sorely. If you can weld aluminum or know someone who can, then it is possible to add water heat to one of these manifolds.

For your stated purposes, with a recently rebuilt 248, i should not want to touch the head or install another camshaft. i think you would see little improvement from a stock 302 cam for the time and money invested. When the time comes that you want serious power in your truck, find a 302 and invest your money and labor in it. Your effort will be rewarded.

God's Peace to you.

d
Inliner #1450

Thats what I really needed to know. I think I may just add a intake and headers that will also fit the 302 when I get one bought and fixed up. In the mean time just be happy with the 248s power. If I add that 5 carb intake with 3 holley 94s (can get them cheap) will it be to much carb and is it hard to set up.