BBC Intake Manifold ID help!

[cottonme173]

Hello all!

I am tearing down my 1977 GMC C25 with a 454. I can not see the block casting numbers to help identify the motor specs. On the manifold though is this information:

GMT2
340218
F21 77

I have found many different pages for identification, but 340218 is not on any of them so far. I would like to replace the manifold (if I really need to, current one is in great condition) with something with better performance and a Holley carb. Street driver, nothing really high performance.

I am wanting to know what ports I have to make sure I get the correct intake. Also, more info on the engine would be great to have!

Please let me know if I need to give any more info to help!

-Rob

[DieselSJ]

Standard early big block truck cast iron oval port (large oval, not peanut port) intake.

[cottonme173]

Thanks for the info!

I am thinking of going with the Edelbrock Performer RPM intake 7161 and a Holley carb. What CFM would be recommended for a BB? 700-750?

[DieselSJ]

Great choice on the intake. A 750 vac secondary is a great street carb. Drop a mild cam into it and you will have a really nice driver.

[cottonme173]

I was originally going to do the cam, but lost enthusiasm when I was told that I would also have to replace a lot of other components?

If you had a recommendation on a cam that would be great! I am very inexperienced on the internals of the engine. I have replaced everything else over the years, but never a cam, valves, rods....etc..

[DieselSJ]

I've been liking the Howards roller-retrofit stuff.

https://www.summitracing.com/parts/h...make/chevrolet

That would be great for a mild build with stock compression. You also shouldn't have to replace anything that you wouldn't already be replacing with a rebuild already.

Even if you aren't doing a rebuild, now is the time to do the cam since you will have the intake off.

[cottonme173]

Well, that sure looks like a nice cam! I however, can't do that price :-)

There must be a more....budget friendly option?

[kdh454]

Ditch the manifold, it weighs a metric ton - your back will thank you later. Performer RPM and the newer Air Gap are both good manifolds.

Unless you plan on making a lot of upgrades later, I'd suggest a 650cfm carb. You would have to spin a 454 past 5500RPM before you would need anything bigger. https://www.summitracing.com/parts/hly-0-80783c

If you want to do a cam, I'd suggest something similar to a Comp 260H. It will work well with your stock valve train, unlike the roller listed above.
https://www.summitracing.com/parts/cca-cl11-203-3

You'll want to replace your timing chain while your in there as well.

[DieselSJ]

I'll agree with the above that a 650cfm carb will be fine for what you want to do.

While his cam suggestion is also good, I have found that split duration cams yield better results. These engines like a little more exhaust duration. Any flat tappet cam with a 210-215 intake duration (at .050 lift) with a slightly longer exhaust duration will suit your needs and should work with the stock valve train.

Here are a few -


https://www.summitracing.com/parts/c...make/chevrolet

A little bigger -
https://www.summitracing.com/parts/c...make/chevrolet

This one is probably on the ragged edge for what you want to do -
https://www.summitracing.com/parts/h...make/chevrolet

[cottonme173]

Thank you guys for responding! I do appreciate the help!

DieselSJ:
When you say "Ragged Edge" do you mean that performance wise it is more than I need? I would have to potentially replace rods, springs and such if I went with the last one?

[DieselSJ]

Originally Posted by cottonme173

Thank you guys for responding! I do appreciate the help!

DieselSJ:
When you say "Ragged Edge" do you mean that performance wise it is more than I need? I would have to potentially replace rods, springs and such if I went with the last one?

You would potentially need to do valve springs. But that is the biggest that I would go on a stock compression engine.