Hey everyone. So I picked up an 350 recently from a friend of a friend. I wanted something to work on and replace the 307 is my car. havent been on the forum in a while and in that time ive done alot. However, the engine is out of a 74 impala and its supposed to be that police interceptor model with the TH400 setup? (Im not expecting anything special).

It has 882 casting heads - 76cc chambers and 1.94/1.5 valves, and i was wondering, if i could find a cheap set of double hump heads, what kind of increases, if any, would i see?

I would try to find 64cc chambers with 2.02/1.6 valves. I have stock dished pistons and i know that the double humps would definitely help raise the compression.

im not expecting a drag racing engine cause im putting double humps on, im just thinking along the lines of heavier casting, better flowing, and higher compression.

Thanks.

 

The double hump (camel hump) heads came with either size intake valves, but most were 1.94's. They also don't have accessory holes on the ends, so keep that in mind.
I would check the suffix code on the front pad of the block to see what it was really out of. It being a "police interceptor" engine is only a "story" without checking it out.

 

I would just go with a set of Vortecs. They can be had for less than $200 and are a much better bolt on than the double/camel hump heads.

 

I too would say go with Vortec heads. They'll make a little more power, but you will need a correct intake manifold to use with them.

 

Well, the suffix code is CMJ which can either be a 1980 305 (definitely not), or a 74 350 "TH400 Police". And I took off the heads and its for sure a 350. Ive heard of the advantages of vortecs, but always was under the impression that they are expensive and you need the right manifold and no big deal, but the valve covers.

Using a compression calculator, i put in all the information for a 350 including the book specified 8.5:1 CR on the CMJ suffix code at 76 cc chambers. when I changed the chamber size to 64 cc's, the compression jumped to 9.55:1. if that was true, what kind of gains would that yield.

Im only considering the double humps because im on a pretty tight budget, and they seem like a pretty good choice for a decently powered street motor.

 

All the double humps I have seen people want $$ since they are "double humps"

Vortec's are the way to go for performance on a budget, valve covers are same center bolt any other and intakes are readily available. You can pick up a complete set of heads off eBay for <$600

 

Vortecs may sound like a PITA to get to work, but they really aren't. You can get a used set from a 96+ pickup with a Vortec 350, usually around $150. Either use self aligning rocker arms, or install screw in studs with guide plates. Vortec style intakes are readily available, and any center bolt style valve cover will work. Keep in mind what cam you want to use, as the Vortecs are limited to around .430" lift in stock form, but can be easily machined to accept a larger cam.

 

I have a set of Vortec heads and intake manifold for you for 600 for both and i will even throw a set of rocker arms in and valve covers if you like. Where are you located as i am in Gimli,Manitoba Canada. Let me know if you are interested. If you are on a tight budget but have a few dollars to spend,Partiot Freedom aluminum heads,.and they make good power and flow very nice. But i have the other option for you if you are interested.Just thought i would let you know as every man likes to build cars for a hobby and i like to help when i can

Denny