350 with 305 heads question.

[7D2N]

After checking casting numbers will 305 heads and 350 work together ok. I have been fighting a small carb backfire issue on my project. any ideas.

Thanks
7D2N

[cableguy0]

Not usually. 305 heads don't flow flow well and will choke a 350. 305 heads also will bump compression often too high for pump gas. What octane fuel are you using? What cam are you using? What is your timing set at? What are the specs on the rest of the engine? 305 heads on a 350 generally wind up with in an engine that doesn't perform great and is a PITA to keep "tuned"

[franken]

My small mind seems to recall that 305 heads are 58cc, and don't go well w/ a 4" bore as cable said.
Sneezing through the carb indicates a lean condition. Backfiring (as in fire) indicates a timing or firing order problem.

[7D2N]

Originally Posted by cableguy0

Not usually. 305 heads don't flow flow well and will choke a 350. 305 heads also will bump compression often too high for pump gas. What octane fuel are you using? What cam are you using? What is your timing set at? What are the specs on the rest of the engine? 305 heads on a 350 generally wind up with in an engine that doesn't perform great and is a PITA to keep "tuned"

I don't anything about the internals of the motor. I picked it up non running, it has the 1972 350 block and the 74-76 305 heads (for some reason) with eldonbrock performer manifold topped with 1406 eldonbrock carb which has been rebuilt. looks like the PO tried to freshen the top end. I can't time the backfire out, checked for vacuum leaks, checked wires, new plugs. I plan adjust valves. kind of stumped. Not sure how much $ to throw at the motor.
Thanks 7D2N

[68c10owner]

Actually the 305 ho heads flow extremely well on a 350. They have the same runner as the old camel humps. Install a larger intake.valve from the 1.84, some bowl work and gasket match and they work well. I beleive the castings to look for are 416. There are a couple others but cant recall at the moment.

You do have to be carefull about the extra compression. Depending on what piston you have it could bump it up too high for pump gas.

[Coach529]

601's are another great 305 casting.

[7D2N]

#462624 head cast 58cc. I don't know if any work was done before but they are painted chev orange. heads are real clean inside no junk or build-up and oil looks to flow good. I 'll get the valves adjusted and see how it goes from there. Thanks for the help guys.

7D2N

[Captainfab]

The 624's are not 305 heads. They are a light weight smog head used on the late '70's and '80's 350's and 400's with a large 76cc chamber.

[GASoline71]

No way would I use a 305 head on a 350. 2 different 350's I've had come through me with 305 heads on them from PO's were useless.

Sure they bump compression but I don't care what anybody says, they will not flow well enough for a 4" bore engine to get any benefit. If they did... then there wouldn't be any 305 heads as available as there are now, because everyone would be doing it.

Gary

[68c10owner]

Originally Posted by GASoline71

No way would I use a 305 head on a 350. 2 different 350's I've had come through me with 305 heads on them from PO's were useless.

Sure they bump compression but I don't care what anybody says, they will not flow well enough for a 4" bore engine to get any benefit. If they did... then there wouldn't be any 305 heads as available as there are now, because everyone would be doing it.

Gary

I desagree because I have seen them work. They were all the ho heads with larger runners, had a little larger intake valve put in and some port work but they worked fine.

That said I wouldnt do it myself. I would just change pistons and use a much better head.

[A1971Blazer]

Originally Posted by 7D2N

I don't anything about the internals of the motor. I picked it up non running, it has the 1972 350 block and the 74-76 305 heads (for some reason) with eldonbrock performer manifold topped with 1406 eldonbrock carb which has been rebuilt. looks like the PO tried to freshen the top end. I can't time the backfire out, checked for vacuum leaks, checked wires, new plugs. I plan adjust valves. kind of stumped. Not sure how much $ to throw at the motor.
Thanks 7D2N

The backfire may not be related to the heads or the carburetor.......some of those old motors were bad to wear off a cam lobe or two.
I had a '72 350.....it had several lobes worn off the camshaft.....I would check that first.....pull the covers off and stuff some rags along the bottom of the head to catch the oil spatter and start the motor......observe the action of the rockers while it's running.....you may see one or two that are barely moving.
If so your cam is shot.

[7D2N]

Originally Posted by 7D2N

#462624 head cast 58cc. I don't know if any work was done before but they are painted chev orange. heads are real clean inside no junk or build-up and oil looks to flow good. I 'll get the valves adjusted and see how it goes from there. Thanks for the help guys.

7D2N

Captain, I found the info on Fastnuf.com Head Identification Charts, I will look for a few diffrent casting web sites.

Thanks
7D2N

[Captainfab]

Here is where I looked to verify. Mortec is a fairly reputable resource.

http://www.mortec.com/castnum.htm

The 462614 is a 305 head. The 462624 is a 350/400 head. I have had the 624 heads in the past and I currently have a set in my shop that I pulled off of an all original SB400.

[7D2N]

Originally Posted by Captainfab

Here is where I looked to verify. Mortec is a fairly reputable resource.

http://www.mortec.com/castnum.htm

The 462614 is a 305 head. The 462624 is a 350/400 head. I have had the 624 heads in the past and I currently have a set in my shop that I pulled off of an all original SB400.

Thanks Captain, I checked 3 other web sites for the casting number and all confirm being 350 400 heads. I should have researched further before posting. I thought 305 heads could have contributed to the engine backfire.

Thanks all for your response
7D2N