Technical Confused sbc head question

I have a 305 pulled from an 86 Chevy truck . I’ve been running this engine for 5 years with no major issues but have decided to do a rebuild as it has almost 200000 on it . Going through what I have the casting numbers on my heads are 3998993 and 3998997 my research shows these are 350 heads but I’ve found some that say they were used as low power heads on trucks in the mid 80s can anyone verify this ? My rebuild kit will be here tomorrow and I only have a limited time to put this back together. Thank you


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No input other than with two different casting numbers, leads me to think someone has had their hands on the engine before


Next thought, if running good and no issues, why take it apart?

 

I get,
3998993 is a 68-76 350 truck head, 1.72 intake valve.
3998997 is a 1972 400 1.94 intake valve. Lippy

 

It was starting to burn oil and smoke and rear main seal started to leak.


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Both heads I have are 1.94 intake valves


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Did you read the numbers right? Just asking. Lippy

 

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https://outintheshop.com/faq/casting/heads.html

 

Some Ford and chevy motors had interchangeable parts but not ford interchanging with gm.

 

I’ve only taken apart 5 or 6 SBCs that I knew the history of, last to mid 80’s up, but all had the same head numbers. I guess GM could have put on something that was the same, I’ve just not seen it

 

3998993 307/350 68-79 1.94/1.50 76cc
3998997 350/400 71-73 1.94/1.50 76cc

I'd say somebody put a set of rebuilt heads on that motor sometime in the past.
Most 400's I've seen had extra cooling holes drilled in the web between the cylinders.

 

I was going to ask for a pic of the other sides. All 400's had steam holes as they are siamesed cyls. I'm still getting 997 is a 400 head. You can run 400's on a 305-350 but not the other way around unless you drill the steam holes in them. Lippy

 

400 SBC heads have what is called steam holes. Lippy beat me to it.

 

But why would anyone put 350 heads on a 305?


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Never saw a 307 with 1.94 intakes lol 350-400 heads on a 305 yes.

 

I would say the normal rebuild shop would just put any head that would fit nowadays. Then when it ran lazy they would say, just the way it is. lol

 

Bigger valves, some rebuilders pushed 350 heads as standard so less part#'s to stock.

 

Until they put 350 heads on a 400, lol Lippy

 

It can be done, all you have to do is drill the holes.
At one time 400 head cores brought a premium price....................

 

I meant till the un knowing shop didn't drill the holes and sent it out. Lippy

 

So other than the loss of compression is there any other draw backs to using these heads on a 305?


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Were you happy with how it ran before?
What pistons are in that engine flat top or dish?
In the past I've put used heads off 350's on 283's, 305's, 307's and 327's simply because I had them and it made the car/truck run again I can't say there were any adverse effects, of course these were not running times at the drag strip just solid running engines.

 

It ran fine but I did notice a little less power at the end of last year.I’m not one of those guys that has to spin the tires everywhere I go or drag race every light this is just my fun cruising car and I do drive it every chance I get ( weather permitting) . So I’m just looking for good and reliable not balls to the wall power after all it’s just a 305.


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That's enough

 

For instance. had a 305 with 350 heads in my Camaro. Bought it that was and had no problems.
Also had a 289 with 302 parts in my Pinto.

 

I’ve gotta roll with lippy, all 307’s had 1.72 intakes.


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Then the loss of power may have been it just was time to freshen her up. You should be fine. Only you know what you need, we just try to answer questions in the best way we can. We always banter back and forth between us. That is how we share info. LOL. I just hope we helped in some small way.

 

The 416 and 601 305HO heads are the heads you need for that engine and are not that expensive, they offer a smaller cc and would wake your engine up as compared to those 350 and 400 heads you have now.

 

Thank you for the input. While I’m disappointed these are 350 heads . They are what I have and know they are good functioning heads. So most likely I will reuse them.


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3998993 307/350 68-79 1.71/1.50 1.94/1.50 76cc
3998997 350/400 71-73 1.94/1.50 76cc