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Old 06-21-2011, 11:54 PM   #1
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350 engine with 305 Heads

I have an 86 305 TPI camaro, I found a used 350 block out of a 94 chevy 2500. He is selling the 350 iron heads seperate. I would like to use my 305 heads, just have them ported polished and larger I/O valves. Would the 305 heads work with the 350 block. I read other threads that it is possible but they dont go into much detail, Ive read that the pistons have to be flat and not domed. Also that I might have to have the intake ports in the heads machined to a different size.

Any info over this would help, and how much should I offer for the block he hadnt set a price.

Last edited by R/T-Z28; 06-22-2011 at 09:54 AM. Reason: Not enough info.
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Old 06-22-2011, 12:09 AM   #2
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Re: 350 engine with 305 Heads

You don't need to do anything, they bolt right on.
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Old 06-22-2011, 09:07 AM   #3
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Re: 350 engine with 305 Heads

Well yeah, they do bolt right on, but the 350 needs to have dished pistons, not flat top or domed.
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Old 06-22-2011, 09:56 AM   #4
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Re: 350 engine with 305 Heads

Sorry about that, I got in a hurry and didnt put enough info into my original post.

I would like to use my 305 heads and intake on the 350 block. I have read that it will work but that there is a serious problems with top end RPMS, could anyone go into greater detail?
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Old 06-22-2011, 11:43 AM   #5
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Re: 350 engine with 305 Heads

There are no top-end RPM issues.
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Old 06-22-2011, 02:11 PM   #6
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Re: 350 engine with 305 Heads

Depends what you mean by high rpm. If you're going to use stock style TPI, then no worries. If you're thinking of an HSR and a big cam, then have the 305's #416 heads machined for 1.94" / 1.60" valves.
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Old 06-22-2011, 03:23 PM   #7
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Re: 350 engine with 305 Heads

Thanks for the info guys I think Im just gonna buy the block and iron heads instead of reusing the 305 heads.
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Old 06-22-2011, 03:47 PM   #8
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Re: 350 engine with 305 Heads

Which heads are you getting? Odds are they're a lot worse than the LB9 heads you've got.
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Old 06-22-2011, 03:53 PM   #9
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Re: 350 engine with 305 Heads

You can use flat top pistons with 305 heads on a 350.
Where are all these misconceptions coming from, seriously?

Do a search on this forum under F-bird88, he posted NUMEROUS times about using 305 heads on a 350. It's very common. The 305 heads are generally better than a lot of stock 350 heads. 1994 2500 heads were probably TBI heads, ie 193 castings. Suited for truck use, ie low RPM.
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Old 06-22-2011, 03:59 PM   #10
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Re: 350 engine with 305 Heads

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You can use flat top pistons with 305 heads on a 350.
Only if you can keep the compression under control.
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Old 06-22-2011, 05:36 PM   #11
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Re: 350 engine with 305 Heads

I searched for post and threads (F-bird88) and couldn't find anything. Maybe I'm just a little weetaded, but the 305 heads and tpi intake should work with the 94 2500 block regardless of pistons. Flat or domed or dished right? Ill take ask for the casting numbers on the 350 iron heads he has.
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Old 06-22-2011, 06:51 PM   #12
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Re: 350 engine with 305 Heads

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Only if you can keep the compression under control.
Exactly. 58cc with flat tops and proper quench will result in 11:1. Fine if you're running a 300 degree cam, or 120 octane race gas, or driving around La Paz.
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Old 06-22-2011, 09:08 PM   #13
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Re: 350 engine with 305 Heads

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Only if you can keep the compression under control.
But of course. This is true of any engine combination however. You should always check your compression ratio when mixing and matching parts. The statement "can't" I typically read to mean "will not fit". Like trying to put Ford 302 heads on your Chevy 350. That's a "can't". 305 heads on a 350 with flat-top pistons is a "be careful".

FWIW - i'm running 305 heads on my flat top 350. It's got 10:1 CR and runs on 92 octane at 4000' sea level. Granted, I did some porting to the heads and they are now 64cc. All in the details. However the heads will FIT on a 350, even with flat tops. It would FIT with domed pistons too, but I can't imagine the scenario where that situation is plausible...

I have no idea what a 1994 350 will have for pistons, but I doubt they are flat tops (5cc).
I imagine the stock heads are 64cc, and the stock CR is ~9:1 (truck right..) So going down to 58 cc heads, with no other changes, should bump your CR up to the high 9's. Good to measure and be sure, but you won't see 11:1 unless you're installing aftermarket flat tops, decking the block, etc.
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Old 06-22-2011, 11:46 PM   #14
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Re: 350 engine with 305 Heads

If I were to buy the block and rebuild with a new cam and pistons (what pistons would you guys recommend), and get the 305 heads ported and polished with bigger valves some new rocker arms, stock 350 injectors. Everything else would be swapped over from the 305. Would this give me a good working combination. Im not looking for a drag build or real high horse power. I just want to upgrade to a 350 for now.
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Old 06-23-2011, 02:35 AM   #15
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Re: 350 engine with 305 Heads

Heed the advice here... your 350 heads are likely worse than your 305 heads. Those 416s/081s are decent heads. I've seen them do 12's on a 305 car! All motor! Paying a little to get larger valves put into your 305 heads would be a very good move IF you've got dished pistons and can keep your compression ratio in the 9's. If you're mid 10s or more, go ahead and look for something else. Just look and see if the pistons are dished or not, dished pistons are very likely a go for the 305 heads, flat tops likely mean your 305 heads will skyrocket your compression ratio too far. As far as the actual parts are concerned, everything should bolt right up with no problems.
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Old 06-23-2011, 11:22 AM   #16
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Re: 350 engine with 305 Heads

Alright, thanks for info guys. It was a lot of help.
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Old 06-23-2011, 11:22 AM
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