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Old 06-10-2002, 09:47 AM
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Question 305 heads on a 350

Is there any advantage in putting 305 heads on a 350? I heard someone mention this one time and was just wondering. Thanks, HRS10

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Old 06-10-2002, 10:45 AM
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Most of the 305(or maybe all) have 58cc combustion chambers which ups the compression ratio on your motor and gives you more horsepower. But beware. If your wanting to run pump gas and already have slightly domed or even flat tops with 2 valve reliefs, you can raise it to hi and will need race type fuel or it will ping and run into detanation problems. HG
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Old 06-10-2002, 11:03 AM
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BE AWARE TO THAT THE 305 HEADS USE A MUCH SMALLER INTAKE AND EXHAUST VALVE, MOST ARE 1.72 INTAKE AND 1.48 EXHAUST COMPARED TO MOST 350 HEADS BEING 1.94 INT AND 1.50 EXHUAST. THERE IS ALSO A SIZE DIFFERENCE IN THE CC VOLUME IN THE INTAKE RUNNERS, THE 305 BEING MUCH SMALLER. SO WHILE YOU MAY INCREASE COMPRESSION WITH THESE HEADS YOU WILL BE CHOKING THE ENGINES ABILITY TO BREATH THUS INCREASING OCTANE REQUIREMENT AND LOOSING PERFORMANCE. I HAVE SEEN MANY PEOPLE DO THIS AND END UP HAVING DETONATION AND OVERHEATING PROBLEMS THAT WERE ONLY SOLVED BY PUTTING 350 HEADS BACK ON..
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Old 06-10-2002, 11:40 AM
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Overheating problems.I don't know.Did this with
a 350 in a 76 GMC pickup I had.Sure ran better
than the over 70cc stocker heads I had.If you are
going to use in racing fasion go ahead use race gas,but I didn't have any problems using 93
octane with em.Good Luck.
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Old 06-10-2002, 12:18 PM
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sorry about the last post in all caps. As to why the heads probably worked on a 76 350 is due to almost all mid 70's smog 350's used dished pistons which would keep your compression relativley tame with the 305's 58cc chambers. I dont by any means consider myself an expert here, I am just going off what i have seen in the past with this. I had an '80 malibu that i put a flat-topped .030 350 in but i used the heads that came off the 305 that was originally in the car and i had to retard the initial timing so far to keep it from detonating that it would run hot from being so retarded. I have also seen others do the same thing with the same results. One of the machinists at the machine shop i use here told me that the 305 heads lack a water jacket below the spark plug hole that all other sbc heads have which also contributes to detonation and heating problems when the compression gets high. Just sharing my experience with them. hope this helps
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Old 06-10-2002, 05:29 PM
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I put 305 heads on a 350 with dished pistons.With a mild cam ,4bbl and headers.The motor ran like a raped ape.Comp was probably around 9.5:1 w/ dished pistons.
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Old 06-11-2002, 05:15 AM
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Just my two cents,Some 305s has a 1.84&1.50 valves,If you do some grinding on the chambers you could eliminate detonation problem by this,is what I mean is to get you a 350 gasket lay it on your heads and you wiil see all the over hang the chamber poses,scribe a line around the gasket on the head chamber and roll back the edges of the chambers to close to your scribe line,and then remove any sharp edges in the chamber and do some work on the intake & exhaust ports removing extra & rough materials.Okay I done this spent a lot of time on these heads I had, but didnt work because the heads had been milled before I got them had no clue how much apparently to much because after I got done doing what I did,I had them milled again just enough to clean them up put them on oil soaked intake valves & smoking like a freight train apparently intake was not sealing from being milled to much.Needless to say didnt work out for me but I think they would have except the mill part went wrong.I know some low buck round track racers that use these because there a dime a dozen.but its important to get those sharp edges out of the chambers.so the moral of this story is make sure you have virgin heads.PS ended up putting 350 hogs on it,cleaned them up some what,( not to bad)Always trying to make chicken salad out of chicken *****.sometimes it works sometimes it dont trial and error,tight budget but Im a gear head.enough rambling good luck (wrenchturner)
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Old 06-11-2002, 11:36 AM
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Sorry about my last post.I had a 1976 GMC
1500 pickup and a 350.The heads are 58cc
but did not have dished pistons.They are
flat top 4 relief style.Compression is about
11.5-1.Anyways no overheating or detonation
problems with mine,but who knows,maybe I got
lucky.If you are going to try this,good luck.
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Old 06-11-2002, 02:03 PM
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Had my 350 w/194's removed and replaced with same--i thought, took it out although it ran better! found out it was a 327 w/305 heads and little intake valves!! Most of the replies that are raving abaout the 305 heads seem to be pick up trucks like mine was. read that lower rpm torqey motors. if that you, you'll love'm.
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Old 06-12-2002, 07:09 PM
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I have been told the exaust manifolds are differnt on 305 heads. All other small block bolt patterns for the exaust are the same. Unless you have a newer late modle engine
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Old 06-14-2002, 10:00 PM
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No problem using headers on the ex.at least the ones I had.(wrenchturner)
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Old 10-19-2003, 04:03 PM
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305 HO Heads on a 350

I have a 350 with flat tops and 14014416-305 HO heads that I ported and polished and a 280/480 cam also a turbo 350 trans with 308 gears so what head gasket is the right thickness for my engine and how will it run ?
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Old 10-19-2003, 04:15 PM
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We had a set of 416 305 heads with 1.94 intake valves in them on our race car one year.They did pretty good up to like 5500 RPM. Another guy in our class ran a set of the 305 heads that he put 2.02/1.6 valves in.They didn't do bad either.
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Old 10-19-2003, 04:55 PM
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Re: 305 HO Heads on a 350

Quote:
Originally posted by smokin
I have a 350 with flat tops and 14014416-305 HO heads that I ported and polished and a 280/480 cam also a turbo 350 trans with 308 gears so what head gasket is the right thickness for my engine and how will it run ?

How far down in the hole are your pistons?
I think youre pushing your luck with compression. I would try to unshroud the valves to gain a few CCs in combustion chamber and run a fiber gasket .040 thick, running a steel/copper shim is just going to aggravate the problem.
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Old 10-19-2003, 05:53 PM
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well im' not to sure. Im' running the engine right now with 14022601 heads and im' not to sure if the swap would be worth it.
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