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Old 06-23-2004, 05:36 PM
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Max bore

What's the most you can bore out a 350 chev before running into trouble?

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Old 06-23-2004, 05:48 PM
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.060 for most, but if you plan to go over that, I`d have the block sonic checked.
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Old 06-23-2004, 05:59 PM
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10-4,
one more thing I forgot to ask:
is putting 305 heads on a 350 a good way to increase compression ratio, or do the smaller heads just choke the rest of the engine?
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Old 06-23-2004, 08:48 PM
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NO, YES
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Old 06-23-2004, 08:59 PM
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What 305 heads, there are some 305 heads that are way better then alot of 350 heads namely the 416's, 601's, and 081's all the other heads are pretty crappy. If you port them up they flow more the stock vortecs. Some people have gotten them to flow more then 240cfm @.500". They will also raise your compression nicely if you have dished pistons.
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Old 06-23-2004, 09:27 PM
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Unless you have a lot of money and experience porting, the last post is pretty useless.

tom
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Old 06-23-2004, 09:38 PM
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What are you talking about?

Porting 305 heads with pics

DIY Head Porting
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Old 06-24-2004, 09:36 AM
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I always say reading is a great thing. But when you read a book and then consider your self to be some kind of expert...

The only thing I see this guy has done was to smooth the walls and roof. This is not porting. This is smoothing the walls and roof. Why even buy a grinder? You can do it with a sand paper and you finger. If he were to try to relocate the port's, then he would find that the heads he is working on will never match any vortec head. Although Vortech heads flow figures are slightly expanded from most of what I've seen in comparison to any of my testing and research. No doubt due to there ever increasing popularity.
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Old 06-24-2004, 09:58 AM
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yeah tom and johnsongrass are right on this one.

i read that post the guy on the F-body forum did on his 305 "porting" and polishing job and was thoroughly unimpressed. I can't remember what exactly it was that he said, but it was something to the effect of "port matching is a load of crap" This is the point where I was laughing and clicking the little X button in IE.

Porting and polishing seems simple, in principle. But the truth is, unless you have experience doing such work, you're unlikely to be part of the "some" that got their 305 heads to flow as well as a set of Vortecs.

tbw
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Old 06-24-2004, 11:05 AM
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Ok you guys can believe whatever you want. I will agree that being a novice you will not get optimum results like a professional porter, but you can really increase the flow with alittle work. All you really have to do on sbs heads is port the bowl and really port the exhaust.

You don't have to be a professional porter to port heads and make your heads less. If anybody tells you different they are morons and a bunch of posers that have never really worked on there car. And you call your selfs hotrodders, i don't know any hotrodders that don't do their own engine work.

305 head =junk, low perf small ports.
Not true. The ports on these heads are the same size as the rest of factory small block heads. In fact they are a little larger
in volume than some 350 sb heads. Just about 165cc's stock.
The exhaust ports are the same as 350 head exhaust ports.
Once ported with 350 sized valves, they are pretty good.
Even with just the larger valves and some proper bowl work
They come right up in flow. about 220cfm@28" with a 2.02.
thats not bad at all. The exhaust needs some porting but nothing someone can't handle at home. Even the intake can be finished ported at home to about 234/240cfm.
Yes they could be considered a High volocity head, which is just what you want on a street 350. A huge head will be lazy at low rpm.
These heads are a good buy for the money and a new set of S/R's will cost more and flow less (out of the box).
As long as the rebuild quality is good, I give then the thumbs up.

Very few changes made to my casting number 14022601 heads. Removed casting flash, gasket matched heads, intake, & exhaust manifolds. Put in a larger cam. I am running precision engine parts 1.84 & 1.50 race valves (stainless, undercut, swirl polished). I also have Z/28 springs, chromemoly retainers and keepers, and new seals. The guides were replaced with bronze guides. The valves were installed with a good 3 angle valve job. The heads were also angle milled dropping the chamber from 58cc to 54 cc. The heads also end up being like 20* heads instead of 23*. Half way to 18* heads!!! They are on my G20 Chevy vans little 305. It is a potent little sucker. The total cost was around $600.00 for everything I have done. That includes cam kit, gasket set, valvetrain components, rebuilt heads, and misc other things.
Here are the flow numbers @ 28 in/H20.


Lift Intake Exhaust
.050 35.60 15.00
.100 72.40 47.00
.150 105.8 72.50
.200 133.4 98.00
.250 154.1 117.5
.300 180.6 137.0
.350 195.5 145.0
.400 209.3 153.0
.450 217.4 155.0
.500 224.3 157.0
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Old 06-24-2004, 12:50 PM
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Good for you, ME Leigh. I'm glad you got such good results from your extensive work.

The reason I was agreeing with tom and johnsongrass about being *cautious* about undertaking a port / polish job in one's own garage is because this thread started with someone asking "What's the most you can bore out a 350 chev before running into trouble?"

Based on that question, I start making assumptions; such as the approximate level of experience of the builder, and what they are and are not likely to be able to accomplish in a reasonable manner.

Of course porting and polishing a set of cast heads like those 305's is going to improve their flow. But should a novice undertake such a project? In my opinion, no. $400 for a set of 305's to port is affordable, yes. What happens when the novice grinds through a thin portion of the head and opens up the coolant circuit? Then you've got a $400 set of wheel chocks.

"And you call your selfs hotrodders, i don't know any hotrodders that don't do their own engine work."

Part of being a hotrodder is being smart about what you decide to hotrod. I do ALL of my own engine work, as do many members of this forum. The trick is not going overboard and ruining a perfectly good part -- that's what a set of practice heads are for!

tbw
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Old 06-24-2004, 04:01 PM
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IF you have the means and talent, yes you can make a set of 305 heads usable. But you still have pressed in studs, thin wall castings, shrouded chambers, etc. If you have to pay someone else to do the porting, stud installation, etc., there are better ways to go.

As an engine machinist, I see a lot of guys who bite off more than they can chew and end up farther behind on there hot rod projects than they started out to be.

I do my own engine work. I also have access to the proper machines to do the work right. To say that someone is not a "hot rodder' simply 'cause he chooses to have someone do the work he isn't equipped to do or isn't sure of the right way to do it is kind of big-headed. Good for you if you can do it yourself, but don't look down on those who have enough sense to have work done for them or buy a head that is better than a stock one to begin with.

tom
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