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05-19-2013, 07:20 AM
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#1 |
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Registered User
Join Date: Aug 2012
Location: Plymouth Devon
Posts: 20
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350 / 305 heads
Hi guys
I am after a bit of your knowledge please I have a 1970 c10 which I got last year,the truck ran fine,plenty of low end torque and no problem laying rubber when the need arose. It did have some oil leaks from the top end and a few weeks ago I decided to pull the heads off and do a top end gasket change. I took the engine Numbers and it has a 73 350 motor in it so I took the numbers off the heads and it comes up as 305 heads. will it be ok with these on ,the truck is not raced and generally I don't go over 70 to 80 mph thanks Si |
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05-19-2013, 07:31 AM
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#2 |
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Registered User
Join Date: Mar 2010
Location: Mechanicsville, Va
Posts: 71
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Re: 350 / 305 heads
That is an old racers trick to get more compression. The 305 heads have smaller combustion chambers and usually run 57cc to 62cc from I can remember. If you plan on running higher RPMs or really pushing the motor, larger runner heads will breath better. But, if it runs ok for what you do now, nothing hurt imho.
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05-19-2013, 08:25 AM
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#3 |
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Registered User
Join Date: Aug 2012
Location: Plymouth Devon
Posts: 20
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Re: 350 / 305 heads
Thanks the engine did seem to breathe a bit heavy ,it has pipes coming off the breathers pointing under the truck
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05-19-2013, 10:51 AM
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#4 |
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laying low
 
Join Date: Mar 2001
Location: Searcy, Ark. USA
Posts: 13,099
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Re: 350 / 305 heads
I ran them successfully on a 327 years ago. Slightly higher compression and in the hot summer time it tended to ping some. Had to watch the timing advance.
__________________
Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross |
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05-19-2013, 01:56 PM
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#5 |
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Registered User
Join Date: Oct 2012
Location: oran,mo.
Posts: 171
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Re: 350 / 305 heads
the 305 heads will have smaller valves,
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05-19-2013, 02:05 PM
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#6 |
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Registered User
Join Date: Mar 2013
Location: Chula Vista (SD) CA
Posts: 50
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Re: 350 / 305 heads
Compression bump yes, breathabillity no. It was a myth with in inline 6's to put a 194 head on the 250's and some guys did a **** load of dyno runs on just about every set up known to man. To find that although it sounds right to use the smaller head, the numbers do not show it but in fact hinder the engines abilities. $0.02
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http://http://67-72chevytrucks.com/v...d.php?t=578181 |
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05-19-2013, 02:13 PM
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#7 |
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Registered User
Join Date: Aug 2012
Location: Plymouth Devon
Posts: 20
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Re: 350 / 305 heads
So with the increased comp will this lead to heavy breathing through the breather caps ,also is it likely to cause oil leaks from the seals/gaskets.
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05-19-2013, 02:50 PM
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#8 |
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laying low
Join Date: Mar 2001
Location: Searcy, Ark. USA
Posts: 13,099
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Re: 350 / 305 heads
Your crankcase pressure is a result of compression getting by worn piston rings, called blowby.
__________________
Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross |
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05-19-2013, 03:03 PM
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#9 |
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Registered User
Join Date: Aug 2012
Location: Plymouth Devon
Posts: 20
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Re: 350 / 305 heads
Damn that don't sound good,the oil pressures good even on a 250 mile run
You can see the vapour mist coming from the breather pipes,it doesn't use much oil,am I being too cautious,it is an old motor. |
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