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11/3/15 4:28am - Original Message: 'Head porting'
Grahamred70
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, - United Kingdom

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1970 convertible in red 350

Joined: 10/6/2015
Posts: 82
I've done a bit of porting in the past on other engines, mainly just tidying up rough edges and a bit of smoothing. The block in my car is a non original 74 truck block which I assume was fitted to get 4 bolt mains, heads are 3927186, performer inlet, Holley carb, Hooker headers and side pipes but no clue as to pistons or cam.
I'm thinking I could put a clock gauge on the rockers to measure the lift on the cam to get some idea about what it could be.
For the future I have a mind to do some porting of the heads to improve them if they've not been touched yet, do I need hardened exhaust seats or are they already OK for unleaded.
In reading up I keep coming across the term "pocket porting" can someone explain this as it's a term I'm not familiar with, also any info as to where best to remove material and areas to avoid etc. would be a big help.
Car is a 1970 350 4 speed convertible by the way.
 
Many Thanks
 
Graham
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11/3/15 8:47pm - Reply: 'Re: Head porting'
kstyer Lifetime Member
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CUYAHOGA FALLS, OH - USA

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1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!

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When many people port, they just do the edges at the openings of the ports.  Pocket porting goes much further into the head and manifolds.  This pays close attention to the area around the valve stem and above the combustion chambers.

There is a lot of variation between heads, so I don't have a good answer about trouble spots.  you can usually tell the runner thickness with your fingers, one in each runner.  Be careful they are even and you don't get too thin.   Remember, if you remove too much on a stock engine you may actually lose performance do to air flow speed.  Engines with performance cams, larger valves and higher compression need to larger ports to do their best.  A good clean up in a stock engine is usually enough without removing a lot of material.
 
Port matching is always a good idea.  Use the gaskets as a guide and make all the edges between the manifolds and head ports match.  An uneven edge will hurt performance.
 
I don't know if those heads have hard seats.  If they do unleaded is fine.  But when you take them off you can see if it has hardened seats.  If not, have them put in and you will avoid and problems.
 
How about it some of you guys with the reference books,  do those heads have hard seats?


|UPDATED|11/3/2015 6:47:55 PM (AZT)|/UPDATED|


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11/4/15 1:11pm - Reply: 'Re: Head porting'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

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#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

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 Those heads were used in several configurations from '66 to '70, including being used on the Z28 Camaro, and the mighty LT-1 engines. They could have 2.02/1.60 valves, or 1.94/1.50 valves. In ANY configuration, unless they have already been updated, they will NOT have hardened valve seats from the factory.
What are the date codes on them? This is a '70 LT-1 head(Jan 28, 1970)



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Joel Adams
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11/4/15 5:35pm - Reply: 'Re: Head porting'
Grahamred70
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1970 convertible in red 350

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I'm guessing these are the original heads from the car mounted on a replacement block, I'll see if I can find the date mark, if I go as far as removing them I'll get the valve seats done but until then I'll carry on using additive.
Graham
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11/4/15 6:11pm - Reply: 'Re: Head porting'
F4Gary Gold Member
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Grapevine, TX - USA

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Pretty sure they went to hardened seats in '71.  But, if you aren't going to race or tow, you really don't need the hardened seats.  Then, again, if you are overhauling the heads, that's the easiest and cheapest time to do it.  I don't know how much that costs.  I went with the 3 angle grind for an extra $60.

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11/4/15 10:11pm - Reply: 'Re: Head porting'
Adams' Apple Lifetime Member
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Yeah...I'm also thinking '71 was the first year they started using the hardened seats. I know by '73 it was across the board.

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11/6/15 5:32am - Reply: 'Re: Head porting'
Grahamred70
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, - United Kingdom

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1970 convertible in red 350

Joined: 10/6/2015
Posts: 82
I'll have a proper look at them over the weekend, I could see the casting number through the oil filler hole so didn't need to take the covers off.
Obviously if I have the heads off any way I'll do the seats at the same time if they're not already the hardened type, I have other older cars which I use the additive so it's not a big issue for me just didn't know when the change came in, I know it tended to be a lot earlier in the US than over here where we continued with leaded fuel for a lot longer.
If I can get the lift and approximate timing of the cam we may be able to figure out what could be in there.
 
Thanks
Graham
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11/14/15 5:48pm - Reply: 'Re: Head porting'
Grahamred70
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, - United Kingdom

Vette(s):
1970 convertible in red 350

Joined: 10/6/2015
Posts: 82
Date code is D2 0 so April 2nd 1970 which ties in with the date on the trim plate so I'm thinking the original heads on a later block.

Graham
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