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Old 04-23-2013, 07:45 PM
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pontiac 350 eng.

what if any heads would increase the hp in my 76 p/350 without valve clearance problems ? Any suggestions will help ! #'s like 48,47, I've seen for sale halfway resonable !

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Old 04-23-2013, 07:55 PM
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Calling all Pontiac experts..........
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Old 04-23-2013, 11:44 PM
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I'm no expert, but I'll try to help. If this is a street engine, 47 heads would give you about 9.2:1 compression, 48s would give you about 10.5:1 which would be too much for pump gas. These numbers are assuming that you have a standard bore and a zero deck with flat top pistons.

Bill
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Old 04-24-2013, 08:27 AM
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Quote:
Originally Posted by f/bird View Post
what if any heads would increase the hp in my 76 p/350 without valve clearance problems ? Any suggestions will help ! #'s like 48,47, I've seen for sale halfway resonable !
Well... your heads are probably 6X 4 s which are supposed to be 92 CCs. that would put your static compression at 7.55 to one. A tad anemic.
#47 are advertised at 73 CC. That would boost you to 8.91 to 1. Much better.
# 48 heads are advertised at 1 CC smaller at 72 CCs which would put you at 9.0 to 1 .
Remeber heads need to be CCed to be sure of chamber size and advertised sizes are rarely accurate.
Since the heads are off the engine it makes them easy to check the chamber size.
What is your goal? street machine? All out dragster? ??
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Old 04-24-2013, 08:52 AM
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use the 48's bigger valves. however 350's are ok, but id build a 400.
more powAr!
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Old 04-24-2013, 09:05 AM
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I want enough power to do a bit of a burnout if wanted , I'm not going to the track to race so speed is'nt a big thing "but it's nice to have the ability" . I presently have 6-x 's now and I'm getting ready to do the intake w/4 brl.Q/jet swap along w/new timing chain/gear , I also have a new distributer/with higher volt coil and such " It's one of the cheaper ones " but it's new. I'm just getting prepared in case the compression test is'nt good when we do that . If I need to do anything w/heads I was thinking of something that would boost the hp. Is there a big gain with some diff heads or is there something that can be done with the 6-x to improve them ? I'm not looking to go high $ as I'm looking to save what I can on this motor and eventually getting a 400 . I can start w/more hp than I can probably get out of this 350 !!! Thanks for any help !
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Old 04-24-2013, 10:01 AM
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Agreed, small-valve heads are "better" for a street engine. The 47 is among the more popular 350 heads. Decent head, decent compression. Does not have the bolt hole provision for the upper power sterring/alternator bracket for '71-newer. A bracket can be fashioned (seen in Jim Hand's book) without great difficulty.

Installing a 4-bbl. is a good idea. A non-EGR intake is best, but the EGR units still flow pretty well. However, simply installing a 4-bbl. will probably not have the desired effect without a cam change. The 2 bbl. cam is quite wimpy. For the compression with 47s, I'm liking Comp XE256H (for a bit more "atttidtude", XE262H). These cams perform very well in lower compression (under 10:1), have a "stock" base circle, so all stock valve train stuff fits (including springs, but I would replace them with new ones on a new cam).

350 isn't the popular Pontiac. Mainly because 400 gets you so much more "bang for the buck". But 350 can be a good performer, torquey and with a semblance of high-end. If you want the 350, by all means, don't let anyone disuade you. Good engine for your stated use.

Jim
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Old 04-24-2013, 10:02 AM
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I wouldnt spend much on the 350 then.
Put a comp cams XE 256 in it , that should liven it up, along with the 4 barrel.
All the high tech ignition stuff wont makle more power.
My old 350 would scald the tire and the new 389 will just destroy it. Both have pointe dizzys with the curve checked and setup correctly.
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Old 04-24-2013, 10:12 AM
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Actually the XE 250 H would be a better choice In my opinion
Part number 51-220-4
When you start getting a bunch more lift than stock you risk pulling out the rocker studs because of the added load on the valve train.
The 250 H has around .444 on the exhaust. Stock heads should be able to handle it.
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Old 04-24-2013, 06:08 PM
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I actually have the parts allready but I forgot to mention that I have a edelbroch cam kit and a E/performer for the intake . It came w/an egr. coverplate . The cam kit was the mid range area . So if the compression if good in all cylinders I'll just go with the parts on hand . If the compression is off should I just get the 6x4's redone ? Later on I can put my $'s toward a 400 ?? The 350 I'm working with has about 55,ooo.on it . It has a 308 pos. for gears. Thanks
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Old 04-24-2013, 06:22 PM
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Determine engine health by doing a compression test. On any low cylinders check them "wet" . Meaning squirt 2-3 squirts of oil in the cylinder and re run the test on that cylinder. If you get a small increase or no increase that indicates the problem is not the ring seal bust most likely a problem in the valves or head,burnt cracked etc.
Once you do that you can decide if replacing the heads would be in the works.
At 55,000 miles I would check her out real good, do a good repair and a slight upgrade and run it. Build something bigger for later, and when you have that running sell the engine or get another street beater to put it in for fun or sale.
I got my eye on a 68 lemans for the leftover 350 I have laying around. It runs too good to just scrap it. Besides it would be neat to smoke the 5.0 mustang guys and all the fart cannon kids with a raggedy A%! ol pontiac. LOL

BTW what is the part numbers on the Eddy stuff you have?
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Old 04-24-2013, 07:49 PM
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that's a good way of thinking about the upgrade to the 350 . I've put about 3,000 or so on it and it seems to run well and so on so I don't expect any problems w/comp. test but you never know . The cam kit is #2157 and the intake is a performer ,not the rpm . I do have a cast intake off a older gto also but the hole for the w/pump bolt is striped out and would need something done w/that . I do have a buddy that has a 400 that I'm trying to get so I think I'll just go w/what I've got planed for now .Any suggestions is appreciated !!!
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