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Old 07-21-2012, 06:44 PM
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Pontiac 670 heads on a 1968 350 bored .060 over

I have a 1968 350 bored .060 over in my 1972 Lemans sport convertible. I just bought a set of 670 heads to put on it. I originally thought the motor was a 400 but as it turns out it's definitely not. Trying to get all I can get out of it without getting a 400. I'd rather have a 400 but after some research it's just going to cost too much. Better to see what I can get out of my already rebuilt 350. Will the 670 heads work with it and if so, what can I do to get as close as possible to my 400 HP mark?? Cam? I need springs for the 670's anyway. Which should I get? Rate and size? And any other would be helpful.

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Old 07-21-2012, 08:24 PM
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Mr P Body touched on this the other day. The cylinder bores will need to be notched at the top (a chamfer) if they are not allready. The valve is so close to the cylinder wall when open that the flow is severley impeded.
i saw you had a set of 7H1 heads. If it were me I would run them.
Actually I have a set of fresh 7H1 heads with BBC studs put in that I am going to run. They have the smaller (1.96) intake valve but the larger 1.77 exhaust. And flow on the exhaust side is where poncho motors seem to have a problem.
The 7H1 heads may have hardened seats also as they are from an era when unleaded gas was on the scene for new cars. (1973)
My set I CC ed them and they were 91 CC s . most of the info I found was wrong about them.One site said 80 CC s .
I had to find this by CCing them myself...so I know for sure.
You need to CC the ones you have to see what they are. As years go buy, if they had a valve job, or have been milled , the chamber size will be smaller or larger...depending.
I had about .045 cut from mine, the chambers are 82 CC s now.I had the intake side milled the same amount also.
I am shoving them on a 389 (bored to 4.120 and with 400 pistons)
My static compression is 9.4 ish. I have also zero decked the block.
Funds and time have slowed the process. I look to finish the engine this winter.
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Old 07-21-2012, 08:56 PM
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I know all about funds and time. My project has been in the works since I bought the rebuilt 350, 12 years ago. The same one that I though was a 400 because that's what the paperwork told me it was. Paid $1000 for it too. Can you imagine the frustration. For 12 years I thought I was building up a 400 until a few days ago. My 7H1 heads are cracked so they aren't useable. As I research buying a 400 the cost just keeps climbing to just do it right.
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Old 07-21-2012, 08:59 PM
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I'm glad to see that you accepted the fact that what you have is a 350. Now to get serious about building it. The 670s are good heads, but with the small bore of the 350, there can be a valve shrouding problem. There are other heads out there that I think would work better, such as some 4Xs, some 6Xs plus others. Since you are building for performance, one thing that you might want to do, is get a set of good rods to replace the cast rods in that engine, although not totally necessary as long as you can keep the rpm down. Jim Lehart (Mr. P-Body), a member here, could probably help you with suggestions better than anyone. He is an engine builder that specializes in Pontiacs. Don't let anyone tell you that that "little 350" isn't any good. I bought a '71 GP that had a transplanted 350, with a built TH350 transmission, that would chirp the tires when it shifted to second, every time, unless I just let it idle until it shifted. A 350 Pontiac is a 400 Pontiac with a smaller bore so it will respond to the same modifications.

Bill
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Old 07-21-2012, 09:04 PM
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Too top it all off I already bought the 670's after about 2 weeks of researching. And they are nice heads. I'm actually looking forward to building them up. Getting in there and doing some port matching and smoothing of the runners and just getting my hands dirty again. I did read about the valve problem. Still going to keep trying to find the right 400. I've had my heart set on it for too long.
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Old 07-21-2012, 09:08 PM
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Dont go overboard spending on the 350. You should be able to get it together without a ton of cash dumped in.
Plenty of other pontiac heads out there at reasonable prices.
A mild cam wont require any pricey valve train compnents, like roller rockers , bee hive springs, BBC stud etc.
You can run the Comp XE 256 in it with stock 8.2 to one static compression and it will run good.
My 64 has a 1971 350 2 barrel in it right now, I drove it today, boiled the rear tire off, its all good.
I am building a 389 bored out, but hey I will keep the 350 in mothballs after the swap, just in case . Nothing wrong with a 350, they just arent the one to start with to make insane horsepower with.
They do make good power and torque , as if you recall they have a smaller bore than a 350 chevy, but they have the 3.75 inch stroke which adds torque. Chevy guys spend big bucks to make a 350 chevy into a "stroker" (3.75 inch stroke) where as the pontiacs all have that from 326-400 cubic inch. (not including the pre 60s engines like the 347 of course)
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Old 07-21-2012, 09:09 PM
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Thanks for all the info. I'd love to get my 350 as close as I can to 400HP. I just bought the 670's and would much rather use them and not get another set of heads. What can I do to get there?
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Old 07-21-2012, 09:17 PM
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I just spent $600 on these heads a few days ago. Didn't find out I had a 350 not a 400 until the other night and I'm pretty pissed about it. I knew nothing about the casting codes when I bought it. I trusted the source and the date code said it was made in 67. Little did I know that they didn't make a '67 350 and you can't bore a 350 .060 over and get a 400. After all this time. 12 years this month too. What a kick in the nvm
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Old 07-21-2012, 09:19 PM
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Those 670 heads should be easy to sell and a pair of smaller valve heads easy to find on one or more of the Pontiac sites. I'll PM some of the sites to you. If you let me know where you are, I'll include some builders and parts suppliers.

Bill
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Old 07-21-2012, 09:20 PM
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Your shortblock is allready assembled isnt it?
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Old 07-21-2012, 09:29 PM
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My whole motor is together. And it came out nice. Chrome does wonders in an engine bay. I built it up with the 7h1 heads anyway and just figured the car ran great with them before. When I can I'll get better ones and put them on. That was quite a few years ago. I haven't even driven it since '00.
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Old 07-21-2012, 09:34 PM
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And I still have all the body work to do also.
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