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Old 07-19-2012, 05:05 PM
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1967 400 with 670 heads. Trying for 400 Hp street

Ok this is a long one, I know. Just want to get it all out there.*I have a remanufactured 400. In actuality it's a 1967 326 bored .060 over to go in my 1972 LeMans sport *convertible. Date code says J317. Although there is a 50 stamped on the lifter valley. There are 3 freeze plugs per side and only 2 motor mount locations. Flat top pistons with no valve reliefs. Not sure what cam or crank is in it. Just purchased a set of 1967 # 670 heads to go with it. *I will be port matching and smoothing the runners. My question is what valve springs (dimensions and rate) would compliment my combination? Also what cam would work well? Hydraulic flat tappet or Roller? 1.5 or 1.65 ratio rockers? Roller or no? Just trying to get up to around 400 HP. Don't want to have to modify the heads a whole lot or go into my block to get it. I have an edelbrock performer intake that I'm planning to up to performer rpm eventually. And don't want to end up replacing parts I've just purchased for the heads. I'm using a Holley E85 carb set up. *I will also be putting a functional scoop on it for some Ram air effect. Distributor is stock with pertronix magnetic pickup, MSD blaster coil, summit headers for D-port heads 1 5/8" primary tubes I believe (eventually i will be buying bigger headers and a 2 1/2" flowmaster exhaust.*THM 350 sits behind the motor (Eventually a TCI Streetfighter 350 with 2500 rpm stall converter). 10 bolt rear not sure what gears. This will be my ground pounding weekend street car. Hopefully! Any advice would be helpful and appreciated.

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Old 07-19-2012, 05:14 PM
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A 326 bored .060 is only about a 331 not a 400.
Keep it simple, run a summit 2800 cam, or better yet a comp cams XE 256
If your heads are 65 CC then your static comp will be 10.5 ish to 1
you'll need to run alcohol to keep from detonation. But if you can get alcohol...very good for you. I cant where I live , I wish I could.
Run a dual plane intake, stock is actually pretty good.
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Old 07-19-2012, 05:18 PM
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You will need to use the valve springs the individual manufacturers recommend for their cams for warranty issues. If you have the money, a retro hydraulic roller is a no brainer. Rocker ratio depends on the cam, how much lift, piston clearances, etc. When you start getting into the 400 hp range, rethink that stock 10-bolt. Depending on your cam choice and build, 2500 stall may not be a little short. JMO
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Old 07-19-2012, 05:18 PM
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Quote:
Originally Posted by 67pontiac400 View Post
Ok this is a long one, I know. Just want to get it all out there.*I have a remanufactured 400. In actuality it's a 1967 326 bored .060 over to go in my 1972 LeMans sport *convertible. Date code says J317. Although there is a 50 stamped on the lifter valley. There are 3 freeze plugs per side and only 2 motor mount locations. Flat top pistons with no valve reliefs. Not sure what cam or crank is in it. Just purchased a set of 1967 # 670 heads to go with it. *I will be port matching and smoothing the runners. My question is what valve springs (dimensions and rate) would compliment my combination? Also what cam would work well? Hydraulic flat tappet or Roller? 1.5 or 1.65 ratio rockers? Roller or no? Just trying to get up to around 400 HP. Don't want to have to modify the heads a whole lot or go into my block to get it. I have an edelbrock performer intake that I'm planning to up to performer rpm eventually. And don't want to end up replacing parts I've just purchased for the heads. I'm using a Holley E85 carb set up. *I will also be putting a functional scoop on it for some Ram air effect. Distributor is stock with pertronix magnetic pickup, MSD blaster coil, summit headers for D-port heads 1 5/8" primary tubes I believe (eventually i will be buying bigger headers and a 2 1/2" flowmaster exhaust.*THM 350 sits behind the motor (Eventually a TCI Streetfighter 350 with 2500 rpm stall converter). 10 bolt rear not sure what gears. This will be my ground pounding weekend street car. Hopefully! Any advice would be helpful and appreciated.
Most likely you have a 350 Pontiac. You can get 400 HP out of one but it will not be easy and it will not be cheap.

My best advice is to lower your goals unless it will see limited street use, or jump up to a 400 or 455 as the foundation for your build. Here are some links to info on the Pontiac.
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Old 07-19-2012, 05:21 PM
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Thanks. I really hope it's a 400 cuz that's what I ordered and paid for. I plan on using E85. It's easily available where I live.
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Old 07-19-2012, 05:25 PM
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Quote:
Originally Posted by 67pontiac400 View Post
Thanks. I really hope it's a 400 cuz that's what I ordered and paid for. I plan on using E85. It's easily available where I live.
If it has "50" cast into the lifter valley, it is a 350. If you were lucky it would be "55" (455). In any event, what are the engine codes off the front?

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Old 07-19-2012, 05:31 PM
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Engine ID info can be found here. If the heads are off, measure the bore. You will quickly see if it's over or under 4".

Last edited by cobalt327; 07-19-2012 at 05:36 PM.
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Old 07-19-2012, 05:58 PM
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It's got a Yn code in front next to timing cover under passenger side head. 3 freeze plugs tell me the block 67 and up but 2 motor mount bosses mean it might be pre 70. Date code ends in a 7. Valley stamp says 50. Usually a 350. My paperwork for the remanufactured short block says it's a 70-73 6.6 liter 400. I'm kinda stumped as to why things aren't adding up. Pistons are stamped .060 over
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Old 07-19-2012, 06:15 PM
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Post the block casting numbers.
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Old 07-19-2012, 06:16 PM
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The J317 date code is October 31, 1967, so it would have been cast for the '68 model year making it a 350. A .060 over 350 would make it a 365 using the stock 3.75" stroke crank. I also looked up the '68 YN code and it is a 2bbl, 265 hp, automatic block and would have had #17 heads.

Bill

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Old 07-19-2012, 06:21 PM
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Bill, arent the 670 heads the old closed chambered heads. If so they have the 22 degree valve angle not the 14 degree like the open chamber heads. Hope it has the right valve reliefs in the pistons.
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Old 07-19-2012, 06:57 PM
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I believe the factory 2.11 x 1.77 heads were all 14 degree. In any event the 670 will work on later shortblocks.
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Old 07-19-2012, 07:01 PM
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Casting numbers can't fully be read. This is what I can read 97???78?. The 670 heads have the closed chamber design. I read that the 670 heads do have the new valve angle.
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Old 07-19-2012, 07:07 PM
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Prolly ends w/"9".
C/N 9790079: 1968-'69 350
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Old 07-19-2012, 07:10 PM
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Prolly ends w/"9".
C/N 9790079: 1968-'69 350
The displacement should be cast into the side of the block as well.
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