[Formulabruce]

Throw on some 1970 #15 heads and youll be fine, I have run these on 350's, 400's and 455 ( with a dished piston).
Although the Comp XE cams do build pressure ( CR, every Pontiac stock Cam made since the late 50's has been dual pattern......

[dmac]

Try to find something with 72 cc or a little more for the 350. If you are still planning on a 400 in the future, You could find something with about 80 cc or more, and that head will work on the 350 and 400. On the 350 with 80 cc, you could use one of the comp cams, and use lower octane without much issue. When you build the 400, 80 cc will give you added compression, and be safe with 92 octane.

Get the combo right, and you may find yourself satisfied with the 350 for a long time.

[cttempest]

gotcha.15's seem good.Hopefully I'll have an easy time finding a pair

[cttempest]

Originally Posted by dmac

Try to find something with 72 cc or a little more for the 350. If you are still planning on a 400 in the future, You could find something with about 80 cc or more, and that head will work on the 350 and 400. On the 350 with 80 cc, you could use one of the comp cams, and use lower octane without much issue. When you build the 400, 80 cc will give you added compression, and be safe with 92 octane.

Get the combo right, and you may find yourself satisfied with the 350 for a long time.

Hopefully!!!I plan on putting this motor in another vehicle once the 400 is done,so I definitely want it done right

[dmac]

This link can help you decide on heads-

http://www.wallaceracing.com/headsearch.htm

But even then, after 40+ years, a lot of heads have been altered, so you need to verify the chamber size with any head you find. There are a lot of choices in the 72-85 cc range that would work on a 350. Either pick the heads based on a cam you like, or pick the cam based on your available heads.

You can get a cam that builds pressure for a low compression head, or a cam that reduces cylinder pressure for a high compression head. If you are buying new pistons, you can get dished pistons and use the heads you have, or maybe shape the chamber in the head to get a few more cc's out of them.

My suggestion would be to look for heads around 72 cc, with screw in rocker studs. Big valves don't matter as much on a 350. But any head can be converted to screw in, so don't automatically discount pressed in studs if you get a good deal.

[cttempest]

I've got a set of 1970 15's lined up locally.

[tom s]

the 15s are a real sleeper head for a smaller bore engine.Dave at SD did mine with a 2.05 intake and his 260 CNC job and they flo that at 600.I have them on my 383 short deck engine.Tom

[cttempest]

Originally Posted by tom s

the 15s are a real sleeper head for a smaller bore engine.Dave at SD did mine with a 2.05 intake and his 260 CNC job and they flo that at 600.I have them on my 383 short deck engine.Tom

Good deal.Seems like they are the way to go.I can't wait to get theese and dig in

[Donovan]

Don't use 400-455 heads on the smaller 350 bore. The chamber cut at the top is cut wider and more shallow to match the bigger bore. This area will have headgasket extending into the cylinder volume on the small bore. 350 Bore is 3.875. All these heads should be used on 4.03 and larger.

Find a 68-70 350 head.

17, 18, 47, 11 are GOOD

Small chamber 400 heads are BAD. Like 12, 13, 14, 15, 16, 45, 46

ONE EXCEPTION - 670 heads. They are closed chamber and don't have the top scallop cut that creates the problem.

Keep in mind you also need to use the correct 350 head gasket for the same reason. The common Pontiac gasket has a cutout at 4.2"

Tom S. is using these on a larger bore engine than your 350! I see Bruce says he has used these on a 350, but even if he got away with it, I respectfully suggest it is not good advice.

[cttempest]

Originally Posted by Donovan

Don't use 400-455 heads on the smaller 350 bore. The chamber cut at the top is cut wider and more shallow to match the bigger bore. This area will have headgasket extending into the cylinder volume on the small bore. 350 Bore is 3.875. All these heads should be used on 4.03 and larger.

Find a 68-70 350 head.

17, 18, 47, 11 are GOOD

Small chamber 400 heads are BAD. Like 12, 13, 14, 15, 16, 45, 46

ONE EXCEPTION - 670 heads. They are closed chamber and don't have the top scallop cut that creates the problem.

Keep in mind you also need to use the correct 350 head gasket for the same reason. The common Pontiac gasket has a cutout at 4.2"

Tom S. is using these on a larger bore engine than your 350! I see Bruce says he has used these on a 350, but even if he got away with it, I respectfully suggest it is not good advice.

Dammit,ok,not what I wanted to hear.

I commited to buying a set of 15's from a member here.It makes sense about the chamber cut,but I was running 326 heads before,which are an even smaller bore??, and it ran fine.I have the head gaskets here and everything seemed normal after teardown.

I HAVE a set of 670's that I had redone years ago from my 400 that I know are in great condition ready to go,but I've been warned to stay away from the big valve heads(2.11/1.77) on the 670's..If theese are the heads to use than awesome,but it just seems like too big of valves.

[Donovan]

Since you have the 670s and the engine is in the shop, mock them up with a head gasket and some clay. You should have a pleasant surprise. The chamber is deep and that block should have at least one relief cut out on the top of the bore for flow. You should have a significant amount of clearance for lift before contact. There is likely room for a 2800-2801 cam plus some.

I think at those lifts under 0.500 the valves may not even leave the chamber. You can check to be sure!

[cttempest]

i've obviously have to check exactly what my 670's are but they came 72cc and 10.5 c.r as listed on Wallace's site.

Wouldn't that make the compression ridiculous on the 350?I want to be able to run pump gas

I should say incase I haven't mentioned it yet.The 350 is:

.030 over,sealed pro .357 pistons,flat top with 4 valve releif's
stock crank
stock rods
not sure on deck height

Stock Pontiac intake,1973 491244
I have a Holley 750 dual feed but I think I want to run a Q-jet
Doug's headers

It's going to be a street motor
Th-350 undecided on stall yet till I pick cam
2.56 one legger for now.I do have other rears,but the most I'd ever do is 3.23

[cttempest]

Originally Posted by Donovan

Don't use 400-455 heads on the smaller 350 bore. The chamber cut at the top is cut wider and more shallow to match the bigger bore. This area will have headgasket extending into the cylinder volume on the small bore. 350 Bore is 3.875. All these heads should be used on 4.03 and larger.

Find a 68-70 350 head.

17, 18, 47, 11 are GOOD

Small chamber 400 heads are BAD. Like 12, 13, 14, 15, 16, 45, 46

ONE EXCEPTION - 670 heads. They are closed chamber and don't have the top scallop cut that creates the problem.

Keep in mind you also need to use the correct 350 head gasket for the same reason. The common Pontiac gasket has a cutout at 4.2"

Tom S. is using these on a larger bore engine than your 350! I see Bruce says he has used these on a 350, but even if he got away with it, I respectfully suggest it is not good advice.

18's? again 10.5 c.r..the exact opposite of what I want.

[cttempest]

If the 670's really make that much sense then that would be awesome.I have them,I had them redone,I would probaly just have to slap them on the way they are.Well,I was running stock stamped rocker arms but I had the valves done,springs done,they are good to go pretty much.
If I should use them my engine build will cost so much less and be done so much sooner

[dmac]

You need to think about combustion ratio a little. If you have a bigger 400 engine squeezing air/fuel into a small head chamber, you have higher compression. If you have a smaller 350 motor squeezing air into the same head, since you have less air, you have lower compression. So your 670 heads on a 350 will have lower compression than if you put them on a 400. Here is a link to a combustion ratio calculator-

http://www.wallaceracing.com/cr_test2.php

Using that calculator shows a combustion ratio(cr) under 9.5:1 on a 350 .030 over with 72 cc heads, depending on exactly which head gasket, decking, and piston relief, but would be okay for 92 octane on a well tuned 350. The bigger the chamber in the head, the less the air gets squeezed. The more it is squeeezed, the more, or higher octane level you need. If you had 80 cc heads, you might be able to use 87 or maybe 89 octane.

You machine shop could 'chamfer' the cylinders in the block to use other heads to create enough valve clearance if needed. I don't know if that is cost effective.

[cttempest]

Originally Posted by dmac

You need to think about combustion ratio a little. If you have a bigger 400 engine squeezing air/fuel into a small head chamber, you have higher compression. If you have a smaller 350 motor squeezing air into the same head, since you have less air, you have lower compression. So your 670 heads on a 350 will have lower compression than if you put them on a 400. Here is a link to a combustion ratio calculator-

http://www.wallaceracing.com/cr_test2.php

Using that calculator shows a combustion ratio(cr) under 9.5:1 on a 350 .030 over with 72 cc heads, depending on exactly which head gasket, decking, and piston relief, but would be okay for 92 octane on a well tuned 350. The bigger the chamber in the head, the less the air gets squeezed. The more it is squeeezed, the more, or higher octane level you need. If you had 80 cc heads, you might be able to use 87 or maybe 89 octane.

You machine shop could 'chamfer' the cylinders in the block to use other heads to create enough valve clearance if needed. I don't know if that is cost effective.

The cylinders are already chamfered,which is factory.I should have checked deck height before i took it apart but really didnt think about it.

I'm going to cc the 670's asap and unless I'm told otherwise,I would like to use them.

Once I get the block back and I assemble it,I can check deck height and calculate c.r.
But playing with the calculator on Wallace,it seems that even with diffrent deck heights the c.r stays below 10.0,which is what I'm aiming for.

[Donovan]

Originally Posted by cttempest

18's? again 10.5 c.r..the exact opposite of what I want.

Depends on your setup. You shouldn't think of the factory number as more than an initial guideline.

18s are going to be difficult to find anyway. I haven't seen more than 2 pair in person, in 20 years of the hobby. Maybe 2 for sale on the forums. But Assuming you don't deck and have 0.02 in the hole...68cc chamber.. 0.030 over. It would be 9.4 to 1! Close to 10 to 1 if zero decked.

The 17s I have were something like 78cc. This is why you need to do your mocking. After this you may want to cut the heads etc.

do you have pictures of the current shortblock?

[dmac]

670s will breathe pretty good for a 350. Big valve, screw in studs. Again, after nearly 50 yrs since the 670s were made, someone could have milled them down, so verify. My 670s are at 68cc which was done when 104+ octane was available as premium gas.

[tom s]

If your going to go to a big valve head why not just go to 48s which were on the 350 HOs?Dave picked the 15s for CR and the smaller valves for a reason.Tom

[screamingchief]

Personally,I'm not a fan of big valve heads w/the 350 bore sizes.

And I dont care to mix early/late heads & shortblocks either.

So I'd be looking for some '68 up 72cc small valve castings to work with.

And yeah,there have been discussions about the 350 cid vs. 400 cid "chamber size" vs. headgasket deal in the past,it seems to hinge largely upon which specific headgasket is going to be used,and that's one of the tougher areas of building the 350 bore size combos these days,headgasket choice.

Everyone pondering a small bore build faces this dilema,even me,though I'm opting to stroke mine (3" main 4" stroke + .030 over = 383 cid) to help add swept volume somewhat improving my head choices,as the added swept volume from the longer stroke crank inturn can use more chamber cc as SOP vs. the 3.75" stroke 350 cid combo.

It can be tricky figuring out which head is "best" for these sorta builds,so take your time and look over all the pros & cons for any given option.

Good luck here.

Bret P.