which heads to use?
 

my build is a mild 400 street only build with a .010 cylinder bore. my goal is low end torque with very little highway driving. i have a set of 5c, 7J2, and 6X heads. i think the 6X are 6X-4 but must check. which should i use? very mild cam is the plan.

6x. Even though the 5c is basically the same head. They have a 4 and 8 version like the 6x.

6X-4 definitely.

5C are next in line if there’s something wrong with the 6X-4 set, but only if they’re 5C-4.

7J2 to the scrap man or donate to a friend who probably should scrap them as well.

7J2, is that a 72 2 Bbl 455 head?

The 7L4 is the 455 2-barrel head.

The 7J2 is the 400 2-barrel head.

Both have pressed-in rocker studs, expensive to ‘make right’. Also missing the end bolt holes for headers or exhaust manifolds, yuk.

It’s getting harder every year to justify putting money into rebuilding iron heads. Definitely choose the ones with the best features, screw-in rocker studs being the first consideration for street performance or just simply reliability.

The only press-in stud castings worth working on are the early high-compression GTO 389 (716, 77 and 093) and big Pontiac 421 heads, most of which are the same as the GTO heads. Because they look right and belong on a period correct engine they’re worth putting some coin into.

In my opinion putting money into essentially worthless castings like the 7J2 would be a mistake, unless you live outside the continental USA and had nothing else available to work with.

The 5c or the 6X if they are -4 castings are are nearly identical, but for the 5 series heads having a bit less Intake port volume which is not a bad thing if your stuck running 3.08 rear gears or less.

If I am not mistaken that 7J2 head had no center Exh port divider extending out from the head bolt to the flange.

Thanks for all the responses. i brought the 400 YX block and heads to the machine shop today. heads are 6X-8's going in my 66 GTO. i want a good drivable torquey street driver i will be running a holley sniper EFI, so next question is suggestions on the right pistons and camshaft to match this setup.
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You’ll have a hard time making that 400 a torquey street driver with the size of the chambers in those-8 heads, as they are more suited for a 455 then a 400!

What is the dash mark on those 5C heads that you have?

they are 5C-8's and based on research they are same as the 6X-8's, 101cc-2.02/1.66. at this point i don't have a better option with what i have on hand. at this point i'm open to head suggestion within budget reason. i'm open to head swapping.

Sell or trade the heads you have for some 6X-4 heads would be the best solution.

Find some 13s or 62s, 6X4s. 64 heads work great on 400s too.
13s and 62s are not 72 cc like the manuals say. More like 77. They will get you 9.4-9.6 CR if they have not been milled.

Where are you getting .010" over Pistons from?

13s, 62's, 62s would be best as 6x4s will have compression too low on a 400, around 8.5

The -8 heads are not the end of the world. My TA had 7.6:1 compression ratio, 2.41 gear, and with the stock automatic, ran nicely. Cliff uses a couple of Crower grinds that help these engines.

If you were to find some 6X-4's at a machine shop, ask them if they'd take the 7J2's as cores. Doesn't hurt to ask...

With only something similar to a 7.6:1 compression ratio for the most part the Crower camshafts would have too much seat duration and /or a wide LSA

Do the homework...

Get the intake closing numbers on different cams.

http://www.wallaceracing.com/cam-deg-calc.php

NOT that it means a whole heck of a lot but look for interest how it affects the DCR

http://www.wallaceracing.com/dynamic-cr.php

Jay S can chime in here with more helpful information.


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Example. The popular Crower 60916 hyd flat tappet cam for a 400......

278 / 289
221 / 229 at .050"
112 LSA
.455 /.470 lift w/ 1.5

Now run the numbers using a custom Bullet Racing Cams with lobe H270/306 on the intake side as an example:

270
222 at .050"
0.459 lift

Then combine it with a exhaust lobe duration that suits the cylinder heads and the cars exhaust system in use. Then consider the LSA.

Then consider the low compression ratio.

Or do we want to throw darts at the catalog for a cam choice ?

Call Tim Goolsby at Bullet Racing Cams

https://www.bulletcams.com/

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My 78 with 97.5 cc(never milled) 6X-8s ran high 14s with 2.56 gears and decent power. Not the end of the word for just a cruiser.

If your tossing around getting the heads milled then look into a set of custom pistons with a like a 8 to 10 CC dome.
The cost of milling the heads a minimum.045” and a custom piston may just be real close to a wash, and going to a standard normal .030” overbore would help out nicely also !

What is your reasoning for going only .010” over?

I think the Crower 60240 was the low compression cam I had in mind.

IRC a guy can cut .070 off pretty easy on those 6x-8. I think the chamber is a little narrower than some other heads, makes them a little more friendly to mill some extra off, .070 would be removing almost 14 cc’s. I think .040” off gets it down into 6x-4 range, if you were going to bother having them machined I would at least go .050”, that would get the compression into the mid 8s.

If you pick a good cam, the upper 7 SCR can be workable, certainly would rather be higher, I think upper 7s would ok for a cruiser though. Steve C mentioned I use dynamic compression designing cams, which is correct. On something really low compression I would suggest working backwards and pick a profile from intake closing targets. I also would not suggest starting with DCR first, I would look at V/P index’s first then work your way to DCR. The DCR on that low of compression will give you a false reading compared to what most people try to run. The compression is so low, if your not careful you will end up with a very tiny cam, likely to small for the head flow you have.. Go to big and it will be a gas guzzling slug. For that upper 7s static compression I would try to get the V/P (using that Wallace DCR calculator) around 120 from as correct as possible .006” tappet intake closings, that should end up in the upper 50s lower 60s for the intake closing. I also recall that the Crower cam Cliff R likes with lower compression is the 60240. It is 270* and has a intake closing of about 67. The Lunati Voodoos are more aggressive, dealing with something really low compression I would rather use something like them. The way those lunati’s are ground the little Lunati 262 voodoo (702) actually has nearly the identical intake closing as the 60240. With the lower compression I would rather run the smaller 701 (255 adv duration) than the 702 (262) or the Crower (270). But both the 702 or the 60240 cams are about as big as you would want to use. Bigger than those the engine will start acting sluggish. Bullet has a Ultradyne grind that is listed as a H00 that would be inbetween the 701 and 702 lunati’s , probably be my first pick, and on a 110 LSA instead of the 112s. I think it would build some more compression and might get better milage