[noalibi]

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.

[PunchT37]

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

[b-man]

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.

[Jay S]

066 copy would be a melling spc-4. Looks like it is available. 066 pretty small, leaving a decent amount of performance untapped with it, the summit 2800 is a decent step over it in lift and duration. But going to have to use what can be found.

Looks like there are some small XE cams available at the big warehouses yet. Xe262 and the 268 both work good for very low compression, especially if your car has loud exhaust and your kind of deaf, valve terrain noise won’t be a issue then. . Suggest using a hylift Johnson lifters though, and not the hi energy that come with their cam kit. Better odds of getting a semi quiet combo. Performance wise that 268 can run pretty good yet even with 8.0 compression, even into the 7s.

["QUICK-SILVER"]

What transmission and rear gears this car have?

What intake/carburetor set up do you plan to run?

Exhaust system being used is also important.. Very important!

Exactly what RPM range do you call low end torque?

Clay

[noalibi]

Originally Posted by "QUICK-SILVER"

What transmission and rear gears this car have?

What intake/carburetor set up do you plan to run?

Exhaust system being used is also important.. Very important!

Exactly what RPM range do you call low end torque?

Clay

-Running 3:42’s 400 trans
-Holley sniper EFI (planned)
-2-1/2” full exhaust w/ magnaflows
-power in the idle to 3000rpm range

[77 TRASHCAN]

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

[b-man]

Originally Posted by 77 TRASHCAN

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.

[steve25]

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.

[noalibi]

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.
??

[steve25]

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?

[noalibi]

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.

[b-man]

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

[Dragncar]

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.

[67Fbird]

Originally Posted by Dragncar

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.

true story there...both sets i have are in the 76 cc area. Had my (now dead) set decked to bring into 74 after I did some chamber work 30 yrs ago.

[noalibi]

Originally Posted by Dragncar

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.

Thanks for the advice, I found a pair of 62’s. The 6X-8,s had one crack and the 4x-4s were both cracked. The 4X-4s were in a running car with not known issues, go figure. Now I just need to match a cam for the 62’s.

[Baron Von Zeppelin]

Originally Posted by noalibi

I found a pair of 62’s.

Things just took another turn for the better .
It hurts to see smog-era parts under the hood of a 66 GTO

[steve25]

Where are you getting .010" over Pistons from?

[grivera]

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

[77 TRASHCAN]

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...