Waking up a '75 TA 400 with a budget of 2k
 

Car already has true duals no cats. Everything else is stock.

I think it's only 7.6:1 compression to ratio.

I know it is a 557 block.

I think 3:23 rear gears, not positive.

Cam, Carb rebuild, headers, different iron heads??

185 hp now.

2000. Budget.

Personally if car is going to be a driver and currently runs decent, I would put my effort into tuning the ignition, carb dialed in, brakes being perfect and spend the rest on gas driving it and enjoying it. Agree it’s fun to enjoy more power but I enjoy reliability and efficiency while driving it all the time

Not sure if those cars had retarded cams. Maybe a timing set.

Stick or automatic?

Stick.

I went from a 9.1 cr 48 headed ping crazy engine to a 7.7 cr 6x4 headed no ping engine. I found it more enjoyable to drive. Even with a bad cylinder it had more power than the run of the mill dd's today. Has a cam close to but not quite a 068 or Summit 2801. Had an rpm with 750 vac. Now with new pistons at 8.2 cr and a modified stock intake with Qjet both done as per Cliff. From what I've read here, other than the compression being a bit low, that seems to be close to the go to set up for a good daily street engine.

I would swap on a fresh set of 6X-4 heads to bump the compression up by a point or so. Mill them as much as .030” but no more so the intake still fits. Keep the stock intake.

Swap in the Summit 2801 cam and a good quality lifter set, Johnson Hylift. Make sure the heads have new springs that match the cam. A good timing chain set that’s the factory link style, available from NAPA I’m pretty sure.

Find out for sure what gears you have before settling on a cam. If you have 3.08 gears I’d suggest toning down the cam to the 2800.

Have the distributor reworked by a good shop that can put a performance curve in it.

Carb reworked with the proper jets and rods and of course a high quality rebuild kit from Cliff. If it’s in need of baseplate bushings have that done.

I would skip the headers but upgrade to 2-1/2” all the way to the mufflers if it’s not already. Make sure your mufflers aren’t restrictive. The second-Gen T/As have poor ground clearance already without making matters worse by running headers.

If it's a 4 speed car it likely has 3.23 gears, good compromise gear. The compression ratio is 7.8 to 1, and it is lowered by the 45 degree bevel cut on the outside edge of the pistons.

If you wanted to swap to 350 heads it would be easier to get smaller combustion chambers, rather than changing pistons, in the low compression Pontiacs of the mid 70 raising compression 1 full point is only going to gain maybe 10 HP. That's a lot of money/time/effort for 10 HP.

There are easier gains to be made with cam change to something close to the 068 cam, and headers, a reworked Q jet, and a good timing curve into the distributor. Basic hot rod techniques that will keep you within you 2K limit. The added efficiency will also gain fuel mileage, and smiles per gallon.

FWIW I had my own garage during the late 70s and early 80s, I used these techniques all the time on customer cars, many were the smog era T/As. For those of you that werent around there were only 2 choices of gasoline at the time, 87 unleaded, and 87 regular leaded, so raising compression was a waste of time, you'd just get detonation with the crap fuels we had available at the time. I'm fully aware that there are premium fuels now that we didn't have back then, but 3% gain in power, for one full ratio of compression on a 300 HP engine, is 9 HP, big deal. Marginal gains, for a rather hefty investment.

I did try to run more compression, and was rewarded with broken pistons, and rings. I just resigned myself to keeping the compression low, and making the engines more efficient.

Gaining efficiency with low restriction exhaust, richen up the carb slightly, and bring the timing in at a good rate. Mild cams that were efficient, and the cars would respond very well to these modifications. You don't need a cam that will rattle the windows when you're running relatively low compression, under camming is the key so you don't bleed off compression with overlap at street RPM.

An H pipe connecting the head pipes in the vicinity of the rear of the transmission will also increase low end, and mid range on a low compression street car. I know there will be a bunch of naysayers, but headers will help much more than RA exhaust manifolds in this type of an engine.

This was my recipe for the TAs of that era, I hope it is of some help to you.

Start off with a simple 40 minute long change that cost you nothing!

Open up the rear of your shaker scoop

Raising just compression will provide more torque from idle to redline increasing efficiency everywhere

Raising just size of camshaft will soften lower RPM with rise in power mid / top therefore decresing efficiency at low RPMs

on a dyno graph that raising the curve or tilting the curve

ideally for max fun you want to do both but if limited raising the entire curve is preferable

I forgot to mention I do have a set of 72 350 2v heads, 7k3 heads, and 62 heads .

Then have your 62 heads rebuilt top to bottom and run a 068 cam or better yet a high lift version of it.

You want to get the lift up to .470” to .490”.

Then re-jet your carb .

You might want to look at this thread.

https://forums.maxperformanceinc.com...d.php?t=855368

Stan

Small correction;
The 6X-4 was a 350 head, on the smaller bore 350 engine (with the specific 350 pistons) those engines made 7.6:1;
When the 6X-4 was placed on a 400 engine, you would see more compression.
IIRC the 77-79 6X-4, with those multi-relief (ect) slugs, the compression was a smidge above 8.0:1;
If your engine had better slugs, you had a little more than that yet.

Both of those heads would be an upgrade;
The less valuable 7K3 combine large valves with 8.2:1 (with the good earlier slugs) - I believe that they are the same combustion chamber size as the 6X-4.
I believe that the #62 heads will have an exhaust cross-over mismatch to your factory intake - so if you run those, block the cross over - that's not too hard to do.

The 1975 5C-7 or 8 have the same combustion chamber size as the 6X-8 - which is larger than the 6X-4.

Honestly, I'd look at the heads you have, and which ever ones look better, I'd pop them on - unless they obviously need a rebuild;
A head rebuild could break your bank right there.
I used to run heads as pulled off all the time with no issues.

According to my Pete McCarthy book, the 1975-400/mt engine still received the 067 cam - and that's a decent cam, so I'd leave it alone, unless you have your heart set on a cam swap.

Good info right there!

Id probably be happy with 275 hp. Sounds doable on a budget.

I had a 79 400 spare engine I used when my 455 self sestructed. It had 7.5 CR. I used a Holley Performer with the stock Q Jet, Cheap headers, Summit 2800. It ran really great and used 87 octane gas.

Here you go:

https://forums.maxperformanceinc.com...1&postcount=22

That's a great 400 build that I never saw before B-man! Love it!

Thanks for sharing it!

Dennis

And based on SD455DJs W72 build mentioned above, maybe you were well above that 270?

371 hp from a stockish W72 with basically just a bump in compression (unless I missed something). That's awesome. Although that sounded like a fairly meticulous build (not that yours wasn't) so maybe it's the little things that add up.

Anyway, it's cool to see that you can pep those things up without going crazy. If only I knew that back in the day...