1966 Tri Power on 1971 455 YC Block…Which heads are best?
 

So a little history on this engine. I bought this beautiful 1966 GTO with 22,000 original miles that sat from 1966 until 1999 in a barn up in Wyoming state. Yup it was a Vietnam vet car, who never came back from the war. The original 389 Tri Power engine block was destroyed (froze). So I bought the car from an older gentleman who bought it in 1999 and took it to Texas.
within 2000 miles of the completion of the car restoration and engine rebuild, cylinder number seven developed a miss. I had good spark and it was firing. I did a compression test and all cylinders were at 187-190 with cylinder number seven at 180. Upon doing exhaust temp check exhaust temp on 7 was low, especially at idle so I did a leak down test with rocker arms off. 8% leak down on the intake valve on number seven.
Upon doing this, I noticed that when I went to readjust the valves that I was not getting any oil up to the rocker arms for at least 4 to 5 minutes at Cold start up. Did an oil pressure test at the oil filter housing and it was at 165 at cold start up.
So decided to pull engine.
Hold on to your seat belts because this get odd.
After talking to the guy who built the engine, and what he told me, and after teardown is a story for the books. Mind you after calculations, this motor only has 2000 miles on it from the time he had it Dyno’d, and the miles that I put on it. Also some Where in the time he had it, he took out the more aggressive cam replaced with Catalina cam, changed 1.65 ratio rocker’s replaced with 1.5’s. This was all because the transmission was slipping, which is a turbo 400 that he put in the car.
Here we go…
The owner put in a 1971 455 YC block that he zero decked to the crank. He had put 1975 6x #4, slightly ported heads on it. To fit in the 1966 GTO he fitted the engine with a 1966 timing cover and 1966 harmonic, Balancer or dampener.
The whole rotating assembly from flywheel to dampener was balanced…yup the dampener too. It had been drilled out in specific places to balance it along with flywheel. ��
The crank was ground to 20/30 and had welds in some of the drilled out factory holes ��
It has Eagle rods and pistons, and pistons were milled .055 off of the top( Thinking this was done to reduce compression)
The engine block still has nice cross hatches, and no ridges, so I know this motor didn’t have many miles on it.
When dismantling the heads noticed, there was three washers on the rockers above the ball and between rocker arms poly locks to make up the distance for too long of rocker studs.
Also, on the heads someone installed harden seats on the intake, valve seats and not the exhaust. I thought 75 Pontiac heads already had harden seats. Thinking someone may have messed up and had to put seats in because of a wrong valve seat grind.
When taking the cam gear off, notice the Timing chain had a deflection of almost 3/8 of an inch. Wrong timing chain, too long after zero decking the block. When he replaced the cam, he didn’t center the cam bolt in the fuel pump eccentric hub and that explains why the fuel pump wasn’t getting a full range of motion and fuel problems.
This also left the cam with more than a 1/4” of end play.
Also, in the teardown noticed that a lot of bolts were from your hardware store that were grade 5 bolts��
After pulling the cam, crank noticed that the bearings must of had too much clearance as it must of had cavitation and wore the first coat of tri-metal of the bearings��
The car that I thought was a great deal ended up not being so. It has a perfect body, beautifully done but the engine is a mess. Buyer’s beware

So with all this being said before I stick a whole bunch of money to make this a Tri Power 455. I would like to know what heads will be a great match to my 1966 Tri Power and this 455 as it is now. Or…
Do I stick with the 6X #4Heads ?
I heard 1971 # 96 heads were good?

I like the 96s.Have them on my 421.Has had a tripower on it,now a Bathtub.Tom

The 6X-4 heads are every bit as good as the 96 heads if not better because of their superior intake port design (proper short turn radius) and hardened exhaust seats from the factory.

The 1971 96 heads were the ones to have for 455 engines for 9 or 9.5:1 compression. However after folks discovered that the 6X smogger heads had better porting potential and a choice of 2 different combustion chamber volumes the 96 heads started to fall out of favor. I’d take a 6X head any day over the overpriced and overrated 96 heads.

As long as the combustion chamber volume of your 6X-4 heads are correct for the compression ratio you want I’d say keep them and save your money for the other components needed for the build.

I’d replace the pistons with either new flat tops or custom dished to dial in the compression ratio to exactly where you want it. Those pistons with the tops cut down have essentially been turned into scrap.

If you use the 6X heads just remember the tripower is not a direct fit for them. You will have to either fill the heat crossover or make a shim to block the top hole just above the heat crossover or you will have an exhaust leak.

Isn't there a set of intake gaskets that works for that issue--with the heat riser passage on later heads?

Thanks for the advice.
Today a pair of virgin 6x -8’s heads landed in my lap. Hopefully they check out okay. I had a pair of 6x- 4’s on the 71 455 30 over engine, but they had been butchered. I will feel better with these heads on there. Now to work on the 1966 Tri Power that’s going to sit on top of this beast.

if you want the Tri-Power restored, I can do it in February or April.

Here are a few '66 setups I've restored recently.

Yeah, I found a set from Butler Performance

Thanks, but mine has been totally restored. I just got to put bigger jets in and drill out idle pickup and air ports. i got all the information on the correct amount from a professional Tri Power restorer

Ouch........

Care to post up who that professional TRI-POWER restorer is?

Tom V.

restorer
 

Waiting................

I’d like to know who that “professional” is, too.