[racerboy]

I started another thread about possibly having to pull the RA III out of my '70 T/A for a rod/piston whap because I think the rebuild on that motor used flat-top pistons and with the #12 heads, I am getting a lot of pinging even though I only run 93-octane gas. Anyway, while that process starts to play out, I don't want to not have the T/A to drive this summer so was considering dropping in a 428 that's sitting under my bench that probably only hsa 10,000 miles on it since a rebuild back in 2002. That engine has 670 heads on it now, which I know is too high, so was thinking what would be the easiest and least expensive ways to keep the T/A on the road while the 400 gets massaged. I'm not really interested in going the aluminum head route, so was considering finding a set of larger -cc heads for the 428. Would the 6X-4 be a good choice? I see these come up on eBay from time to time and I know a lot of guys like these for the 455 builds. What about the 1970 #64 heads?

[John Milner]

I would say that it depends on what pistons are in the 428. If it has factory 13cc dished pistons, it should be right at 10:1. I have actually had good luck with my 428's at near 10:1. I run 670 heads on one and it never pings on 91 octane. Another engine has 614 heads and runs good on 91 octane. I ran another one for years with 62 heads and when I had it back out of the car, the bearings all looked brand new and there were no signs of detonation. It ran on 91 octane as well. You would just need to be careful as to what camshaft you choose for the engine so it won't build a ton of cylinder pressure.

If you run the 6X4's and your engine has the factory style dished pistons, compression would be in the low-mid 8's. Obviously it would run good on pump gas but maybe not the best for performance.

[694.1]

What about a 7K3? Big valves, screw in studs, hardened seats,modest compression.
What is not to like?

[racerboy]

Originally Posted by John Milner

I would say that it depends on what pistons are in the 428. If it has factory 13cc dished pistons, it should be right at 10:1. I have actually had good luck with my 428's at near 10:1. I run 670 heads on one and it never pings on 91 octane. Another engine has 614 heads and runs good on 91 octane. I ran another one for years with 62 heads and when I had it back out of the car, the bearings all looked brand new and there were no signs of detonation. It ran on 91 octane as well. You would just need to be careful as to what camshaft you choose for the engine so it won't build a ton of cylinder pressure.

If you run the 6X4's and your engine has the factory style dished pistons, compression would be in the low-mid 8's. Obviously it would run good on pump gas but maybe not the best for performance.

Thanks John. I’m actually going to pull the heads off later today just to see what pistons I installed 20 yr ago. I’m guessing they were probably a standard 428 .030 forged piston. I certainly didn’t have any money back then for anything like a custom Ross or anything like that. I know it has early forged rods that were shot-permed because I couldn’t afford any aftermarket rods either. I think I ran a Lunati can but don’t remember the specs. Engine made good power in my 1967 GTO. Broke the trans. Broke the posi. Tore front sway bar out of frame. LOL. Funny thing is that I put that engine in the ‘67 back in 2002 when I took out the original 400 HO for a rebuild, and ran it until 2013 when the car was sent down to Barr’s for a frame-off. Now I’m looking to use it as a temporary service-replacement again, but would want it to be more streetable.


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[racerboy]

I’ve got a brand new Crower 60423 HFT and Johnson lifters that I was going to swap into the RA III in my Judge before I traded that car for the T/A. I wonder if that would be a good cam in the 428. If I pull the 400 out of the T/A, which is becoming much more likely, then I would probably go the HRC route when it went back together.


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[steve25]

The semi closed chamber of the 670 heads are less likely to when the same compression is used as a open chamber head ,

[racerboy]

Hi Steve
Are you saying the 670s are less likely to ping then, say, #12 heads?

Here are some quick photos of the partial tear down. Everything still looks really clean (so far).






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[racerboy]

Just before the first cam lobes, you can see the a stamp that says
540
233


On the back part of the cam it says F2


Any idea what this means?


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[racerboy]

You don't think that means .540 lift, .233 @ .050 do you?

[racerboy]

So I did a little research and it appears that 540 233 is a camshaft core number. I have to pull the cam to read the codes that are stamped on the rear. Do I understand that correctly?

[steve25]

Correct, in answer to your ping question.
The 670s chambers do not burn as clean / complete as the later heads and this produces a small EGR effect which cools things down,

[johnta1]

Appears its a factory cam?
The cam code would be on the front nose. If a later year cam could be on the rear. An aftermarket cam would be on the rear.


You do realize the 428 won't bolt in the 70 Firebird without putting some different frame mounts on? (and the engine mounts)

[racerboy]

Thanks John
I did not know about the frame mounts being different. Do I need the mounts for a 455.

I do t think it’s a factory can. I’m pretty sure it’s a Lunati. I vaguely remember ordering a Lunati kit when I was having engine built. I used to run a Lunati in another 428 I had in my bracket car and always thought that car ran well, but that car was 100% strip so I should’ve done more research at the time regarding a cam for the street.


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[SD455DJ]

Racerboy, we ran a 428 (+0.060 = 440) with '71 96 heads (94 cc chambers), iron intake/Q-jet and ran great on pump gas (must have been mid-8's static compression) with a stock 068 cam and factory valves springs, etc. The engine was in a '66 GTO convert with a TH400 and the original 3.55 10-bolt saf-t-track rear end. It ran 14.60's at 95 mph all day shifting at 4800 rpm (it was pretty tired at this point) on skinny snow tires! It was a ton of fun on the street!

Dennis

[tom s]

I had a set of 64s on one of my 428 builds,they were perfect for our calif piss gas.Tom

[johnta1]

I did not know about the frame mounts being different. Do I need the mounts for a 455.

The engine only has the 2 bolt holes for the early style mounts.
(70 and up used the new 3 holes for mounting, total of 5 on the newer blocks)

It would require at least a set of adapter mounts for the engine.
Some companies make them, but not sure how good they are.

Or could use early frame mounts from 68/69 GTO then use the 68/69 engine mounts.

The adapters have a problem of raising the engine from the thickness of the metal adapters. Throws off alignment some I believe?
(never used them. did the early mounts for my car)

Or could use a front engine plate mount.

[racerboy]

Thanks John.
This may turn out to be more involved than I thought. Maybe I should find out just how long it would take to get new rods/pistons in the 400 block. Of course if I’m going that route, I wonder if I should just get one a stroker assembly.

Damn rabbit hole


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[Cliff R]

Since the build was done 20 years ago most likely the pistons are dished.

I had two different 428's in my car decades ago, one had #96's on it, the other 6X-4's. Both of those engines had dished pistons. In the first engine I ran a real 744 cam with high ratio rockers, in the second engine the HO Racing HC-01A.

The 744 cammed engine was "weak" below 3000rpm's and pretty much done by 5000rpm's. Not really impressive anyplace. The second one faired better, but both of those engines needed more compression for the cams I was using in them so I really wouldn't recommend going that direction unless you just want a decent running engine that will easily manage low octane fuel and move the car from point A to point B.......FWIW......

[Thegoatman455]

Could anyone comment on why you wouldn’t put a “larger” cam that bleeds off some of that compression enough to run 93? It would seem like a win win. The High compression would help keep it from having poor street manners?

[tom s]

Bigger cams are put in to make more HP!More HP comes from cyc pressure.Big cams bleed off compression at very low RPMs.Kind of hard to drive a engine that way.Its a crutch IMO.Tom