[Hurlbird]

1969 XF 428 (370HP) in 68 ram air Firebird. Car has AC which I want to keep. Tremic 5 speed with 373 rear end. Running all stock parts including 68 long branch manifolds and Quadrajet.
It runs great right now on pump gas, but is leaking rear main oil and the head freeze plugs are leaking. The motor appears to be untouched. Does not burn oil. I want to freshen it up so I can literally drive this anywhere and enjoy performance and reliability. I’m worried about 50+ year old internals. That said here are some questions I have:
1. Why does it run so well now with pump gas? Most likely due to ring wear or another cause creating less than stock compression? No pinging or run on.
2. Should I check compression to determine ring wear? Or could I be fooled by valve wear?
3. Do I pull heads and look for ring ridge as the best indicator for rebuilding the shortblock?
4. I understand I want to run about 9.5:1 compression for pump gas. How best to accomplish that? Different pistons? Different heads? Both?
5. Is it more effective to purchase after market heads or do I rebuild the #62 heads I already have?
6. Aftermarket heads designed for stock brackets including AC?
7. If I want great performance but lower compression, how do I accomplish that? Focus on heads/exhaust? I want to keep LB manifolds.
8. I don’t beat it. Do I just rebuild/replace the heads/ perhaps a 068 cam/timing chain and other wear parts, and not worry about the short block? See #1 worry.
9. If I’m doing the rear main seal do I do the short block since I’m there already?
Thanks for ideas! -John

[tom s]

Maybe start with a leakdown test.HP is in the heads,if looking for more than heads to be better,that is more flo.EZ to do with aftermarket.With more HP is bigger cam to go with the heads.Usually more RPMs so the rods need to be up to the task.If alu heads you can push to 10.25.One thing leads to another.Good luck with your project.I just got done doing two 428s,one tame and one not so much.Tom

[steve25]

I don’t understand the need for most of your questions if your going to freshen it up!

Take nothing for granted that it may be reusable in the rebuilding process until you tare the whole motor down.
Your lack of knock and or ping with the way it runs now is very likely due to a shot timing chain, or at least one that’s allowing like 4 degrees of retard.
Your current # 62 heads fully rebuilt with a good cam pick can allow 400 hp to be made, and believe me that will feel like a big jump in power as compared to how the motor runs now, even though you say that to you it runs good now.
If you like and they check out good you can reuse the stock rods since it sounds to me like you will rarely buzz the motor above 5400 rpm, however stronger and lighter aftermarket rods will allow the motor to rev up faster and allow longer life to the bearings .

During the rebuilding I would use the one piece type seal that can now be had.

[John Milner]

I would be willing to bet that you are already close to 9.5:1-9.75:1 with your current setup. If your short block is stock, it will have pistons with a 13cc dish. Those 62 heads are likely at a minimum 75cc. I’ve run 428’s for years on pump fuel similar to yours. They are great engines.

[Mike Davis]

Big fan of the 4" stroke engines. If you are planning a tear down, might as well do it right the first time around. Fresh bore, a nice set of forged pistons, forged H beam rods, balance rotating assembly, good 3/5 angle valve job. new cam lifters, Melling 54 oil pump and a Cloyes Billet Timing set. Get another 20 years out of it.

[Will]

Set your compression with the pistons. Re-use the heads you have now, they are an excellent casting. Rebuild with new, one-piece valves. CC them after the rebuild.

Mill block flat and square to crank centerline then measure deck height. Get crank indexed when it gets turned. Once you're sure the stroke is right at 4" where it needs to be and you know the deck height and rod center-center length you can order pistons with the proper pin hole location to achieve true 0" deck clearance and the size dish you need to get your compression into the low 9:1 range with the chamber size of your heads.

your post indicates you just want a strong running, reliable engine for a cruiser type situation. You don't need to do much to achieve that. You can build it to mostly stock specs and make a lot of power and run fine on pump gas.

Here's what I'd do if it was my engine & car:

Heads:
- Replace stock 2-piece valves with 1-piece valves (eliminates major point of failure that could destroy your engine).
- 3-angle valve job utilizing stock 30 degree seat and have shop use a "bowl cutter" to open up/true up the throats in the ports above the valves. Have rough ridges blended by hand. This will pick up flow.
- Install new bronze valve guides. Have guide bosses machined for positive seals and run viton seals.
- ditch metal spring shields as they aren't needed now that you have positive viton seals and will interfere with aftermarket springs.
- Install Crower 68404-16 springs. Reasonably priced and install at stock height and can handle more lift than stock.
- Install 7/16" straight studs and poly locks.
- Stock rocker arms will be fine, but if you want to step it up, Harland Sharp 1.5 ratio would be my pick.


Block:
- Mill flat and true to crank centerline and measure/buy pistons/etc as outlined above.
- Resize stock rods and with new ARP bolts. If you want an extra measure of safety some budget forged rods would make sense but be sure to have them thoroughly checked for proper sizing on both big end and pin end.
- Have crank indexed when resized, as mentioned above.
- Balance new rotating assembly.

Since this is a large-journal engine I'd take a Melling M54DS oil pump and shim the pressure relief spring with a 1/8" thick hardened steel washer. This'll bump pressure up about 10 lbs.

Cam: Crower 60916. Will idle with a little bit of attitude at 750 RPM and pull plenty of vacuum. Should work okay with a stock converter but something just a little looser than stock would help. A custom converter would make a huge difference. Will make LOTS of midrange power and be done around 5000-5200 RPM. Be sure to degree it to ensure it's installed as it's supposed to be.

Ram Air exhaust manifolds with 2.5" pipes all the way out the back will work great.

This engine should be real close to 400 HP/450+ ft-lbs and mild enough to drive every day with the A/C on in traffic.

[steve25]

Here’s the added flow percent increase from no valve angle to a 4 angle valve job with a main 45 degree seat.
As you can see a valve job greater then a 3 angle one would only provide a small power gain to a race motor by means of much increased valve lift, while eating chamber meat on a street motor that could be better put to use in freshen up valve job down the road.

[Hurlbird]

Thanks all. Will recall I have a 5 speed tranny. Manual. Does that impact your thinking?

[Will]

Originally Posted by Hurlbird

Thanks all. Will recall I have a 5 speed tranny. Manual. Does that impact your thinking?

Sorry, I missed that part about the 5 speed. Doesn't change my thinking though, other than that it's perfect - you don't need a looser converter when you have a manual trans!

You *could* go a little bigger on the cam but I don't think you need to. That Crower cam is already bigger than any cam Pontiac ever put in a 428. Only the 744 and 041 factory cams were bigger, and it's pretty much the same as a 744, just a couple degrees less duration, slightly tighter lobe centers and a bunch more lift. It will be a midrange ripper.