360 LA Head Upgrade Question

[74Scooter]

Hi all, first post here. Have a steel head 360LA that the previous owner of my car had rebuilt maybe 15k miles on it. Pretty basic rebuild, .030 over with dished pistons and a Comp Hyd flat tappet .454/.454 110 LSA cam. Double roller timing set. Hardened exhaust seats. Has a Weiand action plus intake sitting on it.

Want to get rid of the cast heads so I picked up a set of 63cc Promaxx (SBM 171 2.02/1.60) aluminum assembled heads, I'm planning on raising the CR to about 9.5~9.7. Also upgrading to a set of Harland Sharp roller rockers, 1.6 ratio to get about .030 more valve lift. I don't know exactly how far the slugs are in the hole at TDC, but I scoped the cylinders and it's definitely not zero deck. Thinking I should be able to get a head gasket set to achieve my desired CR after I get the deck height measurement for the calculation. Will also be installing an Eddy Air Gap intake that came with the car.

So the questions on the plan.

1) Will I need to worry about any interference issues valve to piston with .484 lift on intake and exhaust?

2) The cam specs (Pn: 20-212-2) say good for 8.1 to 9.1 compression. Any downside being slightly above that CR?

3) I ordered a set of stock length "7.500" chromemolly ball & cup pushrods. Anyone think I might need a custom length?

 

[Locomotion]

What pistons? If they have valve notches, you should have plenty of piston-to-valve clearance.....BUT.....the best thing to do is double-check.

You may need custom (shorter) pushrods because typically 7.5" cup/ball pushrods fit solid lifters. Hydraulics normally have the plunger higher in the lifter body. But again, with the different heads, rockers and deck milling, you need to check. Ideally, 1-2 threads of the adjuster should show below the rocker arm when properly adjusted.

 

[74Scooter]

What pistons? If they have valve notches, you should have plenty of piston-to-valve clearance.....BUT.....the best thing to do is double-check.

You may need custom (shorter) pushrods because typically 7.5" cup/ball pushrods fit solid lifters. Hydraulics normally have the plunger higher in the lifter body. But again, with the different heads, rockers and deck milling, you need to check. Ideally, 1-2 threads of the adjuster should show below the rocker arm when properly adjusted.

I believe the pistons are Silvolite PN 1279.030, dished.. no valve reliefs. The carbon I received of the engine build sheet is really difficult to read.

 

[GTX JOHN]

I have race the 360 dish piston combo for nearly 60 years
and I am familiar with that particular piston casting.

That size valve will likely hit the flat spot past the dish or
be extremely close. If and when the Valve float and they probably
will there will be trouble assuming valve seat height is similar.

I would run 1.5 rockers to get another 30 clearance and still cross
my fingers. If you are going to run 1.6 = get a machine shop to cut
ar least a 050 valve notch in the pistons before assembly. You can use and
old head and cut it on assembled short block but it is a real mess and ring lands
must be sealed up to trap chips.

 

[MOPAROFFICIAL]

Hi all, first post here. Have a steel head 360LA that the previous owner of my car had rebuilt maybe 15k miles on it. Pretty basic rebuild, .030 over with dished pistons and a Comp Hyd flat tappet .454/.454 110 LSA cam. Double roller timing set. Hardened exhaust seats. Has a Weiand action plus intake sitting on it.

Want to get rid of the cast heads so I picked up a set of 63cc Promaxx (SBM 171 2.02/1.60) aluminum assembled heads, I'm planning on raising the CR to about 9.5~9.7. Also upgrading to a set of Harland Sharp roller rockers, 1.6 ratio to get about .030 more valve lift. I don't know exactly how far the slugs are in the hole at TDC, but I scoped the cylinders and it's definitely not zero deck. Thinking I should be able to get a head gasket set to achieve my desired CR after I get the deck height measurement for the calculation. Will also be installing an Eddy Air Gap intake that came with the car.

So the questions on the plan.

1) Will I need to worry about any interference issues valve to piston with .484 lift on intake and exhaust?

2) The cam specs (Pn: 20-212-2) say good for 8.1 to 9.1 compression. Any downside being slightly above that CR?

3) I ordered a set of stock length "7.500" chromemolly ball & cup pushrods. Anyone think I might need a custom length?

Stock dish are 8.1 comp

Question 1. Stock lift was .444 on some of those iirr, no interference...then figure 59 degree lifter angle=you arent really seeing .480 at the valve..more like .460 if that.
Now 1.6 is an issue...Checking is always good..like error to the side of safe is best. You need to factor the head gasket in ,it will effect your fine compression and add to the seat distance to piston. That said... I've run the .480 on a 1978 stock 360 with smog heads and they never hit. Just check though for the sake of others and yourself.

Question 2. Inadequate octane/detonation perhaps...from too much cyl pressure. Stick to the recommended ratios..they're tested.

Question.3 Too late...you ordered them before asking. Check and see next time by doing a mock up and preload check.

The head @63cc could bump the compression to 8.7 -9.0 + since stockers are around 72cc -any milling during rebuilds...could be 70cc 'assuming .010 with a couple of rebuilds' ..do the math
Fwiw.

 

[Rapid Robert]

I ordered a set of stock length "7.500" chromemolly ball & cup pushrods. Anyone think I might need a custom length?

watch the utube vid "pushrod geometry for engines" by straub technologies, its the one with the yellow rocker.

 

[CRUZE 418]

Mousetrap. See this alot, hey, I ordered these parts, now that I have them, will they fit?

 

[74Scooter]

Thanks for all the replies.

Mousetrap.. like that one.. it's a keeper.

This is more like a "things change" as Don Ameche famously said.

 

[Locomotion]

Advancing or retarding the cam may also be a factor in piston-to-valve clearance with no notches..

 

[74Scooter]

Will definitely check clearance and do the math once the top end is off and I know what the deck height is.

Rough calculation based on stockish deck height puts me at 8.94:1 CR if I use a stock Felpro head gasket with a .039 compressed height.

If I get into trouble with valve interference I can stick with the stock rockers and bump the head gasket up to .060 for an additional .020 and I still come away with 8.58:1 CR.