I could use some advice on how big of a valve combination I can put in the early Cadillac 390 head. What valves would I use? I want to upgrade the springs so can the spring pockets be enlarged safely? I am adding an intake that will have little to no restrictive turns so a little work on the heads should be time well spent. (The intake will be a small block Chevy). If there are other threads already on the site that have accurate information, please direct me to them. JK
I ain't telling you nuth'in but.........what about the ports going TO the bigger valves? May be an even bigger question. Just giving you a BTTT 6sally6
I've talked about this with my buds over at Bontempo Brothers Competition, as pertaining to an early Olds. The trick for the 324 Olds is to overbore .125" to 4" and use a standard bore 371 piston. Coincidentally, that is also the 4" bore of the 390 Cadillac. The 4" bore is also the same as the 327/350 Chevy, so there should be no reason as to why you could not use a 2.02 intake valve, at least physically fit the valve in there, provided you're not shrouding the valve in the process. A good shop will match a proper valve package from something else to work with your valve spring combination, and you'll probably need custom valve guides. Of course, you'd also benefit from accompanying port work. Depending on what kind of RPM you'll be turning or where your target power band will be, you right be better off with a smaller valve package like a 1.94. Here's a link to a dude that is doing it out in Nebraska, though the article is centered on Pontiac heads. Interesting stuff. https://www.motortrend.com/how-to/hppp-1106-d-port-head-valve-upgrade/
Jon - I'd say, head over to an early Cadillac web forum, get first hand info there ! Yeah, as you know, don't just slap a big ol (2.02 !) valve in the hole without knowing the pocket material thickness ! Either cut up a bad head to check the material shape/thickness, or sonic check the walls. I sonic check Stude heads before I port them. I've seen too much variation in the castings. Mike
A thread called” Tech Info:Cadillac OHV V8s 1949-1962 “ is a great thread with lots of good input. Sorry, not sure how to direct you to it.
The 390 has a weird size valve. I wanna say it’s 1.84 . I think you should be able to swap to a 1.94” without much work. I don’t think a 2.02” would gain you much, since the power band should be limited to 5500-6000. I plan on opening my spring pockets up a tad to accept a later styles spring. I am thinking a smaller beehive spring may be in order.
Another consideration is the location of valve centerline to the cylinder wall. If the big valve is real close to the wall, you won't get much flow along that portion. I like Roothawg's idea of a little bigger like a 1.94 range to limit some shrouding of the valve.
The Cadillac uses a shaft mounted rocker. Harland Sharpe will tool up for small runs, but they are pricey. No one else really makes an aftermarket rocker arm. The factory compression ratio is 10:1.
Not trying to change you plans but........better springs......mild clean up of the ports (maybe do a little port matching) multi angle valve grind...a custom grind cam with more duration and a little more lift with a tighter LSA ....better intake and exhaust has gotta make a huge difference in power!. Bigger valves and ports improve 'upper' RPM performance. (read over 5500-6000 rpm) Guys years ago used them in FED a lot. Maybe one of those fellows will come in! 6sally6
I have a set of junk heads to play with to understand the limits of the casting. I plan on adding stainless valves and larger but nothing stupid. I have a set of Harland Sharp roller tip 1.6 rockers I bought a while ago for one of my Studebaker heard but have not used. I ordered two cam blanks from Schneider and just have to decide on the grind for one of them. I plan on a longer duration and a lift somewhere around .480 total lift. I am of course putting on a Chevy small block intake, an open plenum mid-rise on my adapters. Forged pistons, (probably SBC), on custom rods or stock type forged pistons on stock rods with some lovin'. Equal length stainless tube headers, (by me). I may do an electric H2O pump if I can make it look old school somehow. An "ATI" balancer is in the works also. Lots of work ahead but it'll be fun.
Like all wedge head engines the Caddy will respond to a tight piston to head squish..Around .040 works nicely...Sometimes it's difficult to find .040 ish thick head gaskets. Tight squish can make the compression a bit high depending on the OEM squish...With tight squish comes a faster burn, less total timing needed, lower octane requirements, sharper throttle response..I have done on several engines and seen the improvement..
Since you have some extra heads, I would suggest that you get one of those small horizontal bandsaws. You can find them on Facebook all the time for $100/$200. You can resell it for what you paid for it when done. Then I would take one sacrificial head and slice it at each valve pocket. Then you can see exactly what you have to work with at each valve pocket. I would see how much you can bore the engine before deciding on a valve size. Also by sawing a head, you can set in place and view how a larger valve will interact with the head and cylinder. You might even consider enlarging one valve seat so you can use the actual intended oversize valve.
Here's my thread with some actual porting numbers: https://www.jalopyjournal.com/forum/threads/new-skool-331-caddy-build.803459/
In the obsolete racing engine I use, the spring pockets were opened to 1.550 in 1976 for larger available springs 1.94 Chevrolet intakes were the first used along with 1.50 exhaust. Bore and stroke both 4”. Over the years things were tried and changed ending with 2.08 intakes +.100 in length and exhaust at 1.60 +.100. Latest were beehive springs which easy to get long but now needed needed spring base cups since the pockets were now too big for them. I really liked the beehive tops as the rockers now have needed clearance. Being able to purchase 10* keepers with various heights helped in getting spring pressure correct with the minimum of shims. Things to think about…..
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