Tech Info: Cadillac OHV V8's 1949-1962

About 1/16" down the bore... I did not measure but that is a fair estimate (if my memory isn't failing me)... keep in mind mine is a 51 block bored to 4" with 331 crank and rods...


Yes, one of my faves. thanks to Mr. Edell as well...

 

If that is common, the compression numbers I have shown will be slightly optimistic. I can recalculate to see how sensitive that is. Also, if I can get the thickness measurement from an old (compressed) head gasket, I can add that to the calculation as well.

331 crank and rods should be the same as a 365. Hopefully your pistons have the factory compression height.

When I have a little more time I'll do some measuring on my 331 which has the heads off. I plan to overbore to 365 as well and have some 390 heads for it.

 

Crud, now you got me wanting to pull a head off to give an accurate measure...

I do have a compressed head gasket in the pile, pulled from the stock 331... although the replacement Felpros are much thicker, not sure it would lend much to your calculations, unless you used it as a nominal and applied the same to all the calculations in your spreadsheet. I dunno, I got a C in math.

I also have some 390 heads on...

 

I would think that the Fel-Pro would compress some upon installation, but the difference between the two gaskets is probably minimal. Probably not worth disassembling anything for this exercise. These differences won't be enough to change which octane fuel you'd use.

 

There is a bare set on the 'bay right now, in NY

 

make sure you get the rocker arm shafts too..

 

Great thread!! I've been researching heads for my 331. I found the valves on the 390 and 365 are longer, and the chambers are shallower. Looks like they dropped the valve seats in the heads. This would make the short side of the intake runners longer (better) and unshroud the valves in the cumbustion chambers. Plus raise compression.

Then again I could be wrong....

 

I did a little measuring the other day on my 331. The compression height/deck clearance is about .125 and the thickness of the shim type head gasket is about .017.

My numbers are all based upon book compression ratios, so all this is already part of the equation. If someone could cc the various heads, we could do a more thorough mathematical analysis. I have both 331 and 390 heads, but no burette or plate. If someone wants to loan me the setup I'll be glad to do it.

From everything I've read, a .125 compression height is not good for quench in the combustion chamber so that may limit performance a bit (http://kb-silvolite.com/article.php?action=read&A_id=35).

 

I use a small peice of plexiglass, and a 50cc syringe from Tractor Supply or a vet supply store. Your right on with the deck clearance. Around .050 is ideal for high rpms.

 

What's the difference between the 390 and early 331 rockers? I picked up 390 heads for my 331, but no rockers.

 

I cant remember exactly off the top of my head why they are different but you need the rockers arms and shafts from the 390 for it to work.As well as the Head Bolts for the 390.That much I remember.

 

I think I found some here locally if they are any good. Engine has bottom end problems so who knows how much oil they had going to them.

 

that was it, oil! oiling holes are different on 331 shafts than on the 390..

 

That makes sense. Thanks.

 

Looking around (http://www.speedwaymotors.com/365-390-Cadillac-Piston-and-Ring-Sets,5358.html) at stock replacement pistons, I noticed that the 1956 & 1957 365 had a flat-top piston, 1958 365 & 1959-1963 390 had a dished piston. So there is another tip to find (or give up) some compression.

Can someone cc a '58-'63 piston dish and post the results? We can then calculate how much of a difference that makes.

 

My 62 390 had flattop pistons in it when I pulled it apart. Did not appear to be rebuilt either. ?

 

Hmmmm... Are you sure the engine was original to the car?

I'm just guessing at this stuff- maybe there was a mid-year change?

 

Great thread !

 

Great thread!

I just took apart my 390 and it also had flattop pistons. It was out of a 62.. casting #'s check out.

 

It appears to be confirmed then! Was there a horsepower difference in '62?

 

Im so proud to see this post I created 8 years ago still helping people and kept alive by you guys today.

 

You're so right, I'm in France and I use all the informations available here to build my '60 390 for my Renault station wagon.

 

I picked up a set of 390 heads for my 331. I didn't get the rockers, pushrods, or head bolts. I started comparing the 331 and 390 parts to see what was changed. Here is what I found.
The rocker ratio on the 331 is 1.5. The 390 has a 1.64 according to my measurments.
The pushrod length for the 331 is 9.75. The 390 is 9.562 long.
The rocker stand holds the rocker shaft .060 closer to the head on the 390.
The strangest thing, and I think my 331 was messed up, the oil holes and grooves on my 331 were to the top. The 390 had the oil holes to the bottom (the loaded side).

The increased rocker ratio gets me a little excited. Here is a picture of the rockers. The center rocker is 331 with two 390 rockers to the outside.

And I took a picture of the pushrods

If I find more I'll post it.

One more nugget. I'm running 2.02 and 1.6 Chevy valves in the 390 heads and they fit great. The installed height on the springs came out to 1.830 with no shim. The Chevy z-28 springs work perfect with the needed shim.

 

Today I installed the hard seats in the 390 heads. I used 1 5/8x1 3/8x 7/32 seats and there seemed to be plenty of meat in the heads. I'm impressed with the quality of the castings and the tolorances Cadillac used!! Cutting for 2.02 and 1.6 valves was a cakewalk.

 

Are these part numbers or casting numbers that are shown on the spread sheet? After taking off the valve covers I found the following numbers: 459786-7 (or could be 459736-7 - hard to read 3 vs. 8). Also on the heads are 2-15 and 12-8. The block (with the cast on bellhousing) has what looks like 1480088 and 11N4 cast on top of the bellhousing. The intake is a four barrel. Any way to determine the actual year of the engine based on these numbers? Thanks for your help.

 

Casting numbers.

 

Guys... I have my cast 4x2 log manifolds in the classifieds... check em out!!!

 

So cadi masters... Would a 390 fit in a 49-52 Chevy on a stock frame and no fire wall recess or am I dreaming

 

The numbers that I was reading are on the top surface between valves. Are there other casting numbers (such as shown on the chart) on the underside? Also, on the side of the block is "11M4" which could be what I was trying to read on the bellhousing extension. Could this mean November 13, 1954? That was a Saturday. I'm still trying to figure out what I have. Thanks for the help.

 

I dropped my 58 365 block and crank off for machining today and after reading the earlier posts regarding the 58 heads and the 390 heads being the same castings was wondering if I should hunt down some 390 heads or just get the bigger valves fit to the 365 heads.I was going to go with the 2.02 intake & 1.60 ex valves as is suggested here but should the centre 2 ex valves be left standard as is suggested here in earlier posts?
Did I read this correctly or have I missed something?
Thanks for the help and what a great post.