Hot Rods Let's talk Cadillac 331's, 365 and 390's

I am dying to see the outcome.

 

Oh, Man!

 

Me too! The only thing is I don’t know how accurate the numbers will be on it because we are using the dyno Holley 4 bbl on the stock intake, instead of the 6x2 drag star because I don’t have the Strombergs ready yet. Also the stock exhaust manifolds instead of my chrome headers because they want to install O2 sensors

 

You Cadillac guys might get a kick out of this 55 Chevy Wagon. Phil Stevenson drove it from Southern California in 1972 up to Bonneville. It had a 390 Cad with a Jetaway trans. and made runs in the 140s. Back then the SCTA had an award for the fastest car driven there and he won the recognition.

 

Some simple, yet slick work in there, she'll be a cracker

 

I hope there are a few break in runs and at least a couple power pulls for a graph. How big is the dyno carb? I mean it's not the drag star setup .. but if it's the late 390 intake it should work well no? I hope you get it to 400hp.. but maybe I'm crazy hoping for that. Are you going to rev it to at least 5500 as well?

 

Not sure on the carb size, he did say it was easy to change the jetting without removing the bowls. I have a 650 double pumper I was going to use but he suggested using the dyno carb. Hoping to get one horse per cube so around that 400 hp would be great. We plan on a couple power pulls to see what it likes for timing and fuel

 

I know for the math 650 likely works fine but in reality I wouldn't be surprised if they put a 750 or larger on that thing. Either way I'm excited to see your results as I'm about to start a 390 build myself.

 

some great and innovative info on this thread since I last visited!

 

Thinking about making a small run of this alternator bracket arm I fabbed up yesterday. Local fab shop has a CNC plasma. If I get enough interest I will get prices. Works on 390’s with the accessory hole and a small Denso alternator.

 

Did you ever get the Caddy on the dyno?

 

We did. The stock 4 barrel intake only flows 400 cfm and with the stock exhaust manifolds it put up numbers a little better than factory. Once I get the Strombergs done we are going to run it on the dyno again with headers.

we did play with oil pump pressure relief springs a bit and found we were able to get the cold idle pressure to 60 psi, 30 psi hot idle and 50 psi at 5000 rpm with the engine up to temperature. I’m pretty happy with that. We ended up putting in a double spring and one of them I believe is from a duramax. I’ll find out more information to be sure

 

Nice good to hear an update. I can only live vicariously through others building a Caddy right now. I don’t quite have the funds to start into my 390 sleeping in the garage although I did recently stumble onto a Weiand dual quad manifold that I’m hoarding away. I also don’t have a Model A for it to reside in yet either.

 

I'd be interested to know what the O2 sensors told you about the mixture distribution for all the cylinders...

 

Interesting stuff, Thanks!

 

I would say you could lean it up a bit on the big end and gain some power but that is a safe tune for sure

 

OK, its been four years since I started this project and they're finally ready. I'll post adds next week on the appropriate page here and on other Caddy and hot rod sites. Been battling cancer and that is why it took so long. The adapters bolt on with standard Caddy gaskets and The intake uses a standard SBC gasket, trimmed to length.

 

Very cool stuff. Good job.

 

Mike, did you get the Strombergs set up and dynoed at all?

 

Did you ever post a link? Did I miss it? @60elky

 

Just to put the following into perspective this was a short build thread I did a few years back on another forum for my dad's 331 that he has in his '48 Pontiac custom.
We're also in the UK so just replacing bad parts for good ones isn't always an option.



The engine was a rebuilt take out from a Caddy that had got a SBC conversion in the States.
It ran lovely for about a thousand miles and then started getting a little smokey, then a lot smokey.
On pulling the heads it was found that multiple cylinders had 1” wide, 1/8” deep grooves running the full length of the bores.
Why?
The wrists pins had come lose in the rods and made their into the cylinders walls.
The Caddy motor has push fit wrist pins. To do this properly the rods little end is heated in a special oven that expands the rod end enough that the pin drops through and when cooled the little end returns to its original size tightly gripping the pin.
What others do is take a gas torch to the rod, over heat it and over expand it which means it doesn’t return to its correct size when cooled.
The rod is scrap, the wrist pin comes adrift and takes the block with it.

The block was ‘saved’ with 8 (!) sleeves taking it back to standard bore, a replacement set of used rods from the States and a freshen up had it back running again for the next few years.
Then there was a series of unfortunate events.
First, it blew a core plug at about 90 mph on Pendine Sands without the driver realising and the engine went nuclear.



Then some spirited driving at Prescott Hillclimb caused a “knocking” sound which went away but didn’t as a few months later the car was recovered off the Freeway with a full blown rod knock.
[Yt]

Rebuild 2.

Here’s what was found on strip down.

Cracked pistons probably due to the overheating.



Cracked rocker shaft stands.



Pounded big end shells.



Trashed crank journal.



The crank was beyond economic repair. The rod only showed fretting, possible that it was salvageable but would you want to? Pistons were scrap and the bores showed scuffing from a partial seizure.

 

The scuffed bores in the block were salvageable with a hone and the Schnieder cam were the only reusable parts the short block.



Where do you find a complete rotating assembly for a mid 50’s Caddy engine in the UK?
You dig deep into the memory banks of a vague recollection of a for sale ad that may have had what you needed.
A quick search and find said advert from 3 years previous and it’s all still available. Result!

Beggars can’t be choosers and even though the replacement crank was more than usable the locating dowel hole in the crank flange had been destroyed by I assume someone in the past attempting to drill it out (why?) instead of just knocking it out from the back.
Managed to save it by using the flex plate adapter as a guide to enlarge the oval'd hole and then turn a stepped dowel back to standard size.



On to the oil pump.
Suspicion was starting to rise at this point with the oiling system having issues and being the cause of the failure especially as the oiling system is seen as a weak point on this engine family.

The stock oil pump is this thing.



What’s going on here is a conventional oil pump with a secondary vane pump piggy backed on.
The secondary pump is a vacuum pump. It’s only job is supply vacuum to the windscreen wipers!
The crazy situation is the two pumps are linked internally so when the vacuum side starts going wonky, as it surely will, the oil pump starts pumping air not oil. ‍♂️
Strike 1.

Luckily Cadillac saw the error of their ways and in 1959 there was a cross over of oil pumps which meant you have an early style pump without the vacuum side that retro fits into the earlier block.



Another small issue found.
There should be a felt seal from pump pickup to pump inlet. If it’s missing it can again, suck air.
It was missing.
Strike 2.



The short block had all the oil way core plugs knocked out for cleaning and drilled and tapped for threaded plugs and of course new pistons and bearings and ARP hardware for good measure.
Short block went together and the cam degreed perfect which made a nice change.

 

Moving onto the heads.

The heads had some new SS valves and valve springs thrown at them at some point.
Problem was the valve seats were tired, the valve guides were worn and the valve springs were missing their internal dampers as they didn’t work with the OE spring retainers.

With the heads stripped, they of course they got the ports cleaned up and port matched.



The OE spring retainers had this metal umbrella arrangement that acted as a basic valve guide seal or oil deflector.
This is primitive stuff, doesn’t work very well and as already mentioned created issues with the replacement valve springs.
I couldn’t see a reason why their removal wouldn’t be an issue, so off they came.
I initially tried to face them off in the lathe but the umbrella portion was so thin they just collapsed in the chuck.
The angry wheel then made short work removing them but it took some time carefully grinding them flat and to within a couple of thou of each in width.



The springs could now be mocked up and measured for height. They were all with in 0.010” of each other which is good going and shows these engines were built to tight tolerances from the factory.



A valve guide seal was now needed and luckily the guides were the right diameter for a SBC/SBF modern style Viton seal to slide right on… but… the extra height of the seal on the guide meant there was hardly any valve lift before the spring retainer ran into seal.
The valve guides are quite long from standard so it wasn’t a problem to remove the 0.250” (1/4”) needed to give enough clearance for the valve lift.



The heads were sent off to the machine shop to get new seats, valve guide liners and the guides machined down for the seals.

The rest of the valvetrain was a bit of a mess.
The valvetrain is non-adjustable which is fairly common for US V8’s. This is fine if you’re using all stock components, but change one thing, in this case the cam, and the whole valvetrain geometry goes to curse word.
First job was to find some adjustable rocker arms.
They were available in period but are now rare. Rockers from other engines of the period like Studebaker apparently fit and are adjustable but hard to find. Then I was put onto a company called Harland & Sharp in the US who apparently still made them. I rang them, they would make them to order and would be with me in 4-5 weeks. Yay!



On stripping the rocker assemblies more issues were found. Two stands were cracked which I managed to get replacements for and the rocker shafts were worn probably due to the various sludged up oil holes.
Got the new parts and went to assemble them and found another cracked stand and a mis-matched stand in the set as well because there are 3 different styles and one must have been changed out before in the distant past.
Annoyed that I had been halted on the assembly for the second time I bought another pair of used assemblies so I wouldn’t be caught out again with a lack of spares!
So, 48 rockers, 16 rocker stands and 6 shafts later I finally had two usable rocker assemblies.

 

With the heads assembled and mocked up on the block it was onto measuring the push rod length and setting the rocker sweep across the valve tip.
These engines have a long push rod at nearly 8 1/2” long. The longest adjustable push rod available for setting up is is just over 8 1/2”.



Then things didn’t quite go to the plan.
What I’m trying to achieve is the optimum movement of the rocker roller across the tip of the valve. The reasons for this are to achieve the least amount of lost motion and to locate the movement as close to centre as possible to stop excessive side loads on the valve stem which prematurely wears the valve guides. In extreme cases it’s even possible to roll the rocker right off the edge of the valve tip.
To test you simply engineer blue the valve tip and cycle the valvetrain a couple of times and then inspect and measure the sweep that shows in the blue.
What you want is a central sweep that is no more than 0.050” in width.



This is the best I could get no matter what I did. Off centre and around 0.100” width.
I changed the pushrod length changed +/-. I tried shimming the rocker stands up. I even made caps for the valve stems out of shim stock to change the valve length to no avail.

It seemed to me that there was a fundamental design issue going on and that the real problem was that the whole rocker assembly was in the wrong place i.e it needed shoving back.
Myth and lore with these engines is they have a habit of breaking rocker shafts in high stress (racing) applications. I can believe it after going through this.
Its not unknown to slot mounting holes in rocker assemblies to be able move stuff around but that was a no go with this as the rocker assemblies are bolted down and oiled via the head bolts. Slotting the stands would lose oiling to the rockers and create a pressure loss in the oil system.

What to do?

Nothing!

It is what is. It’s not a race engine. It’s going in a road car with a slush box. It might not be great but it’s not terrible either. Sometimes you just have to accept and move on and it’s probably better now than it’s ever been.

On to the finishing touches.
The engine comes with a rudimentary sump baffle that bolts to the block. I simply added some extra baffles to contain the forward and back movement of oil.
Also made a new dipstick tube to replace the broken, bodged up one that was on it.



An oil filter wasn’t standard but you could have a bolt-on bypass filter fitted by the Dealer.
This engine had the filter fitted but the oil lines were a mess with most of the fittings rounded off.



I couldn’t live with this so I replaced the fittings and remade the lines.



Converted the road draft breather system (rubbish) to PCV instead.



The original dizzy got canned and a brand new Pertronix billet one with igniter II and fully adjustable ignition got fitted instead.
But before it went in I changed the stops and advance springs from the short, lazy curve that aftermarket dizzy’s always seem to evidently come with.



One final job before first start was to make a oil priming tool as funny enough they’re not available for these engines.

[Video]

After having this engine so long I was determined for it go back in and be started.



We blitzed it one Saturday and done…

[Video]

 

@Enbloc I think you have one of those highly sought-after "well seasoned" blocks...Good work sorting it all, I'm glad you're back up and running!

 

Wow thanks for the thorough post. Lots of good stuff in there!!

 

@Enbloc, thanks for the detailed post, I'll begin building my 331 soon and found this helpful.