Improving Cylinder Head Performance

[Dan McNarry]

The stock Cadillac cylinder heads do a good job of getting the fuel air mixture into the engine and exhaust out at lower RPM's but are a little restrictive higher up the RPM range. Here is a little story about the evolution of my cylinder heads. 

First of all, a little disclaimer. I did very little of this work myself. A race engine building friend did the porting and a local automotive machine shop did the machine work and assembly. I did the research on what parts to use. 

The stock valve sizes are 1.87" intake and 1.50" exhaust and as you all know, the middle two cylinders on each bank share an exhaust port. That port is larger than the end ports. What got me started on this whole thing was I took an old head apart and slid in a couple of 1.94/1.60" Chevy valves. It looked like it would be a no brainer to install the bigger valves so off I went.

My engine builder buddy had never touched a Cadillac head before so I cut one up so we could see where the flow could be improved and where the danger areas were where you would have to be very careful removing material. Here are those discovery photos. I'll explain them in a reply.

[Dan McNarry]

The second photo above shows the second cylinder from the front. The head is opened like a book, on the left you are looking down at the head as it would be installed. The right "page" would be looking up at the roof of the ports. The spark plug hole can be seen at the top of the head. In the left hand page you can see the valve seat area with the intake being the larger sooty port and the exhaust being the smaller rusty port. You can see the path that the exhaust follows as it both flows out of the head and the exhaust crossover to the intake manifold. 

The third photo shows the first cylinder on the right. Looking at the head like this shows where material can safely be removed and what contouring can be done to help flow. 

The fourth photo show the Chevy valves that started the whole adventure. I'm on KP tonight so I'll be back after I do the dishes with some photos of the porting progress.

[Dan McNarry]

These photos show some of the porting process. There was a relief around the valve heads that was not good for flow so Jim blended that in to a smoother contour. He also "unshrouded" the valves at the sides of the combustion chamber where they come close to the chamber's vertical walls. This is really important because if the valve is too close to the wall there is a big disruption to air flow. 

In one of the pictures there are some remarks indicating things that were done to the heads. The port pockets were machined out to improve flow and be the starting point for the porting job. The valve guides extended in to the ports a fair bit and were cut back to eliminate the obstruction and increase port volume. You can see that on top of just porting, Jim also polished all surfaces. The one picture is kind of goofy because I took it through the plastic the heads were wrapped in after assembly at the machine shop.

[Kevin Campbell]

Pretty nice work there Dan.

[Dan McNarry]

Thanks Kev. 

[Dan McNarry]

The Cadillac and Chevy valves are identical with the exception that the Chevy valves have a .250" longer stem. Bummer. I had to get Manley to make the valves as a custom one off. They are stainless steel in their race flow profile and are 194/160's as previously mentioned. The valve springs and retainers are from Comp Cams. I've included a photo of the original style springs and retainers and a photo of what is there now. The stock springs are quite long with a big recess in the retainer that allows the rocker to get at the valve tip. The retainers are very heavy by today's standards and the springs are quite weak which leads to valve float at higher RPM's. The Comp Cams springs are their bee hive model. As you can see they have a slight bee hive shape. This reduces spring harmonics and helps reduce both fatigue and valve float. The retainers on a bee hive spring are smaller in diameter as a result and therefore don't weigh as much which further reduces float. They are a bigger diameter at their base than stock springs so the heads had to be machined to accept them. Shims are used to get the proper installed height.

You can see that Matt at the machine shop has a sense of humor as he christened the heads Chevellac Performance Heads in his set up card. There is one mistake in there as he has valve lift at .480" where it is actually .495" as you will see when I get around to the cam.

[Anders]

I wonder about movement control of the valve when the valve guide is shortened. The Cadillac engineers made the guides long enough to avoid any sideways movement. Even if partly restricting the flow. Is there any drawback you can think of with shortened valve guides?

My guess is that shorter valve guides with original springs and the "wobbling" heavy retainer would cause a lot of wear.

[Dan McNarry]

Anders, good question and one I asked Jim. We talked it over more than once before he convinced me that it would be okay. His argument was that in terms of percentage, the Cadillac guide was quite a bit longer than a stock Chevy guide and that a Chevy small block has a 1.5 rocker ratio as opposed to the Cadillac's 1.65. The longer ratio reduces the "swipe" effect on the valve tip slightly. As you surmised, the stronger spring also stabilize the valve. If you look at the single exhaust port in the photo above, you will note that there is still a slight mound around the guide and that he didn't completely eliminate it.

All of this led me to go along with Jim's ideas for the heads and he has been proven right. I put the heads on 7 years ago and there has yet to have been an issue. I listen to my engine several times a year with an automotive stethoscope and did just last week when I fired it up for the first time this year. All quiet under the valve covers and no sign of oil burn.   

[Tony and Ginny 429]

Love the larger valves and the polishing work- sweet  performance flow stuff 

This is a job  best left to those who do this kind of work and have the touch and talent  ( Modello comes to mind ) 

You prior head research  work is very commendable and sets you apart 

My own observation is that running a cleaning tool through the stock head on the intake side of the heads  when possible will clean up a bit of that scaly mess and improve the flow of the fuel mixture in those runners 

That rusty stuff has to be passed thru the cylinders and out the exhaust - not the best thing to be going on 

No idea what was going on in the head intake runners  before your photos ( but now we know - don’t we ) 

Were the heads C-C ed as that would seems to follow this fine  performance head work 

Love what you did and the approach you took to help get the end results right is  a bit above and beyond what the average guy might do 

That does make it a special build due to your own desires and talents combined 

Enjoy my friend 

[Tony and Ginny 429]

Dan 

What’s your red line with your set up ? 

[Dan McNarry]

Tony, I seldom take it past 5,000 and more often than not shift at 3,500 - 4,000. It makes lots of torque so there isn't much point in winding on it, you get more out of an early shift. Oh, and Jim did cc the combustion chambers but I forgot what they came out to. The important thing is that they are even.

[Dan McNarry]

So, while the head work was going on I used Dyno Sim software to help me figure out a good cam profile for what I wanted. My goal in designing my intake manifold was torque and I wanted a cam that would help it out. With Dyno Sim you can change all of an engines variables from displacement, bore/stroke, compression ratio, cylinder heads, valves, fuel system and exhaust to match what you are spec'ng your cam for. You can then start to build the cam you want by changing all of the camshaft parameters until you get what you are looking for.

Knowing that despite all of the head work the heads were still going to be a limiting factor as I could't go bigger than 1.94's. Plus the older 390 has massively heavy pistons so why try and build something that will rev. That's a recipe for lot's of bottom end rebuilds. I have attached a screen shot from Dyno Sim for both my 390 as configured with my exhaust system and intake and my current camshaft. I came to this profile by changing variables until I got the most torque I was going to get over the broadest range starting as low in the RPM range as I could get it. The result is 479 ft lbs starting at 2,000 and holding pretty steady before fading after 3,500. Max HP is 377 at 5,000 RPM which is as high as I ever rev my engine. I've included a photo of the cam card in case you want to see what I ended up with. Feel free to copy it if you want to have your own ground. 

Note that both Dyno Sim sheets show that I am using a 429, one has the bore, stroke and rod length changed to match a 390 and that Dyno Sim correctly predicts the displacement.

For giggles I did a simulation of a 429 block with my heads and systems. HP didn't change but it gained 50 ft lbs of torque. Now my stupid brain is trying to convince me to put a 429 in it. When will the insanity end!

[Dan McNarry]

Forgot to mention, that my current systems grafted on to a 429 run out of steam even sooner as the larger displacement struggles for air over 4,500 RPM. If I was to change to a 390 I would have to profile a new cam anyway as they don't interchange between old 390 and new 390/429.