19 Cadillac Engine Tuning Tips

1. The stock Cadillac ignition is NOT good enough for a tuned engine – or even hard use with a standard engine. You have to change to a high performance points/coil ignition, solid state ignition or use a magneto. Magnetos are period and pass muster for historic racing. This is the first thing you have to do.
2.  One of the weak points in the Cadillac 331/365/390 series the fact that the outer ends of the fronts of the rocker shafts are not supported and tend to break under even moderately hard use. The solution is to fabricate stands for the ends of the rocker shafts, especially for the front. Better still; go to a larger diameter rocker shaft. We use 1950’s Chrysler shafts and after-market rocker arms. Even these shafts, fully supported, tend to fracture under racing conditions.
3. Camshafts and lifters: You do not need to get fancy to have plenty of power. Solid lifters are a waste of time and money unless you are going for absolute maximum power (which most Allards and drivers cannot use anyway). We have always used rather mild Crane camshafts – and fortunately had enough when Crane went out of business. But, most any mild tune hydraulic camshaft is all you will need.
4. Forged pistons are a necessity. Cast iron pistons will not stand up to hard use.
5. It is very important to use post 1952 heads. The earlier heads have terrible, small exhaust passages. You do not need to use larger valves, even on an out and out racing engine.
6. Carburetion: a single Holley 750 cfm double pumper is as good as it gets. More carburetion results in poorer acceleration. Rochester and Carter carbs are difficult to set up and will never be as good as a Holley, especially in acceleration out of turns.
7. The 390 cast iron single 4bbl intake is the best there is – better than all the aftermarket intakes. This is proven by dyno work. The stock intake is very heavy. You can lighten it by milling off much of the bottom and closing it up with an aluminum plate held in place with lots of small screws.
8. If at all possible use a late 390 block. These have full flow oil filters. The earlier 390’s are not full flow. Note: some racing organizations do not allow the 390 to be raced in Allards, which are visually different from 331/365 blocks.
9. High compression ratios (such as 12 to 1) make the engine fragile. If you are not looking for the absolute maximum power, go about 10.5 to 1 max.
10. You do not need nor want a lot of spark advance. 32, maybe 34 or so degrees of maximum advance should be plenty. More advance risks engine damage. Set advance on a dyno, if at all possible. Not all engines will be the same. Initial timing is usually best at about 15°. Confirm on a dyno.
11. Valve springs: stick with stock or slightly over stock pressures. If you use solid lifters and heavy valve springs, you will start chasing an endless array of other problems.
12. A well built Cadillac engine will feel like it wants to rev and rev. You do not need the revs, even for racing. Most drivers should not go above 5,200 or so – maybe 5,500. The engine will go a good bit higher – but you will eventually spin bearings and break crankshafts (usually problem will be at the first or second journal). Cad-Allards have always won races on torque, not bhp.
13. Use a modern crankshaft damper. This will head off a lot of potential harmonics breakage problems. Cadillac engines are known for being subject to harmonics problems. These usually show up in strange places and are not recognized for what they are. It is my opinion that rocker shaft cracking is primarily a harmonics problem. Chevy V8’s experience rocker shaft problems when they do not run a good crank damper.
14. Use an AP or similar multi-plate racing clutch. Standard clutches do not last very long. A good multi-plate clutch is worth its weight in gold – will last and last.
15. Oil pump – use the one with a piston in the relief valve, not the one with a ball. Or – adapt the pump from a 427 Chevy. If you run your engine really hard, you must replace the stock sheet metal oil pump cover with a heavier plate – or the cover will leak and cause oil pressure problems. Do NOT crank up the oil pressure. Forty pounds under load, twenty at idle, is sufficient – really. Remember, what you want is oil flow (plenty of oil). High pressure means less flow in most cases. Think of what happens when you put your thumb over the end of a garden hose. Pressure goes up, flow goes down.
16. For hard use, run plain tap water in the engine. Plain tap water carries away far more heat than water with antifreeze – WAY more. Most people think the opposite – but this is just plain wrong. Do not use distilled water. Distilled water invites corrosion. Average tap water does not. This is another area where most people get it wrong. Add a “water wetter” type of product (lowers surface tension which promotes heat transfer). Surface tension reducers really work.
17. Unless you are going for all out racing, you do not need a billet crankshaft nor aftermarket rods. The stock cranks and rods are darn good. If you want aftermarket rods for safety, that is fine. You still do not need a billet crank.
18. Restrict oil flow to the top of the engine. Plug the passage from block to head and then drill it out to about .040”. If you do not do this, and you run high revs on a long straight, most of the engine oil will wind up in the top of the engine, the pump will suck air, and that will be the end of your engine.
19. Use a strainer for a carb air cleaner (just kidding).