QuestionNeed suggestions on improving this engines performance, it has a stock rebuild. Just would like it to run at its full potential, but I do not want to hurt the engine either. thanks-brad
AnswerHi Brad,
I have no experience with a 39 Chevy. However, I am experienced with performance building. I can probably give you some insight as to what to do and what to expect.
First, you say you don't want to hurt the engine. You must accept that when you talk about raising performance you DECREASE reliability as you raise performance. Reliability can be raised as you go, but at a $ price. For example; As you raise the performance (power/pressure) you increase the strain on the rings, piston, rod, rod bearings, crank and crank bearings and on to the rear tires. I'm sure they hopped these cars up in late 30s and early 40s but I am also sure the knocked out a lot of rod bearing, broke cranks and fried a lot of pistons. So unless you are prepared to sink a lot of loot into this engine you may have to be satisfied with a little boost in power that must be used sparingly.
There are two first major boosts to power. One is compression ratio and the other is cam design with inlet and exhaust flow correction. Reliability with either comes with stronger EVERYTHING. (Big $) It is said among stock car racers; "You don't need cubic inches to gain horse power, you need cubic dollars"
Probably the easiest first move to horse power is raise the compression ratio. I don't know your engine but have hopped up flat heads (side valve) and push rod OHV (overhead valve) engines. I would guess yours is a flat head so it is cheapest to just have the head resurfaced to raise compression ratio. It is difficult to raise the compression ratio too high on a flat head, however, care must be taken to check clearance between the head of both valves. A dab of modeling clay on top of each valve while you hold the head down in place with a couple of bolts and rotate the crank a couple of times, will give you a clearance and thus tell you how much can be removed from the head. On some flat heads you must do the same with a piston. A minimum clearance is .040 inch.
Keep in mind that you probably don't have a forced feed oil system so you can't get very far with a hop-up.
When you raise compression ratio you may want to run a more advanced ignition timing to gain more power BUT! here you must do your homework as this is also an engine destroyer if you do it wrong. Read my tech tip on Ignition timing. http://mg-tri-jag.net/tech6.htm
If your engine is a flathead, you will probably not get the compression high enough to require high octane gas.
A couple other quick inexpensive tips are to change the oil bath air filter to a new paper or "hot rod" type filter and check the exhaust back pressure. This is easier than it sounds. A inexpensive fuel pressure gauge, a short piece of steel brake line (inch or two) and a drill bit a tad smaller than the OD of the piece of line. Drill a hole in the exhaust pipe anywhere in front of the muffler and drive the piece of brake line into the hole and push the end of the gauge hose onto the line and start the engine and have someone run it at idle, fast cruise and give it a few short quick open throttle blips and note the readings. You should not get anything over 1 1/2 inches of pressure on the gauge. If you do, you need a more open muffler. You don't need a larger exhaust pipe system as you are not going to get any benefit from it with this engine. When you finish testing you can pull the pipe out and plug the hole with a short large sheet metal screw.
If your car is a restored show car you probably wouldn't want to modify the engine much as it is probably worth more as is, so if you are looking to improve performance you might be better off saving that engine and drive train and just install a later drive train to make it street useable and have all of the original stuff when you sell it.
I hope this helped you decide what to do and a little of how to do it. let me know.
Howard
