Seen a couple of questions about distributors lately, and I got to thinking about advance curves. What is a good set up for a warmed over small block? I know the total should be around 36, some say 40, but does it matter how you get there? I know about weights, and how fast it can come in, min RPM to full advance. I'm thinking about the difference between 36 total with 20 degrees in the dist and 16 at the damper. What difference if any would there be with say 28 in the dist and 8 in the damper, or static timing? I think stock sbc dist's have 20 degrees built in so what woulld you gain by changing the wieghts vs just adding more initial timing to compensate?
Light springs,20 deg swing,36 total on the street,40 deg at the drags. This set-up has worked well for me .
Yeah, 36 is a good number for all of the old V8 cars I've ever had. With lighter springs on the mechanical advance (centrifical advance), the advance comes in earlier -- it starts ramping up at a lower rpm and comes fully on at a lower rpm. To me, you get better throttle response and a better feeling engine in the low and midrange rpm ranges when the advance kicks in earlier. If you have high compression and a heavy car and are using crummy gas though, you might have pinging problems if it kicks in too early. When you set your maximum timing (at an rpm above full mechanical advance), disconnect and plug up the vacuum advance hose (if you have vacuum advance).
The first few things I would want to know are: 1) What's the actual static compression ratio? 2) What cylinder heads do you have on it? If you don't know that, are they original to the engine, and, what did it come out of? Or if nothing else, got any idea what age it is? 3) Describe the engine a bit....carb, intake, cam, exhaust, anything else you think is relevant. 4) Describe the rest of the drivetrain...trans, rear axle gears...and, the vehicle itself....body style/model, & weight if you know it. 5) What do you expect the engine to do/what do you want? Economy? Performance? Street only? Some bracket racing? 6) What are you willing to put in it for gasoline? All this plays a part as to how I would set it up to begin....followed by a good deal of in-car experimenting. To answer your second question, yes, it matters (or can matter) how you get there....bringing it in too quickly or too slowly can cause driveability issues, or hurt something.... A '68 Impala with 307/Powerglide is going to be set up differently than a nasty 355/4-spd T-bucket...a wide variation but ya get the idea. Different combustion chamber designs, & compression, can make a difference too...."modern" SBC (& other) designs tend to like less total timing, like possibly 28-32 degrees.
Here's what Chevrolet recommends for a racing engine. It's probably a little aggressive for a hot street engine though. For a street engine, I'd probably start with around 12 degrees initial and end up with 38 degrees total, give or take a couple of degrees. This would be for a distributor without vacuum advance. If you plan on running vacuum advance, it gets more complicated. BTW, if you're gonna build a stout Chevy you might think about getting a Chevrolet Power Manual from your local GM dealership. Lots of good information for baselining your engine. Larry T
I guess what is puzzling is that they sell advance kits with different weights to change the amount of advance in the dist as well as springs to change how fast or slow it comes on. With total timimg to be set at 36 what do you gain from more mech advance vs static say 28 mech and 8 static; or 20 mech and 16 static?
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