So I haven't posted in awhile it's been a busy summer. The last time I posted I had lost the cam in a supposedly rebuilt 403. This is where I'm at now. Original #4 heads rebuilt with new valves, kb .039 pistons and comp cams 268h cam. Does anyone have a similar build? I'm playing with the timing now and it really likes 12 degrees base as far as starting. I have adjustable vacuum advance and a spring kit. I'm just looking for a good starting point. Almost forgot 3.23 gears th350 and stock tires 85 cutlass.
403 timing curve
- Thread starter Rpryor
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I find iron head Olds like a lot of initial timing. It makes part throttle more responsive. On a 9 to 1 Olds 350 with a 214/214 cam, I ran 22 initial, 38 total in by 2600 rpm and a 30 degree vacuum can. I had low speed bucking, a 20 degree adjustable vacuum canister fixed the bucking but slightly less responsive. There are a couple of HEI timing curves, most run 20 at 1100 rpm for initial timing. You want 34 to 38 total without vacuum advance in by 2500 to 3000 rpm. You can probably get away the full 20 degrees most adjustable vacuum put out at full adjustment. Are you using the 307 starter? If so a mini or full size starter should be used or slow cranking warm can occur. Good luck👍
I’m at altitude (engines like more timing up here) and my 403 (when it was together) liked a lot of timing. I ran 36 to be safe at WOT but ran 22* as the idle timing (base) and 45* cruise (I have the Hyperspark MSD so I can set a low cranking advance so take that into consideration if you bump it too high you might get starter kickback). My build was ~10.1 static .030 over (racetec pistons) with 272/280 Lunati voodoo hydraulic roller with C heads.
My build was similar and the more timing I added the better it ran. Without knock detection or a Dyno I didn’t want to go too high; but I think It would make max HP with even more WOT timing because the big bore size often make more hp with more timing (you’d have to research the science on this but it made logical sense when I read about it).
My build was similar and the more timing I added the better it ran. Without knock detection or a Dyno I didn’t want to go too high; but I think It would make max HP with even more WOT timing because the big bore size often make more hp with more timing (you’d have to research the science on this but it made logical sense when I read about it).
Put as much initial in it that will not cause starting issues. It helps throttle response and closes the carburetor at idle to increase idle vacuum. Beyond that, total is a crap shoot since you have nothing to base it off of for total HP. Try for 36. In my race car, it was undetectable going down track, but the engine LOST 4 hp on the dyno at 40 degrees compared to 36. Even if it doesn't really show anything, there is no need to force the pistons into the crank any harder than it has to by advancing the timing more than needed. It just becomes added drag on parts.
Yeah, my Olds V8's ran quickest down the 1/8 mile with 36. They felt faster with 38 on the street. Listen for pinging and adjust it to where it feels best.
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