Had a lengthy discussion this morning at coffee,Is there a cheap relatively simple way to have a distributor operate to advance and retard under power on a blown street driven small block chevy. I know there was discussion about using the vacuum advance off a turbo charged corvair, but eas wondering if there was another way other than hitech electronics.
You still build vacumn under the carb, just of course not in the manifold, Also you could go ported vacumn, as in out the side of the carb.... Now it should be said, i'm not an expert, and it may give an odd vacumn signal....
What kind of blower engine are we talking about? I would only use mechanical advance on a low boost stockish set up. I only run locked distributors in all my blown eninges race and street but they are all making some serious power
We did it all the time on draw-through turbocharged SBC's. do NOT connect to ported spark. That always ends badly as it puts advance IN when the compressor spools up. Connect the vac advance directly to the manifold. This gives more advance at idle & cruise which helps make it nice to drive. As soon as you get close to boost, the advance is gone. Worked just fine with 7 to 9 psi of boost. A draw through turbo setup is much like a blower with a carb on top from a dynamic standpoint. B.
if your not afraid of a lap-top ,it can be done electronically ....with our 6530 programmable 6al-2 http://www.msdignition.com/product.aspx?id=16019&terms=6530 it uses a map sensor. and really easy to do. p/m me an email address or phone number if you need more info. if you can work a cell phone....you can program this unit.
I ran vac on my 6-71/454 with no problem. tapped into back of carb adapter. works well to improve mileage, goes away under boost conditions. A lot of people can't understand there's no boost ABOVE the blower.
Always ran locked down 32 degrees on my 671 SBC and it was a pretty tame setup with 7.5:1 static compression and 19% under driven. It did not like being retarded. MSD makes an ignition box that automatically retards on boost. Runs off vacuum. Not cheap but cheaper than a new motor.
You can make the advance work at the carb just lie someone mentioned. I don't know of a way to make it retard under boost without electronix, but MSD makes a box that will do that for you for less than 400 bucks. In the world of blower motors that is damned cheap.
Some of the emissions era Ford vacuum canisters have two ports. The outside one is the usual; the inside one retards the spark under vacuum. If you only use the outside vacuum port, when boost pressure is applied the unit will retard several degrees. I don't know if there is a similar unit for a SBC.
Mustangsix, can you ID that vacuum can a little closer? Looks like it might adapt to a Chevy distributor. Thanks.
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