SBC distributor mapping question

[Pat #25912]

I just bought a rebuilt non HEI distributor for the 350 in my '59 Vette. I plan to check this distributor on a machine before installing it. What should the curve look like?

I believe the 350 is out of a '70 Vette, It has high compression (200# in every cyl), has a mild roller cam and an alum intake from a '64 Vette. The oil fill cap in the intake is the vented type and there is a pcv valve in one valve cover. The engine produces about 12 to 14" of vacuum at about 800 rpm. The vac can on the rebuilt dist has the numbers 446 15 stamped on it.

Recommendations of degrees of advance at certain rpms, and a vac can will be greatly appreciated. Thank you in adavnce (no pun intended). Pat G.

[Duke W.]

Re: SBC distributor mapping question

You need a vacuum can that will provide max advance at 2" less than idle vacuum, which would be 10". The closest match is the NAPA/Echlin VC1810, 0@4" 16@8". I doubt if the installed "446" can will meet this requirement. The VC1810 is equivalent to the can used on all 64-67 SHP/FI engines.

BE SURE THE VACUUM CAN IS CONNECTED TO A FULL TIME VACUUM SOURCE, NOT "PORTED", WHICH MEANS NO VACUUM ADVANCE AT IDLE.

The total WOT timing is the sum of initial plus full centrifugal and should be in the range of 34-38 degrees. Once you find out how much centrifugal the dist. provides you will be able to determine the initial timing range.

The total idle timing should be the sum of initial and FULL VACUUM ADVANCE, and if your initial timing range turns out to be 10-14 the total idle timing should be in the range of 26-32.

Duke

[mike mccagh]

Re: SBC distributor mapping question

boys, ya just got an excellent course in setting up a sbc distributor from a real pro. copy Dukes post for future distributor curving exercises. mike

[Duke W.]

Correction: last sentence s/b "...range of 26-30."

Also,depending on the distributor model the total centrifugal could be in the range of 22-30. Centrifugal can be incresed by milling the "slot" in the autocam assembly and can be reduced with a different limit bushing.

All used distributors should be disassembled, cleaned, bushings checked for wear, and replaced as necessary. Assembly should be done with a new, snug fitting breaker plate and the endplay shimmed to two to seven thou. The 28-32 oz.breaker arm tension points should be installed on engines with redlines over 5500. The standard 19-23 oz. points are okay for engines up to 5500 redline.

Lots more discussion/details in the archives.

Duke

[Pat# 25912]

Re: Correction: last sentence s/b "...range of 26-

Thanks Duke. I have already picked up a VC1810. Also searched the archives and
copied off reams of info. I should be good to go. Thanks again. Pat G.