vacuum advance carburetor vs. mechanical advance carburetor

vacuum advance carburetor vs. mechanical advance carburetor explain the difference and why do 700R's need a vacuum advance. Or so I was Told. I was told I need to use a vacuum advance carb when installing a 700 in my 51 or change the valve body to make a manual shift?? I do not get that. Sorry if this sounds dumb, have never done a trans swap.

 

do you mean vacuum or mechanical secondaries? If so I don't know what that would have to do with the 700R.The older turbo 350 needed vacuum to the modulater valve for proper shift point but I guess this question kinda puzzles me too.Advance compared to mechanical only determines the rate that the secondaries on the carb open.Mechanical meaning right now verses vacuum pulling them open more gradually.

 

yes secondaries

 

i see no reason why the carburetor would make any difference. just make sure you hook up and properly adjust the TV cable

i suggest you read about 700R4's on this website:

http://www.bowtieoverdrives.com/index.shtml

 

Those are the people I have bought my stuff from and told me about the vacuum with the 700r.

 

That makes no sense. Vacuum or mechanical, it's a matter of tuning and choosing a carburetor that's well suited to the rest of the engine, as well as rear end ratio.

 

need a vacuum switch for 200 700 trans!!

 

Ported vacuum ?

 

I’m hoping he has figured it out in the last twelve years


Sent from my iPhone using H.A.M.B.

 

Actually there is a need for a vacuum switch with some installations of a 700R4 when adapted to a vehicle with no computer to control lockup converter function.
I had an ‘82 GMC with a 305/700R4
and the lockup worked differently than the automobile transmissions. There was a firewall mounted “low vacuum switch” and it was wired into the trans/converter to disengage the lockup when the truck was climbing a grade, or in any other low vacuum condition so the vehicle wouldn’t labor against the lockup.

 

I can ***ure you GM had a reason for using that, they don’t spend money needlessly.
The purpose of the vacuum switch was to release the lockup, not engage it. When the throttle was depressed as in going up a hill engine vacuum drops and cuts the lockup circuit. With the trans in OD the converter would be locked up, no slippage to help fuel economy and it also helps prevent overheating the trans fluid. By taking it out of lockup the vehicle has an easier time climbing a grade, or p***ing another car. The slippage in the converter allows the engine to rev into the power band easier, the same reason a higher stall is used for added performance.

 

Why would GM have used a manual toggle when the function could be performed seamlessly, without driver interaction?

 

Keep it simple. Pressure switch and correct t.v. cable geometry. At least that's what I call it.