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Webers & Vacuum Advance ?
I am new to Webers - and let me say that I am mighty impressed by the amount of know how present on this site.
Holleys are no mystery to me, but with the Webers - the relationship between load & air fuel & RPM - I am still learning **) My question (it will most likely not be the last) is how & where do I hook up the vacuum Advance ? I know there is no port - can i just Drill a port just above the idle position of the throttle plates ? (as done in the holleys?) I have all new 48 IDA 4R on a BT 4x2 Manifold. It will sit on top of the 428 with Edelbrock heads in the Shelby. They still have the org. tune and I probably will start out with "Ejaros special mallorca tune" @Eljaro; Stefan in mallorca - are you German?? |
Probably easier to switch over to a mechanical advance.
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I agree with xlr8or. And here's why:
There is no single vacuum advance on an individual runner (IR) manifold like that used for Webers. You would only be looking at one cyliner's vacuum and not the whole engine like on a carb intake manifold. Hope this helps Bill |
You could customize the intake from underneath like this:
http://www.clubcobra.com/photopost/d...ber_intake.jpg |
A new distributor would be cheaper
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If you want manifold vacuum to pull in some advance for a faster idle after startup then fabricate a setup as per Randys pic. However if you want ported vacuum for fuel economy as you initially described you would need to run all eight lines into a small damping chamber prior to fitment to the vacuum canister in the dist, this in turn may affect the idle tuning characteristics of the webers. Far less trouble to run mechanical advance only with the added assurance that you dont have to worry about the possibility of the vacuum advance adding an extra few degrees just when you dont need it.
Jac Mac |
I would forget the vacuum advance and go for an MSD like ignition. It is allready hard enough to get the webers to do what you like them to do, so bringing in vacuum advance to introduce more variables will drive you crazy.
Vacuum advance is for fuel economy, and the webers are for performance. |
Thank you all - I know that I donīt really need the vacuum advance, but I would really like to have it, for fuel economy reasons.
@Jac Mac: Would I really need the signal from all 8? Wouldnīt a single source be enough to add in about 12-15 degrees under cruise I do tune my Holleys & recurve my distributors - I feel confident about that - its just the Webers that are still new & intimidating. I take my car on long drives and even with a Holley 850 DP I still get 17 mpg, cruising at about 75-80 mph (hope I did the math right its 14L/100 km and 130 km/h) In the meantime two more questions popped up: Where do I get the vacuum for the power Brake, PCV and the heater & AC controls? (YES it does have a working AC.) I am thinking of a setup similar to what Randy posted - pretty tricky - then bring out the vacuum fitting thru the road draft tube cover... Thanks for the help! |
Mike
Due to the reverse pulse in the Individual Runner system of the IDA you wont have a constant signal on your ported vacuum as Bill D mentioned earlier, so to obtain it you have to bring all 8 to a common chamber prior to the dist, which all starts to get rather untidy. I wonder if some of the later MSD such as the Digital 7 could be used in the following manner; These have a timing retard for each gear of 5°-- Now you should be able to have that hooked up in your situation so that you run in cruise mode with the extra advance dialed in, but when you stand on the gas to accelerate it retards by 5° to prevent any problems- sort of back to front to its original purpose but would suit your application. These retards etc are operated by solenoids & micro switches fitted to the throttle linkage/gearshift etc. The Power Brake booster will function with a feed from only one runner, but an additional vacuum tank would help if you plan on descending any long mountainous roads requiring frequent brake usage etc. The pic of the valley mounted system is the best if you need to operate the vac controlled systems etc of the AC. Jac Mac |
Thanks Jac Mac , wasntīt thinking to much about pulses...
I will look into the idea of the MSD timing retard: Having it on all the time except cruise - kind of backward, but that should do the trick. Last question for today: Is there any good reading (except the Weber tuning guide) that you would recomend ? |
Hi Mike,
I used a vacuum pump from SSB (stainless steel brakes) for brake booster on my Weber setup. Works great.The Webers won't pull enough vacuum for the booster. I think the mechanical advance distributer is the way to go. Economy with Webers??? Regards, MDN |
Quote:
I get my weber info from all over the place, read a lot and work out what will/wont work from there using a bit of common sense. Its like another thread on the '3rd' progression hole that some folk are all excited about, That is actually a 'factory fix' from weber to cure slight misalignment of the throttle plate in the idle setting ( they also mention very careful machining of the butterfly in that area to accomplish the same thing ). Just because a 'fix' works for someone else does not mean its a cure all for everybody, for example the idle throttle blade setting on your car may be in the ideal position to take advantage of the '2' progression holes while your buddy with a similar setup may find his car would benefit from the mod. This could be due to an exhaust/cam/etc difference that requires a slightly higher idle speed. However Im getting away from the thread now. Jac Mac |
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