Depending on what set-up you will be running, it varies.bruce mckenzie said:Hi team can anyone help me? I have a blown 468 yet to start and I was wondering about vacuum advance, and vacuum for the modulator and power break booster blower's are positive pressure? so how do I run these components
Hi There, I have a 671 and big block thanks for the input I will have to do a bit more spade work, but that wont stop me always wanted to do this :thumbup:cobalt327 said:Depending on what set-up you will be running, it varies.
What type supercharger are you talking about? There are centrifugal or roots-type, not counting turbo. Draw through or blow through? EFI or carb?
Assuming a roots-type, smaller blowers can have "good" vacuum (dependant on the cam- just like a NA set-up is) at cruise. This would allow the use of a vacuum reservoir for the brakes. Another obvious option is to use manual brakes.
If, for instance, you are going w/a HOLLEY blower, like the 177 or 250, there are provisions for the power brake vacuum provided on the blower housing.
From Holley's instructions:
If your vehicle is equipped with a TH-350 or TH-400 automatic transmission, the shifts are controlled by a vacuum modulator that senses manifold vacuum, while kickdown is controlled by linkage, a cable or a switch. In most cases the vacuum modulator will work satisfactorily when hooked up to the carburetor.
Connect power brake vacuum hose and other vacuum hoses to the vacuum fittings on the carburetor or to the port on the passenger�s side of the rotor housing under the carburetor. (The pipe plug must be in this port if it is not connected to a vacuum line.)
There are modifications that can be made to tranny's that use vacuum modulators that allows them to be removed, as well as manual (cable) operated modulators like the B&M Modulink for supercharged engines that don't allow engine vacuum to be used.
AFA vacuum advance, on big-A blowers, it's not used. "A vacuum advance should only be used in a low boost application and should be limited to 10 degrees of advance with engine vacuum above 10 to 12 inches of vacuum."
Timing is very important in boosted engines- that it not cause detonation. One rule of thumb says "The ignition advance curve, in general, is quicker yet shorter than an engine without a supercharger, this helps give better throttle response until the boost pressure kicks in. The advance curve most seen is an initial timing of 18 degrees with a total of 32 degrees; this is just a starting point and must be tailored to each engine."
MSD makes a boost retard for the ignition system. It allows enough timing to let the engine run good while off boost, but takes timing out as boost increases to stay out of detonation. Then there are intercoolers and water injection systems and jetting to all be considered.
This is just the tip of the 'berg. There's no way a post will ever be able to cover even a tenth of what all goes into this.
Keep at it- reading, research and talking to guys who are running blowers needs to be done by anyone considering it before buying the first part.
Hay thanks man :thumbup: that car of yours looks fantastic dose it go as well as it looks :thumbup: :thumbup:camaroman7d said:Get your vacuum signal below your carbs, but above your blower. There will always be vacuum there. If you go below the blower, you will not always have a vacuum signal, there will be boost present there at times.
Thanks, Yes that car ran very well. I have since sold it but, I can't put my new project in my avatar so I just leave the old car there. The new car is a blown 1961 Skylark, should be done in the next couple months. You will like the feel of a roots blower, lots of torque!bruce mckenzie said:Hay thanks man :thumbup: that car of yours looks fantastic dose it go as well as it looks :thumbup: :thumbup: