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Old 04-19-2007, 02:00 PM
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new supercharger

hey everyone i recently installed a 6-71 blower on a 350 chevy that was built by a local shop for a customer. i know nothing about whats in it.. i am just trying to tune it.. it presently has 2 650 edlebrocks sitting on it if anyone can help with metering rods and timing adjustments thanks........

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Old 04-19-2007, 03:36 PM
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Here's is the response I got from Edelbrock tech when I asked them how to set up my 6-71/350...

-If there's any street driving at all, a progressive linkage is a must.
-The carburetors should be our # 1405 600cfm carbs. We recommend starting out with # 1429 jets all the way around, and # 1450 metering rods. You will also need the high flow needles and seats, # 1466.
-Vacuum secondaries will not be a problem with the blower.


If responding to answer, please reply with original email!
Ray Garcia
Technical Dept.
Edelbrock Corporation

Blower motors like a lot of initial advance. I'm running 16* on my MSD set-up. Mechanical advance curve is 1200-2800, with 36* max advance. This was the set-up recommended by MSD. I have their 6AL box and magnetic p/u distributor.

Do you know what your blower drive ratio is? That will establish your boost. If you don't know how your motor is built, I'd recommend you keep the boost fairly mild... no more than 6 or 7 pounds.
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Old 04-19-2007, 05:06 PM
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here is a link to the Edelbrock online instruction book.

The tec at Edelbrock told me to follow the directions on page 17 to set up the carbs for a blower. I have the Wieand 671 with 2 1405 Edelbrocks on it.
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Old 04-19-2007, 07:28 PM
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For pump gas you must limit the total ignition timing to about 28deg while under boost. Yet you want to run lots of intial timing at idle. 20-28deg idle ...28-32deg WOT That means you must limit or lock out the distibutor mechanical advance travel. Install the stiffest power step up springs for the metering rods to ensure they do not get sucked down (lean) while under boost at high rpm WOT. (lean is bad)
Other wise you must modify the carbs to "boost reference the metering rods"
You should install and watch a vacuum guage on the base of the carb. If the vaccuum reading at WOT exceeds 8" vacuum under the carbs at WOT with the stiffest metering rod step up springs you will have to "boost reference the metering rods" or you will damage the motor from exessive lean AFR under boost. Usually you're good using moderate boost. If you get that much vacuum on the guage stop and modify the carbs before continuing.
If your distributor has vacuum advance, restrict it to 10deg max and plug the vacuum hose somewhere on the intake manifold below the blower only. If there is no vacuum port on the blower manifold below the supercharger leave the vacuum advance disconnected. DO not hook up the vacuum advance to the carbs.
Do not test the throttle response on a cold supercharged motor. To start it up cold, pump the carbs a few times to get fuel in the blower. Get your foot off the gas and start it. Let it warm up a good 10 minutes until there is some heat in the blower or you get a lot of back fireing.
Always start a blown motor with the throttle closed. Always warm up the motor and feel the blower for heat before winging the throttle open.
Get or look online for the Edelbrock Tuning manual for your carbs. Start full rich on jetting and rods, using the jetting maps in the manual. use the big high flow needles and seats. Start your tuning rich'er and work lean'er. being a little on the rich side is perfered on a blower motor.
get a few pairs of big accelerator pump shooters for your carbs Again start rich with big shooters.
A 7.5:1 compression ratio is best for reliable blown power on pump gas. A 8.5:1 cr is usable with a good bit of ignition retard and less boost.

use cool(er) than stock non projected tip spark plugs. About 3 ranges cooler than a stock plug for what ever heads you have.

Start with modest boost (6psi), modest timing 26-28deg and rich primary and secondary jetting. (Look on the Edelbrock jetting maps for your model carb in the edelbrock tuning manual) Rich jetting will not hurt the motor. Lean jetting will. Do you know what camshaft is in this motor? Do you know the approx compression ratio.? If you can, start your tuning with 110 octane racing gas.
Edelbrock carbs need a steady 6PSi of fuel pressure at idle and WOT. I recomend two Carter electric fuel pumps #4794
One for each Edelbrock carb using dual 3/8" lines from tank to carb. Edelbrock carbs do not like more than 7PSi but need lots of fuel flow capacity (volume) to feed a blown motor.

Last edited by F-BIRD'88; 04-19-2007 at 07:43 PM.
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Old 04-21-2007, 02:05 AM
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thanks everyone.. the car has passed to the body shop now and i have increased the meetering rod size. keeping inmind the engine vac to blower paressure the car is really fat rite now and seems very responsive.. when it returns i will be tunin it... it is a pump gas car that will see nothing but sheer abuse as the owner is a collector and has a hemi challenger...i thank you for your help... when it returns i will post if i cant use what you gave me and some common sence to make it work..
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