Thread: Tri power Vacuum

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I have An Offenhauser intake with 3 Rochester carbs. I have a power brake booster, 350 turbo trans and a Vac adv dist. The center carb has a fitting in the base plate and a nipple in on the top side. The front carb also has a nipple on the top side. Not sure but there is about a half inch fitting at the top rear of the offy intake. I need to know the best place to hook up the power brake booster vac, the dist and the trans shift valve. Thanks!!!!

Originally posted by loctite
I have An Offenhauser intake with 3 Rochester carbs. I have a power brake booster, 350 turbo trans and a Vac adv dist. The center carb has a fitting in the base plate and a nipple in on the top side. The front carb also has a nipple on the top side. Not sure but there is about a half inch fitting at the top rear of the offy intake. I need to know the best place to hook up the power brake booster vac, the dist and the trans shift valve. Thanks!!!!

the best place would be off of the intake for the booster and trans . as for the dist that would have to come off of the carb. depending when you wont vac. if you wont vac. at idle then go to the base plate, if you wont vac. when you acceierate use the nipple on the top side. hope this helps

Well said lt1s10.

My setup is Rochesters on an Edelbrock intake.

I know one thing for sure, you want to plug the vacuum ports on the end carbs. They'd only give you vacuum out the upper nipple when the carb is opened. And the lower port wont give you much at idle as the throttle blades should be totally closed. I've got the lower one on the throttle plate section hooked up to the PCV valve.

That's my take for what it's worth. Like Viking and lt1s10 I agree about the power booster, trans and distributor.

Originally posted by viking
Well said lt1s10.

thanks

Thanks all!!! I know I will need to come off the middle carb for the vacuum. The nipples on the outer carbs are pluged. There is only one place on the intake for a fitting. It looks like its for a water sender. No other holes in the intake. I have one half inch hole on the center base plate. This one I know you would use if you were running a pvc valve. I am not .. The dist I can run off the middle carb nipple. Asa for the booster and trans I may have to try them on the base plate. I know you are suppose to have 16 lbs of Vac on the booster. Kind of limited on this tri power setup and running modern acc. Thanks for all the help.

Assuming this is a Chevy motor, the distributor should be connected to ported vacuum. That would be a port that registers almost zero vacuum at idle. The power brake needs manifold vacuum, which would be maximum at idle.

Thanks again. The top nipple on the center carb should work for the Dist. Yeah the power booster needs intake vac but theres no intake vac hole. I will have to look into this a little more. Thanks to all for your help....

Originally posted by loctite
Thanks again. The top nipple on the center carb should work for the Dist. Yeah the power booster needs intake vac but theres no intake vac hole. I will have to look into this a little more. Thanks to all for your help....

anywhere on the base of any of the carbs, that you can get a big enough fitting for the brakes will be fine

I have the same intake that you are running and have had it on several different engines over the years (it's currently on a 72 LT1).

First off I would strongly recommend you run a PVC on the engine. Hook it up to vacuum port on the bottom rear of the center carb.

Dist vacuum can be drawn from one of the 2 ports located below the fuel bowl on the front passenger side of the center carb. The lower should be manifold vacuum and the upper is ported vacuum (I think you'll find ported works best)

For the accessories and trans line there should be a threaded hole just in front and on the passenger side of the rear carb, screw a fitting in that hole.

For the brake booster put a 90 degree fitting in the bottom rear carb base.

Just a couple of tips on these manifolds. They were originally designed when the biggest SBC was a 327. From my experience, any around 350 or more CI is very marginal as far as using a small base 2GC Rochester carb. If performance when running on just the center carb is marginal, these manifolds can be modified with an adaptor and a little porting work to accept a large base carb which will really wake the engine up. Also run the biggest aircleaners you can find. I usually set my linkage up to tip in the end card at about 80 MPH and have found the little chrome aircleaners start to choke the engine at about 65 MPH. Good luck.

Thanks Mike. This setup is on a stock 350. That sounds like the way I need to go.

Thanks again!

Theres alot more to running tri powers then you would think. I like it for the look more then the power. Thats why I trying my best to make this work. The air intake with these carbs is something you would overlook. Thanks for pointing this out. I will have to look into the air flow. Just one more thing to overcome but well worth it!

pi (3.14157)

Actually, it's 3.14159 26535 89793 23846 26433 83279 50288 41971 69399 37510

I memorized that in college on a bet in 1962, and haven't been able to dump it . . .

Just personal preference, but I like the looks of the 60's Ford style tri-power/dual quad aircleaners. PAW sells a close copy of them for about $50, but only with a single 4 BBL or dual quad base. Fabricating a new base is not really much of a challenge though. Also check some of the off road places as they sell a some of the smaller aircleaners with offset bases that will clear when oriented right.