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2fox 01-18-2012 07:55 AM

mighty demon.BC carb ?
Ok i got a.489 BBC with.8-71 TBS blower got 2x.750 blower carbs also from TBS. Just got motor.fired up i had no vacuum lines hook up to the carbs
these carbs are boost ref power vavles.i found the nipple that pulls vac.through the vavle are these be tied together.into the back of the blower manifold?

With no vac lines.hooked.up..shouldnt it run rich.?.which i think it is
would this.make my headders at.about 2000/2500 rpms?

This is my first blower carbed engine.

And for my trans. Mod a full vac source off the base plate...did i tee.them together on both carbs to the mod vavle..thanks

F-BIRD'88 01-18-2012 04:13 PM

Power valve vacuum source goes to the intake manifold plenum below the blower.
Preferably with a in line one way check valve to avoid boost pressure acting on the power valve diaphram(s).

Same with the trans vac modulator, to the intake manifold under the blower with a in line check valve. A mechanical (cable acted) trans modulator is another way to work the trans shift pressure. Get one from a GM desiel van w auto trans.

The Rich idle and hot header tubes is mostly caused by a lack of initial spark advance timing at idle. Roots supercharged motors need a lot of timing at idle.

You need to shorten the mechanical advance curve to allow this.
You need a 10DEG or less timing curve.
Fix the timing curve to allow this.

If the blower motor has a fair big cam just lock out the mechanical advance curve and set the locked timing at 28-30 deg BTDC. (street Blown on pump gas, without boost timing retard)

If you are using boost retard, set the locked timing at 36deg BTDC at idle and take 6 to 8deg timing out with the boost retard box, under boost WOT

A roots supercharged motor will idle much cleaner with a generous amount of spark advance at idle. The bigger the camshaft, the more timing it will like at idle. 26deg +++ @ idle

2fox 01-18-2012 04:30 PM

Thanks.real helpfull

whay about this.eze idle.adjustment ?

I thought like you.said.that.boost pressure.would be pushed back on the.power V.

Or.would it be better to take.the nipple.fittn on the boost ref port .back to the base plate full vac source.would.thay work ?

Ans same.with.trans mod.V. Cause the.carbs.base.plate.or not boost

im going to post up so pics.soon from my home do them from cell.and can see and without all the.peroids

2fox 01-18-2012 05:55 PM

ok heres my 68 chevelle i need help on pic 1

pic 2

pic 3

pic 4

pic 5

pic 6

F-BIRD'88 01-19-2012 05:42 AM

No the power valve goes to the intake manifold only.

Never to the base of the carb or any where above the blower.

You do not want vacuum acting on the power valve when the motor is WOT under boost. This would close the power valve @WOT and burn the motor up.

Start with the idle eze closed. Give it all the spark timing it needs at idle.
Make sure both carbs throttles are open correctly at idle, and the same amount.
(idle fuel transfer slot exposure) Flip the carbs over and look and preset them , before install.

The idle eze will only be needed if the cam is huge., if at all.

2fox 01-19-2012 07:44 AM

Cam is a comp cam blower grind
255/262 @.050. Lift is .652 on both. On a 114 lash is .020 .
O got.dart.pro1s rect.port 345 cc intake.runners

is.that a big cam.and heads .thanks man u been big help can i call you still dont fully still dont understand dont mind thanks Gary

F-BIRD'88 01-20-2012 05:58 AM

ya thats a big cam.
Lock out the distributor curve.

NO boost retard box = 28 to 32deg timing.

with boost retard box 38deg timing, reduce to 28-32 when under boost WOT

2fox 01-21-2012 12:24 AM

Okay so my pic #5 the the.vacumm andbboost to the.bottom.of the intake.below.the.blower.correct
so when i fired.up my car.wirhout.rhe.ref.nipple.hooked uo the.power open or.closed.?.. I think.the.boost ref. rich correct my.plug
So of.i hookthem up the.nipple.the.the.boost.ref. It will get vac.closing the.power valve.then when to get more.fuel correct?

2fox 01-21-2012 12:32 AM

In pic.#3.the.big.plig at the rear.of run it to the.vac mod. Valve.correct?

i lock oit said ?.is that to much.i thought gas i might.have less boost then planned on .i as.set.up for 12%ud.but.that.was.with.srock iron heads.i now.TBS.I might.noy see 8psi.bit less pulleys.are.59 /58 upper and.52/54 lower cant rember.but.of i only.see.say 5/6 psi .i will the.swap the.pullehs.and.od.ot.13.5.% i thinllk.

Let me not.thanks

cobalt327 01-21-2012 08:49 AM

What is the static compression ratio?

2fox 01-21-2012 01:09 PM


Originally Posted by cobalt327
What is the static compression ratio?

8.2to 1 compression srp's blower .010 in the hole.not.sure on head gasket thickness .042 ? Flat tops have -3cc

2fox 01-22-2012 06:39 PM

What in the quarter mile. Has.3.50 gears with.dlocker 10 stall speed

cobalt327 01-22-2012 07:50 PM

That CR is fine, my concern was that it may have been on the high side for running any real boost. No idea on the times, though. I'd imagine traction will be a problem. What's a "10 stall speed"?

2fox 01-23-2012 02:13 AM

The.transmission converter is.a.3800.stall speed.with.3.50 gearrs.with.Detroit locked.for.the.street .hopen for.some.low.10' mt et street dot slicks

cobalt327 01-23-2012 04:43 AM


Originally Posted by 2fox
The.transmission converter is.a.3800.stall speed.with.3.50 gearrs.with.Detroit locked.for.the.street .hopen for.some.low.10' mt et street dot slicks

I may be wrong, but that's an awful lot of stall for a blown BBC, IMHO. But that's really not your question. Best thing I could suggest is get the tune to a safe point and start track testing to dial it in unless you can buy some dyno time.

Quarter mile trap speed and ET along w/the other vehicle specs (mainly weight) is as good an indicator of real world HP as most anything. You have enough motor to run your numbers- the question comes down to chassis set up and traction.

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