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  #16 (permalink)  
Old 09-17-2007, 07:45 PM
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Vince I don't know if you have a blower motor or have had one, but driveability isn't a problem with my car. Maybe with a tight converter or something it could be an issue with some motors. The head jerk Arrowhead saw would definitely make me change my setup, I wonder if some of that could have been posing, he he.

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  #17 (permalink)  
Old 09-18-2007, 08:58 AM
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Blower lope in an injected motor...
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  #18 (permalink)  
Old 09-18-2007, 09:27 AM
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I still say a properly set up blower motor is not supposed to roll like the the one in the above youtube video. A properly set up blower motor sounds like this one .

Vince
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  #19 (permalink)  
Old 09-18-2007, 09:44 AM
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302... I with you there. Even our TF fc and Alcohol FC didn't lope like that. I think there is something not quite right when they lope. When you think about it, there is vacuum in the intake and air flowing thru the carb just like any other system so it shouldn't lope any more than the cam causes it it. Even a pretty hot cam with a blower should run pretty smooth. If they run so rich that they lope they surely are going to wash the cyl walls down.
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Old 07-14-2008, 05:24 PM
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I have a ford 460 with an 8-71 and dual 750 Barry Grant Mighty Demons with boost ref pwr valves. Cam = Comp Xtreme Energy 262/270 with 110 lobe centers.

Car idles excellent (900RPM) when all 8 idle screws are all set at only 1/2 turn out. Manifold vacuum shows 16+ inches steady at idle. I did NOT connect manifold vacuum hose to boost referenced power valves on base of carbs because .... the engine has STRONG vacuum at base of carbs at idle.

If I back off even ONE idle mix screw only 1/4 turn...the motor begins to surge immediately. The car won't even run if I set the mix screws to 1 turn out or more.

When I DO connect manifold vacuum source to base of carbs (like BG Tech suggests) no difference at all is observed (para #2 still holds true).

???

Hope I'm adding (not subtracting) to this discussion with above info and the following ?s:

1. Why such strong vacuum at base of carbs? I thought roots type blowers at idle has little/no vacuum, hence the need to connect manifold vacuum at base of carbs to prevent pwr valve from pouring fuel at idle?

2. Does 1/2 turns out all around sound "proper and correct"? Or am I masking something else up.

Plugs look light brown...
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  #21 (permalink)  
Old 07-16-2008, 07:01 PM
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Quote:
Originally Posted by wixomhead
I have a ford 460 with an 8-71 and dual 750 Barry Grant Mighty Demons with boost ref pwr valves. Cam = Comp Xtreme Energy 262/270 with 110 lobe centers.

Car idles excellent (900RPM) when all 8 idle screws are all set at only 1/2 turn out. Manifold vacuum shows 16+ inches steady at idle. I did NOT connect manifold vacuum hose to boost referenced power valves on base of carbs because .... the engine has STRONG vacuum at base of carbs at idle.

If I back off even ONE idle mix screw only 1/4 turn...the motor begins to surge immediately. The car won't even run if I set the mix screws to 1 turn out or more.

When I DO connect manifold vacuum source to base of carbs (like BG Tech suggests) no difference at all is observed (para #2 still holds true).

???

Hope I'm adding (not subtracting) to this discussion with above info and the following ?s:

1. Why such strong vacuum at base of carbs? I thought roots type blowers at idle has little/no vacuum, hence the need to connect manifold vacuum at base of carbs to prevent pwr valve from pouring fuel at idle?

2. Does 1/2 turns out all around sound "proper and correct"? Or am I masking something else up.

Plugs look light brown...
Sounds to me your power valves are removed from the picture if not sourced under the blower.The way you have them set up..they are just along for the ride.The pv chamber is normally sourced thru the carb base.When referanced for a draw thru system like your roots..this source is blocked and the pv chamber is routed with a tube in to the blower manifold.You will not feel this at idle.but the lack of pv enrichment will lean out the main ckt delivery when most needed.Keep in mind..as long as your throttle angle at idle covers up the transition slot correctly..the pv has no effect at idle.It only will fatten up if the diaphram is ruptured and leaking fuel into the pv chamber.
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  #22 (permalink)  
Old 07-17-2008, 07:29 PM
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True - while testing at idle I did not have base of carbs connected to base of intake manifold.

I have since hooked them up to reduce vacuum at PV once throttle is opened up.
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  #23 (permalink)  
Old 07-17-2008, 08:05 PM
8-71 blown 461 Rat on E85
 
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That is the correct way to boost referance your power valves.the pv,s need to respond to engine load not the constant vacuum they see atop a roots blower.it is not unusual to see vacuum under the carbs with boost in the manifold.The carbs are a passive device and respond only when yanked on.Bigger blowers can and will pull more air thru a carb then its fuel delivery was designed for.This may help you understand why supercharger carbs for the street require different ckts and metering vs a n/a setup.
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  #24 (permalink)  
Old 12-18-2008, 07:37 PM
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Resurrecting this discussion. I have a similar bad idle surge. Ford 3.8L V6, plenum style manifold, Weiand 144 and a Holly 700cfm blower carb. Its boost referenced to a port in the manifold under the blower. Idle surges wildly between 800-1500 RPM, great throttle response though. We have strong vacuum that surged with the idle surge from 18inches-12 inches. No vacuum leaks, good cranking compressiion in all 6 cylinders, we've been twisiting idle circuit screws, idle set screws, etc. We can't make the surge go away either.

Has anybody had any success correcting the surge?
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  #25 (permalink)  
Old 12-19-2008, 09:06 AM
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sticky answer...

This is not a generic answer to a seemingly simple question.
I have had some that surge, some not. My fuel or alky motors did not. That being said, these are purpose built motors with one thing in mind. The idles on those motors are 1200- 1500 rpm respectively, (the 8 cylinder fuel burning engines idle at upwards of 2000 rpm) until they are fattened up just prior to take off.
My gasoline motors have surged at points depending on the jetting/metering setups being used but also rotor speed as well. My oldsmobile surged like hell but it never locked up the converter enough to make my head snap! My Liberator would surge a little but spinning a prop didn't realy translate into much jumping either. Over driven blowers will surge more than its underdriven counterparts. Again, depending on how much of what its being fed the surge may be minimal or drastic.
(is this getting anyone anywhere?)

I guess the missing parts to any equation here is engine size, supercharger size, air/fuel ratio, carburator CFM, pulley sizes and idle speeds. This would help in set-up and diagnostics.
Agree or disagree from the peanut gallery?

Last edited by nitrocorsair; 12-19-2008 at 09:15 AM.
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Old 04-26-2009, 02:13 PM
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sorry to dig up an old thread but ive always loved this video

Tell me this aint cool

http://www.youtube.com/watch?v=JPI0aAXI6KY

Btw pretty sure its a small block
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  #27 (permalink)  
Old 04-26-2009, 04:10 PM
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i have a blown SBC i purposely run blower surge because i like how it sounds but i can tune it out i get my motor to surge by running the idle a/f mix lean..heres a vid of what my car sounds like idling..

http://www.youtube.com/watch?v=HKFu0gh-u5U
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  #28 (permalink)  
Old 04-26-2009, 04:28 PM
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My truck idles like that and I don't even have a blower! LOL
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  #29 (permalink)  
Old 03-08-2012, 07:47 PM
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OK try to make this short as possible.I did have blower roll. But I just got it where its smooth as can be.in gear even got tci10"converter.
My set up is a BBC 489 TBS 8-71 750 mighty demons boost ref.to the bottom of the blower tee off into to vacuum / boost gauge.when floats where set to the highest point in the sight glass and mixture screws out 1.5 turns surged very bad not even in gear.
my fix was drop the sight glass level to middle. My 8 mixture sure are like .75 turns out.no surge at all no tachometer in car yet have not drive yet.
My combination is 489 eagle good stuff Srp blower flattops Heads are dart pro 1's.345cc intake runners with 2.30/1.90 valves. Msd 6alfor now w/6000 chip.timing set at 34°total and 16 intail. 2 inprimarys 3.5 collectors with 3.5 dynomax mufflers.came is comp can specs are? 255/262 @.050 appx lift is. 652 with 114lc
.in 68 SS chevelle tubbed with 9"rear. 3.50gears with Detroit locker 35 splines. I hope the gear is okay.? With my set up right not 13.5%OD.is 12psi boost. Of I swap pulleys around I got 12%UD and 6psi boost.
I'm.going to drop.the back down cause am on 93 pump gas with 15 gallon fuel cell with sender.
Any ?'pm me or post here

Need to mount seat.hook up throttle cable.bring toliet paper just in case. And get Rachel
Can't wait to pull it out
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  #30 (permalink)  
Old 03-08-2012, 08:10 PM
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and get Rachel can't wait to pull it out. giggitty you know someone had to go there
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