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Supercharger Roll,detroit Roll,blower Surge???

38K views 36 replies 20 participants last post by  LakeArrowEd 
#1 · (Edited)
What Causes A Blown Motor To Surge At An Idle?. We Have Tried Everything So Far That We Were Told That Causes Blower Surge Or Blower Roll And Still Our Engine Doesnt Do It.our Car Is A Stick But Also Tried Doing It On The Engine Dyno So We Ruled Out People Telling Us You Have To Have An Auto Because Its The Torque Converter.current Engine Is A Dart Chevy Big Block ,edelbrock Aluminum Heads 2.19/1.88 Rec Port,eagle Rotating Assembly H-beam Rods,mls Gaskets,9.5 Comp Has Weiand 8/71 With Two Holley 950 Cfm Blower Carbs,electric Holley Blue Pump, Msd Dist,6 Btm Box,coil.comp Cams Solid Roller .782 Lift .296 Dur 114 @.50 1.7 Roller Rockers,

how Is It Done What Causes It???

Things That We Have Tried So Far,,


carbs-holley Non Blower Carbs 850cfm Double Pumpers #4781 With All Of The Different Power Valves Available From Holley Including Just Solid Plugs And Many Jet Changes This Was Done In The Front And Rear Of The Carbs Jets From 2 To 12 Sizes. Also Fuel That Was Used Was Pump Gas To Torco 116 And Vp 114 And 116.

cams-comp Cams All Solid Rollers .652 Lift .262 Dur 114 @.50 And .690 Lift .274 110 @.50 And .782 Lift 111 .290 @.50 And .748 Lift .292 112 @.50 These Are Split Cams Also Tried 1.8 Roller Rockers

blower- 8/71 I Have Tried All Different Pulley Setups Under Driven To Over Driven 3lbs To 28.6 Lbs Boost We Did Loose The Head Gaskets And The Blower Ran To Hot Over 22lbs Boost.

dist- Msd Changed The Spring Weights To Make It Lighter To Lightest To Back To Where It Ran Good Again.timing Is At 35 Degrees Total Advanced

Also For More Info We Have Done This Same Setup On A 468 (except We Didnt Have Blower Carbs) And We Have A Few Other Blower Cars Here And None Of Them Will Have That Surge Idle.we Have Been To Alot Of Car Shows And Drag Races And Have Heard Alot Of Carbed Cars Surge Small And Big Block, Whether It Is The Right Or Wrong Way Are We Missing Something. We Am Experimenting And Want To Know How It Is Done. We Have Not Tried Alcohol Because We Have Heard Street Cars On Gas Surging.if Anyone Has Any Info Or If Anybody Has A Car That Does It, We Would Appreciate The Info Or If You Have Any Videos Of Your Cars Please Send To Us. Have Found Cars On You Tube To. Link To One Is Below. Thanks
http://www.youtube.com/watch?v=GlGLncfjR-g
 
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#2 ·
Let me get this straight, you have swapped all the parts and spent all kind of time and I'm assuming money because you WANT blower surge? To each his/her own I guess.

Reminds me of a car show a couple of years ago. A guy and his girl were cruising through the fairgrounds and they had a primer 50's type car with a huge blower motor in it. The blower surge was so bad it was snapping thier heads back and forth. I thought it was hilarious.

I thought it had something to do with big cams / loss of vacuum signal / power valves or something like that. Sorry I can't be more help.
 
#4 ·
302 Z28 said:
Why anyone would intentionally want blower surge is beyond me :rolleyes:

Vince
I know guys who put straight cut gear drives on...even though they suck up horsepower and aren't necessary at all, because they make that cool "gear whine noise".

It makes people look though. :rolleyes:

Later, mikey
 
#7 ·
Supercharger Roll,detroit Roll, blower Surge???

I don't know if this helps, but on my, TH350 automatic, 671 blown SBC, I would experience "detroit Roll" at idle. After many hours of double checked timing, gaskets, etc... I tried increasing the idle feed restriction jet on my billet metering blocks. Guess what happened....the surge went away. The blower was sucking my Holley, idle feed restriction dry. So I increased the restriction jet to allow more fuel at idle. Correct me if I am wrong, but this is just my own personal experience. I am not saying this is a cure-all modification, but just an example of unique situation that I ran into and wanted to share my experience with my fellow Hot Rodders. There maybe other factors or issues that are unique to your situation.
 
#37 ·
Yep, it worked.

I don't know if this helps, but on my, TH350 automatic, 671 blown SBC, I would experience "detroit Roll" at idle. After many hours of double checked timing, gaskets, etc... I tried increasing the idle feed restriction jet on my billet metering blocks. Guess what happened....the surge went away. The blower was sucking my Holley, idle feed restriction dry. So I increased the restriction jet to allow more fuel at idle. Correct me if I am wrong, but this is just my own personal experience. I am not saying this is a cure-all modification, but just an example of unique situation that I ran into and wanted to share my experience with my fellow Hot Rodders. There maybe other factors or issues that are unique to your situation.
:thumbup::thumbup::thumbup: Exactly what worked for me. Super simple fix. Don't turn'em but a twitch or you'll run too lean. I run the boat at an altitude of 5K and running 91 pump fuel so I'd rather be a little rich. A roll of about 500-700RPM is okay, any more and it gets out of hand. The cam-roll/idle-roll in my case is a necessity rather than a "cool thing". I'd rather err on the safe side (rich). The motor you see in my pix is in my V-Drive, 22' Schiada Day Cruiser. 468 ci BBC with AFR 305 Alum Heads and other goodies.
 
#8 ·
In the link XNCRTI posted, heed what Royce says. I corresponded with him a lot when building my car, very knowledgeable.

I have a roll in my 8-71 383 SBC, and can tune a good portion of it out by leaning the carbs. BG 750 blower carbs. Add that to the right cam duration and things can change either way.

Some like the roll some don't. One's that don't are next to me at a light after idling and loading up some, when I hammer it a little, he he, sends out a pretty good shot of exhaust, usually into their passenger window. I'll attach a link to my video, which may or may not work from my work computer, they have us blocked from the site. You can also search 'blown nova', mine's gray primer in a pretty dark garage, and yes it has some lifter noise in the video...initial adjustment on a solid roller.

http://www.youtube.com/watch?v=rA6NVVxmhoI
 
#9 ·
No, We Didnt Spend All Kinds Of Money And Time Just To Get That Sound,we Do Own A Speed Shop So That Helps On Parts And Fuel. And Yes There Is A Noisey Gear Drive In It To,we Like It.we Have Other Blower Cars To . None Of Them Surge Maybe There All Running To Good Lol Lol. We Were Dyno Testing And Experimenting.we Have Heard Cars At Shows And They Were Carbed And Wanted To Know How They Got It To Run That Way.like We Said Whether It Is The Right Way Or The Wrong Way Or If Some Like It Or Some Dont We Just Are Trying To Figure It Out How It Is Done,maybe We Should Ask How To Correct The Problem Lol Lol Then Do The Reverse? We Do Like The Sound And Want To Try It! We Ruled Out Power Valves And At The Last Show In Syracuse Ny There Was A Willies Coupe With A Stock 502 Stock Cam And He Had A 8/71 And Carbs And It Surged So Not Sure If Its Even In The Cam? At The New England Summer Nationals 4 Cars There Surged,that We Seen,was Probably More There. 2 Had Holley Blower Carbs , One Had Regular Holleys,one Had Demons.was Trying To Narrow It Down To Maybe Its In The Carbs? No Luck.

68novass -did You Change Anything In The Carbs ? Power Valves/jets ? What Is Your Timing Set At? Initial, Total? Msd/weights/springs? You Running A Large Duration Cam? Another Dyno Shop Mentioned To Us That The Blower Has To Be Teflon Lined, The Weiand Blower We Have Isnt.none Of Our Blowers We Have ,are.is Your Blower? Thanks For The Video And Yes We Have Seen That On You Tube Before.was Trying To Watch The Tach But Video Shuts Off There Right At The End.we Think It Sounds Good.

Would Like To Hear camaroman7d Camaro Run ,he Says His Surges And Runs Better That Way,starts The Best And He Can Tune It Out If He Wants To. Any More Idea's , Thanks For The Replies
 
#10 ·
After a month or so I bought new primary idle air bleeds and opened them up from .070 to .080, leaned it out some at idle. Dropped the jets, pri and sec 4 numbers, that helped with the initial richness, al idle adjustments are out about 1.5 for big roll, 1.25 calms it down some. Also have new accelerator pump cams but haven't messed with them yet. These are Mighty Demons. Cam is Lunati with 50139, solid roller, Isky RedZone liftersn cam # RRA-282-290, .502 I/E. Dur 224/I 232/E @.050, advertised 282/290. I did use 1.6 rockers on the exhaust side. Timing 20 initial, 38 total all in at 2500. Teflon lined?, it';s beens o long I can't recall, I don't think so, the rotors aren't teflon stripped though. The idle when it rolls is 700/1000. Usint a MSD/BRM, no retard set. LSA 112, intake c/l 108, installs 4 deg adv.

I have three videos of Royces Camaro he sent me recorded on his cell. I converted them to .avi, two are 11 mb one is about 4 mb. Maybe I can shrink them more or convert to another type of file. I'm sure he wouldn't mind me sending them, but that's a huge file to send. Later today I will try to post to youtube, acknowledging Royce as the owner if he is ok with it. He sld the car, kept the motor is almost done building a killer '63 Skylark pro street car.
 
#11 ·
I uploaded Royces videos to my you tube, but...they uploaded upside down!!! I may try to convert from .avi to .mov or .mpg and redo, but you can hear his motor. As I said, they were converted from a cell phone format and aren't the best around.
 
#13 ·
I guess I don't understnd why you want this motor to lope. Sounds like you have it running good. Get a Comp cam thumper if you want lope. It will about turn the car over haha.
Usually these blower motors roll at idle because they are running rich. I speed the idle up as I just don't like the things running so rich. Holes in the throttle blades let you get them closer to the idle feed where they are supposed to be. I think some blowers have variable clearances around the rotors so as the rotors turn there is more or less air going in. I like a lot of advance too and this seems to cure it some. A very hot cam makes it worse. Also 4 corner idle adjustments help. Run E-85 and they smooth out nicely.

Our FC idled at 1800-2000 and ran smooth with a 750 lift cam. Except after a burnout it would load up a little but it cleaned out nicely. It was very sharp on the throttle response.
 
#16 ·
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.
 
#19 ·
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.
 
#20 ·
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...
 
#21 ·
wixomhead said:
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.
 
#23 ·
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.
 
#24 ·
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?
 
#25 · (Edited)
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?
 
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