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Author
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Topic: Hesitation under decel on supercharged 93 Cobra? any ideas?
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DMacMilitant
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Member # 9769
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posted
 
 
I've got my 93 cobra supercharged and everything works great accept for this slight hesitation when I let off the gas and its still in gear. It does a slight little jolt a few times. Now I have removed the sc belt and driven it naturally aspirated and this hesitation/jolting goes away. So I know its something regarding the supercharger. Has a Vortech V3 sci trim running 6psi of boost. fuel parts are stock as this is the base vortech kit. I just let off the pedal or down shift and its good...still good...little jolt...now good...maybe two little jolts...then I'm to my stop or put my foot back into the pedal.
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Supercharged 1993 Cobra Mustang #415
Posts: 10 | From: Sonoma County | Registered: Feb 2010
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SmokinLX
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Member # 1684
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posted
Is it tuned? If not might be worth it just to check air fuel ratio. Tune is cheap compared to the price of an engine. Try checking for vaccum leak.
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Dont claim power if ya cant mile per hour. 10 second AOD
Posts: 4388 | From: East Bay | Registered: Aug 2002
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92stangLX
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Member # 3252
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posted
Check your bypass valve if you are running one
Posts: 5302 | From: San Francisco | Registered: Sep 2003
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DMacMilitant
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Member # 9769
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posted
I'm not running a bypass valve. According to Vortech you don't need one for this kit, which I always thought was crazy. Is there a way to duplicate what a bypass valve would do, as in open up the spot for the bypass valve to see if letting the extra air out during decel helps the problem? I realize I won't get any boost this way due to the air being able to leak out, but I'll be able to see letting the extra air out helps. . .right?
Posts: 10 | From: Sonoma County | Registered: Feb 2010
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nonwoven29
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Member # 9780
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It totally sounds like compressor surge Bro!!! You wouldn’t notice it as bad at higher elevation but with that lower elevation cooler Bay area air you will see it a lot more. Get a cheap Bosch BOV on eBay for like $20 new. If you need help hooking it up I can help with the install on line. The surge will some times sound like a grinding or clicking noise. I’ve played with lots of blowers 2 of them where centrifugals powerdyne and vortech's.
Posts: 26 | From: Reno Area/Livermore Area | Registered: Feb 2010
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nonwoven29
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Member # 9780
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I just thought of another easier way to explain what’s happening to your set up. So imagine you’re at 5K rpms you completely let of the pedal where is the boost that the Blower is still making going to go after the throttle body slams shut? no where it cant it feeds back thru the whole intake or rather discharge from the blower causing surge which can cause your maf to foul, After cooler hoses to pop off and transmission gears in the SC housing to jolt around which causes that clicking grinding noise I was talking about above. If you open up the hole and just vent it to atmosphere it will throw your A/F ratio way out of wack sense you have a MAF metering the air. Don’t leave any hole open on your set Bro trust me. Get the recalculating diverter valve hooked up right and then tell us how she runs. PS you have to run the blow off from the DV/BOV intake side of the valve right before and below your TB then the discharge side need to dump right before your intake side of the blower best spot being right near the impeller. Last but not lest hook the vacuum line up to any major vacuum tree you have at the manifold and she will work like a charm. Check Carls site out at 928motorsports.com he has modified a both a powerdyne and my vortech which is my current set up. He is the only guy in the field making aftermarket billet impellers which rock they bring the boost in fast and hard. I have 2 old videos of my old set up on YouTube you can find them under “supercharged expedition” user name nonwoven29 My vortech video will be up soon it sounds even better then the dyne.
Posts: 26 | From: Reno Area/Livermore Area | Registered: Feb 2010
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DMacMilitant
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Member # 9769
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Thanks, I appreciate the info. Just ordered up my bypass valve and will get it hooked up later this week. I'll post my results and ask for any questions if I need help. Thanks again!
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Supercharged 1993 Cobra Mustang #415
Posts: 10 | From: Sonoma County | Registered: Feb 2010
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DMacMilitant
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Member # 9769
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posted
Damn I'm excited to get this bypass valve put in and get rid of that stuttering. The boner that I have can hardly be contained by my pants right now. I was driving the car yesterday and that stuttering was driving me so crazy I took the s/c belt off and drove it normal. It is not noticeable to most people but drives me crazy. Thanks again for the tip.
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Supercharged 1993 Cobra Mustang #415
Posts: 10 | From: Sonoma County | Registered: Feb 2010
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nonwoven29
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Member # 9780
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How does your SC run with the bov on there ?
Posts: 26 | From: Reno Area/Livermore Area | Registered: Feb 2010
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