Boost loss

JGDogg10

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Hey guys, so I’m still in the process of tuning the Mach, but running into some issues. Car is running a ysi with a 2.95 pulley and a 15% crank pulley. Had some belt slip issues and just put the tightest belt I could get on it, figured it would get rid of what was going on, but it didn’t.
So the car runs great, 1st gear and 2nd gear are strong and it’s hitting just about 20 lbs of boost in 2nd. Then I shift to 3rd and I’ll be lucky to get it to about 15lbs. Car just feels like it’s trying to go, but just won’t grab. I’ve tested the intake, intercooler and pretty much everything else for a vacuum leak or somewhere it could be bleeding boost off but everything has held over 20lbs. Only thing that leaks just barely is the egr valve, but even when it was pressurized to 25lbs it was only dropping about a hundredth of a lb of boost per second.

Anyone else ever have this issue?


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omj

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Sounds like regular ole belt slip to me. A YSi is capable of 75k rpms. Get a griptec pulley and you'll probably be fine.
 

JGDogg10

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That’s what’s on there. The 2 piece design pulley.


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JGDogg10

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IMG_3342.JPG



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01yellercobra

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That's a small pulley. Sounds like it's just slip. You might have to get creative with idlers and belt wrap.
 

Badaz01

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Hey guys, so I’m still in the process of tuning the Mach, but running into some issues. Car is running a ysi with a 2.95 pulley and a 15% crank pulley. Had some belt slip issues and just put the tightest belt I could get on it, figured it would get rid of what was going on, but it didn’t.
So the car runs great, 1st gear and 2nd gear are strong and it’s hitting just about 20 lbs of boost in 2nd. Then I shift to 3rd and I’ll be lucky to get it to about 15lbs. Car just feels like it’s trying to go, but just won’t grab. I’ve tested the intake, intercooler and pretty much everything else for a vacuum leak or somewhere it could be bleeding boost off but everything has held over 20lbs. Only thing that leaks just barely is the egr valve, but even when it was pressurized to 25lbs it was only dropping about a hundredth of a lb of boost per second.

Anyone else ever have this issue?


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I had some slip at higher rpm on my d1 2001 cobra. In the spring when she comes back out im gonna put and American racing solutions tensioner on it smaller belt and possibly a grip tech pulley. I had a bbk throttle body that leaked like a sieve around the throttle plate shaft. Put the smaller stock throttle body back on and made the same power at 400 less rpm and two lbs. less. boost idk maybe it’s something like that.
 

JGDogg10

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It has a 3 bolt tensioner front cover with a larger idler pulley towards the passenger side. The belt wraps under an idler pulley, up almost completely around the supercharger pulley and back down around another idler. There is less than an inch of room between those two idlers, meaning the belt almost has a full wrap on the griptech pulley. No where else really to add an idler for “more” wrap. Wish I could post a video, I could show you how tight it is. Could the gates HD belt I got from the local Napa be older and not grabbing the way it should? It feels pretty hard and slick


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Badaz01

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It has a 3 bolt tensioner front cover with a larger idler pulley towards the passenger side. The belt wraps under an idler pulley, up almost completely around the supercharger pulley and back down around another idler. There is less than an inch of room between those two idlers, meaning the belt almost has a full wrap on the griptech pulley. No where else really to add an idler for “more” wrap. Wish I could post a video, I could show you how tight it is. Could the gates HD belt I got from the local Napa be older and not grabbing the way it should? It feels pretty hard and slick


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Try some belt dressing lol.
 

JGDogg10

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I had some slip at higher rpm on my d1 2001 cobra. In the spring when she comes back out im gonna put and American racing solutions tensioner on it smaller belt and possibly a grip tech pulley. I had a bbk throttle body that leaked like a sieve around the throttle plate shaft. Put the smaller stock throttle body back on and made the same power at 400 less rpm and two lbs. less. boost idk maybe it’s something like that.
It’s running the stock throttle body still. And I’ve pressure tested the entire system, throttle body and all.
 

Badaz01

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It’s running the stock throttle body still. And I’ve pressure tested the entire system, throttle body and all.
Dang dude that tugs. Maybe it’s nature of the beast with the small pulley. I have a 10% O.D. Crank pulley and a 4 inch blower pulley that got me 15# of boost I mentioned doing a smaller pulley to my tuner and he said that’s all well and good but belt slip becomes an issue when smaller pulleys come in to play.
 

JGDogg10

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I’m gonna try some of the belt stuff tomorrow just to see. At least if it helps a little it will give me the confidence to know it’s just slipping
 

Badaz01

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I’m gonna try some of the belt stuff tomorrow just to see. At least if it helps a little it will give me the confidence to know it’s just slipping
Wow that’s like a guitar string. My belt is loose as a goose compared to that and mine has a little slippage at 6200 rpm. That thump tensioner is legit to. I did notice the other day the idler pulley behind my procharger was rubbing the back of my procharger didn’t rub when sitting idling idk if it was under load/wot when it made contact because these engines to flex some when big power is in the equation. Idk if my slippage is related to that or maybe yours to. I plan to look at all surfaces that are close with my pulleys and belt and see if there any signs of rubbing in the slightest. You’d think that grip tech pulley would tear the belt up before it would let it slip ‍♂️
 

JGDogg10

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Hah yea when I said it was tight, I meant it was suuuper tight haha. Hoping the belt conditioner might help it a little tomorrow and I guess just go from there…


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JGDogg10

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Not that I can see. There are spots around the alternator pulley and a little on the underside of the shaker setup.


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JGDogg10

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Lol DSG I was kinda waitin for him to chime in too haha. I know he ran something very similar, but he wasn’t running a/c and I am. So not sure if he put a delete in or ran the belt a different way because I think he was using like 90 something inch belt if I remember correct


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01yellercobra

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Just remember that tight belts kill main bearings. You might want to look into the RPM belt.

FWIW, I had better luck with a basic micro V belt than the green belt on my F1A set up.
 

JGDogg10

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The rpm belts don’t come in a long enough length. Yea I was wondering about that. It’s weird because i had on regular belt on that was bigger than this new green belt and it is making about the same amount of boost. Wasn’t quite as tight as this one


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DSG2003Mach1

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The rpm belts don’t come in a long enough length. Yea I was wondering about that. It’s weird because i had on regular belt on that was bigger than this new green belt and it is making about the same amount of boost. Wasn’t quite as tight as this one


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The green belt is tougher. It the downside to that is it’s harder and more prone to slip. I’m in the same boat with the rpm belt lengths
 

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