Pulley change and boost problems...


2.7 Dallas Mustang pulley
 
Fubar

The belt is sliping; You just don't know it !!! The belt is designed to slip SOME; It WILL slip MORE, when you change the pulley, WITHOUT changing the BELT etc. etc. !!!


AMB
 
When a belt slips, even a little bit, you can hear it. They are not quite. When it was cold outside I could hear a slight chirp. I assumed it was from the pulley change, but that has gone away.

I just dissagree with you AMB. I dont think the belt is slipping.
 
I think is is fair to say there is some variation in the cars. When Ford designed the belt and pulley system it was optimized for the 3.25" stock pulley. That mean with normal manufactoring tolerances the belt will have a range of tension around the ideal tension. Swapping the stock pulley for a 2.75" pulley will result in a belt tension that is less than before the swap. It may be still within range if your stock tension before the swap was towards the higher end. Now if you have a car before the swap with a tension below the norm, but in the low range of acceptable and then do a swap. That may give you too little tension.

There is a lot of leadway because of the spring tensioner, but won't cover all cases. Note that the higher boost takes more power thus more tension to hold vs. the stock pulley.
 
I would like to hear some additional input on belt slippage. I have never heard that "all belts slip some."

And if you reduce the pulley from 3.25 to 2.75, you've really only lost a 1/4 inch in actually length for the belt. If it were a short belt I could see that being a bigger issue, but the belt on that GT is huge. Surely 1/4 inch wouldn't affect it much. I mean to say, because of the size of the belt I assume that they would have a very strong tensioner on it. Thus reducing the affect of a 1/4 inch change.
 
Fubar

Belt slipage is a BIG problem on the 03 Mustang Cobra when you change to a smaller pulley!!! That is why Metco came out with LARGER lower pulley for the Cobra's !!! ALSO belt slipage is why Venders came out with the NON-SLIP upper S/C pulley. Belt slippage is also why Ford came out with the 10-RIB Belt System for the 05/06 Ford GT and the Shelby GT 500 !!!

AMB
 
I have never heard that "all belts slip." The theory is perplexing because I have always been told that if a belt is slipping you WILL KNOW IT. Even a modest slip sounds like your trying to kill a banshee.

And so, when you present the idea that my belt is slipping regardless of what I think. It flies in the face of what many trustworthy people have told me.
 
Easy enough to diagnose more rpm, boost shouldn't fall off. If the belt is slipping, fix it. Shorter belt, shim blower up, power steering bracker change. Stop whinning and do whatever is necessary and have fun. The world ain't a perfect place. Heffner said it usually works fine and if you don't want it, send it back. All mods have issues, sometimes easy, sometimes not. If you can't solve it, buy a whipple or go back to stock.
 
we've noticed most dyno's dont monitor boost or at least dont show it.... thats maybe why so many people DONT realize their belts are slipping... I would be curious to see how much boost everyone elses cars are making...
 
Well with just the pulley upgrade to 15lbs you can see it on the stock gauge. On mine it was noticable that it goes to 15 much much quicker than it ever went to 12.5

Matt
 
I don't even think monitoring boost on the dyno is a big deal unless something is clearly wrong. My car pegs the boost gauge. I've driven a friends with the same pulley. It pegs the boost gauge. Might seem inconsequential, but I sat there and watched one make 590 on the dyno. The other went 135mph in the 1/4. And I've seen a 3rd put down ~610. Monitoring the boost seems academic given the results.

The thing is, yes, the belt is going to slip. It's going to be obvious when it does (on the street anyways). But if you're only getting 560rwhp when you baselined 520rwhp, or if you're boost is only peaking at 13-14psi, then there is an issue beyond what's normal. Given that so many people have it now, and so many have put down about the same numbers with no problems, this is clearly the case.

Also check the for the collapsing accordion, as this may be adversely affecting your high rpm results.
 
Graphing boost would all about eliminate the guessing about slip or not. It would show up on the graph and be visible. Post up the sheet, that would be really helpful to all of us helping you attempt to pinpoint the problem.

my car @ 2 days old with a 2.7 and stock belt put down 618whp.

Also the boost gauge in the car is inferred thru sensor data / PCM and not an actual mechanical gauge.
 
Torrie is right, graph the boost. If it stops increasing at a certain point, then belt slip is a good possibility. It could also be that boost is low throughout the entire run, if that the case then maybe there is a small leak somewhere.
 
Belt slip is almost always very apparent when graphed thru the run. I dealt with this exact problem recently on an 06 mustang with a magnacharger. We dropped a pulley size and with the standard belt the boost graph looked like it was made by crayola.
 
tmcphail said:
Belt slip is almost always very apparent when graphed thru the run. I dealt with this exact problem recently on an 06 mustang with a magnacharger. We dropped a pulley size and with the standard belt the boost graph looked like it was made by crayola.
Click to expand...

Interesting... so the belt was slipping but you didn't notice the distinct belt squeal? I suppose b/c the engine was blowing and going but I would have assumed you'd hear it over that.

I still don't think my belt is slipping but I guess I might not hear it.

I was wrong, my apologies.

I posted a graph of my dyno run with the boost attached. I never put up the boost from my baseline but I will do that now.
 
In my experience belt slip is not always audible. Also on the dyno with all of the noise from the whole powertrain and the drum you most likely would not hear it.


Fubar said:
Interesting... so the belt was slipping but you didn't notice the distinct belt squeal? I suppose b/c the engine was blowing and going but I would have assumed you'd hear it over that.

I still don't think my belt is slipping but I guess I might not hear it.

I was wrong, my apologies.

I posted a graph of my dyno run with the boost attached. I never put up the boost from my baseline but I will do that now.
Click to expand...
 
I agree. I have seen many instances of belt slip with no audible symptoms. Boost curves, linearity of power/torque on the dyno, and visible signs (belt dust, etc..) can all indicate belt slippage you can't hear.
 
I have a new pully and I have belt "chirp". Does it go away or is more adjustment needed?
 
Who did the upgrades? You are close enough to us, you should stop by sometime.
 
cmoody32 ,I have the same set up and have no chirp.
 
You must log in or register to reply here.

Top Bottom