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Belt size for 3.17 upper and Incognito lower sleeve?

1606 Views 34 Replies 6 Participants Last post by  2ndgen
Need help finding the correct belt size for this setup. Does anyone else run this same combo? I'd prefer to get the right belt rather than purchasing a separate adjustable idler.
Much appreciated!
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Honestly I would say pretty close to stock size. Put it on and see where it falls on the tensioner
Honestly I would say pretty close to stock size. Put it on and see where it falls on the tensioner
Yes, exactly. I was also thinking that it would be close to stock size - seeing that there isn't much size difference between the two. I have the Gates 594 belt that came with the Incognito, so I'll try that and see where it falls on the tensioner as you're suggesting. Hopefully, it should fit fine. Either way, someone else suggested upgrading to the 594HD belt anyways for added strength. Just trying to eliminate extra costs, if possible. Thanks!
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Yeah, I was just reading through this thread yesterday. Unfortunately, there's no specific info related to my setup. So using some "guess-tamation" I figured that the 3.17/Incog lower should be fine with the Gates 594HD belt. If all else fails I'll just have to fork over the extra cash and get the adjustable idler. Are you familiar with the Bando belts? Any pros/cons that you're aware of? Thanks!
Yeah, I was just reading through this thread yesterday. Unfortunately, there's no specific info related to my setup. So using some "guess-tamation" I figured that the 3.17/Incog lower should be fine with the Gates 594HD belt. If all else fails I'll just have to fork over the extra cash and get the adjustable idler. Are you familiar with the Bando belts? Any pros/cons that you're aware of? Thanks!
There is none for mine either. Put it together and found the stock belt was perfect for what I had done.
I run a Gates Green. Don’t know anything about Bando
There is none for mine either. Put it together and found the stock belt was perfect for what I had done.
I run a Gates Green. Don’t know anything about Bando
Are you running an upper/lower combo, or upper only? If so, which pulley(s)?
The incognito is 6% OD.
MMX has a 7% OD here
The MMX include a gates 594HD belt, and assumes stock upper.

Going from 3.35 stock to 3.17 pulley you need 0.28" (only 7mm) shorter belt (1/2 the circumference difference).
So either the 594 or one step smaller--the 586 would probably do it for you.

I had this chart of all gates belt sizes in my notes. Hard to find. Gates belt search on their own site is awkward to use.
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I've thought about this combo as well. I already have the incognito and have thought about adding the 3.17. Let us know how it works out.
Are you running an upper/lower combo, or upper only? If so, which pulley(s)?
I’m running a 2.95 upper with blower spacers. Ran the quick math on it after I got it back together and realized it was pretty darn close to stock length. Sure enough threw the stock length belt on and it was dead center the tensioner pulley
Stock Lower:8.184
Incognito Lower: 8.675
Difference= .491”

Stock Upper: 3.35
Your Upper: 3.17
Difference: -.18”

overall gain or loss= .311”
Just picking at nits here, but to be more accurate you don't just add the difference in diameters--you have to multiply by 1/2 pi, and to be even more accurate there's about 180 degrees of wrap on the upper but about 225 degrees of wrap on the lower so the 1/2 changes also.

dB = delta belt length
dDl = delta diameter lower pulley = 0.491
dDu = delta diameter upper pulley = -0.18
225/360 = 5/8 = 0.625
180/360 = 1/2 = 0.5
dBl = delta belt length from lower pulley delta
dBu = delta belt length from upper pulley delta

dB = dBl + dBu
dB = (pi x dDl x 0.625) + (pi x dDu x 0.5))
dB = pi x ((dDl x 0.625) + (dDu x 0.5))
dB = 3.14 x ((0.491 x 0.625) + (-0.18 x 0.5)) = 0.681" longer belt

or separately:
dBl = pi x dDl x 0.625 = 3.14 x 0.491 x 0.625 = 0.963"
dBu = pi x dDu x 0.5 = 3.14 x -0.18 x 0.5 = -0.282"

the Incognito lower needs a 0.963" longer belt
the 3.17 upper needs a 0.282" shorter belt
0.963 - 0.282 = 0.681 net longer belt
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The incognito is 6% OD.
MMX has a 7% OD here
The MMX include a gates 594HD belt, and assumes stock upper.

Going from 3.35 stock to 3.17 pulley you need 0.28" (only 7mm) shorter belt (1/2 the circumference difference).
So either the 594 or one step smaller--the 586 would probably do it for you.

I had this chart of all gates belt sizes in my notes. Hard to find. Gates belt search on their own site is awkward to use.
Oh wow - this belt size chart is AMAZING! And yes, the Gates site for belt sizing is definitely "awkward" to say the least. You're a life saver, Bro. Much appreciated!
I've thought about this combo as well. I already have the incognito and have thought about adding the 3.17. Let us know how it works out.
Yeah finding the correct belt size for this combo is definitely a travesty LOL. It seems that the 594HD will work best - as the 3.17 isn't much smaller than the stock 3.35. Some have also gone with the additional adjustable idler for added protection against possible belt slip. I just installed the Incog lower last month with ECM/TCM tuning from Dusterhoff. I got the full 2psi as advertised and great tuning. Couldn't be happier with the results thus far. My boost gauge consistently holds at13psi with brief hits at 14. Just ordered the 3.17, FIC 1000s and a few other supporting mods a few days ago. But probably won't be able to get started until after the New Year. Should be a little over 15psi when finished. Hoping for a minimum of 730-750 to the wheels. I'm staying on pump gas for the time being, but left some headway to potentially add a Flex fuel setup later on. But yeah, I'll definitely keep you all posted along the way 😎
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I’m running a 2.95 upper with blower spacers. Ran the quick math on it after I got it back together and realized it was pretty darn close to stock length. Sure enough threw the stock length belt on and it was dead center the tensioner pulley
Ok that's excellent! Very good news :) Many thanks for the feedback. And how are you liking the blower spacers? Did you also get the thermal blanket? HHP sells this package on their site. I was considering it myself. However, I've also heard from others that it's actually more efficient to go with either the interchiller or heat exchanger. The heat exchanger is a great option, but does add some unwanted weight to the front end. So, I'm undecided. But let me know how the spacers are working for you.
Just picking at nits here, but to be more accurate you don't just add the difference in diameters--you have to multiply by 1/2 pi, and to be even more accurate there's about 180 degrees of wrap on the upper but about 225 degrees of wrap on the lower so the 1/2 changes also.

dB = delta belt length
dDl = delta diameter lower pulley = 0.491
dDu = delta diameter upper pulley = -0.18
225/360 = 5/8 = 0.625
180/360 = 1/2 = 0.5
dBl = delta belt length from lower pully delta
dBu = delta belt length from upper pully delta

dB = dBl + dBu
dB = (pi x dDl x 0.625) + (pi x dDu x 0.5))
dB = pi x ((dDl x 0.625) + (dDu x 0.5))
dB = 3.14 x ((0.491 x 0.625) + (-0.18 x 0.5)) = 0.681" longer belt

or separately:
dBl = pi x dDl x 0.625 = 3.14 x 0.491 x 0.625 = 0.963"
dBu = pi x dDu x 0.5 = 3.14 x -0.18 x 0.5 = -0.282"

the Incognito lower needs a 0.963" longer belt
the 3.17 upper needs a 0.282" shorter belt
0.963 - 0.282 = 0.681 net longer belt
Man you're a star ⭐ Definitely much easier to see the differences once you have all the math laid out. Can't thank you enough, Bro. Much appreciated!
Need help finding the correct belt size for this setup. Does anyone else run this same combo? I'd prefer to get the right belt rather than purchasing a separate adjustable idler.
Much appreciated!
I'd get ahold of Ripatuned (Steven) and he should be able to tell you which size belt would be best.

Never mind..... Just now saw that others figured it out with the calculations.
Oh wow - this belt size chart is AMAZING! And yes, the Gates site for belt sizing is definitely "awkward" to say the least. You're a life saver, Bro. Much appreciated!
Yeah finding the correct belt size for this combo is definitely a travesty LOL. It seems that the 594HD will work best - as the 3.17 isn't much smaller than the stock 3.35. Some have also gone with the additional adjustable idler for added protection against possible belt slip. I just installed the Incog lower last month with ECM/TCM tuning from Dusterhoff. I got the full 2psi as advertised and great tuning. Couldn't be happier with the results thus far. My boost gauge consistently holds at13psi with brief hits at 14. Just ordered the 3.17, FIC 1000s and a few other supporting mods a few days ago. But probably won't be able to get started until after the New Year. Should be a little over 15psi when finished. Hoping for a minimum of 730-750 to the wheels. I'm staying on pump gas for the time being, but left some headway to potentially add a Flex fuel setup later on. But yeah, I'll definitely keep you all posted along the way 😎
Awesome, yeah I used Curt with mine also and have same boost 13-14psi. 2 years and 0 issues.
I'd get ahold of Ripatuned (Steven) and he should be able to tell you which size belt would be best.

Never mind..... Just now saw that others figured it out with the calculations.
Yes, exactly. These calculations are spot on! Also, I did contact Steve a while back when I ordered the Incog lower and he also advised the adjustable idler (his own, of course LOL). Rather than fooling around with belt sizing, he preferred to simply divert to the idler - which makes sense.
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Awesome, yeah I used Curt with mine also and have same boost 13-14psi. 2 years and 0 issues.
Ok very good! Yeah, these Incog's (with tuning) are a perfect Street setup - which is exactly what I was looking for. There are lots of HCs and REs popping up over here in Dubai and I'd like to stay competitive LOL. Curt got me dialed in to absolute perfection. And it's good to hear that you've already gone a couple years so far with yours. Awesome! Are you planning on swapping the upper anytime soon? Just ordered my parts today online from HHP, but won't be able to get the install and tuning completed until after the New Year. But definitely very excited!
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Ok very good! Yeah, these Incog's (with tuning) are a perfect Street setup - which is exactly what I was looking for. There are lots of HCs and REs popping up over here in Dubai and I'd like to stay competitive LOL. Curt got me dialed in to absolute perfection. And it's good to hear that you've already gone a couple years so far with yours. Awesome! Are you planning on swapping the upper anytime soon? Just ordered my parts today online from HHP, but won't be able to get the install and tuning completed until after the New Year. But definitely very excited!
Maybe next fall on the upper. I'm doing a mantic clutch now and then next would be ms109 tune.
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