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Discussion Starter · #1 ·
So there's no way around me upping the boost in spring, it's inevitable. I'm undecided on a 3.2" upper or going for a overdrive lower pulley which would mean no chance of belt slip.

How much boost would the 18% overdrive add? I'm on the 3.4" 6lb pulley, seeing 7-7.5lb on the map sensor with LTH and 392 cam.

Is there any way to make an 11+ pulley work on a '10? I'd much rather use the 5-6% OD pulley so I can use the same belt and not worry about too much boost on stock internals, but that's offered on EVERY year except '09-10. Really makes me wish I had a 2011+
 
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2011 R/T 6M Bright White, 590whp 490wtq, Whipple 10psi, 274 cam, 1 7/8 LT headers, 429 gears
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You could go with ATI and buy the 2009 hub 916246 and shell 917071 and end up with 6%

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Discussion Starter · #3 ·
You could go with ATI and buy the 2009 hub 916246 and shell 917071 and end up with 6%

Sent from my SM-T350 using Tapatalk
Got in touch with ATI and gonna be doing exactly this. Although they said its closer to 4% overdrive. Not exactly sure how much boost I'll be seeing but I'm gonna guess around 1psi.

Anyone know the stock pulley size? This ATI overdrive pulley is 6.780"
 

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104% of 7.5lb is 7.8lb
118% of 7.5lb is 8.85lb

Unless I'm missing something big here...

Maggie is a PD supercharger, so - for relatively small changes, within the limits of efficiency- boost is proportional to:

(Supercharger Flow / Engine Capacity)

18% overdrive = 18% faster charger speed = 18% greater flow (roughly)
 

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2011 R/T 6M Bright White, 590whp 490wtq, Whipple 10psi, 274 cam, 1 7/8 LT headers, 429 gears
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Got in touch with ATI and gonna be doing exactly this. Although they said its closer to 4% overdrive. Not exactly sure how much boost I'll be seeing but I'm gonna guess around 1psi.

Anyone know the stock pulley size? This ATI overdrive pulley is 6.780"
Bad Data removing
 

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Discussion Starter · #6 ·
104% of 7.5lb is 7.8lb
118% of 7.5lb is 8.85lb

Unless I'm missing something big here...

Maggie is a PD supercharger, so - for relatively small changes, within the limits of efficiency- boost is proportional to:

(Supercharger Flow / Engine Capacity)

18% overdrive = 18% faster charger speed = 18% greater flow (roughly)
They way I did my math was by supercharger rpm. I compared rpm of the 3.4 upper and 3.2 upper and then compared the two to the 3.4 upper with the 4% lower. That may not be the right way to do it but it made sense in my head.
Here's my math-
6.52"(stock pulley est.)
6.78" lower pulley(4% OD)
3.4"(6psi upper pulley)
3.2"(~8psi upper pulley)
6.52/3.4=1.917
6.52/3.2=2.037
6.78/3.4=1.994
(Input/Output)•InputRPM= Output rpm
Now this all may be completely wrong but that's where I got my estimate of ~1psi increase. If it's true 18% is only 1.5psi I'll go with that but I thought it was a lot more, like 3-4psi
 

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6.52"(stock pulley est.)
6.78" lower pulley(4% OD)
4% Diameter increase will give 4% circumference increase

You're going from 1.917:1 overall gear to 1.994:1 overall gear (4%) so the charger is only spinning 4% faster.

1psi is 13% of 7.5psi

I don't see how your blower is suddenly going to produce 13% more boost from 4% more speed
 

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2011 R/T 6M Bright White, 590whp 490wtq, Whipple 10psi, 274 cam, 1 7/8 LT headers, 429 gears
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They way I did my math was by supercharger rpm. I compared rpm of the 3.4 upper and 3.2 upper and then compared the two to the 3.4 upper with the 4% lower. That may not be the right way to do it but it made sense in my head.
Here's my math-
6.52"(stock pulley est.)
6.78" lower pulley(4% OD)
3.4"(6psi upper pulley)
3.2"(~8psi upper pulley)
6.52/3.4=1.917
6.52/3.2=2.037
6.78/3.4=1.994
(Input/Output)•InputRPM= Output rpm
Now this all may be completely wrong but that's where I got my estimate of ~1psi increase. If it's true 18% is only 1.5psi I'll go with that but I thought it was a lot more, like 3-4psi

 

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Discussion Starter · #9 ·
Very confused, after using the top calculator you linked there it's showing that I would be correct with a roughly 1-1.5psi increase from the 4% OD. When I entered all the stock specs it came out to 6.4psi which is pretty accurate, and when I entered in the stock lower and 3.2 upper it came out to 8.2 psi, which is also accurate per Magnuson. I'm not really that worried about seeing a specific PSI on my boost gauge more so feeling and seeing a quicker car by a solid 20whp, I know boost is just a measure of restriction. I just wanna make sure I make the right purchase and don't spend $380 on 2hp, or on the other side buy a pulley that gives me an extra 4psi and shoot my stock pistons into space
 

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2011 R/T 6M Bright White, 590whp 490wtq, Whipple 10psi, 274 cam, 1 7/8 LT headers, 429 gears
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Very confused, after using the top calculator you linked there it's showing that I would be correct with a roughly 1-1.5psi increase from the 4% OD. When I entered all the stock specs it came out to 6.4psi which is pretty accurate, and when I entered in the stock lower and 3.2 upper it came out to 8.2 psi, which is also accurate per Magnuson. I'm not really that worried about seeing a specific PSI on my boost gauge more so feeling and seeing a quicker car by a solid 20whp, I know boost is just a measure of restriction. I just wanna make sure I make the right purchase and don't spend $380 on 2hp, or on the other side buy a pulley that gives me an extra 4psi and shoot my stock pistons into space
I hear you, the biggest benefit from going to the ATI is having better dampening on the crank. That is the only reason I switched, pushing the RPMs up to the 7k range which will eventually pull the stock damper apart, and the torsional vibrations at the higher RPMs wouldn't be controlled. Additionally throwing close to another 300hp at the crank will also require more dampening.

If you just want more boost without the extra $$ I would go with swapping the pulley. The nice thing about the ATI is it will last forever with a simple rebuilt every 10 years. The downside is if you needed it honed it's a ***** finding someone that has a sunnen hone to get past the keyway. If you decide to go the ATI route and you can manage the downtime measure your crank and have them set the hub to your specs. It’s really important to have the correct press fit.

Side Note: I started out with a 3.5 pully with the ATI damper on my Whipple and ended up just over 12psi. Whipple’s states *A general rule of thumb is every .125" of pulley change is 1psi of boost. I went to a 3.75 and landed exactly 2lb under where I was. I would think the Magnuson is really close, they have a really efficient system too.
 

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Wow, reading all of these issues with pulleys makes me appreciate going the turbo route. That all being said. I thank you guys for sharing your knowledge as always.


Jay
 

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2011 R/T 6M Bright White, 590whp 490wtq, Whipple 10psi, 274 cam, 1 7/8 LT headers, 429 gears
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Wow, reading all of these issues with pulleys makes me appreciate going the turbo route. That all being said. I thank you guys for sharing your knowledge as always.


Jay
Just had to rub that in didn't you! LOL. let's see how it goes dialing in the waste gate on dual turbos.. ;)
 

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You know I would never rub anything in where you are concerned sir.... I'm not looking forward to getting the waist gates dialed..... Hell I've already had to re-engineer most of the system to begin with.
 

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2011 R/T 6M Bright White, 590whp 490wtq, Whipple 10psi, 274 cam, 1 7/8 LT headers, 429 gears
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All of the reengineering you can call it your own!!! Just to be clear was totally kidding with the waste gate comment.

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