Supercharger Overdrive ratio changes/recommendations

Magnum Powers

Registered User
Been taking with David, he is seeing some interesting effects associated with engine combinations, MPx superchargers, coated rotors, and blower overdrive ratios.

For best results users need the correct combinations of components for their performance goals. I would invite David to share his observations and make recommendations regarding his findings. As a result of this Magnum Powers may need to provide a wider selection of pulley ratios.

Charles
 
Can they be quick change pulleys as well similar to the GTP group pulleys? Ruined a few of the MP 10% OD SC pulleys and tired of it.
 
This is intended as a low cost option for people that will address some common concerns with the current pulley options. A quick change system is not in the discussion.


The point of this offering is that originally the MPX was designed with a 25% pulley arrangement in mind and certain compromises were made to achieve that pulley ratio.

1) Belt offerings that could work properly with that pulley arrangement are non-existent. You can't get a custom length belt so choices are limited to ones that are already made which means either the 400 or 390 length belts, neither of which fit properly. We have made do using spacers to raise the blower up so that the 400 belt will work, but it's a big bother and most people end up with belt slip due to the belt being too long.

2) The introduction of the abradable rotor coating and the improved MP bearing plate mean that at 25% OD the MPX makes too much boost for pump gas which means that most of you, if you upgrade to this new rotor pack, are going to have problems with excessive boost. In our dyno sessions the MPX with the new rotor pack made 2.5psi more boost than the older MPX. This is a big deal. We routinely made 20psi and 390+rwhp with our car using "only" 20% OD. The problem with that is, that even with head studs, alcohol injection, and MLS headgaskets, we lifted the heads after only one season with the car. It's just not reliable to run the car like this on pump gas even at 20% OD, nevermind 25%.

So my suggestion to Charles was to offer a stock diameter 10 rib pulley for people who have or are planning to get the new MPX rotor pack in the hopes that it would provide them a better street combination. One that makes the 400 belt fit much tighter, targets a more appropriate boost level, and reduces belt slip. It seems like a win-win to me.
 
The 25% that were sold say 8 or more years ago were 10% crank, 5% JS and 10% SC correct? I am using the crank and JS, but have the stock SC pulley on. That is what needed to be done to stop the belt slip without going the spacer route and reclocking tensioners.
 
The 25% that were sold say 8 or more years ago were 10% crank, 5% JS and 10% SC correct? I am using the crank and JS, but have the stock SC pulley on. That is what needed to be done to stop the belt slip without going the spacer route and reclocking tensioners.

So, are we talking the 3.16" ones?
 
This is intended as a low cost option for people that will address some common concerns with the current pulley options. A quick change system is not in the discussion.


The point of this offering is that originally the MPX was designed with a 25% pulley arrangement in mind and certain compromises were made to achieve that pulley ratio.

1) Belt offerings that could work properly with that pulley arrangement are non-existent. You can't get a custom length belt so choices are limited to ones that are already made which means either the 400 or 390 length belts, neither of which fit properly. We have made do using spacers to raise the blower up so that the 400 belt will work, but it's a big bother and most people end up with belt slip due to the belt being too long.

2) The introduction of the abradable rotor coating and the improved MP bearing plate mean that at 25% OD the MPX makes too much boost for pump gas which means that most of you, if you upgrade to this new rotor pack, are going to have problems with excessive boost. In our dyno sessions the MPX with the new rotor pack made 2.5psi more boost than the older MPX. This is a big deal. We routinely made 20psi and 390+rwhp with our car using "only" 20% OD. The problem with that is, that even with head studs, alcohol injection, and MLS headgaskets, we lifted the heads after only one season with the car. It's just not reliable to run the car like this on pump gas even at 20% OD, nevermind 25%.

So my suggestion to Charles was to offer a stock diameter 10 rib pulley for people who have or are planning to get the new MPX rotor pack in the hopes that it would provide them a better street combination. One that makes the 400 belt fit much tighter, targets a more appropriate boost level, and reduces belt slip. It seems like a win-win to me.

David, Do you have recommendations for various engine and supercharger combinations? For instance:

Stock Engine/"S" port 94/95
Stock Engine/MPx
Head work w/ Stiff Valve Springs/MPx ------------------------------Pump Gas - Race Fuel
Head work w/ Stiff Valve Springs/MPx + MP Coated Rotor Pack -------Pump Gas - Race Fuel
 
David, Do you have recommendations for various engine and supercharger combinations? For instance:

Stock Engine/"S" port 94/95
Stock Engine/MPx
Head work w/ Stiff Valve Springs/MPx ------------------------------Pump Gas - Race Fuel
Head work w/ Stiff Valve Springs/MPx + MP Coated Rotor Pack -------Pump Gas - Race Fuel

A stock engine works best with 5% OD on an S-port. The new MPX doesn't give up anything on the lower end at this drive ratio on a stock engine, and will climb boost continually with rpm on a stock motor. This isn't a problem so I recommend the same for both applications.

Once you go to a good FMIC and other bolt ons, 10% with the MP plenum on either blower is ok.

With a decent heads/cam package and an MPX you can run 15% on pump gas pretty well, maybe 20% depending on how you use it. Anything more is just breaking parts.

With race fuel and all the right supporting hardware, I don't see where there is a limit except when you start to have blower failures due to rotor rpm. An engine that is redlined at 6000rpm will clearly do better at higher OD levels than one that spins 6800. That 800rpm makes a big difference.

A lot of guys are now building 4.2L's which will allow you to run about 5% more OD in any case. Possibly 10% more if the motor is properly built and caution is exercised.
 
With a decent heads/cam package and an MPX you can run 15% on pump gas pretty well, maybe 20% depending on how you use it. Anything more is just breaking parts.

With race fuel and all the right supporting hardware, I don't see where there is a limit except when you start to have blower failures due to rotor rpm. An engine that is redlined at 6000rpm will clearly do better at higher OD levels than one that spins 6800. That 800rpm makes a big difference.

So a fully modded SC (which I would consider mine to be at this point) SCU Heads/Cam, MPX, MP FMIC, Running 25% OD via 10 rib 15% and 10% crank pulley, #80 injectors...everything supporting that's been beat to death on the forums...if I am reading this correctly I am essentially pushing the limits?

-Tim
 
So a fully modded SC (which I would consider mine to be at this point) SCU Heads/Cam, MPX, MP FMIC, Running 25% OD via 10 rib 15% and 10% crank pulley, #80 injectors...everything supporting that's been beat to death on the forums...if I am reading this correctly I am essentially pushing the limits?

-Tim

im on 43k miles with 25% od. i have some massively worked over heads, headers ext. so long as you can flow the air you will be fine.
 
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