# magnacharger mp112



## hsver8 (Dec 19, 2008)

Hi guys, new here.

Can anyone tell me how to tighten the rear belt on the maggie mp112. I have got a 2.75 front pulley and can only manager 4psi up to 4000 rpm and then it spikes to 6.5 at redline. Any help appreciated.

thanx in advance


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## 6QTS11OZ (Mar 27, 2005)

Try here:

LS1GTO.com Forums - Maggie rear belt tensioner adjustment

Hope it helps.


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## SANDU002 (Oct 13, 2004)

Also sounds like you only have the stock magnasun tune. I had mine dyno tuned and am running 8.5 lbs of boost, 505 rwhp, 525 rwtq


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## hsver8 (Dec 19, 2008)

SANDU002 said:


> Also sounds like you only have the stock magnasun tune. I had mine dyno tuned and am running 8.5 lbs of boost, 505 rwhp, 525 rwtq


The front pulley is a 2.75 inch. the stock one i got with the kit was a 3.2 and only ran 2.5 - 3.5 psi ?????

ATM i am only getting 415rwhp

What sort of boost should i be getting with that pulley?


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## 6QTS11OZ (Mar 27, 2005)

hsver8 said:


> The front pulley is a 2.75 inch. the stock one i got with the kit was a 3.2 and only ran 2.5 - 3.5 psi ?????
> 
> ATM i am only getting 415rwhp
> 
> What sort of boost should i be getting with that pulley?


The stock pulley should have been a 2.8". Well at least mine was. Right out of the box was at 5.5 psi. Right now I'm at 8 psi with a 2.6" front pulley and 10.5:1 CR forged pistons. It was at 8 psi to with a 2.7" front pulley and the stock 10.9:1 pistons.

Did the link I provided help you out any for tightening the rear belt?


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## hsver8 (Dec 19, 2008)

6QTS11OZ said:


> The stock pulley should have been a 2.8". Well at least mine was. Right out of the box was at 5.5 psi. Right now I'm at 8 psi with a 2.6" front pulley and 10.5:1 CR forged pistons. It was at 8 psi to with a 2.7" front pulley and the stock 10.9:1 pistons.
> 
> Did the link I provided help you out any for tightening the rear belt?


Yeah, thanks for that. looks like my work is cut out for me


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## batmans (Aug 16, 2007)

SANDU002 said:


> Also sounds like you only have the stock magnasun tune. I had mine dyno tuned and am running 8.5 lbs of boost, 505 rwhp, 525 rwtq



Just curious for comparison reasons, what other mods do you have and what A/F ratios are you running?

I'm seriously considering getting the 2.6 or 2.7 from Pulley Boys for $75.

My aim is 7-8 psi. Does that sound about right?


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## batmans (Aug 16, 2007)

6QTS11OZ said:


> The stock pulley should have been a 2.8". Well at least mine was. Right out of the box was at 5.5 psi. Right now I'm at 8 psi with a 2.6" front pulley and 10.5:1 CR forged pistons. It was at 8 psi to with a 2.7" front pulley and the stock 10.9:1 pistons.
> 
> Did the link I provided help you out any for tightening the rear belt?


What's the safest psi and A/F ratio for 8psi on the stock 10.9:1 compression ratios?

Was there any change in HP/TQ between the 2 pulley ratios and compression ratios?


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## batmans (Aug 16, 2007)

6QTS11OZ said:


> The stock pulley should have been a 2.8". Well at least mine was. Right out of the box was at 5.5 psi. Right now I'm at 8 psi with a 2.6" front pulley and 10.5:1 CR forged pistons. It was at 8 psi to with a 2.7" front pulley and the stock 10.9:1 pistons.
> 
> Did the link I provided help you out any for tightening the rear belt?


6QTS11OZ, I'm running the a 2.6 pulley and my max boost is just a tad over 8psi.

I just had my GTO dyno tuned over the weekend and actually lost over 100HP since the boost dropped from a little over 8psi to 3psi~ about halfway through the RPM range. Both front and rear belts have been changed.

How can I tell which belt may be slipping?

The front belt has wear along the belt with less than 2k miles on it. Is that the smoking gun?

I used the same size belt for the stock MAggie 2.8 pulley. Not sure if I should have gone with a smaller belt for the front.


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## HITMAN803 (Apr 10, 2010)

it sounds like you have belt slippage......I was told the smallest you should go in the front was 2.8...I would have gotten a overdrive crank pulley, they add 1-3 psi and you would of had no belt slippage with that...Going smaller is not always the best solution...I think that pulley is way too small....and the proof is the belt slipping.Also what supporting mods do you have?? That will be a big faactor too.It not about PSI, its more about engine effiecincy..With that psi goes down but hp goes up...


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## batmans (Aug 16, 2007)

HITMAN803 said:


> it sounds like you have belt slippage......I was told the smallest you should go in the front was 2.8...I would have gotten a overdrive crank pulley, they add 1-3 psi and you would of had no belt slippage with that...Going smaller is not always the best solution...I think that pulley is way too small....and the proof is the belt slipping.Also what supporting mods do you have?? That will be a big faactor too.It not about PSI, its more about engine effiecincy..With that psi goes down but hp goes up...


Tell me more about this overdrive crank pulley. I know nothing about that.

Since I have the smaller pulley would going with a smaller belt make it work?

I had my engine rebuilt with Scat rods, Wiseco 2816 forged pistons with a lower compression ratio of 10.5:1, Ferrea undercut forged valves and supporting springs and hardware, ARP bolts throughout the engine and finally the pistons and combustion chamber have been ceramic coated to improve thermal efficiencies and help reduce detonation.

I contacted Magnacharger and they said that for starters the rear MP112 belt should have 240 ft/lbs of belt tension.

They also said that the only other reason I would lose boost would be if the bypass is not closing all the way or if there was a huge vacuum leak in the system.

According to their tech support, to check for a vacuum leak, I need to have an air pressure regulator that I use to put 10-12 psi of air pressure into the manifold. This can be done by temporarily removing the power brake hose from the supercharger manifold and connecting an air hose with the regulator attached to the manifold. Slowly increase the air pressure in the manifold to the 10-12 psi range and then using a water/soap solution, spray around any sealing surfaces to see if any bubbles are present, this would indicate a leak. A smoke style leak detector could also be used to find a vacuum leak if there is a shop around with that piece of equipment.


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## batmans (Aug 16, 2007)

I just installed a .5" smaller belt and I think I am back in business.

No traction in 1st and 2nd.

I'm going to install a boost gauge/module from PLX devices to confirm.


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## HITMAN803 (Apr 10, 2010)

Sounds good, They make a couple OD crank pulley that most people o to first...Innovations makes one and I know East coast supercharger has one they are 10% OD 8" diameter which is bigger than the 7.5 stock crank pulley and give you 1-3psi more without changing the pulley (front or OD rears)..They are around $500....Those are great numbers with no cam...(or I didnt see one). I would also buy a wideband which I think is a must when you have FI..


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