Mp112 with an underdrive... help
Thread Starter
Instructor
Joined: Jul 2016
Posts: 107
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From: Fort polk Louisiana
Mp112 with an underdrive... help
So I built a new bottom end recently and I installed a powerbond underdrive (25%). It's on and is pinned.
Now I came into a very very good deal on a used maggie that works and has everything ready to bolt and go.
It has 1:1 rear pulleys now.
Let's go ahead and assume I DO NOT want to replace the brand new powerbond I installed and pinned. I understand the underdrive is not congruent to boost on superchargers. But let's say it isn't going to go.
What main pulley am I'm going to have to use now to get a 6-8 psi range out of the maggie.
Now I came into a very very good deal on a used maggie that works and has everything ready to bolt and go.
It has 1:1 rear pulleys now.
Let's go ahead and assume I DO NOT want to replace the brand new powerbond I installed and pinned. I understand the underdrive is not congruent to boost on superchargers. But let's say it isn't going to go.
What main pulley am I'm going to have to use now to get a 6-8 psi range out of the maggie.
Racer
Joined: Jan 2009
Posts: 393
Likes: 14
When rear pulleys are 1:1, you will need 2.4" front pulley to achieve 6.8 psi boost. A pulley that small might not be possible so if you take for example 2.9" front pulley (I don't know what size the stock was), you need 1:1.2 ratio in rear. With 3.5"/2.9" pair in rear you will achieve that.
EDIT: Sorry, I calculated that 25% from diameter, not circumference.. If the -25% pulley is 6.9" as a diameter, then you'll be fine with 1:1 rear pulleys and with 3.0 front pulley (6.7 psi).
EDIT: Sorry, I calculated that 25% from diameter, not circumference.. If the -25% pulley is 6.9" as a diameter, then you'll be fine with 1:1 rear pulleys and with 3.0 front pulley (6.7 psi).
Last edited by Juhatee; Aug 29, 2016 at 04:06 AM.
Thread Starter
Instructor
Joined: Jul 2016
Posts: 107
Likes: 0
From: Fort polk Louisiana
When rear pulleys are 1:1, you will need 2.4" front pulley to achieve 6.8 psi boost. A pulley that small might not be possible so if you take for example 2.9" front pulley (I don't know what size the stock was), you need 1:1.2 ratio in rear. With 3.5"/2.9" pair in rear you will achieve that.
EDIT: Sorry, I calculated that 25% from diameter, not circumference.. If the -25% pulley is 6.9" as a diameter, then you'll be fine with 1:1 rear pulleys and with 3.0 front pulley (6.7 psi).
EDIT: Sorry, I calculated that 25% from diameter, not circumference.. If the -25% pulley is 6.9" as a diameter, then you'll be fine with 1:1 rear pulleys and with 3.0 front pulley (6.7 psi).
You are a lifesaver. I was going to just gradually start putting smaller ones on until I found my desired boost level (which would have gotten expensive)
