Sticking GM parts onto my 4.0 swapped 86 (M62 supercharger install)

[holyford86]

I just finished up my GenV M90 from GTP onto my '98 4.0 OHV, Here. The problem I am facing sounds similar to yours. I am running the 3.8 stock pulley, but I cannot get any boost.
After looking into it, the stock 3800 has a 7" harmonic balancer. The 4.0 OHVs have 5.79 - 6". I am thinking this is the main issue. The 3800 comes with a ratio of 1.85. When swapped to a 4.0, it sits at ~1.58.

When you were running the stock pulley on yours (getting 1lbs), how did your truck perform? Could you even tell the SC was on there?

I was at atmospheric pressure with the stock pulley, the math told me that's roughly where I would be though. I'm running a 2.2 inch pulley now which maxes the blower rpm rating at redline and I'm getting between 5 and 6.5 depending on air temps and density now. I'm looking to get it rebuilt and may need to up the pulley size at that time but I'll see.

 

[Manscout]

I was at atmospheric pressure with the stock pulley, the math told me that's roughly where I would be though. I'm running a 2.2 inch pulley now which maxes the blower rpm rating at redline and I'm getting between 5 and 6.5 depending on air temps and density now. I'm looking to get it rebuilt and may need to up the pulley size at that time but I'll see.

Thanks for the reply! How did you figure your "math" out? Did you use a resource or site? I understand all the physics well, but I'm crap when it comes to actual numbers. I'd like to know before I go throwing money at pulleys.
Because I am using an M90 from a 3800, I have to use a 1" offset pulley. So, I cannot just use a keyed, stock style.

 

[holyford86]

Thanks for the reply! How did you figure your "math" out? Did you use a resource or site? I understand all the physics well, but I'm crap when it comes to actual numbers. I'd like to know before I go throwing money at pulleys.
Because I am using an M90 from a 3800, I have to use a 1" offset pulley. So, I cannot just use a keyed, stock style.

I don't recall what site it was, but it had calculators for pulley size and boost, was quite helpful. It was off slightly, mostly due to the numbers I input but I ended up with one slightly larger pulley that proved to be a touch too large for the boost level I was after.

 

[Manscout]

OK. I have used a few that I found online too.
I just found your old post: HERE that basically says exactly what I was saying. And I never see boost till over 4k. Weirdly, my GenV never whines like I would expect the way yours does in your video. I'm looking for that boost around 2000-2200 too.

 

[holyford86]

OK. I have used a few that I found online too.
I just found your old post: HERE that basically says exactly what I was saying. And I never see boost till over 4k. Weirdly, my GenV never whines like I would expect the way yours does in your video. I'm looking for that boost around 2000-2200 too.

Hahaha, that's from when my buddy put an m90 on his 4.0 powered truck, (truck now has a 5.0) the m62 I'm currently using starts building boost at 1500 rpm ish, which is what I wanted. The truck is like a tractor at low rpm, it's nuts.

 

[holyford86]

Well, a little more than another year and about 5k has passed and not much has changed. Truck is still running around 5 to 6 psi of boost reliably and nothing related to this setup is causing problems as of yet. I'd like to get the charger gone through but don't know who I should trust (does anyone have any input?) I've also toyed with seeing if it's possible to swap the Nissan rotor pack into my housing but can't find a solid answer on if it's possible. I've wheeled it a bit this year and with a hand throttle for easier modulation of the throttle it's great and almost impossible to stall at low speeds. boost starts right off idle at 1200 rpm which has proven to be quite handy. Hopefully the air intake will be finished up this spring and I'll post some updates, I decided to go with a simple but (hopefully) elegant idea.

 

[Manscout]

boost starts right off idle at 1200 rpm which has proven to be quite handy.

I appreciate the update! I've gotten about 5k on mine since Sept. with the only issue being I cannot get over 3k RPM.
Are you running the vacuum bypass valve on your setup? I have it working on my M90, but I wish it closed around 50% throttle instead of around 80%.

 

[holyford86]

I appreciate the update! I've gotten about 5k on mine since Sept. with the only issue being I cannot get over 3k RPM.
Are you running the vacuum bypass valve on your setup? I have it working on my M90, but I wish it closed around 50% throttle instead of around 80%.

I can run right up to limiter on mine without issue. The bypass valve starts closing at around 1/4 throttle depending on how I drive it.