5.9 magnum with M122 blower/intercooler

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Understood. I did realize that was a mock up but wondered why there was so much offset (while also running an idler pulley). Your tensioner sounds very adaptable and adjustable and offers some real benefits in addition to tensioning. What brand / model is it if you don't mind me asking?
 
For comparison, I run a 6-rib with no idler pulley and a tensioner that is barely offset. The 6 rib is what my Magnuson came with.
 
UZswapBarge said:
10

12L Cummins ISX Diesel
But I do also want to know the part number if possible
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Correct.
The part number for the tensioner is 89440 and it'a a Dayco.
The tensioner came with a flat pulley for a 12 rib which was *HUGE* and ridiculously heavy.
I swapped it for a 10 rib double-bearing idler from a Volvo truck that I got off ebay for cheap.

But it seems that any of the 10 rib double bearing truck idlers are the made to the same spec/dimensions.
Which makes sense for heavy duty commercial vehicles that require a lot of maintenance, common parts for many vehicles.

I have an aluminium version of the double bearing idler on my shelf full of parts, i think from memory i got it from american racing solutions.

Any supercharger belt tensioner should theoretically have better action with a lighter idler pulley.
Here's a cool video of a drag car showing the abuse a tensioner has to endure during staging on a two-step, and how much a belt stretches under the horsepower.
Real eye opener!

 
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I think this may be my final mock-up in plywood before starting to fab things out of steel and aluminium.
It's not pretty, but with any luck it can all work and be reliable.

Screenshot_20231105_015645_Gallery.jpg
 
Also I took a pic of the tensioner mounting hub to show how it can be clocked for setting up the desired angle and preload.

You can see that each number consecutively moves the tensioner alignment a few degrees counter clockwise.

Screenshot_20231105_021214_Gallery.jpg
 
earlymopar said:
For comparison, I run a 6-rib with no idler pulley and a tensioner that is barely offset. The 6 rib is what my Magnuson came with.
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6 Rib will have a lot more parts availability and belt lengths. But may slip under lots of load at high rpm.

What size is the magnuson blower and what size pulleys are you running?

The bigger you can run both (crankshaft and blower) pulleys the better, it essentially increases surface area and mechanical leverage on moving the belt, and the only downside is increased belt speed. Which is an excellent trade-off

I went with the 10-rib since that was what the factory used on the gt500 for this blower.

I went with the cummins ISX tensioner after looking at prices for an aftermarket gt500 blower tensioner and deciding that anyone who spends $400+ for a shiny billet tensioner needs their head examined.
I think I got the cummins unit for $79 USD at the time and it probably has 50% more tension and will live twice as long as their shiney one.
 
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I opted to take the path I did so as to have the smallest belt surface area and tensioner force to minimize parasitic loss but without getting into belt slippage. Belt type is another factor in what you can get away with. No issues with belt slippage but if I ever see that I'll increase tensioner force. Mine is a 3 lobe model 112 with 3.4" & 5.375" pulley diameters (6 psi). The 6 rib pulley is what the Magnuson comes with. This is an older picture. I don't have any front-view pictures showing the support bracket and tensioner or belt to pulley path.

CIMG1164 (2).JPG
 
earlymopar said:
I opted to take the path I did so as to have the smallest belt surface area and tensioner force to minimize parasitic loss but without getting into belt slippage. Belt type is another factor in what you can get away with. No issues with belt slippage but if I ever see that I'll increase tensioner force. Mine is a 3 lobe model 112 with 3.4" & 5.375" pulley diameters (6 psi). The 6 rib pulley is what the Magnuson comes with. This is an older picture. I don't have any front-view pictures showing the support bracket and tensioner or belt to pulley path.

View attachment 1716162143
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That's super cool.
What are you changing? It looks quite well sorted.

6 rib should be fine for those pulleys, that m112 blower is capable of a lot more if you ever choose to spin it harder though.

Since you were asking about snouts a few posts back, the closest thing I know of to a snout of that length is a jag one. I used to see them on ebay from time to time a few years back, they're a bit rare but they're out there.
I dont have one here to measure.
I did find this though.
Eaton SC Snout length - Rennlist - Porsche Discussion Forums
 
I hate to rain on your parade, but I doubt the small wrap you have on the alternator is going to provide enough friction for that. What is item bottom left, power steer, or scavage pump? Same deal. You might be able to fix both with backside idlers, pulling longer belts in to wrap them better

this looks like a VERY interesting project
 
You may be right. The alternator gets about 90 degrees of belt wrap.
The power steering pump gets a little less, but it's a much larger pulley, so contact area is probably more.
I'll take the gamble.
If they slip and squeal terribly I'll come up with a more complex serpentine setup later.
Also I've never seen a V-belt with a tensioner on the outside of the belt.
I think it would probably kill it pretty quickly since they're not designed to flex the opposite direction.
 
frosty_the_punk said:
That's super cool.
What are you changing? It looks quite well sorted.

6 rib should be fine for those pulleys, that m112 blower is capable of a lot more if you ever choose to spin it harder though.

Since you were asking about snouts a few posts back, the closest thing I know of to a snout of that length is a jag one. I used to see them on ebay from time to time a few years back, they're a bit rare but they're out there.
I dont have one here to measure.
I did find this though.
Eaton SC Snout length - Rennlist - Porsche Discussion Forums
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I'm currently not changing anything other than adding a Progression Ignition distributor mainly so that I can retard timing with boost. I have a new engine ready for cam break-in and then I'll swap out the current engine for the new. A lot of fun. On the snout, after I had my supercharger mounted and had taken measurements I contacted Magnuson and bought a correct length snout from them.
 
earlymopar said:
I'm currently not changing anything other than adding a Progression Ignition distributor mainly so that I can retard timing with boost. I have a new engine ready for cam break-in and then I'll swap out the current engine for the new. A lot of fun. On the snout, after I had my supercharger mounted and had taken measurements I contacted Magnuson and bought a correct length snout from them.
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Nice one.
Is there a build thread on here? I had a look around I can't seem to find one.
Would love to see/know more about it. should be a real beast with big-block-like torque output.
 
Sorry. I didn't do a build thread. I'm not good at taking the time to take pictures or to document things well enough for them to be clear.
 
8 years ago, I started out with a similar plan to how yours has ended up. I modified an aftermarket manifold with a plenum I made and was planning to run an intercooler in. However the height of the initial assembly was too tall and violated my rule of clearing the hood. That's when I changed course to the current manifold and air cleaner shown above. I have water-methanol injection I'll play with later on the new engine.

Poly with Magnuson.jpg
 
Very cool build. I’m curious if you are going to dyno it. I have a B&M 162 on a 408 and it’s actually too small. But it does work.
 
Probably not just due to the added cost. With my new engine I've calculated 450 HP without the addition of water methanol. This is nothing by today's standards but not bad for "old technology" & 323 C.I. The design of the Magnuson is more efficient than a traditional roots supercharger in that it generates far less heat and only requires 1/3 of 1 horsepower to operate (compared to 25 H.P. or more for a roots style). Due to this and the 3 lobe design, it is very common to see small displacement superchargers on larger engines that appear to be mis-matched or undersized.

I can't speak to your 408 and 162 combo without knowing head, valve, manifold and carburetor details at a minimum but that should be a really fun combo when sorted out.
 
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