# Twin-Screw'ed MK4 12v VR6



## VR6andCabbyMan (Jan 29, 2008)

Hello everyone, I thought I would share a project I have been working on, on and off, for the past year. 

The car in this build is a 2001 12v VR6 Jetta. The following is a slightly choppy, but hopefully interesting documentation of the progress of twin-screw supercharging my VR6. 

I can't stress enough that this was a test (but successful nonetheless), and therefore, the work may look crappy. I am not an engineer. Now that I have a running prototype, I can go back and make things look nice.

Anyway here we go. 

I am using an IHI produced, twin screw supercharger, from a Mazda Millenia S. The Mazda Millenia S uses a Miller Cycle engine, which leaves the intake valves open halfway though the compression stroke. To make up for the lost compression, Mazda used a twin screw supercharger to compensate. Why they decided to use this engine, I have no idea.

According to what I have read, the IHI twin screw has a displacement of 1.7L.

I have no idea if this supercharger moves sufficient air for the 2.8L VR6 or not, but I wanted to try it and see what happened. 

I also want to note that this build was more of an experiment than a full on build with a finished product in mind. I wanted function, and was not necessarily concerned about form. It's ugly, and definitely could have been more primped and polished. Now that I know the system works I am going to go back and start making things look better, as well as function more efficiently. 

So here is my buddy (pictured) and I trying to find a suitable place for the supercharger. We figured if we got rid of the stock manifold we could position it in it's place.





































Once I had a spot for the blower I had to mount it. 

Here is the mount I made. I used the OEM manifold mounting points to mount the blower.










Then I needed a belt. I used a 105 inch serpentine belt from a Dodge 1500.

Here is the belt next to the stock VR6 serp belt.










I did a mock up test fit, which presented it's own problems. The pulleys in the picture are all VW parts. I ended up using a different (much smaller) pulley for the rear most one.



















Then I needed to make a manifold. I had been trying to decide how I wanted to do this part of the project for a while. I didnt know if I should just go with a short runner or make something different. I decided to try a manifold that integrated everything into one unit. 

I started with a MK3 manifold and a sheet of 6061.














































This is the result:




























All welded with my 110v wire machine and no spool gun.



















The car's ECU has a C2 Motorsports FI stage 2 map and is running 440cc Bosch Green Giants.










Once I had everything together here was how she looked initially:























































Then I did this to the manifold:





































(Don't mind the super nasty looking aluminum welds...)

The crack obviously caused some issues with the way it ran. 

But this was the perfect opportunity to fix a couple issues. One issue was noise. The manifold was an amplifier for the supercharger's whine, which is notorious on twin screw blowers. Secondly, I couldn't adjust the blower at all since the manifold was built to the location of the blower and the lower manifold. And I needed to move the supercharger a little. 

This was my solution:




























And here she is currently. I am still having trouble keeping the belt in the actual pulley grooves of the blower. The belt tends to ride out to a certain spot on the blower pulley and then stay there. I have actually been driving the car for about 3 weeks without moving the belt. It just sits half in the grooves, half on the smooth outer part of the pulley. No slippage at all though. 






































The blower currently makes 8psi (current max) at under 2000 RPM, which is the cool part about twin screws. It holds this pressure most of the way through the RPM range before falling off a little to around 6psi. (My next bug to fix). 

Since I run the TB before the blower I don't "need" a bypass. During idle the TB keeps air from going in, so there is nothing for the blower to compress, and therefore no need for a bypass. I have noticed that at times, the car will hold revs for a few seconds even after lifting off the throttle. I am guessing a bypass would remedy this.

I also took a chance at what kind of pressure the blower would make, and it just happened to max at 8psi, which is what I wanted. Had it made more, I was going to use a wastegate to regulate boost by letting it bleed off excess manifold pressure back to the non-pressure side of the blower. If I get a smaller pulley made I would probably have to use this to keep boost levels controlled since I am running stock compression and no intercooler. 

Which leads me to another issue. The pulley on the blower is not solid, rather it has the outer steel "ring" with the grooves, then a rubber core, and then the inner "center" which is steel and where the bolt holds the pulley to the blower. The rubber core lets the pulley flex and twist which I think is why my belt keeps walking off the center of the pulley towards the outside. I would like to get an aluminum pulley made to take care of this, which will obviously be solid, not rubber cored. 

The car makes great boost off the line and is awesome to drive, especially when you wind it out in 2nd or 3rd and get to listen to that blower whine. Boost holds good until high in the RPM range where it starts to fall off a little. The best part though is just how much it pulls from the get go. It just digs in and pulls hard. No lag, no wait, just lots of power, right from the get go.

So anyway, that is my twin-screwed MK4 VR6.

Videos:

http://youtu.be/IG5ZzeM6qn4

http://youtu.be/fUQfS7Rej5Y

http://youtu.be/ulJ6ojc2ino

I hope to get some new videos showing RPM and boost together, as well as outside driving videos and others, just to give a better idea.

Oh, and here is what you can do with a 110v welder, 100% argon, some aluminum wire and no spool gun:


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## Norwegian-VR6 (Feb 6, 2002)

Very cool build! So nice to see that people try out different setups amd actually goes for it! 


Kristian


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## _muppet_ (Aug 5, 2004)

:thumbup: I see you are local, do you know derek anderson by chance? He lived in butler for a while. He has a vr swapped beetle with a custom eaton supercharger setup on it.


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## VR6andCabbyMan (Jan 29, 2008)

Norwegian-VR6 said:


> Very cool build! So nice to see that people try out different setups amd actually goes for it!
> 
> 
> Kristian


Thank you. I figured I might as well try it. I hadn't seen anyone use a twin-screw on a VR6 before.



_muppet_ said:


> :thumbup: I see you are local, do you know derek anderson by chance? He lived in butler for a while. He has a vr swapped beetle with a custom eaton supercharger setup on it.


No, I don't know him. Pretty cool he lived close by though. Although about a month ago I found his videos on YouTube. His set-up is very very clean looking. Much nicer than mine. With that Beetle hood he was able to do what I couldn't, which is mount the blower atop his manifold. That would make everything much nicer, simpler, and clean looking. I am guessing he also ran a dedicated belt for the blower. I'd love to see his set-up up close sometime. 

However, his blower is an Eaton, which is a roots style charger, a little different from mine which is a true twin-screw.


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## Pat @ Pitt Soundworks (Nov 14, 2008)

Very cool project. If you want to get a final manifold design tigged up, I'm in cranberry. :thumbsup:

Sent from my HTC ThunderBolt using Tapatalk 2


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## VR6andCabbyMan (Jan 29, 2008)

Pat @ Pitt Soundworks said:


> Very cool project. If you want to get a final manifold design tigged up, I'm in cranberry. :thumbsup:
> 
> Sent from my HTC ThunderBolt using Tapatalk 2


Thanks man. Good to know you are close by. I will probably end up changing the manifold again, and may end up just having a regular SRI made from the lower runners. This will make it easier if I want to run an intercooler. If I do I will get in contact with you.:thumbup:



I want to know if anyone here has some advice. I am losing boost higher in the RPM range. Could this be because the superchager can't keep up with the engine? As in, could the engine be using more air, than the supercharger can compress? Or am I thinking too hard about this?


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## jettred3 (Aug 5, 2005)

What are your iats, vagcom?¥


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## VR6andCabbyMan (Jan 29, 2008)

jettred3 said:


> What are your iats, vagcom?¥


Not sure yet. I have VAG-Com, but haven't been able to run the car with it hooked up yet.


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## Pat @ Pitt Soundworks (Nov 14, 2008)

That's pretty norm for positive displacement chargers, from what I've seen. Only way around it is a bigger charger, or smaller pulley with a pressure relief valve


Sent from my HTC ThunderBolt using Tapatalk 2


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## VR6andCabbyMan (Jan 29, 2008)

Pat @ Pitt Soundworks said:


> That's pretty norm for positive displacement chargers, from what I've seen. Only way around it is a bigger charger, or smaller pulley with a pressure relief valve
> 
> 
> Sent from my HTC ThunderBolt using Tapatalk 2


Interesting, thanks for the info. I was planning on having an aluminum pulley made up that is a little smaller anyways, so not a big problem I guess.


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## Rod Ratio (Jun 6, 2012)

.


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## mike minnillo (Sep 23, 2007)

Awesome setup! Would love to see some numbers on this. I could only imagine that the blower must get heat soaked like crazy...


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## VR6andCabbyMan (Jan 29, 2008)

mike minnillo said:


> Awesome setup! Would love to see some numbers on this. I could only imagine that the blower must get heat soaked like crazy...


Thank you! No numbers yet, but if/when I get all the bugs worked out I would like to get it strapped to the dyno so we can all see what the torque curve looks like.

Yeah it does get pretty heat soaked. The entire engine bay is much hotter than it used to be. I can feel it if I pop the hood after driving.

Before I added the blower, and the engine was stock I never saw the temp gauge move past 190, even on very hot days or heavy abuse. 

After the blower was added, I took the car for a drive and let it idle for about 5-10 minutes at my destination to see how it would handle long idling. Before 10 minutes were up she was starting to get hot and the temp gauge started rising slowly. I got moving and back down the gauge went.

The biggest issue I am currently having with the car is the sound. The blower is so loud that I dont want to drive it through my neighborhood. I could tell my neighbors were starting to get annoyed by it. Luckily I got my daily MK1 Jetta Coupe back on the road, so I can focus on this car again. 

The high pitch whine is incredibly loud, in part because of the manifold design I think. It amplifies the sound. I also need to think about intercooling. This is going to require a rebuild of the intake manifold once again, which will hopefully kill some of the sound.


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## Issam Abed (Feb 12, 2004)

Cool project. Kind of pointless to mention this now but I am willing to bet that manifold cracked because you tried to secure the supercharger to it while having it hang off 2 M10 bolts from the back of the head.


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## mike minnillo (Sep 23, 2007)

For inter cooling, I would imagine you could do an a/w + sri setup similar to those on vrts, sine the outlet on the blower is close to the same location as most turbo outlets would be.


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## VR6=StrongLikeBull (May 28, 2012)

This is the coolest thing EVER!!!!

I've wanted a twinscrew for my 01 VR6 jetta FOREVER!!!
if we can figure out a better intake mani, i seriously would consider paying you to build me a kit 
Seriously!

Thanx for trying this for all of us... you da bomb!


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## VR6andCabbyMan (Jan 29, 2008)

Issam Abed said:


> Cool project. Kind of pointless to mention this now but I am willing to bet that manifold cracked because you tried to secure the supercharger to it while having it hang off 2 M10 bolts from the back of the head.


 Thanks. 

I can guarentee you the manifold cracked for that very reason. I knew it was a possibility when I did it. With the engine torquing that blower belt it was really stressing the manifold. 



mike minnillo said:


> For inter cooling, I would imagine you could do an a/w + sri setup similar to those on vrts, sine the outlet on the blower is close to the same location as most turbo outlets would be.


Yeah this would be the best option since the belt basically blocks me from running piping down the passenger side of the engine. 



VR6=StrongLikeBull said:


> This is the coolest thing EVER!!!!
> 
> I've wanted a twinscrew for my 01 VR6 jetta FOREVER!!!
> if we can figure out a better intake mani, i seriously would consider paying you to build me a kit
> ...


While researching this project I noticed that quite a few people have talked about twin screwing a vr6 but it didn't seem like anyone had tried it. I figured someone should bite the bullet and see what happens. Hopefully I can continue the testing for everyone else.


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## Bigsmooth311 (Oct 13, 2012)

*Fantastic!*

Well done. It's refreshing to see this build and I can only imagine the time and effort you put into it. You are a pioneer!


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## VR6andCabbyMan (Jan 29, 2008)

Bigsmooth311 said:


> Well done. It's refreshing to see this build and I can only imagine the time and effort you put into it. You are a pioneer!


Thank you very much!:thumbup:


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## VR6andCabbyMan (Jan 29, 2008)

Small update: 

I hated the excessive amount of noise that was coming from the supercharger, which was being amplified inside the manifold. The car was embarrassing to drive, since it sounded like a bearing was going out on something and it was past the point of being a cool supercharger whine. So I pulled off the intake manifold and decided to rebuild it, for the third time. This time I wanted to build a more traditional short runner in the event I want to switch to a turbo. 

I also recently acquired a TIG welder and plasma cutter, which meant I needed a reason to mess around with those fun toys. This was the perfect opportunity. 

I didn't take many progress pictures since I am in a hurry to get the car back on the road, but here are a few things. 

Since I just started TIG welding some of my welds are weird and crappy. Some are pretty good. I'm starting to get a feel for how the puddle flows. On a MIG you make the puddle strictly with the material coming out of the gun. With a TIG you make the puddle with the torch, but then have to add to the puddle with material... Anyways, some of it looks like crap, but I threw some close ups of the good stuff. 
































































As we currently stand. 











I'm hoping the piping, and distance help kill some of the noise.:thumbup: 

If this works, I might have a smaller pulley made up.


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## Pat @ Pitt Soundworks (Nov 14, 2008)

I don't see it in the pictures, but do you have a relief valve installed for the super charger? That'll quiet it down a TON


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## VR6andCabbyMan (Jan 29, 2008)

Pat @ Pitt Soundworks said:


> I don't see it in the pictures, but do you have a relief valve installed for the super charger? That'll quiet it down a TON


 
You mean like a diverter valve? I have a Forge diverter valve sitting here that a friend gave me, but I've never put it on the car. Since the I put the TB in front of the supercharger I didnt technically need to it, but I guess you are right, it might get rid of some of the noise. I think I am going to try that, thanks. :thumbup:


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## Pat @ Pitt Soundworks (Nov 14, 2008)

Yeah a diverter valve is needed even with the tb before the charger. As long as you vent before the blades to after, and not vent to atmosphere, it'll be alll good

Sent from my SCH-I535 using Tapatalk 2


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## VR6andCabbyMan (Jan 29, 2008)

Finally got the manifold built and back on the road. Ran it for the first time today and looks like I am holding boost longer and actually gained a couple psi. I'm topping at 11psi now, which is a 3psi gain. I am guessing that is because the old manifold leaked like crazy.

I didnt add the diverter valve yet, as I wanted to see if the manifold alone would cut down on the noise for test purposes. The noise levels have gone down, but the high pitch whine is still a little more than I want. So I will add the diverter valve to hopefully help with the noise, as [email protected] suggested.

I also bought a Podi boost gauge so I will try to take some video to show boost to RPM comparisons soon.


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## Rod Ratio (Jun 6, 2012)

How does it 'feel' though?


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## VR6andCabbyMan (Jan 29, 2008)

Rod Ratio said:


> How does it 'feel' though?


Initially I would have to say it feels slightly less responsive compared to the other manifold, but that could just be in my head. Overall it feels awesome because it pulls very hard from down low, but seems to be keeping up in the high RPMs as well, which seemed to be a problem with the other manifold. 

Its hard to compare to my ABA 16v turbo Cabby since the turbo is way too oversized on that car and spools very late, but I'd like to think it has much more down low pull. 

I didnt get to really check the psi to RPM "ratio" with the new manifold yet, so until then I wont know if I lost a little responsiveness because of the piping or not.


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## Rod Ratio (Jun 6, 2012)

Cool. 'Seems' like a cool setup. I was never a fan of centrifugal blowers myself. Might as well use a turbo IMO.

I'm going to assume that it'll run better/smoother with the DV plumbed in as well


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## VR6andCabbyMan (Jan 29, 2008)

Rod Ratio said:


> Cool. 'Seems' like a cool setup. I was never a fan of centrifugal blowers myself. Might as well use a turbo IMO.
> 
> I'm going to assume that it'll run better/smoother with the DV plumbed in as well


You are right, this setup "seems" like a cool setup, but in all reality, I'm still on the fence about it. Maybe if this was a brand new Ken Bell or Whipple twin-screw and I had more time to do things right, I'd be more excited, but this old Mazda blower is not the best. Frankly, I just wanted to see if I could do it, and if it would work. I'd like to remake a lot of the stuff I had to build myself, like the pulley bracket and supercharger mounting bracket. They are ugly, and not even painted. But I didnt know if any of this would work when I started, so I didnt want to get too involved until I knew it would even run correctly.

This car is supposed to be my daily also, so I had to speed things up just to get it back on the road. I hate running my MK1 Jetta Coupe in the winter. 

As far as the DV, yeah more than likely it will run a little better, especially at idle and light throttle. 

What I havent figured out yet, which may be solved with the DV, is sometimes at low RPM cruising speeds I will mash the pedal, watch the boost rise, but the engine hesitates momentarily. I know the boost is going to rise no matter what since when I mash the pedal the TB opens, letting boost start to immediately build. What I dont understand is why the hesitation, other than possibly the fact that the computer cant compensate the sharp rise in boost with enough fuel?

I dont know, so anyone's input would be appriciated.


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## skydaman (Dec 16, 2005)

Pretty cool, I dig stuff outside the norm. :thumbup:


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## angelod307 (Aug 16, 2007)

VR6andCabbyMan said:


> You are right, this setup "seems" like a cool setup, but in all reality, I'm still on the fence about it. Maybe if this was a brand new Ken Bell or Whipple twin-screw and I had more time to do things right, I'd be more excited, but this old Mazda blower is not the best. Frankly, I just wanted to see if I could do it, and if it would work. I'd like to remake a lot of the stuff I had to build myself, like the pulley bracket and supercharger mounting bracket. They are ugly, and not even painted. But I didnt know if any of this would work when I started, so I didnt want to get too involved until I knew it would even run correctly.
> 
> This car is supposed to be my daily also, so I had to speed things up just to get it back on the road. I hate running my MK1 Jetta Coupe in the winter.
> 
> ...


If you are obd2, i don't know. But if you are obd1 i had/have a issue of fuel at 5500 rpm with 10 psi. It cuts the fuel off. Otherwise, pretty cool.


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## Rod Ratio (Jun 6, 2012)

angelod307 said:


> If you are obd2, i don't know. But if you are obd1 i had/have a issue of fuel at 5500 rpm with 10 psi. It cuts the fuel off. Otherwise, pretty cool.


He's in a mk4. It's OBD2


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## 02vwgolf (Oct 6, 2009)

I've been following since you first posted this up, I think it's awesome how you stuck with it and fabbed what you needed to make it work... about 95% of the people on this site would have given up if there weren't "off the shelf" parts available. Also I think the new short runner intake is a lot nicer looking of a setup so I was glad to see it also turned out to be a power increase. Keep up the good work:thumbup:

Sent from my VS840 4G using Tapatalk 2


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## VR6andCabbyMan (Jan 29, 2008)

02vwgolf said:


> I've been following since you first posted this up, I think it's awesome how you stuck with it and fabbed what you needed to make it work... about 95% of the people on this site would have given up if there weren't "off the shelf" parts available. Also I think the new short runner intake is a lot nicer looking of a setup so I was glad to see it also turned out to be a power increase. Keep up the good work:thumbup:
> 
> Sent from my VS840 4G using Tapatalk 2



Thank you!

I wish the stuff I made looked a little nicer, but I guess I can always improve it as I go. :thumbup:


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## ArcticFox (Nov 4, 2005)

Awesome build. Love going on the vwvortex to see people going outside the box.


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## VR6=StrongLikeBull (May 28, 2012)

Seriously... i LOVE this!!!
If you had a better S/C (not even that much better lol) i will pay you for a setup like this. I've always wanted a TwinScrew on my 01 vr, but no one has really done it well, if you get something you think you could build, by summer i'd be willing to buy a setup off of you if you'd be willing to make one... Thanx for taking the reins on this buddy


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## stroker6pack (Aug 23, 2007)

*VR6 Supercharged*

Nice work, I think your supercharger is way too loud, maybe something wrong inside of it?
Eventually you will need a intercooler for future reference.
For those who never saw a VR with a twin supercharger....here is my set up.







*My 2nd supercharger in black and new belt set up 8 rib*


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## stroker6pack (Aug 23, 2007)

*VR6 Supercharged intake manifold*

*I had the same problem as you with the intake manifold cracking....mine cracked from the sheet being too thin and I grinded too much of the welds.....I have a thicker sheet now and figured a new way of doing it this winter.*


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## VR6andCabbyMan (Jan 29, 2008)

stroker6pack said:


> Nice work, I think your supercharger is way too loud, maybe something wrong inside of it?
> Eventually you will need a intercooler for future reference.
> For those who never saw a VR with a twin supercharger....here is my set up.


Awesome setup. Much nicer looking than mine. 

What supercharger are you running currently, and how much boost? At what RPM do you have full boost?


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## stroker6pack (Aug 23, 2007)

VR6andCabbyMan said:


> Awesome setup. Much nicer looking than mine.
> 
> What supercharger are you running currently, and how much boost? At what RPM do you have full boost?


The supercharger is from a 1990 Ford Thunderbird with a 3.8 V-6.
I have 2 superchargers with different set ups( porting & coated rotors)
my silver one has about 10-11 lbs boost...my black one has about 8 lbs boost.
I have full boost at any rpm, as soon as i floor it, full boost kicks in
As for your pressure dropping at hi rpm, it my be caused by belt slipping, I have the same problem sometimes at hi rpm and I hear it slipping slightly....kind of hard to hear it with the whine of the supercharger under boost.

I will try to download a video....see how quiet at idle.


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## stroker6pack (Aug 23, 2007)

*Here is a video*


http://youtu.be/un025arf2_0

http://www.youtube.com/watch?v=un025arf2_0


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## VR6andCabbyMan (Jan 29, 2008)

stroker6pack said:


> The supercharger is from a 1990 Ford Thunderbird with a 3.8 V-6.
> I have 2 superchargers with different set ups( porting & coated rotors)
> my silver one has about 10-11 lbs boost...my black one has about 8 lbs boost.
> I have full boost at any rpm, as soon as i floor it, full boost kicks in
> ...


Very nice. Much quieter than mine.

So you are running an M90 Eaton? That would be a roots type supercharger, which is similar in look, but different in operation to the twin-screw supercharger, which is what I am running. 

Either way, your setup is very similar in orientation, which I am glad to see someone else has had success in.

Looks like you also have a dedicated belt just for the blower, which runs off the alternator. Did you have a custom pulley machined for that?


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## Slayer (Aug 8, 2000)

time to get some cogged pulley setups to stop the slipping


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## mldouthi (Jun 26, 2010)

Great build. I love seeing builds like this, home built. I would love to get my hands on a twin screw charger (for a reasonable price). I have a M62 (roots) supercharger on my 2.5 rabbit right now and love how it pulls, but the increase pressure and cooler temps would be great. 

Also nice work on the first tig project. :thumbup:


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## Dubstuning (Nov 1, 2007)

Love seeing builds like this :thumbup:


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## stroker6pack (Aug 23, 2007)

VR6andCabbyMan said:


> Very nice. Much quieter than mine.
> 
> So you are running an M90 Eaton? That would be a roots type supercharger, which is similar in look, but different in operation to the twin-screw supercharger, which is what I am running.
> 
> ...


Yes it is a M90 roots style. The 2nd pulley on the alternator I welded it on the inside...so far so good.


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## GT-ER (Feb 23, 2005)

This is definitely an awesome project. A couple of things that I should mention are the following. 

I have not heard your setup but you claim it's noisy, a HUGE portion of the noise ( assuming the supercharger is in good condition ) is simply due to the extremely short intake. I've had plenty of supercharged cars in my life and they were all ULTRA noisy with a short intake, especially the screw type ones at part throttle. 

As for part throttle boost, this is because of you lacking a bypass valve. Rig one up and you should only have part throttle boost on heavy throttle. This will also allow for more timing in part throttle and better fuel economy.

Also, your setup is PERFECT to install a liquid to air intercooler between the charger and the plenum. You should take advantage of it since superchargers, even screw types, blow molten lava even at low boost ( and 11psi isn't exactly low boost ). AMG uses intercoolers on their supercharged setups and they run moderately low boost yet it makes a HUGE difference. I've seen a 70* intake temp drop from replacing an bad intercooler pump and running only 11psi.

And last, if you can install an idler pulley close to the superchargers drive pulley you will have a decent amount of more belt wrap. There is only so much you can do with a 6 rib so you need as much wrap around as you can get.

Also, for anyone interested in following and doing such a setup...an E55 AMG supercharger is 2.1L and will be good to about 550whp. They aren't cheap ( about $800-$1000 used ) but they are ultra reliable and will turn your VR into a BEAST.


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## Mlawton13 (May 28, 2014)

*That intake!*

How exactly do you have that intake set up? T/b then what is that piping exactly? I'm trying to get my setup going but am unsure how to run it exactly.


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## stroker6pack (Aug 23, 2007)

*New intake update*

*Finally got the time to do my new intake from my last project. All good no more misfires from the short runner intake.*


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