3.8L supercharger?

[Anonymous]

I was looking on ebay for a fairly cheap supercharger and the 3.8L superchargers are going for about 150.00 or 250.00 via 'Buy It Now' with a smaller pully u could probly get about an extra 3 pounds of boost i guess...any idea how much boost these superchargers put out?

 

[rickwrench]

Those are Eaton M90's.
http://www.automotive.eaton.com/product ... rs/M90.asp
This page shows the flow at various psi and rpm.
The Eatons used on OEM engines all have a bypass valve. The supercoupe's is external, while the 3800 has it built into the blower casting. Take note of the intake temp vs psi. Great superchargers, easy to rebuild.
Rick(wrench)

 

[Anonymous]

Thanks Rick, I appreciate the quick reply.

I was wondering where the bypass valve would be hooked up to on a carburated engine?

The Eaton supercharger system incorporates a specially designed bypass valve, which is actuated by a vacuum motor near the throttle body, and recirculates the supercharger air flow when boost is not required. During typical driving conditions, the engine is under boost around 5% of the time, which means the remaining 95% of the time the engine is under vacuum, allowing for better fuel economy and a quieter ride

I'll see if i can snag one of these in a few weeks if there are any for sale then.

nice to see that its used on 5.0L engines too

 

[rickwrench]

Use a blow through setup and you'll be fine. I've ranted before about the perils of draw through on a roots type blower... tick, tick, tick, BOOM.
The bypass system is pre-carb in the intake tract on a blow through. It just recirculates air through the blower to let it freewheel when the engine is not under load.
Rick(wrench)

 

[MustangSix]

Rick, draw thru roots blowers are the classic! That's been the standard for over 80 years.

Blown Alfas, Bentleys, and Mg's of the thirties were all draw thru, many with crank driven blowers that sat between the front frame rails with the carb at the nose of the car. Note the twin SU's behind the mesh screen.

MG race cars of the thirties used them very successfully. Again, crank driven with the SU dashpot visible in the opening.

Shorrock, Wade, Judson, and Potvin all made superchargers for MG's thru the 50's. Here's a pic of a Austin Healey Sprite Supercharger by Jusdon with a Holley carb.

Even today, there are draw thru blower kits on the market that are simple and work well as on this MGB.

Here's an Eaton adapted to a TR6.

There are definite limitations in boost and CR, but it can be a very workable system if properly designed.

 

[MustangSix]

Here's another great shot I found of a Potvin blower. This is a 6-71 Roots on a 371 inch Olds.

And a Potvin 392 Hemi. In both these photos, the round plate on the side is the popoff valve. when blower pressure exceeded the spring pressure, it would simply vent fuel air mixture to the atmosphere!

As Rick pointed out, there are dangers. Not all the installations were successful. Here's a pic of the Chrisman/Cannon Hustler on the cover of Hot Rod mag showing the way the blower was originally added. Art Chrisman used a reconfigured Hallcraft boat V-drive as an overdrive coupling. The large duct to the intake ports was going to contain an intercooler eventually, but a large back-fire interrupted those plans, and demonstrated one of the drawbacks of the front-mounting system - a high-volume plenum filled with an explosive mixture. The next time the Hustler ran, the blower was mounted on top of the engine!

 

[addo]

Some cool pics there. Love the vintage Clay Smith T-shirt in the last one! You been raiding the HAMB archives?

I have a reservation about draw-throughs regarding the nature of city/suburban driving. Fast, slow, hot, cold - operating conditions can vary so much in a regular drive through town. The closer you get to steady-state operation, the better they should be in safety.

That said, I have seen an original supercharged MG J2 (I think) driven in suburban traffic by a little old lady.

 

[MustangSix]

H.A.M.B. among others. 'Ol Hokey is one of my favorite places.

I had the pleasure of driving a 1934 K3 Magnette for a mile or so. It had a blower and a Wilson preselector, and was a joy to drive!

In spite of the draw thru system and the tremendous distance from the blower to the engine, lag was not a problem and neither was startup. It looked similar to this one.

In fact, the only real issue with driving the car was gettng used to the Wilson. Preselectors are a different kind of animal.

 

[rickwrench]

Like Addo, my reservations are for daily driving a draw through system. Without a doubt draw throughs are the old school ticket for WOT performance, drags and the like. Low intake velocities do lead to puddling and fuel dropping out of suspension with roots blowers. Turbos, on the other hand, seem to be fine. Must be the 40,000 rpm hot blades atomizing everything that touches them!
Great pics!
Rick(wrench)

 

[Anonymous]

Love the pics. Looks like a blow through setup it is then...It would sure suck if i went to start up the car and show my buds and it blew up on me

 

[Anonymous]

The Eaton M90 will NOT work in a suck through setup, the rear case bearing are not sealed and the grease could get "washed out" by gasoline. I have a 90' supercoupe which has 3.8L with the M90 stock, it makes 12-14psi boost stock depending on the air temp/air pressure. I was thinking about building an upper intake for my 4.9EFI but the M90 is just too small for a 300 CID engine (would work ok on a STOCK one up to about 6psi and 4000rpm)

 

[Anonymous]

the M-90's are supposed to work up to a 5.0L engine though or is that still only running about 5lbs boost on a stock engine?

 

[Anonymous]

my friend has an M90 kit on his 4.6L SOHC modular ford engine, at 6 psi it cranks out alot of heat, with an 8psi pulley it litterally a toaster and his hp actually goes DOWN on the top end compared to 6psi (proven on a dynojet dyno) he runs faster at the track with the 6psi pulley. the blower is just too over worked on a bigger engine. It would be a GREAT blower for the 200 six though.

 

[MustangSix]

Draw thru seems to work ok on this engine.

 

[Anonymous]

I think i'll head toward the blow thru method, but that hot rod sure looks sweet.

any ideas on pulley sizes for different boost? or would the parts store be able to help with that?

 

[MustangSix]

I think at most parts stores you will only get a stupid deer-in-the-headlights look. :roll:

Boost is a function of many things - load, blower speed, engine speed, pulleys, engine size, VE, manifolding, etc. I think the best bet is to mimic the sizes from a comparable size engine and go from there.

If you used a 3.8 SC blower in a blow thru confiugration with the same size pulleys, you could probably expect roughly the same amount of boost. And that would be a good starting point.

 

[Anonymous]

allright thanks MustangSix. I should be able to order up 3.8L pulleys for certain boost according to specs for the 3.8L from a parts store right? or did they not make different pulley sizes for the 3.8L? i read that a not so great flowing head will read higher boost on the gauge than a high flowing head with the same amount of boost...say i wanted 5lbs boost...and 5lbs reads 8lbs on the gauge..I just want to avoid overboosting. i was thinking 3-5lbs boost on a almost stock engine (with MSD coil and a proper carb for supercharging) and then when i can afford it later i will start buying things like pistons and rockers so that i can run a higher boost later on. Oh and i will be getting a 3 angle valve job and backcutting the intake with some mild port work so it breaths a little better.

 

[rickwrench]

The Eaton M90 will NOT work in a suck through setup, the rear case bearing are not sealed and the grease could get "washed out" by gasoline.

Good point. The rear rotor bearings are just open. I wonder how long until the grease gets washed out in a draw through M90?
Rick(wrench)

 

[MLINE]

Just to note. The the M90 off of a SuperCoupe has a serpentine belt style pulley. So you will need to either find a similar sized v-groove pulley to fit the blower snout or convert your engine to the serpentine pulleys. (probably the earlier). You might want to start with a pulley a little (10-20%) larger diameter than the stock pulley to keep the PSI down. And yes the better the head flows (and exhaust) the lower the pressure in the manifold.

disclaimer: I am by no means and expert.

 

[Anonymous]

the M90 on the SC is also run on a "jack shaft" setup. There are companies out there that will make a pulley for you in what ever ratio you like down to 2.5" (which is as small as will fit on the blower snout). I can't quite remember correctly but the SC is a 2.5:1 ratio from the factory I believe and makea ~12psi boost with pretty crappy flowing heads and restrictive exhaust.