Install SN-60 / R3 Airbox

GM350 c.i.d / R3 Studebaker-Paxton Supercharger Installation

Engine Jasper Class II, (special build by Jasper Engines & Transmissions, Jasper, Indiana)
350 CID (balanced)
4-bolt main bearings
8:75::1 compression
Silvolite hypereutectic pistons
Dart heads, 2.02 / 1.94 stainless steel valves
268 degree duration cam
Forged steel crankshaft
..... Output Power Rating - 330@5800 without supercharger.

Paxton - SN-60 (Special build by John Erb, United Engines & Transmissions, Carson City, Nevada)

4 inch belt pulley - 6 inch crank pulley
High rate internal spring pack
High output impeller
Mounting kit: Paxton (88 Avanti Anniversary model)(modified)
Supercharger Bracket: Paxton Catalog #1111500, Casting # 38818
Idler assembly: Paxton Catalog #1111600 (Mount used, pulley changed / 1 added)
Crank pulley: GM 6" accessory pulley (modified)

Hardware kit to mount to 350 engine

Bolt 1 - 6 Ό " X 3/8 " coarse / Top bolt, connecting blower mount to small ‘L’ bracket of 3/16 " flat steel fastened to 1st intake manifold bolt and bent up to present a perpendicular mounting surface to bolt. . 4 1/8 " thick wall spacer between blower bracket & manifold ear. ( nuts, washers, lock washers)

Bolt 2 - 6 Ό " X 3/8 " coarse / Top water pump bolt to Paxton mount. 2 3/16 " thick wall tubing spacer. ( nuts, washers, lock washers)

Bolt 3 - 6 ½ " X 3/8 " coarse / Bottom water pump bolt to Paxton bracket. 2 3/16 " thick wall tubing spacer. ( nuts, washers, lock washers)

Bolt 4 – 1 " X 3/8 " coarse / Attaches lower outer (fender side) Paxton mount to 1st exhaust manifold bolt thru a 1 " X 8 " inch piece of flat 3/16 " steel , bent & drilled for bolt thru at mount and welded to a two inch piece of thick wall tubing for a 3 ½ " exhaust manifold bolt. ( nuts, washers, lock washers)

The supercharger is fastened to the bracket using three 5/16 " allen head bolts which pass through the bracket and thread into the supercharger body. A 4th hole in the bracket uses one of the supercharger bolts as a locating pin and fits around the head of the bolt.

The Paxton mounting bracket (rear shown above ), Paxton casting #38818, part # 1111500 was designed around a GM small block engine. Since the bracket was not designed with the Avanti in mind, Minor modifications in spacing & location were required to fit it to my 350 engine. Longer mounting bolts were used with thick wall tube spacers to adjust the mount forward and bring the drive pulleys into alignment. In the above picture, the lower left corner shows 4 mount holes of which the 1st and 3rd were used. The only other 2 attachment points are the upper most left to the intake manifold and the lower most right to the exhaust manifold. Three bolts retain the blower with the hole on the lower left of the orbit being used only to locate a bolt head. The Paxton triple-pulleys ( idler & crank ) which use three 7 MM mini-belts were discarded for deeper groove standard dual pulleys.

The location of the dual v-groove idler pulleys on the front right side of blower mount required that a small area be removed from the fan shroud (2" X 3/16") to allow adjustment back and forth. The crank pulley is a modified 1975 GM dual accessory pulley from a 350 engine. There is a 1 " billet spacer at the rear of the pulley to bring it out enough to align with the Paxton and idler pulleys. Three grade 8 periphery and 1 grade 8 center bolts attach the crankshaft pulley. The following is a sketch of the Paxton mounting schema.


Sketch of the mounting bracket


Sketch of the Belt Travel
I added a flat side roller pulley (Point E)to increase the belt wrap around the pulley and prevent belt spin off

Side A – B (10.25 ") A – D (5.5 ") D – E (4.0 ")

Side B – C (12.6875 ")

Side C – A (16.28125 ")

The Centerline of pulley (1) is offset by .5 " to Pulley (2) and the distance is 4.5"

Pulley/Belt Diameters: 1) 5.625 " O.D. / 4.5 " B.D. 2) 3.75 " O.D. / 3.0 " B.D.

3) 4.0 " O.D. / 4.4375 " B.D. 4) 6.5 " O.D / 6.5 B.D



Idler (assembly) A - (picture, top) uses two (2), Imperial #231076, v – groove, 3 3/4 inch diameter, 5/8 " I.D. bearing w/ reducer collar.

(Dayco Products, Eaglemotive, Inc. Ft. Worth, TX, ( SKU 36687-31076))

Each pulley has 1 concave side and 1 raised shoulder side:

To fit: Both concave sides must face each other. The mounting shaft on the adjustable Paxton bracket fits the I.D. of the pulley bearing and has a shoulder to seat and align the pulleys with crankshaft & supercharger pulleys. Both concave sides of the idlers must be milled down a small amount to bring the v-groove in the pulleys closer together. This is to reduce the spacing between belts to match the supercharger and crank pulley profile.

Idler A uses the stock sliding Paxton idler mount and adjustment bracket. Fitted to the front right side of the blower mount with two, 3/8 " coarse thread bolts . The pulleys are attached to the bracket using the Paxton supplied 5/16 " coarse thread bolt, locking washers and large anodized outer washer.

Idler B - ( picture, bottom ) Imperial # 231094 5/8 " I.D. bearing w/ reduced collar. Single flat 1 5/8 inch wide roller, 4 " diameter to support rear of belts. Added to top, inboard area of mount to add tension at the rear of the belts as they come off blower and return to crank. Eliminates belt deflection between blower and crank which caused slippage and blower ‘chirp’. Increases wrap around blower pulley and improves operation.



Idler B uses an L - shaped, cast iron offset idler mount from a mid 70's Ford air conditioner application. The base was milled down to achieve a final fit. A 2 " X 9/16 " SAE threaded bolt attaches the mount to the blower bracket and is fastened as the rear with a large copper compression washer and nut. Another bolt, 1 " X 9/16 " SAE thread, attaches the pulley to the idler mount. Since the pulley turns in a direction that will loosen the bolt, Lock-tite was applied to the threads. This idler is adjusted using a Ύ open end wrench to rotate the mount around the central mounting bolt in an orbit fashion. Incorporating two, adjustable idler pulleys also makes the job of changing belts much easier.


Crankshaft Pulley Arrangement

Blower – Stock R2/R3 Studebaker cast iron (4" diameter)

Crankshaft – Dual GM accessory pulley (6 1/2" diameter), 1" aluminum spacer between PS pulley and rear of Crankshaft blower pulley to allow alignment with blower and idler belt path.

Crankshaft Pulley lineup, from damper out:

    Dual 8" for fan / Alternator / Air Conditioner

    Single 6" for Power steering

    Dual 6" for Paxton


Crankshaft Pulley Spacing

From the front face of the damper:

To the outer edge of the Alternator/Water pump dual pulley = 1 3/8 inches.

To the outer edge of the Power steering pulley = 2 1/16 inches

To the outer edge of the blower drive pulleys = 4 Ό inches

A 1" aluminum billet spacer extends the blower pulley forward.



Airbox Standard R-3 Studebaker ( Part# 1558948).



Modifications:(Throttle Linkage)

A) Throttle Lever. On the stock R-3 airbox, a simple bellcrank lever is provided to accept throttle rod connection. This is attached to a shaft passing thru box to actuate carb linkage. A modification was necessary to allow an attachment point at the correct geometry for a TV control cable for the 700R4 automatic transmission to move in unison with the throttle.

The shaft was retained and the outer bellcrank lever removed, leaving the end of the shaft exposed with a ‘D’ shaped mounting lug. The lever was replaced with a fabricated piece from the butterfly linkage of a Holley carb. The Holley linkage piece was removed from the carb butterfly shaft and the connecting point bored out to accept a press fit of a ½ " steel disk with a filed ‘D’ opening to match the vacated end of the bellcrank shaft. Holley linkage allows the addition of a T700-R4 transmission throttle control cable. Once the press fit disk had been oriented correctly to mimic the throw of the linkage as the throttle was depressed, it was then spot welded and ground clean.

The original gas pedal linkage was retained and the rod that connects the shaft linkage from the bell crank to the throttle plate was bent slightly to pass around the R-3 air box profile.

  • B) Access Holes. The supplied air box had no access points drilled. It was necessary to drill pass through holes for fuel line connections, vacuum ports, front & rear, electric supply to choke and vacuum supply for choke pull off.

    Other modifications to accommodate the airbox included fashioning a 2 " X 4 " flat, 1/8 "steel extender plate to raise and move the TV cable locking mechanism to clear the left side of the airbox. The extender plate uses the two left rear intake manifold bolts and the original locking mechanism bolts to the top edge of the extender.


    Air Filter housing-

    Standard Studebaker R2 filter housing with stock connector hose to supercharger.

    Air filter (2) - Fram CA-102PL

    - Studebaker #1555053


    Airbox to Paxton Volute Connector hose –

    The lowest profile which, the Paxton can accept to clear the hood and maintain a close proximity between the volute and airhorn of the airbox yields an odd angle to connect the two. A section of an air intake (ribbed) connector hose which fits between the air cleaner and fuel injection air sensor on a late 80’s, large Chrysler sedan was used because of its flexibility. The connections are 2.75-inch (I.D.). The distance from the top of the Paxton to the inside of the hood is about ½ ".


    Belts- (2)

    52 inch x 15 mm wide. Both belts must have matching production numbers to assure decent size match. Replace only as a PAIR.


    Fuel Pump –

    Holley ‘Blue’ (Part # 12-802) - 5 – 14 psi

    Holley Oil pressure safety switch (Part # 12-810) - Wired from ignition circuit & fused +12 to safety switch then to Fuel Pump. Fuel pump only runs when oil pressure is above 5psi. (Safety measure in case of accident, to prevent a running fuel pump from feeding a fire.)

    Fuel Pressure Regulator –

    Mallory 4309 bypass regulator (4 port) plus supercharger static tube inlet – to raise fuel pressure on supercharged systems. The fuel inlet is on the underside of the regulator. Outlet port assignments from left side clockwise:

    Port 1 – Local Fuel pressure guage.

    Port 2 - Sender for Autometer electric fuel pressure guage.

    Port 3 - Pressure bypass line (3/8" Aluminum) to inlet side of fuel pump to bleed off excess pressure. This extra line had to be retro-fitted to accommodate the pressure bleed off. A tee- fitting was placed just ahead of the inlet to the fuel pump in the main fuel line and the bypass line was attached there. Some model Studebaker Avantis had a fuel return line factory fitted, but the purpose was to prevent fuel percolation under high-heat conditions. Fortunately, by default, this acts as a pressure bypass also. This was done away with the first Newman & Altman Avantis.

    Port 4 - Fuel line to carb.


    Static pressure inlet tube – (above Port 3) to output side of supercharger. Reference to raise fuel pressure in boost condition.


    More - Aug 2001
    Repositioned blower output connection

    These pages and programming contained therin
    are © Copyright, Bob Johnstone (rfjohnstone at, 1996 - 2006, All Rights Reserved. Some technical opinions are my own from experience, other informational data is from other sources with credits when available and while care has been taken to be as accurate as possible, it is offered only as a guide and caution should be exercised in the application of it.