what is the diameter of the jackshaft pulley?

93 Mark VIII

Registered User
I need to know the diameter of the jackshaft pulley, the part that drives the supercharger.

anyone know?

Thanks,
Brian
 
I believe it is 2 3/4. I know that when I went with the 10% overdrive I replaced the jackshaft pulley for a 3" steel one and was able to retain my gatorback stock length belt. Good luck!
Regards,
TBSCoupe
 
was the crank part of the pulley 2.75" or the supercharger part? I thought it was larger than 2.75", but I could be wrong.

Brian
 
I think the size on the previous post was referring to the tensioner pulley on the SC belt. The jackshaft pulley does actually have two different diameters. One to the crank (7 rib) and one to the supercharger (8 rib). I don't have one handy to measure right now. If you don't get an answer, I'll try and check later.
 
Brian,

The jackshaft pulley is around 5" dia. I've got one in my garage I can measure after work.

For thse who don't know what the jackshaft pulley looks like, here is a picture. The one on the left is stock diameter ESM 10 rib, the one on the right is an ESM 10% overdrive 10 rib. The large portion of the pulley is what changes to make it an overdrive.

JackshaftPulleys.jpg


David
 
Last edited:
Thanks for the help! I needed to determine the drive ratio's to calculate pulley size on the new setup.

Stock Jackshaft diameter 4.75" and the drive ratio is 1:1.725 from the crank to the jackshaft. Here's some other good info I dug up from j57ltr
94-95 pulley is 3.2750" dia.
89-93 pulley is 3.1350" dia.
5% pulley is 2.9350" dia.
10% pulley is 2.8300" dia.

drive ratios are:

94 up 2.59785:1
93 dn 2.71515:1
5% 2.89973:1
10% 3.03428:1

Also, the eaton produces approximatly 1.45 Liters per revolution, and the M112 procuces approx. 1.80L per revolution.
 
Last edited:
Here's what I measured...

Crank Pulley Dia = 6.8”

Jack pulley
from crank = 3.93”
Ratio = 1.7436

To blower = 4.805"
Stock '91 blower pulley = 3.15”
Ratio = 1.5238

Overall drive ratio 89-93 = 2.6569

Blower speeds @

Stock
14612 RPM @5500
15941 RPM @6000

5%
15344 RPM @5500
16739 RPM @6000

That's what I came up with on the pulleys I had an my dial calipers.

Later,
Steve
 
Um, looking at the picture that David provided, what prevents the belt from not walking off the ESM unit.

Notice how the stock unit has a raised lip. Not so on the ESM unit.
 
Yikes....using Steve's numbers (diameters) and adding 10% to the jackshaft pulley (5.368") and my existing blower pulley (2.840"), I'm calculating total drive ratio of 3.269 and blower speed of 22,018 rpms @ 6000.

That is 27.7 % overdrive and I'm still only getting 16 lbs. of boost. Did I do the math right ?

David
 
what is the most boost that one of these motors could take, I wonder?

Thanks for all the pulley info, it's great to have more precise numbers!!

Brian
 
4.9338" Big un'
3.9789" little un'

6.9909" crank

I'll check again. I have all pullies except the crank I got that # from someone else. I calculated that # from circumfrence. All the others I measured. I don't remember where I got the measurement for the 5% pulley.

Jeff
 
Ya Dave, you did it right. I figured this for the ESM blower pulleys with the larger jackshaft ( 3.9" from crank and 5.3" to blower or about 10%):

3.05" = 13%
2.95" = 18%
2.85" = 23%
2.75" = 28%

and yes, it is quite staggering to see what the blowers spinning. Having been rung up that high, you might have butchered the inside of the case. That's why I'm afraid to run the 2.85" pulley I have and use the 2.95" pulley. Wade just sent me a 3.2" pulley that I'll put on for daily driver use. It's pretty f'ing hard to drive right now 'cause it spins too much.

Jeff, I measured mine with dials to the approx middle of the belt. That's the effective diameter of the pulley. A couple tenths isn't going to make a huge difference in the overall calculations.
 
FYI,
Here is a model of the jackshaft pully that I am currently making. It has a 10 rib drive for the supercharger and will be a 10% over drive with a standard 89 supercharger pully.

As some of you may know I am also working on a new top, it is complete and currently deburring to get ready for powder coat.

Mike Tuck
Super XR7
 

Attachments

  • jack shaft pully.jpg
    jack shaft pully.jpg
    52.5 KB · Views: 493
Having been rung up that high, you might have butchered the inside of the case.

Steve,

I was spinning faster than that with the early style ESM ported blower, I had a 2.75 dia pulley on the supercharger. When I pulled the case and plenum a couple months ago to install the MP parts, it didn't have a scratch inside.

I don't think the MP one has any damage either, especially since I'm only making about 16 pounds of boost at full tilt. I do have the upgraded ESM nose cone and titainium shaft, but doubt it helps any with rotor deflection.

I'm only at those rpms for a second or two whenever it happens, so I don't think it's hurting anything.

David
 
What is the diameter of the jackshaft pulley?

I would like to slow down the blower on my 1990. Is the later model pulley the one to use for this ? If not any suggestions. The reason is I am running high comperssion. Tim :confused:
 
The 94-95 pulley is larger than the earlier ones and will slow down your early blower just a bit.
 
what is the diameter of the jackshaft

Thanks George, Do you know anyone that want to an overdrive pulley that wants to sell a late model stock pulley? Tim
 
Back
Top