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View Full Version : Early vs. Late Supercharger Overdrive Ratio



68COUGAR
12-04-2005, 07:17 PM
'89 - '93 Supercharger Pulley = 3.135"
'94 - '95 Supercharger Pulley = 3.250"

The '89 - '93 superchargers are overdriven 250% from the factory. Since the '94 - '95 pulley is larger (all else being the same), the overdrive ratio would be less than 250%. Were the crank or JS pulleys different size on the late models, to maintain the 250% overdrive ratio? OR was the overall overdrive ratio just less?

68COUGAR

darkstar_one
12-04-2005, 07:22 PM
the reason the late models have bigger pulleys is because they are more effiecient... they create the same amout of boost as a 89-93 SC without overdriving it too much.... thats why people get the late model ones because are more efficient and you can port the hell out of them and see better results... the jackshaft and what not are the same jut the SC pulley changed..

CMac89
12-04-2005, 07:28 PM
Late model blowers overdrive 3% more than the early models do. If you put a 5% pulley on an early model blower and compared it to a late model blower, then a 5% pulley on a late model blower would actually be 8% overdrive.

If I remember correctly.:)

68COUGAR
12-04-2005, 07:48 PM
Late model blowers overdrive 3% more than the early models do. If I remember correctly.:)
That's not what the numbers say. I was referring to overdrive ratios only, not flow ratings.

68COUGAR

lube70
12-04-2005, 08:06 PM
Late model blowers overdrive 3% more than the early models do. If you put a 5% pulley on an early model blower and compared it to a late model blower, then a 5% pulley on a late model blower would actually be 8% overdrive.

If I remember correctly.:)


The 94-95 blowers are actually spun slower due to a more effiecient blower case as therefore, could be spun slower. This allowed for the same boost pressures and less drag on the motor giving the 15 HP increase.

The older style blower pulley on a 94-95 blower will give a 3% overdrive.


Don

CMac89
12-04-2005, 08:12 PM
Well, that's the difference between the two blowers is flow ratings. The early model blowers aren't as efficient as the late model blowers so the late model blowers can take a larger diameter pulley and put out the same amount of air.

What is your source for this info? All of the pulleys are the same size for each year, except for the blower pulleys.

XR7 Dave
12-04-2005, 09:47 PM
I'm not sure why people always say that a 95 blower with an 89 pulley is "overdriven". It is overdriven only if the blower is actually installed on a 95 with the smaller pulley. If any M90 is installed on an 89-93 with a 3.15 pulley then it is not overdriven IMO. It may be more efficient, but it's not overdriven. It's running at the stock drive ratio. Since the 95 blower does not have a lower rpm limit, then why would we consider it overdriven when using a stock pulley? I've always found that confusing. I prefer to think of a 94/95 blower as being underdriven if it has a 3.25" pulley on it. :cool:

mannysc
12-04-2005, 09:48 PM
the porting is ok but what really made it work better was tyhe coatinmg of the rotors. the ports didnt reall flow that much better but the filling in of the vee inlet cut into case did stop the air from cavitating. as bad. most of the boost was due to the coating of the rotors the early m90s are very loose and the coating let less air leak back between the rotorsyes 94-95 were better dont know why ford changed the pulleys as 3% is a none critical overdrive.

CMac89
12-04-2005, 09:57 PM
The 94-95 blowers are actually spun slower due to a more effiecient blower case as therefore, could be spun slower. This allowed for the same boost pressures and less drag on the motor giving the 15 HP increase.

The older style blower pulley on a 94-95 blower will give a 3% overdrive.


Don
I hear an echo.:)

XR7 Dave
12-04-2005, 10:01 PM
I hear an echo.:)

Ok, so with the MPIII being more efficient than a stock M90, what drive ratio would be considered "not overdriven" on it?

CMac89
12-04-2005, 10:07 PM
Ok, so with the MPIII being more efficient than a stock M90, what drive ratio would be considered "not overdriven" on it?
I was just talking about equivalence between the two blowers, I'm not saying that each one is being overdriven in particular.

Anwser to your question would be whatever the stock ratio is, but it would have to be "underdriven more" to achieve the same boost as the stock early model and late model blowers with the stock pulleys.

acb92sc
12-07-2005, 11:23 AM
I Was Under The Impression They Downsized The Pulley Due To Their Fear Of The Dreaded H/g's.....

XxSlowpokexX
12-07-2005, 02:50 PM
Being the 94-95 blower never came on earlier cars putting one on an earlier can and running a smaller (89-93) blower pulley would indeed be overdriving the blower being the BLOWER would be spinning fater then originally intended:O)

XR7 Dave
12-07-2005, 03:50 PM
Being the 94-95 blower never came on earlier cars putting one on an earlier can and running a smaller (89-93) blower pulley would indeed be overdriving the blower being the BLOWER would be spinning fater then originally intended:O)

But since the S-Port from Magnusen comes with a 3.15" pulley tells me that they consider the 89-93 drive ratio to be standard for that blower. Certainly the blower itself was not intended to by spun slower. In fact I understand it has upgraded bearings or something from the 89-93 blowers. You can't surely mean to tell me that the later model blowers are intended to spin at slower rpms?

I would say instead that the blower was spun at slower speeds because on the 94 it resulted in excessive boost due to the camshaft which is unique to the 94-95 motors.

For whatever it is worth, my point is that drive ratio is a direct relationship between the crank speed and blower speed and if the displacement of neither unit has been changed, then the drive speed is a mechanical relationship which which corresponds directly to the year of car that it is installed in.

The efficiency of the motor or the supercharger is irrelevant in this case. The drive ratio is key and the engine and supercharger's ability to flow air are not relevant when considering drive ratio.

68COUGAR
12-07-2005, 04:22 PM
Well my original question was answered a long time ago. Which BTW, had nothing to do with efficiency or flow rates, but I have enjoyed the "much ado about nothing".

68COUGAR