Help deciding Roots Supercharger drive ratio

[shomethe$$$]

I am starting the next phase of my buildup, stock 3.0 MTX with a 94-95 M90 SC for a budget man like me. Anyway, I wanted a few opinions for the drive ratio for the SC before I have the crank pulley made

SC pulley size 2.82"

with a 7" Crank pulley, ratio is 2.35 @ 6500 rpm limit SC=15,268 rpm

with a 7.5" ratio is 2.52 @6500 rpm SC=16,359 RPM


I am thinking of going with the 7.5" but it all depends on what rev limit I will run, 6500 sound high enough?
Just for comparison a stock t-bird ratio is 2.77 @5000 limit 13,850 RPM
with 15% OD 15,928 RPM



3.0 engine can inhale 341.5 CFM of air @6500 rpm (cubic inches*RPM/3464)

Excess air = 600 CFM – 341.5 = 258.5 “boosted” CFM

Boost = excess CFM / normal CFM * atmospheric pressure
258.5 / 341.5 * 14.7 = 11 pounds boost

Old 2003 setup, 2.44 ratio, 6500 rpm, 10 psi actual psi, means SC put out 573 CFM to the engine with losses, this is a newer SC but I want 650 CFM



So 7.5" pulley sounds correct but won't pull out 650 CFM since I have no real date to calculate that, let me know what you all think. Here is where I got some info

http://www.mscperformance.com/specpg2.html

 

[SuperHO]

What?

 

[BlackonBlack89]

go with an M112 you be happy you did....... wont have to worry about CFM and that good stuff. The m90 has been shown to run out of breath on the SHO engine. But it does work quite well for 7-8psi

 

[rubydist]

I'm not following your math on the ratios. First, 2.82 is not the stock pulley size for the 94-95 M90, stock is 3.27, so you must have an aftermarket pulley?

If the crank pulley is 7 and the s/c pulley is 2.82, the ratio is 2.48:1, not 2.35, and if the crank pulley is 7.5 and the s/c pulley is 2.82, the ratio is 2.66, not 2.52. 2.66 * 6500 = 17290.

The 94-95 M90s are rated as max rpm of 12k, so I wouldn't run one over 15k. As I've previously discussed, by the time you are at 15k, the efficiency is such that you are not really generating much more mass airflow, just more heat and therefore volume. I personally would have no interest in spinning my M90 at 17k+.

Your calculation of naturally aspirated airflow assumes a volumetric efficiency of 1.0, which is a stretch, even w/ the SHO motor.

Keep in mind that the more heat the blower generates, the higher the boost numbers will appear to be, even though the mass airflow isn't there. The engine cares about mass, not volume, and likes cool charge temps.

Are you planning to run an intercooler of any type?

 

[shomethe$$$]

I'm not following your math on the ratios. First, 2.82 is not the stock pulley size for the 94-95 M90, stock is 3.27, so you must have an aftermarket pulley?

If the crank pulley is 7 and the s/c pulley is 2.82, the ratio is 2.48:1, not 2.35, and if the crank pulley is 7.5 and the s/c pulley is 2.82, the ratio is 2.66, not 2.52. 2.66 * 6500 = 17290.

The 94-95 M90s are rated as max rpm of 12k, so I wouldn't run one over 15k. As I've previously discussed, by the time you are at 15k, the efficiency is such that you are not really generating much more mass airflow, just more heat and therefore volume. I personally would have no interest in spinning my M90 at 17k+.

Your calculation of naturally aspirated airflow assumes a volumetric efficiency of 1.0, which is a stretch, even w/ the SHO motor.

Keep in mind that the more heat the blower generates, the higher the boost numbers will appear to be, even though the mass airflow isn't there. The engine cares about mass, not volume, and likes cool charge temps.

Are you planning to run an intercooler of any type?

Sorry pulley is 2.98 an aftermarket pulley, definally gonna fit a FMIC (any recommendations?) like i had before, your right, the SC will run out of steam thats why I want to try and stretch it out to 17k rpms, I' contacted my t-bird expert and hopefully he'll tell me what overdrive he's using

assume 1000 SC rpm = 88cfm, then with a 7.5 I'm still 77 CFM short of my goal, so this would require a 7.85" pulley

 

[shomethe$$$]

go with an M112 you be happy you did....... wont have to worry about CFM and that good stuff. The m90 has been shown to run out of breath on the SHO engine. But it does work quite well for 7-8psi

I wish I had a m112 but hopefully in the future with more funds

 

[Off Road SHO]

The SHO motor will outrun that M-90 at 5000 engine rpms. After that, it's an obstruction.

Use a larger throttle body if you are putting it on the intake side like I did on The Other Woman. The less restriction on the intake side of a Roots style blower, the better. If you're putting it on the pressurized side, a stocker will do.

I too vote for the M-112, which I already have a brand new one ready to go.

I took a heavy duty charge air cooler from a semi, cut it lengthwise, re-capped it and mounted it in front of her radiator.

My next intercooler will most likely be an air to coolant type with a separate tank, like on the Cobras and Lightnings. The take will have a fill hole big enough for chunks of dry-ice to be added to the mix. Might even run alcohol, water and ice for some sub 40 degree cooling. Can you say COLD pressurized air?


Tom

 

[shomethe$$$]

The TB will be before the SC, its a custom inlet bypass intake for the SC with a 80mm an inlet, I'm thinking of going with a 75mm TB but let me know your thoughts on that.

What M112 are you using, one off the Lightning or Cobra? because there's one more out there which looks just like the M90 perfect for space limited setup but I don't think it has teflon coated rotors, I don't even know if the Cobra one has teflon rotors

how did the semi intercooler workout, did you notice a difference? what was the IC before that? I'll think I'll do a 24X17X2.75

 

[SASHO91]

Is your M90 ported?

 

[shomethe$$$]

Is your M90 ported?

Nope.

 

[kzoosho]

Nope.

Well i would deff port it if you are set on using it. I vote for the m112 also since it flows a **** of alot better . Also how are you planning on mouting it? That would def play a roll in your IC setup.

 

[SASHO91]

IIRC, it's allready mounted to the car. This setup is in the Prelude. It's mounted where the A/C compressor used to reside.

 

[shomethe$$$]

Well i would deff port it if you are set on using it. I vote for the m112 also since it flows a **** of alot better . Also how are you planning on mouting it? That would def play a roll in your IC setup.

Porting is more expensive than putting a M112, plus I'm pretty much out of room on the Honda, just to give you an idea




you can see the remaining thread in SHO related,

You see after last picture, I had to cut that bumper 3" in to get the double core radiator, SHO fan, and AC condensor, so there is almost no room for the intercooler but I have figured a way to do it by removing the hood latch assembly, that should make enough for the intercooler.

So putting ported M90 is near impossible now since the casing is 1" larger, I have to stick with what I got. I talked to my SC expert, he's got a 1995 T-bird with a 2.82" pulley and he claims his engine is able to go to 6000 rpm, he is running a 3.07 ratio which = 18,443 making 16.5 psi for many years.

LMK if did my numbers right ruby (jackshaft 4.9338, 3.9780.....crank 6.9909 on the t-bird)

 

[rubydist]

You can port the M90 w/o having to put on the taller discharge hat, although the taller discharge hat is a significant improvement even w/ the stock blower (although it looks like you'd definitely have 2 things in the same place at the same time w/ the taller discharge hat!)

If the stock SuperCoupe ratio is 2.77 w/ the 3.27" blower pulley, changing the pulley to 2.82 should make the ratio 2.77 * 3.27 / 2.82 = 3.21, so at 6k engine the blower would be over 19k !! (The good news is you have the blower on the front side of the engine, so even if it does grenade its not likely to hurt you or your passenger.) But, if I use the 6.991 / 3.978 * 4.934 / 2.82 numbers you listed above, I also get the 3.07 ratio that you got - I'm not sure which ratio was stock on the Bird...

 

[kzoosho]

You could run a water to air ic and you can put that right on your charge pipe and its more efficient . I forgot about your project man lol.

 

[SuperHO]

....why not use a side mount intercooler from a DSM or something like that? Surely there'd be room off to one side or the other...might also consider an aftermarket oil cooler as well, since that engine bay's pretty tight and forced induction and what have you. I'd hate to see you get it all together only to have the engine eat itself.




and FWIW...you don't like traction, do you?

 

[shomethe$$$]

You can port the M90 w/o having to put on the taller discharge hat, although the taller discharge hat is a significant improvement even w/ the stock blower (although it looks like you'd definitely have 2 things in the same place at the same time w/ the taller discharge hat!)

If the stock SuperCoupe ratio is 2.77 w/ the 3.27" blower pulley, changing the pulley to 2.82 should make the ratio 2.77 * 3.27 / 2.82 = 3.21, so at 6k engine the blower would be over 19k !! (The good news is you have the blower on the front side of the engine, so even if it does grenade its not likely to hurt you or your passenger.) But, if I use the 6.991 / 3.978 * 4.934 / 2.82 numbers you listed above, I also get the 3.07 ratio that you got - I'm not sure which ratio was stock on the Bird...

Thanks, I'll go with a 7.85" pulley, SC pulley 2.98", drive ratio is 2.63 so 17,122 rpm @6500 engine rpm.

You could run a water to air ic and you can put that right on your charge pipe and its more efficient . I forgot about your project man lol.

I don't understand this? is that like spraying water on the IC, I was thinking of using the washer fluid reservoir to do something to that effect.

....why not use a side mount intercooler from a DSM or something like that? Surely there'd be room off to one side or the other...might also consider an aftermarket oil cooler as well, since that engine bay's pretty tight and forced induction and what have you. I'd hate to see you get it all together only to have the engine eat itself.




and FWIW...you don't like traction, do you?

I'm mounting an oil cooler on the driver side under the bumper support, on the right side is the AC drier and some AC piping, maybe I should ditch the AC. I would like one more fan in there, next to the SHO fan, the SHO fan is so big but its a good fan making 2200 CFM and 4800, i think, I tried to look for some slim fans but still looking for low draw and high CFM.

Last time I did this I had great mid-range with a 2.44 ratio but the car felt like it peaked at around 5500-6000 rpm, could of been the stock exhaust, I want more top end Hp this time and less torque on the low end.

 

[kzoosho]

I don't understand this? is that like spraying water on the IC, I was thinking of using the washer fluid reservoir to do something to that effect.




I

http://www.vortechsupercharger.com/product.php?p=19&cat_key=3

follow the link my friend.

 

[SuperHO]

I want more top end Hp this time and less torque on the low end.

Might wanna consider different cams, then..

 

[shomethe$$$]

http://www.vortechsupercharger.com/product.php?p=19&cat_key=3

follow the link my friend.

Thanks, I think they are mounting it where the battery was, correct? How's that little FM heat exchanger (black one) gonna decrease the water temperature?

Basically, a water-to-air intercooler is just an enclosed intercooler running water through or between the core, right? But you can't mount it up front because the casing will block air flow to the engine radiator.

Wouldn't my budget idea work by spraying water on intercooler for a few seconds while u need that extra power or would it cause havoc on tuning and generate a bunch of steam?