MacGyverGTP

Can some of you with Kenne Bells please post what pulleys you are using and what boost they give you?

I only ask because I have the 2.4L Kenne Bell on a stock bottom end.
I changed from a 4" pulley to a 3.75" to get it to what I thought was 10psi.

However, I am hearing from my tuner who says they are getting their info from Kenne bell that the 3.5" is really the 10psi pulley.

I don't think this is correct, as stock, the blower came with 8psi.
What's a 1/4" change worth in PSI?

Can someone help me understand the correlation between pulley size and boost on a 2.4L KB.

The car is at the shop getting dyno tuned, They say my belt is slipping, but my digital boost gauge reads 10psi when I am really on it, so I find that hard to beleive.

How can I be getting 10psi of boost on my gauge that 0's its self every time I start the car if they say I am only running a 8.5-9psi pulley?

I'd like to think I'm somewhat intellegent, but this has me so confused.
Thanks for any clarification.

MacGyverGTP

This is exactly what I am looking for:
http://kennebell.net/superchargers/f...lley_ratio.gif

But does anyone have a chart like this for a 2.4L KB????

dkersten

Couldn't tell you for sure, but I would guess on the 2.4, each 1/8" diameter change would be around .8 psi boost. Of course, as you decrease in size, the boost jump will get smaller as the efficiency of the compressor drops.

Your boost could be fluctuating as you accellerate, which would indicate the belt slipping. However.. I think if you see 10 psi, you have the right pulley.

MacGyverGTP

Thank you!!! This would make sense to me, but I'm no science rocketist.

highline

how do you like the KB? I am going this route soon...where does 8 psi put you (rwhp?)? 10psi? Did you install?

MacGyverGTP

Highline, I've had problems with mine from day one. Mostly the fault of people telling me everything was right when it wasn't.
My goal is 500rwhp.

Th numbers Kenne Bell had on their website when I bought the thing (it's a 2.4L) said 523hp.

Well, I've got 3 different types of dyno's now & I finally found a shop who knows what they are talking about. He says I should be around 480-490 with the 10psi (3.75")
I'm only getting a little over 400hp & not sure where my torque number is as I havn't seen the chart yet. They are working hard to get me the 80+ hp that isn't there that should be.
Once that's fixed, he's going to put on a 3.5" (11.5psi) and get me in the 500hp range.
Sounds to me that maybe whipple may have been the better way to go.

If I had it to do all over again, I'd probably get a turbo...

zkiller

Ill check my pulley size (for 10 psi) and get back to you shortly. I started at 8, then 9, then 10, then 11 and then 12 so cant remember the size but I have them all in my tool box.

zkiller

The 10 psi pulley is 3.5" I just measured it. I have two like new 11 PSI pullies in my drawer if you need one cheap?

MacGyverGTP

Thanks for taking the time to measure it! I went down to my shop today to talk to the tuner face to face (he's like 45 miles away) He & I seem to agree on almost everything now. The other guy at the shop was just telling me what KB told him (which was not correct) I'll be moving to the 3.5" as soon as he figures out why I am about 75hp off of where I should currently be. They initially thought it was a slipping belt but now say that isn't it, they'll have my car for a few more days it sounds like.
Thanks for the help!

dkersten

I found this on the KB website. Hope it helps.

How do I calculate correct pulley ratio for Kenne Bell superchargers? Use the formula:
((14.7+Boost) / 14.7) x (engine liters / 2)) / Supercharger Size liters = Theoretical Pully Ratio*

*Assuming "0" inlet losses and 6.5" crank pulley.


By the way, when it comes to the amount of power you get, there are many factors to consider. First and foremost is, all other things being equal, the only thing that will change from one FI setup to another is parasitic loss, so peak horsepower will only change by the difference in the amount of parasitic loss given the same amount of boost you see at the manifold. If you are reading 10 psi of boost consistently through your 2000-6000 rpm range, and you make 400 rwhp in that range, going to a different supercharger will make little to no difference. The differences are in the tune (AF ratio and spark advance), and other factors such as bolt on accessories (electric water pump, cams, headers, driveshaft, wheels, etc). Yes, a turbo will usually have 25-30 less hp drain than a positive displacement supercharger, but one twin screw to another is not going to matter. Don't forget that a heavy 20" wheel will easily give you a 5-10 hp loss as well.

The other thing to consider is humidity, elevation, and ambient temperature. As any of those increase, you will see less power. There is no getting around it. I am at 3400 feet of elevation, and a built and stroked 302 with 12 psi boost makes around 500 rwhp, but at sea level it will make closer to 580 rwhp. The only advantage we have up here is it is dry (less than 20% humidity), and cool in the mornings and evenings.

If you are running 25% advance, and the computer is not pulling timing from high IAT's, or from detected pings (from too low of octane), and you have an AF around 11.8 at WOT, you are at the max you will see in your area for the given setup. Just for the record, the basic tune from KB is set for 11.2 AF to be safe.. there is easily 40 hp to be gained there, but if you don't know how to drive a supercharged vehicle, you may cause damage if you bump that up.

The 501 rwhp that Kenne Bell advertises is on 8.5 psi boost with the 2.6L stage 1 on a "stock" 4.6 with just an electric water pump. What they don't mention is it is on a race tune with close to 12:1 AF ratio, on a cool and dry morning with the engine just run up to temp. This is the most perfect of conditions, and you will never see those conditions in real life. Personally, when I get my car on a dyno in a few weeks at our International Mustang Meet, I expect to see around 430 rwhp if the day is below 80 degrees and not too humid. If I get higher I will be happy, and if I get lower, well that is the problem with living above sea level.