Whipple pulley question

[doodguy]

Trying to understand this. With 3.3 pulley i made 20psi max boost at 7800rpm per ngauge boost+

I went down to 3.00 pulley expecting to make 22 or 23 max boost, but instead when reviewing log i made 21psi max, though made 14psi all the way down at 3800rpm and quickly climbing to 18psi at 5k rpm and holding as the psi climbed to 21 at 7800rpm.

Is this expected? I thought each .25 down was about 2 or 3psi more. Is it possible the 2.9 can't make much more than 20 psi? Should i go down to 2.8 pulley? I have the 20 percent od balancer with 10 rib by the way.

Sponsored

 

[Highvoltage16]

Maybe an inlet restriction? The C/Js make well over 20psi I'm sure, but they have a much larger diameter intake duct, mass air and air filter. Maybe take your air filter off and put a bellmouth in its place?

 

[GSLSE20B]

Maybe the intake valve springs are not holding your boost

 

[Jmeo]

I believe each drop in pulley size is 1psi increase in boost

 

[kcc0521]

Is belt slip a possibility? I know it is not likely with the 10 rib.

 

[doodguy]

Is belt slip a possibility? I know it is not likely with the 10 rib.

With belt slip i would see the boost jumping. I sent lund logs see what he thinks tomorrow

 

[doodguy]

Maybe the intake valve springs are not holding your boost

I changed the springs went with 70lbs if i remember correctly.

 

[doodguy]

Maybe an inlet restriction? The C/Js make well over 20psi I'm sure, but they have a much larger diameter intake duct, mass air and air filter. Maybe take your air filter off and put a bellmouth in its place?

What is a bellmouth?

Also, can you link me where you read the c/j makes more than 20psi? I'm searching and not finding that.

 

[Highvoltage16]

http://vibrantperformance.com/catal..._1332&osCsid=dc8a80bc8de5bd92006152d09b19dd37
I'm really only speculating on the boost. Ford is hush hush on this stuff so I'm sure you won't find anything on the internet for a while. But to make the power to move them to the mid 8s I think it's safe to assume they're making over 20psi. They come with a 3.25 pulley but I don't think they're making that kind of power with 15psi, which is what a stock diameter damper makes with that pulley. So I think is safe to say the ATI balancer on there is 20% overdrive which would put it making boost similar to your setup. They also turn 8400rpm which can help out a lot.

 

[doodguy]

Holy crap! 8400rpm? What allows them to rev that high?

 

[Highvoltage16]

At the helm of the engine controls is a TriCor PCM loaded with revamped software that allows this version of the CJ 5.0-liter to rev to 8,400 rpm, where its predecessor hit a wall at 8,100 rpm. Perhaps more important than the extended rev range is that Ford Performance engineers built-in the ability to tweak the calibration via the new ProCal 3 tuner, which allows users to download calibrations from the Ford Performance web site and upload them into the PCM via an OBD-II dongle.

Just an excerpt from an interview with a C/J engineer.

 

[pro 5.0]

Could be belt slip you have a 7.86 dia lower pulley and a 3 inch upper that's a big mechanical advantage. Try to compare your logs from your old 3.375 pulley at say 4500 rpm and compare the boost, you should see 3 more psi at the same rpm with the 3 inch pulley. Belt slip is usually above 5500 rpm or so.

 

[doodguy]

Down low i def picked up a lot. Belt is pretty tight. Ill see if i can tighten it some more.

Sponsored