Hello everyone, could I bother you guys/gals to post your mechanical boost gauge readings at WOT and indicate what pulley size you have. I have a 17% and my gauge is showing 14.7psi. Just seems low compared to what I hear it's supposed to be. I'm starting to assume either i have a boost leak or i really have a 15% pulley.

 

I have a Helix 15% pulley and usually hit 15 psi, sometimes when the air is cool enough I can hit 15.5 psi

 

that's what i thought, 15% normally around 15psi and 17% would be around 17psi right?

 

Keep in mind that altitude,temp and rpm will play into boost readings.

I live at about 4000 elevation and I'm seeing boost levels of 16.4 at 7100RPM with a 17%

 

i can live with a psi reading in between 16 and 17, but 14.7 is just kinda low don't ya think?

 

Thought this 2006 NAM Thread / data would be of interest:

https://www.northamericanmotoring.co...d.php?t=112058

Stock crank pulley dia. is 5.46 inch.
Stock SC pulley is 2.58 inch.
Correction for belt is 0.126 inch. (thanks Andy)
Effective stock crank dia. is 5.586 inch.
Effective stock SC pulley is 2.706 inch.

Crank _______SC___________% SC
Pulley________Pulley _______Overdrive
% over _____% under
0 ___________0 _____________0
0 ___________15 ___________16.69
0 ___________16 ___________18
0 ___________17 ___________19.34
0 ___________19 ___________22.12

2 ___________15 ___________18.97
2 ___________16 ___________20.31
2 ___________17 ___________21.68
2 ___________19 ___________24.51

3 ___________15 ___________20.11
3 ___________16 ___________21.46
3 ___________17 ___________22.84
3 ___________19 ___________25.70

4 ___________15 ___________21.25
4 ___________16 ___________22.61
4 ___________17 ___________24.01
4 ___________19 ___________26.90



That is, a 17% undersize SC pulley spins the SC 19.34% faster than stock.
A 15% undersize SC pulley + 2% oversize crank pulley spins the SC 18.97% faster than stock.

 

i guess its time to call Erik from EDGEmotorsports and let him know about my concern.

 

Your boost does not seem low. There are more factors then the ones mentioned. If you were in the 13 or lower I would start looking. But 14.7 is in the figuratively 15. And it is doubtful that you could tell the deference by the butt dyno within 1/2 psi anyway. I hope you get it resolved.

 

I run an Alta Classic 19%
boost reads 18psi. I have seen reading as low as 16psi

 

15%...I see a peak of 15 psi all the time...when its cold (60 and below) I have seen 17 psi. I also have a Detroit Tuned Bypass Valve so that may or may not skew my numbers. I am in AZ and my elevation is approx 1000 ft above.

 

15% pulley, AutoMeter Boost Gauge = 15 psi.

Can you check your rubber coupling boots of the IC if they are tight and not slipping out? A small leak can give lower psi.

 

same here, 15% pully 15 on the gauge. but is the needle on the gauge supposed to be on crack when its wot. meaning its really jittery and not steady. is this normal?

 

What type of boost gauge are you using and has it always read that low?

 

15lbs on a 15%, but there are a ton of factors that affect the amount of boost that your car produces, could be the guage, or a slipping belt, the elevation, bpv, etc...... i guess my point is it's hard to say from over the internet if your numbers are low or not

 

I'm using a Autometer mechanical boost gauge and my needle is pretty steady at 14.7 at wot everytime. I spoke with Erik and he said it sounds about right after "looking at some numbers" and he also said that it depends how tight the supercharger is (i'm guessing he's referring to belt tightness??). I guess I'll take his word for it and put this to rest.

 

miniflip80:

What was meant by "how tight the SC is" refered to the manufacturing tolerance plus any wear that could effect pressure / boost.

The Eaton SC is a Roots type SC. Basicly it is similar to a kitchen mixer w/ 2 beaters rotating together. Each rotor (beater) has a min / max size tolerance they are machined to.

Since Eaton mass produces them, it is possible to get both rotors that were on the high side of tolerance running together for a "Tightest" condition. The opposite would be both rotors at low side of tolerance mated for a "Loosest" condition.

Though the rotors are gear driven (which also have a mfg. tolerance) & would never touch each other, dry static atmosphere conditions could erode a small amount of rotor surface over time loosening the clearance between. The gears will eventually wear causing the rotors to have varying clearance becoming less effecient.

MCG
Manufacturing Engineer

 

^^^ Exactly. Gotta love GD&T.

 

I've got a 17% pulley and get 8 or 9 PSI. But I have a ported, polished head with bigger valves, CAI, cam, header and cat-back. Still running the stock injectors while waiting for the computer tune.

My Cummins diesel twin-turboed Dodge pickup, on the other hand, buries my 0-60 PSI gauge. I just ordered a 0-100 to replace it.

 

I just had a autometer mech gauge put on and it seems to flicker( not steady) between 14 and 16 psi when I'm wot with a 15% pulley.
just wanted to know if its normal and lookin for a little guidance of what it could be if it isnt?
thanks

 

How bad is the flicker? Is it more like a vibration, or are you getting something <1psi?

 

Wow, I would never have guessed thanks for the info!

 

I noticed today that it is a flicker around 1 or 2 psi. when the needle is in vaccuum there isnt any until about -5 vacuum. from then to 15 psi it is shaky

 

gauge scale is also a factor in getting a read.