Dynoisms aside, the first thing I see is a possible dirty air filter, according to your report it has not been changed in a least 15k miles. A JCW belt on a JCW pulley should have one hole showing, if no hole on the stop limiter strap is showing the belt has stretched and needs replacement. You mentioned a tire pressure disparity enough to generate a light, this is another factor. If you’ve never flushed accumulated oil from the IC you’re limiting potential. When the IC is cleaned be sure the boots are degreased at the contact bands for a good seal. Don’t underestimate the potential of new OEM sparkplugs and wires.

As for dynos, load bearing vs. inertia will make a difference in readings across dynos. I’ve used a very unflattering dyno which showed my MCS baseline at 125hp and 111lb-ft torque. The deltas recorded on that dyno since then have been appropriated but the peaks can not compare to the numbers generated on other dynos visited. The graph you showed is smoothed out a bit, so the dips & plateaus normally seen with slipping belts and abrupt ignition timing changes aren’t evident. Performing the conversion on the numbers shown in the graph I get 129hp and 139lb-ft torque rounded off; that makes me think something is amiss in the calibration (or maybe valve timing), although I don’t have experience with high altitude numbers. Adequate air flow through the IC on a 98F day while on the dyno will make a big difference.

There are too many variables for long distance diagnosis.

 

What if it is a faulty gauge? I dropped it about 4-5 inches from the ground accidentally. When I turn the key so all the lights go on, just before the car starts(forgot what that mode is called) - the gauge's arm turns clockwise till about 1.7 bar(24psi) (gauge's max indicator is at 2.0 bar(29-30psi), then turns back and hangs at -0.2(-3psi) bar until I start the car.

The gauge shows -0.6 bar(-8psi) when the car is at idle. Even if my belt is slipping, the vacuum should still be the same on all cars? Or do you think the gauge is toast?

 

So what you are saying is that it is impossible that my belt is slipping according to the dyno sheet?

I'll remember the points mentioned when the parts go in. I will make sure everything in the IC is clean!

What holes? I'm a bit confused on that one, where do I check this?

 

No not impossible, I mean the smoothing technique used on the graph display may have masked some changes or the dyno/program may lack detailed resolution. If we consider the readout as an interval scale, one dyno/program may have wide sampling intervals only appropriate for measuring trends and another dyno/program measures in shorter intervals which would be good at illustrating detailed effects.

Look on the right side of the motor (passenger side in the U.S), at the rear section of the tensioner there is a protruding metal strap with a twisted tab at the top. There are two holes in the strap; the uppermost hole should at least be partially visible above the tensioner & spring. If the strap is buried to a point close to the stop limiter (twisted tab), there will not be enough tension on the belt to prevent slipping at high rpm.

Tensioner strap stop with half hole showing; 5k miles on the JCW belt over JCW pulley.

 

Thanks for the reply! My strap looks the same as yours :( Maybe I just have a weak car lol

 

Here is a video to show you what I mean. Does everything look ok here? Or is my gauge busted?

http://www.youtube.com/watch?v=xadlHhYTsho

 

*sigh* If you had changed the $20 belt, you would know by now. I urge you to take action! This has gone on well over a month now and it is no closer to being fixed. You ask for advice from the forums, we give it, and you ignore it.

 

I appreciate everybody's advice here and I take it seriously. I am getting my belt changed next week - I had to wait for my parts to clear customs from NY. I only brought it up because I had the boost gauge installed and was trying to figure out if it was a faulty gauge or if it was the belt.

 

Honestly it does look like the gauge may be broken, it should stop at 0 when the car is off, not some negative number. But it has gotten to the point where you should just change the belt anyway since it is cheap and might be at least some of the problem...

 

Well, with the car off, your boost gauge should read about 12.7 psi or there abouts. At 5500ft mine reads about 12.1 depending on the weather. I can't imagine you have a gauge that can read anything other than absolute pressure (I mean it can't actually read boost unless it also reads barometric pressure independently.)

 

Damn, I'm going back to the place I bought it from tomorrow and hopefully he has another in stock that I can try out to confirm this

 

It's electronic - it only work when the engine is running. So I can't use that method to compare either. Thank you for your input none the less

 

My ScanGuageII reads manifold pressure in absolute amounts, and it certainly shows negative boost (vacuum), so I wouldn't be too concerned with negative numbers on your gauge. It sounds like your gauge may read the barometric pressure when you first turn it on, then subtract it from the actual pressure reading when the car is turning over. (Just a guess, but it's possible.)
Of course, the SGII reads manifold pressure, not SC boost (which presumably requires a pressure reading before the SC and another after the SC) but I don't know if people are really measuring this anyway.

 

If you have a mechanical gauge that uses an expandable diaphragm to display pressure differences it should have an open canister. Basically if the back of the gauge is open to atmosphere, and atmosphere is in the lines going into the gauge, it should read zero. This is regardless of the density altitude of that day. It should never read negative unless the engine is running, of course unless for some weird reason there is a set pressure inside the gauge and it only measures against that, but I wouldn't want a gauge like that...useless IMO

 

The OP’s gauge is electronic, it recalibrates for atmospheric using that value as zero each time it is powered up. It appears the gauge is functioning as designed. There may be a leak at a fitting, or it may be his head and exhaust system are less restrictive than some others, don’t forget his altitude adjustment as well, however, I think it is more telling the dyno graph shows higher torque than horsepower and the majority of his dissapointment is more likely due to a program misinterpretation than a hardware issue.

Boost forms in the intake manifold on the MCS because the roots blower stacks air packets in faster than can be consumed; air is not pressurized inside of the SC and transported. On my diagnostic tool, I take a static atmospheric reading and manually subtract that from the IM absolute pressure value at a point of interest within a recorded event.

 

Well said! That's exactly what I do, too.

 

Thanks for this post - just checked mine and I need it changed! Thanks again.