I installed a boost gauge recently. The gauge is only showing 16lbs max. What gives? Most 19%ers are showing 17-18lbs. At idle it shows -15-18in. It zero's out okay when off...
Anyone?

 

Where did you tap? What kind of gauge? What RPM?

 

Well, I got around 17 last Oct on my PROMINI boost gauge (AutoMeter).

The set-up I had then included:

Rogue intake, with cowl mod
61mm TB
15% pulley
IK22 plugs
Magnecore wires
PB
QuickSilver catback
EvoTech ECU

I have since replaced the QS with my fabricated straight exit catback (battery box gone), and now have the UNIChip. On an equally cool day, or even cooler, same stretch of road, I'm getting 15's on this same gauge.

Would going with a much less restrictive exhaust create less boost? I doubt it's the UNIChip. Heck, it could be the gauge itself; at least that is what I've been thinking...

I recently got a CarChip E/X which captures data while driving, and I have peaked several times at over 20 pounds for intake manifold pressure. The gauge still shows 17 as my high from back in Oct. I realize that where the pressure is measured is a factor as well, and I'm ignorant in that regard...

I would think your boost should be much higher with the 19%. Maybe it has to do with a slight leak, or the gauge itself...

 

Ah, yes. I seem to have left out the details.

-Autometer mechanical. no kinks/bends, etc.
-tapped in FPR line just before manifold with a "tee".
-16lbs max at rev limiter (stock)
-no leaks

 

If you can, make note of the boost at a couple different RPM in a high gear (say 3k and 4k in 4th gear or higher). I'll compare it to mine.

What exhaust do you have?

 

I believe that logger measures absolute pressure. Are you subtracting ambient?

 

I have a Magnaflow with a Supersprint header. The cat is melting. That will be eliminated tonight. I am also throwing a glasspack into the mix, and modifying the Magnaflow. I have an O2 simulator for the cat elimination.

I'm sure I'll get flames out the rear now! whap-bop-bop-boom!

 

Andy, I did not factor-in ambient. What is a good number to use for subtraction? Thanks for the input.

 

I'm sure I'll get flames out the rear now! whap-bop-bop-boom![/QUOTE]


Kinda like this?





click pic for better view :D
His, Chile RED over, Madness intake, Magnaflow exhaust, Helix 15% Pulley & RDR Swaybar
Hers, Electric Blue / Union Jack on top and BONE Stock

 

Definitely! That's not necessarily bad though. What you're losing in boost, you may be making up in power. Or maybe not. But certainly - the more air you cram in the engine - the more boost and more power. But the faster you get that air out (ie. less restrictive exhaust, header) the less boost (b/c the air is escaping faster) but moving the air faster can also allow air to get in faster. So having less boost in this case could mean more power. But it's a fine line which is why a straight pipe usually isn't the most powerful.

 

Thanks greatgro for the confirmation. At 2.5" starting just beyond the cat, all the way straight back into a Borla Turbo muffler, I must have one of the freeest flowing catbacks out there. I guess that is why I lost some boost. It feels quicker, but heck, it could be a placebo due to the roar . Seriously, I think this system will really shine when I start to produce even more hp (should be around 220 now)...

I'm really thinking of getting more air in with an HAI soon. Moving the air faster is the key. With the easy stuff done, then I'll need to drop some dough to get the internals though...

 

Turn the ignition on, but do not start the engine. Log the air pressure. That's the ambient you should be subtracting to get gauge pressure. It varies quite a bit by elevation and somewhat less by weather.

 

It sounds like you could be experiencing some belt slip. did you change the belt and what kind? is there powder around the blower pulley? if you did upgrade to a new belt, you might want to consider a idler tentioner. try Gatorback belts.
Jason

 

Belt slip is certainly possible, especially with a 19%. The stock belt, including JCW, simply won't cut it with the 19% pulley. Otherwise, 16PSI doesn't sound too far off. What were you getting with your previous setup?

 

Reminder: A better exhaust (less restriction) will lower boost levels. Boost isn't everything. In this case it's boost + flow. My high with a 19% is 16.5lbs but I credit the lack of boost (17lb range) on my UUC exhaust. Interesting note, however, is that I can get 15lbs of boost in the upper 4k RPM range. When you consider boost per supercharger RPM, makes it seem like there is some boost leakage at high RPMs. I wonder if that "special coating" on newer (04 and 05) MINIs that is supposed to seal in higher amounts of boost better really makes a difference? MAYBE that's why the JCW makes a good amount of HP (200) for the somewhat low amount of torque (177). Maybe it's the seal "sealing" in the boost better at higher RPMs.

 

I'm in Florida at sea level with my Autometer Mechanical I get 16psi at redline with my 15% pulley. I have a Borla Race exhaust.. Just for comparison.

 

Dang, someone dug up this old thread?

The funny thing is, I was going to give an update on my boost today anyway..

I still have the 19%, and I only use the Gatorbacks btw, I gave the headbolts another 15 degrees and zip tied the bypass....now I max at just about 18 psi. I would say that the zip tie (Ryephix) gives me a better seal than without.
I have driven about 500 miles ( I'm at Orange County Choppers ) without any issue with my headgasket leak...

 

Did you have the head off or tried torquing the bolts for "fun"? BTW, do you have the JCW head on your car?


P.S. See anything at OCC or is it all crowd control and the gift shop?

 

You're forgetting the valves in between the charger and the muffler! :smile: The degree of effect is related to valve overlap. If there's lots of overlap, then yes, it's possible. With no overlap (I know, that would make a crappy cam), the two would pretty much decouple.

Also, the exhaust ports are referenced by many as a stock restiction. This would also cause a decoupling of the effect of the exhaust on boost levels. but this is all theory. I'd like to see if anyone has actually measured it for the mini.

Matt