Forgive my lame title, it's early and I haven't finished my holiday shopping. :impatient

I'm in need of some NAM brain power here.

I installed a vac/boost guage before putting on my 19% pulley. With my WMS CAI clone, Milltek Exhaust, DFIC, and stock pulley, I was seeing right around 10.5 psi in third gear at redline. Sounds normal right? Maybe even a little high for those mods and stock pulley?

Then, I installed my 19% pulley, and am just hitting around 15.5 psi at redline in 3rd gear. And this has been in our fairly cool 50 degree weather. I kinda thought I'd be seeing around 17 psi?

Also, theres this strange new sound coming from benind me when I have my rear seats down. Only happens at WOT in the upper RPM range... There is this intermittent WHOOSHING sound. and it goes on and off in no particular order or sync... I was kinda thinking it could be the fuel pump, but I dont know why it'd sound like it was going on and off like that?

My second thought was that it's my Milltek exhaust? But I can't hear any leaks any other time?

Please advise oh great NAMmers!

 

Thats a pretty large boost number... any ideas on wheel horsepower???

 

You're right about the boost, it should be somewhere around 17 if not higher at WOT. I'v seen as much as 16.9 with a 16 at WOT.

The WHOOSHING, no idea. Does the exhaust get a little less loud when this happens? If so, do you have a ceramic cat? Or an older fiber glass packed center muffler? Either of these could have failed in a manner that restricts the exhaust, resulting in a whoosh kind of sound. Just a thought.....

 

No, the exhaust is a 3 month old Milltek whose tips aren't quite aligning properly... But thats another story.

The intake is usually louder than the Milltek, so I dont really hear the Milltek that much. I have the OEM header for now.

 

Getting dynoed after my OBX header goes on, then MTH.

 

In that case, it could be the cat. You will know for sure when you put the new header on. There is a post somewhere on NAM with a cat, OE, that lost it's gutts ( kind of ). This could explain the loss of boost - exhaust restriction.

 

But I only have 18k miles!??

 

What type of boost gauge wasn’t mentioned, if it was electronic then it should self adjust for atmospheric, it not, keep that in mind when interpreting gauge readings. The gauge may or may not be providing a glimpse of reality.

I have a 19% with improvements in the flow path and have logged (very rapid scan rate via the T-MAP) boost under many conditions, the highest boost recorded was on a dyno on a 101F day at 17psi. At the drag strip a peak of 16.7 psi on a 77F day was recorded; I’ve haven’t seen more than 15.2 psi on the street.

I've read the woosh or swoosh comment before a few times, as an example https://www.northamericanmotoring.co...ight=swooshing. Somone might interpret a resonant frequency as a noise like that.

If you dig deep enough you will discover Milltek failures are not uncommon and I have yet to see a Milltek fit correctly without bending hangers, and in some cases adding shims. I’ve had two cat-backs and a few headers; this is not second hand experience.

 

Wouldn't exhaust restriction be seen as MORE boost? Less power, but more boost, as the engine has relatively less throughput.

 

Yes, as I noticed this with over a pound lost. Boost is important, but is not the holy grail...

 

Yes it could some of the time because of restriction but not always. If the cat, OE, wrap, for some reason, breaks loose, it's far enough down stream that WOT may not be 100% given what what the ECU is reading.
This is just theory that goes along with "whoosh". Should have asked, "can you get to red line?" and "does the whoosh get worse?" then, the cat would be a good place to look or some place even further down.

What ever the problem, it seems to be intermittent at close to WOT. Yes?

Forgot to add: Mileage has nothing to do with failure - S***T happens

 

With my boost gauge I see 17psi to 18psi in 2nd, 3rd, 4th and even 5th gear. I have basicly a 19% (17%+2%)

 

Those numbers are right about what I would expect.

 

First Off. THANKS EVERYONE for your help! Also, HAPPY HOLIDAYS!

2nd- Does it matter that he has a ported head and cam? Wouldnt that see more boost??

 

Not likely. Same pulley - Engine RPMs = Same boost
See if you are able to get to 6500 easily & quickly. If there is a point at which the engine struggles & "whoosh" then there should be something restricting the exhaust. Post back, by then some other ideas might come to mind....

Thank you for the thought & you & yours have a grand holiday

 

Improved flow through the head (which may include larger valves, more lift from a cam is not as influential as larger valve cross section but a contributor as well) and improved exhaust flow post head, will decrease boost, all things being equal before the intake port and at the same rpm. Those who are seeing 18 psi or greater have an optimistic gauge, or are not subtracting atmospheric pressure, or have a restriction in the exhaust flow path (Eric Rowland got it right), or not running the M45 unassisted; I can’t speak for the M62.

 

Not realy, engine RPM dictates SC boost. If there is an exhaust restriction there is loss of RPMs as well as power.
Vacuum & the BPV are also effected. With the BPV disconected, so the SC boost is always on you would see higher boost.
The link you supplied pretty much says it all. "Whoosh" is not uncommon which pretty much elimates exhaust.
Some how "whoosh" reminds me of how a 54 Buick straight 8 use to sound with that little exhaust pipe.

 

Damn guys! We'll I'm going to Grassroots Garage next week to pick up my coilovers. Maybe I'll get Dan to put it through it's paces and give me his professional opinion.

 

Good idea. It's realy tuff to see the car through a few words, a book maybe. There are many issues that would be hands on only.
If you think your car is running great, it probebaly is.
Best of luck with the visit

 

I have a rear seat delete that I made and I have a similar whoosh sound, but its the fuel pump working hard at WOT.

 

30 degrees, 3rd gear redline, apexi showing 1.28 bar(18.56 psi) on a 15% pulley

 

in 2,3,4 and 5th i hit about 18-18.5. I get the whooshing noise as well, but i have a single sided exhaust, and they are known to make a whooshing noise.

you could always just take the catback part of the exhaust off and shine a light into the cat... if you can see the wrap in good condition it might be fine... but it could always be the pre-cat... still in warranty?

 

yes but the boost created by Roots blowers is dictated by both the restriction after the blower and the RPM of the blower (which is proportional to engine speed). A ported head and/or high-lift cam would create a smaller restriction and thus less boost, even though you'd be making more power, as the CFM number would be equal or even greater. "boost" is only the pressure of the air, not the mass flow of the air, and the more mass in the cylinder, the more power you can make. If your boost is very high, and your temp is very high, your mass flow won't be that much greater....

As an aside, a freer flowing catback exhaust will probably mean less boost, and an intake system will probably raise boost. 10.5 is the boost that a stock MCS would make, so having a catback and an intake cancel each other out a bit.

I was seeing a max of 18psi with stock headers and a 17% pulley, Alta intake and a oneball. Then after adding OBX headers, i was seeing a max of 17psi.

 

The IC, head, Exhaust, valve size & cam duration all play a part in what you see for boost. No argument.

The question is, with a 19, without a trick head, header or cam, what should the boost be?
jymontoya sig indicates that he has only a cat back & DFIC and his post indicates he just added a 19%. If he had 10 before & 15 after maybe that's all there is but in most cases that number is higher.
I also see that you only quoted 1 part of the post.

 

After a SC pulley install, the next best improvement was a freer-flowing exhaust system (think my gallery has an image or two)... where I dropped a good pound. More power on less boost and heat is a good thing!

Shooving golf ***** in the IC end-tanks would increase boost! Don't know if they fit, and don't do it...

A delta in boost readings from Summer to Winter is noteworthy, but not 6+ pounds (thought I was posting in another thread re the UNIChip, and boost drop).