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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Tue, Sep-26-2017, 05:37:32 PM   #1
Turb02
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Default Good power but low boost. Halp.

I recently had a dyno day with the local BMW club and although it was hot and humid (92 with 60+% humidity) my car made decent power on a Mustang.

Weather corrected it made 440whp and 349wtq and peaked at 8.5ish PSI

Thats not too bad, except I have a stage 2 Gen 3 kit, W/M, 70mm pulley and replaced the C38-81 with a C38-91. Frank Smith thinks I should be seeing 11psi.

I have no logs while it was on the dyno, and can upload the graph when not at work, if needed.

I just had a leak test performed and there are no apparent boost leaks.

The belt is less than 3 weeks old, as is the tensioner pulley (tensioner itself is of unknown age but is still pretty strong).

I just ordered ProLogger from TTFS so Ill get it logged as soon as I receive the cable.

What are symptoms of belt slip? Could this cause me to lose almost 3PSI? What else should I be looking at?

Help is appreciated because I want a retune for the bigger blower, but want to make sure the car is mechanically sound.
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Old Tue, Sep-26-2017, 06:02:53 PM   #2
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Default Re: Good power but low boost. Halp.

I'd figure out what expected boost was before looking for something that may not be missing.
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Old Tue, Sep-26-2017, 06:09:30 PM   #3
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Default Re: Good power but low boost. Halp.

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Originally Posted by fattycharged View Post
I'd figure out what expected boost was before looking for something that may not be missing.
Im new to SC cars, and ASSumed the pulley size is what dictates the level of boost.

How would I determine what the target boost is if its not determined by pulley size?
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Old Tue, Sep-26-2017, 06:19:17 PM   #4
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Default Re: Good power but low boost. Halp.

It does. What did your graph look like? Did they run to redline? If they didn't that may be your answer right there.
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Old Tue, Sep-26-2017, 06:28:13 PM   #5
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Default Re: Good power but low boost. Halp.

I had them run it to 7800 as the car was heat soaked already.
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Old Tue, Sep-26-2017, 06:33:25 PM   #6
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Default Re: Good power but low boost. Halp.

This was the second set of 3-runs. The first run I had them go to 7900-8000, but they had the dyno in AWD mode. On that graph, I put down 602whp.

I almost shat myself then immediately knew something was way off.
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Old Wed, Sep-27-2017, 06:48:01 PM   #7
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Default Re: Good power but low boost. Halp.

Any thoughts as to why my boost is low for a 70mm pulley but power is decent?
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Old Thu, Sep-28-2017, 06:53:23 PM   #8
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Default Re: Good power but low boost. Halp.

First, its a centrifugal blower, you make peak boost at peak rpm...

That graph only shows rpm, hp, tq...you don't even have your afr's or map monitored?

Do some logging yourself, you should be able to make peak boost without breaking any laws. You'll only see 11psi at redline, just the way it works. But you're definitely leaving a lot of hp on the table above 6500, it should never flatten out like yours does. Take a look at Actives site and the graph for a stg2 car, you'll see what I mean
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Old Thu, Oct-12-2017, 09:07:30 PM   #9
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Default Re: Good power but low boost. Halp.

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Originally Posted by fattycharged View Post
First, its a centrifugal blower, you make peak boost at peak rpm...

That graph only shows rpm, hp, tq...you don't even have your afr's or map monitored?

Do some logging yourself, you should be able to make peak boost without breaking any laws. You'll only see 11psi at redline, just the way it works. But you're definitely leaving a lot of hp on the table above 6500, it should never flatten out like yours does. Take a look at Actives site and the graph for a stg2 car, you'll see what I mean
Yeah, the dyno shop was a bit understaffed and didnt hook the AFR probe to anyones car.

Im working on getting a solution to monitor map and AFR. As it sits right now, The AutoMeter AFR gauge doesnt have a serial output, just analog voltage line and Im not spending $500+ on their data logging solution, for one gauge.

Im not sure how I can get to redling in either 3rd or 4th without breaking any laws, to log it on the streets. If I recall, I was at 129mph at the top of 4th on the dyno.

After looking at several pics online of people with similar kits, it appears I have a vacuum line attached to the top of my bypass valve to my intake manifold. May research/look at removing that.

I dont really want to throw money into a new ICV and under-manifold hoses, hoping I replace a leaking hose.

I guess the low boost could be a timing factor?
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Old Fri, Oct-13-2017, 03:21:44 AM   #10
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Default Re: Good power but low boost. Halp.

Power doesn't seem too bad for a mustang dyno. They read low. What's your elevation? High elevation will result in lower boost levels on a centrifugal blower system
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Discussing Good power but low boost. Halp. in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)