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by **TWorline** » Wed Jul 25, 2007 7:52 pm

I noticed in some truck pulling regulations it stated that the MWE slot could be no larger than 1/4". If we enlarged our slots would this allow more air to the turbo or is regulated for other purposes in truck pulling?

by **Begle1** » Thu Jul 26, 2007 4:02 pm

I've never even seen a picture of what a MWE slot is...

All I know is that it is supposed to help with turbo bark, and I'd assume the bigger the better.

Altough I'd assume that isn't the primary function of it... I think the primary function is related to enhancing the map width or something...

by **gman07** » Thu Jul 26, 2007 4:17 pm

Here's the best picture I found on a quick Google Image search: http://www.litchfieldimports.co.uk/imag ... r/may3.jpg
The MWE slot is on the inside of the shroud, just behind the leading edge of the blades on the compressor.
Here's part of a turbo I drew in Solidworks... you can see the MWE slot, though it's not quite as wide as I wanted.
http://www.dieseltruckresource.com/pics ... user=34373

The first part of this article describes it: http://www.turbobygarrett.com/turbobyga ... ch103.html

The MWE slot decreases compressor efficiency, so under normal conditions no MWE slot (or ported shroud, or whatever you feel like calling it) is best. However, at low RPM under high load, the compressor will tend to surge without it. This is basically the same thing as turbo bark; when, especially on an auto, you let off the throttle and RPM's drop, the turbo continues to spin and try to create the boost pressures it was before. As RPM's drop, the compressor moves off it's map to the left, past the surge line, and the turbo "barks". The MWE slot widens the map out to the left.

Disclaimer: I don't necessarily know anything.

by **TWorline** » Thu Jul 26, 2007 6:56 pm

DANG!

Thought maybe we could get more air to the turbo by enlarging the MWE.

by **Begle1** » Thu Jul 26, 2007 10:17 pm

Alright, so why is an enlarged slot outlawed then?

Unless somebody "enlarges" it in such a way that it's drawing air from around the inducer, I don't see how it's exploitable. There has to be some advantage for sled pullers if there's a rule against it.

by **gman07** » Fri Jul 27, 2007 6:57 am

The only advantage I can see is reducing compressor surge, but I have no idea why they'd regulate something like that.

The MWE slot will draw some air from around the shroud, but that's actually a disadvantage. The air is hitting the blades at quite an angle; ideally it'd be coming in straight.

by **KTA** » Fri Jul 27, 2007 8:22 am

It is difficult to explain but basically it is like this. Most rules state that the max inducer size is say 3" to limit the horsepower on a particular class. What many would do was put say a 3.5" wheel behind the 3" inducer bore starting where the MWE slot is. They would then widen the slot to allow air to feed the big wheel yet it would still measure the 3" bore limit.

by **CAJUN 93** » Fri Jul 27, 2007 9:02 am

same thing happens in gasser drag racing where turbo inlet size is limited. run a huge wheel and figure out how to get the extra air to it. it would be better to limit the wheel size but the opening is much easier to inspect during tech. this rule just limits the creative ways for guys to interpret the rules..

daryl

by **Begle1** » Fri Jul 27, 2007 9:17 am

KTA wrote:It is difficult to explain but basically it is like this. Most rules state that the max inducer size is say 3" to limit the horsepower on a particular class. What many would do was put say a 3.5" wheel behind the 3" inducer bore starting where the MWE slot is. They would then widen the slot to allow air to feed the big wheel yet it would still measure the 3" bore limit.

Yup. The angle of the air coming in would be a detriment, but still worth it.

by **KTA** » Fri Jul 27, 2007 2:38 pm

I was once involeved with a tech issue on a NTPA superfamr tractor. The rule said the compressor wheel must be no bigger than a 3" at the inlet. The guy had a 4.1" comp wheeled Prostock turbo with a 3" comp wheel stuck on the shaft in front of it. Technically it had a 3" wheel at the inlet, but it wasnt doing anything at all, just trying to press the rule way past the grey area. :twisted:

It was quite the issue when it happened. LOL He did win several pulls with it though before he was protested and a near fight insued over its legality.

by **Begle1** » Fri Jul 27, 2007 5:26 pm

So he had a three inch diameter impellor tack welded onto the front of his four-point-one inch diameter impellor?

by **KTA** » Fri Jul 27, 2007 8:23 pm

It wasn't welded on, the turbo had an extra long shaft and it was on the shaft mounted out in front.

by **Begle1** » Fri Jul 27, 2007 9:42 pm

That man is my hero.

I ever tell you the story about the time in 7th grade when we had the annual "great balloon race", and my balloon was a 2 liter Cactus Cooler bottle pressurized at 120 PSI?

Ahhh, rules lawyering is a lifestyle...

by **CAJUN 93** » Sat Jul 28, 2007 6:24 am

yeah, rule pushing is an art form. we ran a class that said you had to run hydraulic lifters. no problem, buy hydrualics, take em apart, replace the spring and plunger with a solid rod...... instant solid lifter

. when we finally got torn down the tech guy didnt approve. still it was within the letter of the rule. creativity and experimentation wins races.

daryl

by **oldestof11** » Sat Jul 28, 2007 9:37 am

KTA, How can I machine my own MWE slot? I was pushing 30-32# last night at the pulls :twisted:

2nd4lo was really pushing the engine. 1100* and 30#'s was nice to see but the clutch smell :shock:

Jon

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