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Old 10-04-2017, 10:13 AM   #1
Lummox
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Default Maximum power / boost for automatic transmission?

Hi all,

Recent owner of a 1996 940SE auto with a barely-run-in 251k miles on the clock.

Obviously one of the first things I have done to the car is fit a boost gauge and MBC, and up the boost a bit, which has made it much more fun (albeit highlighted the cheapness of the rear tyres!)

Looking for info on modding these cars, almost every post and article starts with "you want an M90 gearbox manual car". Well, I haven't got one of those... can anyone enlighten me as to the limitations of the autobox and why nobody seems to tune them? I can see that the box is a bit sluggish but is it actually significantly weaker and/or likely to fail quicker?

Thanks
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Old 10-04-2017, 10:46 AM   #2
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Search and educate yourself man, its the best thing you can do before you make such a post.
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Old 10-04-2017, 11:30 AM   #3
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I’d be willing to bet that more people use the auto (AW71) than the m90 5 speed. Reason being is ALL 940s in america came auto I believe. And they hold more power/torque than your tiny turbo is capable of producing. If you’re in Sweden, the m90 is probably easier to get ahold of though.

In order to make it less sluggish you need to do the accumulator mod. It’ll shift harder, be faster, and last longer.
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Old 10-04-2017, 12:00 PM   #4
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You've given almost no useful info on your car. Is it at AW71? What turbo? 10 psi on a 13c is not the same as 10 psi on an HX35
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Old 10-04-2017, 12:40 PM   #5
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It's probably all stock if it didn't even have a boost gauge and MBC.
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Old 10-04-2017, 01:25 PM   #6
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I believe Kenny was pulling down low 10's in the quarter with the aw71.... soo that's about 600-odd horsepower... but I think he was rebuilding them often at that power level.

Should do fine for a 250-350hp life provided you're doing the accumulator mod.
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Old 10-04-2017, 02:18 PM   #7
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^^

I think Kenny went to a GM transmission by the time he was running those times. IIRC, he was able to put approximately 400 HP though the AW-71 after doing the accumulator mod. Greg Ervin went through 6 AW-71s in 2 years at approximately 300 hp. After doing the accumulator mod, the same AW-71 has been in there for a few years of very hard racing use at 300+ hp with R comp tires. Stock, an AW-71 is good for about 250 HP.
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Old 10-05-2017, 07:57 AM   #8
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No idea what trans the car is running, it was a bone stock vehicle when I bought it. All I can say is that it is a 1996 940SE 2.3 LPT.
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Old 10-05-2017, 07:58 AM   #9
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PS should state that this is UK car, I'm not based in America.

Thanks!
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Old 10-05-2017, 08:06 AM   #10
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Quote:
Originally Posted by Mogly View Post
Search and educate yourself man, its the best thing you can do before you make such a post.
That was the reason for my original question, because I had looked up a number of articles/posts about tuning these cars and most if not all of them talk about starting with a manual/M90 car as the best base vehicle for mods.

I was trying to establish why, since a lot of these cars seem to come with autos (in the US, all of them as has been said above) so it was weird to me that every discussion on the topic seemed to be about manual cars. Unless there was some sort of inherent design issue with the auto that made them unsuitable for tuning.

Personally I think the auto suits the car, I'm not averse to autos at all, just wondering why most of the discussion seemed to be about tuning manual cars.
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Old 10-05-2017, 10:47 AM   #11
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Because people generally think manuals are more fun. I do. But my 240s came with the inherently weak ‘m47’ 5 speed transmission. Though it hasn’t caused me any issue behind ~200hp.

The 940 turbos I don’t think ever came with an m47 behind them, but they did come with an m90 where you are. The m90 is supposedly vastly superior to the m47.

Both the m90 and aw71 seem to be able to hold some nice power (I think you have to mod 3rd gear on the m90), but if people had the option between an auto and manual, many opt for the manual.
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Old 10-05-2017, 10:59 AM   #12
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I think the M90 was used on the 1995-onwards (and possibly some late 1994) 940s over here, not sure what they had before but assume M47?

The majority of the cars that seem to come up for sale now are autos, probably 4 out of 5 cars (not that 940s in general are plentiful anymore) so it's much harder these days to find a tidy, clean manual car. In the UK at least.

I wonder if more people crashed the manuals, or the auto is just hardier (especially in the earlier gearbox cars)? Or maybe they just didn't sell many in the first place?

Going back to my original question though, assuming an otherwise standard car which I believe is in GWO, running about 10psi boost should be fine for the AW71 box right? Especially if I do the accumulator mod.
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Old 10-05-2017, 12:14 PM   #13
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Yes. As stated earlier, it would be difficult for you to kill the aw71 auto with a stock turbo. The 13c only flows enough to make what, 250bhp? Probably at the absolute best case scenario too.

And you could be right maybe they did give 940T cars an m47 earlier on? I don’t know as we never got them here. My m47 holds 10 psi just fine btw. And it makes more torque because it’s higher compression (+t). It isn’t really happy though. No issues aside from a whining noise.
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Old 10-05-2017, 02:04 PM   #14
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M47 was never put in turbo cars, it was always AW or M46.
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Old 10-05-2017, 04:15 PM   #15
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28 psis
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Old 10-05-2017, 04:27 PM   #16
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Most likely an AW71L. Overseas got the lockup trans, US didn't on the turbo cars. You can verify by looking at the tag on the drivers side of the trans.

I've been running an AW71L with the accumulator mod (search, there's plenty here about it) for the last 100k, on a trans that had 180k on it when I bought it. This on a car with a between 250-300whp during that entire time, and it's not driven nicely on a regular basis.
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