John Stein's User Report

Date: Thu, 7 Sep 2000 15:42:48 -0400

From: "jhstein"
Subject: 745 w/ Tuoma Mod, a users report

 To all:

tngauge.gif (7821 bytes)

 I have had several people ask to see this again.  Why, I don't know, but
here it is.....

 "I have been waiting to write this report until I had a few months experience with the modification.

 Just a quick note.

 The Tuoma mod comes in 2 parts.  1.  A modification to the wastegate (much like the Porsche crowd uses, and 2.  A modification to the Motronic which eliminates the 10 psi over boost shutdown . 

 My experience with the Tuoma mod is favorable..... But ONLY with these caveats.

 I would only consider / recommend the modification under these conditions:

 1.  A boost gauge must be installed.  It is essential.

 2. A 3 or 4 wire o2 sensor and a mixture monitor such as the HALMETER AFR30 should be installed.  This is also essential.  A 1 wire can be used but I prefer the 4 wire.

 3.  For boost levels above 9 inches, a fuel system modification which enriches the fuel mixtures  based upon boost level is absolutely essential to avoiding blown pistons.  The Stock BMW injectors and stock FPRs run out of capacity at 8 psi and start to lean out the engine with potentially catastrophic results if the knock sensors are not fast enough.  I use a Cartech unit.( ).   This raises the fuel pressure by progressively blocking the fuel return line, thereby providing up to 80 psi to the fuel rail versus the 42 psi with  the 2.5 bar FPR.   This unit is very effective because it lets the fuel rail operate at the stock mixtures whilst in the range of idle to max normal boost (6 psi).  Over sized injectors can be used to deliver more fuel but are a very problematic solution because they screw up the entire fuel delivery profile.....

 Obviously 80 psi on the fuel rail also requires the fuel system hoses be fresh,  or better yet, fresh AND steel braid clad.

 Having said all that.....  The Tuoma mod is everything they advertise.  In the past, I have played with elevated boost pressures up to 10 psi by bleeding the wastegate line (using fish tank air valves).  I had good success.  The nemesis is the 10 psi over boost shutdown in the Motronic.

The Tuoma mod to the Motronic completely solves that problem, with no adverse effects on derivability.  While the Motronic was at Tuoma, I had them give it a full health check.

 This was also money well spent.

 They replaced several components which were failing at ambient temps above 85 degrees F.  ( A very common problem in Atlanta...)  So far, all my problems are solved.  I also replaced the 2 flywheel sensors while I had the car off the road.

 Just took the car on a 1000 mile trip.  No problems.....Fun to drive.... All as advertised..

 So is it worth it.     Welllllll............. Yes, not cheap, but worth it.

 The installation process is straight forward, but the finishing out is the bugger.   If you mount the blow-off control valve as they show, (next to the gear shift lever) then you will be dismantling your entire center console from front to back. To do the full job, and make it look nice......... took me a weekend plus a few evenings...... Why?  Because I had never had the center console out and had to learn how to do it.  After that, it is getting the correct fitment to the hoses and the arrangement into the shift handle area....   It all takes a lot of fiddle.

 Now, ..........   add in the time and expense to mount the boost gauge, the fuel pressure modification, and the Mixture meter, and well..... it all adds get the picture.

 What do you get?     LOTS OF POWER


 For you power hungry 745 freaks out there, this is the best answer on the market so far.......

 Yes, you can install this mod on high mileage cars.    Mine has 216 000 miles, and at this point, have no need for the copper head gasket.  However I am keeping it to 14 psi maximum boost (for now).

 What a kick in the ass.

 Find a string of cars on a 2 lane road, set the auto tranny to Sport, then stomp it and HOOOLLLLLDD ON, cuz you're gonna' go somewhere ......... REEAAAAL FAST...........   Even with the stock rear end ( I think it is a 2.93) the car is scary fast.  (The present rear end gives me 3300 rpms at 143 in 4th gear overdrive.   It is still pulling very hard even at the stockboost levels of 6 psi )

 I have not  put it on the dyno yet, but probably will in the near future...

I won't even venture a guess as to how much horsepower it is making....

Certainly a whole lot more that it was before.

 Hope this pushes all  you other 745 freaks over the edge...

 Bottom line.   It ain't cheap, but it is good and delivers what they promised.   However, please read the very strong caveats about the boost gauge, fuel system mod and the fuel mixture monitoring meter.  They are absolutely essential to the continued health of your motor when operating at elevated boost levels.  Enough said!!!

 John Stein

85 745

85 M6