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16 HP Gain with new Eismann Sport Mufflers (archive)
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Posted by scott740iS on February 16, 2001 at 18:45:37:

I finally got my Eismann sports mufflers installed today on my 2000 740iS. The dual 3.25 inch stainless steel round pipes on each muffler look great. Those four large pipes sticking out through my rear apron look wicked.

I had the car Dyno'd (sp?) today before the exhaust was added so I could compare before and after. I have Dinan Stage 2 software with CAI and wanted to see if it really made a difference from stock. I compared the dyno curves with the ones published by Dinan on their web site. I was amazed. My dyno runs were at the wheel while the Dinan curves are engine. However, if they match, theoretically one should be able to find a single, constant drivetrain efficiency number relating the curves of Hp/Torque at the engine to Hp/Torque at the wheels over the entire RPM range. In a very short time, I was able to arrive at a drivetrain efficiency number of 74% (automatic transmissions should lie around 70 to 75%). By dividing the wheel Hp/Torque numbers at different RPMs by this percentage, they should convert to engine HP/torque. When I did this, I found that my car matched the published Dinan curves within 1 horsepower and 1 ft-lbs of torque over the entire RPM range. Even the peek points were at the same RPM. Rather amazing and it raised by impressions of Dinan.

Next I had them install the Eismann Sports mufflers and re-dyno'd the car. I was again amazed and the people at the performance shop were impressed. Hp at the wheel increased by 11.7 Hp (at 5700 rpm) and torque increase by 11.3 ft-lbs (at 3500 rpms). Using the same conversion factor of 74%, this translates into a horespower increase at the engine of 16HP and a peak torque increase at the engine of 17 ft-lbs. This also translate into a maximum Hp rating of 317 HP and maximum torque rating of 365 ft-lbs for my engine. I have to say that my decision to buy the Eismann exhaust over Dinan was correct since Dinan claims gains of only 6 or 7 HP at the engine.

My next step, next week, will be to add the Dinan High Flow throttle body ( and mass flow meter when it is available in 3 or 3 weeks for 2000 year cars). This should add another 10 to 12 Hp and the same ft-lbs of torque. I will have it dyno'd again. The only thing left is a supercharger, but I am waiting for ESS to come out with their new design for the 740i in the next 6 months.

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