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Take it to a dyno... (archive)

[ Follow Ups ] [ 5-series (E28) Message Board ] [ Msg. Board FAQ ]

Posted by JamesM on January 31, 2001 at 13:26:36:

In Reply to: Am I running at 'peak' performance? posted by GREG on January 31, 2001 at 13:03:51:

Go to a shop with a chassis dyno and exhaust gas analyzer and get some runs in. Check your emissions while on the dyno to look for lean/rich areas or a bad catalyst. At 190k, the engine should still feel very strong. 182HP and 215lb-ft of torque is nothing to sneeze at. Also get a compression and leakdown test performed to make sure your engine is still tight. Get the valves adjusted and check the cam for wear, esp on the #1 and #2 cam lobes.

Things that will degrade power (these apply to all cars):

1) Dirty fuel filter
2) Dirty air filter
3) Vacuum leaks
4) Clogged catalytic converter or muffler
5) Dirty injectors
6) Running too rich
7) Running too lean
8) Bad O2 sensor (causes rich or lean condition)
9) Spark leaking from deteriorated plug wires/cap/rotor
10) Plugs too cold (should use Bosch WR9LS silver plugs for 535i)
11) Heavy carbon deposits on intake valves
12) Pitted exhaust valves/valve seats

And specific to 80's BMWs:
13) Bad solder joint from power transistor to board in ECU

My 535i is down on power. Reasons? 4 (muffler) and 13. Also, I had the valves and seats reground at around 220k miles. The 535 naturally runs lean, so that shoots combustion temps up. The exhasut valves and seats were pitted somewhat, so I got a 1 angle valve job when I rebuilt the engine--didn't know any better. I think this killed the power quite a lot. The spec is a 3 angle job on the seats and one on the valves. It makes a difference!!

Once the car is completely sorted, get a 3.73 diff from an E30 325i or a 3.46 diff from a 1988 (only) 528e. Stock is the rather long geared 3.25, which gives you a theoretical top speed of 170MPH!! I've had great results with the 3.73 diff. Your gas mileage will suffer by about 10-15% (max), and the engine will run 14% higher revs with the 3.73.

BTW--what are you used to driving? Porsche? Twin Turbo Supra? Econobox?

[email protected]
88 M5
88 M3
83 535i

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