Bx 16v Rev Limit?

[Guest CraigyBoy]

Hi all,

I have an Mi16 conv in my 205 and it's hitting the limiter at approx 6600rpm. Its running 3 row BX 16v ECU (Motronic 0 261 200 354).

I wondered if the rev counter was reading wrong so got it on the rolling road today.

Result: 172 bhp (not bad std rebuilt eng with K&N!) but definitely limiting at 6600 and the power curve on the graph definitely looks like it has more to give, it's not peaking.

Anyone had the same problem? Or know what i can do about it? Is there a diode/resistor or whatever that can be removed like on the 8V ECU?

Any good advice appreciated.

Cheers

[welshpug 1,648]

how was the rpm measured?

[KRISKARRERA 2 1 Cars]

They do seem to show lower revs in the 205 and 309. My first 405 Mi would show 7400rpm on the limiter and when that same emgine and ecu was put into my 309 suddenly it's limiter is at 6900rpm!

[Miles 331 1 Cars]

As said the Rolling road should have checked the RPM which can be done on the 16v engine with a clamp over the ignition lead, most don;t do this and take the Rev counter figure for the print out, The engine std peaks at 6500

[KRISKARRERA 2 1 Cars]

Well, it's supposed to but the two standard engines I've had are barely dropping off at the limiter.

[Guest CraigyBoy]

Hi thanks for replies,

 

I noticed when it was put on the rollers the computer screen said 'Teaching 3000rpm' so maybe the revs were programmed in by looking at the rev counter rather than having the pick-up on the ignition?

It was a cheapie £25 open day so the car was in, on, 2 runs and out again in 10 mins.

I'll ring them to find out how it was measured.

 

I guess i still don't know for sure what its limiting at but i would like to unleash it! (Assuming its not already revving to 7500 or something!) Whats the best (and cheapest) way to proceed? Is a 405 ECU any better?

 

The bottom end is balanced and has ARP bolts so should be good for a few more revs.

[petert 580]

The 354 is one the most desireable ECU's. It was fitted to late model 405's and has a knock sensor. Your problem is most likely an inaccurate rev counter. The 1.3 Motronics have the rev limit burnt into the chip. So provided your installation has been done properly, and the fuel pump is being controlled by the ECU (and a relay) and not the old tachymetric relay, there shouldn't be an issue.

 

Here's some graphs of different ECU's I tested recently, but on a modified engine.

http://forum.405mi16.com/index.php?showtopic=499

 

Sorry I don't have any std. Mi16 dyno charts, but do a search. There's plenty on here.

[Mikey G 3]

At a guess you went to a rolling road in Newport that i shall remain nameless as they dont have a good reputation. They use the dyno tacho and it has proved to be unreliable. I have known several people who have had dodgy results from there including a revlimiter way past where it was set!

They are still new at this so things may improve but i wouldnt trust the results given on this dyno.

[Guest CraigyBoy]

Ok then, one more question!

 

Can anyone actually recommend a chip with proven results? I've looked through previous posts and it seems to be a bit of a minefield. (My engine is std but with a K&N and may have an exhaust soon)

I wish to have the rev limit raised and throttle response improved-so its lovely and snappy like my 1.6 std 8v rally car The graph seems pretty good in terms of power so I don't want to spoil it either.

 

The rolling road place rekons the rpm was read accurately from a pick-up...hmmm who knows? But if I can get a chip that has the limit set to a specific value (eg 7***rpm) then job done.

 

Any thoughts?

[Baz 421]

Look for a standard '139' 405Mi16x4 Ecu, as these have a raised rev limit of 7400rpm iirc, so a little more than the others. Whether you'll find one or not is another issue!

[petert 580]

Can anyone actually recommend a chip with proven results?

 

There is no such thing. I might be able to give you a bin file of a 158 chip with a 7500 limit, if you can find someone to burn it for you.