Engine tuning M42B18

[PerTore]

So, now the engine is in the car, started, and braked in. I took it for a test run now, and I'm very satisfied with the result. It idles like a tractor, though, but I'll look into that later. It idled bad before I took it apart, so that doesn't worry me much. I don't think I've lost too much in the lower register, and passing 5000 rpm its hysterical! Now the need for a new gearbox is starting to get clear! I had to change the original gearbox, and I got what i thought was an identical box, but it's obviously not. Still it is a Getrag 240, but the range is definitive not meant for rallying. Any good ideas?

I hope to get a dyno run this week. Exited! It feels like 150+hp, but you'll never know...

[wazzu70]

The manual from the e36 has much different gearing.  Its a lot steeper as 5th is a 1:1 gear. Is your car e30 or e36?

[PerTore]

I have a 90" E30. The 4th is 1:1' and the 5th I think is 1:1.4. What I need is a gearbox with a high ratio 1st and 1:1 on 5th.

Dyno is due on Monday

[Warsteiner]

PerTore...if your 4th is 1:1 then your 5th, which is then considered an overdrive, would have to be more like 1:.81
If it was 1:1.4 then that might be a 3rd gear in a close ratio set up.

Cheers,
~Ralph

[PerTore]

Yes, you're completly right, of course!

[kaiser16]

Just in case you haven't seen the website, although you probably already have
http://metricmechanic.com/
they have great ideas on how to get more power out of an m42 if you want to spend $$

[PerTore]

Ok, if I've got it right my 240 tranny has this ratio
1st- 3,764
2nd- 2,00
3rd- 1,33
4th- 1,00
5th- 0,81

And this sound like a "not too bad for rallying"-ratio, right? Does there exsist 240's with different ratios? Or is it bulletproof that this is my ratio when I've got a 240?

It says on the housing, right side bellhouse 240.0.0370 90' and rear housing 240.0.0366 91
And 225 and 1.4.

I've also got a 220 from an E36 lying around, and I think this is the same as the 250. This is considered to be a "close ratio" tranny, but I just can't understand why, considering the ratio
1st-4.23
2nd- 2.52
3rd-1.66
4th-1.22
5th-1.00

With my 4.10 diff ratio the insanly low 1st will be completly useless with the 220, and 95% of rallydriving will be in 2nd, 3rd and 4th. The difference between 2nd to 3rd will be 0.86 (0.67 with the 240) from 3rd to 4th 0.44 (0.33 with the 240) short story, the ratio"gaps" is considerably bigger with the 220, than the 240

Am I completly lost in my theories (or math) here? Please enlighten me...

[PerTore]

Ok, mods! I wrote a long message with high level ratio math and reasearch. It had to be "passed by a moderator" to be posted on the forum. The last time I got this message, my two messages "dissappeared" Hope it won't this time...

[DesktopDave]

I got it.  I know, the spam filters are annoying.  Please accept my apologies.

If my math is correct, you had to wait a grand total of 50 minutes for it to be fixed...how's that for service?

[gearheadE30]

The Getrag 220 and 250 have the same, or at least similar, ratios, but the 250 will be the correct fit for the M42. The 220 is a fair bit longer, iirc. I'm not sure if the output flanges are the same or not.

Just to quell any misinformation right here, adjusting cam gears is in no way a substitute for aftermarket cams. What the M42 really needs is a little more lift and duration (those catcams should work great, and are a step above the usual S50 profile a lot of M42 cams use). Note that you can also get more reliable high revs out of the engine by fitting solid lifters ($$$) and you can bump up the high end by fitting larger valves. Later M42's also have narrower valve stems (6mm vs 7mm diameter) that allow for slightly better flow.

Lighter flywheel will do wonders for the responsiveness of the engine, and acceleration in first and second gears.

When you have the chip made, for maximum performance you will want to have it dyno'd on your car, with your setup. Changes to the intake and exhaust along with minute production and wear differences between engines means that most chips are conservative for most cars.

[PerTore]

Exellent! No problem. I was afraid I had to write it all over again. (I was very tired last night, so please forvgive my harshness

Edit: was ment for DesktopDave

[PerTore]

The dyno run was good today. I've got 152hp at 6000 rpm and 187,5Nm torque at 5400 rpm, and thats about what I hoped for.  Great mix all over, and good driveability from 4500 to 6500 so overall very positive. I'm really looking  forward to race it now!

[Balleristic31]

How much did the cams and chip set you back?

[strypt]

There's a cheap, or should I say less expensive  way to raise the CR a bit to around 11:1. Try to find a set of used M52B28 pistons (328,528 etc..) and shave about 0.2-0.3 mm of the piston top to get the same compression height as the standard M42. I don't remeber the exact dimension since it was about 7 years ago I did this unfortunately. You also need to mill new valve pockets. That piston is also lighter with a different design on the piston skirt.

A bit late information but now you have some time to source the parts before next overhaul.

Lycka till i rallyskogen

[wazzu70]

The dyno run was good today. I've got 152hp at 6000 rpm and 187,5Nm torque at 5400 rpm, and thats about what I hoped for.  Great mix all over, and good driveability from 4500 to 6500 so overall very positive. I'm really looking  forward to race it now!

Any chance you can post a graph?

Nice numbers!