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john vanlandingham


And the diff rotates just a scance more revolution per mile when the ratio has changed from say 4.88 to 5.45---there's 12% more diff rotations per mile. Seems like a range of 17 to 24% depending.

The BMW speedo sensor reads off a trigger wheel on the diff case so changes in final drive don't affect the speedometer accuracy.

I was just wondering a bit ago if we couldn't make a bracket for the Supra diff to hold the BMW sensor and read off one of the diff toe CV adapter rings.

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NoCoast
I was just wondering a bit ago if we couldn't make a bracket for the Supra diff to hold the BMW sensor and read off one of the diff toe CV adapter rings.

My car had ABS when I started, so I've got tone rings on the rear axles and there was a signal pickup on the hub that we could tap into. Just no idea what sort of wiring would be needed to pick-up that signal and transfer it to the ECU.

Dave



Edited 1 time(s). Last edit at 04/14/2011 08:04PM by DaveK.

My $0.02 on ODO's ...

We use a cheap Terrortrip 202, it does the job barely. I don't use it, so I can't sya specifically what else it should do, but one complaint I hear often is "I wish this thing had a clock". We have a drug store clock velcored to the dash. Problem is you can't see it when it's dark, rally computers you can read in the dark. Unles syou rally 100% in the daylight thisis a big deal.

As for the real necessity of a rally computer for stage rally... our #1 use .. we write mialges in our notes of noticable things, so if you get off notes during the stage you can use the references to get back on quickly. If we forget to zero, or don't write enough mileages during recce we always have issues.. if we zero and write lots of milages we never need them...

Pickups: we use the terrortrip blue pickup on a front wheel. I weld a couple of nuts to the back of wheel studs, make a simple bracket to mount the sensor and pick up from these. Make sure the bracket is sturdy enough, and get the sensor really close, like .020. On ice and snow we get the biggest errors due to wheel lock up, but realistrically under normal gravel rally conditions, if you are locking up front wheels enough to affect your milage drastically, you have too much front brake bias... fix that.

Oh, BTW... don't weld on nuts to the back of the wheel studs, use the head of a bolt.. otherwise the sensor will pick up two pulses for each nut, until about 65mph, when it starts reading only 1.. then evereything goes to hell.

Brantz sounds good, but I've never used one.


-Martin.

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MRWmotorsports
Pickups: we use the terrortrip blue pickup on a front wheel. I weld a couple of nuts to the back of wheel studs, make a simple bracket to mount the sensor and pick up from these.

On my volvo 740 I had the standard terratrip sensor reading off the wheel studs themselves. Worked perfectly.

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MRWmotorsports
...if you are locking up front wheels enough to affect your mileage drastically, you have too much front brake bias... fix that.

Its more of an issue in a front drive car when you're measuring off the rear - even though you're not supposed to be locking up anything if you're driving well.

A point on feeding a signal to the factory odo. (which should be obvious.) You need to source the same strength and frequency of signal that the factory sender put out. In otherwords - how many pulses per revolution did the diff sensor read and what was the voltage spike when it did. Since you can't calibrate the factory odo easily, you need know what it wants to hear. If you're trying to duplicate that by magnets on a half-shaft or similar makes sure they are evenly spaced or you will see your speedometer float like it has a bad speedo cable.

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Morison
A point on feeding a signal to the factory odo. (which should be obvious.) You need to source the same strength and frequency of signal that the factory sender put out. In otherwords - how many pulses per revolution did the diff sensor read and what was the voltage spike when it did. Since you can't calibrate the factory odo easily, you need know what it wants to hear. If you're trying to duplicate that by magnets on a half-shaft or similar makes sure they are evenly spaced or you will see your speedometer float like it has a bad speedo cable.

Going to pull open the small case BMW diff I've got and have a look at the trigger wheel. No idea currently how many pickups its got, but I think it's likely 6 or 8. If its 6, we might be in luck trying to get something to read on the axle adapters. Lowish on the priority list at the moment.

-New suspenders (350/110 valving vs. 250/90) nearly on the car - wanted to pick up slightly longer bolts.
-Inside of doors now painted Olympic White instead of Boston Green.
-10 more lbs of dried mud knocked off the car

Still need to hoping to knock out a few things before shakedown #3 on saturday.

-adjust throttle cable to get rid of the little bit of slack (could be how linkage is setup on pedals, could be cable)
-door panels

Dave

Went back to work on the car Friday night. Tried heating and bending the ABS for the door panels, and ended up messing up the first one. After careful measuring, we were 2" short to be able to make two more, so we just made a passenger one. Turned out pretty good I think:



Just need to incorporate a door pull for the passenger side...co-driver mandated, LOL.

Next up was to get the bolts through the new rear suspenders. Easy, right? Nope, turns out that those extra bars we welded on to make those mounts double-sheer got bent when we bottomed out the car. A little bit of cursing later and they fit. Time to figure out how to add some more reinforcements to those.

Guesstimated where the spring perches should be and set the car on the ground. Drove it around the parking lot to get the suspension to settle and took measurements. Ended up about 3/4" too low so set about raising it up. Since the battery seemed to need some charging time, I left the car running.

About two minutes in we start to hear a little lifter tick. No big deal, seems to be a bit common with this motor after a hard run, but after sitting at idle? So, finished up the coil adjustment and hopped into the driver's seat. Noticed the low oil pressure light was on. Shut it off right away and parked it for the night. Yet another item to confirm driving to WA this weekend wasn't a good idea.

Dave

You forgot to install speakers for the transit sound system!

-New suspenders (350/110 valving vs. 250/90) nearly on the car - wanted to pick up slightly longer bolts.

I probably missed it... what are you trying to change/fix with these different rear suspenders?
Curious...

-Martin.

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MRWmotorsports
-New suspenders (350/110 valving vs. 250/90) nearly on the car - wanted to pick up slightly longer bolts.

I probably missed it... what are you trying to change/fix with these different rear suspenders?
Curious...

-Martin.

The car lands after jumps at 90-100 mph just peeeeachy keen on front but there's a disconcerting bounce at the back, and anything disconcerting at 90-100 mph is disconcerting, to say the least. The car is also a bit too tall in back . The shocks he got are minus 1" versions of the ones I use on Xratties, and are valve 260/90 with 175 lb springs.

I don't think it should have firmer springs, so we're trying out some spares for my Ford which are for 4x4 Ford---they're some magnesium bodied 909 Ford things I got from Stig Blomqvist left over when they converted his Escort Cosworth to "World Rally Car" spec----which means they welded in towers and converted to struts in the back----.
Being 4x4 they're valved 350/110 so maybe 20% firmer on compression to help with the bottoming, and 34% firmer rebound, plus they're a bit shorter overall.

We'll see!

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MRWmotorsports
I probably missed it... what are you trying to change/fix with these different rear suspenders?
Curious...

Here's the video from shakedown:





At ~0:40 into the video you can see we're going down a kinked straightaway with a few bumps. When we hit the dip at 0:53 the front rolls through it nicely, but the rear gets bounced.

At ~2:35 we're approaching the 'step up' jump on the course and at 2:46 you can hear the car get jounced again...this time enough to pop the airbag cover off.

At ~3:00 I confirmed that the car will do donuts in 2nd with no problems.

Dave

Thanks for the explaiantion guys...will be intersting to see if it works out.
I thought thinsg lookdpretty good in the video except for a couple of minor bumps in that nice smooth test track :-)

-Martin.

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MRWmotorsports
Thanks for the explaiantion guys...will be intersting to see if it works out.
I thought thinsg lookdpretty good in the video except for a couple of minor bumps in that nice smooth test track :-)

Agreed - for a new car its coming along. Biggest issue holding me back was the slack in the throttle cable. Made it a bit difficult to pull off smooth shifts, and I think we weren't actually getting 100% throttle as a result too. That little issue is all solved now. I think with the stiffer suspension and throttle solved, we'll be able to attack the course a bit more. Its actually got some rough spots that I was intentionally avoiding when that video was taken, so we can shake it down harder too.

Have to get the oil pressure issue solved (likley new oil pump & will add a baffle while I'm in there) and hopefully we'll be back out testing again soon.

Dave

Productive but expensive day. Ugggghh.

-Oil pump nut that's prone to loosening was found sitting at the bottom of the oil pan
-Other misc aluminum bits found in the bottom of the oil pan
-Confirmed that the oil pan had been removed at some point in the past
-New high volume oil pump installed with fix so the nut can't back off
-Oil pan baffle installed while oil pan was off

The thought from the tech's at SCR was that the timing chain may have snapped at some point in this motor's past. When they snap, often they'll break a few bits off the timing chain guide, so the thought is that when the pan was off to fix that, they might've missed a few pieces. I'm hoping that's the case because a blown motor (or one that's about to) would likely mean no racing for the BMW this year.

Dave

Kind of a kick in the nuts to have engine problems after all of the effort you've put in. Let's hope the oil pump fixes it. It would really suck to not get out on stage this year.

-Martin.