Wednesday, September 25, 2013

Lotus 'Ice Mode' Explanation

The Lotus have suffered from a phenomena under braking that feels like you've lost your brakes - this is something we mentioned in our recent blog entry with our Switchblade.  I found an explanation for this issue from a noted Lotus Engineer at the UK factory.
The symptoms being described are a result of the Electronic Brake Distribution (EBD) system operating. This system is also referred to as Dynamic Rear Proportioning (DRP) and is, as the name implies an electronic system which, through the ABS control valve block restricts the line pressure to the rear brakes automatically to a pre-programmed algorithm. You can consider it as an electronically controlled proportioning valve which measures parameters like the rate of deceleration and rate of pedal application and uses this data to anticipate a rear wheel lock-up and then reduces the braking effort at the rear wheels as necessary. If the ABS system is left to do this, it can only react to a wheel as it starts to lock and therefore the car can already start to spin before the ABS can start to work. In extreme circumstances, if the driver brakes very suddenly the EBD system can lock off the pressure to the rear wheels completely; what pressure was at the rear brakes as the EBD system engaged remains there and the rear brakes are still working as a result, but further increases in pedal effort will not increase the braking at the rear of the car because the pressure to the rear brakes cannot increase. When this happens the brake pedal goes hard, as it is now pushing against the front callipers and a closed valve only, instead of against the front and rear callipers. The rear callipers are single piston and therefore quite flexible, so they are a major factor in making the brake pedal feel 'soft'. When the valve closes, the brake pedal pressure no longer flexes the rear callipers, hence the increase in pedal hardness. The front brakes are still working just as well as before the valve closed and will give more braking if the pedal effort is increased, while with the rear brakes working as hard as they can the braking is NOT affected. The problem is the driver feels like braking is reduced (even though it is not) because of the change in pedal feel. If the driver continues to push hard on the pedal, the car will continue to slow as fast as it possibly can in the circumstances. If he increases the pedal effort the front braking effort will increase and the rear effort will remain where it was. If he was to back off the pedal for a fraction of a second, the valve will reopen and the rear brakes will operate as normal again, with the pedal feel going back to normal.
In the case of releasing and re-engaging the pedal the car should not be able to slow any faster than it was with the system engaged unless either 1: the driver triggered the system in the first place by stamping on the pedal too fast or 2: the system triggered because a rear wheel was unloaded when the brakes were applied and would have locked up but is now fully loaded once again and able to sustain a greater braking torque. If the rate of deceleration does improve when the pedal is reapplied then it is telling the driver that he is over braking either in terms of the ultimate ability of the brakes (cause 1 above) or the track condition (cause 2 above) and needs to adjust his driving style to suit. If the system were not fitted or disabled and he continued to drive that way he would be in danger of spinning when applying the brakes. 
The suggestion that the system is running out of vacuum is just plain wrong. The system carries an internal reservoir of vacuum sufficient for three full brake applications. As with every servo system ever fitted to a car there is a one way valve which prevents the vacuum being lost when the car is on boost. The only way this reserve can be depleted is if the driver is maintaining boost while applying full brakes, i.e.: left foot braking very badly. In this instance I would argue that depleting the vacuum is probably a good thing as it should provide him with a warning that he is doing something awful to the car and it may reduce the speed of impact when he finally hits something as the brakes fade to nothing!! In normal use the throttle is closed when the brakes are applied, there is therefore no boost and the vacuum is automatically replenished as it is used."
So there it is, 'Ice Mode' is an inherent issue that can be addressed with some old school brake pedal pumping.  I think the pedal feel, when it goes 'hard', tends to be the most disconcerting as it happens when you are approaching the corner at high speed.  Many racers have disconnected the ABS system in an effort to reduce this issue and frankly it is a good solution for advanced drivers.  

We think that the brakes on the Lotus are still awesome even though they lack the firm feel that you get from other sports cars like a 911.  The flexible single piston rear caliper appears to be a key reason for the softer pedal - but we'll take it as we go 2-3 cars deeper into every corner than those massively powered GT3, ZO6 and M3s...

Another solution is to upgrade the front brakes to our 308BBK  or 308vBBK and move your front calipers to the rear with our FCRbracket.  We disconnect the ABS with this set-up.  One nice feature is that you can keep the stock rear caliper so you can retain your handbrake.  For about $2k you can effectively have a complete BBK kit for your Lotus.  We ran this successfully on our Art Car with great results including two track records in Lotus Cup.

Tuesday, September 17, 2013

High Mileage Lotus - Benefits of 60pt Prep

Recently we serviced a repeat client who puts a ton of miles on his '05 Elise.  With 94,000 miles, this may be the highest mileage Elise in North America.  It is definitely the highest mileage car we have seen.  James first brought his Elise to us in Jan 2010 with 56,000 miles on the odometer.  At that time we conducted our 60pt Prep on the car.  This preparation checks over 60 of the critical areas, of a Lotus, that tend to loosen up.  Our service removes the fasteners, threadlocks them, torques them to spec and then paint markers each one.  You can find our 60pt Checklist on our Tech Tips page: HERE  Feel free to download this and use it to prep your car.

The picture below shows the old paint markers that we had put on James' car at the 56k service.  Even after 40k additional miles, you can still see them.  This technique allows you to visually inspect your car to quickly verify that your critical fasteners are still torqued correctly.  If you see that a paint line has shifted, this is a good indication that you need to retorque.

Once we inspected the car, we noticed that most of the fasteners had not moved.  We still removed each fasterner, reapplied threadlock, then cleaned off the old markers and repainted the joints.  These paint markers are readily available at auto parts or hobby stores.

One of the issues that we found during this inspection was the rear bushes had moved and the wishbones were making contact with the subframe.  The picture below shows what we found.  

Typically we see this on track cars but even high mileage street cars that are driven with some enthusiasm can exhibit this problem.  Luckily we have a couple of solutions that can help:  SL Bushes and the MONOballs or Nitron Bearings for the track/race focused cars.  We have a previous blog entry about this issue: HERE

We are big believers in the fact that these Toyota powered Lotus can be reliable cars.  The two basic requirements are that you:

  1. Keep the fluids & filters fresh
  2. Keep the critical fasteners torqued correctly
If you follow these basic rules you can run your Lotus for years with confidence and a grin on your face.

Sunday, September 8, 2013

Switchblade Track test at SMMR

I took our Exige S to the track to do some initial testing.  We have several items on the car that needed to be evaluated, including the new clutch and suspension.  It was the first time in years for me to drive an Exige S on track and it was interesting difference compared to the Elises that we have had the last few years.  The car performed well and had some good points and some bad ones.  I ran her on SMMR's 1.5 mile configuration.

The Exige was very fast as we installed our BLADE275 kit on it.  This car accelerates like a scalded cat!  The auxiliary ducting kept the proICduct well fed with air so it did not feel as heat soaked as with the stock set-up.  The ambient temps were well into the mid to high 90s during my testing.  Water temps stayed below 203degF.

 The new clutch felt great.  During the initial break-in the car was a bit touchy when you launched it from a stop on the street in 1st gear.  I'm embarrassed to admit that I stalled her a couple of times!  The clutch now has approx 500 street miles and feels fine.  The pedal effort is slightly higher than stock but the power rating is much higher so I think it will be a very good option for clients with more power and who run on track.

The suspension is very soft and glides over the bumps very well.  It had great grip.  The car swayed much more than our last couple of Elises thanks to these softer spring rates but you could also feel the weight up high on the Exige.  The IC coupled with the roof, hatch/wing make for a car that feels more 'top heavy' than the Elise.  You really notice it on the track.  The 'inch down' ETHOS wheels and larger sidewall Toyo RA1s also contributed to the compliance and slightly slower turn-in.  The car was very fun and easy to place.  We still have the stock seats and no harnesses and I moved around quite a bit as a result.  We'll add some harnesses soon.

The single biggest negative was the 'ice-mode' issue that I was experiencing on a couple of turns.  This is a known issue with the ABS system on the Lotus.  I ran with the ABS on but many racers defeat it as it can cause this disconcerting feel of having no brakes.  Truth is, the ABS system thinks you are slipping so kills any additional rear brake pressure but your front brakes are still working.  If you get off the pedal and immediately back on, it corrects itself.  Of course that is never fun when your corner is quickly approaching!  We were running stock pads with our ULTRAdiscs so the initial bite was also a bit lacking thanks to the pads.  Different pads will make a huge difference.  We were testing a new brake fluid and it appeared to work fine as it is hard to boil fresh fluid in a Lotus.

I also had some shifting problems.  I think our cable adjustments need to be looked at but I was mostly having some shifting issues on the track.  Again it is well known that the 2ZZGE moves quite a bit with track use - especially with the addition of an IC on top.  We installed our sportINSERTS to help this issue.  I need to look closer at our adjustments to see if that was the cause or if we need to run stiffer mounts.

I drove the car to the track to see how comfortable it would be.  The TRACKpipe sounded great on track but was a little bit intrusive while cruising along the freeway.  The Exige is a louder car than an Elise.  Mufflers that do not drone, like the TRACKpipe, in an Elise, will be louder in an Exige.  I think the rear fastback clam of an Exige creates a bit of an echo chamber that causes it to be louder.

The day I arrived, a SMMR member took delivery of his new Spec:Race Atom.  He will be running it in our Winter Race Series.  Barry got one session in the car and we made a quick video of his initial impressions.