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NONACK
NONACK Reader
8/14/13 2:42 p.m.

I have rallycrossed both mk1 and mk2 mr2s, and am the former owner of the car of which irish44j speaks. My mk1 understeered at low speed, and as a stock class car, the only thing I could do to correct that was alignment- toe out up front and zero toe in the rear helped, but did not completely eliminate it. On my mk2 (modified), I removed the proportioning valve to get more rear bias and ran a similar alignment- with that setup, trail braking would eliminate any understeer in short order.

Removing the front sway bar will also get rid of understeer to the point of making the thing extremely tail happy when off the throttle, but I wouldn't recommend it unless you have an LSD in the rear since you'll be unloading the inside rear tire a lot more.

irish44j said: I prefer to brake hard in a straight line before initiating the turn. In slow out fast works best for me... I know jack about driving an MR2 but have to image it's all about driving style.

To this I say "not quite." If I need to do a ton of braking before a corner, I do it going straight, but on dirt I ALWAYS leave a little bit extra to either scrub off while sideways, trail brake, or both. It should feel like "not quite slow enough in, fast out"

Oh, and never add weight. Lightness beats balance every time if you tune for your weight distribution- look at the damn Deltawing.

cghstang
cghstang HalfDork
8/14/13 3:56 p.m.

Jerry, when you come over to groove tires I can give you an ear full regarding what I would try on your car and relate some of Pete and Evan's experiences with theirs. And I would also be happy to drive it some more. (Thanks for letting me drive it last Saturday!)

dean1484
dean1484 UberDork
8/14/13 4:43 p.m.

Invest in good struts and lowering springs.

Another thing to do is reinforce the trailing arms on the rear suspension. They bend easy if you hit a curb or something and they flex under heavy loads. We sleeved them with U channel and then welded the entire length of both side of the U. Another set we sleeved with chrome moly tubing. . .. . Or maybe we just replaced them with home made ones I don't really remember. You need to beef these up to make the rear suspension work in a repeatable manor by eliminating the flex in these.

aussiesmg
aussiesmg MegaDork
8/14/13 6:54 p.m.

In response to the brake bias valve, this only REDUCE the amount of rear brakes as it reduces the amount of fluid to the rear.

You would need a full adjustable pedal box to increase rear braking.

EvanB
EvanB PowerDork
8/14/13 7:27 p.m.

In reply to aussiesmg:

Not if you replace the stock proportioning valve with the adjustable valve.

True it will still reduce the amount of rear braking power but you start with much more than the stock proportioning valve allows.

Knurled
Knurled UberDork
8/14/13 8:58 p.m.

Also, don't be too terribly afraid of understeer. It can be beneficial.

Example: On morning course last weekend, there was what I shall call the F.U. Section after the turnaround. Uphill turn left through a very tight gate with a cone wall to the outside that EVERYBODY WAS HITTING (but I ain't mad) followed by a right turn with no outside wall.

Understeer in to the lefthander to keep the car narrow. Toward the end the front end WILL bite unless it's really sloppy. This upsets the rear, and you can utilize this as the start of a flick to get around the second corner.

http://youtu.be/1TtdBNnMvkU?t=49s

Rear drive is way more fun because you can play the car instead of just mushing around.

One thing I haven't got around to doing on this car is to replace the stock prop valve with a brake union. That worked very well on my previous car. I simply cannot find any M10x1 double flare unions, everything is bubble flare. I tend to use the handbrake as a variable brake bias but it's tricky.

Warren v
Warren v Reader
8/14/13 9:31 p.m.
aussiesmg wrote: In response to the brake bias valve, this only REDUCE the amount of rear brakes as it reduces the amount of fluid to the rear. You would need a full adjustable pedal box to increase rear braking.

Does this car not have a factory proportioning valve? In many cases, replacing the factory valve with a fully adjustable unit can allow you to increase the rear brake pressure.

zipty842
zipty842 Reader
8/14/13 10:32 p.m.

We pulled the guts out of the factory valve on our race car, it helped get a lot more rear brake but sometimes we still want more.

Jerry
Jerry HalfDork
8/15/13 6:40 a.m.

In reply to cghstang:

Sounds like a plan. On all counts.

EvanB
EvanB PowerDork
8/15/13 7:40 a.m.
Knurled wrote: One thing I haven't got around to doing on this car is to replace the stock prop valve with a brake union. That worked very well on my previous car. I simply cannot find any M10x1 double flare unions, everything is bubble flare. I tend to use the handbrake as a variable brake bias but it's tricky.

This kit appears to include a m10x1.0 double flare union.

http://www.jegs.com/InstallationInstructions/500/530/530-567-1516.pdf

http://www.jegs.com/i/Hurst/530/567-1516/10002/-1

Of course you have to buy the whole kit but it is an option.

Knurled
Knurled UberDork
8/15/13 8:39 p.m.

So is just reflaring to bubble flares and using common unions. Or installing standard fittings. Or just running new, longer brake lines. For some reason, whenever I make a change, I like to make it reversible even though I never go back.

Heck, I only recently got rid of the interior I took out of the car five years ago, that I kept in case I wanted to return to stock...

chaparral
chaparral HalfDork
8/27/13 2:13 p.m.

For batteries, don't relocate the weight, get rid of it.

A 4s2p Zippy LiFePO4 battery costs $90, weighs 2 1/2 lbs, and will start a Chevy LS1.

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