GKR IS300 Racecar - Lexus IS Forum
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post #1 of 6 (permalink) Old 03-20-2017, 08:34 PM Thread Starter
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GKR IS300 Racecar

Hello My.IS!

I just made an into thread a few nights ago. My name is Nik, and I recently decided to start doing IS things.

The goal is to build the car for NASA wheel to wheel racing in the PTD class. I'll also bring it out to other events like the SpeedSF challenge (a grassroots time attack event and track day organization), and maybe some TRD Cup events.

My history with IS300s started with one Mr. Joe McGuigan, an SF Bay local ProAm drifter and one of my best friends. Over the years I helped him with his car as it changed form over and over, from a GE to a 1UZ, to a 1J-GTE. I always liked the car, but I was happy playing around with Miatas and didn't need another project. Here's that car in its final guise, on one of two laps I got to do some skids in it:


At some point, I got involved with a Hayward-based tuning shop, and I helped them to build this:



It ran at the 25 Hours of Thunderhill, and despite some major braking issues early on and not really having time to tune the car to its potential, it finished the race in 7th place. It would have been neat to see what it could have done when the power to weight was up to spec and the suspension was dailed. Alas, it was not to be.

Fast forward to last year, I decided one day that I wanted to build a first-gen racer, and that same day I called up a guy with a Craigslist posting, drove to see the car, then bought it and drove home. I had to take an Uber to get my other car back home. #planning

That very day:







The photos hide the bad clear coat well. It had a cold-start rough idle, what is likely the top-o-tha-fuel tank leaky valve, and a slushbox...but at $2500, the price was right, and I'd be disassembling the entire thing anyway. I DD'd the car for a few months, immediately began regretting my plans to take my only practical car with an auto, AC, 4 doors, useful trunk, power windows, and comfortable suspension...and using THAT one to gut and cage. Seriously, the whole thing is a totally dumb idea. Why am I doing this. Halp.



The first order of business was engine maintenance. There was some oil dripping off the front end, so I decided to tear all that mumbo jumbo out and replace the oil seals. Turns out, the crank bolt in these cars is good fun to take off. It must have taken 1000lbs of force to get it to budge. Two dudes both pushing on a breaker bar with a cheater pipe on it, and we almost couldn't get it done. I can get my Miata's crank bolt off with a stern glance.

The leak ended up being the VVT cam gear, so I bought one of those handy do-it-yourself kits consisting of a sheet of printer paper and an o-ring, and went to town. Half of this job was to fix the leak, half was to familiarize myself with a new (to me) car and engine. Once you get the hang of this car, it's not so bad.

With everything all buttoned back up, it was time to actually do some racecar things.
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post #2 of 6 (permalink) Old 03-20-2017, 10:00 PM Thread Starter
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Before making any modifications, I wanted to get a baseline for the car's weight and balance. This "before" measurement is with me in it, 100% stock with the full interior and the automatic transmission.



The "base weight" for my class is 3255lbs, which is a measure of the minimum weight the car is allowed to be on track, with driver and at the end of the race after fuel has been burned off. So ~250lbs need to come off. Should be doable, between the sunroof, seats, interior panels, carpet, windows, sound deadening tar, etc. I'm also allowed to use carbon body panels and a lexan windshield if necessary.

The seats and the carpet were the first to go.



Maybe I'm just used to dealing with older cars, but it seemed remarkably clean under there. No nasty liquids, grunge, or poo stains, just a single, solitary, presumably stale Goldfish. I'm also liking how all of the plastic bits come apart without much of a fuss. On 25+ year old Mazdas, the interior parts will break if you look at them wrong, sometimes even if you look at them right and they are just in a dodgy mood.

Plenty more stripping to be done, but then I moved on to do some suspension work. I'm using a fair number of FIGS Engineering parts on this car. I've had some experience with Mike's parts before, on Joe's drift car and on the 3IS endurance car so I'm already intimately familiar with how well designed and built they are. Mike is a hell of a guy too, and I couldn't be happier to have his stuff on the car.

First up, the rear toe links:



Using these does a few things; the length is adjustable, which means we can set the factory eccentric bolt to the furthest inboard position and lengthen the rod out. That will make the rod follow a larger arc, reducing the amount of bump steer for a given amount of suspension travel. Of course, the rubber bushing is also eliminated in favor of a spherical joint. On a track with sticky race tires, the forces applied to the bushings are a good bit higher than the factory ones were designed for. One place you certainly don't want a lot of deflection is on the bushing that determines the direction the wheels are steering. This should be a nice improvement to stability and predictability.

Next, it was the MEGAarms.



These do even more. First, they are lighter and stronger than stock. The factory arms aren't boxed, so they will twist from the torque of the engine and, essentially, not put that power through the wheels. These are boxed, so they don't have that problem. Next, the lower shock mount is slotted. This means you can make small adjustments to the motion ratio of the rear suspension. The farther out you push it, the stiffer the spring (and shock) act. Ultimately it would awesome if the motion ratio was higher from the factory, but this will have to do. There are three choices for the sway bar end link mount, which means you can get them closer to being perpendicular to the bar itself (or farther, depending on how much leverage you'd like). Just like the toe rods, these eliminate the rubber bushing and replace it with a spherical joint. The lower arm will be the most stressed member during lateral load, so this will play a big part in making sure the wheels are pointed where you want them while cornering. And of course, these are length-adjustmable, which means you get way more camber adjustment than stock.

I've done some more work on the front end and interior, but I don't have any photos yet, so those will have to wait for next time
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post #3 of 6 (permalink) Old 03-20-2017, 10:32 PM
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You're off to a great start, keep it up!

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Originally Posted by GKR_Nik View Post
useful trunk
^ Going to have to disagree with you on that one lol
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post #4 of 6 (permalink) Old 03-21-2017, 12:24 PM Thread Starter
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Quote:
Originally Posted by khrisz View Post
^ Going to have to disagree with you on that one lol
Hah! Well, I'm coming from Miatas...I literally cannot fit one of my 15" wheels in there.
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post #5 of 6 (permalink) Old 03-23-2017, 01:19 PM
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What's goin on with this one...
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post #6 of 6 (permalink) Old 03-24-2017, 07:15 PM
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Interested to see what this ends up as.

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