Project Gen 3 STi: Suspension upgrade with M7

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Project GR STi Gen 3 stock suspension before
Project Gen 3 STI GR lowered M7 coilover suspension installed
The obligatory before and after shot. Matching angles to reveal the difference was tricky but here you get a sense of how the rear is close to tucking. This was the ride height as taken out of the box from M7 and installed on the car. As we progres with our suspension build the car will be corner weighted and optomized to use 2/3 travel in bump and 1/3 in compression. 

We first wanted to spend some time with the car on the street as, after all, this is an all purpose car! As you read these impressions please remember that we have not adjusted anything at this stage. All of this is out of the box and we are tweaking from that reference point. We felt this prudent as many people looking at this suspension are very likely to buy and install it that way. We formed the following impressions over two months of street driving in various conditions on midwest roads. Remember that this project is located in Wisconsin and our harsh winters leave quite a bit to be desired when it comes to the shape of our roads. Aww hell who am I kidding, they are shit and look like that bump test strip at an automotive proving grounds…

That being said I was surprised how well damped these coil overs were whendealing with abrupt bumps and cracks. Despite being lower the design helps to retain suspension travel and that was evident. With our OEM wheels and tire size (245 40 18) we experienced no rubbing of any kind. In some cases I prefer this setup to the factory as they tend to be soft under certain conditions yet harsh in others and they are certainly better balanced. Yes they are stiffer but that does not correlate to teeth rattling and remember we are on the stiff end of their adjustment range.

I did notice that they were not the best under undulating conditions and the head bob was there despite the lack of a bumping track, we do understand that a softer setting would help to eliminate some of that. The car certainly improved in overall handling and body roll is greatly reduced. The car takes a better and more predictable set versus the stock suspension. Even on the street during spirited driving the car handles bumps pretty well while in a set mid corner. The car is still on stock roll bars and we expect further overall improvements when those are replaced. In living with the car we have very little criticism other than the bounce over undulating surfaces when the coil overs are set on the stiffer side of the spectrum.

In addition to street driving we have began to test the car a bit more through auto crossing. Being one of the few MotoIQ staffers who has a previous autocross history I decided it was time to knock the dust off and get back out there for some fun. Despite the large amount of time working and the small amount of seat time, I always felt that I learned more in one season of auto crossing than I did in years of other driving. You typically only have 4-6 runs through a 70 second or less course with no practice runs other than walking the course. While our STi is certainly not prepped to run in any certain class it was a great way to put the suspension through it's paces. Within the regional SCCA groups they have street tire classes that allow you to run your car against other cars of the same drivetrain configuration using a handicapping method. In our case we competed in the All Wheel Drive class and our raw time on course was multiplied by the index for our class.

Our modifications put us in the ASP or A Street Prepared class which has an index of .866. Each class has allowable modifications and combining these cars into one indexed class makes for interesting competition on a level playing field. I did not expect much relative to being competitive in the All Wheel Drive class given that the car is drastically under prepared for this index and that I was running Yokohama Advan S4 all seasons of the 245 40 18 variety. On the morning of the event I woke up to 50 degree's and rain and was honestly quite happy about that. I expected that the S4's would be a good fit for these conditions and I always have been comfortable driving in the rain. As I arrived at the event to register the first thing I was concerned with was my work assignment for the day! I didn't want to be shagging cones in the rain so I used my charm and good looks (OK I paid them) to procure a job announcing the times which came with a dry warm seat inside the timing (short) bus.

I then walked the course to try and memorize the line as best as I could. The ground was slightly wet with a few standing puddles yet it had stopped raining. The event is broken down in to 4 heats where you drive two heats, work one heat, and have the other heat as a break. In our case we ran heats 2 and 4 which meant we would be on a partially wet course in the morning and, as the weather would have it, a dry course in the afternoon. 

 

As I prepared for my first run I tried to remember how to put my helmet on. For the first run I turned traction control completely off but left the center diff in auto. With the torque our car makes I wanted to take it easy during the wet sessions and not get too aggressive. As I launched I short shifted into second to try and keep traction and it seemed to work well. Right away I noticed the lack of body roll compared to the stock suspension and despite the slippery conditions the car turned in well and the rear end followed. It was predictable in rotation and I could tell that if I were to dial in rear bias on the center diff that you could gain rotation with the throttle. The car really shined through the turns that were constant radius and steady state throttle yet would understeer if pushed too hard into tight sections.

We blame this on a lack of anti-roll bars as well as an all season tire, it had nothing to do with the crappy driver, we swear to that! Considering how low the car was it handled quite well and as we continue to tweak the suspension we will be adjusting ride height to optimize droop versus travel. After my three morning runs I was pretty quick in the car. My times were good enough to be the third fastest RAW time in my class and First overall based on the index. I attribute this to all season tires and AWD with a bit of dumb luck!

I knew that the weather would dry up and I fully expected tires to make a larger difference going in to the afternoon and that is exactly what would happen. As I set the car for the afternoon runs I decided to run the center diff. in manual mode at full rear bias. I prefer to drive the car this way on the street as I find it the most responsive to throttle and it did help in the afternoon. With the drying conditions it was easier to induce understeer by carrying more speed into turns and the throttle could be used to help rotate the car. Despite the changes the all seasons would limit me in the afternoon and I would slip from first position in to second place where I would finish for the event.

Overall I was very happy with how the car felt given its very minimal preparation and I am confident that as we progress with suspension development as well as wheels and tires it will be quite quick. Remember that we will continue to elaborate on our impressions of this suspension in future installments relative to its performance as well as durability on the street and in the elements.

Please stay tuned as in our next installment we upgrade the fuel system to make the car “less likely to blow up”. 

Without these people Project GR STi would suck! 

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