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I think a front diff on it's own would make a big difference, especially if you have wide tyres and can avoid wheel spin. The stock center diff isn't strong enough to counter wheelspin on tarmac.
 

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I've spent 13 years modifying my car to handle better on the track. The transverse TTV6 isn't the problem but the differentials are.

The Evo's are known for it's good handling has a very similar engine layout but much better diffs and we all know how they handle.

Among all the modifications I've done to my car (big brakes, Öhlins coilover, DR750 etc) I've replaced all 3 diffs on my car one by one and the car behaves completely different now.

The stock viscous center diff is too weak and too limited in it's ability to redistribute torque which make it unsuitable for track use. On winter road it may work fine with it's 45/55 torque distribution but when your putting the power down on the track if one axle starts to spin it will keep spinning because the viscous center diff is unable to transfer more than 50% of the torque to one axle.

So I started by installing a Supercar torsen center diff with it's 20/80 front/rear torque distribution and it really changes how the car behaves on tight tarmac tracks. The on throttle understeer heavily reduced and the car behaves much more like a rwd car. It also makes the behavior of the car much more consistent since the mechanical nature of the torsen diffs makes it much more predictable and faster in it's reaction compared to the stock viscous center diff.

Here is a video I made that shows how rear wheel biased the Supercar torsen center diff really is.

https://www.youtube.com/watch?v=fTQEldXlCDc

Even with the 80 of the torque going to the rear wheels I could still get the inner front tire to spin a bit when exiting tight corners as seen in the clip below. I cured that by installing a Quaife front diff which essentially removed all traces of on throttle understeer when used in combination with the Supercar torsen center diff. I ran that setup with great success at many events for a while.

When I upgraded to DR750's and water/meth injection I started having problems with the inner rear tire spinning wildly during acceleration out of some corners due to the weak stock rear LSD in our cars. Here is a video of that:

https://www.youtube.com/watch?v=a0saF10a-94

I ended up replacing the rear differential with a Mitsubishi torsen/visco hybrid diff that after a rebuild has worked great and the rear really stays planted now during acceleration.

Here is a video from an event a month ago that shows how the car drives now (fastest run is at the end).

https://www.youtube.com/watch?v=9YTso_nYFv0

As you can see the car tends always oversteer except in the really really tight breaking turns. During oversteer I can usually just keep the foot down and counter it easily which makes the car easy to drive on the edge for great lap times. However it doesn't always go as planned as you can see in the video above.

I run Öhlins coilover with SCE adapters on a very low ride height and 265 tires on 9,5 rims. I have 2.7° of camber in the front and 2° in the rear. The front camber is really important on these cars else you will eat up the outside of tires quickly and overheat the tires.

I've attached a few photos of how the car sits on the track.

I don't think the on throttle behavior of our cars can be changed significantly without replacing at least the center differential.
It sounds like you've done a lot of good work as what you've posted agrees with what I've experienced on the 1g DSM. You've got me so tempted to start autocrossing my 3/s but I know the tires I've got right now aren't up to it. A couple questions:

What Mitsubishi torsen rear diff are you talking about?

Why 265 wide tires? Seems small given the weight of these cars and the power I would expect you to make with those turbos.

I didn't see any mention of swaybars. Have you done a rear swaybar?

It sounds like perhaps you've posted more information on another website that doesn't get along with 3si or something? Do you think you (or perhaps wrongwheeldrive) could PM me the name so I can read up on what you've posted there? Or perhaps post a link here to a thread on 3si that explains why links to this other site cannot be posted?
 

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It sounds like you've done a lot of good work as what you've posted agrees with what I've experienced on the 1g DSM. You've got me so tempted to start autocrossing my 3/s but I know the tires I've got right now aren't up to it. A couple questions:

What Mitsubishi torsen rear diff are you talking about?

Why 265 wide tires? Seems small given the weight of these cars and the power I would expect you to make with those turbos.

I didn't see any mention of swaybars. Have you done a rear swaybar?

It sounds like perhaps you've posted more information on another website that doesn't get along with 3si or something? Do you think you (or perhaps wrongwheeldrive) could PM me the name so I can read up on what you've posted there? Or perhaps post a link here to a thread on 3si that explains why links to this other site cannot be posted?
Try this link: http://bit.ly/2Afg07r
 

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Wow, just came across your build thread. We have almost identical set-ups!! I'm just in the process of adding a 99 front with a splitter and ducts for the SMIC and cool intake air.

I'm also working on ideas for venting heat from under the hood and especially the rear turbo as the ambient air temperature is typically 90-100F at the tracks here in CA.
 

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Have you found a way of cooling the rear turbo without disturbing the rest of the airflow in the engine bay?
Looking at a couple of different approaches. I'm starting with the reasonable expectation that the front of the hood is a low pressure zone but the rear of the hood (close to the windscreen), is a high pressure zone. I plan to validate that with testing.

I'm going to add a hood vent at the front to vent from the radiator and front turbo. I'm also looking at deleting the fog lights and mounting two 4" air feed trumpets and ducting where the fog lights would be on a '99.

So the two approached I'm looking at are:

1) modeled off the EXO X which has a rear mounted turbo. That has a scoop at the rear of the hood to take high pressure air from outside the engine bay to cool the rear mounted turbo. I'd pair this with a hood vent for the front turbo and ducting to route air from the rear turbo out of the front hood vent. The downside of this approach is that hot air exiting the front vent may end up feeding the rear scoop and it will probably make the hood look messy.

2) ducting air to the rear turbo from the front of the car similar to what you did for the air filter.

I think 2) would make a cleaner install, so my initial plan is to route the passenger side air trumpet to the air filter and the driver's side air trumpet to inside the splitter/undertray to the rear turbo and then use ducting from the rear turbo area back to the hood vent at the front.

The general idea is to manage the flow in the engine bay so that cold air enters through the radiator and the two new air trumpets - goes to where its needed and all of it exits through the low pressure zone at the front of the hood. However, I may also add venting at the rear of the splitter/undertray to suck hot air from around the rear turbo.

Its going to be a work in progress. Managing heat from a transverse mounted twin turbo V6 is a PITA - probably why nobody uses this configuration any more. With the levels of HP we are making, there is at least 2x the heat to remove.
 

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I like your approach I've been considering something similar using duscting.

I'm afraid a vent at the back of the hood would press air into the engine bay from the wrong direction reducing the amount of air going through the radiator.

I've done measurement with an IR-thermometer (always carry one to the track) and the read turbo runs at least 100° C hotter than the front turbo after a hard session.

My solution so far has been to make a custom heatshield that sits a about 10 millimeter from the firewall to reduce the amount of heat transferred to the cabin and stock insulation.
 

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I like your approach I've been considering something similar using duscting.

I'm afraid a vent at the back of the hood would press air into the engine bay from the wrong direction reducing the amount of air going through the radiator.

I've done measurement with an IR-thermometer (always carry one to the track) and the read turbo runs at least 100° C hotter than the front turbo after a hard session.

My solution so far has been to make a custom heatshield that sits a about 10 millimeter from the firewall to reduce the amount of heat transferred to the cabin and stock insulation.
Yes I have a heat shield on mine but there is limited airflow to that area.

For me, heat management is the single biggest challenge for those of us who run higher output on road courses and autoX. The drag racers have much less of an issue with heat accumulation over a sub 11 sec run down the drag strip. We have to deal with up to 30 min of heat soak from glowing turbos.

My approach is that I want to remove as much heat as I can. I'm reluctant to heat wrap the turbos as that runs the risk of heat soaking the compressors over a 20 minute hot lap session.

I'd rather duct as much cooling air to them as I can and restrict radiant heating of surrounding parts with shields.
 
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