Updates to my white AXR

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Updates to my white AXR

Post by jtmineha on Thu Jan 12, 2017 3:47 pm

We kicked off some upgrades to my White AXR this past month. Trying to get that extra half a second to win that E Mod championship.

The three key things are a dry sump system, a smaller bellhousing/clutch/flywheel, and lighter transmission (Custom T-5 from Astro Performance). The weight reduction should translate into better weight distribution, since I was already close to minimum weight, we'll be adding ballast to the frame in front of the rear axle. I was at roughly 48.5/51.5 (front/rear) and I'm hoping for closer to 54 or 55 % on the back to get better grip on the back and ease some of the load on the smaller front tires.
The biggest hurdle was getting a drysump pump that would fit and we have managed to flip a particular mount from an Aviaid 3 stage pump system and hack away at the block a little, use some 45 degree AN fittings, and I think we have it fitting without interfering with the lower control arm mount on the passenger side (though I think we had to cut it down to not be able to use the top hole). We had to do some other tricks like move the engine back and offset the LS3 water pump .75" to match up with an LS1 style crank pulley/damper, but I think we have it all in place now and things fit! The shallow 2" dry sump pan combined with the Tilton Bellhousing (and 7.25" clutch/flywheel) allows us to run a full flat bottom undertray under the motor for better aero, and lower the car up two inches from the current ride height, which was currently limited by the oilpan/bellhousing/transmission (I'll probably only lower it an 1" or 1.5" at the most)
The lighter drivetrain (clutches and flywheel are 42lbs lighter!) and drysump system should free up some horsepower, and were trying out a new muffler setup that should add some power as well. The car should be up and running in the next week or two. The drop in ride height may require some more tuning to the suspension to get dialed in, but I'm getting pretty excited about this next year of Autocross.
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Re: Updates to my white AXR

Post by Bonjo2 on Tue Apr 04, 2017 3:48 am

Very nice.. Lowering drive an inch and still being able to run a flat floor and add ballast in lower right rear will make a huge difference. I now drive mainly street, but there was a time I was considering a jerico or brinn with a quick change rear, would top 65-85 in 2nd or (low) and only weigh 50-60lbs vs 160.

Give the old bug eye hell this year! We're rooting for you.

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Re: Updates to my white AXR

Post by jtmineha on Sun Apr 09, 2017 11:51 pm

Thanks. It's coming together. the car is handling great with the new ride height adjustment. After lowering it, we adjusted the roll center by raising the LCA's on the front, up one setting to the middle holes and adjusted the toe links/mounts for bump steer correction.
Had a few issues that stemmed from too much motor movement. I had the regular rubber motor mounts before and just installed some Polyurathane ones this past weekend. The dry sump lines were too close to the motor mount and one of the fittings failed and started leaking. Another issue was not enough clearance from the pan to the new floor under the engine compartment. That interference caused the oil pan gasket to leak in a few spots. So as part of the motor mount upgrade, I added some 1/8" shims under the mounts to get a little more clearance. Just driving it around, it seems to be good now. The poly mounts actually make the car feel more smooth at idle. I highly recommend the poly mounts if you have the standard GM Blazer V6 mounts. Energy suspension 3.1145R
https://www.amazon.com/gp/product/B0018LMSOG/ref=oh_aui_detailpage_o01_s02?ie=UTF8&psc=1
Its a replacement for the rubber part, you just have to drill out the rivets that hold the two halves of the mount together, then replace the rubber part with the poly one.
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Re: Updates to my white AXR

Post by jtmineha on Thu Jun 29, 2017 3:33 pm

My latest part testing on the AXR this past few weeks has been trying out a Quaife differential. The Quaife differentials for the CTS/Saturn Sky/Solstice are the only other off the shelf LSD currently available (other than the stock Getrag clutch type) and can be found really cheap these days (like $350), so I figured it was worth the experiment to see how the differential makes the car handle differently. I've always the suspected the Getrag 2-way causes a corner entry push that is really difficult to dial out. While it makes the car more stable and predictable, the slow speed corners like tight 180's can be a real test of patience to get through without pushing the entry to overslowing too much.
So the thought was to try the Quaife gear-type differential and see if it can make improvements in that area and see what the compromises are. Generally, the common theory is that autocross cars favor a clutch type because if it picks up a rear wheel in a corner, the gear type is going to send power to the lifted wheel and you end up spinning that inside wheel. However, the Stalker AXR has pretty good droop travel with it's independent suspension and no swaybars, so lifting a tire is not really a common thing.
So far, I've got one practice event on the new diff. The handling results were about what I expected. The slow stuff drives much tighter and quicker without the corner entry push, though there is more oversteer in the fast transitions, and you can induce a lift throttle oversteer mid-corner. Other than shock adjustments, I'm also working through some brake bias adjustments, as I seem to be getting more rear lock-up with this diff- I suppose because there is less torque on the wheels in decel, so it's easier to lock up. So I'm still trying to dial out rear bias and get it stopping from high speed without the back end wanting to step out. I haven't had any competition to compare to yet, and it'll probably take a few more events to optimize the car for the differential, but I'll probably run it at Nationals to really see if it's faster or not.
I have a feeling a good 1.5 way clutch diff like a Cusco or OS Giken will probably be the best solution, but we'll need to talk with them about building them as they currently don't have an application for us yet. I'm thinking OS Giken might be the best bet, since they are into the autocross scene, but if you know of anyone else that might be able to make a diff, let me know!
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Re: Updates to my white AXR

Post by d hills on Mon Sep 11, 2017 2:48 pm

Congrats on your second place finish at solo nationals! A nice 1.7 sec cushion over Brueck in the YC-J. The green Sprite appears to be very stout competition. I'm wanting to build an AXR and was wondering if I could check your car out some time. I live in Cedar Park just off of Lakeline. Cheers, Doug

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Re: Updates to my white AXR

Post by jtmineha on Mon Sep 18, 2017 8:52 pm

Doug,

Thanks! I was actually a little disappointed in my performance this year. Made a bunch of changes in the last couple months leading up to Nationals and never really got very comfortable with the car setup, made a few mistakes on the fast runs. So a little off pace compared to last year, but happy to keep that second place finish! Jeff was pretty happy with the Sprite this year, so he had it working right. I'm going to try to get all my updates/refresh work done over the winter so I'm not messing with the car so much late in the summer. Atleast that's the theory Smile

I live in Cedar Park off of Lakeline as well! Should be easy to stop by and check out the car sometime.
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