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Box4VIR
Box4VIR Reader
4/1/22 12:01 p.m.

 

I think its time for a new thread, my previous thread below "Boxster Journey into TT5 (NASA Time Trials)" doesn't seem appropriate anymore now that I've gone off the deep end and I don't come anywhere close to fitting into TT5.  Now that the car is finally running in its new twin turbo V8 form timing seems perfect.  Hopefully I'm not breaking any rules here, and if you want to catch up on the build the old link is below.  The next stop is Hyperfest/Grassroots UTCC which is happening in 6 weeks!  Tons of work to do between then and now to get the 800hp car back on the track after this week's VIR test and tune.  :cheers:

https://grassrootsmotorsports.com/forum/build-projects-and-project-cars/boxster-journey-into-tt5-nasa-time-trials/146213/page1/

 

some teasershots of the build so far

 

 

https://grassrootsmotorsports.com/forum/build-projects-and-project-cars/boxster-journey-into-tt5-nasa-time-trials/146213/page1/

Javelin
Javelin MegaDork
4/1/22 12:04 p.m.

Holy guacamole!!! That's wild!! I hadn't checked the TT5 thread in a long time obviously.  I need to catch up on reading!

ian sane
ian sane Dork
4/1/22 12:20 p.m.

One of the best cars on the forum.

Lof8 - Andy
Lof8 - Andy SuperDork
4/1/22 12:26 p.m.

Wow!  

Keith Tanner
Keith Tanner MegaDork
4/1/22 12:28 p.m.

This is truly nuts.

birdmayne
birdmayne Reader
4/1/22 12:39 p.m.

Holy E36 M3... That's amazing. 

APEowner
APEowner SuperDork
4/1/22 12:56 p.m.

Crikey! That's nuts and awesome!  I don't know how I missed the build thread but I'm going to have to take some time and read it.

rustomatic
rustomatic Reader
4/1/22 4:43 p.m.

All I can think is yes, yes, yes.  This is what makes going to a random track event inspiring.  That's some well-managed sickness.

dherr (Forum Supporter)
dherr (Forum Supporter) Dork
4/1/22 11:17 p.m.

Well that is something else, sort of has the 918 look and probably similar performance! 

DrMikeCSI
DrMikeCSI New Reader
4/2/22 8:22 a.m.

Wow. That is awesome. 

Box4VIR
Box4VIR Reader
4/6/22 2:46 p.m.

Thanks for all the support guys!  Its great to having it running but...I can't wait to get going on the next project.  Speaking of the next project I want to lower the car another couple inches, not only to lower the center of gravity but so I can add some aero to the bottom the car.  Currently the car is as low as it can go without a bad control arm angle.  The right way to do this would be to buy 911 Cup wheel carriers that have higher hubs.  Those wheel carriers are about $2k/piece if you can find them, and they only accept cup car brakes, bearings etc so it only gets more expensive.    Instead I'm on the hunt for another Mcpherson wheel carrier/spindle that could work.  The good news is Boxster's have the same Mcpherson setup on all four corners with the same wheel carriers/spindles.  So if I can find a car that has front wheel carriers that will work I can use them on all four corners (if there is a provisions for axles).   There's a photo of a Boxster wheel carrier and an e46 wheel carrier below.  They look....close, and the hub is definitely sitting much higher on the e46.  ABS pulse ring design is the only thing that may be a real hurtle, the rest I think I could fab my way out of.    That being said I have a couple of questions....

 

Questions 1:  Any ideas on a replacement spindle / wheel carrier that is close to the Boxster's design with a higher hub?    

Question 2: Has anyone gone down this road with another car?  Is there a better way?  

 

Bonus Question:  I've read that the rear of the car should have a much high roll center than the front.  If this is true, could I use "lowering hubs" up front to maintain my roll center and then use my stock hubs in the rear and just lower the car beyond the point where my control arms are perpendicular to the ground?  

 

I understand that the brakes, wheels etc etc would all have to change.  I need new brakes and new front wheels anyways so if I can get by with only modifying the front (see Bonus Question) than this is a no brainer.

 

 

Boxster Wheel Carrier

 

BMW E46 Wheel Carrier

nocones
nocones PowerDork
4/6/22 3:33 p.m.

Generally you want the roll couple (CG height relative to RC height) to be lower in the rear then the front.   I'm not 100% remembering the why, but what I remember is this will tend to bias the vehicle to understeer which is good because you can change the slip angle of the front wheels with steering angle but not the rear.    But what you want is a lower rear Roll Couple not just higher rear roll center.  On my MG the rear roll center is about 2" higher then the front.  On the LMP360 the rear roll center is level with the front.   That's because the Subaru the CG is lower at the back of the car then the front.   

For your build given that Boxster aren't known to handle poorly I would be hesitant to move the rear RC substantially without full kinematic analysis of the front and rear suspension, spring rates, roll stiffness / etc.   A small change may be worth it though based on your likely higher rear CG then a stock Porsche engine (V8 with Turbos, rear wing etc).  

 

If you move the hubs up on the geometry would you do both front and rear?  That obviously would impact your RC height and you would want to look at correcting the RC heights based on the final front and rear arm geometries following hub changes.  But I would still tend towards using what geometry Porsche used with success on race versions with modifications specifically targeted to your weight distribution.

 

Byrneon27
Byrneon27 Reader
4/6/22 4:11 p.m.

J.J Jackson comments on this topic in his book Fast Days regarding being "forced" into using Corvette uprights on the early Shelby Can-AM prototype. "JJ, you don't want to FIND uprights, you want to MAKE uprights don't you" 

 

Probably reading too far into that exchange I looked into fabricating uprights/wheel carriers/knuckles for my particularly outlandish projects, the off road guys do it all the time with great success. The fabrication section of Pirate4x4 will help. If you want the perfect geometry and attachments it's probably best to buy the right ones or make what you need. 

Box4VIR
Box4VIR Reader
5/25/22 11:35 a.m.

 

To everyone's surprise the car survived Hyperfest last week!  I'm shocked, I actually drove it back onto the trailer at the end of the weekend.  I admit I had so little faith I even rented a garage at track, which is where its sitting in the pictures below.   Overall the car did really well, but I did have some problems.  At a 140mph the roof lifted about 8"s up and forward, fortunately the hinges held and I was able to hold the roof down with my hand until I could into the pits (the flaggers were not impressed with one handed driving but I was allowed back out).  The second time out the rear fenders were sucked into the pavement but a few rivets later that was resolved.  The only real problem I had was over around 4,800rpm the car would misfire badly at full throttle (anything under that, or just off full throttle it was perfect).  I was adjusting the fuel table all day (it was running rich) but I don't think it ended up being a mixture problem.  I pulled the plugs and they were perfect, I think the problem may be related to the stock weak coils I have.  Maybe under boost they're just not strong enough, has anyone experienced a problem like this that was resolved with stronger coils?  The coils on these old Audi motors are notoriously bad.  Garage glamour shots below, real track pictures to come and maybe even a Grassroots feature wink   

 

 

Javelin
Javelin MegaDork
5/25/22 12:00 p.m.

I am in lust with this build! Can't wait for the GRM feature.

golfduke
golfduke Dork
5/25/22 12:05 p.m.

SHEESH!  

 

What a freaking car. Man.  

 

10001110101
10001110101 Reader
5/25/22 1:59 p.m.

I can't get a good look at the coils in the photos posted, but I know a common upgrade for the FSI/TSI 4 cylinders is to swap to the red top Audi coils. Not sure if yours are similar or not. Crazy build!

Cheeks
Cheeks New Reader
5/25/22 2:27 p.m.

wow, I'm not even a porsche guy and I'm impressed 

Box4VIR
Box4VIR Reader
5/25/22 5:38 p.m.

In reply to 10001110101 :

I should have upgraded to the red tops, I just wanted to limit my variables at the time and save the cash but wouldn't you know it the problem is I didn't spend enough money.   Hopefully the red tops fix the issue.  Unfortunately I live in the city and can only troubleshoot and tune the car at an event which really is a pain.

also thanks for the kind words guys!  

Box4VIR
Box4VIR Reader
5/25/22 8:57 p.m.

PROOF!  It lives.  Full disclosure the first pic us under full course yellow 35mph, so I'm not leading the pack nor leading a train.  

 

 

trumant (Forum Supporter)
trumant (Forum Supporter) Reader
5/25/22 10:03 p.m.

My boys and I were at Hyperfest and I distinctly recall us seeing you and your car on track during UTCC and I immediately recognized it from your build thread.

Absolutely epic build and I feel lucky to have seen you out there and more fully appreciate all the awesome.

MrJoshua
MrJoshua UltimaDork
5/26/22 12:08 a.m.

I have a different, possibly unreasonable idea to solve your desire to lower the car without messing up the geometry. It looks like the front and rear suspensions are largely contained on subframes. Could you just section the appropriate frame rail mounts and move all the mounting points up 2"? The forward arm on the rear suspension would be outside of the subframe, but they are mounted between what looks like two stamped pieces that have room above them. The tops of the struts would have to be moved up, but you look to have room above at both ends. The steering rack is even mounted to the front subframe so you may be able to get away with a minor shortening of the steering column.

dps214
dps214 Dork
5/26/22 1:02 a.m.

I only just saw the suspension situation. Have you looked into normal 996 GT3 wheel carriers? Looks like they're compatible with all the normal suspension and hub parts but have different part numbers and I would *assume* that the difference is spindle height but I have no idea. On later models the GT3/GT4 have substnatially different carriers that I can only assume include higher spindle heights since those cars are lowered beyond any other model. No idea of the cost but they've got to be cheaper and more available than old cup car parts. Also, less than ideal control arm angles aren't the end of the world, especially if you have a lot of static camber and a substantially stiffer than stock suspension. If you looked under a 981 cayman with the sport suspension option you might be surprised by the lower control arm angle.

iammclovin804
iammclovin804 New Reader
5/26/22 7:44 a.m.
Box4VIR said:

Maybe under boost they're just not strong enough, has anyone experienced a problem like this that was resolved with stronger coils?  The coils on these old Audi motors are notoriously bad. 

I had an issue with stock coils on an RB20 under boost and upgraded coils fixed it.

Box4VIR
Box4VIR Reader
5/26/22 2:39 p.m.

In reply to iammclovin804 :

Great to hear!  Hopefully I'm not throwing money with this upgrade.   

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