GTM roll cage modifications and race car build log

[kabacj]

NASA did a promo this summer and although I did not have my racing license yet I got a few cameo milliseconds in the video.

It's a well done video. See if you can spot the factory five cars

[buffalojr]

After watching it like 4 times, found the GTM at 0:47.

[crash]

Pretty cool video. I hope NASA does more of this stuff in the future.

[kabacj]

Pretty cool video. I hope NASA does more of this stuff in the future.

Yep I agree Crash. Very good publicity for NASA. It makes you want to try it out.

After watching it like 4 times, found the GTM at 0:47.

Buffalo, when you look at this car as much as I have its ingrained into your psyche. When I watched this video the first time I did not even know I made the video. The few flashes of the car I was like wait a second. Was that my car?

here are the shots where factory five cars made the video.





and here Pat McMhan with is modified cobra.



I love racing with NASA. Its a great organization. If you are not into wheel to wheel racing, they have HPDE and time trials which get you out on the track without the pressure of racing.

If you try it you will be hooked

John

[kabacj]

I hope to make a trip down to Virginia International Speedway the third weekend in March, so its time to wrap up the winter projects.

Last year I mounted the power shut off switch in the cockpit.



It was an easy spot to mount the switch and I did not have the time to do any fabrication. I always wanted to use a cable operated switch because that would mean a shorter path for the power to get from the battery to the starter, and less total wiring.

I decided the best place to mount the switch was on top of the battery, but that means I needed to do some fabrication. Its great because at this point in the build I have tons of scraps so I can just use them to make the parts I need.

After making paper templates and lots of head scratching, I cut out the parts in aluminum.



Next a little bit of welding to put all the parts together. They turned out to be very strong as i had hoped.



Then a test fit. Its really tight in there so I hope it all still fits now that its welded.



After a little testing I was able to route the cable so the pull to switch the power off is very easy with very little effort lost in the cable path.

I am sure the high quality bicycle cables helped make the pull smooth.




Finally I made a loop in the cable and added some red covering after I took the photo I added some heat shrink tubing over the fitting that holds the wire loop to prevent the allen screw from backing out and prevent the metal from wearing the paint if it touches.



Lots of work to make a simple improvement but I am happy with how it turned out.

John

[longislandwrx]

A lot of work but it sure beats shoveling snow.

looks great!

[kabacj]

A lot of work but it sure beats shoveling snow.

looks great!

Funny you should mention shoveling snow. One of my biggest problems for the trip to VA is getting my trailer out of storage. It's trapped in and blockaded by the snow and ice. It's going to take a few hours or maybe a tractor just to get it free.

I hope it warms up quickly!

[longislandwrx]

Tell me about it, I made the mistake of not clearing 100% of the snow in a small section of my driveway during ONE of the storms. Its now a 3" thick block of ice. I won't see asphalt for a month.

[kabacj]

Its time to kick things into high gear as my things to do list is always longer than my time available to work on the car.

A whole box of GTM goodies arrived from Performance Shock today.



The shocks have been rebuilt and revalved to increase the damping rates allowing me more adjustment in the range I tend to use on the track.

In addition to the rebuilt shocks I also got an assortment of springs .



I am going up to 650 on the front and have 800 and 900 lb springs to try on the rear. I was trying to support the car with the anti roll bars and damping rates and I think the stiffer springs will allow me to use the damping and anti roll bars to fine tune the car instead of control the weight of the car.

and finally I got an assortment of bump rubbers.



The bump rubbers allow you to fine tune the motion of the wheel in compression. The Bump rubbers effectively create a rising rate spring that you can fine tune. Thats why I have so many hardness bump rubbers to try.

If I lived on the West coast Performance shock would allow me to use their shock dyno to verify the setup. Their shop is right outside Sonoma Raceway. For now ill just try them out on the track but later in the season Ill try to get out there and get some hard data.

John

[johngeorge]

John, I have and use spring rubbers to make quick adjustments at the track with spring rates, you shove them in the middle of the spring coil. I do have a bunch with me if you want to try them out at VIR March just let me know.

http://www.steelerubber.com/2-5-inch...-spring-rubber

[kabacj]

John, I have and use spring rubbers to make quick adjustments at the track with spring rates, you shove them in the middle of the spring coil. I do have a bunch with me if you want to try them out at VIR March just let me know.

http://www.steelerubber.com/2-5-inch...-spring-rubber

Hey John. Yes definitely. I've never used them before but they sound like a great tuning tool. I'm really looking fwd to driving VIR. It's the fastest track I have visited yet.

Thanks!

[crash]

Hey John. Yes definitely. I've never used them before but they sound like a great tuning tool. I'm really looking fwd to driving VIR. It's the fastest track I have visited yet.

Thanks!

I know you are probably aware, but beware the grass! High speed and grass equals lots of $$.

[kabacj]

I know you are probably aware, but beware the grass! High speed and grass equals lots of $$.

Very true Crash when you leave pavement at 100+ the grass barely slows you down.

However, I prefer grass to a track like LimeRock where you are hemmed in by walls a few feet off the pavement in nearly every turn. Go off there and you do real damage every time.

This will be my first time at VIR so I don't intend to set any track records. Just get familiar with the layout and find a good setup

So far I have not had the opportunity to air it out in fifth.
The strait following the oak tree turn should be my first chance to do that with the Mendiola S5R sequential geared to pull hard at the 4->5 shift at 150. We will see how it goes.

With better aero, more grip, and with stiffer suspension the whole setup should be better, but we will see about that.
John

[kabacj]

UPS man left some fun stuff at my house last night.

My rear tires and rims arrived. Unfortunately they were not at the same warehouse so getting them mounted and balanced would cost me valuable time. It's possible they would have arrived in time, but missing tires would ruin my race weekend so I was not willing to chance it.

It's a sad sight when your race tires arrive and are covered in snow.



Light weight and strong rear rims


John

[crash]

Just a heads up, both the recent tire manufacturers that we have used said that their race slicks COULD NOT be subjected to freezing conditions without adverse detrimental effects occurring to the tires. Also, if the temperature is at all not warm, then handling of the tires is also critical to avoid damage. In other words, we had some small sidewall cracks on a couple of the tires that we were worried about and the manufacturer said that that was common when people throw or drop tires in cold weather. After he mentioned it I did see and recognize how the dealer reps handled the tires. They always roll or place them as opposed to tossing them.

Those look like they may be DOTs so probably not as sensitive, just be aware.

[kabacj]

[QUOTE=crash;190944]Just a heads up, both the recent tire manufacturers that we have used said that their race slicks COULD NOT be subjected to freezing conditions without adverse detrimental effects occurring to the tires. Also, if the temperature is at all not warm, then handling of the tires is also critical to avoid damage.

Those look like they may be DOTs so probably not as sensitive, just be aware.[/QUOTE

Yep DOT tires this time.

Good advice Crash. I have heard the same. I went with the Hoosier A7s front and R7 rear this time to try that combo out.

The Yokohamas are next month. Hopefully it will be above freezing.

John

[fuggles]

The strait following the oak tree turn should be my first chance to do that with the Mendiola S5R sequential geared to pull hard at the 4->5 shift at 150. We will see how it goes.
John

Hi John, Do you have the standard ratios or custom? For the standard ratios with 3.55 final drive, looks like 5th gear is not useful. I was thinking about going with the 4.11 final drive to be a bit quicker (but possiblty more shifting).
Are you happy with the ratios or would you make any changes?

Kent

[kabacj]

Hi John, Do you have the standard ratios or custom? For the standard ratios with 3.55 final drive, looks like 5th gear is not useful. I was thinking about going with the 4.11 final drive to be a bit quicker (but possiblty more shifting).
Are you happy with the ratios or would you make any changes?

Kent

Hey Kent,

Fifth gear is not “useful” on a track where I am going no more than 150 . However my motor has 550 ft lbs of torque. And I find that running slightly taller gearing makes it easier to avoid spinning up the tires constantly and also is less work rowing the gear box . Sometimes grabbing another gear for a few seconds gains you very little. When you just spin up the tires is not worth much at all. Note that I can still spin up the tires pretty easily with the tall gears so I don’t want to make that easier.

I think more importantly if you are very serious about matching the ratio of the gear you pull out onto the longest strait and other important corners on the track you really need to plot your gear and power curve to the track and optimize for the most important ratios.

For example the SDR which is geared taller allowed me to run out 4th gear to 156 where I need to shift the Sequential on the same strait. A few mph don’t really gain you much for a second or so and I just back off a little so I don’t bounce off the rev limiter.

However on a track like Road America , COTA or Daytona you are going to exceed 150 and then its great to have fifth which on my transaxle is a little shorter than the SDR.

I also wanted a gear that I could pull to 200 mph bc I think it will be cool to go that fast and want to try.

I have lots of experience gearing a very high strung 125 GP bike where I had a box full of sprockets to get just the right gear to match the narrow power band in all the right corners. In my view its better to have an easy to drive taller gear setup as long as you have plenty of torque. It does depend on the tracks you drive. Mendiola will make you gears if you need them so I figured go with the taller setup as I liked the SDR. (The H pattern 5 speed)

I would not change the setup if you offered me the option to change to 4.11 gears for free.

I know team PDG run the 4.11 gears in the S5R and they also seem to be happy with that setup. Crash can chime in on what he thinks about the pros and cons. The LS motor really helps your transaxle choice. Its such a flexible power plant you cant go wrong.

[crash]

And that is the beauty of these cars. The amount of TORQUE per pound of vehicle. Yes we run the 4:11 in the S5RR. I worked with Ian quite a bit to get the ratios right the first time. All went pretty well with the exception of the initial 2nd to 3rd split. 2nd was technically the right gear for the very slow corners we saw on the tight tracks like Button Willow, and 3rd was the correct gear for the low speed corners at Thunderhill, but the split between the two was too much. We raised the 2nd gear by 1 or 2 teeth(can't remember now) and it is now just about perfect. We can't run over about 160-170, but we don't have the tracks here to do that anyway...at least not with our 550 HP.

We tuned the gear box to run at both BW and TH without changing gears between races and are very happy with the results. Not optimal for Laguna or Sears, but we run many more, and more important races at BW and TH so that is what we geared for.

It really is great to be able to change a gear ratio by one or two teeth depending upon the requirements. You would be hard pressed to find another gear box that you could do this with...especially at the price point of the Mendeola.

[fuggles]

Thanks for the comments guys.

I am familiar with the idea of tuning gears for the longest straight. Back in my karting days we would do this with the rear sprocket. Also we could tune the clutch engagement for corner exit.

For the car, I do not expect to have the skills or funds to tune the gearing for the track. I am trying to balance street fun, maybe some auto-x, and track days. Tracks would be Sears Point, Laguna Seca, Thunderhill and maybe Buttonwillow. I like the idea of running the 4.11 with its quickness. Sacrificing top end. I'm not so sure how it will work in practice.

Unfortunately I can't optimize for everything! So I value your opinion about what you have done and how it works.

Thanks,
Kent

[kabacj]

Some VERY cool new carbon fiber parts arrived on my door step today.

Just in time for install over the weekend before I head out to Virginia International Raceway.

A new splitter to replace the one I destroyed last year and new Canards hot off the presses.



The new splitter is VERY nice. Too nice to take out on the track with all the rocks and flying stuff, but maybe this one will last a little longer.

Courtesy of the 818 production factory five were able to outsource the Carbon Fiber splitters for the GTM and boy are they nice!.

Perfect vacuum molded parts. No voids and very light.






Hot off the presses are a set of Canards that fit right over the details on the GTM Body.



Made to be trimmed to fit the theme of your car.Notice the traced line as a suggestion of the finished shape. I am going to keep them full size for max down force for now.



Woo hoo. I love carbon parts!

[Presto51]

John pretty cool parts but have to ask.

You finally found something you can't make?

What are your dates for VIR?

Ron

[kabacj]

John pretty cool parts but have to ask.

You finally found something you can't make?

What are your dates for VIR?

Ron

Ha ha. Well I am actually in process of making a few carbon fiber parts. The factory five parts are great quality and although I love to make things I need to focus my time on the things that I can't buy as nobody makes them.

More to come on that in the next few weeks.

My current plan for VIR is to leave early thurs the 19th and arrive at the track late afternoon. Then roll out of there early as possible on Sunday afternoon for the drive home.

Maybe I'll see you there?

[Presto51]

John let me check with my CFO about making the trip down there. Sounds like it will be fun

Ron

[The Stig]

Hi John,

I've been a "lurker" on your thread for quite some time. And i have to say that I've been impressed every step of the way. You've brought a ton of innovation to the build of your GTM. It's really fun to keep up with.

And beyond the obvious build skills that you've shown us, it's extremely cool to watch you hone your race skills as well. When I read the line about you taking the Oak Tree turn shifting from 4th and pulling hard theough 150 mph into 5th, all I could do was grin at the thought of it. I get to race vicariously through your endeavors. Keep up the coolness Dude!!! ��

It reminds me quite a bit of our friend Dave Borden... ��

[kabacj]

Thank you Mike for the kind words.

I was watching the early stages of your build when i decided to purchase a GTM. Your willingness to share your experience building allowed me to see what a build is really like as well as get ideas for my build. Thank you for that.

I think we all love to see each other go through the build process. Dave B, Hugo, Mike in fla, Gene , Tino, yours , and Eric and Mr Andreson getting started. Every build has great personal touches.

You are going to have a great time driving your car in Cali. It has really turned out well. You think you get attention on the forum here, Just wait till you are out in public!

Now that you are nearly done. What are you going to build next!

[The Stig]

Now that you are nearly done. What are you going to build next!

That one is still up in the air. I have about 4 different cars that I would like to build at some point. Not sure which one will be first, might be at this point.

I've always liked the shape of the FFR Type 65, and Dave's making the Mk-IV look like a great idea also.

A 62 Corvette resto-rod would be pretty cool also...

But I'd like to enjoy my GTM for a while first.

Mike

[mikespms]

Hey John,

Check the link to the APR performance site http://aprperformance.com/racing-veh...tory-five-gtm/

[kabacj]

Hey John,

Check the link to the APR performance site http://aprperformance.com/racing-veh...tory-five-gtm/

Thanks for the link Mike.

I think APR might need to add a new picture because this just showed up on my door step!





72 inches of double element down force producing awesomeness! This wing will make up to 1600 lbs of down force at 160. That will be enough!

Since aero tuning is my goal this year I figured having tons of tuneable low drag downforce would be a good start! Cant wait to try this baby out.

John

[kabacj]

Last season I had the CV bolts loosen up. Prior to that I meticulously prepared the CV bolts and never had an issue, but after not having an issue I figured I was over killing the process so I just tightened things up and they did not stay tight for long.

The process that works without issue.

1) Install the CVs using RTV or your goop of choice to seal the CV joint to the transaxle or outer stub axle and the CV boot holder to the CV joint. Tighten to spec. I use 35 ft lbs or so. Your torque may vary depending on the hardware you use.
2)after the RTV is dry remove 3 of the 6 bolts. Scrub out the grease and RTV out of the threads. Then using a Q-tip. Clean the threads in the transaxle or sub axle. Add red locktite and retighten. Then do the other 3 bolts.
3) mark the bolts so you can see if they have loosened without putting a wrench on them.
4) look at the back of the flange on the transaxle / stub axle to make sure the bolts are not sticking out. If so grind them down a bit when you pull them out to clean them. I have had to remove 1/16 an inch on some bolts as they hit the bolts attached to the hub on the upright.

This process worked 100% of the time without failure.

At the track I don't have time for this process so i decided to drill and safety wire the bolts. This way its a one step install without wait then safety wire and im golden.



John

[kabacj]

Spent the last few days prepping for my first race of 2015

I re aligned the car and set the toe.

I am going with -3/16 on each side up front and rear toe at - 1/4 on each side.

I also dialed out a bit of rear camber going with -.09 left rear and -.08 right rear .

I reset the ride height to allow for .04 degrees of rake. According to recent articles in race car engineering. A flat floor car like the GTM can create significant downforce using just the underside of the car.

The rake in the car moves the downforce bias forward which is very important. Notice how the pressure is lower under the front of the raked car




I hope this condition is even more pronounced now that I have covered up the opening under the engine.



I just need to install the 1/4 turn fasteners at the rear of the engine cover sheet aluminum and that's done.

[crash]

As I have posted before, the GTM is very sensitive to rake. What is your difference in frame heights front to rear at the axle center lines?

Also, I think you are going a bit overboard with a total of 1/2" toe in in the rear. Don't be surprised if the car "fights" itself. Also, from our experiences, it may be very uncomfortable going down the straights at a good speed with that much toe in, so take it slow at first.

[carbon fiber]

Thanks again for sharing all this info John. You're paving the way for all of us who want to get the most out of our setups. I'm looking forward to seeing how these changes will affect the car. Good luck at the track.

[kabacj]

As I have posted before, the GTM is very sensitive to rake. What is your difference in frame heights front to rear at the axle center lines?

Also, I think you are going a bit overboard with a total of 1/2" toe in in the rear. Don't be surprised if the car "fights" itself. Also, from our experiences, it may be very uncomfortable going down the straights at a good speed with that much toe in, so take it slow at first.

Take it slow? Ha ha ha.
Just kidding.

Good point. Speeds will be higher for longer. I'll take 1/8 out of both sides in the rear.

I run a bit more castor then you guys if I remember correctly but with the speed less toe might also be a plus.

I use a long acre digital angle guage to verify the rake on the frame rails but I'll measure.

[kabacj]

Thanks again for sharing all this info John. You're paving the way for all of us who want to get the most out of our setups. I'm looking forward to seeing how these changes will affect the car. Good luck at the track.

My pleasure.

I keep a log of all the changes I make now, but I have been checking the thread to see what I did and how it worked too.

We all share what we know and what we learn and we all end up with better cars. It's a win win.

[Presto51]

Saw John and his GTM in race mode.

Great guy, great car, great time.

I'll let John fill in the blanks, until then I'll throw a couple of pictures at you

Ron

[kabacj]

It was a great race weekend at VIR.

I had the pleasure of meeting Ron. We had a great dinner at the restaurant at the track. Which serves the best food I have ever eaten at a track. It would be a good restaurant in a big city. Unexpected way in the county at a racetrack.

I also met a few our factory five brothers who drive the challenge series.



It's great pitting with folks who share the build experience and love racing.

When i was not bench racing I was wrenching on the car while talking to people. I literally could not stand near the car without being asked what is that. Who makes it. How much hp does it have. Who makes the motor. How long did it take to build.

I love to talk to people, but when you are trying to subtract fractions in your head setting the toe or any other task that requires focus and considering you are trying to get it all done quickly so you can get back out on the track. it can be difficult

A few things you can learn from.

I mounted the diffuser. And tested the airflow using oil drips. It seems to flow much like predicted in the simulations






Now I need strakes and to close up the transaxle clearance hole.
I wanted to test clearance going in and out of the trailer before I made strakes. Those will be ready next time.

The other thing that happened that you all can learn from

I somehow got a big hole in my cv boot during the race. I guess it was a rock. But after the hole cv grease was flung all over the passenger side of the engine compartment.



My last laps were pretty smokey in the cockpit but I didn't realize It was cv grease. I figured it was just a bit of oil on the exhaust. I need to Lower my oil pressure again as the long full throttle high RPM sections were causing oil to blow by the main seal.

After 2 hours of cleanup. I resealed the cv flange ( that's where I thought the grease was escaping) is cleaned and lock tite all the bolts .

The next AM I Went out for my first run. More smoke. Now I knew it was leaking again. Since the bearing still had grease on it after running a race with a holy boot I figured I'll just stay out here till the session is done.

I need to add a split cv boot to the spares kit. Removing the cv boot takes too long as a quick track repair. Anybody know of one that fits a 930 cv?

Ideally I'd get the one that bolts together.

Thanks
John

[fastthings]

Cool, any video of the 150+ runs? Did you race, or was it a track day? Did you like your alignment canges? Who did you want to keep up with, and did you do it?

Fun stuff keep it up John

[crash]

I have plenty of CV boots like the one you sent me a picture of. They can be found here...http://www.myraceshop.com/930_CVs.html

Just click on the "add to cart" button above the $10.95 price on the right. That is for the one piece GKN boot like you have. Apparently I forgot to get a picture up there of that. I will do that ASAP.

On another note, if you are using the Bel Ray recommended grease very little should come out, even with a hole in the boot. We used to have big problems with grease liquefying and coming out of the boots, but not after switching to the Bel Ray. Are you using that grease?

We actually end up swapping out to spare axles almost exclusively due to boot issues now. With the good internals and the right grease we get over 50 hours of run time on the axles and CVs before we replace them out of caution. That equals all of the 25 hour race, and then we repack the CVs and run an entire season of endurance races without needing to service them with the exception of when/if a boot is damaged. You may want to think about carrying at least one spare, ready to go, axle assembly with you to the track.

[kabacj]

I have plenty of CV boots like the one you sent me a picture of. They can be found here...http://www.myraceshop.com/930_CVs.html

Just click on the "add to cart" button above the $10.95 price on the right. That is for the one piece GKN boot like you have. Apparently I forgot to get a picture up there of that. I will do that ASAP..

Thanks I placed the order. Great part and great price.

On another note, if you are using the Bel Ray recommended grease very little should come out, even with a hole in the boot. We used to have big problems with grease liquefying and coming out of the boots, but not after switching to the Bel Ray. Are you using that grease? ..

I do use the Bel Ray, and that kept the CV well lubed while some of the extra grease I put in the boot sprayed out

We actually end up swapping out to spare axles almost exclusively due to boot issues now. With the good internals and the right grease we get over 50 hours of run time on the axles and CVs before we replace them out of caution. That equals all of the 25 hour race, and then we repack the CVs and run an entire season of endurance races without needing to service them with the exception of when/if a boot is damaged. You may want to think about carrying at least one spare, ready to go, axle assembly with you to the track.

Good idea. I do have all the spares, I probably should store them assembled. This was a freak thing where a rock punctured the boot but next time I will just be able to pull out one assembly and mount the other.

Thanks for the advice.

John