GTM roll cage modifications and race car build log

[JCHRacer]

Hey John,

How is your progress getting sanctioning approval for the cage? Any updates?

[kabacj]

Hey John,

How is your progress getting sanctioning approval for the cage? Any updates?

Hi Joel,

The local scrutineers have signed off that the cage "looks good to them". They actually said its over kill. I was happy to hear that. Sadly these guys don't have the authority to approve a non standard cage. Their job is to enforce the rule book. The next step is to lobby the NASA national Safety board regarding the structure. Of course they want an engineering opinion on the strength of the GTM setup compared to the standard setup they show in their rule book. I am not an engineer. In the end I need to show them some proof that this cage design is at least as strong as their approved design which allows them to continue to have insurance. It always boils down to that these days.... oh well.

The current NASA rules have exceptions for other rear engine production cars, however none allow the setup we have in the GTM.

Regarding SCCA they have a spring tech event locally here ill bring GTM and see what feedback I get. SCCA also have a auto cross event April 7th. I will bring the GTM to the autocross so I can get some slow speed setup info.

Since I need to sort out the car for at least a few weekends I hope to try to lobby folks/ make connections at those events and go from there.

Unfortunately the first NASA event, March 30t at Lime Rock Park in CT, has a noise restriction of 88db. Clearly none of our cars are that quiet. I still have plenty of loose ends to tie up before then so building an 88db exhaust and re tuning the motor are out of scope. The next event is April 19th. I will attend that one and sort out the car and see how close I am to race ready condition.

BTW love your car. It sounds awesome! The finish is in sight!

John

[GTM RACER]

John,
Mike has a muffler set up that is quiet enough for Lime Rock. Get a hold of him. I went through an unorthodoxies cage design that would withstand 150 mph = rollovers and NASA wanted numbers. I provided numbers from a structural program and still. because it did not look similar to the three designs, they declined the effort. You are right it is all about insurance and who would pay out in a court case. I was told that the wagon wheel approach has a very good chance of approval on its own merit! Sometimes too many bars are not a good thing. A race friend of mine had a Toyota that had a very strong cage...hit the wall and the impact went right to the seat and broke his back. The car was too rigid. Great work, by the way!

[kabacj]

This weekend I finally had some reasonably nice weather, and no little projects getting in the way of a drive, so I decided it was time to take the car for its first drive around the block.




I was just taking it easy and figured I would just get on it a little to see how it accelerated. Holy cow!! Barely any throttle and I broke the rear tires loose. It did not do anything evil. Just stepped out a little. HA that was fun! I know they are stone cold, but still. Sheesh what was I thinking to get a 630 hp motor. Oh well with warmer weather and a bit of setup I'm sure it will be just fine. Man this is going to be fun to drive on the track.

John,
Mike has a muffler set up that is quiet enough for Lime Rock.

Thanks GTM Racer.

[RumRunner]

John,

Looks good, sounds great. The first drive around the neighborhood is a big milestone - for you and your neighbors - Congrats!

-Michael


GTM # 327: In prime, wet-sanding time.

[Kalstar]

This weekend I finally had some reasonably nice weather, and no little projects getting in the way of a drive, so I decided it was time to take the car for its first drive around the block.




I was just taking it easy and figured I would just get on it a little to see how it accelerated. Holy cow!! Barely any throttle and I broke the rear tires loose. It did not do anything evil. Just stepped out a little. HA that was fun! I know they are stone cold, but still. Sheesh what was I thinking to get a 630 hp motor. Oh well with warmer weather and a bit of setup I'm sure it will be just fine. Man this is going to be fun to drive on the track.





Thanks GTM Racer.

Go Daddy, go Daddy, go Daddy. Very cool, congrats on a couple of fronts.

[kabacj]

Guys thanks so much for the congratulations. It was definitely a marathon few days, but the pay off was great.

I think the problems I had with the clutch and shifting were due to a faulty Master Cylinder. At least that's the working theory. I was not getting enough throw from the master cylinder so I had to adjust it so I was not fully engaging the clutch when my foot was off the pedal and still not fully disengaging the clutch when I put pressure on it.

I compared notes with Hugo (kempo) who has the same transaxle, clutch and MC, and I seems pretty clear I have a problem with my MC.

I have the stock 3/4 bore so I will just swap that in and see if that solves the issues.

Crash, the ACT dual disk is an organic clutch but its designed for street / track. Its SFI rated With 800 foot lbs of holding power im sure its up to my 530 ft lbs of torque.

It slips very nicely without any vibration but its up to the abuse of the track according to the ACT marketing. I figure if I can make it work as both a street and track solution its a good choice. If I need to its easy to swap out the twin organic disks for sintered pucks. We will see if that's necessary.

If I can sort out all the little things I want to fix ill be back on the track in a few weeks. As soon as I unload the car and can take some more pictures ill post another update.

[crash]

140-145 is pretty darn fast on a closed course. We just recently did 145 at Thunderhill and that is considered really fast for a club raced car. If we break 150 we think they may want to add some restrictions to us as the speed differentials are pretty great between us and other cars.

[crash]

Yep, these cars are more fun than a red head and a jug of whiskey on a Friday night!

Glad you got some laps in. If the clutch is adjusted properly, this may be part of the break in process. All performance clutches I have run require a little bit of time where you have some slippage to transfer material from the disc to the pressure plate and flywheel surfaces. Are you, hopefully, using a sintered copper puck disc, or is it "organic"? The fact that you can smell the clutch leads me to think it is organic, and IMHO you should not be running that with that much HP/TQ. Either sintered copper or a carbon/carbon setup should be used.

[Presto51]

Yep, these cars are more fun than a red head and a jug of whiskey on a Friday night!

Man Crash did it again.

Manage to slip in a woman reference into a thread.

Have to admit, this boy does have a certain talent

[crash]

I'm told Mendeola really is in development of a six speed and I was also told that we may be testing something for them soon.

That said, as you stated, I think the GTM could get away with a 3 speed if the engine is an LS3 or better. In other words over 420 FT/LBS of torque.

[Presto51]

How many times did you say?

[JCHRacer]

Hi Joel,

The local scrutineers have signed off that the cage "looks good to them". They actually said its over kill. I was happy to hear that. Sadly these guys don't have the authority to approve a non standard cage. Their job is to enforce the rule book. The next step is to lobby the NASA national Safety board regarding the structure. Of course they want an engineering opinion on the strength of the GTM setup compared to the standard setup they show in their rule book. I am not an engineer. In the end I need to show them some proof that this cage design is at least as strong as their approved design which allows them to continue to have insurance. It always boils down to that these days.... oh well.

The current NASA rules have exceptions for other rear engine production cars, however none allow the setup we have in the GTM.

Regarding SCCA they have a spring tech event locally here ill bring GTM and see what feedback I get. SCCA also have a auto cross event April 7th. I will bring the GTM to the autocross so I can get some slow speed setup info.

Since I need to sort out the car for at least a few weekends I hope to try to lobby folks/ make connections at those events and go from there.

Unfortunately the first NASA event, March 30t at Lime Rock Park in CT, has a noise restriction of 88db. Clearly none of our cars are that quiet. I still have plenty of loose ends to tie up before then so building an 88db exhaust and re tuning the motor are out of scope. The next event is April 19th. I will attend that one and sort out the car and see how close I am to race ready condition.

BTW love your car. It sounds awesome! The finish is in sight!

John

Congrats on getting it running John. Looks Awesome.

As far as the sanctioning bodies go, you have had the same experience that many people have had when you just can't make it the rule book. While I have performed a structural analysis and determined that my cage (and yours) is as good or better than a cage built to the rule book under most loading conditions, I can’t guarantee that it is superior under every possible circumstance. Plus you have the liability thing....I feel safe in the cage I built but I'm not going to take the responsibility and the liability of certifying the design for someone else's use. Blame the lawyers and insurance companies.

Let us know if you make any progress with the scrutineers.

[kabacj]

While I have performed a structural analysis and determined that my cage (and yours) is as good or better than a cage built to the rule book under most loading conditions

Joel your cage design is awesome. I think it both looks nice and of course unlike me you can actually test what design is best. Thanks so much for sharing the design. I will get the cage approved. I totally understand the lawyer / insurance thing. Its a sad state that we all must fear for our lively hoods at the hands of ... well don't get me started. Ill find a way to get it approved and hopefully give back a little.

Very Nice John, very nice Ron

Hey Ron Thanks!

looks good man! i'm digging the details of your build. good to see you're at the go-kart stage. keep it up!

Thanks CF! Hopefully ill have some cool CF details to add to my car pretty soon...

Go Daddy, go Daddy, go Daddy. Very cool, congrats on a couple of fronts.

HA, HA. Thanks Jim. I owe the ITB idea to you. Yeah I am a pretty lucky guy that the family are always cheering me on.

John,

Looks good, sounds great. The first drive around the neighborhood is a big milestone - for you and your neighbors - Congrats!

.

Thanks Michael

The video does not do the sound justice. I am really pleased with the package. It definitely is more work to package the ITB setup, however it just sounds special. And nobody called the cops! That was nice.


John

[kabacj]

Guys Crash does not over state how much fun this car is on the track. In order to get back out there asap I have a laundry list of things to fix.

Saturday AM I un loaded the trailer and took inventory of the issues I had with the GTM

First was the brake circuit.

The Isis indicated that I had a broken circuit. I knew the brake lights were ok from the light bulb to the weather pack connector since they worked fine when I ran power directly to them. I checked the fuse in the Isis. It was fine. Clearly there was a problem between the power cell and the connector in front of the light. Next I checked the continuity of ground wire in the wiring harness. No ground! I pulled the ground wire out of the harness. It was clipped!

I soldered the wire back together. Ahh all the lights work again. Well that took all of 5 min. Amazing how easy it is to troubleshoot problems on a full nights sleep. This was an impossible problem to fix on Saturday night with an hour and a half of sleep in the prior 24 hours.

The positive of this ordeal. I got this great switch to control the brake lights. I also learned to trust the Isis. When it says their is a circuit fault. There is a circuit fault.



Here is the part number for the brake light switch.



The shifting problem:

I compared notes with Kempo to confirm how the Mendiola setup should work. Hugo had a few suggestions regarding the possible issues. I dove into my problem.

I took out the master cylinder.

First problem. The push rod was bent. As I adjusted the pedals lower and lower the excess rod contacted the pedal arm. The rod was only one thread too long, however as the rod hit the pedal arm it jammed and slightly bent.

Next removed the circlip and opened the master cylinder. Immediately I knew I found my problem. One of the seals has a gouge in it.




That was why I could not fully disengage the clutch and shift easily. Pressure was bleeding off. The bore of the master cylinder is smooth and undamaged. A 13/16 bore rebuild kit and I'm back in business. Just to be sure I swapped in a spare 3/4 inch bore master cylinder. Imagine that I can shift now! I ordered a 7/8 bore as I want a very short throw to go from the fully engaged position to the fully disengaged. Of course Kempo reminded me that I should be careful not to overdrive the clutch springs. I will start with a large air gap between the fork and throw out bearing and sneak up on the correct throw. I'll add a stop to limit throw if needed.

I did not notice the problem with the clutch testing at home. I had adjusted the clutch so the little pressure I could generate with the damaged MC would disengage the clutch. Unfortunately that meant the clutch would not fully engage. I could not even test half power driving in the neighborhood to get the clutch slipping.

I mentioned in my weekend recap that I went to the track with my gauges still in the original box taped to the dash. This setup got more then a few joking comments. In order to pass tech I needed something that looked a little stronger. I had sheets of aluminum to make a dash but that was going to take too long.

I had cardboard to make templates. Well the templates are going to be the final solution. I don't have time for anything else.

I did'nt need a speedo or gas gauge. So I mocked up a cluster with the tach, oil, and temp. Duct tape and cardboard actually make a pretty sturdy dash.





I also added a screen with backup camera. I had this on full time as my rear view mirror. Also not mounted when I got to the track of course. I saw more people walking up to check out the motor while waiting to go out on the track then cars following me , but the camera is very useful.



Next track test session is may 18th. A few more things on my list to fix before I am ready for another test.

John

[kabacj]

Some how in my hurry to address all of the finishing touches needed on e GTM I neglected to verify the ride heights. The front looked high but I thought it was just because I spent 5 min installing the hood. In fact, my front ride height was way too high at 5.5 inches where the rear ride height is 4.5 inches which is ok.

With the stock springs I had expected more compression at static load in the front. Since i only got a half inch or so of spring compression my ride height was a bit too high. That left me operating in the upper half of the stock travel.

To fix this I swapped out the 8 inch stock spring for a 7 inch eibach at the same 450 lb rate.



Now I have the required 4.5 inch ride height

The spring just rattles free with about 1/8 inch gap at full droop when the front is jacked up. I can either send the shocks back to install droop limiters, leave it as is, I can move the Lower shock mounting hole slightly so I can preload the spring and still get the proper ride height. I could also shorten the spring again and install tender springs that expand under no load conditions and compress flat under static load. I need to speak with the experts at performance shock to see what they recommend.

I don't think I need any stiffer springs in the front as the anti roll bar keeps the car very flat. The 450 lb springs support the car well under max braking . Maybe when I switch over to slicks ill need to stiffen things up but for now I'm happy with the stock rate.

John

[Roger Reid]

Nice write-up. All your hard work is paying off. Congrats.

[claybags]

John, simply OUTSTANDING!!!! Great write up also. Thanks.
Jeff