IMSA GTU vintage racer build

[AydinZ71]

Agreed  I have been building my war chest of paint over the past few months haha

I have silver, orange metallic, and black base coats. All are acrylic urethane with separate hardeners and reducers. I also have urethane clear coat is gloss and matte. I had to clear a whole 5’ square section of the garage just for bodywork stuff haha. 

[clarkspeed]

3 hours ago, AydinZ71 said:

Agreed  I have been building my war chest of paint over the past few months haha

I have silver, orange metallic, and black base coats. All are acrylic urethane with separate hardeners and reducers. I also have urethane clear coat is gloss and matte. I had to clear a whole 5’ square section of the garage just for bodywork stuff haha. 

It's funny when you talk about painting a car, most everyone thinks about the physical act of spraying it. When it comes to bodywork, spraying is equivalent to the last 5 minutes in the history of the universe.

[AydinZ71]

ahahha, no kidding! The color is just the "sexy" part folks want to know about. I also built a war chest of bodywork material first. Durablocks... five rolls of varying grit paper, AL filler, regular filler, ahahha. 

 

Sanding sanding, and more sanding....

 

I have DA'd the existing finish down to primer/filler/bare steel. Using the existing filler matrix so I have less work to do, but down to bare steel on most of the car.

[clarkspeed]

Slow progress. Close to finishing up the rear suspension. I keep finding things I need to clean and paint. But it is getting there. 

 

I suppose its time for the big reveal. Based on Cary's sugggestion, I am going with an external shock. Not sure I can get away with it, but its easily reversable. It was surprisingly easy to do. I used adjustable shock brackets from AA Manufacturing with a some angle iron for strength.  Even easier in the front to connect to tubing. I used 1/2 threaded rod with rod ends to mock it up. I 3d printed a shock body to make sure there was clearance. I took a set of cheap Toyota MR2 struts and drilled a little hole in the bottom to drain out the oil. They are loaded in the strut tubes just for keeping geometry, no friction.  The only tricky part is the motion ratio is different than the strut.

 

Right now I am thinking Penske 7500's for the shock. They are reasonably priced,  come custom valved to my parameters, have multiple lengths, and are double adjustable. 

Edited July 4, 2022 by clarkspeed

[tube80z]

Looks vintage to me.  It should be interesting to see if they allow it.  I'll look through some of my really old photos to see if I happen to have any pictures of this done in period.  

[JMortensen]

The MR2 struts will still see friction at the piston and upper strut bushing. Don't imagine it will be a problem to run them without oil since they won't be doing anything other than taking the side loads from the struts and you've eliminated all the heat from them actually damping.

Very cool idea. 

[AydinZ71]

Looking good Clark! Suspension is not my specialty so I can’t don’t have much to add, but mechanically it looks solid! 

[clarkspeed]

On 7/4/2022 at 4:21 PM, JMortensen said:

The MR2 struts will still see friction at the piston and upper strut bushing. Don't imagine it will be a problem to run them without oil since they won't be doing anything other than taking the side loads from the struts and you've eliminated all the heat from them actually damping.

Very cool idea. 

Yes, you are correct. There is friction present. It takes maybe 3-4 oz pull to make them move in my estimation. I could measure but it will not help me. I think over time it will be less. But main thing is there is no change with velocity. It took a lot of pumping to get all the oil out.

 

I made a design for a bearing loaded strut tube with a HD strut shaft (low friction). I would cost maybe $100/corner. I decided I would postpone because this is cheaper and I need to proove the concept.

[clarkspeed]

No comments on my color choices? 

 

Step by step. I have designed a measuring tool that fits to the front crossmember control arm holes. It will allow me to thrust align the rear wheels to the chassis. Then at a later date I will align front with rear and set toe. I spent many a nights thinking about this and studying alignment methods and machines. If both front and rear control arms have adjustable toe and adjustable length, and you want symetric, then there is no fixed reference other than suspension pick up points. I will post pics when available. 

[clarkspeed]

I am quite proud of this little tool. I did a dry run tonight and it looks like it works. The 3d printed brackets have pins that slide into the front control arm holes. The 24x1" scale is really just there to keep everything square. The 60x2" scale slides through the brackets and is aligned to center of chassis by the marker pins in the bracket. 23.5 between holes. I installed cast iron rotors on the rear and measure to the rear control arm bolt to adjust control arm length even on both sides with zero camber. Then will use a line laser to the the front scale to set rear toe to zero and verify the left and right CA lengths are the same. 

That should ensure rear is aligned with chassis and later, much later, I can thrust align front to rear.  I'm not sure all this is necessary, but with double adjustable control arms Front and rear, it sure seems easy to get the track and toe uneven left to right and have the chassis tracking sideways. I ran these rear control arms on another car and first thing I found were the lengths were different even though the rod end stick out looked the same.

[AydinZ71]

looking good Clark! Looks like you are getting close! how much longer you think before you will hit the track? 

[tube80z]

I found I needed to change the rear toe-link design from left-right threads to using different thread pitches as it was super sensitive when adjusting.  I planned for but never made it far enough to change this all over to shims.  I wanted a faster at the track way to make changes that didn't involve needing a lot of precision and had to be repeatable.  I noticed most of the pro teams and car designs from 2000 on starting using that method instead of left-right threads.

 

Your 3D printed tool reminds me of the flag alignment system I've seen some of the formula car guys use.  It mounts over the top of the chassis and uses that to establish center.   Measure camber, caster, track this way.  Flip 90 degrees and measure toe.  Much quicker than strings to setup and make adjustments.

[clarkspeed]

Now you tell me!. Just kidding. I have been running this design for years and never noticed it before, but yes adjusters are super sensitive.  A full turn is probably over 1" of toe change or more.  If I ever make some more rear arms, I will definitely address this. 

 

This exercise has been very beneficial so far.  I found I had the wrong springs installed, interference with the helper springs, and L/R cambers uneven due to stack height of the hats/bearings.  All corrected yesterday.  In the end, I have exactly 1mm wider track on passenger side than driver's side, but stub axles are not fully torqued down and that is location of the error.  Rear set to 0 camber, 0 toe nominally to start and "centered" to chassis.  I am satisfied with the rear.

 

I have another idea that has been baking in my head for a couple years.  I want to fab a hub mounted alignment system that also incorporates scales for corner weighting.  I don't know why no one had done this before.  Heavy duty inline load cells are $50-100 and a digital read out/load cell amplifier/programmer is less than $10. It would need to have a leveling mechanism (laser reference) and ablity to slide a little so camber can be adjusted.  Lasers are also super cheap.

 

 

[clarkspeed]

Let's get a update in. I had a damn sinus infection which slowed me down for a couple weeks, but I'm still chugging along.

 

After the rear alignment I dropped it off the rotisserie onto jackstands. Spent a couple hours planning out the final welding push up front. I've got to mount a radiator, oil cooler, along with G-nose braces and air dam braces. Along with shroud for radiator and pulling cool air for the engine and brakes. Quite a bit of packaging. 

 

The good news is I got the front sway bar all worked out. It was a leap of faith that everything would clear.

[clarkspeed]

Here is a shot of the front brakes (For Aydin). Custom hat from Coleman, wide 5 floating adapter, floating T-nuts, and 11.75x0.810 rotor. This will be combined with raidial mount 6 piston Wilwood SL calipers.

[clarkspeed]

Prototype for my hood pins. 3 of the brackets with 1/2 round aluminum pins will mount on underside of hood by firewall. 3 receptacles will mount in firewall. Hood slides in, then latched at the front.

[AydinZ71]

On 8/18/2022 at 8:19 PM, clarkspeed said:

Here is a shot of the front brakes (For Aydin). Custom hat from Coleman, wide 5 floating adapter, floating T-nuts, and 11.75x0.810 rotor. This will be combined with raidial mount 6 piston Wilwood SL calipers.

 

 

Thanks for sharing Clark! let me ask you, do you feel cooling is better with the hat and rotor in a 2-piece configuration like that? I assumed having your ducting feeding right into the vanes without a gap would force more flow through the vanes, but I'm just guessing. I could section the 280zx rotor on a lathe, but from what I am reading they are intended to be "disposable" after one or two races? 

 

I'm going with the 3" velo stack in the headlight recess, like all the other EP cars (sigh). I was trying to get fancy, but we cant cover the headlight bezel so might as well use the 7" hole for something. 

 

I asked Greg about the knockback, and he didn't seem to have much trouble with his setup. 

[clarkspeed]

On 8/31/2022 at 9:22 PM, AydinZ71 said:

 

 

Thanks for sharing Clark! let me ask you, do you feel cooling is better with the hat and rotor in a 2-piece configuration like that? I assumed having your ducting feeding right into the vanes without a gap would force more flow through the vanes, but I'm just guessing. I could section the 280zx rotor on a lathe, but from what I am reading they are intended to be "disposable" after one or two races? 

 

I'm going with the 3" velo stack in the headlight recess, like all the other EP cars (sigh). I was trying to get fancy, but we cant cover the headlight bezel so might as well use the 7" hole for something. 

 

I asked Greg about the knockback, and he didn't seem to have much trouble with his setup. 

I don't a clue how these will cool. Maybe a little better due to more air fanned around. But I personally think cooling is mostly influenced by mass of the parts. Pretty simple heat transfer problem. Friction from pad generates heat, heat transfers through conduction to pad, caliper, rotor, hub, and on. Air blows on rotor to remove the heat with convection hopefully before parts get too hot.

 

Ducts in the headlights works well. You need to direct the air centrally to the rotor so the cool air moves radially outward through the vanes. I will post a pic if I rember too.

[AydinZ71]

@clarkspeed all good Clark! I think you shared a photo way-back-when, at least I remember seeing it. The idea is to feed the center of the hat/hub just like you said. Some dynamic pressure from the headlights helping get the air to the hub, and the centrifugal force from the spinning rotor/vanes do the rest, woohoo. Il fabricate something out of sheet metal once I get the car rolling. Gotten pretty good at fabricating small, light custom stuff out of sheet metal. I think il try some of the 20-gauge stainless I have on hand. Nozzle will be a 3” sectioned tube. 

[clarkspeed]

Here is a shot of the cooling on my last car.  I use an inlet flange for a Mazda MAF attached with the existing threaded holes used for the backing plate.  Shown with stock rotor.

 

I noticed the ones I purchased are not available any more but this looks the same:

 

https://www.amazon.com/Filter-Mass-sensor-Adapter-plate/dp/B07F7QC9N5/ref=sr_1_19?crid=2RAHB1KPVS2ZW&keywords=1986-1994+Mazda+323+1.6L+1.8L+Air+Intake+MAF+Sensor+Adapter+Plate&qid=1662394870&sprefix=1986-1994+mazda+323+1.6l+1.8l+air+intake+maf+sensor+adapter+plate%2Caps%2C136&sr=8-19

Edited September 5, 2022 by clarkspeed