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IMSA GTU vintage racer build


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Well that looks damn sturdy. The best firewall mount structure I have ever seen. 

A lot of people watch these restoration shows on TV now. As long as the welds are solid they will look great after paint. I'm sure you grind off the blobs like I do.

 

Got the floor pan in tonight. Now I need to paint and assemble the suspension.

 

 

20220521_201444.jpg

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Woohoo. Final stretch! That’s awesome man. Hey is there any particular reason you painted the cage a different color than you will the interior? I planned on painting my cage the same color as my interior except for everything that was driver-facing. That will all be flat black. 
 

I appreciate the compliment! Especially as someone who genuinely doesn’t know what I’m doing. A part of me still has imposter syndrome with all this fabrication work. Yes it has been dozens and dozens of hours but with no formal training I’m just using intuition. 
 

 

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On 5/22/2022 at 1:14 PM, AydinZ71 said:

Woohoo. Final stretch! That’s awesome man. Hey is there any particular reason you painted the cage a different color than you will the interior? I planned on painting my cage the same color as my interior except for everything that was driver-facing. That will all be flat black. 
 

I appreciate the compliment! Especially as someone who genuinely doesn’t know what I’m doing. A part of me still has imposter syndrome with all this fabrication work. Yes it has been dozens and dozens of hours but with no formal training I’m just using intuition. 
 

 

I don't know what I am doing? Is that a good answer? I usually shoot cars just like you are doing. Having painted 3 or 4 like that, I decided to try something different. My last car was painted a battleship grey  which came out great. For interiors, I usually shoot a straight cheap industrial urethane (no UV protection), with hardner, no primer. But I don't usually shoot over so much bare metal as you have. 

 

I did some research on the Google and found a log of drag racers using the hammer tone paint to good effect. Plus I had some mental pictures of a titanium color interior. The hammer tone is easy to brush, easy to match spray, durable, and super easy to touch up. So I thought why not a 2 tone? Not really much more difficult.

 

What did I learn? Shooting the interior with a gun is still best way to go. But the 2 coat rattle can spray hammertone on my interior panels came out decent and seems durable. And easy to touch up if needed. But not as "nice" a finish as I would like.

 

IF you want to do the cage in a different color, I HIGHLY recommend the brush on hammertone. For some reason it lays down perfect on the curved surfaces. And you don't have to mask off anything. On the downside, I think the brush on only comes in silver, grey, and black.

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Hmm, il have to look into the hammertone. My biggest pet peeve with anything out of a can is how easily it scratches off or delaminates. Even the self-etching stuff does a great job at bonding with the steel, but then has a hard time making a good bond with whatever I spray over it. There just doesn’t seem to be anything that gets anywhere close to the performance of 2X epoxy. I’m going to use it on everything from now on, even subframe components and struts. 
 

so my plan is to stay the entire interior with DTM epoxy, followed by a thin silver base coat, and one thin layer of clear-coat. Maybe a light sand on the epoxy, just to highlight any MIG spatter I missed, but otherwise it will just be coat-coat-coat. I need to get one of those 3M head-to-toe onesies. 
 

The bar’s facing the driver, the window sill, the cowl… really anything facing the driver I plan to hit with jet black then flat clear. Is that silly? It just seems logical to me but I may be over-doing it 🤷🏽‍♂️

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  • 2 weeks later...

No picture updates. 2 tasks before I take it off roterssire. I am measuring all the suspension points to put into my simulation software program. If I play this right, all future adjustments will be predictable and repeatable. Trying to get all the points within a couple mm. It is much easier now than on the ground. 

And the last thing will be painting suspension parts. I debated over this for weeks on end. I just could not decide. I ended up choosing a 10 Yr old+ can of red Glyptal I had sitting on the shelf I had used for some block coatings way back when. It stirred out like new, flows out beautiful to reduce brush strokes, durable as hell, looked great on my sample part, and essentially free. Problem solved.

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It's the stuff used to coat internal windings of electric motors. Developed many years ago and hot rodders picked up on it to coat internal engine blocks. Sheds oil well and encapsulates casting flash forever. That's what I bought it for and it works well, but it is expensive. I'm not building many engines now and was amazed it still looked great after all these years. Again, why not? Otherwise it will sit another few years. Durable finish is an understatement. 

 

A good idea I found for suspension is stainless steel spray paint. Steel it is the brand. Kind of a dull silver finish but again, durable as hell and easy to apply. It also is expensive, but doesnt take a lot of product to fully cover so it goes way longer than say a color spray paint. I bought a couple cans to use, but since everything else is silver or black I wanted a different color for the unsprung stuff.

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I have measured all the hard points for input into software. I use a program called Susprog3d. There are others out there. I think I have every hard point measured to within 2 or 3 mm. It is difficult and time consuming but the chassis diagram from the FSM does help a little if you have stock chassis points. 

So why invest all this time any money? If you study suspension design, there are certain targets you want to hit. Some critical are suspension frequency, roll angle, F/R stiffness %, and roll center. I have a good idea of where I want these based on study and past experience. Taking all the measurements and putting into software will let me know where I am. Even if I did not know what I wanted, going through the process at least let's me know where I am and any changes can be documented and reversed along with a possible direction to pursue.. Bottom line, if I get this right, it will save countless hours of testing time on the track. For example, I took a wild guess on my sway bar rates when I bought the bars. And the arm length is just what I needed to make it fit. I needed this all just to mock up the suspension. After I got all the data input, I think I am much closer to a desired roll rate and F/R stiffness than I thought. I believe I can at least start testing with current rates. And if I purchase a few extra springs or bars I know which way to go. Springs at $60-70ea and roll bars at 100-150ea are relatively cheap, if you have a plan for what you want.

I have been ask before "can you give me your measurements". There are a few problems with that. I spent a lot of time doing it and perfecting my methods, every car is different, and most importantly, doing it yourself is about the only way to understand what you are doing. If someone just gave me the numbers, I would be lost forever.

However with that said, if anyone is trying something similar with Susprog3d software or an alternative, I am more than happy to provide guidance. I have been working with my own developed Excel based system to make it more simple, but I just don't have enough time to finish it.

 

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Ahh... that's cool! I didn't realize you could use the insulating coating on motor windings for other applications. Good stuff :) 

What irritates me is how difficult it is to get a real-good tangible understanding of all the different available coatings, without direct experience (buy it and try it). Enamel, Epoxy, Urethane, Acrylic Urethane (the crap we have to use in CA), moisture cure, 2-component cure. so on... What is advertised by the manufacturers is so far from a "spec" or even valuable for a DIY'er. Silly, but I gained most of this experience using all these various chemistries on model cars. Yes, they even make 2X clear urethanes for model cars now 🤣.

 

For example, people have been using enamel spray cans for decades... It's what most auto-parts store will recommend and sell you if you walk in. It chips and has terrible adhesion. the paint itself cures hard, but what's the point if the failure mechanism is a loss of adhesion and not abrasion. I have tried it with and without the dedicated primer, paid super close attention to surface cleanliness and roughness. There must be a very particular technique that evades me, but its not on the can. I suppose that is the point of being a professional... understanding the ups and downs of all the various chemistries and taking it further. Like, which brands provide a superiors chemistry even in the same class/type of coating.  

 

So far I have been really happy with products sold by Speedokote. I have an order of Eastwood basecoat. I'll let you all know how it goes!

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Clark, 100% with you on the inexpensive role of swapping springs and bars. In lieu of being another "give me your numbers" offender, could you coach me through it once I have the suspension all back on? I understand the general concepts (camber, caster, RC, etc.), but have zero experience on how to set-up a car. If I understand correctly, I need to set my ride height first, then my camber, then my caster and so on... I don't even know what ride height I should be going for, or even what point on the car I need to measure from 🤣

 

Prather says 4" high, but that's from the ground to the bottom rocker of a miata. I assume its not transferable. 

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16 hours ago, walkerbk said:

I powder coated my suspension and the up front cost is high , but now everything is basically free ($20 bag of powder goes a long way). I have coated all suspension, cross member, valve covers, transmission case, oil pans... all for 2x bags of powder and the stuff is as durable as it gets 

Sorry, I should have mentioned powder coating. It really is the best solution for finish quality, color selection, and durability. 

Some of the most stupid stuff I post on this tread are when I take strange things off the shelf and use them for solutions on this car.

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3 hours ago, AydinZ71 said:

Clark, 100% with you on the inexpensive role of swapping springs and bars. In lieu of being another "give me your numbers" offender, could you coach me through it once I have the suspension all back on? I understand the general concepts (camber, caster, RC, etc.), but have zero experience on how to set-up a car. If I understand correctly, I need to set my ride height first, then my camber, then my caster and so on... I don't even know what ride height I should be going for, or even what point on the car I need to measure from 🤣

 

Prather says 4" high, but that's from the ground to the bottom rocker of a miata. I assume its not transferable. 

That post wasn't directed at you Aiden. My advice for you is "ask Greg". If you still need some holes filled, I'm sure myself and others can chip in. And there are relatively simple equations that can ball park most stuff.

Being an engineer and more importantly, a part time race engineer, I want to know my car intamately. And hopefully I can save a lot of time when actually dialing it in at the track. 

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Posted (edited)

Got a little painting done this afternoon.

 

I started putting together my suspension "targets". I will post it as soon as I clean it up.  It can answer some questions others may have on what I am trying to do.  Just general guidelines that put you in the ballpark.

 

 

20220606_194305.jpg

Edited by clarkspeed
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Hi Clarke,

 

Can you get away with a toe-link system in historics?  If you can then I'd suggest the low friction mounting of the ARBs.

 

I also use Susprog3D.  I can remember my weekend of 16 hour days thinking all I have to do is measure this thing and it should take what, 4 hours max :-).  I'm a hopeless optimist when it comes to estimating how long it takes me to do anything.

 

BTW, I ordered this book in case you want a review or recommendation https://www.amazon.com/gp/product/3658351993/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 based on favorable feedback from the advanced data aq group on FB.  Some good nuggets come from that in case you aren't already a member.

 

Cary

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Sometimes stopping to collect your thoughts makes a world of difference.  I had pages and pages of notes and book excerpts that have been directing my general path along with past experience on things that I know work.  So I stopped and put them all on 1 sheet which was definitely beneficial in making things clear for me.  I call it my chassis KPI's.  Some are starting points and some are must have.

 

Most of my modifications to this tube car were adding adjustment where there was none or little before.  All production based cars have limits on what you can do for adjustment and alignment, along with plenty of fixed dimensions and weights you cannot overcome.  My goal all along has been to transform this shell into more of a purpose built race car like a spec racer or formula car, but keeping the basic strut suspension.  The fastest setup may end up being something very close to a limited prep Improved Touring car, but it does give me almost infinite adjustability and possibilities for for radical changes in the future.  One of the basic goals was the lowest ride height (and CG) I can stand without botttoming while still maintaining suspension performance. That is not in the KPI's but implied.  That is not easy so easy to achieve with a MacPherson Strut car.

 

I use SusProg3d for my chassis simulation software.  By measuring everything on the rotisserie with giant t-squares, with 24" and 6" machinist scales, I was able to measure things out much closer than I have in the past.  The usual process is the car level on jack stands and plumb bobs pointing at masking tape on the floor. When I start weighing everything and get the car sitting on wheels. the final calculations can begin.  So why did I do this?  Well knowing what I know now, I think I could actually get in the ball park with most of these suspension KPI's without resorting to such detail.  I have been working lately with some Excel based equations that approximate the software output.  But each equation takes you down a path, making it difficult to see how changes affect other things.  For example, if I extend the front control arm 1", how would that affect camber gain, weight transfer, toe change, Ackerman, and so on, and so on.  With the software I can change virtually anything and instantly know what other things change with it.  In addition, it provides a baseline for the car I can track over time up to and including damage assessment.  Most importantly for me,  it provides a basis to understand and visualize what is happening when I make changes at the track or the garage, it gives me "hints" on what changes I may want to make, it documents the "formula" for what works, and it can answer most of my future stupid questions.

 

So here are my KPI's.  I invite Cary and others to chime in if these are in line with what they have experienced.  Based on my experience these numbers will get you close enough to where you want to be to begin track testing and the car will be docile at high speeds.  The 3 catagories are things that I will just verify, measurements I will make in final configuration, and predicted results from the software.  Some of my initial results are listed although may not be exactly what I wanted.  I may change springs and bars again before I even get to the track.  But not ready for that decision yet.  This is really the first time I got all the numbers in.  All of the settings are nomimal at the moment until I can get the car on the ground.

 

Clark

 

 

 

Suspension Design Parameters.pdf

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18 hours ago, tube80z said:

Hi Clarke,

 

Can you get away with a toe-link system in historics?  If you can then I'd suggest the low friction mounting of the ARBs.

 

I also use Susprog3D.  I can remember my weekend of 16 hour days thinking all I have to do is measure this thing and it should take what, 4 hours max :-).  I'm a hopeless optimist when it comes to estimating how long it takes me to do anything.

 

BTW, I ordered this book in case you want a review or recommendation https://www.amazon.com/gp/product/3658351993/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 based on favorable feedback from the advanced data aq group on FB.  Some good nuggets come from that in case you aren't already a member.

 

Cary

Thanks Cary,

My front ARB is mounted with needle bearings enclosed in a fixed tube. Aka stock car style.  The rear is located in Delrin bearings because I ran out of time and space getting that one to comply.  Maybe a future upgrade?

I use SusProg3d also.  Let me say it is sooo much easier on a rotisserie. But even with that I probably have 8 hours in this round of measurements and still have a few I want to verify.  If you ever want to compare anything let me know.  I think (hope) I finally have the damn struts dimensioned. Not easy even on a bench.

 

That book looks very interesting.  I probably have room on my shelf for 1 more :-).  If it can expand on what I  presented in the attachment of my previous post, let me know!  A resource I recently found on data acq is "Your Data Driven" from Samir Abid. Website, book, and podcasts.  I have not had time to explore deeply yet but looks promising. I picked it up from Bentley's "Speed Secrets" podcast. I have been slowly going through that entire collection.  A lot of great driving instruction, but some interesting engineering insights also.  I have been doing a lot of podcasts recently.

My "free" time outside of work, family, real estate adventures, and building this car have been consummed with my recently acquired 77' Alfa Spider daily driver. That cost me 4 new books recently.  Anyone on this forum care to know how I perfected tuning SPICA fuel injection? The AlfaBB forum doesn't like things that deviate from the norm.  Don't ever mention engine swap on there.  I guess that's why this forum has Hybrid in the name.

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On 6/6/2022 at 12:37 PM, AydinZ71 said:

Ahh... that's cool! I didn't realize you could use the insulating coating on motor windings for other applications. Good stuff :) 

What irritates me is how difficult it is to get a real-good tangible understanding of all the different available coatings, without direct experience (buy it and try it). Enamel, Epoxy, Urethane, Acrylic Urethane (the crap we have to use in CA), moisture cure, 2-component cure. so on... What is advertised by the manufacturers is so far from a "spec" or even valuable for a DIY'er. Silly, but I gained most of this experience using all these various chemistries on model cars. Yes, they even make 2X clear urethanes for model cars now 🤣.

 

For example, people have been using enamel spray cans for decades... It's what most auto-parts store will recommend and sell you if you walk in. It chips and has terrible adhesion. the paint itself cures hard, but what's the point if the failure mechanism is a loss of adhesion and not abrasion. I have tried it with and without the dedicated primer, paid super close attention to surface cleanliness and roughness. There must be a very particular technique that evades me, but its not on the can. I suppose that is the point of being a professional... understanding the ups and downs of all the various chemistries and taking it further. Like, which brands provide a superiors chemistry even in the same class/type of coating.  

 

So far I have been really happy with products sold by Speedokote. I have an order of Eastwood basecoat. I'll let you all know how it goes!

I am no coating expert for sure.  I do deal with coatings in my job just not paint so much., more like hardness and TBC.  But as you already know, any coating is a system that has to work together.  Every material laid down must bond with the previous layer.  Surface finish, mixing, cure, thickness, and cleanliness must all be controlled along with chemical compatability.  If you follow the rules, I think most stuff will come out ok from a durability standpoint.  No one uses laquer anymore.

I have never been really happy with anything our a spray can at an auto or big box store. Just fast and convienient.

 

If you really want durable, look into single shot industrial coatings and fleet coatings (sherwin, ppg, etc). 

 

As a do-it-yourself amateur, I personally like working with single shot acrylic urethanes with a hardner mixed in. No can spray can match the pop of a real paint.

 

 

 

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