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Pedal Smasher
1973 Opel GT
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Discussion Starter #1 (Edited)
Howdy Everyone,

The time has finally come to start this thread, after a few years of planning, buying a GT, and collecting some of the parts I’ll need. I’ll start by giving some background on my GT. I first saw this car back in high school, it was how I learned about Opel. A GT definitely sticks out in a parking lot. After college when I wanted to get a cheap classic car to work on, the GT came to mind. I’d love a 1967 Fastback Mustang but that is out of my price range. So I started looking for a GT and eventually found out that the yellow GT I saw in high school was for sale. So I bought it roughly 10 years after first getting to know of the car. This GT does have some sentimental value for me because of that. I don’t like yellow however LOL. My avatar though is a photo I took as a Senior in HS.

So my plans for restoring this GT are…
-Replace the 2.0L (supposedly) with a 2.4L I purchased from Charles Goin. I will start this project by building the engine so I can free up some space.
-Replace the 4 speed with a Getrag 240 5 speed I bought from Charles Goin. I plan to rebuild this myself and I have the Opel and BMW manuals to do this. I have synchros already and will get more of the parts soon. I have some special tools as well.
-Rebuild the rear axle and install a Blackline RA18 LSD. I already have many of the needed tools to rebuild the axle.
-Install a Watts Link for the rear suspension and either Koni shocks or maybe Ohlins if they make something that would work, along with sway bars. I also want to lower the car either 1 inch or 1.5 inches. Lowering the car will require some modifications so the driveline works correctly, RallyBob has covered this in the past really well.
-Install vented front disc brakes and convert the rear from drum to disc brakes. The parking brake might still be drum brakes.
-Repainting the car in Strato Blau Metallic. My plan is to have my GT dipped and e-coated to protect it against rust. I believe I have a low rust content body. It’s a CA and NM GT, so rust should be low. All welding is planned to be done prior to having the car dipped unless there is some damage revealed by dipping the car.
-Replacing most of the worn out interior with a new black interior. A mold will need to be created for new seat foam. A 4 point roll bar and 4 point harness will be installed. A new stereo will be installed as well, with a custom Retro Sound head unit. The design for the radio head unit is already done and I’m working on creating it now.
 

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1970 Opel Gt - Purchased July 1972 - Chartreuse - restored - 3000 miles as of 02-16, 2021 -
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980 Posts
Good luck with your build - a dip, what a great place to start - would be nice not to have to worry about rust. Enjoy your project, slow and steady wins the race.
 

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Looking forward to your progress. Your GT certainly looks like a good starting point for a great build. Good luck.
 

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Pedal Smasher
1973 Opel GT
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3,157 Posts
Discussion Starter #5
My research on dipping a car revealed it’s not that expensive. I’ll definitely share information about that when I have it done, including what it cost and where I went.

At any point during this build, if I don’t include what something cost I don’t mind if someone asks. I don’t mind if people know how much my restoration cost and at the moment, my estimation including tools is going to be somewhere around $30-35k. Which is actually pretty cheap when you consider classic car restorations. I’m benefiting from wanting to do as much as I can myself. It would cost a lot more if I paid someone else to do all this. I’m also not trying to do all this in one year or even two years. So the total cost means less to me than creating something I’ll be very proud of. I don’t know every skill I’ll need but for me, this is an awesome chance to learn. So I’ll take the time to do it right, according to my OCD standards of quality when it’s something I really care about.
 

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The Young One
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My research on dipping a car revealed it’s not that expensive. I’ll definitely share information about that when I have it done, including what it cost and where I went.

At any point during this build, if I don’t include what something cost I don’t mind if someone asks. I don’t mind if people know how much my restoration cost and at the moment, my estimation including tools is going to be somewhere around $30-35k. Which is actually pretty cheap when you consider classic car restorations. I’m benefiting from wanting to do as much as I can myself. It would cost a lot more if I paid someone else to do all this. I’m also not trying to do all this in one year or even two years. So the total cost means less to me than creating something I’ll be very proud of. I don’t know every skill I’ll need but for me, this is an awesome chance to learn. So I’ll take the time to do it right, according to my OCD standards of quality when it’s something I really care about.
Once you are done with it I bet it definitely will be worth it.
 

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Just Some Dude in Jersey
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16,241 Posts
Wow! Sounds like an awesome project. You'll benefit greatly from all the new skills you will acquire. We'll all be eagerly watching your progress! :love: 🤩
 

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Pedal Smasher
1973 Opel GT
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3,157 Posts
Discussion Starter #8 (Edited)
I’m starting with the engine, so I will start to cover the plans for that with this post. I want to provide enough information so someone else could replicate at least the guts of the engine. This is what I have right now for my 2.4L.

-2.4L factory warranty block, from Poland. $1,500 for the core.
-C24NE Wiseco 96mm pistons, comes with ring pack and wrist pins. $450 from Ostar Motorsports. These pistons will need to be machined down a little, they protrude 1mm according to the specs.
-C24NE MaxPeeding con rods, 134mm rod length. £150 on eBay from the UK.
-Harland Sharp CIH roller rockers, 2nd version. $420 and it took a few years to get a set. They only produce these in small batches roughly once a year or so.
-Aasco Motorsports aluminum S10 flywheel, $325 during a group buy on the forum.
-Rebuilt 0.8 kW Bosch starter, 134€ from blauweissautosports on German eBay. They rebuild starters to like new condition.
-New ‘75 Manta water pump, GMB p/n 155-2010. $38.18 each from eBay, so I got two.
-NOS Opel fan clutch, p/n 8960124. £57 from a Croatian seller on eBay UK. I also got a replacement Beck Arnley one from Rally Bob and I know various alternate part numbers for this.
-NOS ‘75 Manta 5 blade fan, 57.75€ from Classic Opel Parts Emmen. I also found one of these on German eBay a long time ago. So I have two, because spare parts can be good to have. So I have everything I need for two viscous fan clutch water pumps.
-Opel 35 Amp Bosch alternator, p/n AL51X. $174 on eBay. I managed to get a rebuilt one someone still had from when Opel was around but I can’t find the listing anymore.
-Opel CIH alternator engine bracket, 71.29€ on German eBay. I know it sounds crazy, but this was already clean and pretty with the needed hardware.
-Mechanical fuel pump, made by a Slovenian company called PTZ, p/n 4271 and sourced from European Parts Company for $45 each so I bought two of them.
-Rebuilt distributor and a used distributor bought from a couple forum members. Can recall what I paid for these.
-Cam cover with adjustable screw to set clearance, 70€ on German eBay and will be worth every penny. I sold the earlier version of this on the forum not that long ago.

I’m not done sourcing parts for the engine but I have a BHJ honing plate arriving soon that will work for bore sizes from 95mm to 97mm. It cost me $644 but I will sell it once I’m done using it, so what it cost me for this tool in the end is unknown right now. My immediate plans are to disassemble the block and clean it with Gibbs brand. It will safely remove any junk and rust from the block and can be left on the block while at the machine shop. I have two companies in town I am considering, for the the machining work I need done.

My plans for this engine are to make it look stock, for the most part. I’ll still use the Opel GT valve cover and a Weber 38 DGAS. I’m going with the 38 DGAS for two reasons. The first is I will use a coolant operated choke. While it’s not as clean looking compared to an electric choke, it’s actually working off of engine temp. The second reason I’m going with the 38 is a custom dual plane intake. The intake will look close enough to stock but will hopefully flow better. I haven’t completely ruled out a Holley carb however, since I’m creating a custom intake.

Another custom engine part I’m considering is an oil pan. I want to create a large capacity aluminum oil pan that has a transmission support built in, which is how the Senator 2.4L did it. The Senator oil pan was front sump however. There would also be a built in oil accumulator with an electric valve to open and close it. This would hide the oil accumulator pretty well and while it’s not necessary to have one, I like the idea of being able to prime the engine before a cold start.

I have a 3D printer and a kiln for lost wax casting of aluminum parts. I plan to use both to create a few ideas of mine, like the radio. The radio will likely be the first thing made. So if I can pull off the radio, I have no doubt I can do the intake and oil pan.
 

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Nice! What is the C/R of a stock 2.4 vs your plan for the new build? What hp/torque are you hoping for?
 

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I would look at the build threads of both Keith Lundholm and Tom King in regard to the dip process. I personally would like to find out if any place out there does a primer dip after the solvent dip. It would seem necessary to get primer to those hard to get places. Also I seem to remember Tom saying some hard to replace stuff got ate up in the process.
 

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Just Some Dude in Jersey
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16,241 Posts
According to Dennis Gardner in another thread:

<<< The 2.4L engine runs a 9.4:1 compression ratio.
The pistons in a 2.4L is are dished from the factory to relieve some
of the compression ratio created by the "long stroke". >>>

This bit about dished pistons is why my previous 2.5 had 200-225psi compression. Too much! It has been repaired with new dished pistons.
 

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Just Some Dude in Jersey
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I would look at the build threads of both Keith Lundholm and Tom King in regard to the dip process. I personally would like to find out if any place out there does a primer dip after the solvent dip. It would seem necessary to get primer to those hard to get places. Also I seem to remember Tom saying some hard to replace stuff got ate up in the process.
I remember that his yellow GT is pretty special in this regard. He had his GT dipped in 2 types of acid that removed paint, rust, putty, everything. Then he had it dipped in galvanizing solution. WOW! Then primer/paint dipped. I think that's how it all went. Galvanized steel is tough to get paint to stick to, I wonder if he used a special primer?
 

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Pedal Smasher
1973 Opel GT
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3,157 Posts
Discussion Starter #13 (Edited)
I would look at the build threads of both Keith Lundholm and Tom King in regard to the dip process. I personally would like to find out if any place out there does a primer dip after the solvent dip. It would seem necessary to get primer to those hard to get places. Also I seem to remember Tom saying some hard to replace stuff got ate up in the process.
Ok, I'm home from work so I can give more details about my plans. I will have to go on a road trip to have my GT dipped and then e-coated. E-coat is the shortened name for the electro deposition process that is now commonly used in manufacturing to seal a metal chassis. I have found a company in Louisiana that does this. It's a pretty involved process they have and I'm sure it's worth it if you really want to protect a classic car when doing a full restoration. It's very important that you remove everything from the body during this process and any body work that needs to be repaired is already done. So I'll likely remove paint in key areas to check for rust before having this done.

I want my GT to become a long lasting treasure that celebrates the 100th anniversary of the GT. It's this mindset that also has me thinking I should get a modern 1 stage paint made and not use a common base coat / clear coat. Kyler recently shared some photos of his Kadett before and after being buffed. While the paint wasn't in good condition, those photos showed just how fantastic a good 1 stage paint can be. If the paint is still in great condition, you just have to buff it to make it look new again. Clear coats eventually get hazy. I think how the car will be painted should be factored into the decision to have the car dipped and e-coated. A 1 stage paint could really be the last time a car gets repainted. Put several layers on so there is plenty of paint there to last a lifetime of buffing. I'm not 100% sold on a single stage, but I'm not fond of the idea that 10 years is about the lifespan of a clear coat.

Galvanized steel is tough to get paint to stick to, I wonder if he used a special primer?
I think an acid etching primer is used.
 

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It sounds like a very thorough & thought out plan and course of action, Joe. Wishing you every success and will be following your progress carefully.

If I may about single stage and an expert like Keith can add his experienced opinion into the mix: Single stage solid colors like Kylers or my own 73's red can be brought back to life with some dedicated work with various buffing and polishing compounds. I am not so sure the same can be said about metallic colors. If anything, 20 years down the line and using that buffing compound could result in some splotchy looking portions on the body as that strato blue is removed in some areas while remaining intact in others.

2 part paint systems, with the clear featuring the latest UV inhibitors, might deserve a second look before you commit to that single stage metallic.

Mike
 

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Just Some Dude in Jersey
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Dunking unibody cars like ours is an incredibly good thing to do. We have many sealed compartments, cubby holes, and places you can't get to and that no sort of spray can get to. Many of those places seem to have never been painted. If you can get a car totally stripped with dunking and then dunked in some sort of epoxy primer, electro deposition, galvanizing, etc. it's good thing. :)
 

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Pedal Smasher
1973 Opel GT
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3,157 Posts
Discussion Starter #16 (Edited)
Nice! What is the C/R of a stock 2.4 vs your plan for the new build? What hp/torque are you hoping for?
So, that's not ironed out yet as far as dynamic compression ratio goes which is what has to be carefully considered. I have an Isky OR-77 (solid) cam, OR-77 hydraulic cam, and an Isky cam blank. To really get the most out of this engine, I'll need a high lift cam. I probably won't end up using the OR-77 or OR-77H cams that I have. I do have lash caps and hydraulic inserts from two forum members on here, so I can use the roller rockers with either a solid lifter or hydraulic lifter. I like the idea of not having to worry about checking the lash adjustment but hydraulic lifters probably won't work well with a high lift cam. I need to figure out what I want to do for the cam and I still need to buy valves and valve springs. I'm happy to hear what people think would be the best option for these. This is also why I haven't included any cost information yet on valvetrain.

The static compression ratio I have worked out. Wiseco states these pistons are 11.2:1, but they also protrude past the deck by 1mm. Machining the pistons down so they are flush with the deck so there is zero deck clearance, my math is below...

Bore: 96mm
Stroke: 85mm
Displacement: π(96mm/2)² x 85mm / 1000 = 615.25 cc
Combustion chamber volume: 55cc, approx.
Piston dished volume: 4.9cc (flat top with valve reliefs)
Compressed head gasket volume: π(97mm/2)² x 1.016mm (this is a compressed thickness of 0.04") / 1000 = 7.5cc
Ring land volume: estimated at 1cc

Compressed volume: 55 + 4.9 + 7.5 + 1 = 68.4cc
Uncompressed volume: 615.25 + 68.4= 683.65cc

Static CR = Uncompressed volume / compressed volume
SCR = 683.65 / 68.4 = 10:1

Wiseco says stock is 9.2:1.
 

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Dunking unibody cars like ours is an incredibly good thing to do. We have many sealed compartments, cubby holes, and places you can't get to and that no sort of spray can get to. Many of those places seem to have never been painted. If you can get a car totally stripped with dunking and then dunked in some sort of epoxy primer, electro deposition, galvanizing, etc. it's good thing. :)
Does dipping cleaner also remove seam sealer? My worry is that seam sealer might be removed from seams that are inaccessible.
 

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Pedal Smasher
1973 Opel GT
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Discussion Starter #18
Does dipping cleaner also remove seam sealer? My worry is that seam sealer might be removed from seams that are inaccessible.
The process at that shop in LA, seals the whole car when they do e-coat. It does a sealant and an epoxy coating at the end, which I imagine is an epoxy primer.
 

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1970 Opel Gt - Purchased July 1972 - Chartreuse - restored - 3000 miles as of 02-16, 2021 -
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Wow Joe, after reading all of the technical information on your to do list - how did you get so smart - what is your background...I now realize just how little I know. Again good luck with what sounds like the build of the century. Glad you will be around with a perfect GT to celebrate the 100 anniversary - I will most likely miss that by a few years but hopefully my daughter will be there with her Yellow, actually Chartreuse, GT. Which will then be a California GT. Looking forward to watching and learning from your build.
 

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Pedal Smasher
1973 Opel GT
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3,157 Posts
Discussion Starter #20
Wow Joe, after reading all of the technical information on your to do list - how did you get so smart - what is your background...
Thanks for the compliment, I just feel average around this group. My background is mechanical engineering and having a somewhat unhealthy addiction to cars, and a very active imagination.
 
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