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About a month ago I got a pretty decent 93 Base Coupe/6-spd for very cheap about 2500 bucks. I'll put a pic or two below.
I've decided to have a local shop do the build for me. The shop doing this has lots of C4 expertise so I'm mostly taking their advice on the details. He builds custom harnesses for instance for LS swaps and LT1 Opti deletes. They should be starting in a couple of weeks. The intent is to have a Street/HPDE car that doesn't cost as much to maintain as my last two 911's. I also really like the C4's body...and I needed a front engined V8 car this time around. I usually drive German stuff (my daily is a B9 S4), so I figure it's time to rumble.
The main parameters of the build are:
Rebuild the LTI as a stroker 383 (420+ hp, whatever it turns out to be)
Send the stock heads to Lingenfelter for CNC porting, valve job, springs, etc.
Removing the OptiSpark and replace with one of these EFI 24x™ LT1/LT4
Medium length custom built headers
Custom analog gauge conversion
New weather stripping + minor interior/exterior nip and tucks
C6 brakes all around
Complete suspension rebuild
Haven't quite figured out what to do with the front suspension, maybe a coil over or just some slight lowering springs with some adjustable shocks
Same for the rear suspension, a bit uncertain. The builder likes the stock spring with upgraded shocks.
285's all the way around with probably Cray wheels...or maybe a staggered C5Z set up.
Plus some other stuff that I can't remember right now, will update later.
So why the LT1 rebuild vs a swap? Well, I just like the idea of a built 383. I know the swapped motor would be lighter...but meh just doesn't have the pizzaz of a built SBC.
Why not just buy a C5Z? Well I wanted a creation not just another used sports car.
I plan to update the thread every couple of weeks.
Advanced Induction would be my choice for stock casting CNC heads.If you aren't limited to stock castings I would consider AFR or similar aftermarket heads.
Cool project.
I'd skip the 24x ignition system and save that money for something else. I'd avoid the coilover route, unless you have some specific need to swap springs quickly (at the track, for example). Look at the Xtreme front spring from VB&P and a matching rear Sport spring from them (e.g., my rates are 1125f/550r), which gives you full height/preload adjustability at all four corners. Also, you may want to look at offset urethane bushings up front for extra negative camber, and a full set of rod-ended links in back (Banski is a good option for this), for the same reason (and other reasons). On the heads, be careful that what you're going to spend on porting doesn't cost just as a much as a nice set of AFRs, which will likely flow a good bit better.
Don't mess with 285/40/17 tires. They are tall and you have very few choices among them. You need to figure out which brand/model of tires you plan to run, and purchase wheels accordingly. You're somewhat limited in 17" tires, but there are choices available. I'd want a 17x11 wheel and a 315/35/17 tire to go on it. But you have more choices in 18" tires. 18x11s (or 10.5 if you rear four rear C5Z wheels) gets you options in 315/30/18 tires. You may end up with two sets of wheels tires: one for street and one for track.
Why custom built headers? Sounds expensive.. there are options out there already.
do you plan to rev the engine past 7k? I like the torquehead set up but I think you have to ask yourself if it is really necessary? The LS computer and coil on plug do have their advantages though.
also as said before I'd look else where for heads. Lloyd Elliot, AI or AFR depending on goals and budget.
excited for your build! I decided to keep my LT4 and build it for the same reason. I have other LS stuff anyways...its cool to be a rebel.
Last edited by blackbelt; Mar 13, 2018 at 10:35 AM.
I'd skip the 24x ignition system and save that money for something else. I'd avoid the coilover route, unless you have some specific need to swap springs quickly (at the track, for example). Look at the Xtreme front spring from VB&P and a matching rear Sport spring from them (e.g., my rates are 1125f/550r), which gives you full height/preload adjustability at all four corners. Also, you may want to look at offset urethane bushings up front for extra negative camber, and a full set of rod-ended links in back (Banski is a good option for this), for the same reason (and other reasons). On the heads, be careful that what you're going to spend on porting doesn't cost just as a much as a nice set of AFRs, which will likely flow a good bit better.
Don't mess with 285/40/17 tires. They are tall and you have very few choices among them. You need to figure out which brand/model of tires you plan to run, and purchase wheels accordingly. You're somewhat limited in 17" tires, but there are choices available. I'd want a 17x11 wheel and a 315/35/17 tire to go on it. But you have more choices in 18" tires. 18x11s (or 10.5 if you rear four rear C5Z wheels) gets you options in 315/30/18 tires. You may end up with two sets of wheels tires: one for street and one for track.
My builder seemed to want to just remove the OptiSpark completely...even avoiding the LTCC route. If the 24x stuff is really reliable, I'm willing to go with it. I can absorb that in my budget.
Does the C4 have enough strength in the front end to handle a 315 tire up front? I used to run an HPDE boosted Miata where I've gone through Azenis, RS2/3's and R1R's. Of those three I really like the R1R's the best but those don't seem to be an option. Looks like the 315/30/18 setup has the most options. I checked the sidewall height the 315/30/18 has almost 4 inches of sidewall which should be enough to keep them from being too stiff on the street.
As far as running 4 rear C5Z wheels, with those 315's, is there enough clearance without running lots of camber on the front? I assume that the rear is ok.
Why custom built headers? Sounds expensive.. there are options out there already.
do you plan to rev the engine past 7k? I like the torquehead set up but I think you have to ask yourself if it is really necessary? The LS computer and coil on plug do have their advantages though.
also as said before I'd look else where for heads. Lloyd Elliot, AI or AFR depending on goals and budget.
excited for your build! I decided to keep my LT4 and build it for the same reason. I have other LS stuff anyways...its cool to be a rebel.
I plan to run the motor at around 6300-6500 rpm for the time being.
As far as the custom built headers, he already has the jigs and the set-up for a design that is in between a shorty and a long tube. I've read enough that I think long tubes are over kill.
Advanced Induction would be my choice for stock casting CNC heads.If you aren't limited to stock castings I would consider AFR or similar aftermarket heads.
Cool project.
Talk to AI and tell them your goals, their head porting and cams will get you where you want to be at and beyond.
Does the C4 have enough strength in the front end to handle a 315 tire up front?
For sure. My avatar is actually with 17x11.5 CCW wheels and Toyo 888s on a track (previous owner). But I can top that: last year I ran 315/35/17 Hoosier A7s on those same wheels at several autocrosses. That combo makes stupid amounts of grip, and it doesn't hurt anything. I would make sure to leave the roof on, but the suspensions on these things are pretty stout.
I used to run an HPDE boosted Miata where I've gone through Azenis, RS2/3's and R1R's. Of those three I really like the R1R's the best but those don't seem to be an option. Looks like the 315/30/18 setup has the most options. I checked the sidewall height the 315/30/18 has almost 4 inches of sidewall which should be enough to keep them from being too stiff on the street.
Most of my autocrossing is done on 315/30/18 BFG Rival S tires (Hoosiers aren't legal for my usual class), and I drive on them to and from events and occasionally other street driving when I get too lazy to swap them out. They actually pretty well on the street - better than worn-out Kumho Ecstas in the 315/35/17 size, for example. As always, it depends on the particular tire you choose. But there are cars coming from the factory these days with far shorter sidewalls than the 315/30/18 has.
As far as running 4 rear C5Z wheels, with those 315's, is there enough clearance without running lots of camber on the front? I assume that the rear is ok.
My 11" wheels with 315-width tires (either 17s or 18s) all fit fine at all four corners, with 50mm offset (7.96" backspacing). That offset is the real key. Off the top of my head, I think the 10.5" C5Z wheels have more offset, and therefore may require a small spacer to avoid rubbing on the inside edges. That's not a problem, as long as you install longer ARP wheel studs in your hubs. Those wheels are a cheap and good-looking option, if you can find a set of four. Ideally for a 315 tire, you'd want 11-11.5". I got some Forgestar 18x11 CF5s, which look good, are easy to clean, and don't break the bank....just in case you're looking for options.
Thanks for the input. It's hard to find C5Z wheels that aren't chromed to death.
Originally Posted by MatthewMiller
For sure. My avatar is actually with 17x11.5 CCW wheels and Toyo 888s on a track (previous owner). But I can top that: last year I ran 315/35/17 Hoosier A7s on those same wheels at several autocrosses. That combo makes stupid amounts of grip, and it doesn't hurt anything. I would make sure to leave the roof on, but the suspensions on these things are pretty stout.
Most of my autocrossing is done on 315/30/18 BFG Rival S tires (Hoosiers aren't legal for my usual class), and I drive on them to and from events and occasionally other street driving when I get too lazy to swap them out. They actually pretty well on the street - better than worn-out Kumho Ecstas in the 315/35/17 size, for example. As always, it depends on the particular tire you choose. But there are cars coming from the factory these days with far shorter sidewalls than the 315/30/18 has.
My 11" wheels with 315-width tires (either 17s or 18s) all fit fine at all four corners, with 50mm offset (7.96" backspacing). That offset is the real key. Off the top of my head, I think the 10.5" C5Z wheels have more offset, and therefore may require a small spacer to avoid rubbing on the inside edges. That's not a problem, as long as you install longer ARP wheel studs in your hubs. Those wheels are a cheap and good-looking option, if you can find a set of four. Ideally for a 315 tire, you'd want 11-11.5". I got some Forgestar 18x11 CF5s, which look good, are easy to clean, and don't break the bank....just in case you're looking for options.
Magna Flow Mufflers (stock exhaust between the headers and mufflers)
Service Transmission (6sp ZF)
Rebuild Power Steering Rack
R-134 Retrofit
Complete suspension rebuild with QA1 dual adjustable shocks front/rear
Wilwood brakes front and rear (14" front/12.88" rear)
Road Race Wet Sump Pan from Canton (8 quart capacity)
Custom Analog Gauges
18x11 Forgestar CF5 wheels w/315/30/18 BFG Rivals
Short shifter kit
Rebuild Dana 44 diff, ratio = 4.11
Paint touch up
That's gonna be a car with real speed! Here are a few thoughts I have on what you're planning:
Make sure your brake package will fit inside those wheels.
Research the short-shift kits for the ZF6 before you buy one. There are threads on here about that, and I seem to remember that the ZF Doc version is preferred, but I don't know if it's still available.
My car has a Dewitt aluminum radiator and it never gets hot on track, even when the previous owner ran it in Houston summers. He found the need for an oil cooler, though; so you'll want to plan for that if you are really going to track it. He removed the a/c condenser to maximize flow the radiator, and basically stuck the oil cooler in its place (but it's much smaller, of course). You can probably fit an oil cooler while retaining the a/c, though.
You'll want to research the compression ratio vis-a-vis the piston shape and height carefully. On my car, I remember the previous owner (who built the engine) didn't get as high a CR as he was planning. That may be easier with the AFR heads, though (mine are stock LT4 heads ported to roughly AFR195 Comp flow numbers). I'm not sure.
My car's previous owner has lots of experience with Canton pans and road course work, and it wasn't good. He used to be the lead technician at a prominent speed shop, so he installed a lot of them.
Quality has been an issue, and I'm not sure the baffling all works well during high-G cornering. He went with a Kevko and it has worked extremely well for about 12 years.
For the clutch setup, I'm assuming you'll be ditching the stock dual-mass 40lb flywheel for a single-mass unit? A lot of people go with steel at 25lb or heavier. That has its merits for street driving, but a light aluminum flywheel at half that weight really frees up rolling power in the lower gears and high rpms, and it makes shifting quickly really nice on track. You have to pay more attention to feathering the clutch when you're starting up from a stoplight on the street, but then again with 4.11s that will be easier than with the stock 3.45s also.
Re the gearing, that will be interesting for track work. With stock gears and the ZF, the gearing is pretty tall. Going from stock redline (6400rpm) and using the 315/30/18 tire diameter (25.6"), 5th gear is good for 188mph. That's not within reach on any track, and 4th gear is good for 141, so it's basically a 4-gear car for track work. Switching to 4.11s puts the top of 5th at 158mph, with 4th good for 118mph; which is probably pretty good for track work with your engine plans. I'll be interested to get your impressions after you use it.
PS - Did you mean titanium valves instead of rods?
Last edited by MatthewMiller; Mar 26, 2018 at 10:25 PM.
That's gonna be a car with real speed! Here are a few thoughts I have on what you're planning:
Make sure your brake package will fit inside those wheels.
Research the short-shift kits for the ZF6 before you buy one. There are threads on here about that, and I seem to remember that the ZF Doc version is preferred, but I don't know if it's still available.
My car has a Dewitt aluminum radiator and it never gets hot on track, even when the previous owner ran it in Houston summers. He found the need for an oil cooler, though; so you'll want to plan for that if you are really going to track it. He removed the a/c condenser to maximize flow the radiator, and basically stuck the oil cooler in its place (but it's much smaller, of course). You can probably fit an oil cooler while retaining the a/c, though.
You'll want to research the compression ratio vis-a-vis the piston shape and height carefully. On my car, I remember the previous owner (who built the engine) didn't get as high a CR as he was planning. That may be easier with the AFR heads, though (mine are stock LT4 heads ported to roughly AFR195 Comp flow numbers). I'm not sure.
My car's previous owner has lots of experience with Canton pans and road course work, and it wasn't good. He used to be the lead technician at a prominent speed shop, so he installed a lot of them.
Quality has been an issue, and I'm not sure the baffling all works well during high-G cornering. He went with a Kevko and it has worked extremely well for about 12 years.
For the clutch setup, I'm assuming you'll be ditching the stock dual-mass 40lb flywheel for a single-mass unit? A lot of people go with steel at 25lb or heavier. That has its merits for street driving, but a light aluminum flywheel at half that weight really frees up rolling power in the lower gears and high rpms, and it makes shifting quickly really nice on track. You have to pay more attention to feathering the clutch when you're starting up from a stoplight on the street, but then again with 4.11s that will be easier than with the stock 3.45s also.
Re the gearing, that will be interesting for track work. With stock gears and the ZF, the gearing is pretty tall. Going from stock redline (6400rpm) and using the 315/30/18 tire diameter (25.6"), 5th gear is good for 188mph. That's not within reach on any track, and 4th gear is good for 141, so it's basically a 4-gear car for track work. Switching to 4.11s puts the top of 5th at 158mph, with 4th good for 118mph; which is probably pretty good for track work with your engine plans. I'll be interested to get your impressions after you use it.
PS - Did you mean titanium valves instead of rods?
Yes valves.
Ditching the dual mass. I had a supercharged Miata with about 200whp and a binary switch for a clutch, so I'm hoping the torque will make it easier to handle. Not sure about the material on the flywheel.
I will tell the builder about the Canton pans.
About the wheels. Yea we will be checking fitment before ordering the brakes and/or wheels. The deep concave wheels should put the widest part of the barrel over the brakes.
Last edited by Jaye Bass; Mar 26, 2018 at 10:48 PM.
Ditching the dual mass. I had a supercharged Miata with about 200whp and a binary switch for a clutch, so I'm hoping the torque will make it easier to handle. Not sure about the material on the flywheel.
Make sure that you use a sprung-hub disk with that single-mass flywheel, whereas the OE disk is a solid (unsprung-hub) disk for the dual-mass flywheel.
My limited experience on disk materials may be useful. To be clear, I've kept the stock pull-type clutch setup, and I'm assuming you're planning to do the same (there are conversions available to use a hydraulic throwout bearing and a push-type clutch). The Previous owner actually use a OE-equivalent organic disk, because he was paranoid about not hurting the ZF. His thinking was that the disk would be a "fusible link," and somewhat protect the trans. It worked for a number of autocrosses and HPDE events, and finally crapped out years later (on me...of course). Long story short, replaced the whole clutch (probably should have kept the pressure plate and bearing, more on that below) and went with a SPEC Stage 2 disk, which is Kevlar. That disk was probably a pretty good compromise: a little more grip and heat tolerance than organic, but I could still modulate its engagement for street driving. That setup failed due to the cheap-*** Chinese throwout bearing that came with it. I now have a Centerforce Dual-Friction disk in it, which is half organic and half metallic. It's more abrupt, but still streetable. It probably has more grip than the Kevlar disk. It took ages to stop smelling like burning metal (I am really, really nice to clutches - maybe I was too nice?), but it doesn't do that now. I would not want to go more radical than that. You'll probably have similar power levels to me (I might have a bit less power, but a bit more torque, and torque is the key to clutch choice), so I'd say that either a Kevlar or dual-friction disk would work for you.
The sad thing is it's almost impossible to find a non-Chinese pressure plate and bearing for these pull-type setups nowadays. After the SPEC kit, I found an old GM Racing pressure plate, which is an OE American-made Valeo unit from around 1990 (I think from the Challenge series) with increased clamping force and 2.2lbs lighter. I also found a NOS OEM bearing (brand is INA). Otherwise, it's a crap shoot.
About the wheels. Yea we will be checking fitment before ordering the brakes and/or wheels. The deep concave wheels should put the widest part of the barrel over the brakes.
I think you'll be okay. I believe a friend of mine that runs Vorshlag (Terry Fair) has been able to fit 18x11 Forgestars over a Mustang's front brakes with the track package. I believe that has 14" rotors and Brembo calipers. I have 13" Wilwood rotors and 6-piston Superlight calipers for my car, and even a lot of 17" wheels fit those, fwiw. So you'll probably be in good shape. But I'm glad you're going to verify everything!
Make sure that you use a sprung-hub disk with that single-mass flywheel, whereas the OE disk is a solid (unsprung-hub) disk for the dual-mass flywheel.
My limited experience on disk materials may be useful. To be clear, I've kept the stock pull-type clutch setup, and I'm assuming you're planning to do the same (there are conversions available to use a hydraulic throwout bearing and a push-type clutch). The Previous owner actually use a OE-equivalent organic disk, because he was paranoid about not hurting the ZF. His thinking was that the disk would be a "fusible link," and somewhat protect the trans. It worked for a number of autocrosses and HPDE events, and finally crapped out years later (on me...of course). Long story short, replaced the whole clutch (probably should have kept the pressure plate and bearing, more on that below) and went with a SPEC Stage 2 disk, which is Kevlar. That disk was probably a pretty good compromise: a little more grip and heat tolerance than organic, but I could still modulate its engagement for street driving. That setup failed due to the cheap-*** Chinese throwout bearing that came with it. I now have a Centerforce Dual-Friction disk in it, which is half organic and half metallic. It's more abrupt, but still streetable. It probably has more grip than the Kevlar disk. It took ages to stop smelling like burning metal (I am really, really nice to clutches - maybe I was too nice?), but it doesn't do that now. I would not want to go more radical than that. You'll probably have similar power levels to me (I might have a bit less power, but a bit more torque, and torque is the key to clutch choice), so I'd say that either a Kevlar or dual-friction disk would work for you.
The sad thing is it's almost impossible to find a non-Chinese pressure plate and bearing for these pull-type setups nowadays. After the SPEC kit, I found an old GM Racing pressure plate, which is an OE American-made Valeo unit from around 1990 (I think from the Challenge series) with increased clamping force and 2.2lbs lighter. I also found a NOS OEM bearing (brand is INA). Otherwise, it's a crap shoot.
I think you'll be okay. I believe a friend of mine that runs Vorshlag (Terry Fair) has been able to fit 18x11 Forgestars over a Mustang's front brakes with the track package. I believe that has 14" rotors and Brembo calipers. I have 13" Wilwood rotors and 6-piston Superlight calipers for my car, and even a lot of 17" wheels fit those, fwiw. So you'll probably be in good shape. But I'm glad you're going to verify everything!
Thanks for the info. I pretty stoked about this build. I'm about 3 yrs away from retiring, so I thought this would be a good time to build a beast of a car by giving me a couple of years to get the knack of driving it through AutoX and HPDE before I do more extreme stuff...whatever that is. All of my serious motorsports experience is in karts which I miss quite a bit.
Frankly, I could have purchased a cherry ZR1 for what I am paying on this 93 but the idea of a weaponized small block based C4 with a TransAm vibe is exactly what I'm looking for...big meaty tires, functional stance, loping thunder under the hood, and IMO the best exterior styling of all the "modern" Vettes.
Last edited by Jaye Bass; Mar 27, 2018 at 12:03 AM.
Frankly, I could have purchased a cherry ZR1 for what I am paying on this 93 but the idea of a weaponized small block based C4 with a TransAm vibe is exactly what I'm looking for...big meaty tires, functional stance, loping thunder under the hood, and IMO the best exterior styling of all the "modern" Vettes.
Even with a ZR1, you'd have to do everything you're planning save for the engine build. And your planned engine will be faster than a stock ZR1 motor. It also has the benefit of being considerably lighter, too.
93 LT1/6-Spd Build Thread
