Hey, please allow myself to introduce myself.... I'm Giovanni and I'm Building a fun C4 for DE road racing. I dont know... what I dont know.... so lookng to get up to speed quick. First track day is May 30th 2024 and car must be fully shorted for the 'Empire Cup'.

What I'm stating with is a 1988 Z52 4 speed with an rotational clanking engine noise. Noise remains with the clutch in so I'm thinking it's in the engine. Dragged the C4 home for a great price on the coldest day of the year around the holidays. It was the best Corvette I could find for the job having been the right price and already too far gone to ever be a nice / valuable car.

I dont know much reguardng C4 suspension, safety, transmssion, cooling, and other mods needed to be sucessfull at DE

My plan so far....
SBC 406, Lngenfelter intake, mild cam (engine was in another car and perfromed great on the track, see pic below)
Power steering oil cooler
Bilstein Shocks. Lower B5 Z51's on the rear
OE 17 wheels wth R compound tires
Lower the rear end 1 inch
C5 front brakes
EBC blue Track pads
Convertibvle brace
Delph 0119 fuel pump, (enough for 500HP ?)
Headers, X pipe, Borla's . (Some DE events now have noise restrctions)

My goals:
-Under a minute at Limerock Park this year. In 1985 an 1984 C4 did it 1:04 with a good driver. I'm hoping I can get to 59.9 wth double the HP and better tires.
-Under 0:58 next year.

I know the engine is up to track duty...I tracked it for 3 years while installed in a '76 Jaguar. And just took it a part to rebuild and it was in far better condition than I feared.
The detals on a 406 block, Scat rotatng, mild cam, LPE intake, Short travel Johnson Lifters, full CNC AFR 195's, Northstar DIS, Custom '7730 tune. basic 7 Qt Sump and windage tray. - No joke, I was able to just barely keep up with a Supercharged C5 LS1 on the streighs in a 3800Lb car , I have video so dont flame me please.





Engine in it former home.

 

Good luck with your build.

@winstonc had a 406 and I think he went road racing with it on many times at Summit Point. He had headers, which were wrapped. Car was an automatic though, still 4 gears. Maybe he can give you some insight from his experiences. His C4 now is a 555ci monster

Again, good luck.

 

Your going to want to replace every Bushing in the suspension. For racing the Bilstein's have kind off fallen way to Koni's and the Koni's have fallen to the QA1s If your car has the J55 Brakes you might just keep them but maybe they were not offered in that year. Stainless Brake Lines. The 4+3 Trans overdrive can be an issue for some and not for others. Most agree the 6 Speed ZF is an advantage I have made the swap.

 

Since the track was reconfigured with a chicane before the hill in the mid 90’s, I would not set that lap as a goal. If you are hoping to hit 59.9, you would be 6 tenths off of what a C6R did.


As far as the build, there have been plenty of build threads documenting different C4’s but people seem to disappear on subsequent follow ups/improvements. Heat control, brakes, suspension, weight and aero will need to be addressed to meet your goal.

There is going to be a line you are going to have to cross. It’s either a street car or a track car. If you try to blend the duty, it never works out well.

 

We're amateurs and run the No Chicane configuration. The Chicane at LRP is narrow and would be a disaster at this level. I've often run both configurations in Sim racing so I know the track well. IRL with out the Chicane it's a fast track and you have to average 90 MPH to get under a min. There are many cars under a min at this event and 1 or 2 make it into the low 0.50's. There are usually two other C4's at this event and they claim run in the mid 0.50's which I think is plausable becasue they're out of my site mid way through the first green lap. They both were still running the OE TPI on 383's I think. Clearly their cars were setup well and they know it so they weren't interested in chatting last tme I was there but those C4's looked lightly modified and idled with a lope. They looked driven to the track too.

I know the line you are referring to, usually starts wth a cage, R compound tires and camber. That's how / why I ened up with a C4. No good way to put a cage in my Jag and too heavy to start with and too much frontal area.

What Aero? That's what I need to know. I dont have a lot of time so where should I focus front spliter or rear wing? I'm thinking wing wth the power I was making. The motor was able to make it into the mid 120's pushng a 3800LB brick so in the C4 I should be well into the 130s

 

Thanks, I forgot about the lines. I dont thnk I have j55. Brakes are puny on this C4. I think I'll be OK with the 4+3 this year. LRP is a fast track and the LPE intake is strong from 3500 to 5550 so it will be probably a 2 gear track. I have a TKX 5 speed at the ready for next year if need be. Dont know if I'll have time to fit that this year. The 4+3 is clunky, I know but on the track when everythbng is happening fast it might be good to have an trans that needs a firm and direct hand. I have another track car with a T56 and the gears are so closely spaced that I often mis-shift. We shall see. I might feel diffrent after being on the track

 

Just curious what is DE road racing?

I have a 1988 that is moderately modified for road racing and it works great.

A few pictures are attached.

 

I've got many many laps at LRP in a C4 under my belt. I won't tell you a 59.9 isn't possible, but it's a very high bar (non-chicane layout) I'm typically running 1:02.* with R compound rubber and somewhere around 425 - 450 RWHP.

I run the J55 (13") brakes with full on race pads, and I am regularly outbraked by Porsches, BMW's and other cars that have better developed brake systems. The C5 front brakes are better than the C4 J55 system, but I don't think that it's a dramatic improvement,

IMHO - Add in a Weld in roll bar to your list - Autopower makes them. You'll need to cut out about half a square foot of SMC on each side of the car interior to get to the frame, but it will stiffen the car up.

Oh - and one other thing - I've been kicked out of LRP twice for noise violations running headers to a Corsa exhaust. You need to be a bit careful here -

 

You are doing the right thing.

buy a c4 cheap, soup it up, and then send it out to shut down the c6r and c7r race teams that will have way more $$ invested thru the initial upfront cost of their race car.

You can afford to get more aggressive going 10/10ths driving, bc again, if you crash it you can simply buy another c4 cheap - transfer the race parts, and repeat

i used to race time trials at Nelson Ledges when my car was mostly stock.

the only weird thing i ever ran up against was i one time had put EBC green stuff brake pads onto j55 calipers and Baer 13” eradispeed rotors. the car couldnt handle a single 80-10
mph stop (back into the pit) without brake fade.

now, i know green stuff isnt meant for racing, but come on, not a single stop. Even on the street, in a panic brake situation (highway stop) - those pads would fade,

everyone here runs Hawk brake pads. I had great luck with hawk hp+ on the track (though dusty, squeaky when cold), Hawk has more aggressive track pad options than that also

good luck

 

add brake cooling to your list.

 

One my road race vette with the C5 front rotors and stock rear rotors I run the Hawk DTC 70's on the front and Hawk DTC-60's on the rear. They work great and I also have brake duct cooling.

 

I have some thoughts. You aren't going to want to hear the first one: you may have bought the wrong car. An 88 has something different about the shock fitment than any C4 before or after. It's kind of a bastard child in this regard, and it means it's going to be difficult to get track-worthy shocks for your car. I'm not sure what else is unique to the front suspension of an 88, if anything. I also don't know if it's possible to change the 88 to allow the use of 89-96 front shocks. But if you can't, then you're already pretty much sunk.

If I were building a car specifically for track use, and assuming I didn't want to strip it all the way out to true GT-car levels of prep but did really want to focus on lowering lap times with it, I would:

• Get good coilovers with standardized spring dimensions so you can swap them out and try different spring rates. The two cheapest ways I know of to accomplish this are with the Ridetech coilover kit or the Viking options sold by After Dark Speed. I'd do the latter, because the proprietor of ADS has lots of experience in C4 track and autocross use and will give you his tech support with the parts. There's nothing magical about coilovers, but there are no good aftermarket monoleaf spring options anymore, so this is the best way to get useful spring rates. It also makes ride height adjustment and corner weighting quick. If this is out of the budget, then for a later C4 I'd try to find a set of 89-91 Z51/Z07 "challenge" leaf springs and then try to get Viking shocks from ADS to go with them. Honestly, I don't know if this would end up being much cheaper by the time you actually bought a set of springs in good shape, though. Those are fairly sought-after OE springs. They are also more than 30 years at this point, and if they've been sitting out in the elements...
• Get the Delrin front control arm bushing set from ADS that include their offset lower bushings. This will allow you to get the -3 degrees (or more) camber setting you need in order to get good grip and wear from your tires on track.
• Get new rear camber rod links (aka strut rods or lower lateral links) with rod ends so you can delete the stock rear eccentric camber adjusters (which can slip) and get at least -2 degrees rear camber you will want. Again, ADS sells a nice set that also offers adjustable inner mounting height so you can play with roll center geometry.
• Buy a few sizes of OE rear sway bars. They are available in 19, 22, 23, 24, and 26mm sizes that I know of. On the 23mm bar is a little rare and hard to get (it was 84 Z51 only). They are super easy to change out, and that's an easy way to adjust steady-state cornering balance (understeer/oversteer). You can use cheap poly bushings for these. It's nice to have an assortment, and you can even change them out at the track between sessions to try different setups.
• If your stock trailing arms' rubber bushings are in good shape, you can use those. If not, then replace them only with Super Pro soft-poly bushings, not regular hard poly. You can search my other posts on the reason for this. If you are feeling spendy, get the rod-ended trailing arm set from ADS.
• Track use is the one place I really recommend aftermarket "big brake systems." You only need to upgrade the fronts. Wilwood makes a ready-to-bolt-on kit using their 6-piston compact fixed radial-mount caliper and a 12.88" floating disc and hat setup. It works well with good track-oriented pads (which will suck on the street, btw). I would bypass all the J55 and C5 options. Once you look around at other BBSs, this kit will seem very cheap and simple to install by comparison. It also may allow the use of stock 17x9.5 sawblade wheels, but I'm not sure. You should look into air ducts that begin at two oval holes in the front air dam and funnel air into the centers of the rotors. You should probably get new brake lines, and you might as well get stainless braided ones. Flush your brake system and add Castrol SRF fluid. It's not cheap, but it has the best wet boiling point and will be good for a full year of track use. You might also benefit from the different brake bias spring sold by Doug Rippie. That was in my car, but I never had the stock one in it and so I never got to do a back-to-back comparison.
• Get a supply of front and rear wheel bearings, practice swapping them out, and bring the tools with you to change them out at the track. This is the Achilles heal for C4s. All the new replacements now are Chinese garbage unless you spend thousands to convert to Xtracker bearings.
• I would recommend 18x11 wheels with 50mm offset, front and rear. Having more rubber on the ground is always good on a dry track, and you can fit these with no problems. There aren't tons of track tire options in sizes that fit the 17x9.5 wheels. and 315/30/18 tires (or 295/35/18 in the case of Bridgestone RE71RSs, since that's the biggest they make.
• For tires, it depends on what you actually mean by "R compound." True R-compound tires are pretty much limited to Hoosier A7/R7s, Goodyear Supercar 3Rs, or maybe Michelin Pilot Sport Cup 2Rs. The Goodyears are cheapest, none last very long. With Hoosiers, you'd want the R7, because the A7 is for autocross and qualifying and really won't last long. Probably the R7s are faster than the Goodyears or Michelins, but I'm not actually sure. If you really want to set good lap times, these are the tires to consider.* If you'd rather pump in a ton of pretty fast laps on long-lasting tires, I recommend the Goodyear Supercar 3 (not 3R) or the Continental ExtremeContact Force. These tires love heat and will hold up to several track days where you get the typical 4-5 sessions of 20 minutes each. This is far better for your budget and for building seat time (which is how you make yourself faster).
• Regarding aero, in the big picture you'd want a good wing because it's more efficient than a spoiler (less drag for a given amount of downforce). You can buy those from AJ Hartman or Nine Lives, but you'll probably have to build your own mounts. The challenge will be to balance the big rear downforce you can easily make with enough front downforce. You have tons of front overhang, so there is a lot of room for a big front splitter with proper diffusers ahead of the front axle line. However, you need to build an air dam from the very front edge of the bumper straight down and build in a front opening for the radiator. The stock setback air dam and "mouth breather" setup isn't good for this at all. This may actually be enough front downforce on a C4. If not, you'll need to fab some front wheel "flares" so the sides of the splitter can terminate into them and create more downforce. If you really want to go for the gusto, you could fabricate a flat floor for the whole car and pair it with side skirts and a rear diffuser. The C4 also has lots of rear overhang with a great "ramp angle," so the diffuser practically builds itself. You could truly make serious downforce with all of this! This would easily achieve your lap time goals, but you need to ask yourself if it's worth all of that and what your goals really are.* Aero is the last thing I'd focus on unless I were truly trying to win a competition.
• I think you're engine is probably fine for this. I hope your pan is not a Canton, because they have a bad habit of having baffles fail or generally just not working well. Kevko makes a great 7qt road racing pan. I had that one plus a real oil cooler, and the oil never overheated on track, even on hot Texas days. If your pan is a Canton, then I recommend a warning light to alert you if pressure falls in a corner or during braking.
• For a radiator, there's no good reason to avoid the obvious: get a DeWitts radiator. My car had one and made over 400rwhp, and it never overheated the coolant, even on the hottest Texas days at track events.

*I am confused about your goals. DEs aren't a race. They are track days where drivers work on improving their skills. The person you are trying to beat is your own prior laps. Lap time goals for DEs are about making the driver faster, not the car. If you are in fact entering some form of competition, then you need to first check the rule set to know what mods are allowed and then work within those allowances. I suspect that you really just need to build a reliable car that works well on track but isn't necessarily a lap record setter so you can build seat time. A lot of the above is still a good idea for this goal, but forget the aero altogether. If the stock wheels will fit over the front Wilwoods, then we can discuss tires for those.

 

All good responses here.

My best at that track (original configuration) was a 103.9 This was with a 1992, stock LT1 with headers, 1.6 RR, and Nittos. It made 286WHP. I have seen stock C5 Z06s with good tires go under 1.0 minute. Their is a guy with a blue C4 running with EMRA who goes under 1.0 minute.

My same 1992 is now a drag/street car

Good luck with your build.

 

Oh, I forgot to add something: that TKX transmission sounds great, but it won't be anything close to a drop-in replacement for the Nash 4+3. You'll need to fab a C-beam mount on the tailshaft, figure out a push-style clutch setup that will adapt, probably need a custom driveshaft, and possibly need to cut the floor to make the hole for the shifter line up. In short, it would be a lot better to keep the stock tranny in one piece, if possible.

 

Thanks for taking the time to write this. I appreciate it and take it to heart. For now I do DE events or HPDE (high performance driver education) Just racing the clock. I do so with the SCDA and Empire drivers. Empire drivers is kind'a invite only subgroup of the VSCCA and on track is great with them. Familiar faces, loose rules with very experienced drivers so it all works out. SCDA is just HPDE, very fast groups with lots of new 100K cars, like the GT3, GT4, ZL1 and C4 to C8 Corvettes. I run intermediate1 for the time being with SCDA and Novice with the Empire Drivers because there are many retired pro drivers who show up with the most pedestrian of cars and participate in all the groups, even novice.

As for the numbers, I have a personal goal to hit 0.59 at LRP. That's my focus right now. I work fulltime and many of my weekend / evenings are spoken for...wife, 4 kids, elderly parents that need help now and then. So I need shortcuts and have to pick my battles for this year. At some point the ultimate shortcut is to drop 100k on a ready to go track car but I cant do that responsibly at the moment so I'm going to have some fun along the way.

I'm running high 1:08's in a 1986 Porshce 928, that made 288HP 38 years ago. At this point it has a cranky 5 speed that needs gentility, patience and a short prayer before each shift. Mostly stock, on good UHP street tires. I went all out on the brakes... it took buckets of money, a year to get the brakes done. Required custom machined spindles, hats, etc to make all the geometry work out. The brakes are great though. Besides that.... all the low hanging fruit has been picked. Engine upgrades are multiyear process and successful only with luck form the Alusil gods, the solution for the transmission is to install a T56 from a C5 unit and I'm just not going there. After a myriad of problems, including persistent vibrations.... someone recently suggested swapping in the full rear subframe from a C5, silly and that's another Rubicon I wont be crossing.

Last time I ran with SCDA there was a ZR1 C4 on the track, first time I saw that, and I was thrilled to see the King of the Hill as it was a hero car for me back then. It ran away from me and most other cars everywhere and I could only hang with it if there was traffic. Cars with a 100 more HP and 400 less pounds tend to do that. Bottom line I've taken the 928 as far as I want and can with the time I have. Just takes too long and too much to do anything track facing, and everything done devalues the car. Same drill for my other track car, the Jag Coupe that was tracked with the 406 SBC. After seeing the ZR1 at NJMP Lightning, I came to realize I need to focus on one car and I had the engine with the SuperRam intake so the C4 was a natural fit.

Quick Vid of my last LRP day

Below is my tow vehicle for track weekends. I just think it could be way cooler to do all this somewhat in the family with another GM product in tow so the C4 is a good fit.

 

None of that is an issue for me. It's the time, I know what's involved with swaps in general. I've put a TKX or a T56 mag in a few places that they don't belong.... including a V12 Jaguar, super charged I6 Jaguar and a LQ4, All track tested.
Just won't have the time this year and LRP is a 2-gear track with the torque of a 406. If the C4 doesnt make in time... the Jag that presently holds the LQ4 and TXK is my plan B.

 

If you have been willing to work on and track a 928, then you must have the patience of a saint. A C4 will mostly be a revelation in ease of wrenching and low costs. I'd do everything I wrote above except the aero to start with. As some sort of reference, my C4 (the one in the avatar) had a similar setup and power. After I sold it and bought a 2020 Camaro SS 1LE to go warranty racing, a friend took that C4 to a track day at Autobahn Country Club in northern IL, and I took my Camaro. That C4 ran away from me on 315/30/18 Falken Azenis RT660 tires front and rear (18x11 et50 wheels) with me on my stock Goodyear Supercar 3 tires. It was way faster on the straights (that C4 would pull a stock C6 Z06) and on those tires at least, it cornered much harder as well. If you did all the things I suggest except aero, then this car on Hoosier R7s would be really fast. But really, on Continental EC Force tires in the same size, it would still lap fast and they would last a lot longer. Bridgetone RE71RS tires (295/35/18, probably, since they don't make a 315) or the Falken RT660 would be in between the R7 and EC Force. Of all these options, only the Hoosier is not really streetable.

My only concern about the 88 is the front shock situation. Good off-the-shelf shocks don't exist for this car. by "good," I mean something better than stock Bilsteins. I don't know exactly what is different, but suspect it's all in the shock tower design. If that's true, then at worst you could cut the stock towers off and weld 89+ towers on in their place. Once you made the front-end compatible with 89+ shocks, you could have your pick of good coilover setups. For example, $2600 would get a set of four Viking double-adjustable Crusader shocks and springs from After Dark Speed, which would be a real jump up from the stock spring rates and Bilsteins, especially if you put sticky tires on the car. And with that, your purchase of springs and shocks would be complete. I mean, $2600 buys you maybe a headlight or a cigarette lighter for that 928, right?

 

Oh, for the exhaust, ARH long tube headers are really nice, but pretty pricey. I ran Hooker Super Competition (2151) headers on mine, into a custom 3" dual exhaust with cats and Corsa mufflers. Sounded amazing and not too loud. You could eliminate the cats and custom X-pipe and use a Magnaflow "muffled X" where the stock resonator goes, then run that into the Borlas or whatever mufflers. That would not be too restrictive and would probably satisfy any noise regs.

 

One more thing (sorry). You will need a plan to tune the 88 ECM for the 406, or else a plan to integrate an aftermarket ECM system so that the dash in the 88 works properly. For the stock ECM, I think you'll be burning PROMs to dial it in. i have no idea what's required to get the dash to work with an aftermarket ECM. My 96 was a lot easier, since you can flash 94-96 PCMs with new, edited calibration files, but you won't have that luxury.

 

Yes, carrying on with a 928 is costly in time and money. I'm done with that. The on/off race dual 6 pucks are coming out, the race rash on the body will be repaired, and android auto is going in. She'll be returned to cars and coffee / GT duty.

I have the 1227730 tuned with the harness from the Jag. Even has a Northstar DIS and ready to run electric fans too. The 1227730 will run a Northstar DIS quite well.
I know I should have started with an 89 but too late now. I'll fix what need to be fixed, harness wise.
I'm not all that concerned wth the front shock issues, I'm fairly certain I can reach my goal none- the-less. If not I have a welder and I'm not afraid to use it. We shall see.

As for headers, the budget frienly Headmans were available. I called and emailed TPIS and got no reply on availablty. The Headmand are cheap and I'm OK with this becasue , I will cut them up and configure them as I like wth Vbands, the right length collectors and a propper X pipe. If it all works out OK I'll get it all cermanic heat coated.

I got the SuperRam back from the sand blaster today and I got some valve cover that clear so looks like engine is going in this weekend so long as the bell housing registers correctly.

Few Questions.
1. Will engine go in wth headers attached or will I have to install them from the bottom?
2. Wll the pan with the kick out as show work or or is there some interferance issue I need to be concerned with?