Hi All,

I recently purchased a 93 Corvette with the 6Spd ZF with around 42k miles on it. The car is in fantastic condition but has been driven less than 100 miles a year for the past 10 years and has not seen more than 1000 miles averaged per year since the late 90s. I have been going over the car and changing fluids, spark plugs, ect. to get the car back into the best shape it can be. The car starts and runs fine, but for a car that weighs 3500 pounds with 300 horsepower it really does not feel fast. I have not timed it yet, but im coming from a 2018 RS Camaro and that felt so much faster... and that's a V6 with 335 horsepower that weighed nearly 500 pounds more (convertible), hell it doesn't feel much faster than my buddy's 2013 FRS . Any ideas on what could be holding the car back? I'm wondering if the fuel injectors are clogged from the lack of driving regularly for so many years, possibly the fuel filter too? Also the graphite on the climate control off switch has worn away so I can not turn the A/C off to see if that is the reason for less than expected performance. Let me know what you guys think... i'm not expecting this car to be modern car fast, but it seems that it should be a low 5 second 0-60 car within the range of my old Camaro. I can post a picture of the options list under the center console lid if anyone is curious... it has the standard 3.45 gears. Thanks for any suggestions/help in advance!

-Joe

 

Well…I have a 93, 6 speed that now has 46k on the clock. It is no slouch for me…

is this a subjective thing, or are you actually timing it? If timing it you could compare to original 0-60 times, 1/4 mile etc…

if it’s just SOTP, then I’d suggest a cat back is in order (I have a corsa).

if it’s objectively slower than it should be, Could be clogged cats or some other restriction. Id check fuel pressure too… also ohm the injectors etc…. Perhaps you are down a cylinder due to above

Also the AC really makes a difference on mine…get that off even if you have to pull the fuse then drive it. WOT I would assume it cuts the AC off. I had to fix my hvac c68 head unit…was very easy to do and I believe batee provides instructions
, but mine was due to connections/solder

 

This sounds like it might be normal. My daily driver is a ‘17 Impala with that same V6 engine. Pretty sure the Impala would win a 0-100 race but the Vette would beat it to 40. I found some published 1/4 mile times: Impala 14.2, Vette 14.1 so I think it would be a close real life race.

 

That sounds right... 0-60 should be low 5 seconds, 1/4 around 14... if the OP is seeing something waaaay off that then could have an actual problem. I didn't buy mine for straight line speed.

FWIW I hate driving mine with the AC on...not sure if my compressor is not healthy or what but it really makes a differences at low/mid throttle and makes it feel sluggish. I use the AC sparingly and just to keep it exercised.

 

Did you check codes? Does the check engine light ever turn on? (I.e. is the bulb burned out?)

The performance should be great but not comparable to modern stuff considering it is 30 years old and been sitting. Put a couple thousand miles on it and my bet is it starts to wake up some

 

I'm curious if yours does the same thing as my 92 Vette. It is a 6 speed convertible with 3.45 gears as well. I call it my turbo vette issue and have posted about it (its stock, no turbos or anything). It idles smooth, no codes and runs great. When I get on it, WOT or even just doing a heavy pull, it gets a boost over 3500 RPM like a turbo kicking in. It happens with the ASR on or off. My AC clutch fell off, so there's no AC. I feel it should be faster if it has the same power below 3500 RPM as when the boost kicks in above. So, does yours do something similar? I am wondering if there is something pulling timing down low or not letting timing advance when it should.
Also on a side note for the acceleration on these ZF 6 speeds, the ZF is geared very low numerically. It has a 2.66 first gear. Most 6 speeds are a 3.0 first and modern ones are even up to 4.0. So comparing a 2.66 first speed to a 4.0 first speed is like comparing a car with a 2.66 rear end to a 4.0 rear end. They have a .5 6th which is pretty low. That gives it lower RPMs on the highway and able to step on the rear axle more. A lot of 6 speeds only go down to .68 or so.

 

I replaced the serpentine belt and hit the coolant sensor on the water pump so it threw a h15 code... replaced the sensor and no problems since. I am going to attempt to replace the fuel filter and cut the old one open to see what the condition of the filter was to see if that may improve fuel pressure. I 100% standby Berrymans B12 chemtool and am wondering if putting a can of it into the fuel tank would hurt it? I've only used that on carbureted engines so I am unsure if it is safe. Thanks for the input ill keep updating with what the deal is.

 

It feels like it has a load of torque even at low throttles at low rpms but when I hit the pedal nothing really happens until around 3500 to 4 grand in terms of how fast it feels. I know its not supposed to be super fast but it really feels like a 6-7 second car. Im gonna take it out here soon and try a zero-60 with ASR on and off and get back to you guys. Im wondering if ASR is retarding the timing when it shouldnt be even though the rear end isn't slipping. I feel like Chevy wouldnt have put 285s in the rear tires if the car didnt have the power to spin the wheels!

 

Whats your opinion on cleaning the injectors? In my opinion it has to be a fuel pressure issue. Im going to try and change the fuel filter today with any luck. With it only running a few times per year for the past 10 years is not ideal. Ethanol gums up pretty bad if left for too long. Definitely running on all eight cylinders, new spark plugs. Theres nothing objectively WRONG with the car its just the last owners pretty much tried to keep it like it was from the factory and just rubbed a diaper on top of it in their garage since 2000.

 

If you have Multec injectors (light gray bottoms), they can be ruined by the ethanol in the gas. It causes the insulation in them to fail, causing them to have a short. Many owners on this forum have have gotten replacements from Fuel Injector Connection. They can test your old injectors if you want and clean them.

 

That's how mine feels, but it gets an extra boost over 3500. Is that what you feel too? Mine literally feels like a turbo kicks in.

 

Mine does not turbo... make sure AC is off, make sure ASR is off, then hammer it....

 

My AC clutch is missing, ASR off and I replaced my injectors with Bosch IIIs. Still does the turbo. I'm wondering if the OP's does the turbo lag too. My car feels powerful below 3500 rpm, just gets that extra boost when I get on her. Makes me believe there is more power to be had down low. Even with this she is a lot faster than my 89 auto was.

 

OK so after pressing the AC off button as hard as i could like 3 times it finally turned off and HOLY CRAP does that make a huge difference. I havent done a 0-60 test yet but it is noticeably faster. i would say that it does certainly feel like it has much more power over 3500rpm like you said but it doesnt feel like the kind of boost you get from old school turbos. With ASR off it spins the back end out like it should. Pretty happy with the car now. Will do fuel filter and injectors just to be safe. Thanks guys!

 

Thanks for the detail on yours. Mine doesn't spin the tires at all. I must have some pesky issue that is different. I have bought all the tuning/data logging software/hardware and haven't gotten to using it yet.

 

BINGO, awesome!

I'd leave the injectors alone...if it ain't broke!

Assuming you have the C68 controls (digital) you have the same issue my HVAC control had. If so it's an easy fix. remove the head unit, pull it apart, pull the front controls/board off, resolder the connector pins on the board, clean all switch contacts with rubbing alcohol then re-assemble. BATEE sells a shim for the back plate to hold the thing together more tightly...I just used a piece of cardboard to hold it together more tightly. Works perfectly now. Again BATEE has videos/instruction how to do this OR you can send it to them if you are really uncomfortable.

 

I remember your issue/thread. Did you do knock sensors? I can easily whip my end around if I want to, but I also don't have the stickiest of tires (yet!). I think you need to get that data logging rolling if you really want to figure it out...odd problem.

 

I did the timing chain, lifters, knock sensors, o2 sensors, intake gasket, oil pan and changed the zf fluid. Still does it. Then changed the injectors. Still does it. Yes, I need to do the data logging, just been so busy with other stuff. I even found and downloaded the adx file I need for the program which was one of the hurdles. Now I just need to plug it in and go. I also notice a lack of power on the freeway at 65. When I go up a hill it won't hold 65 in 6th. I have to downshift to 5th. Tom mentioned his 6 speed will hold 65 in 6th up steep Utah mountains.