Best performance mods for 1985?
Thread Starter
Heel & Toe
Joined: Aug 2021
Posts: 22
Likes: 1
Best performance mods for 1985?
I bought an 85 corvette as a project car last year and it’s been fun but a little lacking in power. i was wondering what mods i should start with, preferably pretty cheap ones because i'm a high school student lol. i've heard that the best place to start is with the intake system ? any suggestions are appreciated because i’m not the most knowledgeable on performance. thanks!
Team Owner
Joined: Sep 2001
Posts: 62,141
Likes: 1,729
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Having started with the "free" mods in college with my 86, I'd still tell you to not bother with anything but the intake and exhaust. But, I'd still cut open the air filter lid and expose most of the surface of the air filter.
You get more bang for the buck from headers first, and either remove the cat entirely or replace with a newer modern unit. Go with TPiS or Hooker, ceramic coated. Delete the AIR at that time and leave the pump in place or put an Eliminator pulley in its place.
You can do the cat back but make your choice based on sound, all give about the same power upgrade. You need to hear a few different sets of mufflers to choose properly. It will resonate either way (aside from Corsa) but its a matter of what you can deal with.
If you can do the work yourself, you should take off the intake and port the base, siamese the runners and port the plenum.
The heads/cam will hold you back after that, and that requires more of a plan for what you want the car to be long-term.
You get more bang for the buck from headers first, and either remove the cat entirely or replace with a newer modern unit. Go with TPiS or Hooker, ceramic coated. Delete the AIR at that time and leave the pump in place or put an Eliminator pulley in its place.
You can do the cat back but make your choice based on sound, all give about the same power upgrade. You need to hear a few different sets of mufflers to choose properly. It will resonate either way (aside from Corsa) but its a matter of what you can deal with.
If you can do the work yourself, you should take off the intake and port the base, siamese the runners and port the plenum.
The heads/cam will hold you back after that, and that requires more of a plan for what you want the car to be long-term.
Melting Slicks
Joined: Sep 2010
Posts: 2,422
Likes: 202
I bought an 85 corvette as a project car last year and it’s been fun but a little lacking in power. i was wondering what mods i should start with, preferably pretty cheap ones because i'm a high school student lol. i've heard that the best place to start is with the intake system ? any suggestions are appreciated because i’m not the most knowledgeable on performance. thanks!
Congrats, lucky, HS student. I think you made most of us very jealous.
Are you in votech? This can net you popularity. Modifing your C4 in class shop time.
Pound for pound dollar for dollar intake, cam combo in a C4 can net a significant HP gain. One catch.
You need to pull the PROM. learn and burn EFI tuning. To take full advantage of new air, VE and related values. Unless you carb swap. That equals very frequent trips to a gas station. Modern times. That could equal multi day/s paycheck.
Very educational. You can elevate your status as a mechanic near expert.
I seriously would get some real driving seat time.
A vette and similar cars. Can get. even the best.
in serious trouble. Don't believe.. take a look a Copart or similar yards. Amazing to see. Just released cars. Some custom order LONG wait times..
i took my son out. Took a serious corner approx 260+ deg turn. No room for error guardrail just outside of white line. almost no pull off area due to a small stream.
the vettes very short wheel base took me around sooo. Fast!!! Only fast, natural, reaction. thank god i have excellent driving experience.
Again congrats with your new ride!!
Pro
Joined: Dec 2018
Posts: 733
Likes: 424
From: Wisconsin
2023 Corvette of the Year Finalist - Modified
2022 C4 of the Year Winner - Modified
Finalist 2020 C4 of the Year - Modified
I say boost, specially turbos, but that's not even close to budget friendly. (But a LOT of fun if done right!)
The exhaust manifolds on the early C4 leave a lot to be desired in terms of flow.
Before I built the turbo system for my 85, I swapped in the manifolds from the later LT equipped cars. They flow better (for a stock manifold) than the stock ones for the TPI cars. You might be able to find a set of them for cheap from someone that has upgraded to headers. If memory serves me correctly: you will have to delete the air injection since the later manifolds don't have the same provisions to run them and slot the holes on the collector but they are a pretty bolt on part other than that. That would get you a slight SOTP upgrade for relatively cheap.
The exhaust manifolds on the early C4 leave a lot to be desired in terms of flow.
Before I built the turbo system for my 85, I swapped in the manifolds from the later LT equipped cars. They flow better (for a stock manifold) than the stock ones for the TPI cars. You might be able to find a set of them for cheap from someone that has upgraded to headers. If memory serves me correctly: you will have to delete the air injection since the later manifolds don't have the same provisions to run them and slot the holes on the collector but they are a pretty bolt on part other than that. That would get you a slight SOTP upgrade for relatively cheap.
Drifting
Joined: Mar 2004
Posts: 1,818
Likes: 156
From: White Oak PA
Some Inexpensive Mods
Try these cheap mods:
New air filter
New fuel filter
Clean Mass Air Flow Sensor
Clean Throttle Body
Clean Idle Air Controller
Load test battery
Change plugs and wires
Do not throw money at it. Most low cost mods will not yield much performance gains. It takes serious money to make more hp. Your C4 has great torque and should provide great seat of the pants acceleration on public roads. The earlier C4's had restricted air and exhaust systems. changing these is not cheap and may fail to meet your expectations.
I assume your C4 has a 2:59 rear differential axle ratio. I had an '87 and would leave the transmission in third gear instead of overdrive.
Start cheap. Do it yourself. The C4's are relatively easy to work on. Have fun.
Best of luck.
Check my old dormant site for some great C4 info:
https://corvettebuyers.com/c4vettes/facts_launch.htm
New air filter
New fuel filter
Clean Mass Air Flow Sensor
Clean Throttle Body
Clean Idle Air Controller
Load test battery
Change plugs and wires
Do not throw money at it. Most low cost mods will not yield much performance gains. It takes serious money to make more hp. Your C4 has great torque and should provide great seat of the pants acceleration on public roads. The earlier C4's had restricted air and exhaust systems. changing these is not cheap and may fail to meet your expectations.
I assume your C4 has a 2:59 rear differential axle ratio. I had an '87 and would leave the transmission in third gear instead of overdrive.
Start cheap. Do it yourself. The C4's are relatively easy to work on. Have fun.
Best of luck.
Check my old dormant site for some great C4 info:
https://corvettebuyers.com/c4vettes/facts_launch.htm
Instructor
Joined: Mar 2021
Posts: 169
Likes: 25
If I was a broke HS student this is what I'd do I this order. Just a suggestion.
1st: Full tuneup, wires, plugs, o2s, belts, coolant flush.
Reason being, I know my car is fresh and should run like it should. I would rather spend $300 on a tuneup and have a stock car run 14.5 then spend $500 on headers instead of a tuneup and run 14.3. You get those headers later and run a 13.9.
2nd: 160 thermostat and a fan switch run cooler make more power. Basically free power.
3rd: Shocks <----hands down best mod.
4th: tires and brakes <---2nd best mod..
5th: Exhaust
6th: stall (if you know already know step 7)
7th: heads and cam probably be out of college by this point, so Good for you!
1st: Full tuneup, wires, plugs, o2s, belts, coolant flush.
Reason being, I know my car is fresh and should run like it should. I would rather spend $300 on a tuneup and have a stock car run 14.5 then spend $500 on headers instead of a tuneup and run 14.3. You get those headers later and run a 13.9.
2nd: 160 thermostat and a fan switch run cooler make more power. Basically free power.
3rd: Shocks <----hands down best mod.
4th: tires and brakes <---2nd best mod..
5th: Exhaust
6th: stall (if you know already know step 7)
7th: heads and cam probably be out of college by this point, so Good for you!
Last edited by 93TALT4A4; Sep 27, 2022 at 07:48 PM.
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