L81 performance
Thread Starter
Instructor
Joined: Sep 2018
Posts: 228
Likes: 13
From: Arizona
L81 performance
Okay so I know this is a naive question, but, what can you do to an 1981 C3 to get more horsepower out of it without going with a crate motor? Also what would the cost be versus dropping a small block in it? Thanks guys
Pro
Joined: Jul 2021
Posts: 719
Likes: 156
With a free rein, you can make your motor powerful enough to scare you.
what modifications do your local and state laws permit ? Know, KNOW if an '81 requires any emissions testing OR if emission Inspection for presence of OE emissions bits is required. Know all this Before you get in too deep. Quickly make acquaintances with experienced old car enthusiasts.
what modifications do your local and state laws permit ? Know, KNOW if an '81 requires any emissions testing OR if emission Inspection for presence of OE emissions bits is required. Know all this Before you get in too deep. Quickly make acquaintances with experienced old car enthusiasts.
Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,398
From: SW Florida.
any 75-newer corvette can be upgraded about 50 hp with a good exhaust system and properly set up ignition curve. your 81 needs it's carb, distributor and ecm sold on ebay to a "purist."
Burning Brakes
Joined: Dec 2017
Posts: 1,043
Likes: 414
2023 C3 of the Year Finalist - Modified
Nitrous is a lot of fun and is probably best bang for buck out there. 100 shot kits are under $600.
Racer
Joined: Oct 2001
Posts: 473
Likes: 64
From: Portage La Prairie Manitoba
What HP numbers are you looking for? Budget?Do you need to pass emissions?
Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,398
From: SW Florida.
ok, looks like pima and maricopa counties require emissions. except for senior citizens cuz of covid. and collector car insurance gets a waiver.
now, all of us who have a 75 and newer with no catalytic converter could be cited by any cop who chooses to peek under our cars.whether the state has emissions for their year or no emissions whatsoever. my 75 with sidepipes? cop doesn't even have to get out of his car. BUT it seems to be rarely if ever enforced except in PA CA and a few other states that require inspection for 75-newer cars. your 81 if you live in those 2 counties and are under 65 with regular insurance will have to pass idle and roller emissions test and visual check. plus evap system pressure test.
now, all of us who have a 75 and newer with no catalytic converter could be cited by any cop who chooses to peek under our cars.whether the state has emissions for their year or no emissions whatsoever. my 75 with sidepipes? cop doesn't even have to get out of his car. BUT it seems to be rarely if ever enforced except in PA CA and a few other states that require inspection for 75-newer cars. your 81 if you live in those 2 counties and are under 65 with regular insurance will have to pass idle and roller emissions test and visual check. plus evap system pressure test.
Last edited by derekderek; Dec 12, 2021 at 09:32 PM.
Thread Starter
Instructor
Joined: Sep 2018
Posts: 228
Likes: 13
From: Arizona
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
* Long tube headers (Hedman makes CA approved sets with AIR tubes, though you should check with your smog tech if this is good in your jurisdiction)
* True dual 2.5” exhaust with dual cats (same concern as above)
* Make sure the carb and distributor are in good shape
That should get you 25-30 HP and some low end torque. It’ll wake the motor up a lot.
I’ve not experimented with aftermarket heads and cam on a E4ME+computer controlled spark vette. I’d assume you can do that and the stock curve would be “ok”, not great. Figuring out how to re-curve it would be a big win whether you do aftermarket heads or not.
If you can get the spark curve configured to work well, then with exhaust, heads, roller cam, good carb & spark tuning and a bottom end rebuild for higher static compression ratio you should be able to take this thing to 400+ HP.
* True dual 2.5” exhaust with dual cats (same concern as above)
* Make sure the carb and distributor are in good shape
That should get you 25-30 HP and some low end torque. It’ll wake the motor up a lot.
I’ve not experimented with aftermarket heads and cam on a E4ME+computer controlled spark vette. I’d assume you can do that and the stock curve would be “ok”, not great. Figuring out how to re-curve it would be a big win whether you do aftermarket heads or not.
If you can get the spark curve configured to work well, then with exhaust, heads, roller cam, good carb & spark tuning and a bottom end rebuild for higher static compression ratio you should be able to take this thing to 400+ HP.
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Racer
Joined: Oct 2001
Posts: 473
Likes: 64
From: Portage La Prairie Manitoba
* Long tube headers (Hedman makes CA approved sets with AIR tubes, though you should check with your smog tech if this is good in your jurisdiction)
* True dual 2.5” exhaust with dual cats (same concern as above)
* Make sure the carb and distributor are in good shape
Thats about as far as you can go and retain emissions compliance.
A rear gear change to 3.70 will also feel like 50 hp increase but will decrease highway mpg
If you highway drive a lot.... changing your trans out to a 700r4 will give you a lower 1st gear and better highway mpg while retaining your emissions
* True dual 2.5” exhaust with dual cats (same concern as above)
* Make sure the carb and distributor are in good shape
Thats about as far as you can go and retain emissions compliance.
A rear gear change to 3.70 will also feel like 50 hp increase but will decrease highway mpg
If you highway drive a lot.... changing your trans out to a 700r4 will give you a lower 1st gear and better highway mpg while retaining your emissions
Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,398
From: SW Florida.
i don't think any inspector is gonna notice the lack of an electrical plug on top of the carb. and it will probably be easier to pass emissions without that E4ME setup. when it doesn't work, it is horrible. and since it is controlled by a 40 year old ecm, it usually doesn't work. collector insurance is cheaper than adding it to your daily driver policy. but they all insist on photos of your car in a garage. i think that is mainly so if it is stolen from your house you gotta call the homeowner's ins company. does AZ have antique or collector plates? they also usually come with emissions exemption.
Last edited by derekderek; Dec 13, 2021 at 10:42 AM.
Pro
Joined: Jul 2021
Posts: 719
Likes: 156
But, from what you just wrote, it seems you're hogtied. Suggest you first purchase "Collector Insurance." Only then, it seems, you can have "free rein" with performance mods.
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
i don't think any inspector is gonna notice the lack of an electrical plug on top of the carb. and it will probably be easier to pass emissions without that E4ME setup. when it doesn't work, it is horrible. and since it is controlled by a 40 year old ecm, it usually doesn't work. collector insurance is cheaper than adding it to your daily driver policy. but they all insist on photos of your car in a garage. i think that is mainly so if it is stolen from your house you gotta call the homeowner's ins company. does AZ have antique or collector plates? they also usually come with emissions exemption.
The 80 California Corvettes are easier to mess with, since they only have computer controlled mixture; spark timing is still mechanical. Plus no check engine light.
Even staying smog legal and correct, I'd rather be on a collector policy to avoid the hassle of working with inspectors who don't wanna look at your old pain-in-the-butt car (at least that's the impression they give me).
Drifting
Joined: Mar 2006
Posts: 1,263
Likes: 188
From: Wabasha Mn
* Long tube headers (Hedman makes CA approved sets with AIR tubes, though you should check with your smog tech if this is good in your jurisdiction)
* True dual 2.5” exhaust with dual cats (same concern as above)
* Make sure the carb and distributor are in good shape
Thats about as far as you can go and retain emissions compliance.
A rear gear change to 3.70 will also feel like 50 hp increase but will decrease highway mpg
If you highway drive a lot.... changing your trans out to a 700r4 will give you a lower 1st gear and better highway mpg while retaining your emissions
* True dual 2.5” exhaust with dual cats (same concern as above)
* Make sure the carb and distributor are in good shape
Thats about as far as you can go and retain emissions compliance.
A rear gear change to 3.70 will also feel like 50 hp increase but will decrease highway mpg
If you highway drive a lot.... changing your trans out to a 700r4 will give you a lower 1st gear and better highway mpg while retaining your emissions