corvette cam swap

**jiveass** · 10-26-2009, 05:32 AM

i have a 1981 corvette with the l81 engine which puts out 180hp...i drive this car everyday. i would like to make more power and still be decent to drive daily. im not to good with numbers so i was looking for help as to which cam i should get for it. here is the engine specs.

Displacement, liters/cubic inch
5.7/350
Bore X stroke, inches 4.00 X 3.48
Fuel management
1 X 4-bbl.
Horsepower @ rpm
180 @ 4,200

Torque @ rpm, pound-foot
280 @ 1,600

here is factory cam specs...

3896962 Hydraulic Flat Tappet
This hydraulic flat tappet is used on the 68-81 L-46 and L-82 Corvette. The duration at lash point in degrees (intake/exhaust) is 312/312; duration at .050" tappet lift (intake/exhaust) is 222/222 and maximum lift with 1.5:1 rocker ratio (intake/exhaust) is 450/460. Valve lash is zero/zero and lobe centerline is 114 degrees....

any help would be greatly appreciated.

**0rion** · 10-26-2009, 10:38 AM

you should send a PM to firebirdjones.....he's knowledgable about that kinda stuff.

**Printmanjackson** · 10-26-2009, 10:51 AM

I had one of those years ago and from what I remember '81 was the last year they came with a carb with a computer before they changed to fuel injection in '82. I think you can get a HP chip for that car to increase performance.

**jiveass** · 10-26-2009, 11:08 AM

firebird jones huh? ive seen him around....ill give him a shout. thanks.

**jiveass** · 10-26-2009, 11:14 AM

Originally Posted by Printmanjackson

I had one of those years ago and from what I remember '81 was the last year they came with a carb with a computer before they changed to fuel injection in '82. I think you can get a HP chip for that car to increase performance.

im not sure if the car has the origional carb or distributor...lot of extra plugs runnin around in the engine compartment. ...

**Firebirdjones** · 10-26-2009, 12:07 PM

I'm flattered, thanks Orion.

I'll try to help.

First,,,those L82 cams aren't that bad. GM still uses them today in their 350/290hp crate engines.
With .450/.460 lift and .050 duration of 222 degrees, it's a nice little cam for the street and relatively mild 350's.

To improve on that while still keeping all the other stock components will be tough but I have a suggestion.

I'm going to assume you want to stay hydraulic flat tappet, keep the stock torque converter, keep the stock intake and carb, exhaust etc...

I would go with comp cams XE line,,,it has a faster lobe design than even just a few years ago,,,but would be a big change comparing to a 30 year old camshaft design.

With that said I would probably go with the XE 262 grind. It's close to the specs of your original L82 cam but will still work with stock converter and other stock parts.
It's specs are 218/224 duration at .050 (compared to 222 for the L82) and the lift is .462/.469 (compared to .450/.460 on the L82)
Biggest difference is the lobe seperation 110 verses 114. This gives you more low and midrange power. Keep in mind this cam also has faster lobe rates.

The lift is still within reason of the stock cam, so it wouldn't require any machining of the heads, odd length pushrods etc....and you could get by with your valve springs but I wouldn't do that on a 25+ year old engine.
You usually have to start worrying about retainer to valve guide clearance when you jump up around .480 lift on a stock gen 1 cylinder head.

This cam would work with stock diameter LT-1 style valve springs that have about 110-120 lbs. seat pressure. Which is similar to what your engine had originally.
Check your springs to be sure, but if they are originals I'm willing to bet they are too weak.

Really a pretty straight forward swap that won't require much in parts. Cam, lifters, and springs would do the trick.
The only issue you may have is the 110 lobe seperation if you are still running the stock computer controlled quadrajet. Those are finicky, the power piston is computer controlled, and in low vacuum signals will lift the primary metering rods causing a rich condition at idle. Not much you can do with the computer controlled quads, very primitive system.
I would personally switch the distributor and carb out to an older design without the computer controls if it hasn't been done already. Hope this helps.

**justinmc978** · 10-26-2009, 12:19 PM

agreed^ the motor just cant breathe, you need to free it up with heads/intake than maybe a different cam later, as with all motor mods. also rid of that computer system, its really stupid, my.02

**jiveass** · 10-26-2009, 12:57 PM

i did forget to mention that the engine was rebuilt 2 yrs ago and has pretty much sat in in my girlfriends dads yard undriven until recently....maybe has 5000 miles on it...as far as the heads are concerned i dont know if they replaced any springs or valves when they did the rebuild. i know the carb isnt stock because its a holley with no electronic plugs on it. same case with the distributor. the car runs great but the main reason for this swap is that the car falls on its face at around 3500rpm...i am worried that the cam you suggested will give me a similar issue if it is close to stock....what do you think? i do not mind changing the carb or the intake if necessary..but i would like to keep the same converter if possible....although a stall would add to the cool factor.

**jiveass** · 10-27-2009, 07:09 AM

also what size carb would i need to upgrade to?

**Firebirdjones** · 10-27-2009, 11:04 AM

Falling on it's face would be some other issue. Could be valve springs, or maybe a fuel delivery issue.
That L82 cam should run to 5500 rpm no problem in a 350.
It's the same cam GM also used in the famous L79 327/350hp engine that would spin to 6-6500 with ease.
As far as the carb,,,how did you get a holley on a Q-jet manifold?? Did you use an adapter or has the manifold been changed??

**jiveass** · 10-27-2009, 12:00 PM

Originally Posted by Firebirdjones

Falling on it's face would be some other issue. Could be valve springs, or maybe a fuel delivery issue.
That L82 cam should run to 5500 rpm no problem in a 350.
It's the same cam GM also used in the famous L79 327/350hp engine that would spin to 6-6500 with ease.
As far as the carb,,,how did you get a holley on a Q-jet manifold?? Did you use an adapter or has the manifold been changed??

its got an adapter under the carb...although the carb looks like a quadrajet its not.....and maybe falling on its face is a bad choice of words...it just feels like theres nothing left after 3500-4000rpm. redline is 4500 according to the tach. rpm keeps climbing but it feels like its not doin anymore than what its already doin.

**Firebirdjones** · 10-27-2009, 12:20 PM

Originally Posted by needls1again

its got an adapter under the carb...although the carb looks like a quadrajet its not.....and maybe falling on its face is a bad choice of words...it just feels like theres nothing left after 3500-4000rpm. redline is 4500 according to the tach. rpm keeps climbing but it feels like its not doin anymore than what its already doin.

You are saying you have a holley, that looks like a quadrajet but it's not.

Do you mean you are running one of the old holley spread bores?? Those are made to bolt to the quadrajet manifolds without adaptors.

Either way, I'd look into getting the adaptor out of there, whether that means switching manifolds or carbs, that's up to you. You may have a tuning issue or possibly a fuel starvation problem, without being there and knowing what we are working with it's hard to pinpoint, especially on the internet.

**jiveass** · 10-27-2009, 02:01 PM

i will take the carb off this weekend and get some pics posted....as well as pics of all the loose plugs that dont seem to have a home....that should help clear up some of the questions...thanks for the answers and future insight.