I got a 79 L48 corvette that i bought about 3 months ago with 92k orig miles

The thing did not come completely stock, as i opened the hood and there it had some headers, a holley carb, and an edelbrock air filter. engine doesnt look very stock at all from what i can tell. (im not really sure cause im new to these kinds of cars)

It does NOT have a cam in it. I can tell because of the sound it makes

This car is quite fast, i wont lie. ive noticed it really ramps up speed even when i only mash the peddle half way to the floor. it doesnt take much at all.

however, i am wondering what else i could do to it to "wake it up" some more, even though it has already been monkeyed with before.

I dont really care to have a cam installed, since i just dont want to spend that kind of money right now. but surely there is something else i could do?

lemme know yall, thanks

 

OK, so, you recently purchased a 1979 L48 Corvette.
That's great! Whoo Hooo! That is truly great!
We all love Corvette's here.
And, .... and this is the kicker. You think it's fast!
A 79 L48, and you think it's fast!
So, one of only 2 possibilities here.
One, the previous owner has done a fair bit of work to it already, ....
Which is a really good thing! Really good! But without knowing what all has been done. Making further recommendations is absolutely impossible.
And Two. This is a L48 and your totally delusional!
Which is it? Is it a really quick car? Obviously been worked on.
Or are you totally delusional? As a 79 L48 is anything but quick.
Bottom line.
No one can recommend anything without knowing the starting point!
Much, Much more information is needed on what you actually have.
If it is indeed quick, heads, cam, header's and numerous other mods have already been done.
WHAT ARE THEY?

 

One of the biggest variables of engine performance is your ignition timing. It determines when the spark plug fires in relation to the position of the piston moving in the cylinder bore. Optimal ignition happens at around 17 degrees of crankshaft rotation after top dead center, but a burning fuel mixture doesn’t fully ignite instantly. You can “lead your shot” of firing the spark plug earlier to achieve complete combustion at the correct time. Every type of engine is different, and will like different amounts of advance to run optimally.

I would buy a timing light, and get a reading from your car with the vacuum line going from the carburetor to the vacuum advance on the distributor removed and plugged off. This will give you your initial timing at idle, which you can go from there.

 

Quote: "engine doesn't look very stock at all"

So as far as you know, it could already have aftermarket heads, cam, new Intake, etc and be pushing 400+ horse.

If it runs well, just leave things as is. However, you could spray down the carb with GumOut.
Wipe off any carbon tracking under the distributor cap.
Remove one of the easiest sparkplugs and check its color.
Check all the vacuum hoses condition and call it good.

 

It must already be modified. A stock L48 you can read a book during 0-60

 

The first thing you should do is post some photos.

An L48 4-speed with some exhaust work will feel a lot faster than a stock L48 auto.

If you don't want to pay for a cam, the low hanging fruit would be to email @lars, as for his timing, HEI, and Q-Jet papers, and do a proper ignition tune.

Please take off the air cleaner assembly when taking photos. And check your garage for mice, I bet there are no cats under your car.

 

A thick book in braille.

 

Well, you didn't have to be rude and call me 'delusional', and also if you read my entire post I already explained what was on there already.
Headers, holley carb, and an aftermarket edelbrock air filter.
NO CAM. I've heard cars that have been cammed, and I can say definitively that my car is not cammed.
I am simply asking what i can also do to the engine that doesn't involve installing a better cam to further improve performance. I've heard that these 350's are very easy to upgrade.

 

You'll get people like that on the forum. Best to filter out the good from the bad.

Sound alone is not a good way to tell if a car has a different than stock camshaft. The stock L-48 cam is the same as the 327-300 stick used in almost everything. It’s 195/202 .390”/.410” 112 LSA. Very mild, but the number you should be most concerned about is the lobe separation angle.

There are cars with “thumpr” cams, with a very narrow LSA, but small on the lift and duration side. This gives them the “cammed” sound despite not being as fast as the sound would lead you to believe. A lot of those cars are only driven to car shows and only exist to show off. Different strokes for different folks I guess.

On the other side of the spectrum you’ll have “sleeper” cams, with lots of lift and duration, but a near stock LSA. There is some power lost as certain RPMs by reducing the amount of overlap, but a reason someone might have one is to improve the output of the engine while retaining the smooth idle of the stock cam, for street racing or other reasons.

There is a possibility that one of those cams might be in your car.

Everyone judges speed differently. If you want to get an accurate reading of your cars/engines performance you can do 0-60 and 1/4 mile tests. These are hard numbers to go off of, and can show the difference as you make modifications.

And post some pictures!

 

As bikespace mentioned, check under the car for catalytic converter. A cat delete probably worth 30hp and takes little effort.
advancing the timing to ideal SBC spec is also easy power. There’s a ton of threads on how to set timing to maximize performance.

Other upgrades start to take a lot more money and time.

Any markings on the heads to determine if aftermarket or original?

 

Very helpful.
As I said I'm new to this kinda thing, so that was really informative. I appreciate that.
I will post some photos later on today.

 

Don't mind that rude crab ***. It's just the result of being a mechanic working 6 days a week for 50 years without a vacation.

 

Since we have brought up Lars.....When he rebuilt my QuadraJet he suggested that I cut out the carpet in back of the gas pedal, it may sound odd, but for sure gave an extra kick to my 427..... A more common and subtle problem is the issue of inadequate throttle cable travel. This is very common on Corvettes and Camaros. With a helper in the car and with the engine “off,” have the helper fully depress the gas pedal (with the engine hot and the choke wide open to assure that the lockout lever is disengaged). Observe the carb on the driver’s side and see if the secondary throttle moves to the wide open position: You can grab the throttle lever once the assistant has the pedal to the floor and see if you can move it further. If the gas pedal does not fully open the secondary throttle, you have one of several methods to fix this:



a. Remove your floor mat. I call this the “25 horsepower floor mat tuning trick.”

b. Install the throttle cable in the correct position on the throttle lever. The Q-Jet has an “upper” and a “lower” cable attach hole: The upper hole was used for trucks and station wagons. The lower hole was used for Corvettes, Camaros and Novas. If you install a Corvette throttle cable in the upper hole, you will never achieve wide open throttle since there is not enough cable travel to open the throttle from the top lever location.

c. Straighten your throttle cable attach bracket. The bracket that supports the cable at the carb is often bent slightly forward. If the bracket is bent or moved forward, it will not allow enough cable travel to open the throttle fully. Simply bend the bracket back just a tad: I use a big hammer and a steel rod to give it a whack. I call this the “25 horsepower hammer tuning trick.”

d. Fix your gas pedal linkage. Very often, the actual steel linkage coming off your gas pedal will be bent a little “flat.” This will cause the pedal to hit the floor before the carb is wide open. You can give the pedal more travel by simply grabbing the gas pedal and bending it up off the floor. Care should be taken not to damage any plastic pedal rod bushings when doing this: Support the plastic pivot points when bending the pedal rod so the plastic bushings do not break.

e. Fix the slop in the gas pedal attach lever. Many C3 Corvettes have a bit of wear on the lever that attaches to the gas pedal rod: The rod is "D" shaped, and the attach lever has a "D" hole with a screw tightening feature. If this "D" hole is worn, you can remove the lever, grind some material off the locking feature surfaces so it snugs up tighter, and re-install it to gain some travel.

 

Here you go

 

I like the blue. It looks like an original intake manifold, although repainted as evidenced by the overspray on a few things. It’s a spread bore design, and your square bore Holley carburetor has an adapter plate to fit on it. This is not ideal for peak engine performance. Here is a thread that outlines some of the issues with doing this.

You have two options, either replacing your intake manifold to a square bore/dual pattern one, or changing your carburetor to a spread bore one.

Not necessarily a performance increase, but another thing that would help your engine would be using a PCV valve. Replacing the breather on the drivers side valve cover with one then running a vacuum line to the carburetor would pull a vacuum on the crankcase when it needs to vent, preventing oily fumes from getting all over your valve covers.

It’s hard to tell from your pictures, is your vacuum advance line teed together with something else? It also looks like there’s an open port on the vacuum fitting on your intake. This is a massive vacuum leak, and should be capped immediately.



Another thing that would impact engine performance is your radiator fan. It appears to have been solidly mounted with a spacer to the water pump pulley. This is fine at idle and low speeds, but once you’re moving this places an unnecessary load on the engine. Changing this out for an original fan clutch or an electric setup would fix this.



One of your throttle return springs is hooked to the other one rather than the throttle lever on the carburetor itself. There’s nothing wrong with only running one spring, but I would either remove it entirely or make sure it’s connected to the right spot.



Only other thing I notice would be making sure your spark plug wires aren’t touching and inducing a current in each other. Specifically the #5 and #7 wires, since they’re so close together on the distributor and the block.

 

1. Carburetor isn't necessarily a performance increase

I've talked to quite a few people and they have sworn up and down that the holley is helping the performance. I mean so many people say the l48 is a slow dog but I've driven it quite a bit now and it's either been hopped up, or maybe it's just the torque. I don't know. My thing is: why would someone change the carburetor to a racing one if it didn't really help the engine? The thing will scoot.


2. Ive looked at the advance line, i dont think ive noticed any leaks in the line. I haven't heard any hissing that would come from a vacuum leak, nor has any of the vacuum driven systems been affected so far. Engine runs great.
I don't think it has a vacuum leak. Yet...


3. The fan is actually plastic for some reason. What do you mean it puts "unnecessary load on the engine"?
is it okay to leave it how it is? Or is that something that needs to be fixed?


4. I have no clue what to do with that spring. I'm very new to these sorts of things...


5. I didn't see any of the plug wires touching. Just had a new distributor put in with a new rotor and spark plugs.

 

a compression test will tell you if it is a L48, maybe

 

1. A Holley carburetor isn’t a bad thing, they were used on many late 60’s early 70’s performance cars. The original Quadrajet carburetor wasn’t bad by any means either, just set up on the lean and on the lazy side from the factory. Any carburetor can be set up to produce any air fuel ratio you want, leaving you with the other variables of top end air flow and fuel emulsification abilities. Your Holley carb should have plenty of flow for your L48, but the adapter mating it to an intake with a different mounting pattern throws the fuel emulsification abilities all out of wack.

2. I don’t believe there is a leak in your vacuum advance line, just concerned that it is spliced in with something else. The vacuum advance should have its own individual line to a full manifold vacuum source. I do believe there is a leak in your 3 pronged intake manifold fitting. Take a closer picture of the piece I circled in my previous post.

3. Your fan will function just fine the way it is as long as you don’t notice your car overheating. But changing it out to an original piece with a fan clutch makes the fan “cut out” at a certain temperature because there is adequate air moving through the radiator from the car itself moving. With a solid mounted fan it will constantly try to pull air through the radiator, regardless if it needs to or not.

4. Doing nothing to that spring will be fine, but if you want to get a shiny brand new one most parts stores sell them for fairly cheap. You can use one or both, depending on how stiff you want your gas pedal to be. Personally I only run one.

5. If your distributor was replaced I would definitely check your timing. If you don’t already have one get a dial back timing light, and check your timing at idle with the vacuum advance unplugged. There’s lots of resources online that can help you with this.

 

If you think your '79 L48 is pretty fast, leave it alone and enjoy it. Either the previous owner did some "stuff" to the engine which pepped it up or some mechanic tuned it properly. You are likely not going to get much more out of an L48 without some major upgrades.

P.S. When you make major upgrades to a late-70's Corvette, it also requires modification to the differential, suspension, transmission, etc. It gets expensive to put real power in a late 70's C3.
Enjoy what you have and save a lot of money and grief.

 

I wasn't rude and I didn't call you delusional! Perhaps you need to reread that! Certainly it was said tongue and cheek, and if you took it any other way I believe you miss read it.
Yes we can all help you. No after that I'm not inclined.