ShipmanPhotos

77 L82 4 speed. All smog stuff gone. Stock intake and QJ but open 14" air cleaner. 2.5" true duals with power stick mufflers.

Supposed to have non stock heads and cam but not sure any details. Doesn't sound like a wild cam. (As an aside, any way to find out details on things like this without taking things apart?) Anyway... Let's assume cam and heads are mild upgrades over stock.

Runs really strong after a tuneup, carb adjustment and timing advance.

Aesthetically I like the muscle car look of the open air cleaner, so chasing cold air over flow isn't a priority, but would be open to changing intake manifold.

The 2.5 "exhaust is bolted up to stock manifolds.

Basically I'm very happy with where it's at but want to maximize its ability to breathe in and out - IF I makes a difference you can feel. Will intake manifold and/or headers yield a noticeable difference you think?

I don't want to spend money on them if it takes a series of Dyno tests to see a 7 hp gain that you can't really feel.

fishslayer143

headers will give you some gain with free flowing , no cat , duals

ShipmanPhotos

I thought so, but am wondering if it's enough to be worth the expense and effort.

Same question for an intake manifold.

Let's be optimistic and say between the current mods, I'm at a nice round number of 300hp. What do full (not shorty) headers and edlebrock performer intake get me up to? Ballpark?

LT1M21Vette

Make sure you have mandrel bent tubes.

NOT good.



Good.

REELAV8R

The stock L-82 manifold is pretty good as is.

By giving up cold air for the intake you are giving up a significant amount of flow. The density of the air IS flow to the engine.

Say you have 600 cfm available to the engine. But the air density is only 90% (conservative) of that at sea level on a 60* day due to drawing in hot under hood air.


600 X .9 = 540cfm

The 600 CFM is still available just at a reduced density. So you just reduced your effective flow due to temperature, as far as the engine is concerned. You also reduce your HP potential and torque.

The air under the hood can reach 130* to 150* easily. If you are at seal level and it's 110* under your hood that is effectively like operating at 3500 feet.
You loose about 3% of density per 1000 feet. So in this case you have lost 10.5% of your air density.
Check out this chart for air density calcs.

http://www.ascentgroundschool.com/images/ct80802e/8.jpg


If aesthetics is a priority then to regain the loss due to air density it will cost some time and $$ to do it.

Better cam and heads come to mind as well as long tube headers. Increase your flow to the engine by 10% and you'll be back where you started. However it is hard to quantify the results without before and after testing, either on a dyno or in the 1/4 mile.

jb78L-82

Headers will help noticeably as will a roller cam with non stock heads. Which non stock heads to you have? A non L-82 flat tappet cam you have should help a bit, around 10-15 HP, over the L-82 cam assuming more lift. A .015 head gasket (Felpro 1094) with stock 8.9:1 pistons along with 64 CC heads would get you to 10:1 compression.

The L-82 intake is pretty good below 6,000 RPM so I would not mess with it. I reused my L-82 intake on my roller cammed, L-82 355, 10.2:1 compression with AFR aluminum 180 64 CC heads with new JE Forged Racing pistons in 2014 with my rebuild...engine screams.

Jebbysan

A performer RPM Q-Jet manifold and a set of quality long tube headers will net you a solid 25 horse increase and a boatload of increased torque off idle.....

Jebby

ShipmanPhotos

Exactly what I was looking for. Thanks! That's worth chasing.

ShipmanPhotos

Thanks. I understand the point about air density, but I definitely did not give up flow when switching from the single snorkel stock lid. The difference was an immediate and obvious net gain. I know a different (non-stock for 77) dual snorkel type set up has worked really well for other guys and I respect the search for high flow cold air, but I'm sticking with the old school OEAC. If anything, I will look at hood scoop options someday. Maybe.

Now, as to your point about air density, I guess I do have a bit of a concern about what long tube headers will do to the under hood temp and will they potentially rob Peter to pay Paul by making the intake air a lot hotter?

macka75

I put 1.6 roller tip rockers on my 75 L82 4 speed
definite seat of pants improvement

ShipmanPhotos

Any way to figure out specs on an aftermarket cam you didn't install?

Shark Racer

It would help if you knew what heads and cam were in there. If you're running a <210* cam and a stock replacement head (IE any factory iron head other than Vortec), you won't be making enough power to justify going to a new manifold.

Headers and good exhaust are by far the best upgrades you can do to these cars. Start with headers.

You can pop off a valve cover to find the casting number for the heads. If you have Vortec heads, you'd have a different manifold anyway. Any pictures of the engine you can share? Casting number on the intake?

Are the current heads and intake aluminum or iron?

As far as the cam, you can get reasonably close with a degreeing wheel and a dial indicator. Figure out when the valves open and shut and how much. Divide by the rocker ratio of the rocker arms you have to figure out lobe lift and then you'll be able to figure out what cam you have to some degree.

REELAV8R

You could also put a vacuum gauge on it and see what it reads at 800 RPM. That may give us an idea if the cam is anything even semi-performance like.

This is assuming you don't have any significant vacuum leaks though.

Also could measure the lift on the pushrod end of the rocker with a dial indicator to see what the lobe lift of the cam is.

ShipmanPhotos

Thanks man. No vacuum leaks. We checked that out recently when the carb needed some adjusting, just to rule it out as a cause of a rough idle that was corrected by adjusting the QJ and advancing the timing.

REELAV8R

That's good.
Then if you are getting say 18" to 20" of vacuum you got a L-48 stockish cam.
18" to 16" and you slightly better than L-48 stock. This is probably where an L-82 stock cam would fall.

16" to 14" and you got better than stock cam.

14" or less and you're getting into a pretty good performance cam.

Less than 10" and you got something that has more higher RPM potential and performance.

You will need to know this in any case to get a vacuum can that is appropriate to the vacuum available.

lurch59

The close proximity to the hood makes fiddling with the air cleaner very productive to maximize the horsepower. The shop that dyno'd my car squeezed like another 34 horsepower by changing the air flow/air cleaner setup on my engine. Granted it's a 496 big block, but I was stunned at the difference, and that was measured at the rear wheels.

wilcar

A 3.73 gear would give you some really good seat of the pants performance!

ShipmanPhotos

I was told by my brother in law (it was my father in law's car) that it had a 3.70 final drive ratio, but I guess I need to verify it.

7T1vette

You have "advanced" the ignition, but have you re-curved the distributor? Probably the simplest and least expensive way to add another 10% HP (or more) to your engine. Do a SEARCH for Lars paper on recurving the distributor. If you can't find it, send Lars an e-mail at V8FastCars@msn.com and ask him to forward you his latest version of this 'easy to do' process.

ShipmanPhotos

Thanks! No idea but I'll find out!