Yeah i know its only an L48 but it has been previously rebuilt and runs dual exhaust and goes OK..

I was thinking of adding a cam only to add a bit of poke.

Will a hot cam on its own make a difference or do i need to change heads, manifold, etc. Something i porobably dont want to do.

What type/profile should i be looking at.

I am suprised how cheap cam kits are and like the lumpy idle that comes with it.

 

Well, you will probably get arguments from some folks, but if you just stick a big cam in an otherwise stock engine, you will probably be disappointed with the results. The duration of the camshaft is roughly analogous to its powerband (commonly defined as the area of the rpm range from peak torque to peak horsepower) i.e. the more camshaft duration, the higher the rpm where the engine will make it's best power. The rest of the engine components which are involved with moving fuel and air (carb, intake manifold, intake and exhaust ports, intake and exhaust valves, exhaust manifold/header) are in roughly the same category: the bigger they are, the higher the rpm where the engine will make power. So, if you take a stock L48 engine which has carb, intake, heads, and exhaust that ore optimized for lower rpm operation, and stick a big, huge cam in it that is optimized for high rpm operation, you're gonna end up with an engine that really doesn't do well at any rpm. All the parts need to be designed to work at a similar rpm level in order to see dramatic gains in power. I know, it's tempting, you can get a cam and lifters kit for less than a c-note, and a great big cam costs the same as an itty-bitty cam, but don't go crazy! A slightly larger cam might make some more power if you don't stray to far from the rpm range that the rest of the engine is built for, but stay conservative. An old rule of thumb that I have heard often is: decide what cam you want, and then buy the next one down.

You can get a used Edelbrock Performer intake manifold on ebay or craig's list for less than $50.00, and a set of Flowtech headers from Summit racing for about $110.00, then have a muffler shop fab up some pipes to connect the headers to your existing tail pipes, shouldn't cost too much. Something to think about.


Scott

EDIT

Sorry, I just re-read your post, and I see that you have a dual exhaust system already. Does the car have a set of headers installed yet?

 

Do a LOT of research on this.

Adding a cam with the loping sound you like without changing your heads for compression or other components to match it will probably result in a disappointing result. You may even lose power down low.

I would investigate cams that make lots of torque down low. They will probably have a smooth idle but what is more important?

 

[QUOTE=corvettdreamin;1577813406]Yeah i know its only an L48 but it has been previously rebuilt and runs dual exhaust and goes OK../QUOTE]

Unless you know what cam is in it right now,how can you know what a "better" one may be?If the engine was rebuilt by anyone that is reasonably competent,they hopefully picked a cam that works well with the other components that were used in the rebuild.Without more information you may likely make performance worse as the others have mentioned,take your time and do the research first.

 

I have always heard the primary power limiting factor on the L48 is breathing first, then exhaust flow.
Sounds like you have the exhaust part down. Try a carb/intake manifold before you try the cam and you may find you get better results to "wake up" what you already have.

 

remember, you can only get so much fuel past those small valves... and even if you could get more, it would never burn well with such a low compression ratio

 

if you do know for sure that it is a stock L 48 camshaft, the comp cams high energy 268 cam is a pretty good stock replacement cam. it has a slight rumble to it and will wake up a stock motor especially if you run a set of headers. its an off idle cam to 5500 rpm so it will work fine with a stock stall converter. the specs of the L 48 cam are are low lift and short duration which makes it a real low rpm torque cam with not much rpm potential.

 

If i pulled the old cam, would there be any markings on it to indicate what type it is.

Also is this an easy job or does the manifold have to come off as well.

What manifold would you recommend to compliment a mild cam.

 

If your going to put a mild cam you have to remove intake, rad, and timing chain cover,and loosen front of oil pan. You may be able to squeeze cam out without removing rad but would be risking replacement if you hit it. You may be able to trace cam by #'s if its not too old but there are no guarantees. You could also check what it was ground to if you know a shop with a degree wheel. As for intake I would use something like a performer RPM, and a 700 to 750 cfm carb.

 

you may be able to rig up a dial indicator and measure the valve lift by just taking off a valve cover and turning the engine over by hand. L-48 cam would be .390 on the intake valve and .410 on the exhaust valve. id really hate to pull the cam and find out you already have the right cam for your build already installed. it really is a lot of work to swap cams. lopey cams require an engine that is built around the properties that the cam requires. its not the cam that you want to run, its the cam that your engine needs to run properly.

 

you have to take the intake off to get to the lifters and they have to come out to pull the cam out, and the fuel pump pushrod is driven off the cam so the fuel pump has to come off also.

 

Don't forget about removing the harmonic balancer too.

 

i tape a piece of cardboard to the radiator to protect it and my hands when i do a cam change.

 

...why not replace heads while at it??? Dart Iron Eagles:"^) But before that - i'd suggest replacing the pistons too Don't forget the hi-volume oil pump. You might want to simply yank the engine and do it all on a stand.

 

Thanks for the input.

I now agree that just changing the cam aint gunna cut it so i have decided that the only way to do it, is to do it properly, ie: with a head, manifold, headers and cam package.

From what i have read on other posts this engine may be good for 350/400HP with the right goodies.

I plan on doing this step by step starting with a manifold and headers.

Can anyone recommend a manifold that will work now, but will also work with heads that are rated to 400hp that i may purchase in the future.

 

Your only problem is those dished pistons, your gonna be lacking in sqeeeeeeze! A 64cc combustion chamber will give you a decent amount of compression along with a .015" compressed thickness head gasket, around 9.5 to 1, not really enough for a REALLY hairy cam, but enough to get you up to maybe 350 or so with the right combo of parts. Look into Edelbrock's top end kits, Twisted flow makes top end kits, among others. If you want 400 horses and still have some bottom end torque, give some thought to a roller cam.


Scott


Scott

 

That'll work on a schoolbus or wrecker.
C3 rad must come out
sbc camshaft is almost 22 inches long.
I doubt any OE sbc C3 has more than 15 inches between front cam bearing and rad; mine sure don't!

L98 aka ZZ4 heads (58cc), $100 summit cam-lifter kit, YOUR L48 intake, headers and good tuneup will make nearly 350fwhp on pump gas.

 

Your '75 has tons of headroom under the hood. so you can easily install a tall manifold. The Catch 22 about going incrementally is that most all the same stuff has to come off each time you perform an incremental step!

 

Suppose you left the cam alone and simply installed 1.6 ratio rockers and new valve springs?

What do yall think?

 

I think its waste of money. Install the cam for the build and use. As for a good intake a Performer RPM, Weiand Stealth, Holley Street Dominator (LT1) copy can fit under the hood with the right air cleaner. I suggest pull the intake and a head to see what pistons are in there so you can do an accurate compression calc and choose parts from there.