I have a 77, L48, with over 100 K on motor. I'd like to swap out the motor
down the road, maybe this winter but for the time being, I wonder if there is any simple changes I can do to get a little more pep out of it.
Maybe change manifold, carburetor, distributor, ? It runs good now but still is a little poochy. Any suggestions that won't break the bank?
Thanks!

 

The best way to get a few more HP is improve the engines breathing capability. Better air filter, better manifold or port what you have, headers and freer flowing exhaust system. You could add the improvements to this engine and then swap them over to the other engine.

The carb and distributor should also be optimized for the engine that its on.

 

Professionally speaking.... I would wait and put in what you REALLY want during the winter and ENJOY the summer. With 100K+ miles on it.. It is a waste of time and energy to get a "little" more out of what you have now. Modifing exhaust, replacing the carb and intake and ignition can be transfered over to what you MAY install in the winter. But I feel your energy would be better spent getting your "game plan" together and focus on your future engine swap. With an old tired engine. You are not going to get a major gain for the time spent in an engine that you are planning on swapping out later. But to each his/her own. Any doubts, put it on a chassis dyno and see what you have now.. It is not that expensive to get the reading on what the engine produces and that may help in making your decision easier. I have to do it often for my customers and let them see what is "reality" versus ummmmm "fantasy".
"DUB"

 

Dual exhaust and no cats. Otherwise wait for the new engine.

 

Removing factory emission equipment IS against FEDERAL LAW. They do make high flow cats for performance cars. Because the factory still uses cats and look at the power they are achieving nowadays. If you want a car without cats, but one that didn't come with them. Many muffler shops will not alter your system just because of the fines that they can get.
"DUB"

 

Agreed, but unless he has a California car would a '77 have cats?
Mine is a '79 and it sure didn't have cats, just something that looked like 30 year old 1/2 inch pipe with hideous bends in 'm.

 

EVERY Corvette built after 1974 had catalytic converters. Someone removed yours in the past.

 

YEP!!! My Moms 75 Impala had one of the first CATs. Man,, what a MONSTER that thing was!!! The first cats were Palladium Single stage cats and they were packed full of little Palladium coated ceramic pellets.

BC

 

There are enough L-48 upgrade threads to keep you busy reading all winter

Seriously - start with a tune; don't scoff at this - many times when a car is a bit of a pooch, a solid tune makes a huge difference. Then headers and exhaust. A good dual-plane intake. That's just about as far as you go without getting into the engine.

You may also find an investment in gears and/or torque converter makes a huge difference as well. Bottom line - maximize what you have, then seek more.

 

I have a 78 and yes it has cats

 

Thanks folks for your replies. I know a "game plan" is very important but summer time fun ranks right up there too. Whats confusing to me is what's available today to what was available back in the early 70's when we were street racing appears to be night & day. What was hot back then is nothing compared to the tech now. Costs changed too, what was dollars back then, are pennies to today. if I put money into the 77 today, I'd like to use the same on the next motor. here's where the game plan takes effect. I would think small block is still small block, correct? But I'd like the new motor to be 400 + HP. Will the L48 handle future ideas or am I just spinning my wheels & wasting $ ?
And yes, I do have cat's. But on a 30 + year old car, do you think the cat police are really going to care? Here in Illinois, we don't have any state testing on something this old.
Thanks again.

 

Newer heads (stock Vortec) are good for 30-50 HP over the '77 heads.

 

Headers and exhaust will work for an other GEN I smallblock as long as you don't change the plug angle or port height. A good K&N filter will last forever and work with anything else. An Edelbrock Performer EPS is good to about 400 flywheel horsepower, but locks you into GEN I-style heads (no Vortecs). You need to decide if you're going to swap carbs - there's no additional performance there, but a good aftermarket carb is more easily tuneable by the average guy than the Q-Jet (which is sure to start an argument ) So there are some great things you can do now that will work with whatever you do next, within a few constraints.

If you're looking to go further, then a top is your next choice - but those components may not be a good match for your future engine...

These are real general answers to real general questions

 

Check out the 'Sticky' at the top, and click on the lbfun link by John Hinckley. You can gain a few HP by changing the weights and springs in your distributor. PG.

 

Building a potent power plant is like building a house. You MUST build it on a solid foundation. The newer LS engines are deep skirted 4 bolt main blocks. You have to look at what you plan on doing with the engine and RPM limitations that you want.

Yep,,,HP hardware has dropped in price. Well sort of! Its more available and easier to produce plus all the engineering patents are expired and there are a LOT more people producing very similar cool SB stuff.

Some important things to consider:

- Have the block fully checked out and sonic checked.
- New Heads is a must! There are some inexpensive heads that flow very well and have good compression ratios. They make stock heads good boat anchors! By the time you machine old heads and buy new parts, you can just about purchase new heads.
- Machine shop services will consume a major part of your rebuild budget. Don't skimp. DISCUSS YOUR PLANS WITH THE MACHINIST! They will help you make decisions and sometimes correct ones!
- Use ARP Bolts where you can. There excellent reliability insurance!!
- Have the rotating assembly BALANCED! This makes a big difference in how the engine runs. Discuss this with the machinist!
- Use a quality aftermarket damper
- CAM The heart of the engine and selection needs to be done carefully. Don't fall victim to installing a GIANT cam. Pick a street able cam that will give you a good HP and TQ level and work up to 6500RPM
- If it were me, I would up-grade to a roller cam with improved rockers, better push-rods and guides. Consider Titanium retainers.
- Double roller timing chain
- Do you want stock cast, Hypereutectic or forged pistons??? The machine shop will need to know prior to machining. Same Displacement????????????????
- Better oil pump!

There are so many things to consider and money to spend on go fast goodies that it will make your dead spin.

Things that I would replace/up-grade/make better

Distributor
Ignition system
Carb
Oil pump
Oil pan windage tray
Port the intake manifold to the heads
De-burr the block before machining
Four bolt main conversion
Consider a 383 conversion "Theres no replacement for displacement"
Forged crank
Better rods

Holy crap,,,,,that means that your going to need to beef up the rest of the drive train!!!!!

Good luck on your rebuild and please bounce your Ideas off of us. It good to listen and help make rational decisions. I have the same project to undertake on my 71. The little base 350 is getting tired also!

 

Lots of good thinking here, but this one point is the most critical. For a home rebuilder, finding a good shop and forming a relationship with them is the key to success.

Guys that <fail> are the guys that buy all their parts, then take stuff to the machine shop...only to find wrong parts, bores that need to go to .040 instead of .030, wrong CR calculations...the list is endless.

Just as bad are machine shops that don't like home rebuilders. They push people into race-only parts and machining, or they're a "job shop" that can't hold a performance tolerance.

Bottom line - if they can't take 5 minutes to talk through the build, they're not the right shop

 

VERY, VERY, VERY, VERY GOOD ADVICE from Bill Curlee and billla in post #'s 15 & 16.

As for the question you asked and wasn't directly answered. Is you L48 able to handle 400+ HP. In respects to longivity... I personally do not think so. This is because the crank and rods were changed from the eearlier years when 300+ HP was common. They (GM) changed the forged cranks to cast, and the rods were also changed due to the lack of high compression. No need in putting good parts in an engine with only 185HP.

So...unless anyone out there cares to debate this issue...which is fine... I would be careful when you start to build this engine because unless you make your "bottom end" strong and reliable, you may be performing an "enginectomy" sooner than you think. Will the cast components work. YES they will, but I nor anyone out there has the "crystal ball" to tell you actually how long. Over doubling your horsepower at the crank, may be worth looking into the 383 cubic inch option previously posted. That way you can get a good crank, rods and pistons.

This will be a complete package that you are looking into which requires many calculations to make sure that the choices made WILL produce the desired end result. Sometimes it seems to be a waste of time, but the math and choice of parts is important. This is why it is IMPORTANT that you find a machinist who KNOW WHAT IS GOING ON and KNOWS HOW TO DO IT. Some machinists have performed this same work for others and may already have the recipe, and if they DYNO the engines. They can show you what you engine produces...in PRINT. If thehy do not take the time to talk with you...like what was earlier written....RUN. And find another. You are going to spend some $$$$ and want this engine to be reliable and LAST. The machinist should RESPECT this FACT and be willing to work with you and ADVISE you CORRECTLY.

This may, if not WILL also require the "beefing up" of the transmission and rear differential. It is the "chain effect". the "weakest link" will ALWAYS show itself in time.

The market offers high performance cats for engines and YOU should care that they are in there even if your state does not perform emissions testing. Be a part of not being the cause of bad air. And you never know, the new Washington DC leader(s) just may "flex" their muscles and impose guidelines on all classic cars. Things change all the time there and who is to say it won't change. They have already started and it just may branch out.

Last but DEFINATELY not least is to make sure that you are AWARE of the hood to air cleaner clearances. Eventhough some parts are the best for your project, they MAY cause a conflict when you go to install the hood. Make sure you take measurements and use clay if you have to to make sure you know how much room to have to "play" with....which in some cases is not much.

Good luck and keep us informed on your thoughts.
"DUB"

 

I agree with your advise 98%! I do question the statement of the 300 horse motors in earlier Vettes. They are almost the same as the L-48, they just used different cams and a lot more emmissions, plus they were rated differently. an L-48 can put out more then 300 horses easilly.
I AGREE with everything else though. My 77 L-48 is built up some but lately, I've been thinking of placing everything stock, back on. If I run 300 or 350 horses, they are not going to beat a newer car, even some V-6's will outperform an older Vette. Then IF and I say IF with a heavy heart, the Feds bring a Federal emmission package, they will most likey go by California's laws. That might mean even 'Live Free or Die' stateslike NH may end up requiring cats and EGR's. I use mine as a weekend cruiser and if someone is not going to race their car, wait until this new Carbon Bill passes or not before throwing a lot of money into something that may need to be taken off.

 

I think we can net this out to note that a GEN I factory cast crank is good to about 1 HP/CID (flywheel) at < 5500 RPM. The chances of a reusable GEN I crank after 100K miles is relatively low - it happens, but not all that often any more. The price of a new cast crank that would be capable of 400+ HP is almost always less machining cost for the old crank.

 

Wait and do it right once. Buy/build a 500+HP motor whenever your wallet dictates it's okay.