Hello C3 Shark Owners,
I have a 1973 C3 Coupe with stock L48 automatic engine and stock exhaust/manifolds. The only upgrade added was an Edelbrock performer intake manifold that came with the car when I purchased it.
I want to bump the car up from stock 190 hp to 300-350 hp range. I do not want to race or take the car to the track but get a great exhaust sound.
with extra throttle response. I still have my stock quadrajet carburetor that I plan to keep. I prefer to keep the original engine inside the car and not swap
for a crate or stroker kit. I still want the car to be streetable. It would be great to get your recommendations for engine performance upgrades.
-stock quadrajet carburetor - plan to keep original
-previous owner added Edelbrock performer carburetor
-parts I have bought, but not installed yet: pair of Flowmaster 40 series 409 stainless mufflers, Pypes 2.5" stainless X-pipe with cutouts kit, & Doug's D350 ceramic coated long tube headers
***parts I want to buy AFR 180cc 64cc aluminum heads - plan to buy
***Edelbrock timing chain - plan to buy
***what cam configuration should I add for this type of set up - from my reading it seems like a hydrualic roller would be better than a flat tappet? any thoughts
***should I get performance flat top pistons and rings?
***I want to purchase a B&M shifter kit
***Do you think I should still add 383 Stroker Kit?
My goal is to do justice to my C3 Corvette above and beyond the stock 190 hp that it arrived from the factory with. I really appreciate everyone's help and support!

 

Welcome, slow down a bit with the parts cannon 😎. Do the headers and exhaust system then recurve the distributor and bump up the timing. Adjust the carb to suit. I think you’ll be surprised at the performance improvement. Drive it for a while and continue to research cylinder heads and cams ( you’ll get plenty of advice on this forum). Your next steps may require a torque converter swap and/or rear diff gear change. That’s a lot of labor, parts cost, tools and time. Establish a budget for the future modifications and a timeframe to accomplish it in. Do it in small increments and you’ll have less down time and avoid the all too typical “tear it apart and never get it put back together” routine that plagues many a DIY car projects.

 

The L48 came with dished pistons to lower compression, but you can bump up the compression significantly, without pulling the motor at all! Just about every small block head comes in two CC flavors or 'Cubic Centimenters", either 64cc or 70cc+. If you reduce the Combustion Chamber area, you raise the compression! The early Fourth Gen or C4 Corvettes came with the L98 TPI or Tune Port Injection and these motors had very small 58cc aluminum heads. I put these on my '74 L48 car with excellent results. It already came with an old Edelbrock Quadrajet Performer manifold and headers, but I added a Lunati Voodoo RV-4x4-Marine Camshaft that made most of it's power in low RPM torque. Make sure to check these heads carefully around the valve stem area, as some have a tendency to crack (but can be repaired). You can pick up a set of these heads for $500 or so. Add another $500 to go through them and your golden. I've tried the cheap Chinese heads and it didn't work out well for me (tho, others have had better luck). A set of LT1 beehive valve springs is a good add on too.

Dart makes the Iron Eagle heads in 49cc flavor, which would even bump up the compression higher, possibly 10:1! They go for $1,020 or so, fully assembled and ready to mount. You'd only have to remove the water pump, timing chain and radiator to put the new camshaft in. This is a relatively low budget build and meanwhile, you can get an '87-'91 bare GM Roller Lifter Small Block and start to slowly build that up, as a future replacement.

 

Hello 210ken, thank you for your time to provide a reply and great advice, I will slow down and take care of one modification at a time. The first thing I plan to do per your recommendation is to get my exhaust system installed then work on distributor recurve. I will let you know how everything goes with the first modifications. Thank you again for your help!

 

Hello F22,

Thank you for your time and help to provide some great information. I will definitely look into purchasing some better heads for performance upgrade.
I will be sure to provide an update on the progress of the L48 performance upgrades.

 

Start with what you have. A free flowing exhaust, and a tune, might wake it up a lot.

After that, the biggest thing robbing power is the low-stall RPM torque converter. The best way to fix that is to add a third pedal. Don't waste money on a B&M kit.

Find posts by @lars, and email him for his timing and Q-Jet papers. You may need to re-jet the carb to optimize the setup.

 

Hello Bikespace,

I really appreciate you taking the time to provide some good advice. I am going to get my complete exhaust kit install first then work on low stall torque converter upgrade. I am also looking to upgrade with an MSD ignition distributor kit. I will contact lars for information for timing and carb tuning. I am really looking
forward to waking up the L48 for better performance.

 

Hope you are keeping your original points distributor. Jeff at advanceddistributors.com in Minnesota can rebuild and recurve it based on all your engine specs. He rebuilt my carbed 84 C4 65 chevelle points distributor and also my 65 gto points distributor with excellent results!

 

Hello wilcar,

Thank you for providing a reply with very helpful information. I was planning to upgrade the stock distributor with a MSD distributor kit.

 

If no one’s been into the car for the past 50 years that’s a surprise. Once you start getting into it you may find a few surprises and that’s a common and potentially expensive thing to find out.
If you want more of a performance sound your mufflers will add the noise but not a lot of power in the range you probably will be driving in most of the time.
If engine is in good condition- not fouling plugs and smoking you should do a compression and leak down testing. Then you can determine if adding a cam or heads is worth it. It might be better to just pull the engine then build it to what you want otherwise it can easily come back to haunt you.
You should have a Th400 if it was an automatic new.They’re good transmission and had a low stall converter about 1500-1700 if I recall. Your cam,TC and differential gear ratio all need to match for the best performance.
The rear gear std with that car is a 308 whichever is not going to lite up tires unless you have torque and the stock engine with a few modifications may not make it if that’s what you want.
All this costs a lot and more today than ever before.
How you build the transmission and differential are critical to the level of the engine ignore or go cheap you will revisit it again.
Good luck do your research and put a lot of thought into it

 

Been there done that. My advice for a 300 horse mostly stock 350........Install an Edelbrock Performer cam. Keep the stock stall, gears, exhaust, carb and you WILL see 300 horsepower. Later if you insist,....put on the headers, but honestly for a 5000 rpm engine, you will not see that much difference.

Once you cross that line there is no end. Big cam needs high stall, gears, free flowing heads, better exhaust, better cooling, more fuel,.....then it gets expensive. You start blowing trannies and rears, half shafts, need bigger tires, etc........

 

All great advice above and given by the pro’s.
Just remember, everything needs to work together to put performance to the tires and onto the pavement.
Start by knowing for sure what gears are in the rear differential, a prior owner may have swapped them in the past.
Then start planning your compression, heads, intake, cam and every component in the engine to work with your rear end and transmission gearing.
Determine how you plan to use your car.
Some spirited driving, twisting mountain roads, highway cruising, a day at the drag races or occasional auto crossing?
If you don’t plan to do the rear differential now, just remember it was put together 50 years ago and there will be wear on the internal components, so make a plan and save to get it done in the near future.
Same with your transmission.
Does your plan include swapping to an auto overdrive in the future?
Plan ahead.
Since you want to retain the original engine, talk with a reputable engine builder and get a quote from them to go through the engine and make the necessary changes you want based on what your needs will be.
Good luck and keep us posted.

 

Hello GTR1999,

I really appreciate your reply to help and providing a lot of great information. I will get the engine tested first per your recommendation to avoid spending too much money up front and discovering surprises. You have given me some great advice and plenty to think about before tearing into the engine with parts. I am going to get
my new exhaust system with headers installed first and keep a few modifications at a time as money allows. GTR1999, thank you again so much!

 

Hello The Money Pit,
First, I want to tell you that the C3 in your Avatar looks amazing, the paint seems to have a beautiful gloss. I really appreciate you taking the time to provide me with some great advice from your prior experience from going down this route. Based on what you have told me, I feel that the 300-horsepower range is comfortable for me.
in addition to being able to hang to many of my stock parts. I am going to look up the Edelbrock Performer cam for add on. How do you feel about adding an MSD distributor kit or do you feel that I should keep my stock distributor and have the timing properly set? Thanks to you I feel that I can save a little money and be thankful with what I have from being able to go from 190 to 300 horsepower! Thank you again so much for your support!

 

Hello OldCarBum,

I really appreciate the detailed advice that you provided and for also taking the time out of your schedule to reply and try to help. I really love this forum, so much support and wisdom. I have been in love with the C3 Shark since first seeing the 1978 Corvette Summer Movie starring Mark Hamill. I am going to take your advice and get the rear differential and transmission checked along with internals. My goal is to only take the C3 on car cruises, carshows, and when I have a stretch of highway or road to get some throttle response for a spirited run, but no intended track or street racing. I will take me time and focus on one upgrade at a time as money allows. Thank you again so much!

 

GTR1999 gave you the best advice, do a compression test and see how worn your engine is.

Then set out the timing for performance.
Here's how:
https://www.corvetteforum.com/forums...long-post.html

Just drive and enjoy your new dream car for 6 months.
How many miles on your car?

Do you have a garage and tools to do the work yourself?


Regards Pete.

 

I agree with money pit. Been there, done that. I have a 375HP L48, possibly a little more. After taking back a couple of steps and looking where I was and where I am now in the project and the money I have dished out and what I expected as far as speed. I might have been better swapping my engine to an LS, but I stayed with mostly all original.

 

If your buying a distributor just get one from progressive ignition. Has app on phone, you can put any timing curve you want in it. At any rpm! Which can help driveabilty depending on your combo. No more weights or recurve this or that. I put one in my kids mustang. I also got one for Xmas for my C3. Would never go back, ever.

 

If you are comfortable with the points distributor, keep it.
Once you set the points and dwell correctly, you won’t see any performance gains swapping to an electronic or HEI distributor.
If you were building a beast, or adding an efi system then you could gain something swapping over.
When you contact Lars, ask him his opinion.

 

That depends on your combo, your ign curve. Depends on everything.
It's 2022. Not 1970. Having complete control of the ign is part of driveabilty.