Performance upgrades
 

I have a 1975 L-82 4-SPD and would like some advice on the following minor performance upgrades:
1. Best Intake manifold upgrade option (I have read that Edelbrock Performer RPM is a good choice)
2. Can I upgrade the M4MC Rochester Carb and re-jet it? Should I look at other options that may compliment the Intake Manifold?
3. Best option for performance distributor replacement.
4. Best option for High Ratio Roller Rocker Replacements
5. Best options for headers and an X-Pipe

I'll answer for #3 if I may: unless you are spinning the engine above 7k RPM the factory HEI is the best bang for the buck. Cheap and realiable with parts that can be had at any auto parts store if it fails.

Something to consider for #1 is Vortec heads and matching intake. Many options are limited if you want to keep factory hood.

My car is all stock so I can only really comment on what I have done to other cars, but a SBC is the same across the board. You have a decent base to start from, except maybe the rear gears (depends on ratio).

I got a '75 with a stock hood. The cowl on the 75 hood has enough clearance to run a performer RPM, with a holley. I use a 14" drop filter with a 3" element, plus the K&N airflow lid. Some other C3's have lower cowls, and cannot run the RPM manifolds.

Best headers are Thorley or Doug's Headers. Don't 'upgrade' the carb, get the car dyno tuned. The carb will be set up on the dyno for what the engine needs.

RE: Ignition there's a million choices but the GM OEM HEI is good. I use a Mallory Billet aluminum dist but it's based on GM's HEI.

Re: Intake, dunno if the RPM is the same height as the Performer or not. I have heard the Air Gap series is too tall for our hoods but never tried it. I use a standard Edlebrock Performer.

RE: Rockers here again, there's too many choices. I use Crane 1.6 Roller Rockers and a Crane cam.

Perfomance Upgrade Info THANKS
 

Goody, Rob75383, SanDiegoPaul,
Thanks a bunch for the prompt feedback!

1.Best Intake manifold upgrade option (I have read that Edelbrock Performer RPM is a good choice)
a.Sounds like Edelbrock Performer RPM with a Holley 750 is the right choice and will fit fine with a 75 hood

2.Can I upgrade the M4MC Rochester Carb and re-jet it? Should I look at other options that may compliment the Intake Manifold?
a.I’m abandoning this idea in case a rebuild does not solve all the minor Carb issues.

3.Best option for performance distributor replacement.
a.Sounds like just about any HEI types will be fine, so it will likely amount to the best bargain. I have a 3.70 Rear End and want to take advantage of the low end torque so I’ll be looking to lighten the centrifugal advance springs for even better bottom end performance.

4.Best option for High Ratio Roller Rocker Replacements
a.Looks like any one of many 1.6 options will work. Again it’ll boil down to best price.

5.Best options for headers and an X-Pipe
a.Sounds like Thorley or Doug’s.

Any other input that may be valuable?

Sounds like a camshaft is in order for any of the above parts to be of any performance upgrades. your factory cam will not handle a 750 Holley, I am afraid you would be wasting good money. If you want it to have some spunk, cam and heads first, you will be a lot happier.
I too own a 75, and I believe when I first got it my mower would probably beat it in the 60 ft.

Cam and heads and then go from there ( If you have a good bottom end )

Good Luck

:lurk:

1. Best Intake manifold upgrade option (I have read that Edelbrock Performer RPM is a good choice) RPM is a good all purpose manifold for the street.

2. Can I upgrade the M4MC Rochester Carb and re-jet it? Should I look at other options that may compliment the Intake Manifold?
I agree get it tuned, but that is becoming more and more difficult now days. Last dyno shop I visited new NOTHING about carbs. :willy:

3. Best option for performance distributor replacement.
GM's HEI is a good distributer, but get a recurve kit and adjustable vacuum advance for it. Do a search for other threads on the details of this, but for a few dollars its well worth it.

4. Best option for High Ratio Roller Rocker Replacements
I don't know who is best, but I would stick with a name brand.

5. Best options for headers and an X-Pipe
Dynomax makes good headers for a very resonable price. In addition to the X-pipe make sure to replace the whole exhaust with true duals and new cats. The exhaust on the 75 & 76 vettes were death to HP. Out of these mods, this is where you could probably get the most HP on a 75 (assuming everthing else is tuned).

Actually, the L-82 cam is pretty good other that the 114 LSA is a little wide for max power (but it does give a smoother idle and better vacuum).

3896962 Hyd. - 222/222 @.050" - .450"/.460" I/E lift - 114 LSA - 350 L-46, L-82

The biggest issue with a '75 L-82 once you open up the exhaust and intake are the crappy heads. Get a set of nice AFR 180's if you can afford them or other good aluminum heads and enjoy.

+1

The L82 cam isn't that bad for a mild build. I would probably leave it in there if the mileage is relatively low. No reason to risk cam failure on a new cam break in if you don't have to. If it was my car I would:

1) Install either some Vortec heads(budget) or AFR 180s
2) Edl RPM intake (either vortec style or regular)
3) 1.6 roller rockers (check for clearance and geometry)
4) Holley 750 DP 4779. Or vac sec 3310....I prefer DP
5) 1 5/8"x3" headers from any decent manuf.
6) Good 2.5" exhaust, x pipe and free flowing muffs.

All that stuff should get you in the high 13s and be reliable as stock. Ofcourse a cam swap would gain some serious power if you are willing to go into it that far. It all depends on what you want to spend and gain.

A few things I wanted to mention...
The RPM air-gap is the same height as the Performer RPM.

Either intake will not allow the use of a holley carb unless you plug the vacuum hole or if you buy the special fitting from edelbrock that will clear the rear fuel bowl.

A rochester carb will not bolt up the performer rpm manifold unless you have an adapter. Those adapters are typically an 1 in tall. Buy a factory LT1 style drop base air cleaner and you should be able to fit a 3 in. element along with the adapter. I say this because I use to run a sbc with the rpm manifold, LT! air cleaner and 4 in element.

Vortec heads are great heads for the money, but be careful. If your L82 is all stock, you have a compression ratio of 9:1. Slapping these heads on will put you in the 10.5-11:1. I truly believe you will have detonation problems due to the size of the cam.

Just something to think about... L82 shortblock + vortec heads + performer rpm manifold + 750 Holley DP is the main recipe for a 1970 LT1 engine.. I strongly urge you to change cams..

Phil Zell, Jason Staley, SteveG75, ajrothm, FRSTR90

Really appreciate all the suggestions so far. It’s helping to narrow the focus for this Winter’s upgrades. I’ll need to do a lot more homework but I’m getting a much better idea of the direction I want to go in. Thanks again to all for the info so far.

1. Best Intake manifold upgrade option. No one has mentioned anything negative about the Edelbrock Performer RPM and it seems that it will fit fine under a 75 hood with e Holley Carb provided a drop filter with a 3" element is used. That seems like a solid decision for me.

2. Can I upgrade the M4MC Rochester Carb and re-jet it? Should I look at other options that may compliment the Intake Manifold? That’s where my performance issues seem to persist with the stock L-82 after all of the grooming and tune up efforts I’ve completed so far. It lacks stock low-end performance that I should be seeing due to the Carb. (Car sat for a long time) But for the upgrade, many have suggested a Holley 75 DP but others (Gearheads/Friends) suggest that 750 is too much. A 600 CFM will be perfect. Any feedback/comment there?

3. Best option for performance distributor replacement. I have a 3.70 Rear End already and want to improve low-end torque even more. Not concerned about top end performance, so a recurve kit and adjustable vacuum advance for the OEM HEI Dist. seems like the right/most economical upgrade for the ignition since I’m targeting improvement from 1K to 3K RPM. Any details on recurv kits would help.

4. Best option for High Ratio Roller Rocker Replacements. Many 1.6 options will work. It’ll boil down to best price/quality. Would I really need to upgrade the CAM as well? I think I’d like to see how much improvement I get with the 1.6 Roller Rockers before moving on with the CAM. I think the issue may be that this will drive the Carb. CFM choice a bit.

5.Best options for headers and an X-Pipe. I already have a stainless dual exhaust system with Dual CATS but the previous owner did not install a crossover. I should see some improvement with the header upgrade but expect most of the improvement from my current status in the exhaust effort to come from the removal of the CATS and installation of a proper X-Pipe Crossover.

Right on, Phil...

If leaving the cam alone, I'd also leave the stock L-82 intake. I remember the stock L-82 intake I took off a 1977 L-82 I had years ago to put on a Performer. It was actually a fairly decent looking dual plane medium riser manifold.

Do the exhaust first - they now have some neat true X pipes for our C-3's.

Then consider new roller rockers as a way to effectively make your existing cam run with higher lift and longer duartion. By the way, that cam is likely pretty good as the L-82 motors actually got some decent performance parts to include cam and big valves heads...

Then tune your carb for the changes (likely will go up a couple jet sizes perhaps after all is done...?) and enjoy!

Thanks again to all so far for the help.

After carefully examining all the options, I’m narrowing the first pass effort for this Winter to detailing under the hood (lots of work) and some lesser cost performance options before I launch into cam, intake and heads for my 75 L-82. Beyond Headers/X-Pipe and 1.6 Roller Rocker Arms, which are a definite, I’m looking for more info on the following:

1. Distributor recurv data - There is a lot of info out there and I wonder if anyone has the real spring/weight scoop for best low-end torque and pull with a factory HEI Dist?

2. Quadra jet M4MC - Again, after grooming the car in the last few months, I know this is still an issue. As well as a standard rebuild, (which is necessary), I’ve found a place or two on line that claim to do custom rebuilds, changing the jets and metering rods to accomodate what your looking for. Again this would be low-end torque and pull. Any help out there for that type of info?

2, 3, and 4 are not necessary and a waste of money...nothing wrong with a Q jet carb but a GM 151 cam [350 hp cam} would be a nice choice and dependable.....