My 1974 350 L82 does not make enough power. The engine is rebuilt to stock specifications but is too friggin slow.
I appreciate suggestions for hop ups that produces substantial power increase without engine teardown.
I was thinking ignition, carb and exhaust mods but wanted to know what works and what does not work before I start messing with it. :D

 

Seventies vintage Corvettes are heavy and there's no way you are going to get a "substantial" increase in power with only external modifications.

About the best you can do is disable the inlet air heaters and place light springs in the centrifugal advance mechanism. Don't know the particulars on your exhaust system, but if it doesn't have 2.5" pipes and low restriction mufflers, you could use them. Backdating to the earlier 2.5" manifolds can also help. Be thankful you don't have a '75 or later model with a single catalytic converter. That cost about 40-50 HP.

You should also review your gearing. Don't know if your car is an automatic or manual, but a shorter final drive would definitely improve acceleration performance.

Internally the L-82 has decent heads, inlet manifold, 750 CFM Quadrajet, and a good cam, but the CR is only 9.0:1 because it was designed to operate on 91 RON fuel, and the combination of emissions and low octane fuel requirment also dictated a lazy centrifugal curve and probably less than the optimum 38 degrees total WOT timing - the sum of initial plus maximum centrifugal. The entire ignition map is calibarated emissions so a quicker centrifugal curve along with more initial timing so the WOT maximum advance is in the range of 36-38 degrees would really wake up the engine across the entire rev range.

Duke

P.S. If you have specifications for your initial, centrifugal, and vacuum advance systems, post them, and I can give you more specific guidance. Also, what octane fuels are available to you in Sweden - number and rating method - research? motor?





[Modified by SWCDuke, 6:44 PM 4/29/2003]

 

Thanks for the reply Duke.
It´s an auto car with air so the gear is 3.55. Don´t want to change that.
I´ll look into the ignition mods. I was thinking 12-14 initial 36-38 total all advance in by 2500rpm. How´s that sound to you? Would I be needing some mods to the carb as well if I change the ignition curve to a quicker one?
The best pump gas we can get here holds 93 octane (RON+MON/2)
What is the highest static compression that an engine like this can manage on pump gas?

 

How far would you be willing to go?, tuning with new ignition parts (stuff like changing springs in the distributor) can give you some power, but its not like youre gonna get serious gains from it. Headers definitely can wake it up, but dont expect neck-snapping acceleration or a night/day difference.

You could change the cam and get whatever power number you want, assuming the stock heads are good for power. (i dont know if they are or not)

 

The ignition curve you suggest is excellent. The engine was designed to operate on R+M/2 87 octane that we call the Pump Octane Number (PON). Also, be sure the vacuum can provides full vacuum advance at idle vacuum and sees full manifold vacuum at idle. If it has TCS disable it. You want vacuum advance all the time, but the can may not be ideal for full time vacuum advance. With 93 PON fuel the engine would probably take about 10-10.5:1 without having to slow the advance very much, but it's probably not worth going through an otherwise good engine just to raise the CR.

A 3.55 is plenty short for a Turbohydramatic.

Carb tuning might be beneficial once you have disabled the inlet air heat stove and retuned the ignition map. Once thing you can do is modify the secondary linkage to open the rear throttle bores quicker. This can really aid SOTP response. You should get the Quadrajet book from HP books.

Duke

 

I improved my 1980 L82 with no internal mods at all! I did howver replace the L82 motor with a much improved ZZ4 motor.

The L82 is old tech. It was not bad in it's day, but the cam is the biggest limiting factor. I've had the car for 17 years and carb, timing, etc did improve performance, but not a lot.

I went with a new motor because of the roller cam. Wow what a difference. Lot's more torque, better mileage and it's a real sleeper.

Dave

 

Hello fellow '74 shark driver,
G-tech makes a couple of cheap accelerometers that can be used to measure perfomance changes - easier than finding a 1/4 mile drag strip. This is a great way to learn tuning effects without much investment (dynomometer time).
First get your distributor dialed in including vacuum advance. Then you can try a few little tricks like 1.6 high ratio rocker arms (~$75). A "new" Edelbrock performer or Wiend intake (~$150) - yes they do make small improvements over stock. Also a set of good headers (~$350) - Doug Thorley or Dynomax - with a O2 sensor bung welded to colloector. Now in that sensor bung belongs a good O2 sensor for a mixture Air/Fuel indicator and I recommend Edelbrock (~$150) - this is the modern way for carb tuning.
Engo, if your on the learning curve this should the place to start before installing expensive high performance engine parts and not knowing kind of results to look for. It can actually be a fun and technical hobby.
All the little improvements can add up - just look at how NASCAR gets 500-600 HP out of a small block under restrictor plates.
Almost forgot, K&N makes low restriction filters - an easy place to start - and make sure the cowl induction system is functional.
Plenty of good books on the sb chevy and I'd like to recommend my favorite by David Vizard (the Wizard): How to build Max Performance Chevy small blocks on a budget. Good Luck. :chevy

 

Thanks for all suggestions. I am not a newbie to modifying engines, been doing it for over 20 years, it is just the CSB engine that is new to me.

I will do the ignition and carb mods this year.
Right now I have a stock points distributor (however not Corvette original). I don´t think it is a good idea to start messing with it. I like the Mallory distributors but they doesn´t seem to have one for the Corvette, with mechanical tach, vacuum advance and breakerless.

Can anyone recommend a good aftermarket breakerless distributor with vacuum advance and a connection for mechanical tach? I see there is a MSD distributor but it requires a MSD control box too and I feel that is an unnecessary expense considering my goals with this car. :)


[Modified by Engo, 7:28 PM 5/11/2003]

 

What's your basis for this statement? ]

The Delco single point distributor is just fine and is easy to modify, but since it's over 25 years old a good overhaul/cleaning/blueprinting/greasing would be in order - check that the shaft bushings are snug, shim up the end play to two to seven thou., install a new snug fitting wobble free breaker plate, and use the 28-32 oz. breaker arm tension points if you plan to rev over 5500.

Giving your original distributor a good going over will be much cheaper than buying an aftemarket distributor, which will very unlikely have a suitable igntion advance map, anyway, so it will require rework.

Duke

 

putting in a higher stall speed convertor will make a world of difference as this is what we did when these cars were new to get them to accelerate quicker. if you do not want to spend the big bucks for a aftermarket convertor one out of a gm V-6 with the same trans will help.

 

Duke.
The basis is that I have been down that road before. The distributor I have now is old and looks worn. Eventually you find yourself replacing everything in the distributor because of worn down parts. I know that a points distributor in good condition can function as well as almost any kind of distributor. But a brand new breakerless distributor will cost about 200$ and I think that is a fair cost for having it brand new and not have to worry about points wearing and dwell changings in the future.



[Modified by Engo, 8:25 AM 5/12/2003]

 

It's your money, but assuming the shaft bushings are not excessively worn, the single point distributor can be blueprinted for about 50 bucks in parts. I've been stranded at least least four times in the last 30 years by electronic igntions that suddenly failed with no warning. A point ignition has never stranded me!

Duke

 

The L82 is basically the same as the L46 350/350 (gross hp). I've got about 100,000 miles each with the L46 and the L82. The whole personality of the engine seemed to change without the 11:1 compression. By the way, Chevy pads the compression by 1/2 point to account for expected carbon buildup in the combustion chambers. The same 11:1 pistons are rated at 10.5 when purchased from TRW. I believe the same is true for the 9:1 pistons being only 8.5:1.

I don't remember if the L82 has the same 2.02" valves as the L46, they may be smaller. The L82 combustion chambers are about 76cc's for the L82 instead of 64cc's. Changing to the smaller 64cc heads and making sure you have 2.02" valves will really wake the motor up. I put 64 cc angle plug heads on a stock L98 (85 Vette) and it made a very big difference. The car ran fine without pinging as long as I used 91 octane [(RON+Motor)/2] fuel. Cruising mileage was also up a couple mpg's as a nice byproduct of the higher compression. I greatly disliked the L98 because it had the personality of a truck motor - good low end grunt, but the engine was through revving by 5000rpm.

I often hear that the 2.02 valves are too big for the street, I have never believed this to be true. What little difference there may be at low rpm’s is more than offset by the vastly superior breathing at the higher end. They could still be made to idle nicely at about 800 rpm and trundle about town at 2000rpm if I wanted. Small port heads are great for someone who never sees above 4000 rpm. This probably isn't you since you are looking for more power than the respectable L82 already puts out.

Chuck

 

Ok. I got to borrow a friends points distributor that already had a suitable advance curve. It made a big difference. The engine runs more smoothly and feels more reponsive. However, it still lacks both low and high rpm power but has a decent midrange. I can understand the lack of low rpm power due to the engine/cam size but I am a surprised that it doesn´t wake up at higher rpm (+4000rpm). I would expect it to pull strong to at least 5500 rpm.


[Modified by Engo, 4:29 PM 5/22/2003]

 

what kind of budget do you have?
enough for new heads and cam?

 

It´s not a budget issue. It´s about time and convenience.
Original cam and heads seem to be fine according to some.
As I understand from the information I have so far the design shortcomings of this engine is a too low static compression for the cam/engine size as well as a stock tune up with focus on emissions rather than performance.
As I said from the start of this thread, I don´t want to dig into the engine. Only external mods.
;)

 

i consider heads and cam mods i can do without removing the engine, external.
AFR heads a matching cam, and electronic ignition(re-curved), with headers and a high flow intake will bring power up around 400hp with no mods to the short block assuming it is in good condition. :cheers:

 

yea sure Matt, but a heads, cam, intake, header swap isn´t done in a lunch break. it would take me several weekends doing that, time that I rather would spend driving the car.
Headers might be an option I consider doing though. :thumbs:

 

Engo,

For the power you are expecting your engine is starved for air. Headers will help a little, but getting the bad air out doesn't help much when you aren't getting enough good air in. There were sound reasons guys like me hated the stock engines of the 70's and 80's. They were strangled and left with too little compression to make much power compared to previous engines.

In the scheme of things, changing heads and cam really is fairly modest surgery. But you are not going to get much success finding a "snake oil" miracle product to do what you really want.

Chuck

 

In that case, just buy a new crate engine and have a pro install and tune it. As others have already said, external mods can give some improvement but it sounds like you are looking for more than a little. If it's "too friggin slow" now, bolt on's can make it less slow but don't expect fast.