glenga

OK. I have not posted for a long time and feel guilty about it so here is a few tips that I will share with those of you who wish to wake up that lazy L48. These are all things that I have done and I am now achieving much better performance. Have not done 1/4 mile yet.

The folllowing is designed to be done without any engine work and I thank alot of the members on this forum for their support. Of course these are just temporary measures until you can afford cam, intake, heads, etc. All work was done on a 78 vette with 3.55 gears

1) Set initial timing to 12-16. Mine is set to 12. Make sure advance is working properly. Use good quality rotor, cap & wires. I use Accel for cap & rotor. I use an Accel super coil however dont believe it does much to improve performance. Gap on plugs for 78 vette is .045. I have set to .035

2) Air cleaner - Definately use a K&N element. I have tried open element however this suffers once engine compartment heats up. Suggest using K&N with original single snorkel or upgrade to L82 dual snorkel. Cooler air is much better than underhood air for performance.

3) Original rochester carb is good if tuned properly. make sure secondaries are working. Easy way to find out is to take off air cleaner when enigine is at normal operating temperature. Stand at a spot where you cam see the secodary flaps & at the same time have your foot on the accelerator. Punch it to WOT for about 1 sec. You sould see the flaps just starting to open. If not then you may need to adjust tension spring.

4) Smog equipment & A/C rob power & add weight. Can be removed for off road applications.

5) Exhausts - Has been a big topic of discussion on this forum many times. I have run true duals with hi flow cats & mufflers. Performance difference was very noticeable compared to original set up. you will need to check pollution compliance requirements in your state. There are a few combinations you can try and still be smog compliant. Others here may have more ideas.Don't believe headers will make much difference with L48. I still run original manifolds. Some say that 10-20% performance increase is achievable with exhaust upgrade.

Thats it. Do all this and you should be able to actually spin the wheels when you floor it. 300hp with L48 is achievable with cam, intake and some head work. That is my next project.

P.S. What happened to all the oldies on the forum. I don't recognise any of the names any more

diablo kid

"I use an Accel super coil however dont believe it does much to improve performance. Gap on plugs for 78 vette is .045. I have set to .035"
Refferencing the above quote.
I have read that with a hotter coil a person can use a wider spark plug gap to take advantage of the more powerful & hotter spark. Maybe try .050 gap and see what happens.

NHvette

I'd agree - for an HEI system: larger gap .050 or .060 sounds right.
I don't think it will buy much, if it already runs OK.
Dual exhaust - yup big improvement to go true dual - no cats.
Headers to complement the new exhaust tubes.

Cam and intake - yeah , but replace the heads, not rework them.
The L48 heads have a large combustion chamber.
Replace with smaller chamber heads and get compression up
to get the potential ponies.

If you've got an auto - then a shift kit can add to the fun/tire chirping.

So, who do you remember here, Glenga ??
I've been here a couple years now. Not the oldest member, but
far from a newbie.

Gooday.

lostpatrolman

dont forget NAAAAAUUUSSSSS

redwingvette

Corvette Fever did an article back in 96 on how to get 26HP out of you L48 and keep it stock on the outside. It consisted of total reworking the heads, Crane Cam (H272), and going with flattop pistons to make up for the large CC heads. All the work they did was internal so it still would pass judging events. They claimed that on the dyno with stock exhaust got 326hp and with headers they gained about another 4hp

glenga

Thanks for the feedback. It is difficult to keep up with threads due to the time difference.

flood

my L48 is pretty respectable for being stock. I think having a manual tranny and a new gear in the back (3.70) made a bit of a difference.

I g-tech'ed it and it ran a 15.8 here at 4500ft ASL. That would be a low 15 at sea level.

I think dual exhaust is in my future. But the thing that is the most tempting is a Vortech kit. Fully assembled heads and an intake for around 700bux. Add a Cam and I should have quite a bit of power on tap for less than $1000.

Of course this is considered major work.

glenga

The problem I face is if I put any more power into it I don't believe I will get to use it often unless I take it to the track, however its always good to know that its there when you need it. There are alot of stupid drivers here that use the street to race. we have already had numerous driving fatalities this holiday season and its just started.

aussiejohn

Glenga,
I haven't seen you here before, welcome. It sure hurts when our antipodean friends say that they can get "heads and manifold for 700 bucks". What would that be in Australian dollars??? Without a doubt, the best bang for the buck on a L48 would be better flowing heads with more compression and it is cheaper, even out here, to buy a set of performance oriented late model heads, even cast iron ones if the budget is really tight. The main advantage of aluminum heads is that you can run about one more point of compression ratio than with cast iron ones. But then you're stuck with the stock, non performance camshaft.

The only real way to have a good overall package is to get the manifold/heads package WITH a camshaft designed to go with the above. Of course you will need a new set of lifters to go with the cam and why not throw in a double row timing chain while you're at it? Then the exhaust becomes the restriction, but a good header can always be added at a later date if the budget doesn't allow it at first. At least the engine doesn't have to be pulled apart again. Then you'll need to re-tune the carb once the headers are fitted.

By this stage, you should have 300 horses at the rear wheels and be out of pocket over AU$4000 . Is it worth it???

Only you know that.

Refards from Down Under

aussiejohn

BKbroiler

I started with an L48 in my car. Did mods similar to what you are discussing. Also added the stroker crank. Used the stock connecting rods (reconditioned). See my sig for specs and performance data.

TedH

Not 300hp at the rear wheels but I can smoke 'em into 2nd gear at will...

Alwyn678

Heads and a cam I found 041 Heads work quite well

glenga

Yes. heads, cam, intake all to be done next year. I would have done it sooner but I'm having too much fun driving it.

PS Aussievette: Thanks, I have actually been a member with this forum since 1999. I try and make the effort to be involved as much as I can in this forum but I tend to have my quiet periods. Cheers

KJL

Put headers on, advance your timing as far as she will let you but make sure you don't go over 36 degrees total with vac advance disconected. You would be amazed at how much snap you can add to your low end with a correctly tuned advance curve. My original 350 had Edlebock rpm heads with an the Performer intake, dynomax headers and a conservative cam and she made 260hp and 330 ftlbs at the wheels. I also installed a Transgo shift kit which REALY made a difference!! Make sure all 36 degrees of advance are in by around 2500 rpm. My initial setting was 21 degrees with 15 dregees mechanical advance. My vacuum advance gave my 16 more at cruise for a total of 52 degrees at cruise with vacuum advance figured in. If you get any pinging you will need to dial back on you initial setting till it goes away.

Good luck.

Boofers

This setup dyno'd 240hp, 295ft/lbs rear wheel.

Stock 1977 L48 (rated 180hp, 270ft/lbs flywheel) with:
Comp Cams H268
Weiand 8004 intake
Hooker Comp Headers
Dual 2.5" exhaust
High flow cats
Magnaflow mufflers
Richened up stock QJet
Flamethrower ignition coil
Set timing 36 degrees max mech advance at approx 2500RPM
3" drop base with a $3 paper air filter
fuzzy dice hanging from rearview mirror (good for at least 5hp)