timgman

Right not I have a l48 with a single 2.5" exhaust. Tell me if this plan sounds good.

1 replace with true duals and headers
2 install 87 aluminum l98 heads (already have a lead on them for a good price)
3 upgrade the cam.
4 install a new intake
5 have someone tune/rejet my quadrajet.

Does this sound good?

where do I get a direct bolt-on true dual exhaust ? (best deals for a good part obviously)

How do I determine if my l48 is worth doing this to...

what Oil pressure does a l48 generally run at? mine seems liw at 25psi when hot.....

will a compression check tell if it's worth putting heads/a cam on?
What kind of hp would I be at...

well actually who cares.....
Will it move along in a halfway decent manner after these are done to it????

Thanks guys
timg

Durango_Boy

Your plan sounds just great. You should see a huge difference from the stock L48 motor.

You should for sure do both a compression test and a leak down test. This will give you a better idea of if your in need of a rebuild. That oil pressure reading is very common and not dangerous. It indicates worn main and rod bearings...common of high mileage motors.

Doing a complete rebuild will only add about $700 to the total if you have the block bored, new freeze plugs, cam bearings, rod bearings, main bearings, crank turned, and some parts and gaskets.

That would ensure a long engine life and you'll get the most out of the top end rebuild.

Glensgages

I think the L98 heads, with 58cc chambers, will raise your compression from 8.5 to approx 10:1 (ball-park?..... unsure of CR of your L-48 with 76cc heads ), about the limit you'd want for today's pump-gas
(I understand that SUNOCO is phasing-out the Ultra-94 grade..... I haven't seen it here in Floriduh since I moved here 15 months ago )
with a nice hydraulic cam, something-like .450"-lift and 220*-226* @ .050" lift, it'll make nice power while remaining below 5500 RPM, probably as-far-as you'd want to spin a well-used L-48 bottom-end.....

a free-flowing exhaust, improved intake and gears, and she'll run very-low 14s, possibly even 13s at close-to 100 MPH

neuroclast

My 79 is an L48, only a 383 now with 11.5:1 compression, and I can run 93 gas fine.

Glensgages

I was scared to run anything less-than SUNOCO-94 in my 10.4:1 iron-headed 355" SBC:
good-work!

Bowerss2

Corvette central exhaust seems to have a fairl deal on bolt on exhaust systems, i was thinking of geting a true dual for my 1980. good luck m8

timgman

Corvette central ..................

Thanks for the heads up.....

I plan on starting small.. first....

dgruenke

Corvette Central has the complete system, but they bolt up to exhaust manifold, not headers.

panic

Before buying my new 406 engine, i had an L48 procharged in my '77...the boy tried his best (i must say with some results) but i didnt consider sufficiently the low end ...story ends with the engine (and procharger) kicked out the engine bay in pieces...

timgman

Yeah, That's what I'm afraid of...... of course not using any boost might help me... but I'm increasing the CR on a fossil....hehehe

79L48

My 79 L48 runs 40 psi on any kind of part throttle up to high cruise speeds and 25 when hot at idle. Are you seeing 25 psi max, even at high cruise? If so, you should spend your money on freshening your engine. The rule of thumb I learned here is 10 psi per 1000 rpm. 75 mph in my car with 3.55 and an auto trans is 3750. Assuming you have a similar setup, you're too low on oil pressure at speed if it is only 25. My apologies if I misunderstood your post to mean you were pulling 25 psi at hot idle and things went up from there.

timgman

I'm thinking that either way I should put new bearings in it.. and at that point I can get a low hp 350 anywhere for 400 bux or so... so I may just bag the original and get something that's already stronger on the lower end....
I think I top out at around 38-40 psi at cruising speeds......
she has about 82 k on it and for a 77 350 that 3/4 of it's life-span prob....

jcurrie

I have an L48 that I changed over to dual exhaust. I went with Dynomax Cyclone Ceramic coated #86008. Then took it to the muffler shop and they built it from there back to the new mufflers. They put an H tube in just a little past the tranny so I could hopefully change it out later. Changed to an Edlebrock performer cam and intake. Rejetted to .074 but have run .076 (which I like better but haven't gone back to). I want to change the heads to 58 cc but don't know what will fit and work. I am pleased with it so far. Head advise anyone?

KevinK

I am in the process of doing the same. I have true duals, though they are custom, as I know a guy who knows a guy...and I have an aluminum intake, as the only two real power adders. It's a pretty large difference, really. I havn't dynoed it, and at some pount, I think I'll need to tear it down, to get the block bored .30 over, and put in new, stronger main bolts (just to be safe, lol). But anyway, with the added power, all I have really done is broken stuff, lol. SO watch out. SO far, I have had to replace my u joint, and my leaf springs are now in dire need of replacing, as well as the shocks. They just can't handle the added strain of harder starts. Just a word of caution.

timgman

The previous owner replaced most of the suspension parts...
a new fb monospring and shocks all the way around and new u-joints...
I'm more concerned about the th350... it's solid as it is but a few more hp migh be the straw that broke the camels back..............