1976 L48 Mod Suggestions

majortom75 · 03-18-03, 10:18 PM

I am buying a '76 4 spd L48. I would like to have 300-350 HP and torque. What mods should I make and in what order by expected HP gain. Budget wise, I'd like to spend no more than $1,000. I was originally thinking headers & conversion to true dual, but some past posts seem to indicate that there this not much low-end gains here. Any thoughts? Thanks for your help and suggestions.

vetteKID · 03-19-03, 12:37 PM

im on the same quest as you, a 300 horse L-48.

what i have been told so far is,
a well tuned Q-jet
performer manifold
Comp cams 268H .454 lift.
headers
2 1/2" duals (mandrel bent) with a cross over and some good turbo sytle mufflers.

they say thats a good basis to start from.

after that i think the next suggestion was aluminum heads.

Bob Chadwick · 03-19-03, 12:50 PM

This post is headed the same direction.

http://corvetteactioncenter.com/foru...threadid=25342

03-19-03, 01:42 PM

good luck on $ 1000 PREFORMER KIT $465.( MANIFOLD,CARB,CAM & LIFTERS) CLY. HEADS $1000. TIMING CHAIN $ 40. PUSHRODS $35. GASKETS $ 55. HEADERS (COATED) $ 225. OIL & FILTER $ 25 ANTI-FREEZE $ 14. TOTAL $ 1854. NOW YOU HAVE TO PUT TOGETHER AND THAT SHOULD GET YOU JUST ABOUT WHERE YOU WANT TO BE.

majortom75 · 03-19-03, 03:20 PM

I am alternatively thinking of yanking the engine out and putting in the GMPP crate ZZ engine (not this year, budget won't allow) but next year. Would it make sense in that case to do true duals with headers and freer flowing cats this year? Accd'g to NY, this car is exempt from emissions testing, but has to have a cat. Also, what is the advantage to ceramic coating versus non-coated?

03-19-03, 04:15 PM

I'm not sure but I think if you put headers on this motor they won't fit the zz you can check that. but if they do go for it. you'll get a little boost for the summer,it'll sound better. now the coated headers for one thing last longer (pain in the ass to change) 2: they keep more heat IN the exhaust witch makes them work a "little" better 3:they help keep engine compartment heat down again "a little" I've been using coated SS header for some years now life exp.went way up due to heat disapation and a protective barrier from the salt. and @ $4000. a set it's nice to get more than 2 seasons out of them!

majortom75 · 03-19-03, 04:37 PM

offshore:

Thanks for the info. I'll definitely check on the compatibility with the ZZ engine, and thanks for info on the coatings. I figured it was something along the lines on longer life. I'll probably at the very least upgrade the exhaust.

Jack · 03-19-03, 04:39 PM

If C3 from 71-81 ... One of the first things to do for more power AND economy is the easiest & cheapest. Go through the distributor. Make sure everything is in good condition ... then pay close attention to Lar's papers on vacuum & mechanical advance curves ... make recommended changes to the curve. I recall Lar's papers are archived here through knowledgebase ... and other sites. An $8 vacuum can & a $5 mech advance spring kit ... carefully dialed-in ... does wonders for cars that came from early days of anti-smog era.
JACK

Jack · 03-19-03, 04:44 PM

Quote:

Originally posted by majortom75
Accd'g to NY, this car is exempt from emissions testing, but has to have a cat

If no testing required, sounds like an excellent candidate for gutted cat(s).
JACK

majortom75 · 03-19-03, 05:12 PM

Jack,

By gutted, you don't mean a free flow cat, but literally just the shell of one, correct?

Jack · 03-19-03, 05:27 PM

Quote:

Originally posted by majortom75
Jack, By gutted, you don't mean a free flow cat, but literally just the shell of one, correct?

Correct ... only a shell ... merely the outward appearance with no heart. Most economic approach is use of old cat ... beat/break its honeycomb ceramic guts out with large long screwdriver & pipe ... go right through the inlet /outlet ... its a messy job but simple ... if you're real fussy, ya might wanna wear a dust mask. I've never done nor seen it done on a new cat ... dunno if new stuff breaks up as easily or may be more easy ... dunno?

BTW, a real neat trick I've seen is where the guy split the two shell-halves ... gutted it ... but welded in a length of thick exhaust pipe ... then closed it all back up. Lotta work. This because sometimes a gutted cat will resonate unpleasantly ... something to keep in mind as you proceed.
JACK

03-19-03, 05:28 PM

by gutted I mean just the shell. $20,000 fine.

majortom75 · 03-19-03, 05:34 PM

$20k. Ouch! Seems harsh for a cat. Does anyone have any experience with the free flow replacements? Any reccomendations?

Jack · 03-19-03, 05:43 PM

Regardless of any federal law ... different state/county jurisdictions have different laws & enforcement policies. Here in SC, there is currently NO process for emissions testing nor inspection ... zip. Here in SC, the only one who sees your cat on a routine basis is your neighbor's cat. I dunno what you can get away with in NY, MA etc ... only what others here suggest is possible.

For instance ... I understand it maybe legal and is routine practice to scalp event tickets in NYC. Not so here in SC ... an acquaintance's son was busted Monday by SLED for trying sell two Busch race tickets for $10 above face value ... this happened in front of track ... within view of his family & friends. As I said, different jurisdictions ... different laws ... different enforcement policies.
JACK

Ganey · 03-20-03, 08:23 AM

Ex. is first if your ex. is stock single. See Why Exhaust is problem for HP on 75-81
what many refer to as my Exhaust topic.
http://www.corvettefaq.com/c3/ganeyexhaust.htm

Next is cam, HE268H is a good start for 4 spd. & max. for stock valve springs. Intake has to come off so is a good time to intake.

vetteKID

You have seen this before, yes after this is heads, though Al. is not necessary, i.e. optional.