MrJlr

I'm riding the fence on crate motor or having my rather tired L48 rebuilt...

Numbers matching but it's pretty much stock...

So here is the question:
If I used my original heads and block, have the compression ratio bumped up, a bit of cam and head work, is 375 - 400 HP possible ?

Thanks in advance!

MelWff

I dont see it going that high, low 300's at best. Without different heads you arent going to increase the compression much and I'm sure you cannt go too radical with the cam because you are too restricted elsewhere. Read this link

http://forums.corvetteforum.com/c3-t...o-numbers.html

1977L48

i would say for that power number get a crate engine, that way it has a warrenty, and you know what you are getting, that way you can store your original engine for a rainy day!

AirborneSilva

Just my opinion but I'd put away your numbers motor (mine is tucked away safely), and build another motor. You can piece together the main pieces from Craigslist such as block and heads. You are going to have to do machine work to your numbers motor if you build that so put that money towards a motor that if you grenade it then you still have the numbers motor if you ever want to sell your Vette...

Commodore

If numbers matching is important do a rebuild with flat top .030 over pistons, change the intake for one that breaths a little better, sweeten the carb and throw in a 4 bolt mains lower end kit. Add exhaust headers and a free flowing exhaust if your haven't already. Your gain will be noticeable and the reliability of your engines internals will go way up but the rebuild will not likely net you anywhere near 375 HP for your time and money. For a few bucks more a 375 - 400 HP crate gives you the four bolt mains, better pistons, a free breathing intake, re curved and updated distributor, considerably better flowing heads and a better cam profile and valve train.
If I were yanking the engine and wasn't interested in a NCRS top flight judging experience I'd not be returning that L48 to its original home .
RB

MrJlr

Sound advice from all - thank you....

Guess I'll stick with the crate idea...
I'm just worried about accessories not mounting up right with alum heads and non-stock block....will my headers still work, etc.....

1977L48

these are all great questions to ask the company who you are looking at buying the engine from, the only concern i would really have is if the intake they supply would fit under the stock hood.

7t9l82

i wouldn't put much stock in the numbers matching motor thing and its value, on a 70's small block . i do agree on a crate engine being the best route.

dochorsepower

Either way, don't put those stock heads back under your hood. A hydraulic roller cam is also a significant improvement whether in a crate engine or retrofit.

jb78L-82

Car Craft did an article a few years back with an L-82 changing the heads, Carb to a holley, and cam and the L-82 with a slightly higher compression ratio than the L-48, 9 versus 8.5, did 414 Gross HP which is how the crate engines are rated, NOT Net or RWHP obviously. You could get 350-375 Gross out of your L-48, all things being equal. Just an FYI.

CaseyJones

My original L-48 was toast with spun rod bearings. I bought a stout short block assembly (4 bolt mains, forged crank, steel rods, 10.5:1 with 76cc heads hypereutectic pistions), added a Comp Cams 268H cam and kit, bought some early L-82 heads and had them reworked, used an Edelbrock Performer under the original Q-Jet carb, added Hooker long tubes and true dual exhaust, double roller timing set, and a reworked Mallory HEI distributor. It's kinda old school but it sure runs good. Very satisfied, even with the automatic and 3.08 gears. I didn't want a racer but just a good cruiser that I can take on a long road trip or to church on Sunday. Horsepower estimate: enough for me.

augiedoggy

Sounds like my build... 4 bolt high nickel block .30 flat tops and180\ 64cc dart heads 9.6:1 268h cam performer rpm intake with edelbrock 600 Carb, hei and obx headers\sidepipes... still on the engine stand.
I also decided to store the numbers matching 2 bolt main L48.

Tim H

Not with those heads.
But the block is fine, I could build 400 horse easy starting with the L48 block.

GOSFAST

The HP numbers you have in mind are within reach.

Couple items, first, built as a 9.6:1/9.75:1 unit on the (350") "flat-tappet" platform will put you in the 360 HP range, this would be with a "lightweight" piston (Ross) and a 1/16" ring pack.

Add a retro-hyd roller setup and you get much closer to 400 HP. All this can be done with keeping the entire build 100% stock-appearing AND having it as a "full" roller setup including the rocker arms. Comp's "Pro-Magnum" rockers fit under the factory covers with a single V/C gasket!

We've handled a bunch of these type builds over the years!

(Add) Just pulled one off the dyno, 355", L-82 "flat-tappet" cam (224*-.450"/.460"-114LS), Ross 9.75:1 pistons, stock heads (2.020"/1.600", no porting), and factory intake. Made 360 HP @ 5800 and 385# Torque @ 4100. The retro-roller alone would have brought that number to near 400 HP. We were NOT "chasing HP" on this unit, it "was what it was", customer was very satisfied with the end result!

Thanks, Gary in N.Y.

P.S. There are a few "pro's & con's" with a substitute powerplant, the most obvious is the ride is NOT original, you will do no "judged" shows. I would not be concerned with "blowing-up" the original block, this is a stretch, if it's built correctly.

1977L48

if this changes anything, i remember an episode of my classic car and the host said, "you know you can restore a car many times, bringing it back to near new, but a car is only original once, and you will never it get that feeling back". thats why i vote for crate engines. it is original, why mess with that

AGVI

Buy this, be happy.

350 HO

http://www.jegs.com/i/Chevrolet+Perf...10007/10002/-1

AGVI

http://forums.corvetteforum.com/c3-g...-wondered.html

cardo0

It reads like someone else will do all the wrenching on this car. Unless u have a shop u have a lot of confidence in go with the GM crate of your choice and budget. That way u will get a warranty that's good also.
Been burned too many times to trust all the work to another shop. Most small time shops are interested in profit not quality and want to joy ride the car also before u get it.

Good luck,
cardo0