MBrianB

What should be done to up the HP of a '75 L48 4SP?

Other than a LS1 Transplant?

Cam, intake etc???

I know this is a lump in the stock configuration but without going too deep into the block, are there some suggested mods to meet it get out of its own way?

Dynra Rockets

The recipes are endless. There is no 1 route.

A dizy recurve, cam and headers would probably be the least expensive but then you are still saddled with very low CR and poor flowing heads.

HP is addictive. You think now that "all I need is another 20-30 hp and I'm good", but it doesn't end. For least cost and most driving time think about the long term. A crate engine may be more cost effective.

R

fede

I have a '75 and replacing the engine now but when I considered upgrading my existing one the idea was:

- True dual exhaust with headers and cat-delete
- New heads and cam
- New (Edelbrock) intake and possibly carb (quickfuel)
- Recurve and tune

That could easily double the HP but ended up buying a dressed crate engine in the end.

derekderek

1 point of compression is worth 3% gain in power. You change to a smaller chambered better flowing head, cam and exhaust and you won't feel the difference between that and the same top end on flat pistons. Now, if engine is tired and rings are worn, this is a different story...

dochorsepower

I disagree. Get rid of those 882 heads. With modern technology heads, a performance cam and a good tune the engine will feel alive.

The Punisher

So what head and what cam would be best?

Calibear2003

You can gasket match the intake to the heads along with a small RV type cam. In the past, guys put on a set of 305 601 heads for cheap performance. The 601's were the high flowing heads in the mid to late 80's that came on the L69 optioned engines. I believe that engine was rated at 190hp vs the standard 305 of 165hp. Another trick was to unshroud the chamber and install larger valves if they were going into a 350 application.

MBrianB

Thank you! This is the kind of information I was looking for. I looks like the '75 was more than just de-tuned. CR, heads and cam were all involved in making a good engine a poor performer and a real lump.

Calibear2003

Yes indeed!!! The 1975 year was the most gutless of all years. However, if you had a nice sounding exhaust system, they all sounded mean and great. I remember reading that if you were to simply (lots of work) gasket match the heads to the intake (preferrably and edelbrock), clean up the heads, small RV cam and add headers. That engine would see 350-360hp on an engine dyno. This of course was always thru high flowing headers, no accessories and the most breathing of air cleaners available to man kind. The same way they would run and rate them back in the 60's thru 1970. You can turn the old L-48 into a L-82 stomping machine very cheaply.

stingr69

Some GM Vortec heads would wake it up nicely on the cheap. Need an intake to match those heads. Get a cam designed for a higher RPM torque peak/higher static compression ratio and just fine tune the rest. Done.

derekderek

I was saying ditch the heads. But 9:1 with dish pistons won't be noticeably less than 10:1 with flat ones. With 64cc vortec or aluminum heads. Don't go 58cc, cuz then you can't use flat pistons later.

Calibear2003

I forgot about the Vortec 906/062 heads from the late 90's along with an Edelbrock Performer 2116 intake. Great catch as I forgot about the Vortec's which was really bolt on power

dochorsepower

There are companies that make heads with Vortec type chambers and ports but are interchangeable with early manifolds and valve covers. Do a search.

Dynra Rockets

?? I have 58cc heads with 4 eyebrow flattops. 11:1 cr. No issues.

cv67

edit:see you dont want to go in the block
whats your budget?..a port match/rv cam will not get you anywhere near 350hp sorry

https://www.corvetteforum.com/forums...low-heads.html

lvmyvt76

replace it with a 383!

gmcman52

I have a 75 L48 that I have owned since 1985 that had 165 HP. Now it's bored 30 over, mild cam, Alum intake with 650 Holley carb,stock heads with Hooker headers and 3.70 gears and all that it could mustard on the dyno was 204 HP at the rear wheels. Not to bad but at what cost. Now I'm looking to replace the motor with a create motor ZZ4 350/355 or the next unit up with alum head listed at 385/385. If I had to redo it all over again I would just replace the complete motor more power and less work