I'm not an engine expert, so I need input from all performance guys out there. I have been in the process of restoring a 74 convertible L48. This engine was only rated at 190 hp and as far as I can tell it is stock. I'm not interested in making a race car out of it, but I would like to get the hp up to the 300-320 range and it still be a good daily driver. Can someone(s) suggest what combination of specific parts I need to accomplish this?


Thanks in advance for your expertise!

JM

 

No expertise here, just an opinion.

More cam, better heads, open up the exhaust and you should be in that range.

Can someone give him a link to Bryan's car page? Plenty of dynoed combos there.

 

And here's your link. http://www.ryanscarpage.50megs.com/combos1.html

 

An engine is an air pump. The easier it is to get the air in and out the more HP it will make. The stock heads are poor at best and the cam is a dowel. The stock iron exhaust manifolds can use some help also. A decent set of heads with a cam upgrade and headers. A decent intake and a good dual exhaust and you will be in the 300+ HP range.

 

Thanks, guys for the link. I have been looking over the combos and am leaning toward #52. Is the primary difference between the L82 and L48 engines the heads? Are the cams different as well? Just curious as the L82 I believe is rated at 270hp.

Thanks again,
JM

 

The cam, heads and intake were different on the L82. The L48 was usually 2-bolt mains and the L82 4-bolt. The L82 had a forged crank, l48 had cast crank. Also the carb was configured a little differently.

That combo you're looking at has pretty high compression for the power it's putting out(not very efficient). I basically have combo 1 and am very satisfied with it. You wouldn't have to get very expensive heads. A pair of iron vortec heads are by far the best bargain that I've heard about.

 

There's little significant difference in heads.
The primary "performance" difference is camshaft and compression ratio ... L48 has smaller cam & low comp "dished" pistons ... L82 has larger cam & higher comp "flattop" pistons. The method HP was "measured" and "reported" changed over the years.

Reality check ... in all actuality, if you run ANY year OE L48 on same engine dyno with open headers ... and duplicate each ones ignition timing ... all OE L48 will make about 275 HP. For example ... both 71 and 75 OE L48 share the same cam & pistons ... only significant differences are tuning & exhaust ... and the way HP was measured & reported.

 

Any inexpensive Flattop pistons and inexpensive Summit cam kit P/N K1103 and felpro P/N 1094 head gaskets will put your 74 L48 just inside the 300HP range.

 

Thanks to all who have shared their insights to my question. From what I have picked up so far, the following is what I'm now leaning toward:

Summit Vortec heads PN SUM-151124
Summit Stage I Intake (for vortec) PN SUM-2206818
Possibly some flat top pistons

My question at this point is what cam to match up to the above? I want a pretty smooth idle at stoplights, yet enough performance to pass someone on the highway when I need to .

Suggestions welcome.

JM

 

To accomplish what you want, it will be far more cost effective to simply buy and install a crate engine. I have a car with a 350 300 gross horsepower engine and replaced it with a GM Performance 350HO with 330 net horsepower...plus I added fuel injection instead of a carburetor.

When you figure shop time and labor, the fact you have to assume you need to bore out the engine which requires new pistons, plus the other additional hi-po parts required to turn that L48 into a 300+ hp engine, you're spending more than what a crate engine will cost that will accomplish what you want.

Add to that the new engines, due to improved casting techniques, weigh somewhat less than your original, and come with a warranty, makes the decision easy, at least to my mind. You can either sell your original engine, or save it if originality is important in case you decide to reinstall it.

 

I have an comp cams XE 262 cam. It has a small lope to it, not much though, and pulls pretty hard from idle to 5500. You don't have to change your torque converter, and this cam also makes plenty of vacuum at idle(power brakes and power steering work fine).

I have and L48 engine and it was fun to rebuild it myself. IT'S NOT THAT HARD TO DO!

 

Thanks to everyone who contributed to my question. Based on the post by RoughRider, I am on whether to go with a crate engine or not. I may go with Seth's advice and try to rebuild it myself with my dad's help, who is an engine person. It may be a good learning experience.


Thanks again,

JM

 

For what it's worth.

My car came with a new motor when I bought it. Just a regular ol' 350 long-block. Probably rated around 200hp.

I too didn't want a basket-case, head gasket burning, drag car. Just a nice, beefed up small block capable of safely going on long road trips & a nice streetable daily driver when the weather's nice.

So, I put in:
1. a nice mild/ slightly lumpy cam.
2. Edelbrock EPS performer alum. intake manifold
3. Edelbrock 1406 600cfm performer carb
4. Stans Tri-Y headers
5. True 3" dual exhaust w/ dual cats
6. New Distributor (machine shop dialed it in).
7. New Spark Plugs
8. New Spark Plug Wires
9. Took off the A/C

It now can roast the tires at a stop light and even chirps the tires when it goes into second gear...It's an automatic BTW
(it could never spin the tires before, even when I would try and power-break it).

The above mods were all very easy & match well with eachother. Anything else (in my opinion) would cause me to want to change out the rear end, get a new tranny etc etc etc...I wanted a car that earned the name "sports car" and not just sporty "looking" car. I feel my mild mods did this well


Good luck!

 

Ryanscarpage !! WOW Great Link !!!

 

Depending on your budget, I'd look into a crate motor, maybe a 383 stroker and be done with it. Before I would start installing aftermarket parts such as heads, cam, intake, etc. I would do a cylinder leakage test. I would hate to see you replace all these parts and then find out you need a complete rebuild. If you need to rebuild the motor, I'd just buy a crate motor, 383 stroker, install it and be done. That way you can keep the original motor if it's numbers matching on the side to sell with the car if that day ever comes.

 

Summit Vortec heads PN SUM-151124
Summit Stage I Intake (for vortec) PN SUM-2206818

vey good start... I would get a 268 comp hyd cam...

Or if you want to spend a few extra bucks... hyd roller cam...(gm HOTCAM) would be a good street cam and be worth another 15-20 rwhp over standard hyd cam.

hooker headers.

2800 or 3000 stall converter

and holley 650 double pumper or a 750 vacuum carb.

You should make about 300 to the rear wheels and run with a ZZ4 for less money.

 

As long as you're looking at Summit, check this

http://store.summitracing.com/partde...w=1&N=700+150+

Nice upgrade, very streetable around 400 HP, heads will support 500 HP, don't let anyone tell you you need larger intake ports. Very reasonable cost.