L48 engine rebuild question

[Steve L.]

I just pulled my 73 coupe engine. It seized by sitting for 15 years. I want to rebuild it over the winter. So I'm sure that it'll need to be rebored. It's from my "new" 73 that I bought in 73. It's all numbers matching and I'd like to keep it that way.

However, when I rebuild it should I consider beefing up the HP (195 is pitiful) by stroking or whatever -without changing the heads or carb(visible items) or just accept it and rebuild to factory-presumable oversized (0.030)pistons.

Steve L
73 coupe

[Duke W.]

Re: L48 engine rebuild question

The best way to improve performance is to install the L-79 or L-82 cam. The former will be a little torqeyer and the later will make more top end.

Pocket porting/port matching the heads is also a good idea and will improve top end power about seven percent regardless of what cam you run, and increasing the exhaust valve seat to accept the 1.6" valve is worthwhile according to simulations I've run, especially with single pattern cams like the above, but retain the 1.94" inlet valve. I'd recommend OEM or equivalent replacement parts for everything else.

Visually, everything will look the same, but if you ever do a PV with a SHP cam it will be detectable from the idle quality, and you will fail.

You didn't mention what transmission you have, but the cam change will work best with a manual.

Duke

[Joe L.]

Re: L48 engine rebuild question

Steve-----

Basically, the bottom end of an L-48 engine was not designed to support the kind of RPM that 60's and 70's Chevrolet SHP cams, flat tappet hydraulic or mechanical, produce their maximum horsepower at. That's why Chevrolet used forged pistons, forged crankshaft, specially-prepped connecting rods, and high RPM harmonic balancer on the L-46 and L-82 engines (actually, the L-82 is nothing more than a lower compression version of the 69-70 L-46).

If you don't intend to upgrage the bottom end of the engine (which gets expensive), then I'd recommend using a modern, dual-profile, retro-fit hydraulic roller cam kit.

Using one of these, you can keep your bottom end basically stock. However, an upgrade to hypereutectic cast pistons and ARP Wave-Lock rod bolts would be advisable, especially if you're rebuilding the engine at the same time. You can continue to use your stock connecting rods and crankshaft, suitably serviced, and don't really need to replace them.

I would recommend a Speed-Pro CS-1071R hydraulic roller camshaft with Speed-Pro retrofit hydraulic roller lifters. Special length push rods, camshaft thrust button, and camshaft thrust bearing/washer are also required.

This camshaft, with your other stock components including your 1.94/1.50 heads, will produce power levels exceeding the L-82 and will do so at 5500 RPM, maximum which is within the limits of the basic L-48 bottom end. Producing higher-than-L-82 horsepower at lower RPMs is also a bonus inasmuch as the lower RPM maximum power is much more "usable" for street operation. Truly, the best of all worlds. Why didn't Chevrolet do this in the first place? Simple; they didn't have dual profile, hydraulic roller cams in the 60's and 70's. But, you have them available now. And, externally, no one will be the wiser that there's one in there.

[Edward McComas]

RE: Rebuild Alarm Horn

Steve;

Another possibility is to pull the original engine and store it somewhere safe. Then build the kind of engine you want using a non matching numbers block, etc. Three advantages to this approach are: 1) You still have the original engine, which is unmodified, 2) you won't take a chance (however slight) of damaging the original engine beyond repair (rod through the side of the block, etc., and 3) you can build exactly the engine you want, with the horsepower you want. You could get a crate motor and save yourself the effort of a rebuild.

The original engine could be rebuild at a later time, when and if you decide to do an original restoration.

[Jim T.]

Re: L48 engine rebuild question

This is what I did to my original owner 70, installed a ZZ1 years ago and really enjoy the extra performance, gas milage is pretty good for a performance engine like this. The removed 350/300 is still sitting in the storeroom of the garage. The DEC issure of Chevy High Performance has an article about the GM crate engine 350/330 which would require the special bolt pattern intake becasue it has the newer higher HP heads on this engine.

[Steve L.]

Re: L48 engine rebuild question

Thanks all for the response.

Reading through the options is interesting. But I think that the only option is to rebuild the engine to factory.

The only safe option is to store the original engine and drop a crate engine in. Although it's only a lowly L48, I've had it for 30 yrs and I would be disheartened if it threw a rod and broke the block. But it would be fun playing with a crate engine.

But, I betya that a lot of vettes started like this and then something happens (divorce, deaths, health deteriation whatever), the car gets sold, the original engine gets separated, then lost, and bingo, the vette has lost it's originality. And although it's only a '73, in another 10 yrs when the daily drivers are smashed, rusted,etc, the '70's maybe desirable collectors. And in another 20 yrs, we'll be dropping in electric power packs and electric motors just to keep them running because gas will be found only in specialty shops :-)

Steve L.
73 coupe since new