I have a 75 L48 and was wondering , is this a 4 or 2 bolt main and also what size valves are in the heads? Going to do an engine rebuild to keep the car numbers matching. Thinking about some head work and a mild cam. Not looking for a lot of H/P, just something thats fresh and a little pep in the mid range for cruising the 4 lane when needed.

Thanks,

Gary

 

Flat top pistons and a cam will bump you to 300 hp range...
heads are a much easier way to get hp....
numbers matching includes heads..... does it include dish pistons? hehehehe

 

I know I'm starting to sound like a broken record on this, but my suggestion would be to pull your original #'s matching engine and drop in a crate motor. Alot of folks on this forum build them, but you're working with a 2-bolt motor with a cast-iron crank, not to mention 30-year old metal.

 

30 year-old metal??? What's the issue? All that means is that it has worked successfully for over 30 years...so the metal must be of pretty good quality. Depending on the source, 30 year-old metal can be much better than some present-day stuff. If you re-use the block, etc....just make sure it get checked for cracks. If none, it should be just fine. [Probably want to replace the cap bolts, etc. with new stuff, though.]

 

Yeah that's the way I want to go, nothing drastic. Hmnnn heads, matching. pistons?, hehehehe

 

Yeah I know, that crate motor thing is nagging me and there are some good ones out there. And you did answer my question about the 2 bolt. But I don't plan on running this thing hard. Thanks, much to think about now. Of course there have been some great 2 bolt rebuilds.

 

I've seen some good 2 bolt rebuilds and motors rebuilt that are much older. The machine shop I'm going to use has already told me the cap bolt replacement etc. As I stated previously, just looking for some good mid range, not going to race the thing, just cruises and car shows and getting back and forth to them.
Thanks

 

If you're just looking for a little boost in power, go with the head/cam replacement. Sure you have dished pistons, but get a small enough chamber, 58cc?, and you can bump that compression up. I would think you're not looking for power in the high revs, so being cast really shouldn't affect you.

Honestly, I think a crate motor in bumper cars is a bit of a waste, especially if you're just looking for a modest improvement. These cars aren't worth a whole lot in prestine condition, so keeping your car #'s matching seems to be a bit rediculous.

As far as valve size, the stock L-48s were 1.94"/1.50"

 

thanks for the info

 

If you're set on keeping the original engine but doing a performance overhaul you can definitely get what you're looking for. Key questions are exhaust (headers? free-flow mufflers?), transmission and gears.

There's unfortunately no way to tell the main cap type from the outside, but a 2-bolt block is fine for the power levels you're building to. Shoot for around 9.5 CR.

The head is most likely #333881 (casting mark like a right triangle) with 2.02/1.60 valves and a 76cc chamber - not a great head by any means (and a new aftermarket would be better in every way and likely cheaper) but with a little bowl clean-up and a good valve job they're good for your power level. Go ahead and invest in screw-in studs and valve springs to match your cam; I wouldn't bother with roller-tip rockers but just a good set of new Crane rockers, sticking with the 1.5 ratio.

One of the CompCams High Energy series is fine for your build; avoid going to an extreme cam if you're sticking with the stock intake and not using headers. While I'd still want your gearing, I'd suggest the 260H if you're sticking with stock intake/exhaust, and maybe the 268H if you're using either and/or both.

It'll be really easy to overbuild; keep your targets in sight

Finally, I agree with prior posters that more power is available for less money in a crate or other engine - but there's nothing wrong with doing a good performance overhaul on your original engine.

 

Hey, thanks for all that info. I do have headers an the rear gears are 3:90's, auto tranny. I'm kinda leaning towards the crate motr right now, with all everyone said and just my own gut feeling.

 

Billa, shouldn't they be the 882 heads with 1.94/1.50 valves?? Only the L-82 had the 2.02/1.60 valves, 75.47cc? How could he get 9.5:1 compression with these heads and dished pistons?? He'd have to mill the hell outta them. And the 268H is for high rev motors, somethign he's really not looking to do with that 2-bolt block.

Definitely check your rear gear, and what tranny do you have? What kind of HP numbers are you raelly looking for?

 

Quite right and my bad - 333882 with 1.94/1.6 and still 76 (75.47)cc chambers.

During a rebuild, any piston can be selected - definitely agree that if it's just a top there really aren't any options it takes about a .006 mill to pick up 1 cc, and 10cc to make 1 point of CR difference. I read this as a completely overhaul - if that's a mistaken impression then the situation is definitely different regarding CR!

The 260H is as far as I would go for a cam, the rest of the information is valid.

THANKS for catching!

 

[QUOTE=billla;1563405656]If you're set on keeping the original engine but doing a performance overhaul you can definitely get what you're looking for. Key questions are exhaust (headers? free-flow mufflers?), transmission and gears.

There's unfortunately no way to tell the main cap type from the outside, but a 2-bolt block is fine for the power levels you're building to. Shoot for around 9.5 CR.

The head is most likely #333881 (casting mark like a right triangle) with 2.02/1.60 valves and a 76cc chamber - not a great head by any means (and a new aftermarket would be better in every way and likely cheaper) but with a little bowl clean-up and a good valve job they're good for your power level. Go ahead and invest in screw-in studs and valve springs to match your cam; I wouldn't bother with roller-tip rockers but just a good set of new Crane rockers, sticking with the 1.5 ratio.

One of the CompCams High Energy series is fine for your build; avoid going to an extreme cam if you're sticking with the stock intake and not using headers. While I'd still want your gearing, I'd suggest the 260H if you're sticking with stock intake/exhaust, and maybe the 268H if you're using either and/or both.

It'll be really easy to overbuild; keep your targets in sight

 

If the engine is fine and you're just looking for more "grunt", consider investing in a new torque converter and headers...you'll be surprised at the difference.

You'll definitely be happy with a crate with those gears - no reason you can't paint it the right color and make it look "factory" in every way

There are a bunch of crate engine options, but IMHO the best "bang for the buck" in the market today is the GMPP 350/330 (P/N 12486041) - but there are many choices out there, so once you have a budget established you'll have lots of options.

 

That car is not numbers matching if its got 3.90s in the rear and headers on it. Or do you just have the original rear end and exhaust manifolds stored away?

 

gears and exhaust are in fact stored. thanks for catching that!!!

 

Thanks all for all the tips and pointers. Going to check out a few more options and the GM crates.

 

I checked out the GMPP 350/330 Part number 12486041 and that seems like a great way to go and the price is right on. Best of all it's in stock locally. I just hope the factory a/c compressor, alternator, etc match up without too much bracket changing. Can't see why it wouldn't, but we'll see. Going to call dealer tomorrow. Any suggestions on a converter?

 

Hey Billla, I just ordered the crate motor GMPP 350/330, wound up with an excellent price for a ( complete ) motor, ready to drop in. Just need to check my flexplate size and get a decent converter. Since it is a Gm/Chevy dealer, the guy had all the necessary info on a/c. alternator hook ups, etc. Great advice man, Thanks