all this time I was thinking my 81 had a 4-bolt main. was planning on doing a few upgrades to the motor. am thinking not much I can do with a 2-bolt main. I don't want something that will jump over the moon but would like more than what I got. any suggestions!!!!!!!!!

 

2 bolt main is fine for most builds under 450 hp. I wouldn't lose any sleep over it.

 

Not much you can do with a 2 bolt main? That's my original 77 block below with over 200 quarter mile passes on it making enough power to go 12.17 at 109.

 

Ya, who said a 2 bolt main is weak anyway? Heck we spin small block 2 bolts well over 5k rpm for hrs upon hrs. Now, I do believe if you wish to super charge a 4 bolt with studs is optimal. Al

 

2 bolt 010 blocks are great for splayed cap conversions

 

Wow, that sucks. Everybody knows that 2-bolt main bearing caps will self-destruct once you get over 300 horsepower. I feel bad for you, man, with your completely, utterly useless 2-bolt main block. If I were you, I'd throw it away, and spend a whole bunch of money on a Dart block for my 350 horsepower build. I'm sure you must be very depressed over this, so try to stay away from drugs or alcohol for awhile, and don't do anything rash. Remember, suicide is a permanent solution to a temporary problem. You can always just buy a Dart block.

Seriously, though, do you know how many 500 horsepower small blocks are running around out there with 2-bolt main caps and re-used stock bolts? I don't know, either, but I would be willing to bet there are a whole lot more than you think. My suggestion is to stop being such a ninny and soup up your engine!

Scott

 

what he said

 

You can safely install a 383 Stroker kit into a L48 Engine which will get you up to about 300 HP and you can go up to about 350 HP on this engine which many of the pre 1972 engines were about 350 HP.

Just a little history on the L48

The L-48 is the original 350 cu in (5.7 L), solely available for 1967 in the Super Sport version of Camaro SS 350 (1967-up) or Chevy II/Nova in '68-79. In '69 it was used in almost all car lines; Camaros, Impalas, El Caminos, Chevelles & Novas. 1969 L-48's use a Hyd Cam, 4bbl Quadrajet carburetor, cast pistons, 4-bolt main casting number 010 Blocks & casting number 041 or 186 heads. Power output was 300HP and 380 lb·ft (520 N·m) torque. Compression ratio was 10.25:1. The compression ratio of the L48 was lowered to 8.5:1 in 1971.

From all the reading I have done and performance shows I have watched the L48 2 Bolt main can safely be increased to about 350 Horse Power and just as many foot pounds of torque with the right conversion kits.

Now the only way to tell if it is a 2 Bolt main or a 4 Bolt main is to pull the pan on these engines or look at the casting on the block but most produced in 1971 and beyond were probably 2 bolt main engines. All the L82 engines had 4 bolt mains but some early model L48 engines had them.

You will not really blow the crank out of the bottom end if you use a modern day 383 stroker kit they use the longer stroke to increase HP and Torque then really only increase compression to 9 to 1 than were manufactured to increase the HPand mostly Torque of the L48 2 bolt main engine to around 300 HP. It is a very safe conversion for the 2 Bolt Main L48 Engines and you can get more HP from headers and exhuast systems to about 325 + HP

I almost bought a 1976 and a 1978 Corvette with this conversion but they removed the CATs from the exhaust systems and I did not want to put the emission controls back on them so I passed on buying these 2 cars. Would have cost me close to a grand to get them into passing emission testing again.

 

If it's the original engine in the '81, hang onto it. It's a 1-year engine that went into nothing but 1981 Corvettes. Find a good 4-bolt block and beat hell out of it without worrying about blowing up the original. Drive the car as you build the new engine, no down time!!!

 

Just to be a stickler for details; the 1981 Corvette came with the L81 engine, not the L48.

 

I put a Comp cam and Edelbrock EPS intake Holly carb Accel dist and stripped all the emission crap off. It feels twice as fast I beat on it daily with 126 K on the odometer. I wouldn't be afraid of adding more HP maybe ported polished heads, duals and better headers.
The worse that can happen is you blow the motor and have to do an LS1 swap or 383 stoker. At least then you have an excuse.

 

Lol.. Do not worry. Simple cost effective ARP stud upgrade will help your 2 bolt block with correct upgrades to produce more HP than 4 bolt main block. Trust me on this one.. I got 2bolt main 400 sbc with ARP upgrade pushing out over 500HP.

 

thanks to forum for the advice. what have I got to loose. will go ahead with top end build. now what do you suggest for a nice top end kit? I want to keep the electronic quad and computer. had it worked over and it works great. have true dual exhaust.

 

This looks like a good deal:

http://www.summitracing.com/parts/sm...-400/overview/

I don't know if it'll be too much for the computer to handle, though.

Scott

 

2 bolt blocks are fine!

 

Buy components that would be usefull on a 383 later. Afr 180s, good dual plane, performer orperformer rpm, roller cam, 1.75" headers. Put you over 400 horrse, all usable for a 383 later. Good luck.

 

I'd start with the exhaust first then top end second. The carb and intake should be fine but the L81 heads stink. I bought a set of Summit iron heads years ago and they were very good for my 81.

 

The 2 bolt block is OK but your cast pistons are junk. That's the limiting factor in the stock bottom end parts.

 

I'd also say cast iron rings limiting power expectations. When I did the top end on the l48 it only took 10,000 or so miles before I started to get blowby and it got worse from there. Bk makes a good point, let's say you spend 3000$ on the top end and the bottom ain't up to par then there ya are 10,000 or so miles later pulling it to least redo the bottom end. If you spend another $2k on the bottom end now you won't have to later or do what I did, spend $2k on the first top end & $10k later. Maybe you'll have better luck than I did.

 

When it comes time to do the bottom, you can just dish out about 1300 bucks for a short block, (ya gotta ship it!) and move your heads, cam, intake, carb, and dist into it. Done and done.

http://www.summitracing.com/parts/hpe-sp01/overview/

Scott