joerob727

Hey guys, would like some knowledgable assesment of an L48 bottom end.

The engine was rebuilt with a fresh 30 over bore and new bearings etc. just a couple hundred miles ago. Stock L48 crank and rods, flat top hypeurtectics.

I have a pair of Eddy RPMS I am thinking of throwing on it and a roller cam in mind. My question is how much power can/will my bottom end take?

Thank you in advance.
Joe

bluegtp

Not sure here....I bulit my 2bolt L48 with some brodix ik200 heads with a decent size cam edelbrock intake w/holley 750 and bottom end is a 383 scat stroker kit w/cast crank/forged rods/Hyp. pistons bore is 30over. Compression ratio is roughly 10.4:1. Had the rotating assembly balanced.

It's been running strong for about 4 years now and I've run the mess out of it. No clue on the HP/TQ range maybe 450hp and the tq will through you back in the seat if the car actually hooks up. It mangled my old transmission, ended up putting a tci th350 in.

Very fun little engine for a street car and on the cheap. Aluminum heads were about 1k and stroker bottom kit was $560.

7T1vette

Unless you are using nitrous, supercharging, or turbocharging a 350 block, OR you are winding it up past 7000 rpm, I don't believe that you will have any problem with a 2-bolt main lower end. The high stresses occur at very high rpm's with normally aspirated engines or with non-normal aspiration methods.

gcusmano74

Man told me once the bottom end of a carefully assembled SBC will handle 500 HP with no trouble as long as there is no preignition.

MotorHead

412HP

63mako

If your talking the stock crank, rods, bolts I wouldn't go over 350 HP and 5500 RPM max. Chevy chose to upgrade to forged crank and pistons and 4 bolt mains for anything over 1 HP per CI and redline on factory cast cranks is under 5500 RPM. The forged crank engines redlines are up to 6500 RPM. The new aftermarket cast cranks like the Scat 9000 are supposed to be good to 500 HP and 6000 RPM but at that level I would go forged.

joerob727

Thanks to all.

I didn't plan on spinning it much above 5500, but the 350 horse limitation is kind of a bummer. I was hoping to coax a little north of 400 out of it.

Shark Racer

Increase hp until the crank snaps in two, then decrease by 5 hp.

63mako

It has been done many times. Some hold up well, some end up with a window in the block..

joerob727

Gee, . . . . . THAT'S reasuring

427Hotrod

I'd go ahead with the build. If it's built right it should be OK. The hypereutectics are the only wild card. It depends on quality they are....decent ones or cheapo claimer type.

Just be careful with the tune and never let it detonate and it should be fine to 425-450 HP and 5500-6000 rpm or so.

I had an original untouched cast piston '71 350 with a set of heavily ported 207cc heads using 2.10/1.625 valves, a solid flat tappet..and nothing else except a $3 HP spring in the stock oil pump. I ran it several years and spun it to the moon...and it lived. Gave it to a buddy who ran it for many years more.

JIM

cv67

You can get 400 out of it and be reliable
RPM kills motors not so much power

Korevette

I ran a 2-bolt main and used ARP fasteners with 375 HP at 6200 RPM shifts and put 413 quarter mile passes on it with no troubles at all.

They will take a fair bit before all hell lets loose.

joerob727

Thanks Jim,

That IS reasuring.

These are the pistons we used. http://www.summitracing.com/parts/slp-h631cp30

I don't remember how much volume the original dish pistons gave up but I went with these to help the meager compression of the L48. They are hypereutectics but hoping not 'cheapo'.

These (5cc) and the RPM heads at 70cc should give me decent compression.

Joe

Matt Gruber

The few that blow up are often over-reved. There is a "tell-tale" tach that records the max rpm. A guy will swear he shifted at 6k, it reveals the TRUTH 7k 7500, whatever.
The cure is an RPM activated switch set to max rpm. Hook it to a stun gun under the seat. This will cure driver error

AirborneSilva

Doesn't the MSD 6al have a rev limiter built into it? If so then why not install one of them? Of course the stun gun might be fun to watch too

MotorHead

My 412HP wasn't really trying to be funny, I made that with my stock bottom end L48, it will handle 400HP but I would keep it under that, 350HP would be better to make, 400HP you have to spin it pretty high for an L48 bottom end. The life of the motor suffers over 350HP after that you can start looking at good cast parts like the Scat 9000 and better rods not necessarily forged and good hyperutectic pistons and perhaps ARP main bolts

The truth be known I would personally shoot for 400HP with an L48, not a huge loss if it grenades, but it's really not that easy to make that HP as one might think with an L48

63mako

This is right along the lines I was thinking when I posted. Flat tops, 70 CC Rpm heads and a Roller cam can be 400-425 if you keep the operating range under 5500 so your right there. RPM will kill it.

Doug1

Doug1

I've been researching and I've come to the conclusion its not worth sinking money into the L48, save up and get crate motor stroker 383, from what I can tell, your not really gonna build one for much cheaper then pre=assembled, and the crate motors have the components that work together well and the experts have assembled and they warranty the motor, also, no dissapointments in the power dept. of that engine