Hey Guys,


Im going from a 305 carb. to 350 L31 vortec TPI. My question is, do you guys think that besides the Vortec heads that the L31 is a better engine than the L98 as far as compression and connecting rods and pistons and crank? I dont remember the compression of the L98 off hand but I know the L31 has 9:4:1 compression and i believe it has powdered metal rods and is basically built for Torque, being that it was built for truck applications.

thanks,

 

L31 4-bolt, L98 2-bolt.

L98 compression 9.3:1.

As far as I know, the cranks are the same.

 

Out of the three vortec L31's I have had only one has been a 4 bolt main. I would also agree the rest of the motor is porbably comparable to an L98.

I built a L31 for a friend using stock crank/rods/pistons, ported vortec heads and a hot cam that made 400 horse and is holding up just fine.

 

Yeah I know the L31 had a 4 bolt main and the L98 had 2, but does anyone know if there was a difference in the pistons themselves?

67SS. was that the LT4 hot cam you used for your friends L31?

 

Pistons are both cast from the factory. Whether they have the exact same dish/valve reliefs, I don' t know.

If you're buying a new shortblock, the only difference will be 2- vs. 4-bolt main. Are you thinking of buying new, or finding a used engine?

 

Neither, I already have the L31 engine all built and in the car now, just waiting for the weather to get a little warmer to hook everything else up so i can get ready to fire her up. Just thought id see if there was any other real difference between the 2 blocks besides heads and the mains.

 

Yes, lt4 hot cam kit with the 1.6 rockers and such. Think it was 525 lift and 218 duration or something like that.

 

Not anymore.

 

I have seen alot of 350 vortec motors with rods hanging out of their pans or cylinder walls. The powdered metal rods tend to occasionally break where the beam of the rod goes into the crankshaft big end. The one in my dads truck did it at 52,000 miles. After talking to some machine shops and looking around GM dealerships it became apparent that there are alot of these motors where the rods break in the same place.

 

HMM, thats new to me. I work at a chevy dealer, and ive never seen that happen. The only thing ive seen is the, crankshaft snapped on one, most likely due to heavy towing or nuetral dropping into gear.

 

As is often related here, ARP rod bolts will go a long way toward making stock rods last a lot longer.