L31

[Hobie]

Not too bad of a day, I was basically given this L31, body had 308,*** miles, and #8 rod bearing has spun, but I see cross hatchings in the bottom of the cylinder. Picked up a set of rods/pistons for $40, and still going over what cam I should slap in. I'll be tearing down the engine this next week to see what I'm working with for sure

What do you guys think?

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[Supercharged111]

I think you should make a 383 out of it.

 

[kennythewelder]

Cam choices depend on what you want to do with the engine, or how you want it to perform. Also are you keeping the CPI, or swapping to something else. Keep us posted, as on what you do. LT4 hot cam is a good choice if you keep the CPI, for a street cam, but there are a lot of choices out there.

 

[Schurkey]

Consider NOT using the L31 pistons.

Pick up a set of Caprice TBI pistons instead. The '92-ish B-body TBI used flat-tops instead of the L31 dish. The ring package is different from the L31, so get the proper rings to match the pistons. (2.00mm x 1.50mm x 4.00mm, where the L31 is--if I remember correctly--1.5, 1.5, 3mm)
https://www.summitracing.com/parts/slp-h597dcp

SQUARE-DECK THE BLOCK to get decent squish/quench distance. Last engine I did, I had to have .025 cut from the deck to get where I wanted--but I probably should have used a thinner head gasket and only cut .015. The TBI pistons listed above are .010 short on compression height, take that into account when you cut the decks.

Cross-hatch in the BOTTOM of the cylinder means very little. Cross-hatch at the top is pretty wonderful, though. My block had unknown miles, and about .0015 taper. I ran a *********** brush through the holes and called it good. (Except for #8 which had a rust ridge from water trapped against the rings. That cylinder had to be bored .030 to clean up.)

 

[Hobie]

I'm thinking about swapping over to the marine intake, and a larger throttle body. I've had my eye on COMP's Xtreme Energy 230/236. From what I've simulated, it seems to have a good power curve for what I'm looking for. I work the truck, and do tow with it. But I still like to have a good amount of top end horsepower. I know I could put a RV cam, and get a good amount of low end torque, but when all is said and done, it's still a small block Chevy. And it will never make enough low end torque for me to justify a huge top end sacrifice. Heads will be sent off for the screw in rocker studs, and valve spring seats, and I'll probably end up doing a port polish on them

 

[Hobie]

Consider NOT using the L31 pistons.

Pick up a set of Caprice TBI pistons instead. The '92-ish B-body TBI used flat-tops instead of the L31 dish. The ring package is different from the L31, so get the proper rings to match the pistons. (2.00mm x 1.50mm x 4.00mm, where the L31 is--if I remember correctly--1.5, 1.5, 3mm)
https://www.summitracing.com/parts/slp-h597dcp

SQUARE-DECK THE BLOCK to get decent squish/quench distance. Last engine I did, I had to have .025 cut from the deck to get where I wanted--but I probably should have used a thinner head gasket and only cut .015. The TBI pistons listed above are .010 short on compression height, take that into account when you cut the decks.

Cross-hatch in the BOTTOM of the cylinder means very little. Cross-hatch at the top is pretty wonderful, though. My block had unknown miles, and about .0015 taper. I ran a *********** brush through the holes and called it good. (Except for #8 which had a rust ridge from water trapped against the rings. That cylinder had to be bored .030 to clean up.)

I have a set of 4 valve relief flat tops that I hope I will be able to use. And I understand that bottom end cross hatch doesnt mean too much, but i havent been able to tear it down to see how the top looks yet.

The block will be machined, even if cylinders are square, i will still bore it out, deck the cylinder head mounting surfaces, and will have the cam/main bearing journals checked, if not line bored.

 

[L31MaxExpress]

I'm thinking about swapping over to the marine intake, and a larger throttle body. I've had my eye on COMP's Xtreme Energy 230/236. From what I've simulated, it seems to have a good power curve for what I'm looking for. I work the truck, and do tow with it. But I still like to have a good amount of top end horsepower. I know I could put a RV cam, and get a good amount of low end torque, but when all is said and done, it's still a small block Chevy. And it will never make enough low end torque for me to justify a huge top end sacrifice. Heads will be sent off for the screw in rocker studs, and valve spring seats, and I'll probably end up doing a port polish on them

If you do that I highly recomeend Rhoads VMax lifters to tamd the idle and low-speed. I would go with something more in the 222/230° range.

 

[Hobie]

If you do that I highly recomeend Rhoads VMax lifters to tamd the idle and low-speed. I would go with something more in the 222/230° range.

What exactly is the advantage of the rhoads lifters compared to stock?

 

[L31MaxExpress]

What exactly is the advantage of the rhoads lifters compared to stock?

More low-end torque, more vacuum, and a more stable idle. The only disadvantage if you want to call it that is they sound like a solid cam at lower rpm because the valves close more quickly. With the VMax lifters you can adjust the lifters to control how much duration decrease they provide and at lower rpm they can reduce your cams duation between 5 and 20° @ 0.050. My 218/228 @ 0.050, 110 lsa, .578/.578" lift cam, 1.7 rocker, Rhoads VMax lifter 383 idles like the stock cam 350. I had them in the 218/218 @ 0.050" cammed 305 Vortec as well. Idled like stock at 650 rpm. The full valve lift is not restored until about 3,500-4,000 rpm. Just for grins model that setup with 10° less at 0.050 and about 0.040" lift reduction on both intake and exhaust. Look at how much torque you gain in the 2,000 rpm range.

 

[L31MaxExpress]

222/230 @ 0.050 spec I rec9meended is what the old GM 846' cam is that works really well in LT1 B-car Impalas. I have run that cam in a Vortec 350 and added standard Rhoads lifters to one and barely had to touch the tuning pf the black box. It would start, idle and drive on the stock tune. All I did was clean up the fuel maps, play with the timing and the shift points to get the most power. Compared to smaller cams I have messed with that would not even idle before tuning.