Slalom4me

Was the L31 a flat or roller tappet design as built by GM?

If it is a roller design, am I right to conclude that it has the cam retainer
plate, stamped roller spider retainer and the one-piece rear main seal?

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cv67

L31, is that a Vortec truck motor? What year?
If it has a roller cam it should have the spider hold down and the bosses in the center of the lifter valley where it bolts down.

kopbet89c4

In 87 and later, GM changed over from the flat tappet to the hydraulic roller tappet design.

Widebody

The L31 as used in the 96/97 CK trucks and old body tahoe/yukon are hydraulic roller. Off the top of my head, the cam was really mild, like 192/197 degrees at .050 and about .404/.414 lift.

cv67

If it is the 96/97, may be a 4 bolt main also, many of them were.

cv67

The trucks still got flat tappets in 87, I believe only the Camaro (5.7)and Vette got rollers that year. My 87 van has a flat tappet/TBI.

kopbet89c4

They still make enough power down low to push a 6000 lb hog around town and still beat stock Civics! I did it once with my friend's `99 GMC Suburban and stomped a 5 speed Civic pretty badly.

Slalom4me

Sorry, I ought to have included the years. '96-'97 for sure, I'm not certain
but I think they might have been used for some specialty vehicles
beyond this.

The cam sounds right, these engines came with the iron Vortec heads
and the heads do not tolerate a lot of lift as is - with a minor massage,
they are supposed to be good for > .500.

Four bolt mains sounds right, too. Unfortunately, the L31 crank and
pistons are castings.

Thanks for filling in the blanks regarding the style of tappets & cam.

I bet there are a bunch of these things lying around in wrecking yards.
I remember one of the magazines putting a plain jane 2-bolt 350 on
a dyno and adding juice until it blew. They were well above 400 HP
before the guinea pig called it a day. I imagine a gently used L31
would be an inexpensive replacement capable of supporting 350-400
CHP with a set of E-Teks, a cam and an intake.

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Widebody

Drop in a set of Comp # 26918 springs with the 787 retainers and you're good for .550" plus. The 787 is for our 11/32" valve stems and allows the beehive 918 springs to fit the Vortec head. Car Craft used the Hot Cam with these springs and 1.6 rockers on a 350 H.O. and got over 400 hp. The 350 H.O. is basically a L31 Vortec with a carb, intake and different cam. Hope this helps.

Slalom4me

Was it just the spring pocket that people were enlarging to permit
different springs (w/ no coil bind) or do the iron Vortecs need
clearancing on the top of the guide, too, to provide for the high lift?

I'm under the impression that the 170 E-Teks are an improvement
over the iron Vortecs and of course they are lighter, but for a
budget build-up, a tweaked all-iron package rescued from the salvage
yard would really be easy on the wallet and hard on the tires.

Thanks,
Ken R.

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Widebody

Previously the vortec head required machining to the spring seat to allow for larger diameter springs for additional lift. The top of the valve guide boss also needed to be clearanced for retainer to seal clearance. The Comp 26918 spring uses a 1.800" installed height and on the vortec should come in with about 1.750" installed. My 96 pickup has been my guinea pig for most of this stuff. Researched a lot on the springs/retainers on the Impala SS forum. Their iron head LT1 is just a reverse coolant flow version of the vortec.

cv67

Sounds like an excellent building block for a motor, especially a stroker. My machinist says he doesnt like going more than .030/.040
over with those, but you are right, should be tons of em for cheap with standard bores. THere is a member here who has offered me his (96) thats .030, less than 3k miles, but has a scratch in one cyl, not suire if it would clean up at .040 . 4 bolt,roller block though.

Good tip Slalom, something to keep an eye out for. Hmmm, 396 C.I....

Slalom4me

Some considerations for anyone thinking about going this route.

Just keep in mind that an intake manifold suitable for Vortec heads is
required. SDPC used to be the sole source for a TPI/Super Ram base
but now Edelbrock offers one. Per SkankZilla: "EDL 3817 is the TPI
high-flo vortec intake base."

Member opel has mounted an SR on the base, but he needed to do
some reasonably significant clearancing on some of the runners
- pics and descriptions appear in his thread. (BTW - I notice that
SDPC no longer appears to promote the ZZ383 with a Super
Ram.) Opel is close to firing his engine.

Also, the iron OEM and aluminum E-Teks both have straight plugs.
So spark plug / exh manifold clearance may be a consideration.
Depending on the manifold/header, short plugs like those offered
by Accel may solve this clearance issue. Another thread by opel
has some information about plugs available from different vendors
for the Vortec head.

I believe the Fast Burn heads have angled plugs, but for my purposes,
the port and valve sizes are not as suitable as the OEM & E-Teks.
- YMMV.

A final thought is that the L31 may have an 8" harmonic damper.
I believe this engine is internally balanced and that you would just
need to confirm it. If it is, then an OEM L98 Corvette damper or the
6-3/4" Street Damper from Fluidampr should be suitable replacements.

.

Slalom4me

I came across L31 block and head casting number information which
will be useful for anyone trying to identify the parts at a wrecking
yard.

Block
10243880...350ci/5.7L...95-00...2 or 4 bolt mains
Vortec truck (& other apps), roller cam, one pc rear seal

There is also a smaller version
10243878...305ci/5.0L...96-98...2 bolt mains
Vortec truck, roller cam, one-piece rear seal

Heads
10239906 and 12558062...center bolt valve covers and narrow body
"self-aligning" rocker arms.

At this time, I do not know what the differences are between
the head castings. Perhaps someone here could provide
some background.

These casting numbers came from Mortec.com where they've put
together an extensive listing of casting numbers for Chevrolet engines.

.

Slalom4me

Cited from this Chevy High Performance article

Iron Vortec Head
All the Details You Need to Know
Other information useful for identifying engines at wreckers
.

RWDsmoke

I used a motor from a 96 one ton truck. It had rollers, four bolt mains and pm rods. Bought an engine kit from summit, had it bored and ballanced, installed hotcam and lt4 intake, runs good.

MR NICE

I read 906 heads flow the same

Slalom4me

If someone didn't feel like buying used, here are some part numbers
for an L31 short block and two L31 long block assemblies.

Do your own due diligence to be sure that the part numbers and
descriptions are accurate. Use the p/n's to check current prices
at your favorite supporting vendor for GM parts.

p/n #12556121p/n #12530282
p/n #12530283.

CentralCoaster

Hmm. I better check this out on my truck, see if it has the crappy heads. That 8 digit p/n is the one cast into the passenger side of the block right?

Easiest way to identify vortec heads is the intake bolt pattern. But I'll compare with those p/n's as well.

Slalom4me

The 906 head may or may not be a less desirable choice.

In this thirdgen thread, member RB83L69 says about the
Chevy High Performance comment to avoid casting number 10239906:

I didn't find any confirmation of that after I came across
his remark. I meant to search it out further and post one
way or the other, but ...

In that thread, crazy3rdgen cites two other comments against
the 906. In our CF thread here, Mr Nice and RWDsmoke
speak in favour of them. Bottom line, if I had some, I'd use
them - if I was looking for used Vortecs, I'd prefer the 062
but still look at the 906. If I was buying new, I'd chose the 062.

BTW - The part numbers 12556121, 12530282, 12530283 are
the numbers for ordering from GM or one of their third parties.
These do not appear on the parts themselves.

To check what you have or find, you will be interested in the
casting numbers posted further up the thread. These are
the raised numbers that are visible on the block and the heads.
Typically at the back of the block past #7 cyl and in the rocker
area of the head.

The Mortec.com site has a couple of pages about where to
find casting numbers.
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