383SB or 400SB retro into a L31 1998 Suburban

[1998_K1500_Sub]

I've had a plan on slow simmer to build a 383SB to swap in place of the Suburban's L31. The project's underway, as it has been for... 3yrs maybe.

A machine shop in Saginaw has the block (from a treasureyard donor L31), crank (new), rods (5.7" H-beam), and pistons. There's also the heads and intake from the donor L31, plus misc parts (oil pan,...). Nothing's been assembled. The next step would be to clearance the pan rails for the crank / rods. I learned this most recent status this past Friday when I visited his shop.

Meanwhile, a friend in Saginaw was cleaning out his own shop and discovered a 400SB long block (he has a LOT of engines) which he believes has four-bolt mains. I learned of this this past Saturday, while visiting. This started me thinking of course...

Should I euthanize the 383SB and refresh the 400SB for the Suburban?

My intent was/is to re-use the L31 intake, with the upgraded MPFI (injectors-on-the-tubes).

I haven't made any decisions or investment in heads or cam, although the donor L31's heads are usable.

I would likely put longer-than-stock rods in the 400SB.

I don't want to use headers; given that, I'm not sure what my options are other than the truck's existing L31 log manifolds.

These are the thoughts in my head on my way home from Saginaw this morning.

I won't say "money is no object" but I'm not expecting this to be a budget build.

 

[Scooterwrench]

No doubt 383. You couldn't chase me down and beat me up to give me a 400. Some people like 'em,I ain't one!

 

[Erik the Awful]

There weren't a whole lot of 400s produced, and most of the blocks are ragged out. I'd have that block checked carefully. If it's good, that's a score, and I'd probably go with a 400 over a 383.

 

[1998_K1500_Sub]

No doubt 383. You couldn't chase me down and beat me up to give me a 400. Some people like 'em,I ain't one!

I literally laughed out loud I appreciate other's comments, for or against.

What's to hate? The Siamesed cylinders / concerns for cooling?

I would improve the 400's crappy rod/stroke ratio with a longer rod.

 

[RichLo]

Over-bore kills OEM 400's. First thing to inspect is if its been bored already and if so, how much. If its more than .030 or needs more than that, it's not worth building. Some people have done .060 on lightly used classics but they cant run them hard.

If its a untouched block, only bore it enough as needed. I have one that's fresh with .010 overbore and 427 stroker kit (its technically 418CI because it wasn't bored .030). I still haven't run it, that's one of my 'long term' projects.

Also, be sure to pay attention to the lower end and get internally balanced if your not re-using OEM. Then you can use any other SBC flywheels and harmonic balancers. OEM's are externally balanced and are are tough to find correctly balanced externals for them.

 

[L31MaxExpress]

I would build a 400 myself. I love those engines especially a near stock build. If you stay externally balanced you will need a 400 style balancer cut down 0.110" to make room for the L31 crank reluctor. There is nothing wrong with a stock 400 bottom end in a 5,500 rpm application. The stock Vortec heads will flow better on a 4.125 or 4.155" bore than they do on a 4.000 or 4.030 bore. The one disadvantage to a factory 400 block is the lack of roller cam provisions. Money no object it would be a Dart SHP 400 block with 1-piece rear seal, roller provisions, 350 main bearing size and a 3.875" stroke. That puts you at 414 cid at a 4.125" bore. The stock 400 is weaker as a 4 bolt main than a 2 bolt main although in a low rpm Vortec truck application the 4 bolt does not scare me. A flat tappet cam also does not scare me as long as you use the Delco hardened foot lifters and stay away from Comp cams. Sonic testing is important with the 400. Some are thin and others have more material at 0.060" than a stock bore 350. The cooling concerns are something I have simply not seen on the 400s. I put one that was 0.040" over into a 1995 G30 cutaway RV and my buddy that owned it ran the absolute dog snot out of it towing a heavy boat behind the RV. That one got a Crane 260 truck cam, stock 810 TBI swirl ports, stock TBI manifold bored to 46mm and a 46mm TBI. It ran very well, about 330 hp and 450 tq.

 

[L31MaxExpress]

SHP Chevorlet Small Block Iron Block - 4.125 In. Bore, 9.025 In. Deck | 31161211L | Dart Machinery

Dart SHP Iron Small Block Chevy Blocks

www.dartheads.com

 

[Schurkey]

There's a 400 in my 'Camino, with ancient Trick Flow heads that have steam holes. Flat-tappet Summit 1104 cam that I put in as a "temporary", and 20-something years later it's still in there.

Mind you, this is not a computer controlled vehicle. It is, however a smooth-idle engine.

If you're using Vortec heads, be sure to drill the coolant bypass hole (I'd drill both heads.) I'd also want the steam holes drilled in the heads.

Have it honed with a torque plate, get the piston-to-head distance right, and get an aftermarket balance job. Internal or external balance won't really matter at low-to-moderate RPM, but don't rely on factory balance.

 

[df2x4]

You could always build both and find another use for the 383.

I vote 400, I think that engine in a Suburban would be awesome. I love the one in our '70 Monte Carlo.

The only useful advice I can give would be to echo Schurkey's comments about modifying whatever heads you use accordingly for the coolant bypass and steam holes. We used an Edelbrock aluminum head (forget which model...) and had them drilled.

 

[Spareparts]

Years and years ago i had a Suburban with a 400 SB, Th400. Pulled a 4k boat all over the place without a problem.
I would have another if i could find a solid std bore block now.