skinny z

In doing the research regarding the next step for a replacement shortblock (whether a permanent one or interim) I've come across GM's L31 several times.
https://www.summitracing.com/int/par...0283/overview/
At one point, I thought I had read that despite being new assemblies, there's not much cylinder wall available for a re-bore.
Does anyone have any insight into this?

sofakingdom

iTrader: (1)

Most newer blocks in general don't have very thick cyl walls. .030" is the most I'd count on being able to bore that one out. Shouldn't be necessary for at least acoupla hundred thousand miles though, being a NEW motor.

skinny z

Being a new motor is the operative phrase there. And the engine's lifetime may well exceed my own so the issue of a rebuild may be moot. That said, that wall thickness does enter into durability to some degree. I had heard that there was no room to rebuild but that may have been in reference to the Goodwrench engines on the basic level.
Regarding the research, I'm seeing that cost wise, the L31 from GM looks to have better value that the ZZ350. The variable to me is in the strength of assembled parts. The ZZ350 no longer has a forged crank (so it's reported), so any advantage on the shortblock side is pretty much a wash.
And I'll admit, I'm looking to get back into the racing game and do it on the cheap considering I've a bit invested in the supporting parts.

GeneralDisorder

iTrader: (1)

When and if a rebuild is required, with modern synthetic oils, and from what I have seen of L31's with near 200k on them - boring them oversized just isn't necessary. Even honing isn't necessary. Normal rings will seat just fine (and quickly) on a good used bore.

Since the 80's it has been common practice to rebuild without touching the cylinders in any way unless they are specifically damaged. I've done a ton of re-rings on used bores and never had a problem. Modern (talking 1980's+) rings really don't require any honing. Just so long as the bore isn't out of round or taper - and that isn't likely with modern oils and air/oil filtration.

GD

sofakingdom

iTrader: (1)

Yup, EFI IN PARTICULAR has reduced the amount of cyl wall wear that motors enjoy; since most of that wear occurs in the first few minutes after a cold start, and is due to fuel washing the oil off the walls, which doesn't happen anywhere near as much as it used to with a carb. Better oil helps too but the main factor IMO is the end of the carburetor.

The worst culprit of all had to be the old 2G carb. We used to see old motors that had so much wear they'd have to go .060" the first time just to clean it all up, and we called a motor like that "Powerglided"... but then after the PG disappeared, and it became obvious that otherwise similar motors with a Q-Jet on them were in MUCH better shape than 2-bbl ones after acoupla 100k miles, regardless of the transmission, we had to re-think that. Even something as recent as mid-70s 350s, the vast majority of which came with T-350 behind them and the same heads and cam and everything else no matter what carb, you can tell which blocks had 2-bbl carbs and which had Q-Jets, in a pile of stripped-down bare cast iron.

However if you put a carb on that new motor, it'll wear just like an old motor with a carb; not stay fresh, like a new motor with EFI.

Just the same, I wouldn't use the thinner cyl walls of modern blocks as a criterion for rejecting them.

skinny z

I won't realize any advantages of EFI as this will be carbed as is the current running engine.
And that carb is mostly responsible for the situation I'm in now and that's (what I am surmising are) severely worn cylinders. Chokeless too I might add.
That said, a new block is looking to be the logical choice and with what I anticipate to be less accumulated miles than before (I used to drive a lot as in tens of thousands of miles in a driving season) it may be that a rebuild will never materialize.
Always the best oil and changed regularly too.
Now to decide whether the OEM rotating assemblies (of either engine) will live up to what I may potentially put it through.

GeneralDisorder

iTrader: (1)

Why not install a FiTech system? Carbs wreck engines. Sofa is absolutely right about that.

GD

skinny z

Most of the reasoning to staying carbed is because I've already got the platform well established. Tuning is easy enough albeit time consuming and cold starts notwithstanding, it's a reliable setup.
Even the LS swap I have envisioned may be going with a carb and aftermarket ignition controller so the LM7 could be up and running in short order. But that's another matter altogether. I'm anxious not to lose another season of racing and this route, that is taking the fresh top end off of my current engine (and spec'ing a new cam) and dropping it onto a ZZ350 or L31 is the shortest (and least expensive) route to that goal.

GeneralDisorder

iTrader: (1)

FiTech is pretty reasonably priced and is self tuning for the most part. Wiring is minimal, and it works with your existing carb manifold, intake/air cleaner, etc. You would spend some time on it, sure - but probably less overall considering tuning a carb vs. self-learning EFI.

GD

Out-Cast

iTrader: (1)

I am also looking at the L31 motor, keeping my TPI System and adding a Vortec Intake, ZZ4 Cam. Street Driven car just want more performance.
I got my info from guys on here who have been a great help.

skinny z

The L31 does seem a popular choice. What's more, considering how it's priced against the ZZ350, I'd end up with more or less the same shortblock and have a set of new Vortec heads to stash or sell. My Vortec RHS heads have been worked over and are a step up from the stockers.
As for EFI, I'm loath to let the computer do all of the tuning. Our experience has shown that there are several places where tweaking the self-learning tune is necessary and laptop access is required. Not sure how the FITech stacks up in that regard. I'm certainly not closing the door on fuel injection but for this project, it's keep it simple.

GeneralDisorder

iTrader: (1)

five7kid has recently posted his experiences with FiTech and done some racing with it.

https://www.thirdgen.org/forums/ltx-...rd-fitech.html

GD

skinny z

Interesting. Thanks. I'll check it out.