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Project822
Project822 New Reader
9/7/21 8:01 a.m.
03Panther said:

If I dig deep enough, I could prolly find the patterns I downloaded to make your own... but you might could find 'em online just as easy. They are available. after ya fab them, it a bolt in affair.

For $85 from jagsthatrun.com, I'll just buy a set.  As much as I like to build things, I am trying to do a swap that is as little "building things" as possible.  I would turn those adapter brackets into a day-long affair.  They would be beautiful and strong when finished, but even at 3-4 hours, I am money ahead just to buy them.  The only part that I am not certain about is the fact that it reuses the 4.3 engine mounts instead of V8 engine mounts, which I assume would be stronger/build for the heavier engine.  

SkinnyG (Forum Supporter)
SkinnyG (Forum Supporter) UberDork
9/7/21 8:38 a.m.

The adapters are seriously just a piece of 1/4 or 3/8" plate, with holes drilled for the block, and holes to relocate the mount.  You're talking a hacksaw and six holes each.  I've made them; they are easy.

pres589 (djronnebaum)
pres589 (djronnebaum) UltimaDork
9/7/21 8:56 a.m.

This thread is two weeks old.  Where's the finished 350 that's ready to go in the van?

Project822
Project822 New Reader
9/7/21 8:56 a.m.
SkinnyG (Forum Supporter) said:

The adapters are seriously just a piece of 1/4 or 3/8" plate, with holes drilled for the block, and holes to relocate the mount.  You're talking a hacksaw and six holes each.  I've made them; they are easy.

You don't know me, so I forgive you for underestimating my predilection for complicating even simple things.  

The ones from jagsthatrun.com have tabs that are bent up to use the stock Astro engine mounts.  It sounds like you are using V8 engine mounts instead.  Is that correct?  Are you bolting the adapters to the engine to move the mounts back 3" (I think that's the number) or to the subframe to move the mounts forward 3"?

eastsideTim
eastsideTim PowerDork
9/7/21 9:28 a.m.

Regarding the mounts, I used the flat plate style V8 mounts in my S10 initially, but ran into clearance issues, then switched to the 2.8V6 style JTR mounts and they fit better.  My S10 seems to be a victim of all the tolerances stacked in the wrong way, though.

Opti
Opti Dork
9/7/21 12:01 p.m.

If it was me. Id be looking at a L31 with a very small cam, something like a stock LT4 (not hot cam, at like 203/210, you used to be able to get these for almost nothing) or an LPE 211/219. So it idles and runs super smooth, stock vortec heads with alex's springs, and the GMPP intake to mount a TBI on the vortec heads. Go throught the TBI and do the ultimate mods, and and up the fuel pressure.

The stock LT1 cam was used quite a bit of TBIs and L31s back in the day and was very similar to what most companys called their RV cam, the LT4 is just a little more duration and lift, but still has oe drivabilityh.

My thoughts would be it may not make 350 but it will probably make 300 and lots of torque. Idle and run like stock. The TBI setup is reliable as gravity and you can get any parts you need at any store. It also uses a very simple PCM and wiring setup, so it would be very easy to put in. I think but dont quote me on this the astros used the same pcm at some point, so you could grab a harness and computer from a suburban or something and easily integrate the electronics.

Id be reluctant to do any type of weird or aftermarket injection for a road trip vehicle incase something breaks. The other option the vortec injection system isnt really known for its reliability.

 

06HHR (Forum Supporter)
06HHR (Forum Supporter) Dork
9/7/21 12:08 p.m.
Opti said:

If it was me. Id be looking at a L31 with a very small cam, something like a stock LT4 (not hot cam, at like 203/210, you used to be able to get these for almost nothing) or an LPE 211/219. So it idles and runs super smooth, stock vortec heads with alex's springs, and the GMPP intake to mount a TBI on the vortec heads. Go throught the TBI and do the ultimate mods, and and up the fuel pressure.

The stock LT1 cam was used quite a bit of TBIs and L31s back in the day and was very similar to what most companys called their RV cam, the LT4 is just a little more duration and lift, but still has oe drivabilityh.

My thoughts would be it may not make 350 but it will probably make 300 and lots of torque. Idle and run like stock. The TBI setup is reliable as gravity and you can get any parts you need at any store. It also uses a very simple PCM and wiring setup, so it would be very easy to put in. I think but dont quote me on this the astros used the same pcm at some point, so you could grab a harness and computer from a suburban or something and easily integrate the electronics.

Id be reluctant to do any type of weird or aftermarket injection for a road trip vehicle incase something breaks. The other option the vortec injection system isnt really known for its reliability.

 

Not trying to threadjack, but except for the 383 rotating assembly i want you just described the future set up for my GMT 400 perfectly.  Thanks! laugh

Project822
Project822 New Reader
9/20/21 12:52 p.m.

I have an L31 lined up for delivery probably this weekend.  

As I think about displacement, I wonder why more people don't use a 400 SBC bottom end instead of starting with a 350, which must (for gaining displacement) be stroked and bored and only the wildest stroking and boring results in 400CID.  Most people who stroke and bore get off the bus at 383CID.  Why not just use a 400 bottom end to begin with?  It seems like a cheaper path to more displacement than a 383.  

Is there some external difference that makes the 400 block less directly compatible?  Are the accessory and mount bungs different/in different places?

eastsideTim
eastsideTim PowerDork
9/20/21 12:55 p.m.

In reply to Project822 :

Externally, it should be the same.  I think it's just internal differences.  I may be repeating debunked info, but I seem to recall that between thin cylinder walls and possible core shift that the 400 was not considered a great candidate for rebuilding back in the day.

Project822
Project822 New Reader
9/20/21 1:36 p.m.

In reply to eastsideTim :

I have been reading some of that also, but also others saying that the cylinder thickness is an overplayed concern on stock and .030" overbore engines.  There are aftermarket 400 blocks that address all of the 400 SBC concerns, even ones with a taller deck height to allow for longer rods and beefier cams on stock base circle, but then that's another $2000 (plus crank) on a build that could otherwise be nearly done for $2000 on stock 350 stroke in a stock 350 block and meet my adjusted power and torque goals.  The 400 SBC question is more of a matter of wanting to know; 400 SBC blocks seem to be very easy to find, and the sought-after opportunities to increase performance tend to be harder to find and more expensive.  

APEowner
APEowner SuperDork
9/20/21 1:52 p.m.

The 400 block had siamesed bores.  Meaning, there's no gap between the cylinders for coolant flow.  The theory is that this can causes the cylinders to be out of round at temperature and that's why they weren't all that popular. While there's some validity to that it's not really the big deal that it was thought to be back in the day.  In the '80s I messed around with circulating hot water through the block when doing the boring and honing so that they'd be round at temp.  I don't remember the numbers but we were able to measure a difference in roundness when they cooled.  However, the improvement didn't seem to show up in power on the dyno.  Many aftermarket big bore small blocks use siamesed bores and as far as I know, nobody is doing the machine work hot on those.

 

 

tuna55
tuna55 MegaDork
9/20/21 1:59 p.m.

If I were building today, I'd run a 400. No messing about with stroker kits, and you get a bigger bore instead. The myths started because people were swapping heads or head gaskets without using the steam holes to get around those siamesed bores. I ran one a long time ago and was pleased.

ClemSparks
ClemSparks UltimaDork
9/20/21 3:00 p.m.

I've never had a $50 400 SBC fall in my lap.  I've had several such deals on 350s (and the last one...a vortec 350 was given to me)

If I was in your enviable position of not having a hard time finding a good 400 to build, I'd definitely give it a shot.  

Anytime I've seen a 400 advertised around here they wanted a premium for it because it's a 400.  They are out there but I don't spend time looking for them because 'round here, 350s find me.

Project822
Project822 New Reader
9/21/21 7:12 a.m.
ClemSparks said:

If I was in your enviable position of not having a hard time finding a good 400 to build, I'd definitely give it a shot.  

...'round here, 350s find me.

That's an enviable position.  Certainly not $50, but I have seen several not-expensive (let's say cheaper than a basic cheapie 383 stroker kit) 400 bottom ends for sale within an hour from my house.  Of course, then the questions come: does it have good bores?  Has it been bored already?  Can it be bored in its current condition?  Is the crankshaft good?  And so on, and so forth, until all the questions have been asked.

Then there would be the matter of lifters.  I don't know how 400 flat tappet lifter cams held up, but what I do know is there was at least a time and a place when SBC engines would eventually eat their cams.  This limited knowledge leads me to fix the problem by converting to roller lifters on any non-roller SBC block, and that is another expense on a 400 block. 

Eh, forget the 400.  

Project822
Project822 New Reader
9/21/21 7:22 a.m.

How about rod length?  Stock 350 is 5.7".  Is it worth it on a street engine that probably won't rev past 5500RPM and wants to run on 87 octane if possible to sacrifice oil control ring support and run a 6" connecting rod?  

The back and forth arguments about the importance/effects of rod length are numerous, but one thing seems to be certain: longer rods increase knock resistance.  

asphalt_gundam
asphalt_gundam Reader
9/21/21 7:41 a.m.

Don't even waste time thinking about rod length itself. The things that count are the piston stability at high rpm and overall weight of the parts. Engine Masters did an episode on this and drastically different rod ratios made the same power with slight differences.

Even when I was building engines I thought putting a lot of thought into the rod was ridiculous. The crank is fixed, you make the piston as good as you can, and the rod just connects the dots.

Project822
Project822 New Reader
9/21/21 8:04 a.m.

In reply to asphalt_gundam :

Another way of looking at it is: put the wrist pin as high up in the piston as it can be, measure down to the rod journal, and that's your rod length.  

I'm not exactly putting a lot of thought into it.  I am going to buy rods so that I can have floating wrist pins (something I am accustomed to having after a couple of decades in the import world and don't want to let go of,) and am going to buy pistons (assuming that the stock bores are going to be imperfect after 160K claimed miles,) so I might as well use a longer rod as long as the opportunity is presenting itself.  If 6" rods were custom parts requiring custom pistons, then I wouldn't do it for this engine.  But this is a SBC, and 6" rods and matching pistons can be bought off the shelf.  

asphalt_gundam
asphalt_gundam Reader
9/21/21 8:48 a.m.

In reply to Project822 :

Looking back at your original post of criteria a Vortec 350 should work great for you. Those late 90's heads had good ports in them, and the block was roller cam already. I used to refresh bread delivery truck engines, mostly 5.7 vortec and 6.0LS that would come in anywhere between 280K-350K and they'd need a bump hone and valve job. Idling for hours and highway miles are shockingly easy on an engine. Its pretty easy to get 400-420HP out of a 5.7 with stock heads + compression bump, cam, intake, headers. I'd recommend the Holley terminator X over the Sniper. Well worth the extra money, plus it opens up an electronic OD trans as an option too.

GasTungstenArc
GasTungstenArc New Reader
9/21/21 10:32 a.m.

In reply to asphalt_gundam :

Yeah, I'm set on the Vortec engine.  It's probably the best starting point that is still compatible with the Astro's accessory drive.  

I have pretty much left aftermarket injection behind.  As much of an FI guy as I am, it seems that a well-selected and correctly tuned carburetor is going to be a better, more reliable choice for my intended use.  

ClemSparks
ClemSparks UltimaDork
9/22/21 9:04 p.m.
Project822 said:
ClemSparks said:

If I was in your enviable position of not having a hard time finding a good 400 to build, I'd definitely give it a shot.  

...'round here, 350s find me.

That's an enviable position.  Certainly not $50, but I have seen several not-expensive (let's say cheaper than a basic cheapie 383 stroker kit) 400 bottom ends for sale within an hour from my house.  Of course, then the questions come: does it have good bores?  Has it been bored already?  Can it be bored in its current condition?  Is the crankshaft good?  And so on, and so forth, until all the questions have been asked.

Then there would be the matter of lifters.  I don't know how 400 flat tappet lifter cams held up, but what I do know is there was at least a time and a place when SBC engines would eventually eat their cams.  This limited knowledge leads me to fix the problem by converting to roller lifters on any non-roller SBC block, and that is another expense on a 400 block. 

Eh, forget the 400.  

And there (you've said it better than I did) is my answer to why more people don't (or at least why I don't) build 400s.  I'd have been buying them and stacking them up for the past 20 years if they were deals.  But I haven't been able to justify the price they (apparently?) command.  It's entirely possible that a core 400 SBC has never actually sold.   They're all just squirreled away in the same few folks' shop.

And I'm with you on the roller lifter issue.  I built my as-yet-unfired 350 with a flat tappet camshaft (my machinist suggested I should go roller cam unless I was prepared to use only special oil/additives for the life of the engine).  I just wasn't up for the added expense of a roller cam conversion on this old 2-piece-rear-main-seal block.  And really, replacement roller lifters are expensive even if you start with a roller cam block.  I don't know what their lifespan is but I'm guessing they should be new when you start with a freshly-machined build.  (says the guy who just re-used original 5.0 ford roller lifters for the Fairmont engine...damn I'm cheap).

SkinnyG (Forum Supporter)
SkinnyG (Forum Supporter) UberDork
9/22/21 9:19 p.m.

I put a flat-tappet in my '77 C10's 350 back when I built it 7 years ago.  Snotty cam, with appropriate valve springs. I usually run a quality oil (often Rotella), but I also add a half-liter of Lucas "Break-in" oil with every oil change.  Cam is still holding up just fine.  I'm with you - retrofit roller cams add a pretty big financial bite into a motor.

I got a Vortec 350 for free a few years ago. The "ticking noise" I was told it had, was two spun rod bearings.  The money to properly fix that, is easily "just get a different motor." It still sits where I took it apart.

GasTungstenArc
GasTungstenArc New Reader
9/23/21 7:21 a.m.
ClemSparks said:
And really, replacement roller lifters are expensive even if you start with a roller cam block. 

I'm not a rich man.  In fact, I'm so far from being rich that the light coming from being rich takes nine years to reach me.  With that said, I must have a skewed sense of what expensive is from living in the world of unobtanium import cars for so many years where I had to adapt, hand build, or custom order every go fast part.  The idea of paying $300 for a set of 16 new lifters (assuming that my lifters need to be replaced) doesn't seem so bad.  I had to pay $600 or more for a set of four or five forged pistons and wait weeks to get them, whereas now I can buy any set of eight pistons off the shelf and pay substantially less.  It feels like I am cheating somehow.  With that said, I will probably reuse roller lifters if my engine machinist says they're OK.  If not, $300 at Summit or Jeg's.  

asphalt_gundam
asphalt_gundam Reader
9/23/21 8:48 a.m.

Here you go you cheapies: Rebuilding lifters - pricing for automotive rebuilders, Mizpah Precision Manufacturing

Rebuilt factory lifters. Can even send in yours (on their list or not) and get them rebuilt or swapped out.

I've used them for some odd ball stuff and OEM roller setup engine builds before.

GasTungstenArc
GasTungstenArc New Reader
9/23/21 9:12 a.m.
asphalt_gundam said:

Here you go you cheapies: Rebuilding lifters - pricing for automotive rebuilders, Mizpah Precision Manufacturing

Rebuilt factory lifters. Can even send in yours (on their list or not) and get them rebuilt or swapped out.

I've used them for some odd ball stuff and OEM roller setup engine builds before.

Interesting.  I wonder what gets replaced during the rebuild.  

barefootskater (Shaun)
barefootskater (Shaun) PowerDork
9/23/21 12:04 p.m.

In reply to Project822 :

Part of why you don't see more 400 blocks out there is just production numbers. The 350 was around in a billion configurations in production vehicles from the late 60s until the early 2000s. GM still makes new ones. The 400 was only in production from 1970-1980. And they had a reputation for overheating that made a bunch of folks I know steer clear of them. The actual issues that caused overheating have well documented fixes and were overblown to start with. If you can find one that is serviceable, I'd say go with that. 
As for flat tappets, I think that issue was a bit overblown too. Cheap metallurgy from malaise-era production cost cutting started a bad reputation that just stuck around. A quality cam and quality oil makes it a non issue. 
That said, rollers are good. Quieter and less parasitic, and they allow for a more aggressive cam. But usually add $12-1500 to the cost of an engine build if you're retrofitting.  

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