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My V8 Questions

2K views 18 replies 9 participants last post by  GasTungstenArc 
#1 ·
Let's say for the sake of argument that I have a 2000-onward Astro/Safari RWD and want to swap in an L31.

Here are my questions:

1) My understanding from reading here is that all of the 4.3 accessories bolt up. Do they bolt up with correct alignment to the crank pulley and to ALL Gen 1 and 2 SBCs? Does anything need to be clearanced or extended (thinking about AC and PS lines?)

2) When the 4L60E explodes, what is involved in replacing it with a 4L80E? Does the factory TCU control a 4L80E correctly? If not, can it be reflashed to do so? If not, does the whole TCU and harness have to be replaced?

3) Does the factory L31 engine management respond well to minor power upgrades such as camshaft, headers, exhaust, and cylinder head porting?

I have done enough swaps to know that nothing of the sort is exactly easy, and there will be plenty of opportunities to lose sleep. But making the right choices in the large parts will make everything downstream of those choices a lot easier.

I feel embarrassed not knowing more than I do about SBC engines with as much automotive experience as I have, but my whole automotive life to this point was lived in the import world.
 
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#2 ·
Without info on the van, gen1 or gen2, 2wd vs AWD etc, its hard to be specific on what is needed. Mine is a gen1 AWD so its a lot simpler of a swap than gen2.

AWD complicates things some because of motor mount and oil pan issues and unless you want to do something really exotic headers won't work. I looked at an LT1 Camaro engine but it would require an ECM and harness change because of the fuel intake and optispark ignition system that would change the accessories placement.

The TBI is almost plug and play with only minor changes to wiring. All my accessories will bolt directly from the 4.3 to the 5.7 so I won't even need to change the belt.

I don't know where you got the idea that you can't put a 4L60e behind a V8 because GM used it in everything from Corvettes and Camaros to trucks. I'm building a stage1 performance 4L60e to put behind mine but a stock one will work just fine.

My suggestion is try to find an engine that is the same year as the van to minimize the alterations that will be needed.
 
#3 ·
As to computer control gen1 uses a PROM chip and you can have custom prom chips burned to accommodate cam and intake upgrades. Never burn over the stock chip, get a separate one.
Edit: You have to have the stock PROM chip from the donor vehicle because the V6 chip obviously won't work.

Gen2 is OBD2 and can be reprogrammed with Tunerpro or something similar on a laptop.
 
#4 ·
Also some transmission notes.
Prior to 92 all vans had a 700r4.

92-93 had a 4L60 still controlled by cable and vacuum.

94-95 are the only gen1 to use the 4L60e so they have a specific ECM to control the transmission.

Gen2 96-up went to a 2 piece transmission with a detachable bell housing and there are variations of those depending on the year. Again it pays to find a compatible year engine so that everything plays nice together.
 
#5 ·
1- AC and PS lines reached just fine on my swap. I even used the stock mechanical fan with no clearance issues.

2- I stuck with the 4L60E that was behind the 4.3. I even kept the 4.3 torque converter. Looking back, I should have swapped it with the 5.7 converter. The stall speed is different (iirc by 200rpm), and I think that contributes to my van liking to stall at traffic lights. I kept it because it was a known good unit in a junkyard swap, and I wanted as many known quantities as possible. I do have the trans and converter from my donor vehicle (G20 van, same year), I may swap it in one day.

3- I'm not much help here, I kept the TBI that was in the donor van. I added the plug for the second injector by reusing the 4.3 tuning valve wire and moving it to the proper pin at the ECU. I had to replace the connector to (I think) the IAC, but that was color coded wire for wire solder and splice. The rest of the wiring was plug and play. I'm still running the 4.3 ECU with the 5.7 chip. I have the 5.7 ECU, it's the same part number. I did swap them around when I had a problem with the engine dying, turned out it was unrelated.

I'm not familiar with newer injection systems so I can't be much help there, sorry.

Good luck with your swap!
 
#7 ·
5.7 vortec has the spider injection, the MPI conversion is still a spider. So if you dont want TBI, spider or carb you really have aftermarket FI. I would not go with them. Need a part you get to wait, need tech help get to wait for emails for trouble shoot. All that does not work send it in and wait weeks for them to check it out and then decide if its warranty or not. Nephew just went through this with a MSD atomic. Found out bad ecm or what they call it.
 
#9 ·
Personal prefrence, I would way rather have the spider FI assy, can easily be upgraded to Delphi/Multec individual injectors - than the Optispark iginition of the LT1. I know the Optispark system is more advanced in regards to timing control, seems like it can adjust cylinders individually. Known too many people have issues with replacements. Not an ideal placement either.
 
#10 ·
Bikley said:
I don't know where you got the idea that you can't put a 4L60e behind a V8 because GM used it in everything from Corvettes and Camaros to trucks.
I didn't say that it can't go there. I said that it shouldn't be there. The 4L80E is a way more durable transmission, which I would prefer to have over a 4L60E.

I didn't provide specific information about the van because I don't have it yet. But it will likely be 2000 or later, and very likely a RWD simply from a numbers standpoint.
 
#11 ·
GasTungstenArc said:
The 4L60E probably shouldn't be behind a V8. ...
I want to avoid ALL spider injection and TBI engines, and I am not willing to go carburetor.
GasTungstenArc said:
I have done a lot of swaps and turbo conversions in my life. I can create pretty much any part I need.
Looking forward to your 'Decision(s)'. 5.3?, 4L80E?, Turbo down under?, woohoo.
That Pallet of Popcorn is going to come in extremely Handy.
 
#12 ·
02GMC said:
Personal prefrence, I would way rather have the spider FI assy, can easily be upgraded to Delphi/Multec individual injectors - than the Optispark iginition of the LT1. I know the Optispark system is more advanced in regards to timing control, seems like it can adjust cylinders individually. Known too many people have issues with replacements. Not an ideal placement either.
That is true about the Optispark. The late Optispark Corvettes had a vented unit that was supposed to stay cooler and dryer than the earlier units, but those are still going on 30 years old, and with GM ceasing production on replacements, the aftermarket replacements are questionable.
 
#13 ·
sixsix said:
Looking forward to your 'Decision(s)'. 5.3?, 4L80E?, Turbo down under?, woohoo.
That Pallet of Popcorn is going to come in extremely Handy.
For this one, I have to keep it as simple as possible--no turbochargers and no heavy fabrication.

Reading input from others here on this thread, I wonder if I might not be better off with some LS based engine (such as the 5.3 you mentioned) and dealing with accessory fitment/adapting instead of old injection and ignition.
 
#14 ·
After a whole lot of looking around, I think I have come to the decision that it would be better to deal with the difficulties of installing an LS-based engine instead of a TBI or spider-injected Vortec. I realize that those latter two are good engines, but I would be leaving lots of power and potential on the table and would probably lose efficiency compared to an LS type engine. I have a friend with an LQ4, and I can buy it for $600 with harness and ECU. Maybe it's worth wrestling with making the driven accessories work after all.
 
#16 ·
Personally I would love to have a 5.3LS but I already have a 5.7 TBI in which I totally rebuilt both the engine and the TBI for performance and I built my 700R4 with shift kit and all the upgrade parts so I would be throwing money away so to speak. As for the 4l80 transmission I have no idea if it will fit and how much mods would be needed to install one. So if you do go that route I would be interested in what you have to do to make it work. FOLLOWING! Mark
 
#17 ·
dcsleeper said:
an L31 with a belt driven supercharger would be easier than that. Read some LS based threads here.
That might well be. My issue with TBI and spider engines is the engine management, not the engine itself. I like conventional SBC engines. But the engine management was never great. The TBI and spider (CPI?) systems are physically limited in their ability to deliver fuel. The LT1 has the Optispark issues, which would probably be worsened in the Astro's hot engine bay.
 
#18 ·
TBI can be modified much more then the spider systems, You can have a chip custom burned add larger injectors, add a fuel pressure regulator to up the pressure. Add a riser to the injectors, port and polish the TBI unit for more air in and better fuel atomization. I have done all of these except the adjustable regulator since I just added a higher pressure spring and am happy with it. I also swapped the intake manifold out for a Edelbrock version. My 350 was originally from a 91 Silverado but I ported and polished the heads, added a cam from a 96 Caprice police car, timing set for a LT one Camaro. According to an online dyno my engine is right around 360 hp at the flywheel and 380 torque also at the flywheel which is pretty good for mostly stock GM parts. Some day I would like to build a 355 or 383 with vortec or aftermarket heads but keep the TBI set up the same. I also have police car injectors on my engine. All my notes for the engine are in storage as is my van so I am going on memory only at this time. Mark
 
#19 ·
I talked to a friend yesterday who made some good points about modern SEMS. It has come a long way from when I last used it, and systems such as the Holly Terminator are able to learn and build maps as they go. Concerns over engine management are what have held me back from going with the easier-to-install L31 over the albeit-superior LS based V8.

Would a 2000-2005 Astro have a discrete TCM that did not care how many cylinders the engine had?
 
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