'99 L31/4L60E into 71 C20: Observations

[Tim240Z]

Well, I got the engine fired and running. I haven't driven it yet as I have some more yet to do, but I found some interesting things during the conversion:

1: The PCM needs a brake switch that is open when the pedal is depressed. The regular brake light switch is closed (provides current) when the pedal is depressed. So I need to run 2 switches....no biggie, but one more thing!!

2: The L31 sounds pretty sweet with open headers

3: The Helms FSM is written and organized like a Taiwanese VCR manual!! The "Carline" FSM that I have for the LT1 is wayyy better.

4: After hours in the back reaches of two parts stores, there is no possible solution for oem radiator hoses for the L31 and the 71 radiator. I had to use one of those crappy flex hoses for the top, and splice 2 hoses together for the bottom. Not ideal, but I want to eventually get an aluminum radiator, so I am not too concerned about the cosmetics of the setup right now.

5: The L31 runs the oil through the radiator in the Suburban. So, since the truck did not have that provision, I was faced with a choice. Either block off the external oi lines, or run an oil cooler. I chose the latter and mounted it under the radiator on the core support. It will get some air flow, but not much. I was worried about keeping the oil too cool.

6: Driveshaft. Had it shortened 3.25" and overhauled. All I can say is that I am very very very glad I did that. One universal had 4 needle bearings (for the whole universal!!!) Center bearing was toast too!!!

Well, I have all the gauges working except the speedo (needs to be electronic). I think I will make a new dash panel with all aftermarket gauges though......later though.

7: Tilt Column: This was very easy!! Since all the transmission activity for the 4L60E occurs at the tranny, I could just bypass the PN lockout and the reverse light switch. Made the install very simple!!!

8: Fuel system: I got ALL the hard lines from the Suburban, so I used them. I used the original truck feed line for a return. I drilled a hole in the bottom of the tank and welded a fitting to it and ran some 3/8" Aluminum fuel line to feed the L31. Used the MSD 2225 inline fuel pump that I used with the LT1 in the Z car with a high flow filter before the pump and the OEM suburban filter after.
That's about it for now, I guess.......now that everyone is asleep

[HugrOrang71]

Originally Posted by Tim240Z

1: The PCM needs a brake switch that is open when the pedal is depressed. The regular brake light switch is closed (provides current) when the pedal is depressed. So I need to run 2 switches....no biggie, but one more thing!!

Use your existing switch to control a relay with a normally open position (5 pin) to signal the ECM.

[incoma]

Please keep us updated on this conversion. I'm absolutely fascinated with these conversions.

[Tim240Z]

Originally Posted by HugrOrang71

Use your existing switch to control a relay with a normally open position (5 pin) to signal the ECM.

Would you mind explaining the wiring on this one? I have completely rewired several cars, but I have ALWAYS used the std 4 pin relays.

Incoma....I will post some pics with some more info later this week. It has been an interesting conversion. Good news is that TunerCat now has editting software for these engines now!!!

[HugrOrang71]

This relay is also known as a single throw- double pole relay

Normally open


Relay pinout


Relay energized

[NPilot1975]

You can buy a brake switch that has 4 connections. 2 work as normal on the brake switch you have and 2 work the way the engine needs. I am overseas and can't get the part number right now, but I bought one when I installed the LT-1 in my truck. I seem to remember 2 connections on the side and 2 on the end.

[Tim240Z]

I looked at the suburban brake pedal switch at the parts store, and decided against it as there was not 'plunger' to speak of. I was unfamiliar with the setup and it looked like it would take a fair bit of engineering to get it working on the truck so I opted for the regular plunger switch.

HO71....could you fix the broken links? I can only see the second (middle) image

NPilot, What vehicle was that switch originally for? MAybe I can hunt it down by application and have a look see?

Thanks Guys!!!!

[dmec]

you can use a brake light switch from any car that had cruise control. it has terminals for no and nc and screw into the original mount. simple.

[Tim240Z]

Originally Posted by dmec

you can use a brake light switch from any car that had cruise control. it has terminals for no and nc and screw into the original mount. simple.

Of course...that makes sense!! Thanks man!

[NPilot1975]

http://www.painlessperformance.com/a...0509Manual.pdf

Look at the above link, page 12. That should give you what you need.

[HugrOrang71]

Hmm... its showing up on mine. Here's the direct links. Hope they work

Normally open

Relay pinout

Relay energized

[Tim240Z]

Jason.
I get the forbidden error when trying to access the links:

Forbidden
You don't have permission to access /45/3/3/27/319930327TJzvHu_ph.jpg on this server.

I should be able to figure it out from the Painless link above.
Thanks!!

[HugrOrang71]

Hey Tim, Try this one. I figured the info from painless perf would get you what you need. But, I'm trying to get this to work for my future posts.
Thanks,

[Tim240Z]

Get the first, but not the second (red X of death)

[Hart_Rod]

How is the truck coming? I'm thinking about purchasing an 05 vortec to put in my 69 suburban. What harness did you use? Motor mounts? Tranny mount? Was there an issue with the column shift? Any clearance problems? Thanks,

Rob

[minibike]

The stock brake light switch for cruise control applications works fine. I have the LT1/4l60e in mine. Also, the relay idea will come in handy when you get ready to control the fans. The computer probably is similar to the LT1, in that it sends a controlled ground for most of the commands to the engine/fans/ac, etc. You have to supply power to one post of the relay, and let hte contolled ground activate it for fans/ac, etc.

[Tim240Z]

I used the brake switch for a 94Z28 ( I have one of those, so I figured what the heck) with cruise control. Works just right!!

I have driven the truck a whopping 10 or so miles now. Drives smooth and the lower RPMs are great!!
(BTW, my 350/350 that I took out with <10k mile is for sale in the parts forum....little plug there!!!)
I used the oem harness and just pinned out the wires with the FSM in hand. Everything appears to work just fine, except the electric speedo. I used the PCM output wire for signal, but I know better....I need to splice into the wire coming directly from the speed sensor at the trans.
The L31 Vortec engines use the same mount locations as the old school SBCs, so mounting was not an issue. Even the tranny X-member bolted to existing holes in the tranny after moving it rearward...
The only clearance problem was the linkage at the tranny. The part that slides over the bracket on the chassis was too close to the tranny (I guess the 4L60E is about 3/4" wider at that point). I just cut the arm and re-welded it...no prob....

Some more info:
http://67-72chevytrucks.com/vboard/s....php3?t=153872

http://67-72chevytrucks.com/vboard/s....php3?t=154482

[NPilot1975]

Rob-

You can bolt the 4L60E straight to the original auto crossmember. I used the Lokar column shift linkage in my first project, which worked great. I am thinking of going with a floor shifting in my new project due to having a console. I had no clearance problems at all with the 4L60E and a low hump floor.