71 C10 LQ4/4L80E Mounting Questions

[SabbathFanatic]

Hey guys, got my front clip pulled off as an assembly last night. Other than one of the core support bolts being a pain, that was ridiculously easy. I love this truck! Pulling out the 350/TH350 combo this afternoon. Got a few questions for planning the next stage of the build once my LQ4/4L80E combo gets here next week.

My plan for moving the crossmember is to measure from bellhousing face to trans mount on both the TH350 and the 4L80E and move the crossmember whatever the difference is. Got a few questions for people who have done this before:

1. The engine mounts I'm using can put the engine in four different places:

• Stock location
• 7/16" forward
• 1-3/4" forward
• 2-1/4" forward

I'll have to take whatever placement I choose into account when I'm calculating distance to move the crossmember. I'm not using A/C, so my understanding is that the placement should only matter for header clearance. I basically don't have any money after buying the engine/trans, so I'm going to use some of the cheap eBay LS swap headers. Do I need them before I choose where to put the engine? I'm thinking stock location so the shift linkage lines up right. What is you guys's experience with engine placement and header clearance issues?

2. I've got the front clip off, and the bed is coming off for the fuel tank. Is it worth it to take the cab off too? It seems like that would make crossmember relocation and engine/trans install way easier, but it would also mean I have to redo the front clip alignment when I put it back on. I also wouldn't know about any firewall/trans tunnel clearance issues until I put the cab back on. Opinions?

[izzy_Britton]

i can only speculate as to what i have seen on many of the other builds and what i can remember. but it seems to me that the 4l80e isn't much different in diameter (height) than the the TH400, the TH400 fit fine under the cab so the 4L80e should fit fine as well. i don't recall off hand any builds where the floor had to be modified for the 4L80e to fit unless the engine was moved rearward. so removing your cab shouldn't effect that portion of the install.

also the LS in the stock SBC location will actually give you slightly more firewall clearance because there is no distributor to interfere with the firewall, typically that was an issue in the past with distributor equipped engines.

i cannot answer anything about the header question, i am not a header fan. I like the fit of my factory camaro exhaust manifolds. did/does your purchased engine come with manifolds? if so you could use them. there may be a slight frame clearance issue but most people just notch the frame a hair to get them to fit in there.

[mongocanfly]

definitely leave the cab on....if your gonna use headers, getem before you set the engine...don't put the trans crossmember in until you have the engine and trans installed in proper location...guesstimating where to put it will mean it'll probably have to be cut back out...don't forget about keeping a downward angle of about 3deg or so...needs to match rear yoke upward angle..

[SabbathFanatic]

>> it seems to me that the 4l80e isn't much different in diameter (height) than the the TH400, the TH400 fit fine under the cab so the 4L80e should fit fine as well. i don't recall off hand any builds where the floor had to be modified for the 4L80e to fit unless the engine was moved rearward. so removing your cab shouldn't effect that portion of the install.

>> also the LS in the stock SBC location will actually give you slightly more firewall clearance because there is no distributor to interfere with the firewall, typically that was an issue in the past with distributor equipped engines.

Awesome. Thats what I thought.

>> definitely leave the cab on....

What's your reasoning?

[mongocanfly]

I say leave it on because its gonna suck if you pull it off and then find out you missed a measurement somewhere and have to start cutting and moving..having it in place gives you a reference point. .

[SabbathFanatic]

Awesome. Sounds good to me.