L67 GXP build (update: 9/16/13)

[harofreak00]

Time to get the thinking cap on.

I want to remove the N*/4t80e combo and replace with a modded L67/4t65e-HD combo. I'm fairly confident I can this swap without much guideance, but I want to just go over it in case I'm missing something.

Things that are different:
Engine/trans mounts
Exhaust
Radiator
Overflow tank
Coolant hoses
Fuel lines
Wiring harness
Fuse box
Brake fluid reservoir
Axles

Pics for reference:

[93 SSE 4 ME]

Good luck and congrats for having the nuts to take this on. I wish I was closer to MN, I'd love to lend a hand on this one. Still may take the SC route in mine someday.

Mark

[repinS]

- Only the front trans mount is different. The remainder are the same, though somewhat moot since you'll be subframe swapping.
- Any way to keep the twice-as-thick GXP radiator? I notice the hoses go to the opposite sides.
- Throttle and shifter linkages?
- Fuel pump and system should be the same?

[SSEiMan01]

If there's no way to keep the GXP rad, you could go with an aftermarket for an SSEi that would be thicker...
I would think that the fuel pump for a GXP may be higher volume, and the fuel line routing may be different, That was an issue on my swap from TPI to carb on the 85, the fuel lines ran down opposite framerails...IDK about a Bonneville though. My concern would be, like Jerry said, the shifter and throttle linkages...
Looking forward to seeing this come together!

[repinS]

Rock Auto does list an interchangeable AC Delco pump between all years and trims of 2000+ Bonneville, so I would assume it shouldn't be an issue. Where the lines come past the firewall and go to the motor may be more of the issue.

The more I think about it, I'd even venture to say that the subframes are the same between the two cars - there wouldn't have been a reason for GM to change it a whole lot. That front trans mount is different ONLY in the upper section; the place that it mounts to the subframe looks awful similar to the 3800's. It's an annoying difference, if Andrew does end up removing the N* front trans mount, he'll quickly see why you can't easily do a hockey puck mount

[harofreak00]

I may or may not swap the subframes. I'd love to swap over the subframe from my SSEi since it has the new control arms and end links, but it might not be worth the time. You say only the front trans mount is different? I know for a fact that both driver and passenger side mounts are different. The rear may or may not be different.

The GXP radiator isn't worth keeping, too much different. the hoses and trans cooler lines are completely different.

Good call on the throttle and shifter linkages, they probably will transfer though.

Not sure on the fuel pump. I'd assume that the N* would require the same or more fuel than the L67. I'll have to make new fuel lines.

[00Beast]

AFAIK the only "Aftermarket" radiators for SSEi's are either stock replacement or one-off's.

[repinS]

Is it a big difference? I've been chasing a lot of mount issues with my N* and being such low production volume, I've been cross-referencing part numbers between other cars a whole lot. To my knowledge, based on GM and/or aftermarket part numbers, the rear and two side mounts are the same.

GM Parts East seems to say the same for the side mounts, but lists a different rear mount. Odd, considering I currently have Anchor part # 2898 in my car, same listing for all 2000+ H-bodies. I suppose you're in the best position to confirm since you have both in front of you

Also: The only actual difference in the front mount is that the top stud comes out at an angle, rather than parallel to the bottom stud like on the 3800.

[Bing]

Might be out in left field with this one, but are the front spring rates the same between the cars?

Is there much of a weight difference between the drivetrains?

[00Beast]

The GXP suspension is the desirable one, lol. The difference in spring rate will help handling.

From what I can tell the N* is around 470 lbs and the 3800 is around 400 lbs.

[swampthing]

If I recall correctly the gxp exhaust will bolt up to an ssei downpipe and it is a little larger then stock ssei size. Do yourself a favor and keep the gxp exhaust and get a zzp downpipe to go along with it

[repinS]

The GXP suspension is the desirable one, lol. The difference in spring rate will help handling.

From what I can tell the N* is around 470 lbs and the 3800 is around 400 lbs.

That seems to make sense. The LD8 Northstar should theoretically be a bit lighter because it is all aluminum, but the difference is lost with the extra two cylinders and the (massive) 4T80 being 100lbs heavier than the 4T65.

[00Beast]

GXP exhaust is only marginally larger than a stock SSEi exhaust. A Hogan 3" DP would be a more feasible option, it would bolt to the exhaust.

[olblueeyesbonne]

Are you sure the cradle is going to be the same?
I tried checking on gmpd and another source and can't find any pertinent info.

[repinS]

GMPD and GM Parts East both show two cradle types - not split between LD8/L67, but rather FE5 and FE1/FE2.

[00Beast]

Probably because 3800 bonnes all had FE2/FE1, and the N* Bonne had FE5...

[swampthing]

GXP exhaust is only marginally larger than a stock SSEi exhaust. A Hogan 3" DP would be a more feasible option, it would bolt to the exhaust.

According to once source on bpro, its 2.5 which is a decent improvement over stock without being too large.

[00Beast]

And I've been under 2 GXP's on a lift, multiple times, and more SSEi's even more times. There is only one spot where it really appears that the GXP exhaust is bigger, and it's between the cat and the resonator. The SSEi exhaust is technically 2.5" to the Y, where it splits into 2.25", which the GXP also appears to do.

Someone remind me next time I'm under our cars, I'll measure them with a calipers and give you all the cold hard facts, except I'll measure 3" between the cat and res, LOL.

[Sadden]

Whats your goal here andrew?

[repinS]

Here's a big difference: The GXP doesn't have a resonator

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Andrew, more points to confirm/consider (just throwing things out there):

The A/C setup in your pics next to the fusebox. Is that a difference or are the parts just different colours?
What about vacuum hose routing? Will there be any leftovers once you gut the engine bay?
Cruise?
Steering component locations (rack, lines)?
Brake line routing downstream of the master cylinder?
EBCM location?
Would you have potential issues on 4T65-E outputs for HUD compared to those from the 4T80? Or does it pull from the WSS at each wheel?