99 SLE Motor swap

[99bonnie]

Hi again guys. I have a GTP that I can rip the guts out of for the L67 and tranny. I was wondering if it is possible to swap the Motor and tranny into my Bonnie. Any advice or issues that I will come against or if this whole idea won't work at all for me. Thanks guys

[J Wikoff]

Sure it's possible. Make sure you get the engine harness and PCM. There might be an axle difference, I'm not sure.

[LeSabreUltra]

I'm almost positive that there is an axle difference between S/C and non S/C.

What year GTP?
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[99bonnie]

I think it is a 2000 gp and I have the entire car too play with. It is a two door not too sure if that will make a difference don't think so though. Do you think I will need to take all the tranny and motor mounts.

[1fatcat]

It can be (and has been) done, but it is generally much easier, better and maybe even cheaper to just sell the N/A car and buy an SSEI.

[LeSabreUltra]

True, it is a lot easier to just buy a S/C car. Good advice there.

And leave the mounts with the GTP, they are different than the ones for the Bonneville. It's a good idea to just get new mounts anyway.
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[95naSTA]

Hi again guys. I have a GTP that I can rip the guts out of for the L67 and tranny. I was wondering if it is possible to swap the Motor and tranny into my Bonnie. Any advice or issues that I will come against or if this whole idea won't work at all for me. Thanks guys

You'll need a passenger side axle from an ssei, you'll have to make sure there are threaded holes in the rear of the trans so you can use the h-body rear trans mount, and you'll have to possibly get a ssei front tensioner assembly to run the passenger side T/A mount.

[J Wikoff]

Is there a different alternator bracket as well?

[99bonnie]

Ok thanks guys The only problem with me selling my car is I won't get anything close too what I have put into my car. But in all seriousness I want the supercharged version really bad. Would it be worth my while too just swap the top end

[J Wikoff]

It can and has been done. Some have had good results, some haven't. The L67 bottom end is stouter to handle the boost. If GM determined the L36 bottom end was good enough for reliable boosting, they'd have made it common to the L67 to save cost, but they didn't. If you do the top swap, there's a good chance you'll be doing a full swap later because of a spun bearing.

[LeSabreUltra]

Well, there are two big issues that make a top swap even more difficult than just swapping for an L67.

First is tuning. The L67 and L36 internals are not the same. Neither are the transmissions. You will have to do a custom tune to account for this which means some form of a tuning kit like HP tuners, and then on top of that I believe you will have to buy credits for your car so that you can actually tune it. That altogether is roughly $600, maybe more. And, you also have to know what you are doing with the tune lest you want to encounter severe engine damage.

Second, is again the transmission. The transmissions attatched to the L36 are not built to withstand the extra power output of an L67. You can either swap...which begs the question since you are going to all that effort, why not swap in an L67...or drive with a featherfoot all the time. Which leads to the question of why bother with a supercharged engine in the first place, if you can't even enjoy it.

Top swaps have been done with success on the L36, in fact they actually make more power than a stock L67. But they take a ton of work.

To get a supercharged car, the method of preference from easiest and cheapest, to hardest and most expensive, seems to be buy an SSEi, L67 swap, then top swap.
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[95naSTA]

The main difference between the 4t65-e and the HD is the differential. There really isn't much beyond that. Swapping an HD diff/sun gear/diff cover/ssei axle is fairly easy.

And top swapping is all about flow and tuning. The top ring landing is thinner on an L36 piston and it will be more prone to chip from KR. But, tons of hars have top swapped without issues.

Is there a different alternator bracket as well?

There's no difference between the L67 and L36 alt bracket but they did change the alt and tensioner assembly in 98 or 99 or both.

[99bonnie]

Ok guys you made the decision pretty easy. Drive the sle till it blows and go out and buy myself an ssei. Although I love my Bonnie now I just can't stand not having the supercharged like my old Buick had. Appreciate the help I'll let you guys know how it turns out.

[00Beast]

If you have the time, money, skills, patience, tools and space to do it, go for it. I'd recommend swapping the entire powertrain. From a GTP you'll need to change the motor mounts, and you'll need a different passenger side axle, and while it's out you're going to want to replace gaskets as well so you don't have to deal with it in the future. You also will need the harness from a 98 or 99 supercharged Bonneville, as a few of the w-body connectors are different. You will also want to have someone with a tuner flash your PCM with the correct tables, or get yourself HP Tuners and learn how to use it.