In over my head

[WhatIsItThisTime]

Hello all,

This is my first engine swap that is not a direct fitment, & I'm starting to believe that I may be in over my head (as the title suggests). So, I'll try to keep this short:

I have had my '83 Grand Prix Brougham for quite some time now, it was actually my first car. The 3.8 bit the bullet years ago, so I parked it. I obtained a '69 Pontiac Bonneville & pulled the 428 & TH400 (all running) with the intention of swapping it into my GP. I currently have the 428/TH400 resting in the car. Now, there are obviously not many white ups that I have found detailing this swap, so I have done plenty of homework based on what I could find. I know I will have to mod my Driveshaft, I have found the Jegs crossmember I need, I have the engine mounts & have ordered the clamshells to mount. I'm not sure what to do about the exhaust & do not have the means to modify exhaust.

However, lately I have been considering selling the 428 & LS swapping it, but I'm lost at this point & could use some pointers. I want somewhere between 300 - 500 hp out of it, nothing crazy, she will not be spending much (if any) time on the track. I do intend to stick with a carb. What LS do you guys recommend? Do you recommend going the 428 or LS route? Should I keep the TH400 or sell it paired with the 428? Keep in mind, I'm working on a pretty limited budget.

I'm sorry if this post does not belong here, it just seemed to fit best & any help I can get would be appreciated!

 

[fleming442]

It's no secret that I am 95% anti-LS; anybody can do it (and they do). So, naturally, my vote is going to be 428, but I'd do a built 2004R instead of the TH400. You have the engine mounts; just get the crossmember (AND frame extension for the driver side) and have a driveshaft made.
You'll have to do the rear regardless of which route you take as the 3.8 would have a 7.5" behind it. Some will say they are fine with 28 spline axles and a posi, but for peace of mind, I would get something stronger (8.5, 9, 8.8, S60, etc.).
What's the exhaust problem, headers? Then, it depends on what you do to the engine; you can get away with manifolds fine up until about 450-500hp. Ram Air Restorations has some high flow cast units. There are a bunch of bolt on "cat back" or header back kits for G bodies. Some have issues with tailpipe fitment. Or, you could piece together your own as MBS apparently has some nice-fitting tail sections.
There's a bunch of talent on this board. Post your location, and maybe someone can recommend a good Poncho guy in your area.

 

[tdvick]

I have to agree on Pontiac power. The ‘69 motor makes it a little more challenging for the mounts, but you said you have that covered? A ‘70 and up block will bolt right in using the g body 301 block mounts and new clamshell frame mounts. You’ll need adapters to bolt up the block mounts to that ‘69 block. The ram air exhaust manifolds are a nice option. I believe they sell the front pipes too that will go between the manifolds and pretty much any aftermarket header back system. If they don’t have them, Pypes does. If you want headers, I think if you call Maddog, they’ll make you a set. For your power goals the RA manifolds would be plenty good though.

 

[joesregalproject]

I'll also throw in my .02 and tell you to stick with Pontiac power, especially a 428. That's one you don't see nearly as much as 350s, 400s and 455s. Put the 428 in it and you'll have something cool, out an LS in it and it'll just be another LS swapped car. If you do decide to go with an LS, the LQ4 is the best bang for the buck IMO. LQ9s are great if you can find one but they usually sell for a premium.

 

[lilbowtie]

You have the 428 - use it !! No matter what engine you put in there your going to have some problems. An LS swap will probably be more detailed than what your doing. The Pontiac v-8s are the same size and the early G body Grand Prix used 301's, you might learn something there. The 400 is a tough trans, keep it - in all my years of racing I haven't hurt one yet. Take your time, if you start feeling overwhelmed ask for help. Google is your friend.


http://pontiac-g-body.tripod.com/id48.htm

 

[Turbolq4]

I'm pro LS engines unlike some around here. Abandoning the setup you have and starting an LS swap will actually be more trouble than you have now. Big inch Pontiac power is good stuff, just don't overrev them.
Keep the poncho plant, it's cool, simple, and you have it already.

 

[DRIVEN]

428

 

[ssn696]

LS swaps are easy these days. If you don't have emissions testing in your area, keep the 428 and figure it out with advice from the Forum. "We choose to go the moon, not because it is easy, but because it is hard."

 

[olds307 and 403]

It sounds like you have all the hard stuff worked out, stay 428. There are a bunch of good manifolds for Pontiac, go with the Ram Air selection above. What stall converter and gears are you planning? The 7.5" on slicks may not last long with the 450+ ft/lbs of torque. The only way an LS is worth the swap, if mpg or boost are in the equation. As said 6L and up, is the best way to go. The 5.3 is a gutless dog down low in stock form, more cam, stall and better gears would be neccessary. Good luck.

 

[pagrunt]

I'd go Pontiac power. Best is you already got it. Like as posted by fleming442 get a good TH200 4R behind it. Then find the just right rear ratio. I think you would get more lookers with it than an LS. As for the adapters, here's a link.http://www.firebirdcentral.com/1967_1969_Firebird_Engine_Conversion_Bracket_Kit_p/enc-2242.htm