Stroked LS3 '81 to '87 Grand Prix

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GR8ONE68

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Jan 9, 2015
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OK, I've been lurking, researching, and learning. First of all, I'm a Pontiac guy through and through. I had a '68 GTO for 25 years. I traded it back in 2017 with no regrets. I had run my course with that car and had a lot of fun along the way. 1967 was my favorite year for the GTO and all GM cars for that matter. My plan was to get a '67 to retire with, but the way the old car market has gone in the last 5 years, I'm out on that idea. I refuse to pay $50k for an average condition car. The first new car I ever bought was a 1983 Pontiac Grand Prix LJ Brougham. I have loved that body style ever since. With the '67 GTO out of the picture, I've decided to pick up a 1981 to 1987 Grand Prix and do an LS swap. I won't go into details of what I want, but I'll be looking for a while before I get one. I have been researching and putting together a plan and wanted to throw it out there for comments to make sure my logic is right and recommendations on some areas that I haven't settled on yet. I plan to go with an LS3. I will bore it out .010" and use a 4.1" stroke crank. Why, you ask? Nostalgia! If you do the math on that combination, it comes out to 427.8 cubic inches. Most would call that a 427, to me, it's a 428. This wasn't the way I really wanted to get there, I wanted to bore an LS3 .060" (4.125") and use a 4" crank. That is almost exactly what the Pontiac 428 bore and stroke was, 4.12" bore x 4" stroke. But that was the old cast iron block thinking, you can't bore an aluminum block that much. Oh well, the .010" overbore and 4.1" stroke gets me there. I will put old '67 to '69 Grand Prix 428 badges on it. Below is a breakdown on what I plan so far:

Motor:
LS3, +.010", 4.1" crank
Cam, TBD based on recommendations with my goals in mind.
Heads, stock LS3 heads, upgrade the valve train if my cam choice dictates the need.
Intake/throttle body, Stock LS3, but willing to change if it's necessary to get me to my goals.
Rotating assembly will be forged and balanced.
I will want/need an alternator, P/S pump, and A/C, I read something about an F body pulley for one of them to clear, help? Will a stock serpentine system work? Which one?

Transmission:
4L80e, will I need to upgrade it to handle my goals?

Controllers:
Holley Terminator X Max to control the motor and trans. Is there any reason to go with the Dominator other than "It's better"? Does it have any features that I may want? What are some of the inputs/outputs available that may be nice and I'm not thinking of?
Dakota Digital ECD-200 to keep the stock speedometer with the electronic trans.

Rear:
12 bolt Posi with disc brakes. If I get it going, I want to make sure it stops...
Gears: TBD based on the combination. I'm thinking 3.55's, but I want it to match the cam choice so it gets me into the right RPM range.

Wheels/Tires:

I want a stock looking car. I plan on using Wheel Vintiques Pontiac Rallye II's 17" x 9" with 275-40-17 tires in back and Wheel Vintiques Pontiac Rallye II's 16" x 8" with 225-50-16 tires up front. Will 235 50 16's fit up front without rubbing in turns?

Goals:
I want a stock appearing, very fast car. A sleeper. I would like it to hit 500 hp. I think this is a very reasonable goal, the LS3 is 430 HP stock. I'm thinking that with the added 52 cubic inches and a mild cam upgrade, I should be there. I'm not trying to squeak out every HP I can, I don't want a lopey cam. I had that in my GTO and loved it. But, at my age, I'm past that.

Thanks in advance!

Thoughts and recommendations?
 
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Texas82GP

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Apr 3, 2015
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Subscribed. It sounds like a well thought, fun build that will make for a fun car. I have 235/60/16's on mine. There was some rubbing at full lock when turning right with suspension compression. It will depend on backspacing and ride height.
 
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Streetbu

Know it all, that doesn't
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May 22, 2011
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Sounds like a fun ride! You might find getting a crank with that stroke to cost too much $ though. Sloppy Stage 2 cam would be fine for your build, and won't have much lope with that many cubic inches
 
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Tony1968

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Jul 1, 2018
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Easily capable of 600hp with those cubes depending on what you do to the heads and cam. Just be careful with the 4.1 stroke. Make sure the combo doesn't allow the pistons skirts too far out of the bore at bdc. Maybe discuss with your machinist
 
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Osmobile Calais

Not-quite-so-new-guy
Mar 19, 2023
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wow! can wait to see your dream come true. You make me want to swap my 307 A.S.A.P.
 
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maxi426

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Sep 20, 2018
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Can't wait to see this come to life. I would like to see it with a stick, but I get it.
 
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GR8ONE68

Not-quite-so-new-guy
Jan 9, 2015
13
12
3
Subscribed. It sounds like a well thought, fun build that will make for a fun car. I have 235/60/16's on mine. There was some rubbing at full lock when turning right with suspension compression. It will depend on backspacing and ride height.
Thanks, Tex. That's the information I'm looking for. I'll stick with the 225's if it's even going to be close.
 

GR8ONE68

Not-quite-so-new-guy
Jan 9, 2015
13
12
3
Sounds like a fun ride! You might find getting a crank with that stroke to cost too much $ though. Sloppy Stage 2 cam would be fine for your build, and won't have much lope with that many cubic inches
Street, I'm looking at this rotating assembly (https://www.texas-speed.com/p-1019-tsp-427-or-429-cid-ls3l92-rotating-assembly.aspx) I called and spoke with them, I can get it with 4.075" pistons. Does anyone know anything about Texas Speed and Performance or their parts? The forged 8.1" stroke crank is $875 by itself.
 

GR8ONE68

Not-quite-so-new-guy
Jan 9, 2015
13
12
3
Can't wait to see this come to life. I would like to see it with a stick, but I get it.
Years ago, I would have wanted a stick as well. At this stage of my life, an automatic is almost mandatory. I had a '99 Z28 and it had to have the manual 6 speed. In '99, I had no idea the the motor I had there (LS1) would be so used in swaps.
 
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GR8ONE68

Not-quite-so-new-guy
Jan 9, 2015
13
12
3
Easily capable of 600hp with those cubes depending on what you do to the heads and cam. Just be careful with the 4.1 stroke. Make sure the combo doesn't allow the pistons skirts too far out of the bore at bdc. Maybe discuss with your machinist
Tony, yea, I was thinking my goals should be fairly easy to hit. Do you think I can do it (500 hp) with a mild, non lopey, cam without doing any port work?
 
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