Stroked LS3 '81 to '87 Grand Prix

Tony1968

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Jul 1, 2018
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I'd like to add to RabbitHoleSS by saying before you buy anything new, talk with your machine shop of choice. Many can get a far better price for blocks, rotating assemblies etc for less than the average guy. I saved quite a lot by doing this. Just an FYI
 
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64nailhead

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Dec 1, 2014
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I’d tell you to save your money on that rotating assembly with a 500 hp goal (unless it’s a 500whp goal).

An LS3 with a proper cam, valve springs and headers will make 500 all day long.

Regarding the 4L80, a proper stock rebuild will last you a lifetime. Let the cam choice make your converter decision.

11.9 compression will work if you can keep your intake temps under control, but it begs the question if ‘why’? 10.5-11.1 will be more than adequate for a daily driver.

And for a daily driver, the Term X Max is way more than enough (I make double your goal with an X Max and properly setup stock 4L80 and a 5.3 with a little boost).
 
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Tony1968

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Texas82GP

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Apr 3, 2015
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I’d tell you to save your money on that rotating assembly with a 500 hp goal (unless it’s a 500whp goal).

An LS3 with a proper cam, valve springs and headers will make 500 all day long.

Regarding the 4L80, a proper stock rebuild will last you a lifetime. Let the cam choice make your converter decision.

11.9 compression will work if you can keep your intake temps under control, but it begs the question if ‘why’? 10.5-11.1 will be more than adequate for a daily driver.

And for a daily driver, the Term X Max is way more than enough (I make double your goal with an X Max and properly setup stock 4L80 and a 5.3 with a little boost).
A little boost? :sneaky:
 
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64nailhead

Goat Herder
Dec 1, 2014
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No boost needed for 500hp if you can stand a rumpety thump cam.

But a little boost will make everyone smile (or at least me).

I’d tell the OP or anyone looking for 500-800hp, a little boost goes a long way. Spending money on a built short or long block is a humongous waste of money when a 150k mile 4.8 from a JY van with a Wuhan war whistle for the same or less money will whip you like it’s an early 19th century plantation owner.
 
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GR8ONE68

Not-quite-so-new-guy
Jan 9, 2015
13
12
3
I’d tell you to save your money on that rotating assembly with a 500 hp goal (unless it’s a 500whp goal).

An LS3 with a proper cam, valve springs and headers will make 500 all day long.

Regarding the 4L80, a proper stock rebuild will last you a lifetime. Let the cam choice make your converter decision.

11.9 compression will work if you can keep your intake temps under control, but it begs the question if ‘why’? 10.5-11.1 will be more than adequate for a daily driver.

And for a daily driver, the Term X Max is way more than enough (I make double your goal with an X Max and properly setup stock 4L80 and a 5.3 with a little boost).
64, I hear you on the rotating assembly. It may not make sense to some, but being an old Pontiac guy, I want 428 cubic inches. 500 hp isn't mandatory, just what I had in mind. Thanks for the information on the Terminator X and the 4L80e, that's what I thought, just looking for confirmation. I don't want the compression to be on the edge, if I can get the pistons that will get me down under 11:1, I will.
 
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Shinobi68

Not-quite-so-new-guy
Mar 6, 2023
21
13
3
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?
Also subscribing. Being this is my first G Body swap, I will be watching your thread for tips.

My grandfather left me a 1985 Pontiac Grand Prix with a 3.8l. I was going to sell it but it's actually a really nice car to drive to the store or when I need to drive comfortably somewhere, it's easy to jump in and go. After driving a few months I noticed other people taking notice of the car and giving thumbs up as they would drive by. I have had/have a lot high HP cars ranging from 500-1040hp (Mustangs, Camaros, Firebirds, CTS-V, Twin Turbo C5, C7Z Maggie 2650, C8 Z51, Telsa Plaid etc.) so I'm used to having fast cars on the street, strip, and track. Being that I'm looking to have a nice daily driving G Body with more hp, I started looking into swapping in a V8. I have a newly rebuilt '69 327 w/TH350 in the garage, it would have been a straightforward swap into the Grand Prix, but at the end of day it would still be a SBC that got 10-12 mpg making 285-300hp. My hp goal is between 350-400, while getting over 18 mpg, I looked into buying SBC heads (TFS, AFR), cam, Holley EFI intake to increase the hp to 350-385 and get maybe 15-16 mpg...but it ended up coming out to around $5k for those mods.

I then looked at doing an LS swap specifically LS3 or an LT (I still have the stock LT4 supercharger from by C7Z), but while researching and planning I came across an '04 LS1 (Vette) with 50K miles on it (complete drop out w/harness, ECM, TAC/Pedal) for $3500. Any LS1 past 11/2001 had the newer style (LS6) block and intake. The '04 Vette LS1 is rated at 350/350 hp/tq and is all aluminum, so it weighs (450lbs) which is about the same as the Iron 3.8l motor (500lbs), and it's good for about 22-26 mpg while cruising on the freeway. At 450lbs I can keep the OEM ride (stock suspension) and maybe will just replace the shocks and upgrade the rear brakes.

So far I have picked up the following Holley Swap parts:
Pan, Crossmember, Mounts (motor, frame, and clam shell), OEM tank EFI Fuel Pump (return on pump).
I still need to pick up a 4L60e, LT1 F Body Radiator w/support, and ICT Mini Air Con Pump so I can retain the AC in the car. I contemplated the ICT or Dirty Dingo AC high mount relocation, but my friend owns A&A Corvette and I'm sure will make me a great deal on one his C5 Vette Supercharger Kits should I ever decide to move the HP level up to 500hp. But I'm really trying to not do that with this car, I want it to be a tame, smooth, a nice driving car that can pass easily when needed, work well in the hills, and cruise while getting 22-26 mpg.

I still haven't nailed down which dual exhaust to get to mate up to the OEM Vette LS1 manifolds, I may have to go with the Black Heart headers, but I was hoping to retain all of the stock parts from the LS1 drop out.

I was happy to see your post because I haven't found too many Grand Prix threads.
 
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GR8ONE68

Not-quite-so-new-guy
Jan 9, 2015
13
12
3
Also subscribing. Being this is my first G Body swap, I will be watching your thread for tips.

My grandfather left me a 1985 Pontiac Grand Prix with a 3.8l. I was going to sell it but it's actually a really nice car to drive to the store or when I need to drive comfortably somewhere, it's easy to jump in and go. After driving a few months I noticed other people taking notice of the car and giving thumbs up as they would drive by. I have had/have a lot high HP cars ranging from 500-1040hp (Mustangs, Camaros, Firebirds, CTS-V, Twin Turbo C5, C7Z Maggie 2650, C8 Z51, Telsa Plaid etc.) so I'm used to having fast cars on the street, strip, and track. Being that I'm looking to have a nice daily driving G Body with more hp, I started looking into swapping in a V8. I have a newly rebuilt '69 327 w/TH350 in the garage, it would have been a straightforward swap into the Grand Prix, but at the end of day it would still be a SBC that got 10-12 mpg making 285-300hp. My hp goal is between 350-400, while getting over 18 mpg, I looked into buying SBC heads (TFS, AFR), cam, Holley EFI intake to increase the hp to 350-385 and get maybe 15-16 mpg...but it ended up coming out to around $5k for those mods.

I then looked at doing an LS swap specifically LS3 or an LT (I still have the stock LT4 supercharger from by C7Z), but while researching and planning I came across an '04 LS1 (Vette) with 50K miles on it (complete drop out w/harness, ECM, TAC/Pedal) for $3500. Any LS1 past 11/2001 had the newer style (LS6) block and intake. The '04 Vette LS1 is rated at 350/350 hp/tq and is all aluminum, so it weighs (450lbs) which is about the same as the Iron 3.8l motor (500lbs), and it's good for about 22-26 mpg while cruising on the freeway. At 450lbs I can keep the OEM ride (stock suspension) and maybe will just replace the shocks and upgrade the rear brakes.

So far I have picked up the following Holley Swap parts:
Pan, Crossmember, Mounts (motor, frame, and clam shell), OEM tank EFI Fuel Pump (return on pump).
I still need to pick up a 4L60e, LT1 F Body Radiator w/support, and ICT Mini Air Con Pump so I can retain the AC in the car. I contemplated the ICT or Dirty Dingo AC high mount relocation, but my friend owns A&A Corvette and I'm sure will make me a great deal on one his C5 Vette Supercharger Kits should I ever decide to move the HP level up to 500hp. But I'm really trying to not do that with this car, I want it to be a tame, smooth, a nice driving car that can pass easily when needed, work well in the hills, and cruise while getting 22-26 mpg.

I still haven't nailed down which dual exhaust to get to mate up to the OEM Vette LS1 manifolds, I may have to go with the Black Heart headers, but I was hoping to retain all of the stock parts from the LS1 drop out.

I was happy to see your post because I haven't found too many Grand Prix threads.
Shinobi, I should be watching your thread, you're way ahead of me. Good luck, it sounds like you have thought this through, like I'm trying to do. I want my plan set before I move forward with anything. If this plan goes like most of my plans, it'll change 10 times before I settle on one. But that's OK, it just means that I'm learning more about the LS and its capabilities.
 

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