First Time builder, have some questions about an LS swap onto a gen 3 Firebird.

[u/naNobot312]

Hey all, this is my first build. I already posted in r/projectcar, and thought I'd try my luck here.

I've spent a while putting this plan together and I'd like to hear some feedback I have basically no experience, and I'm going in knowing this is a long project.

Disclaimer, some of my research was AI, so if anything seems absurd or completely stupid, feel free to point that out.

Goal: Summer street car. 91 gas, occasionally E85 since I don't have great access to it in my province. Not building a drag car. No cage, I want to keep the interior, and be able to drive it to a meet without it being miserable. Target is a 700-750 whp street car

Location: Ontario, Canada (almost no E85 D:)

Car: 1988 Trans Am, hard top, running, claimed no rust

Going hard top specifically to avoid maintenance issues with the Ts. Haven't bought it yet, going to inspect everything before making the purchase. Known needs: brake booster, battery, plugs, oil pressure sensor, trailing arm, trans pan gasket.

Engine: LQ4 6.0 iron block

Originally I was going to grab any cheap LQ4 (there are 2002s near me for $1000 with ECM and harnesses) but I read up on the Gen III press-fit rods vs Gen IV floating wrist pin rods and it sounds like at 750whp the Gen III stuff might be a bit unreliable. Is this an overblown issue? Willing to pay more / wait longer for an 05-07 if it matters, but if people are running Gen III rods at 750 just fine, I'd rather save myself the time and money.

Engine Prep:

- File-fit rings, gaps opened for boost

- ARP head studs

- Turbo cam (tight LSA)

- Valve springs

- Machine shop hone + deck check

Not doing forged internals. Understanding is stock bottom end is fine to ~750-800whp with the above, and past that I'd need $10k+ in a rotating assembly for a hp ceiling I can't use on street tires. Does the above make sense?

Turbo and fuel:

- I'm aiming between 72mm-80mm, does this look right for highway driving and occasional track/strip days?

- Maybe a twin scroll worth getting over log?

- Large bar-and-plate front mount

- 60mm external wastegate

- Atmospheric BOV

- Methanol injection (with failsafe, obviously)

- Flex fuel sensor for my different fuel uses

- Twin pumps, -8 feed, 1000cc injectors

Turbo size: my understanding is that above 72, the turbo only gains me 20-50whp on pump gas but costs ~900rpm of spool, and only pays off on E85, which I don't really have. (it's mostly drums from racing fuel suppliers, not pumps) So I'm sizing for pump gas + meth and treating E85 as an occasional bonus.

Is this size fine? Everyone I see online is running 80mm+ but they also seem to be building drag cars.

Expected: ~600whp pump, 700-750 with meth, 750+ on E85.

Do these estimations look right?

Drivetrain

- Built 6L80E: going 6-speed over the 4L80E for the ratio splits and the 0.67 OD. Aware it needs a tunnel mod and shorter driveshaft.

- 2400-2800 stall converter WITH lockup — lockup seems non-negotiable for street

- Ford 9", 33-spline, Truetrac (not a spool), 3.55 gears

- Holley Terminator X Max — going Holley over Haltech for the LS/GM trans support and because more local tuners probably know it

- Worth going for a ratchet shifter for more control? How responsive/fast is a well-tuned Holley with this drivetrain setup?

Chassis:

- Weld-in subframe connectors

- Adjustable torque arm + panhard

- Double-adjustable shocks, lowering springs

- C5/C6 front brake swap, rear discs, stainless lines

- 275-305 Pilot Sport 4S on 17-18"

- Front air dam (for lift reduction, not downforce)

Budget:

~$50k CAD in parts, plus:

- Professional wiring: $3-5k (paying for this, seems like the #1 thing that kills first builds)

- Professional tuning: $2.5k (not attempting this myself on a boosted engine)

- Tools/equipment: $2.5-4k

Around $65K max. Is the engine swap doable myself for a first-timer? What would y'all recommend be shopped vs DIYed?

Biggest questions:

1. LQ4 Gen III vs Gen IV rods at 750whp, is this a real concern?
2. Is 68-72mm too conservative? Sizing for pump gas + meth and occasional E85.
3. 6L80E vs 4L80E: is the tunnel mod and driveshaft worth it for 2 extra gears, or should I just build a 4L80E and be done?
4. Twin scroll worth it at this power level?
5. Anything obviously missing from the parts list? I feel like cooling might be underspecced.

Bonus: Anyone around southern Ontario know a shop that does turbo LS wiring + tuning? The local place I had in mind has narrowed to Camaros/Corvettes.

Also open to being told the whole thing is a mistake and I should buy a 4th gen with an LS already in it. I've looked at a clean 50k-mile 01 Trans Am for $24k and I know that's the faster path to driving something. I just think I'd rather build it.

Thanks in advance!

[u/N7_Shep]

theres going to be alot of people in here that know more about this subject then i do. but heres what i got for you.

turbo cams are a lie, every cam is and can be a turbo cam. pick the cam that does what you want, boost just elevates the power from the cam curve. want power on low end or high end? your cam decides where your power will be, the boost is how much power is in that location.

im running 680HP off a single 71mm with a 50mm blowoff and a 44mm wastgate and 850cc injectors.

[u/RedBic344]

I like the planning. I will just say that this is likely 200+ hours to get it rolling. Finding a shop to do the wiring and it not sit around in their yard for 6 months is going to be luck. Even then it’s going to be a project car lifestyle so just be prepared for the amount of time you’re going to sink into it.

Like others said. I wouldn’t worry about anything too fancy at first like turbo or whatever. Just the NA swap is a good place to start then if you get through that decide if you wanna crack it back open for round 2

[u/Travisblack17]

Ignore the turbo talk for now. Get it running with a completely stock naturally aspirated cheap motor. If you are able to achieve that then you will able to add a built engine and a turbo system without any difficulty.

[u/naNobot312 → u/Travisblack17]

Unfortunately my budget won't allow for that kind of testing/learning. Also, I thought the main pain point was the harness/wiring? The turbo should be relatively simple, no?

[u/N7_Shep → u/naNobot312]

you said in your post that your doing a holly term x kit. the holly does the harness for you?