Hi, okay so I've been wanting to build an ls swapped third gen trans am for years now, I've been researching it for years. Now what I want to do is build a reliable 500+whp daily that can get about 30mpg now i plan on fully building the suspension, I want to do also try and keep full interior but make it weigh as light as possible maybe buy fiber glass hood, fenders, trunk lid, spoiler, bumpers, doors, etc. Now i would love some opinions on the best route to go. I was thinking about buying a 408cu stroker lq9 iron short block with a turbo or procharger. But I want to build it right and I have little expeirence so Ill admit I dont know what im doing. Any help would be great. I would like to find best routes money wise. Im trying to budget around 15k-20k for everything (engine, suspension, tires, fiber glass parts.)

 

Not realistic. Smallish cube motor with boost and a 6 spd may get close to 30 mpg highway in a light car but vast majority realistically get low to mid 20's at best.
The big cube stroker stuff can do 500wjp easy but suck on gas when not on highway in cruise gear. Aka daily average stop and go will be teens mpg

 

Like i said i really dont know much about what works best. So would a boosted 5.3 be better for mpg? I mean i know 30mpg was probably a unrealistic number. I mean for transmission wise ill probably be using a 4l65e or 4l80e

 

A 6 speed LS1 4th gen can pull 28mpg in ideal conditions.

GM doesn't offer an active fuel management (displacement on demand) LS engine with manual, but that's where I'd start is trying to combine those 2 things. The manual takes less power to turn. The "run on 4 cylinders in light highway use" mode would get you closer to your goal. The parameters needing met to enable the AFM to activate may need changed, but allowing it would

408? No. Smaller.
Iron? No. Why add weight?
Supercharger? A constantly belt-driven accessory and boost at times you don't need it are why you shouldn't go this route. Turbo would be a way to go; less parasitic drag and yet enables a large power gain when needed.

A high-feature (aluminum, AFM) 5.3 (I think a 2005 Rendezvous had it) is a starting point. Undercarriage panels to reduce aerodynamic drag would be a good step.

A late model PCM from a car that had optional MPG reading on a gauge panel (through BCM?) isn't a great way to determine improvements, but it will help tell you your mileage at 60mph is 3mpg better than at 70mph.

 

Thanks glad you told me before i bought the 408 short block. So an aluminum 5.3 with a turbo is the best way to go if im understanding you right. See im planning on buying a brand new short block from like texas speed performance. Just for the reliability and so i know its built professionally.

 

Just dont use texas speed springs for the heads

I dont know anyone running high performance setups in DOD. I hear the lifters are weak. I know a few that had them collapse in stock motors. So be careful there

A vvt setup would also help if you decide not to do DOD

 

Yeah Ive heard bad reviews about their springs. I was just going buy the short block from there im either going buy a 5.3 block or 6.0 ls2 block. If i buy the LS2 short block I can use cnc ported ls3 heads correct me if im wrong. What cam would be best to use? I dont want an agressive cam. I dont like the really lopey sound the big cams make especially on a daily driver. Id rather have a more quiter cam. Thats just my personal preference.

 

Also look at late model engines for a short block

I like the power ls3 heads make for the dollar but not sure they are most efficient for what you are tryin to do. Mild cleaned up 243 cathedrals should do well here with good valve job. You dont need them ported just cleaned up and bowl blended with valvejob. Boost will make the power
Again i think you are better off with small cubes here. 5.3 or even a destroked 4" bore build

 

Soo like lets say 5.3 with a 76mm turbo would that make about 500whp?

 

S366 66mm would make 500 whp on a 5.3.

I like the aluminum 5.3 deal or 5.7 ls1/ls6. Those are likely gonna be most efficient

 

Soo now if i bought a used 5.3 from the junkyard and used stock internals would it be safe to push 500whp well i mean would the internals hold up? I know some can handle 1000hp on stock internals. How much boost would i need to push?

 

Yeah they will hold. Mild cam and 9-10 psi should get u there. If some head port work definately get you there

Try to find a later model 5.3 if using a 5.3. The aluminum ones are hard to find but i like the idea of alum here for weight savings and mileage. 5.7 ls1 is more abundant and makes more sense here if goin aluminum. Try to find a used short block and have it checked over. Throw on some 317 truck casting heads to reduce compression but if dont want to do that then just keep an eye on cyl 7. It seems to be the most problematic cyl when guys boost stock ls1. Keep motor cool and it will easily live

 

Take a 58x 5.3 with displacement on demand and the cam phaser, stuff a 4.8 crank and rods in it. Put a T-56 behind it and run a 4th gen 3.42 gear. Add a turbo with a part-throttle open wastegate. 2.4L on the highway and plenty of power when you hammer on it. The 4.8s short crank throw, lower piston speed and longer rod will allow for reduced friction losses and better MPG than a 5.3 all things equal. For the final touch add a LED to the cluster connected to one of the DOF solenoids to let you know when the DOD is active.

 

Its not that they collapse. The POS plastic lifter trays fall apart around 60-100K, allowing the lifter to spin, the roller wheel to get out of alignment and the cam to get eaten away. Had a 6.2 Escalade at work with under 100k, that happened to last week.

 

The ones i have seen collapsed