408 ls1 build, need advice
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Teching In
Joined: Jun 2017
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408 ls1 build, need advice Im from the tuner side of the car community and I've been doing an STi build and it's done now and it was a huge pain the whole time and not to mention super expensive. So I'm making the switch to the ls world. I've been planning an ls1 swap 240sx that's all motor and 400hp but I don't think it would impress me coming from a 400awhp STi so I figured why not sell the STi and go all out. So I'm planning on buying a TSP 408 forged shortblock and buying a donor ls1 for all the other stuff that's needed. And I'm leaning towards the ls3 heads on the 408, they will be ported with .680 dual springs and tsp pushrods. Will that be good for the big 408? and what cam size should I be going for? I'm planning on the cxracing single turbo kit with a pt76 turbo, 80 lb fuel injectors, big fuel pump, ls6 intake, Tick performance level 2 t56 build.l, m295 oil pump. I know I can probably call tsp but I'm in the very first steps of just planning this, this won't really even start until I part ways with my STi so this forum is perfect for advice. If I'm not picking the right head setup please let me know, I'm not 100% educated on the compression I'll need for a boosted engine so any advice is appreciated. Will I need different fuel rails with this setup or will the ones from the donor ls1 work, or would you recommend aftermarket rails? Im hoping to be running around 700whp on this setup, am I being realistic? And would you think going to the iron block 408 is gonna have a huge affect on the weight distribution in the 240? It's like a 100 lb difference from the aluminum block I've heard. Thanks guys
Last edited by Audioslave1; Sep 8, 2017 at 12:10 PM. Reason: spelling error
TECH Fanatic
Joined: Aug 2009
Posts: 1,845
Likes: 255
From: Coast of San Mateo County Between Pacifica & HMB
OP said Turbo, pretty easy on a 408" but a 370" would do it just as easy
With a better rod/ratio, and the stock Crank will work for 700+ WHP.
I would look at the Mamo Motor Sports 235 Cathedral Head with the
NFI Exhaust Port, more money but an awesome Forced Induction
Head on a 370" 10.0:1 Comp and 12 PSI Will give awesome throttle response
And make 700+ RWHP with a pretty mild cam as well. Use LS2, or LS3
Block to save 100 lbs, both strong enough for ~800 WHP with stock Crank
And Aftermarket forged rods & pistons.
BTW LS6 Intake is for Cathedral Heads not L92/LS3.
Use the stock Crank vs stroker, put extra money in good
Heads. My .02
Good Luck
With a better rod/ratio, and the stock Crank will work for 700+ WHP.
I would look at the Mamo Motor Sports 235 Cathedral Head with the
NFI Exhaust Port, more money but an awesome Forced Induction
Head on a 370" 10.0:1 Comp and 12 PSI Will give awesome throttle response
And make 700+ RWHP with a pretty mild cam as well. Use LS2, or LS3
Block to save 100 lbs, both strong enough for ~800 WHP with stock Crank
And Aftermarket forged rods & pistons.
BTW LS6 Intake is for Cathedral Heads not L92/LS3.
Use the stock Crank vs stroker, put extra money in good
Heads. My .02
Good Luck
Im from the tuner side of the car community and I've been doing an STi build and it's done now and it was a huge pain the whole time and not to mention super expensive. So I'm making the switch to the ls world. I've been planning an ls1 swap 240sx that's all motor and 400hp but I don't think it would impress me coming from a 400awhp STi so I figured why not sell the STi and go all out. So I'm planning on buying a TSP 408 forged shortblock and buying a donor ls1 for all the other stuff that's needed. And I'm leaning towards the ls3 heads on the 408, they will be ported with .680 dual springs and tsp pushrods. Will that be good for the big 408? and what cam size should I be going for? I'm planning on the cxracing single turbo kit with a pt76 turbo, 80 lb fuel injectors, big fuel pump, ls6 intake, Tick performance level 2 t56 build.l, m295 oil pump. I know I can probably call tsp but I'm in the very first steps of just planning this, this won't really even start until I part ways with my STi so this forum is perfect for advice. If I'm not picking the right head setup please let me know, I'm not 100% educated on the compression I'll need for a boosted engine so any advice is appreciated. Will I need different fuel rails with this setup or will the ones from the donor ls1 work, or would you recommend aftermarket rails? Im hoping to be running around 700whp on this setup, am I being realistic? And would you think going to the iron block 408 is gonna have a huge affect on the weight distribution in the 240? It's like a 100 lb difference from the aluminum block I've heard. Thanks guys
Just to clear something up, if you run LS3 heads on the 408, which I think is a good idea, you would need to run an LS3 style intake. The LS6 you mentioned is for cathedral port heads, like the 243 castings for example. I wouldn't really bother porting the heads or manifold either.
Also, I would suggest getting the cam and rockers figured out before deciding on springs. A .680" lift spring kit works great for a cam with that much lift, but many camshafts, especially for turbo combos, have closer to .600" lift. Max lift of a spring is usually determined by installed height and coilbind height. Springs usually work better when you install them at an installed height that will open the valve and compress the spring to .060" or so from coilbind.
In my opinion, the turbo will be too small for the 408. There's a Forced Induction section on this site which you could browse and see most experienced people would suggest a larger T4 flanged turbo, like a PT88, or just going straight to a T6 flanged turbo for a 400ci engine.
For that power, your builder would likely run your bearing clearance a little loose so the M295 pump may be inadequate. The higher volume M10296 would work well, or the 10355 if you have auxiliary components like a big oil cooler, etc.
10 Second Club
Joined: Jan 2010
Posts: 2,317
Likes: 20
From: Hurley, VA
I would just do a 370, forged rod and piston with the stock crank. Stud top and bottom. Get some decent heads, a LS6 intake, cam. With boost and only planning 700 I would think a 408 would be over kill. We had a forged LS1, 853 heads, stock LS1 intake, cam motion cam, and twins (not sure what turbos they were all ready on the car) make 600 on 93 and 11 pounds.
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TECH Veteran
Joined: Sep 2014
Posts: 4,893
Likes: 706
From: Mississippi
You don't need to spend 2500 dollars on cylinder heads to crack 700 horses with a turbo with a 408ci setup..... Call lil John motorsports. Guy is really intelligent with turbo builds and so it Joe Nova a member here.
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