408 need plan checked
Thread Starter
Teching In
Joined: Dec 2012
Posts: 20
Likes: 0
From: Russian River CA
408 need plan checked I am building a 2003 LQ4 for my jet boat it ran at 3000 RPM at slow plain and 5000 RPM at full throttle be for #8 and #7 piston let go.
#A I have a new stoker kit 4” stroke, 4.030 bore 10.4 to 1 compression with 72 cc cambers and trunnion up grad kit. I was going to run the rest stock I think I could be ok with stock tune.
# B And later add L92 heads, valve spring, push rods, and have a cam specked, LS6 truck intake,90mm throttle body, bigger injectors and tune on engine dino. Compression will be about 11 to 1
#C Then I thought I might have enough money to do valve spring, push rods, and have a cam specked with my stocks heads and intake and be done.
Question #1 is #A and #B an ok plan?
Question#2 Should plan #C need a retune?
Question # 3 How much more tork and HP could I get from #C {Guess}
Question#4 How much more tork and HP could I get from #B over #C? {Guess}
I need a torch monster it will need to last and it gets road hard I cant spec a cam till I have a plan.
Any comment wood be aspirated.
Kerch
#A I have a new stoker kit 4” stroke, 4.030 bore 10.4 to 1 compression with 72 cc cambers and trunnion up grad kit. I was going to run the rest stock I think I could be ok with stock tune.
# B And later add L92 heads, valve spring, push rods, and have a cam specked, LS6 truck intake,90mm throttle body, bigger injectors and tune on engine dino. Compression will be about 11 to 1
#C Then I thought I might have enough money to do valve spring, push rods, and have a cam specked with my stocks heads and intake and be done.
Question #1 is #A and #B an ok plan?
Question#2 Should plan #C need a retune?
Question # 3 How much more tork and HP could I get from #C {Guess}
Question#4 How much more tork and HP could I get from #B over #C? {Guess}
I need a torch monster it will need to last and it gets road hard I cant spec a cam till I have a plan.
Any comment wood be aspirated.
Kerch
TECH Regular
Joined: Dec 2012
Posts: 414
Likes: 0
From: San Diego
The L92's wont fit a LS6 intake. L92's are square port and the LS6 intake is cathederal port. The cheap way to run L92 heads is to order a stock LS3 intake from GM and run stock LS9 injectors with the Ls1 whiring harness adapters. The ls3 intake is like 360700 and the injectors with wiring adapters are like 550. Im using a ls3 intake and LSA heads on my 408 build. Pm me if u have any questions on my setup.
I dont know if id go with ls3 heads unless they are small bore style. I believe you would be better off staying cathedral and be able to have more compression and a bigger cam.
Launching!
Joined: Jan 2011
Posts: 200
Likes: 0
From: Arizona
if 5,000 rpm is your high target, then then cathedral's will build a lot more torque down low (coming up to plane) where you will be pulling skiers etc... Put the money you would use to buy heads and have yours ported by AI, AFR, etc.... Do you have an Ls6 or truck intake now. LS6 would be best but truck intakes work great too especially for the torque. I would personally have it tuned after the stroker kit to make sure your injectors aren't maxed out. Get a cam and valvetrain spec'd out. You will be amazed. There is a jet boat here in az running stock 6.0 bottom with cam, LS6 intake, and ported heads- it F'n flies. The torque pulls it out of the hole like a monster and pulls HARD to 5,500.
