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LQ9 408 with 243 heads and nitrous

This is a discussion on LQ9 408 with 243 heads and nitrous within the Internal Engine forums, part of the LSx Technical Help Section category; Hi guys, I just bought a LQ9 with 317 heads. My plans is to build a 408. My question is ...

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    LQ9 408 with 243 heads and nitrous

    Hi guys, I just bought a LQ9 with 317 heads. My plans is to build a 408. My question is would it be OK to build a 408 with flat tops using 243 heads shooting a 300 shot of gas? Or would it be to much compression and better to keep the 317 heads? I plan on running a good forged bottom end with the MS3 cam.

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    I am building a street car that won't be a daily but it will be drove often. Want to run on pump gas. I may run a stand alone progress nitrous system.

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    Spaz is My Mentor SMWS6TA's Avatar
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    My 403 has forged internals, flat top pistons w/3cc relief cuts and currently a Polluter stg cam and stock 243 heads. Only work on the heads was new valve guides. BTR spirngs and trunion upgrade. When I'm ready for more a new cam and heads. I'll most likely be switching over to LS3 heads & intake with a custom grind cam.

    I'm putting down 450/450 hp & tq to the rear. Rear is a 8.8 w/4.10 gears, M6 car.

    All my internals can safely handle a 250 shot of Nitrous. 300 you'll want to get a cam, piston, and valves that can handle that much.

    You'll also need to beef up the injectors and fuel pump and get at least a wideband to watch the A/F ratio for lean conditions otherwise you'll burn a piston. Plugs will also need to be taken in account as well.
    http://www.ls1.com/forums/f7/my-6-liter-build-174257/

    http://www.ls1.com/forums/f8/my-8-8-rear-build-165553/

    6.0L Block - Forged 403 built, breaking it in , Polluter Stg3 Cam, FAST 102mm Intake, NW102 TB, MSD wires, NGK TR6 plugs, Truck Coil Packs, LS3 Fuel Injectors, CC Pacesetter LT Headers, TS&P ORY, QTP e-Cutout, Magnaflow Muffler, 104mm Air Lid & Line Lock, Catch Can, Stage 2 T56, PRO 5.0 Shifter, Tick MC, Monster Stg 4 Clutch, QT SFI BH, MWC DSL, UMI: SFC, PHB, LCA's, LCA Relocation Brackets & TA, Hotchkis Springs (1" Drop), YR1 Snowflake Wheels wrapped in NT555 tires & Custom Fab Ford 8.8 rear w/4.10 Yukon Gears, WSQ Hood, 3"CM Strange Eng Drive Shaft.

    Horsepower never lies, but is often lied about!

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    Spaz is My Mentor SMWS6TA's Avatar
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    The 317's are good for boosted builds. The 243's flow better than the 317s and have a higher CR. You can use the 317's and have milled down to raise the CR and also have Port & Polish to raise the flow.

    My 403's CR is 11.5-1. I use only 93 oct and it is practically a daily.

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    OK thanks

    Quote Originally Posted by SMWS6TA View Post
    The 317's are good for boosted builds. The 243's flow better than the 317s and have a higher CR. You can use the 317's and have milled down to raise the CR and also have Port & Polish to raise the flow.

    My 403's CR is 11.5-1. I use only 93 oct and it is practically a daily.
    Thanks for the info. I am still debating between 403 or 408, probably not much HP difference and with a 403 I still have some room incase something happens then I can bore it to a 408.

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    Spaz is My Mentor SMWS6TA's Avatar
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    LQ9 408 with 243 heads and nitrous

    That's kinda why I stayed with my bore 4.005". It started out as a stock bottom end rebuild. Had a rod bolt failure on test drive and that destroyed the crank. so new crank, new build.

    Has a K1 forged crank.

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