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iTrader: (1)

Looking through all of the Dyno threads on a 408 (Stroked LQ4/LQ9) and it appears that everyone is looking for high horsepower, which means high revving (typically) as their builds are going into Camaro's and the like... Which makes sense.

However, my build is going into a 4,500lb (curb weight) 4x4 (and that's with weight cutting measures in place). I need torque and I need it low in the power band. Stock engine for this truck was 160hp @ 4,200 RPM and 245ft lbs @ 2,200rpm. In other words it was a certified dog. I mean 65MPH was entirely possible, but only if you were going downhill with a 60mph tailwind. Hence my goal of AT LEAST 100 more ft lbs of torque in the same RPM range (or lower). Don't get me started on trying to take a relatively small incline when offroading.

Anyway, the current plan was to build a 408 with a relatively stock LS3 top end and a 224r as emissions are still a concern (unfortunately). After doing a few weeks of research it seems that, the recipe I just mentioned, won't get me where I want to be. Ill be at the 500+hp mark, but torque will be up in the 4,500 range. Am I wrong in making that assumption? I doubt this engine will ever see +4,500RPM. Any thoughts? Right track? Wrong track?

JC316

iTrader: (1)

If you are looking for that kind of torque down low, why not go with the old tune port L98? Those things are designed for massive torque on the low end and it doesn't take much to make them NASTY. Check this build out.

http://www.superchevy.com/technical/...n/viewall.html

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iTrader: (1)

Because a built 408 will get better gas mileage and more power across the board than ANY TPI build. Did you notice the cam they had to run? I'd never pass emissions with that engine. It's old technology... I have an LQ4, no 350 block... 408, built correctly, will be much more reliable, its OBDII... Could go on and on, on that one.

JC316

iTrader: (1)

Ah, I assumed that it was going to be a strictly off road vehicle. It's not going to be easy to get that kind of low end torque on an engine that wasn't designed for it to begin with and with an aftermarket geared toward high revving. You are likely going to need forced induction.

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iTrader: (1)

Uh, the LQ4 and LQ9 are both truck engines... Designed for that exact purpose... The 350 TPI, was not. While the 350 was thrown in a lot of things, primarily was a TBI or carb in Trucks...

Burken01

iTrader: (88)

Who wants a 350 tpi?

Lol

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iTrader: (1)

exactly

96capricemgr

iTrader: (1)

You are trying hard to waste a lot of cash here.

Put in a junkyard 6.0l engine and give the truck some reasonable gears. No need to do a 408 and aim for diesel low rpm torque numbers.
Before you whine about fuel economy vehicle aerodynamics have more to do with economy than engine rpm let the engine turn an rpm that isn't lugging it and it will be happy.

What is the axle ratio and tire height now?

intenseblue

iTrader: (1)

If youre looking for low rpm torque id look into 317s and a factory lq9 intake. L92s arent gonna be the ticket and if you already have them and arent gonna get rid of them do NOT mate them with a single pattern camshaft.

redtan

iTrader: (5)

He'd be wasting alot of torque by the lower compression, what he needs are a set of 243s or even 5.3s with a 218/224 type cam and tight LSA.

Geared and stalled right that will put plenty of torque down low.

1981TA

iTrader: (7)

As others have mentioned, you might best best off focusing on low-speed torque, instead of low rpm torque. Have you considered 4-series gears and a tranny with a good overdrive? I put a t56 in my car, with 3.73s, and it cruises at 2k rpm at 80 mph, AND it takes off like crazy - gobs of torque at low speeds.

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iTrader: (1)

I haven't picked up the trans yet, but it will either be a 4l80e or a 4l85e. Gearing right now is 4.56, though I may move up to 4.10's. Ill try it out with the 4.56 first and see how the highway RPM's go as well as general acceleration, especially under load.

JC316

iTrader: (1)

The 5.4l ford was a truck engine too, but it didn't magically change it from a high revving car engine. The LQ4 was designed to make peak torque at 4K RPM, this is a common gripe from the truck owners that are looking for torque on the low end. If you are talking about off the line punch for hill climbing and are dead set on the Lq4, your best bet is either going to be more displacement, or a super charger.

The Jeep guys use the old TPI a lot thanks to the low end torque. Thats the main reason that I suggested it.

SSCamaro99_3

iTrader: (1)

One thing to keep sight if, is that just because the torque peaks higher than people are used to does not mean that there is no low end torque to work with. My torque peaks at 373 at 5000 rpm. I still make 300 to the tire by 2400 rpm and 350 by right around 3000. The peak is not very material as long as you have a broad curve.

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iTrader: (1)

That's honestly what I am looking for. I mean if I make 500ft lbs at 5200RPM, that's fine as long as I'm at 350 (my goal) at 2,400. Would like to be over 225 at idle (900RPMish).

JC
True the Jeep guys move up to the 350, but that's because many of them are coming from a 4cyl or the 4.0 I6. That 4.0 can pull stumps, but acceleration is horrid. But like you mentioned I'm going to need displacement. Hence the 408. Plus since it's going into a Ford, I can still freak the Ford guys out by saying it's got a 408, though admittedly that is far from being the primary reason.

I've just never seen a cam profile setup for torque. Even the "torquer" style cams seem to make the torque up way too high for most truck style usage.

badassracing

iTrader: (13)

I would just use 317 heads. With a 408 and a cam spec'd for low end torque you won't be able to run the compression everyone usually runs anyway. The smaller ports will have more velocity in the rpm range you want to run but will fall off quick on the top end. If your really not running over 4500 often it wont matter if it falls off in the upper rpms.

garygnu

the ls3 head design is 12.5*,making for better head port flow then a l98 head .the more cubes the better ..the engine combo you listed will make the power ,the cam is the key .with great flowing heads you don't need high rpms to make great power .check out Texas Speed on ls engine prices .

LilJayV10

iTrader: (39)

6.2 liter

intenseblue

iTrader: (1)

Stroker engine. 317 heads take him into race gas territory of compression with the right piston. Larger chambers and less piston dish is a better combo than large dishes and tiny chambers.

intenseblue

iTrader: (1)

Not recccominding twelve to one compression. just pointing out 317s are fine.