I just recently built a mopar 408 that falls on its face at 3500 rpm and basically has nowhere near the power anyone else who has built these are getting.

This thread shows what was done.

https://www.performancetrucks.net/fo...igning-542152/

What the heck did I do wrong? I'm at the point I'm about to just find a 5.4 and swap it in TBH.

 

24lb injectors on a 408 stroker?

That's like way too small in my eyes.

And you kinda really want to be watching fueling here, get that WB installed and get to tuning this thing. Can't just slap stuff together and hope for the best.

 

Welcome to the forums! Don't waste all of your hard work by giving up and putting a 5.4l in!

I am unfamiliar with mopar products but:

1) Like FFDP said, tuning is huge! Fueling is critical. 24lbhr injectors are way too small. You could be maxxing the injectors out by 3500rpm with that 408. Get the wideband installed, tune in increments up to 3500rpm, and log the injector duty cycle. Once you hit 90% duty cycle, get bigger injectors. With a 408 I would think that you'd want at least 40+lbhr injectors...

2) If other people are using (I assume you're using the TWIN 52mm Holley throttle body) the same throttle body on 408s then you should be fine HOWEVER, doing the math a TWIN 52mm throttle body is equivalent to a 72mm single blade throttle body - which is pretty small for LS engines. Most LS guys run 90-105mm single blade throttle bodies on 408ci engines. Like I said, I'm unfamiliar with mopar engines but your throttle body seems like it could be a restriction to me.

3) You didn't mention anything more about your fuel system: pump, return/returnless style, fuel line size, fuel pressure, etc. I would think you'd need a pump capable of flowing atleast 300+lph (liters per hour). If you still have a stock pump/fuel system that may be something to consider?

4) You stated you're running 1.7 rocker arms, but stated cam specs for 1.6 rocker arms which means that your valves are opening further than what they would if you had 1.6 rocker arms. Did you or the engine builder verify 1) Your valve springs are sufficient for the increased effective "lift" and 2) you don't have any piston to valve clearance issues?

5) For the rack and pinion, seems like you may have a plumbing or some sort of relief valve problem...

Hope this helps. Good luck!

 

The only thing I might add is that your steering issues may be from the hydroboost swap, could the brakes be overpreasurizing the steering system?

 

It blew up before that, only had the hydro since the new engine was in. (bout a week)

 

Okay so I now have the wideband in and have started to collect logs. However I need help with tapping the trucks wiring for the tach signal. I tried to tap the coil and set the pulses per revolution to 4 in the software but was getting over 14000 rpm registered.

When I changed it to 14 it seemed to be more accurate than any other setting however regardless of where I set it the number seemed to "twitch" around eraticly up and down 300-1000 rpm.

Where am I supposed to wire the tach signal in?

 

What year is your truck?

 

2003 ram 1500 Laramie 4x4 5.9L ECU with reflash

 

I have no clue about that one!....