I have a '05 5.4 Lariat Screw with some LT headers, air intake, hi flow exhaust/cats, and I still can't spin the tires at a stop and they have 50K miles on them. I believe I have the 3.75 LS though. I get that same delay you are getting, but I just always assumed that the computer was taking over at that point and adjusting the fuel flow to get a smooth acceleration. If I'm in the rain or I go around a small corner I can get her going no problems, I even had the tires jump when I was going 30 MPH the other night and gassed it quick to spook some deer that were in the ditch. I know the power is there, but I just keep thinking the computer is stealing the glory. At least I hope that's the case.

 

Prolly your exhaust since you don't mention it

A tune makes a big difference as well.

 

Well, if you want brand names, I have the Dynatech LT headers w/cats, Gibson Extreme Dual exhaust SI/DO(I bought this hoping it'd keep the noise down somewhat since people say they are quieter, I won't put in a true dual system until it's no longer my primary vehicle so don't mention it unless you really think it'll help out that much), and a K&N FIPKII. I have it tuned, but it's not a chip, I have a programmer, but I don't want to buy a chip until I have everything else completed I want to. Either way, there's plenty of power there to turn the tires IMO, even before the upgrades.

 

yeah seems like all those new f150's are dogs off the line even with superchargers. They do nothing the second or 2 after you nail it.

 

If the RPM's are raising when you nail it but the truck isn't moving I would be looking at 3 things right now. Tranny, rear end, computer and in that order. I am not sure if the computer has some way of limiting the tranny when you nail it to prevent spinning but considering others here can spin there tires it would make me lean to the tranny slipping or the diff being screwed up.

Don't wory about the exhaust or the cats, even with a straight pipe you aren't talking about enough of a low end tq loss to even make a difference. To give you an example and I know this is not apples to apples here but none the less. My Mach has no cats, 2 1/2" pipes from the headers back to SLP Loudmouth mufflers which you can see straight through and I am running 10" wide drag radials. We can't compare going from a stop as I have a MT but from a second gear roll doing about 25-30mph if I stomp it I can break the tires loose all day long.

 

Yea, now that's bad - Long tubes and Gibsons + a tune? That thing is still slow? Unbelievable.. It should fly . I think your what, 1000 lbs heavier than me. Prolly more now , I shaved a few pounds. My tires(silent armors) have a 45 Lb rec pressure rating.. I don't know , but my 98 two valve is a runner . If I had long tubes, PI heads - It would really fly..

 

It doesn't matter what you think , on these motors exhaust + backpressure is everything ...

 

Well its not what I think its more or less what I know. Like I said too little or much back pressure might take some tq off the table but not enough to make the difference between being able to spin the tires and not.

From a Mechanical and operational standpoint there is no difference in Fords 4.6 & 5.4 other than displacement. Heads, ports, valves, all are dsigned the same so if backpressure, within reason, has little effect on a 4.6 than it has the same effect on the 5.4.

If it was too little backpressure you might be talking at max 10-15lbft of torque, that 10-15lbft is not going to be the difference between tires spinning and not spinning. Another thing to notice is that at higher RPM's the more free flowing the exhaust is the better, sooooo if he had too little back pressure he would not find the truck struggling to get from 70-80mph as he posted.

Another item to consider when we talk about this whole black art of backpressure and torque loss. The exhaust flow and any air volume/velocity measure you want to take to figure it out does not end until it exits the tail pipe. Now Ford built these trucks with single exhaust pipe, by adding a SIDO muffler and an additional tail pipe you are effectively reducing backpressure in the system, by dumping the exhaust directly behind the muffler you are reducing backpressure, by running larger exhaust tubing you are again reducing back pressure. Can I see a show of hands as to how many of you have switched out to SIDO, Dumps, or increased exhaust tubing size and lost the ability to spin the tires from a dead stop???

 

Oh no, don't misunderstand me, when she finally kicks in, she flies. With the new setup she really opens on the higher speeds. It's just I think the computer is taking over the foot when you are at a stop, like it was sent the signal "Full Throttle" and it just adjusts everything for a second and "optimizes" the acceleration so it doesn't just fully open the engine. Basically, I'm saying the computer is controlling the accel rate, not the pedal. During that second, there are no RPM's if I remember right, it's just a delay then it starts going. It's just annoying sometimes when you want to squeel for fun, but it's actually saved my rear in beating cars off the line that don't know how to drive and peel out at the start, it gives me a nice head start.

 

That's 'soccer mom' torque management at it's finest.

Plus the factory ETC algorithm is not optimal - at least from an enthusiast's standpoint.

The only really dead-nuts effective way to address this is a custom tune - even a generic tune is an improvement, but with this implementation seemingly at the whim of specific strategy codes (some better, some worse), only custom can nail it for every one of them.

What tuner do you have?

bubba

 

Sounds to me like the torque converter is not locking up. 3.55 should put you at 2000 rpm (+/-) on the tach at 70. How many miles do you have on the truck? If the tranny isn't building significant enough pressure when you rev the engine, it is going to shift slower and less efficiently. It will not be "Transmitting" the HP form the engine effectively out the drive shaft.

 

I haven't looked back but i remember your rpm's being all screwed up also right??Edit^^^^ya your tranny is F'ed up.Fix that first.Have you even changed the fluid or know when it was changed????
After the tranny is fixed you may need a custom tune to cure the hesitation.Depending on computer code some trucks are worse!!!
Have you tried power braking it yet???Mine will smoke them right off of it if i power brake.

 

Yea I have 3:55's - 9.75" Rear Gear and cruise about 79 mph @ 2200 RPM.

 

I can't remember what i turn but it sure isn't 3,000 at 70.
I think that is about what i would run with OD off.

 

I ran without cats for awhile , I KNOW !! I couldn't do sh^t off the line and it sucked - so save it..