I'm going to be buying a larger pulley to work with my intercooled Roush on a 5.4 24v. Some say adding long tube headers will lower boost. How do I know approximateky how much I can add for a 2lb, 4 lb etc pulley, and how can i determine the belt size needed? Thx

 

Longtubes reduce the backpressure of the system therefore reducing "boost" that you see on the gage but actually moving more air than at the prior higher boost level. It all depends how restrictive your setup is now, but IMHO LT's aren't needed till way over the 500rwhp level.

Just because you have less boost with the LT's it doesn't mean it's safe to make up that boost.

 

Very true!

 

So how much boost can you run on stock internals, and if you can't go by teh gauge, how can you measure teh stress on the engine?

 

Well a quick reference would be the gage on a mostly stock setup. Once you go beyond what's normally done you'll have to do some datalogging. Keep the IAT's down, timing resonable and make sure you don't max out fuel or MAF and you might beable to creep up higher than you think. It's hard to say these motors are good for "X" amount of power depending on how they are setup.

The Lightning has been out since 99 and even today there are guys pushing the stock blocks to new levels. It just depends on how many pervenative measures you take.

 

The weak link in the "standard" F-150 engine is the cast pistons.

I would say that with a safe tune, you can push them to 400 rwhp,--- sometimes. Others have had them let go at 360. Unfortunately there seems to be no guarantee. It only takes a split second of detonation to break a top ring land.

I have had customers run 14 psi with no ill effects but I would have to say that is the exception rather than the rule. However, since "indicated" boost can vary with the exhaust system, the horsepower rule would be a better indicator. Remember, 400 at the wheels is close to 500 at the flywheel. I don't think there are many small displacement engines at that power level, N/A or SC that don't have forged slugs.

 

Thanks. And forged slugs? I like that. It would seem there is something major wrong to let go at 360. With just teh intercooled Roush I should be around 360 plus to the rear. Your advice of course is prudent, because the point is that as you near the boundaries, the margin for error is small. I hope to get to low 400s rwhp. Then if she goes, I'll have an excuse to get a built block.

 

He is refering to the 2V 5.4's. The 3V 5.4's will be higher. And a positive displacement blower will be harder on the lower end as compared to a cent as compared to a turbo.

 

Mad,

I was getting 365 rwhp before the LT headers and 3" dual exhuast with a Whipple. I don't have a boost gauge yet, so I'm assuming that it was pushing 8psi out of the box. If I go to a smaller pulley to get back to 8 or even 10 psi, how much do you think I will gain and do you think this scenario is too muck for the stock internals. I do have access to a really good dyno tuner, so I'm confident that he won't get the A/F too extreme. BTW, my truck is a 3v 5.4.