Hi,

I have a 5.4L F150 4x4 with the following mods:

- Superchip
- K&N FIPK
- Ravin Z-55 SI/SO

The Ravin was a muffler only replacement and I kept the factory 2.5" pipes. Given this (and the future modifications I still want to make) at what point should I seriously think about upgrading the diameter of the pipes to ensure I am maximizing the overall efficiency of the system?

Thanks in advance

 

1)2.5" pipe will manage up to 300HP just fine. There is some reduction in the press bends, especially in the rear section/tailpipe. Also, it won't help you performance wise to add larger pipe anywhere behind the 2.5" exit on the OEM Y-pipe (that's the most forward restriction). What are the future mods that you're considering??

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2000 F-150 XL, RC, LB, 5.4L, 4R70W, 3.55LS,
Class III tow, Payload #3, & Convenience pkgs.,
4-wheel disc/ABS, Chestnut/Parchment 40/60,
Ford bedliner w/Paintsaver & gas/wheel/spare locks,
K&N F.I.P.K. w/Outwears pre-filter, Superchip,
Dynomax ultra-flow welded 3" cat-back w/ 3" Y-pipe,
Hellwig front & rear anti-sway bars, Rancho RS 9000s,
Mobil 1, K&N oil filter.

 

Thanks for the reply Max.

I assume when you say it will do no good replacing the pipes to 3" alone, you are implying that I would have to replace the Y pipe to a larger diameter as well. True?

Regarding the other performance mods that I am considering:
1. Underdrive pulleys
2. Electric fan
3. Gear change

I would love to do the gear change first, however, I cannot justify the financial investment at this point given all of the other mods I have already made on, essentially, a brand new truck -- read: my wife would kill me

Thanks for your help!

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2000 F-150 XLT Supercab, 5.4L, 4x4, 3.55 gears

• Premium AM/FM Radio with CD
• Smittybuilt sure step bars
• Ford (Duraliner) Bedliner
• Class III Tow Package
• Superchip
• Ravin Z-55 SI/SO Exhaust
• K&N Gen II FIPK

 

Yes, you are correct and that was my implication. At the exit of the factory Y-pipe all you have is 1)2.5" pipe w/everything flowing through it. Since your exhaust comes from the engine back, that's all you can flow rearward with larger pipe, or even single in/dual out muffler setups (you're stuck with your most forward restriction). There are several Y-pipes that provide a smooth transition as well as 1)3" exit; of course "true duals" eliminate the Y-pipe altogether. Both options are against Federal law from what I can get in in writing from the EPA (not the "I did it" or "it passed here" crowd). From your existing mods list I can see that you're just over 300HP now. With your future mods you will be freeing up parasitic HP loss, not requiring more exhaust flow. I have some future plans as well, so I understand your position. Finances, "the wife", and 2 differentials; I get it Bud!!

 

Thanks for the help (and clarification) Max!

Best Regards...

 

From what I have seen the mandrel bends are larger size will help slightly at these "normal" HP levels, but really don't make a large difference until you're making serious HP.

You should be in the clear for now. The pulleys and fan should help your mileage some also. This will of course save money, and makes it easier to justify to the "boss"! You do want us to save money, don't you honey?

 

To clarify my initial post; The tailpipe section (being 2.5" with multi-press bends) reduces the size down even further. This section has the most curves and pressing of any pipe section after the Y. I have also seen some trucks with more wrinkling and deeper pressing in these areas. Obviously, on a physics level, larger pipe diameter has a larger flow, and mandrel bent pipes have this.

 

Max/Signmaster,

From both of your posts you indicate that the 2.5" pipes will be fine until serious HP comes into play. Could either of you (or anyone else) provide additional insight into when changes to the exhaust setup should be considered (at what HP level)? While the mods I mentioned above are those that I can foresee within the next 18 months -- I can also see a set of headers sometime in my future as well .

Also, if changing the Y pipe or going true duals are considered illegal AND the Y-pipe is the forward most restriction, then is there any LEGAL way to deal with this dilemma (or am I just misreading the post)?

Thanks again!

 

It's only illegal if they catch ya'!!!

Mike

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Stay Out Of My Taildust

2000 Black Harley Davidson F-150
5.4 Liter v-8
K&N Air filter
20" Polished Aluminum Wheels
275/45/20 Goodyear GSII's
Billet Front Grille
Front Valence W/ driving lights and Billet Insert
3.55 Rear End
Leather Interior
Heated Seats
Hidden Hitch
Orange Pinstriping
Front and Rear Light Blackouts
Lowered 1" Front & Rear
Block heater

 

On my '95 the rear section looked like a snake when I took it off! I've never seen to many bends to accomplish the simple turns. Some of them were good, others crimped more than was needed.

I've often wondered if the idea of going to 3" mandrel on the cat backs is simply to ensure that there is little if any restriction after the muffler. This would ensure that the forward Y-pipes and the muffler itself would be the only factors when considering backpressure.


Cyclone,

You could have custom Y-pipes made with a larger collector if you wanted. Personally I don't think it would be needed except in extreme applications. There are blower apps putting over 300 HP to the wheels with just a cat back system. Of course, until someone compares the two on a dyno, it's somewhat up in the air. Check for a post on "A nice 4.6 mod" in this or the other exhaust forum. One of the members showed a Y-pipe modification that he did.


[This message has been edited by signmaster (edited 04-09-2001).]

 

cyclone- Pipe sizing charts have been around forever; the max 300HP/350cid for 1)2.5" answer I gave you came directly off of one. As mentioned in the previous responses, the pipe diameter is reduced even more in the tailpipe section of pipe. Having a mandrel bent 2.5",3", or dual out tail-section can change this. You're reading my opinion correctly: substantial HP over 300HP needs a 3" pipe(we're talking high rpm/WOT/max flow; directly off a pipe sizing chart), that it needs a 3" pipe feeding it, and that changing the Y-pipe or using true duals is illegal(This doesn't seem to be everyone's opinion, and I'm not saying people: don't have them, get them passed, or gain performance from them). It is the EPA's opinion and that's all that matters.