Hi.
My exhaust pipe rusted out of my ´89 F150 4,9l and i was wondering if i just replace the whole system from manifold back. I´ll going to put single a 2.25" or 2.5" pipe and some free flowing muffler on it also.
So,will i see any performance gains if i junk original cats and put a single "hi flo" unit in there?
Junk both cats and use a modern high-flow 3 way + air cat. The Ford OEM cats on your truck are dated designs (pellets instead of a honeycomb), and look like they were sized for a Tempo!
3 way means it reduces hydrocarbons, oxides of nitrogen and carbon monoxide. The "oxidation" means it's hooks up to a smog pump to pump air into it to help burn off the hydrocarbons. Those cats do everything, and are the ones you want.
For your EFI '89, cut the second cat off altogether, and gut the pre-cat built into the Y-pipe, if the Y-pipe isn't rotted out. I believe it's stainless. That should give you a 2.5" outlet, which you can slap on your favorite aftermarket converter (Summit, Catco, etc..). Otherwise, there's a Walker Y-pipe that'll do the same thing available for $65 or so from Advance Auto and other consumer retailers everywhere.. It's not as good a quality as the OEM piece, but it bolt-on works. Another option is headers.
My understanding is that the "donut shaped gasket" between the cast iron split manifolds is actually a casting on the manifold, and the steel/stainless Y-pipe that bolts to it is simply flanged/flared. So if that's leaking...could be that the Y-pipe is mis-aligned on the truck due to not being properly supported by the rotted out exhaust.
Your 2.25-2.5" sizing is right on target. These engines can't effectively utilize anything larger. The outlet size from the individual iron manifolds is 1 7/8".
I agree with everything above except that the OE cats are not pellets, they are honeycomb. At least mine were.
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1990 F-150XLT Lariat Stillon the original engine with no squeaks or rattles at over 300k miles
4.9/M5OD/3.08
16.89@77.09
145 rwhp, 272 rwtq
2001 Lightning #127
13.18@104, no chip, no pulley, no nitrous
Confuscious say "Man who have no use for jackstand have promising career as jackstand".
Some have been reporting hit and miss quality with the Walker lately. Magnaflow also makes a direct fit replacement that actually looks better in my opinion. It's a little price, average seems to be a little over $200. Outlet size is 2.25" instead of the 2.5" with the Walker. Bends appear to be mandrel formed, no crimping on the inside radius of the bends like the Walkers seem to have. Part number is 93302.
Not saying it's better, just another option out there.
For $200 one might be able to get a muffler shop to fab one with a Y that would certainly be better than the Walker. If I hadn't obtained the Walker cheap enough I would have done that.
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1983 F150 300 I6, Comp Cam 260h and lifter kit, Port/Polished head, Offy DP Manifold, Holley 4360 Economizer 450 cfm, EFI Exhaust manifolds, Walker Y Pipe to 3-Way Cat, generic Turbo Muffler, Recurved DSII, Mallory HyFire 6a & MSD Blaster 2 Coil, Taylor Spiro Pro Wires, EFI plugs.
So,3-way cat it is. I´m also wondering what size it should be?
The one on my link says GVW is 5500 lbs. How can i tell if it is big enough for 4,9l? Should i get a bigger one?
5500LBS should be just fine for your truck. As long as the inlet and outlet of the cat match your Y-pipe, you'll be fine. 4.9L doesn't flow much.
Nope, no gasket. Works the same way as the flared water hookups for your sinks at home. There's enough surface area, and the soft Y-pipe material just deforms to fit the large round nipple on the manifold.
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