2.25" Stroker Exhaust Manifold / Exhaust System Recommendations

[etnlvn]

Good Evening All,

I'm spanking new to the forum but really excited about drawing from the community's knowledge and experience. I own an '06 Jeep TJ Rubicon with a recent, and perhaps inevitable, cracked head. I've made a few decisions: first, my old 4.0 is out. I'm replacing with a stroker. I've also decided to go with S&J Engines out of Spokane Valley, WA. I'm going with their updated head as well as the COMP Cams Xtreme 4x4, Hydraulic Flat Tappet; 205 Int./213 Exh. at 0.050 in., 0.450 Int./0.450 Exh. Lift;113 Lobe Sep 205/213; Torque/Throttle Improve; (EFI w/OEM Head), and the COMP Cams High Energy Timing Set. I think I have all, or at least most, of the related questioned resolved except, for the exhaust system. I'm less concerned about sound than I am providing the right amount of airflow. It's easier to find the right 2.25" exhaust system but not sure about which exhaust manifold to mate it up with. I've read too many negative articles about cracking in Banks exhaust manifolds to confidently pull the trigger on their product. I've looked at other exhaust manifold manufacturers but it can be overwhelming. So my question to the community is: what's your experience and/or recommendations for the ideal stroker exhaust system. Thanks in advance for your engagement.

[Cheromaniac]

It depends on the spec of your stroker engine. Ford a mild 4.6 that puts out up to 250hp (crank), a 2.5" exhaust from the header collector back would suffice.

[mpgMike]

If you are in California (or one of those other states with emissions requirements), you should probably use your stock manifolds. Having mandrel bends in the exhaust will reduce restriction. The specs provided suggest more of a low-end torque/fuel economy build. You won't need a bunch of flow; and in fact, a large diameter exhaust will hurt your usable RPM range power. Stock exhaust manifold should be adequate, even for a stroker. (I have a low-end torque 4.6 stroker in my '95 ZJ and use stock exhaust with no complaints.)

[etnlvn]

Great feedback. Thank you!

[SCRMBLDXJ]

I can offer some info here from my experience... I had a 4.0L in a 2006 LJ. I installed a set of ceramic coated Doug Thorley SS 3-to-2 headers for the dual cat factory '06 exhaust, along with a Magnaflow 93649 cat and a MBRP 409 SS 2.5" exhaust. I added new rubber hangers and checked the frame hangers while I was there. I wanted to fix the exhaust and not worry about it for years, so I dumped $$$ into new, quality/expensive parts...

Note - I already had Brown Dog motor mounts and a poly trans mount so the exhaust should not have been moving much, and the motor definitely had less movement than in stock form. The motor also had a 62mm throttle body, AEM cold air intake and no other mods.

The Thorley headers cracked in 18 months of mostly street driving & easy forest trails/over-landing. The Thorley headers had a warranty, but they weren't making them anymore, so they offered a credit (if I remember correctly). The fact that they cracked relatively quickly was frustrating! So I bought a set of Banks TorqueTube headers thinking that was the solution, and they cracked in about 18 months too. After that, I put the factory cast iron exhaust manifolds back on. I sold the LJ a couple years after and fixed up a 4 dr XJ for the family.

My thoughts from my experience:
-The headers (both brands), Magnaflow cats, 2.5" exhaust, CAI & 62mm TB definitely increased seat-of-the-pants power from ~3000-5500 RPMs.
-The motor had a "warbling" tone above 3500 RPMs that was distinct with the headers, and sounded unique compared to any other headers on 4.0L.
-The late model 4.0L factory exhaust manifolds are much more durable than the headers I tried; they lasted for years. They are also restrictive in the higher RPM ranges, but the other 'breathing' mods still helped the engine perform better than stock as far as seat-of-the-pants feels. I wish I would have chassis dyno'd it...

If I had a late model 4.0L , I'd consider gasket matching a set of factory exhaust manifolds and adding high flow cats. If you're building a stroker, I'd get a 1991-98 header (I like the Banks Revolver) and have an extra O2 sensor bung welded in. My experience with the late model 3-to-2 headers was not good.

[Gorilla]

I had specific concerns about the issues noted with collectors cracking but have been thinking I would go with the Edelbrock head. I live in an area with emissions testing and wanted to keep the mini-cats (pre-cats) on my 04.

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I went with the AFE Power header. I chose it specifically because it uses one gauge thicker stainless than others. I was aware of the problems others have noted, though they seem more common with the earlier TJ 6-1 headers. I'm only at 6-7 months, but no sign of trouble so far. Fingers crossed.

Every test will show airflow of a straight-through muffler of the Magnaflow style will have the best power, though they're louder. Dynomax makes a 2.5" Super Turbo in an 18" case that should provide the best balance of stock-like noise management and the added 2.5" flow. Flowmaster sells a mandrel bent 2.5" 409 stainless tailpipe with their Force II TJ exhaust which is their Delta 60 chambered muffler. I ran it for a little while, but ended up with a Walker Quietflow SS. Sounds reasonably good, but radiates out through the floor around 110hz. It doesn't drone, but I wanted stock-quiet and have that in full stainless now.

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There is also an AFE Power 3" catback with their straight-through muffler. All stainless, all mandrel bent.

[Gorilla]

The AFE Power headers also have a CARB EO. Not so with their replacement cats.

[Gorilla]

This is the specific model for the 2.5" dynomax super turbo I referenced. Unfortunately it isn't available in stainless.

https://www.summitracing.com/parts/wlk-17664

You can also get a 2.5" generic 14" case version of this which fits in the TJ

https://www.summitracing.com/parts/WLK-17733

And this is the stock Walker 2.25" Quietflow SS I'm currently using welded to the 2.5" 409 stainless tailpipe from my Flowmaster catback.

https://www.summitracing.com/parts/WLK-21456

[etnlvn]

Thanks everyone for all of the great feedback. I’m settling on the OEM exhaust manifold. A lot of good options for the cats on back. My search also now includes Motor mounts, trans mount, clutch, and flywheel. Thanks again to everyone and once I get to the final solution and complete the install I’ll circle back with this group to let you know how it worked out.

[mpgMike]

Unless you intend to spend a bunch of time off-road, may I recommend using stock replacement rubber mounts. The poly mounts last quite a long time, but transmit way more drivetrain noise and vibration to the passenger area. Stock mounts are typically good for over 100k miles.

[etnlvn]

100%. My off-roading never exceeds moderate Appalachian mountain trails so advice taken. It’s not my goal to over build my TJ. Thanks.