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Old 01-25-2022, 05:41 PM   #1
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Thorley THY-312 Headers install on W series

As I reported earlier I ordered Thorley Headers for my 2003 W20 chassis. The 2001-2004 chassis utilized a EGT valve that is not used on newer W series chassis. Banks has stopped production of the non-EGR headers for the early W chassis. This left Thorley as the only choice.

Thorley excepts orders for these chassis but does not stock them. The except the order and then at a later date convenient to them they build, charge your credit card and ship the headers. In October Thorley estimated a ship date of April or later but I have mine already. Alas, it is too wintery to think about an installation now. Possibly in April!

Banks still makes headers for 2005 and later chassis without the EGR.

Image 1 shows the headers and everything in the box.

Image 2 is a spreadsheet where I attempt to point out the differences between the headers and highlight where each brand has an advantage if any. I am not trying to convince anyone of anything, just pointing out the differences.

I am currently putting together a list of supplies and tools needed for the complete install. My stock mufflers are starting to leak so it is time to change them too. Closer to the time of installation I will document all the supplies and my installation plan. I think the cost of the mufflers, miscellaneous supplies and special tools will be ~$450. This added cost is the same regardless of header brand.

I think that once installed the differences in performance, economy and durability will be too small to measure.
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Old 01-25-2022, 06:14 PM   #2
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With the long tube headers you should get a boost in torque and maybe a little HP. An H or X pipe may help a bit.
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Old 01-26-2022, 06:47 AM   #3
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Long tube headers increase the hp and torque at lower RPM's . Headers alone will make a slight difference , but the real gain comes with a intake upgrade and an ECM tune.
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Old 01-26-2022, 08:05 AM   #4
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Quote:
Originally Posted by yeloduster View Post

I think that once installed the differences in performance, economy and durability will be too small to measure.
I'm quoting myself here because I didn't fully convey what I was thinking. I meant to say, "I think that once installed the differences in performance, economy and durability between Thorley and Banks headers will be too small to measure."

I expect to see a boost in performance from the headers. I already have the UltraRV tune. I've yet to see before and after dyno tests that show ANY increase in performance because of changes in intake air flow on a stock 8.1L engine. The 8.1L intake manifold has a built in restriction that hinders air flow. Until this is addressed improvements in airflow before the intake manifold don't do much. Raylar Engineering modifies 8.1L intake manifolds to remove this obstruction. They have dyno tests to show how effective this modification is. However, they want >$900 dollars to modify your manifold! I'm not sure they are still in business. Their website is up but they don't answer the phone.

My primary reason for installing headers was to help insure against a broken exhaust manifold. All my past heavy vehicles broke an exhaust manifold sooner or later. Exhaust manifolds and headers are becoming difficult to find for the 8.1L GM engine. I didn't want to take off a broken cast iron manifold and replace it with another cast iron manifold. I thought I would be proactive and add headers while I could still get them. Headers tend to be more resistant to cracking than cast iron manifolds.

The bonus is more performance.
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Old 01-26-2022, 10:42 AM   #5
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Great thread Duster. I think you will love the Thorley headers. I have the Banks headers and full exhaust on our W22 Itasca. I also have the URVP ECU and trans tune. Banks CAI and larger throttle body. I've looked at the Raylar intake manifold mod dozens of times but never could bite that bullet.

You're rig is gonna rip.
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Old 01-26-2022, 10:59 AM   #6
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What about engine noise levels? My experience with headers on cars is that tube headers tend to transmit more noise to the interior of the car than cast iron manifolds.
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Old 01-26-2022, 06:32 PM   #7
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What about engine noise levels? My experience with headers on cars is that tube headers tend to transmit more noise to the interior of the car than cast iron manifolds.
Thorley uses a heavier pipe, so they end up being quieter than stock exhaust. What happens in practice is that headers help the engine breath so you are not into the throttle as hard, thus resulting in quieter than stock at cruising speed. That was my experience when I switched to Thorleys on my previous motorhome.



My current motorhome I installed Banks because Thorley does not make a Tri-Y for the W22. From every independent test I've read, Tri-Y makes more power across the board over straight tube headers.



I would also strongly recommend getting Magnaflow mufflers. Get the longest muffler you can find in the size you need. They are will be fairly quiet, even though they are straight through.The pack around the muffler prevents drone from radiating from the case. All the noise goes out the tailpipe a long way away from the cockpit. I could carry on a conversation from the front seat to someone laying on the back bed without yelling.
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Old 01-26-2022, 07:15 PM   #8
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You say that the Thorley’s are equal length but from your pictures it sure doesn’t look so. The rear two tubes on both sides go straight into the collector so they are no way near equal length.
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Old 01-26-2022, 08:09 PM   #9
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I received my Banks kit for my 2003 W22 last week. Also too cold for me (in Kansas) to install right now. Haha.
I’ll try and lay out what came in the kit like you did this weekend and post a pic to show what comes in it. There were a couple of reasons I chose the Banks kit over Thorley’s. One was availability and the other I just liked the look of the Banks headers better as they’re more uniform in coming off the heads and they have a crossover pipe included. Like others have said I don’t think anyone could go wrong with ether kit. Both Mfg’s make great products.
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Old 01-26-2022, 08:22 PM   #10
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You will smile a lot more with those long tube headers. BB Chevys love them, they need to breath.

I used header wrap on my Banks headers. Quiets it down and keeps the heat from melting things. I did all the individual tubes as far as I could, then did all the way back to the collectors. Costs a bit, but worth every penny.
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Old 01-26-2022, 10:17 PM   #11
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Are both brands ceramic coated or did you get that done?
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Old 01-26-2022, 10:36 PM   #12
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Oops, just noticed, those are not Tri-Y. I asked Thorley why they got away from the Tri-Y on the W22 and they could not give me a real answer. Makes me wonder if they got lazy or cheap.



I would also mention that headers noticeably cooler than stock exhaust as the engine does not produce as much heat for the same amount of output HP. Open the engine cover after running a long hard run and you will be pleasantly surprised with how much cooler everything is.
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Old 01-26-2022, 10:51 PM   #13
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Thorley Headers..........

Haven't even thought of those since my Muscle Car days......LOL
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Old 01-27-2022, 06:21 AM   #14
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Quote:
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Are both brands ceramic coated or did you get that done?
Both brands are stainless steel, no coating.

Wrapping the header tubes was mentioned by someone. I have no opinion on that other than to say that wrapping the tubes voids warranty on both brands and all other brands I am aware of.

jcgribks says the Thorley headers in the picture I provided do not look equal length. I stand corrected. I'll have to modify my chart. However, for what it is worth, on each side it appears that the front 2 tubes are somewhat matched in length and the rear two tubes while shorter than the front are matched. I have no idea if that makes any difference to anything.
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