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2021 GT500 headers & cats on a 2021 GT 5.0 w Roush blower, will they fit?!?!? UPGRADE....

monte87

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Hey guys,

Im interested and curious to know will stock 2021 GT500 exhaust manifolds fit a stock 2021 mustang GT 5.0 w Roush blower?? I am looking to upgrade to GT500 cats. The stock cats don't seem to be upto the task. And knowing the GT500 comes stock w a blower, I would think there cats are better than N/A cars. Will this work? and what does it entail.....

Thanks Anthony
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K4fxd

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I know they will bolt to the heads, might have to move some studs, what I don't know is if they fit the body.

I'd assume they will but haven't done it.
 

Grimreaper

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Interested to know. Looks like pass side cat might bolt to stock header. Driver side looks like a flange needs to be welded to header or re orient flange on gt500 cat and use gen1 header.

The firing order is different and the primaries come together differently than the yote. Believe it matches the gt350 ordering.

Id vote for a retrofit to stock headers. Don't tell the Shelby guys, but chassis is not much different than any other s550. Would expect headers to fit though.
 

K4fxd

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I think the OP is asking about both the 500 manifolds and cats.
 

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NFG_Coyote

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Unless someone is giving you GT500 manifolds and cat's this seems like an egregious waste of time/effort.

Just get "off road" delete pipes for your factory manifolds or reputable cats for boosted applications (i.e. GESI, Kooks Green, etc.), or long tubes.
 

engineermike

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Yes I’ve done this.

The 5.2 (both of them) head stud pattern is different for the flange. Iirc the two middle tubes are clocked 90 deg different.

The gen1 drivers side manifold was separate from the cat, with a flange. However, the 2 flange bolts are clocked 90 deg different from the gt500.

The gt500 passengers side cat will bolt to the coyote passengers side header, but it winds up too tight against the floor pan. It will work with a spacer though.

Gt500 drivers side is a bit more work and requires a flange to be welded to the stock coyote header.

On the other end, the gt500 cats connection to the resonator is 2.75” vs 2.25” coyote, so that will need mods too.

And finally, I personally do not believe any of the aftermarket metal substrate cats will ever be as reliable as stock gt500 cats.
 
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monte87

monte87

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Yes I’ve done this.

The 5.2 (both of them) head stud pattern is different for the flange. Iirc the two middle tubes are clocked 90 deg different.

The gen1 drivers side manifold was separate from the cat, with a flange. However, the 2 flange bolts are clocked 90 deg different from the gt500.

The gt500 passengers side cat will bolt to the coyote passengers side header, but it winds up too tight against the floor pan. It will work with a spacer though.

Gt500 drivers side is a bit more work and requires a flange to be welded to the stock coyote header.

On the other end, the gt500 cats connection to the resonator is 2.75” vs 2.25” coyote, so that will need mods too.

And finally, I personally do not believe any of the aftermarket metal substrate cats will ever be as reliable as stock gt500 cats.
Hi Mike-
Thank you for the definitive 411 regarding this topic. WOW, this is a whole lot of work to make this thing work. Question, would i be able to just cut the GT500 cat and attach it (weld) to GT piping? would that just work.
Thanks Anthony
 

engineermike

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Technically you can. In fact, I may do something like this on my truck. However, I don’t think it will save you any work and if you add the flange then you can swap them out easier in the future. Also, you’re not going to want them bottlenecking into a 2.25” factory connection anyway.
 

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monte87

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Unless someone is giving you GT500 manifolds and cat's this seems like an egregious waste of time/effort.

Just get "off road" delete pipes for your factory manifolds or reputable cats for boosted applications (i.e. GESI, Kooks Green, etc.), or long tubes.
Yes, I have a good price on some GT500 cats hence the question. As for off road cat delete, it seems NO ONE has them anymore as a kit. I can find a local exhaust shop that may do the delete for me. I heard all the aftermarket cats are all made in china junk and wont last.
 

NFG_Coyote

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Yes, I have a good price on some GT500 cats hence the question. As for off road cat delete, it seems NO ONE has them anymore as a kit. I can find a local exhaust shop that may do the delete for me. I heard all the aftermarket cats are all made in china junk and wont last.
Ok, makes sense, I totally get that.

I will say there are still reputable "off road delete pipes" and kits for S550's out there online, not name dropping, but any amount of digging on M6G will yield you some results. A local shop like you mentioned would also be a good option.

If NY has emissions inspections that'll be the draw back, if they don't, I wouldn't risk any cat on a boosted car.
 
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monte87

monte87

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Ok, makes sense, I totally get that.

I will say there are still reputable "off road delete pipes" and kits for S550's out there online, not name dropping, but any amount of digging on M6G will yield you some results. A local shop like you mentioned would also be a good option.

If NY has emissions inspections that'll be the draw back, if they don't, I wouldn't risk any cat on a boosted car.
Thanks for reply! PM sent. As for NY inspection, I would take them on and off, no biggie.
Ant
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