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Another Down Pipe - Front Pipe Thread

Hello,

I own a stock LHD 93 RX7 with a PowerFC. I am planning to start at slow pace some reliability mods.

I am looking between two downpipes at quite different prices and would appreciate some feedback.

1) Revolution Front Pipe 90mm (I can get for around $400)
https://www.rhdjapan.com/revolution-...90mm-fd3s.html
SPECIFICATIONS:
Piping Diameter (mm): 90
Material: SUS304 Stainless Steel
Weight (kg):
-Stock OEM: 7.5
-Revolution: 4

2) Custom 75mm Downpipe that looks like an HKS ($150)
https://i.ebayimg.com/images/g/7aUAA...1W/s-l1600.jpg
https://i.ebayimg.com/images/g/hisAA...1W/s-l1600.jpg
https://i.ebayimg.com/images/g/6eAAA...1W/s-l1600.jpg

New vs Used
$400 vs $150
Stainless vs Mild Steel
90mm vs 75mm

I am also wondering if the 90mm would be plug and play like the 75mm or would have to change the rest of the pipes and about the extra flow, requiring a possible ECU tune.
Also, my car only does, if, 2000 miles a year (I live abroad), how would you guys rate the 75mm pipe in terms of oxidation?

TIA & Regards

IMO the 90mm downpipe is a waste unless you're trying to get every ounce of power out of the factory or upgraded twins. I would definitely recommend a quality manufacturer and just go with 75mm or 80mm. RHD Japan has the Greddy/Trust 80mm as well as the HKS 75mm, either of those would be fine and just over $200 + shipping vs that one that "looks" like an HKS at $150.

Thank you @AE_Racer . I am not based in the US so the prices for an HKS would add around 100$ more on top of that custom. As I do only 2000 miles a year, I think I will settle with the $150 one, will also help with the annual car inspection as I am replacing old for old rather than shiny new. Anything that is not like the stock pre-cat should already do wonders.
I am not intending to wrap the downpipe (read multiple threads) so I might also buy an used heat shield guard just for some extra layer of heat
https://www.ebay.co.uk/itm/MAZDA-RX7...wAAOSwlvNco0jb

My vote would be for the genuine HKS as well. The welds look pretty sketchy on that ebay mystery pipe. You can't have a lot of confidence in the flanges either. Yeah, looking like that it won't draw attention during inspection. But if you're going to the trouble to change it, I wouldn't want to do it a second time because of leaks or failures. Gaskets are kind of pricey too.

It's looks like another Ebay mystery pipe, probably made in China, and probably not from the finest materials. It was probably sold originally with a matching mid-pipe. We'll never know the numbers, but those DP/MP "kits" were probably responsible for several blown engines on these cars over the years from Boost Creep.There is also no mounting ear or provision at the down-stream end of that DP for securing it to the transmission like OEM. That will lead to vibration and potential for gasket failure. But they ARE shiny.

Know that a rotary's exhaust is almost twice as hot and energetic than the average piston engine. I strongly recommend sticking with known and proven brands...like that HKS mentioned above.

Convinced! Will wait for the HKS be back in stock :naughty: