Hello forums, I am about to become the proud owner of a completely stock (down to the OEM radio!) 1993 R1, 50k mi, and am looking into reliability mods, specifically the downpipe as it seems to be one of the most universal (I don't like cooking my engine bay). Yes, I used the search function quite a bit and came up with a couple possible ideas but many of the posts are from years ago (I can't even find an M2 DP anywhere), and was wondering if there is new information on this subject. I think I narrowed it down to these two:

1. Buy a 'good' downpipe (HKS, etc), bolt it in and call it a day.

Pros - collectively accepted as a quality fitting piece, but some have seen issues with all the brands.
Cons - price, $350+/- for just a DP is a stretch, though I understand the whole reasoning behind it.

2. Buy a 'not as good' downpipe + MP combo (prolly megan racing), get a restrictor plate (between MP and CB?), bolt it in and call it a day.

Pros - Cheaper, removes both clogging possibilities, ready to be a true full exhaust once the rest of the supporting modifications are in place.
Cons - Could not fit as well (though have heard megan racing is a better company as far as quality goes today), plate must be made properly for boost creep issues (i've heard 2.25" ID is an accepted value, is that correct?)

Feel free to correct an fd novice, but this is what I've surmised from the 30ish threads I've reviewed. At the end of the day, I just want to do whats healthy for the car, I'm not looking for performance yet, so if there are other more pressing matters that should be attended to let me know, I'm also looking into AST delete, air intake solutions and vacuum hose replacement as my short list.

 

Pettit racing downpipe? Slightly cheaper than the HKS at 300. Is that Megan racing a two piece pipe? that would be another con imo.
If your research has shown that the HKS is a quality fitting piece, I say go for it. I've bought so many parts for my seven because they were less expensive only to have to rebuy because of fitment/quality issues.

 

I always say "you get what you pay for".
Not always the case. But, something as important as a fitment item (body kits, intake/exhaust, etc) is important to think about, else you end up spending more in the end.

 

Thats the thing. Though most say the HKS (which is just an example, but it seems to be the most prevalent) is a good fit, there are also several that had issues with it, not just fitment but quality. So if all I heard were good things my choice would of swung in favor of the brand name DPs, but that was not the case.

The Megan is a two piece because it includes MP as well, which is a bad idea to put on a stock car without adding restriction, hence the restrictor plate.


True, and though I've heard trying to use only the DP portion of the megan is a no-go (won't line up), i haven't heard of fitment issues with the entire kit, then again I've yet to see a post of someone with a megan commenting on fitment.

Also, if this was only DP vs DP I would also swing in favor of the HKS/etc, 9 times outta 10 your quote is right, but since the megan comes with the added benefit of removing the main cat (A clogging hazard?) it brings me back to the table. (EDIT - Also i notice it is sold at rx7store so can it really be terribad?)

After thinking a bit more, I guess a more direct question would be toward anyone with a megan DP + MP as to if they had issues with fitment, welds etc.

Those with restrictor plates or experience with them, what size would be appropriate? Mind you I'm not looking for the perfect one just a conservative number to stay away from creep.

 

Bonez, Pettit or rx7store should be fine and personally I'd recommend them in that order. Look for nice thick flanges. Stainless is nice and DPs with the support bracket on the down-stream end that attaches to the side of transmission is also preferred IMO. If you have the funds, get it jet-hot coated. If not, some DEI wrap with the DEI sealant. The latter isn't as pretty, but you can't really see it with twins anyway. Either way, it helps ALOT with underhood heat.
The only HKS DPs I've seen have been made for RHD. They're designed to fit under the steering shaft by being flattened at the up-stream end. Never seen any figures, but it seems like it would be slightly more restrictive and unnecessary on a LHD. Also harder to wrap.

Personally I stayed with a Bonez hi-flow cat...I don't have to worry about CREEP, it's quieter and the exhaust doesn't make your eyes water. But full disclosure, my car is also been kept at near stock boost so I don't need a full exhaust like others.

COOLING should be your next focus IMO. Everything else is dependent on it. Change the coolant out keeping as little coolant to distilled water as possible...but with some coolant to retard corrosion. Aluminum radiator. Fluidyne, Koyo are popular choices. Fluidyne is 150% larger than stock and Koyo is 200%, but the larger you go, the more fitment issues and not necessarily better cooling. Check your coolant hoses closely. Especially the turbo coolant lines which even at 50K may be starting to swell and bloat. If you need to change caps don't exceed .9 bar.

 

Thanks for the coolant tip, didn't think I'd need much antifreeze this being Florida.

Definitely will be wrapping it, also I mistyped, the DP + MP combo on rx7store has the same pic as the megan racing ones on ebay, got mixed up. It is on optionimports.com, but I dunno if that means quality or not... The bonez DP is starting to emerge as the primary option 1 candidate, more I read.

But Option 2 seems to still have more merits, as long as I can be sure (as much as you can be sure when it comes to any exhaust fitment) that it fits and that I won't kill my car with the proper plate. What size have others used?

With this post I will be able to actually read the parts classifieds, maybe that will open up different avenues

 

Re-reading your original post....IMHO go with option 1. Get a decent DP and call it a day. I don't know anyone with a "restrictor plate". They either keep a cat (usually hi-flow), go with a resonated mid-pipe or a full-on mid-pipe (requires porting the stock wastgate with twins or a single turbo system with appropriately sized wastegate).
In your case, if you intend to methodically add modifcations, I recommend a good DP and if your stock cat is still good, continue to use it....for now. Then get those reliability mods in place.

My .02.

 

will a down pipe alone on a stock 93 FD cause boost creep?

 

^No. Enough back-pressure is maintained with a main cat and cat-back (even aftermarkets).

In fact if you are one of the very few who still have the stock pre-cat on the car, you should replace it ASAP. It was something MAZDA put on the car to help emissions when cold but it can collapse and take out your main cat. In a worst case senario, that can cost you an engine.
IMHO adding a downpipe is one of those rare modifications that is both a reliability AND a performance modification.

 

awesome, thanks. i've read its even better heat reduction to get the down pipe ceramic coated. has anyone ever seen this? Jim, you mentioned a jet hot coating, what is that? is it similar to a ceramic coat?

 

My car was also COMPLETLY stock and I would recommend getting a used Pettit or M2 down pipe and having it coated which is what I had done. The price for the coating is around $80.00.

http://www.jet-hot.com/

 

The REAL HKS downpipes fit perfectly. The reason a lot of parts get a bad rep is because counterfeit crap made out of tin-foil is purchased on ebay.

 

3" downpipe is usally al the same

 

Where can you get a downpipe ceramic coated on the west coast?

 

Resurrecting this old thread. I'm replacing the engine on a bone stock FD. Based on the research I've done, the downpipe needs to be replaced during the process for reliability reasons (so I will do that with a good quality aftermarket DP). How do I know if the main cat is still in working condition?

Thanks in advance for constructive input.

 

 

I can't agree more. I've bought too many crappy parts for my previous cars, and always regret not paying for quality.
...then again, a down pipe is a steel pipe, so...

I'd go for the best that you're comfortable paying. ;-)

 

They may be just "steel" but there are definitely differences in quality of the downpipes. See post #5. I've seen the cheapo DP's from ebay etc. Crap metal, thin flanges that aren't true and no mounting tab on the downstream side. That means flanges that warp over time with the higher rotary exhaust temps, flanges that aren't true mean expensive gaskets that fail or simply can't seal. And not having that mounting tab means the leveraged weight of the downpipe is all sitting on the mounting flange at the turbo manifold... which can also compromise the seal. And remember....it's not much fun changing these with the engine in the car.

Cost and price...two very different things.
I recommend buying a proven downpipe from one of our sponsor vendors. Bonez or HKS would be two names but there are others.

 

I'm actually on the same page as you, and intend on dishing out for FEED, but while we're on the topic, does anyone actually have a stat with the largest volume DP? (Including diameter of the outlet to the cats) That would be a great bit of info to have...

 

 

Wow, GREAT link (of course, it's internal...)
Thanks!! We may as well just lock this thread and reroute it to that link.

 

So I looking into replacing my old rusted oem downpipe that has a belly (cat), but do not want the new high flow downpipe to increase exhaust sound, don’t want the popos to be giving me a headache.

Which high flow dowpipe that does not increase exhaust sound? Or at least the quietest?

thanks

 

Downpipe doesn't affect sound. The midpipe and catback do that. Get whichever you want

 

I've searched on the web regarding this topic, and this is what I found: "A downpipe absolutely does affect exhaust sound. Replacing a stock downpipe with an aftermarket one typically makes a car's exhaust note deeper, more aggressive, and noticeably louder."
The stock downpipe has a cat, so going catless will increase the exhaust tone because there'll be less air flow restriction.

Did you replace the downpipe to a catless one and notice no exhaust sound increase?