Downpipe Comparo

Last updated: February 22, 1999

The downpipe is a straight pipe that replaces the pre-cat section of the exhaust. When replacing the cat with a straight pipe, the pre-cat section can be replaced as well. i.e.- you can use a mid-pipe or the ASP exhaust or similar to replace the cat and muffler. Then replace the pre-cat with a downpipe.

Another option is to have the downpipe hollowed out, but that probably won't flow as well a true downpipe. --Steve


Date: Mon, 5 Apr 1999 02:02:05 -0500
From: "Steve Wynveen"

The pre-cat is more properly known as a light off catalyst or close coupled catalyst. It is located close to the heat source (engine) so that it get up to light off temperature (~50% conversion efficiency) quickly. This is necessary for the 3rd gen to pass US cold start emissions requirements.

It is nigh impossible to test a car for cold start emissions. You would have to leave your car overnight at an emissions test station to do it properly. I don't think that would ever go over with the general public (not that I think it ever should either!). Once the main cat is up to operating temperature, the conversion that takes place in the pre-cat is minimal, when compared to the main catalyst. That's why a car with a down pipe will pass an exhaust sniffer test.

Unfortunately, it is a violation of federal law to remove it, or any other emissions control equipment on a street driven vehicle. On the upside, no one is ever going to catch you, unless you have an emissions equipment visual inspection in your state. Even then, it will take a very sharp inspector to catch it. Does sharp and pay of $6/hour ever go together - rarely!


Date: Fri, 24 Sep 1999 13:57:18 -0700
From: "Ulen, Robert S" (

These are the issues I'm looking at while researching DPs:

1) Is it all stainless, or just the tube (prefer all stainless)
2) Mounting details (prefer stock stud/nut setup)
3) O2 sensor location (must be able to change O2 sensor easily)
4) Fit at turbos and main cat inlet flange (must align without force)
5) Clearance of tube through its routed path (must be routed well)
6) Construction (nice welds, or welded by a chimp?  Machined flanges)
7) Price (low on list if the rest are satisfied)

It may seem like this is alot of nit-picking for something as simple as a DP, but if any of these things are AFUed, then people tend to cuss. So which of all the DPs out there is closest to satisfying items 1) through 6)? For the cost of most DPs ($300 to $500), it would seem possible to do all this and still make a profit.

Date: Tue, 23 Dec 97 14:33:18 -0500
From: (Christopher C. Costantino)

The consensus of the posts I have received is this: with just a downpipe, there may be some boost spiking at 4.5K when the second turbo comes on line, however, it is possible to have quite a few mods _without_ upgrading the computer or adding a boost controller.

A stock Rx-7 with just a downpipe (and even a K&N filter, intake and cat-back as well) can handle the added power without the computer or boost controller. If needed, a manual boost controller can be fabricated for about $20 according to one of the replies. This info is from first-hand knowledge and testing (exhaust temperature gauge,etc.). If anyone else has something to add according to first-hand accounts feel free.

But replacing _both_ converters most likely will cause a big problem without a computer upgrade or boost controller, due to the big decrease in exhaust restriction.

And just in case...I'll keep my extended warranty papers handy! ;)


Date: Thu, 26 Feb 1998 13:45:56 -0500
From: Tom Walsh

First off, Always go with stainless steal. It lasts longer and with the amount of heat that the exhausts on a rotary engine give off it is simply a way of prolonging your investment.

Second, The downpipe replaces the pre-cat which only helps emmissions on startup. The reason a 3rd gen over revs to 3000 RPMs when it is started is to bring the main cat up to temperature, so it can start doing its job sooner.

Third, with a downpipe you are removing one of the failure points of most 3rd gen cars. The pre-cat traps allot of heat in side the engine compartment and inside the engine itself. By replacing the downpipe you are also freeing up the flow on the exhaust side which makes the turbos spin easier and produces more boost. This leads to your next problem.

Over boost can damage your engine very quickly. If you plan to keep your main cat on your car I don't think you will encounter a problem. If you do wish to remove your main cat (which I believe is 50 state illegal) then you will need to install some type of boost controller, like the Greddy Profec B, and a fuel computer. The Profec B is designed to keep your boost levels in check and prevent over boost from killing your engine and the fuel computer will adjust the fuel levels going to your engine so it doesn't lean out and cause detonation.

Now noise levels, noise levels always depend on a couple of things. Your turbo setup is one of them, if you are running a non-sequential setup then that will be louder than the stock sequential setup. Pre-cat, the pre-cat acts as a mild buffer for sound, but if you keep the main cat the noise level will be okay. The main-cat, this is by far the biggest gainer for HP per dollar spent, and depending on your muffler, will also be the loudest.

Date: Fri, 11 Apr 97 14:57 PDT

Pettit Racing:		SS Downpipe (T-304) $470.00
				Mild Steel Downpipe  $385.00

				I have heard from 3 different sources that the SS
				pipe flanges are not quite right, but with a little work
				can be made to fit correctly.

Tri-Point Engineering:	SS Down pipe (T-304)   $425.00
				Mandrel bent true 3" pipe throughout.

Rotary Performance:	Mild steel mandrel bent true 3" pipe $375.00
				Home grown, i.e. not a Mindtrain pipe.
				Can also be had with Jet Hot ceramic coating for $475.00

Precision Imports:	Mild Steel $350.00

Peter Farrell:		Mild Steel $387.00

I finally decided to order the Tri-Point Engineering SS unit, and I will be getting a ceramic coating on the pipe. I also strongly considered getting the unit from Rotary Performance as the coating seems like a real good idea to me. I'll let the list know how the downpipe works after I get it installed. Tri-Point has a real good reputation over here on the left coast. They prepped Craig Nagler's RX-7 that won ASP nationals in auto-cross this year. I've actually had a chance to see this car and their work in person and I was impressed with the workmanship. A note about the mild steel units.

Most of these are, I suspect, the unit builts by Mind Train. I have been told that this pipe is not a true 3" thoughtout unit as it is not mandrel bent. i.e.- it's crushed a bit at the bends. HOWEVER, I do not know this to be a fact. If somebody out there has a Mind Train pipe, perhaps they can let us all know if its mandrel bent.

Spencer Hutchings took the following pictures of his Pettit downpipe:



Date: Sun, 12 Sep 1999 16:08:06 EDT

As you may recall, I installed an N-Tech Ceramic coated Downpipe on Labor Day weekend. The car really seemed to drive a lot better. Turbos seemed to spool quicker and I gained an additional pound of boost.

Today I did some G-Tech Horsepower runs to compare them with the numbers I got while the car was still completely stock. The Downpipe is the only modification made to the car so far. Here are the results before and after the Downpipe:

9 runs over two days at 85 degrees, average RWHP = 211.1

6 runs today at 85 degrees, average RWHP = 225.8

This represents an approximate horsepower gain of 15 horsepower, which is pretty much what I was expecting, and is consistent with the horsepower gains shown on the dyno with Project Rx-7 in SCC (although that car had already had other mods done, such as intake, catback, and ECU).

I am definitely happy with the Downpipe. 15 RWHP for around $300 is definitely worth it!

________________ I installed my N-Tech downpipe a few weeks ago, and had some product feedback for you. I had you ceramic coat it, and the shop you had do it got the coating all on the O2 sensor threads. It took me over an hour to scrape this out if the threads, and I didn't get it all out. This slightly bunged the threads of the sensor, which didn't bother me that much since the nect time I take the sensor out it would probably be to replace it anyway. Yell at the bastards that coated it! ;-) Regarding the downpipe itself, the horizontal part of it (after it has curved down and out of the engine bay and points towards the back of the car) clears the body by only about 1/4". it is pressed up against the heat shield and forces the shield up towards the body. So far, I have had no vibration problems, but I haven't driven the car at anything other than idle around the block. (Suspension problems and me being out of town have prevented me from getting the car out.) It also doesn't line up perfectly with the main cat. If the pipe was bent a little differently, it would fix this problem as well as the clearance problem mentioned in the previous paragraph. ---\ \ ---\ \ \ \------------- \ \------------- ^ | | | This is the part I am talking about. It needs to be about 1/2" - 1" to the right (passenger side). There is plenty of room for it to be bent so it is spaced over that far.

Date: Wed, 06 Aug 1997 19:04:33 -0400
From: Alan Smith

I have a Mind Train unit (that I paid 150 for). It is most certainly not mandrel bent. In fact in looks like it was made by a child borrowing dad's torch. The top is pressed into an oval shape that gradually opens up to a full three inch round. I think Rob Ryder may have a picture of one on his site.


Date: Thu, 06 Aug 1998 17:34:25 -0700
From: Gene Kan

My experience is that the Mindtrain does not fit too well. They saved a few bucks on an extra two bends which causes the pipe to rub the frame heat shield. Also the pipe near the O2 sensor is squashed like the stock pipe.

Date: Wed, 22 Oct 1997 14:17:04 -0700
From: "Hung-Jen Hung"

> Does anyone think that adding a downpipe along with a cat-back (and
>changing the intake sometime down the road) will cause problems?

I've seen people using front pipe w/o any fuel computer, but I won't ever do it on mine since it's too risky. Tri-Point is right, to be safe using fuel computer is a wise way to do.

>What downpipes do people have experience with? And how much louder is
>your car with the pre-cat gone?

I just had the chance to see the front pipe made by Tri-Point. All I can tell you is this is the best one I've ever seen. I am currently using the Mind Train one, but the quality is poor is my opinion, rough inside, bad aerodynamic, also the shape is same as stock one, not smooth enough. On the Tri-Point pipe, it's round and smooth inside. I believe they're using aluminum instead of steel which makes weight lighter. If money is not a problem, Tri-Point pipes are definitely a good buy.


Date: Fri, 26 Jun 1998 23:09:18 -0600
From: SCJ

I just got my downpipe from Tri-Point, and my first impressions are less than stellar. Maybe I'm being overly critical, and these are not relevant issues, but for the kind of money they charge I was expecting perfection. Since others feel this is the best downpipe out there, maybe I'm way off base here. I'm gonna describe a few points to you guys, and I'd appreciate it if you could tell me if these are legitimate complaints. Could be that I just got a bad one.

First, the main bend is not completely smooth. It is obviously not a crush bend pipe, but there are ripples in the inside bend that I can readily feel. Nothing major, but they are there. I was expecting mandrel bends to be completely smooth.

The flanges are mild steel, for some reason I was expecting full stainless. Anybody have stainless flanges?

The lower portion of the flange at the cat section sticks out about 1/8" beyond the end of the pipe. The top of the flange is flush. Basically, it's as if the flange were tilted forward when it was welded. I am concerned about fitment problems here. Also at that end of the pipe there is also a small bracket which is welded to the pipe. On the interior of that weld there is a piece of weld that sticks out into the pipe more than 1/8". Kind of as if it's like a burn through.

OK, lets go up to the manifold end. The mount for the O2 sensor was also welded in cock-eye as well. The part near the opening sticks into the pipe 1/4", while the back region is flush. This seems unbelievable unless there is some good reason for it to be at that angle. Also, there is a joint where the top portion of the pipe is welded to the main pipe and the inside of that is again loaded up with slag. I can't believe these areas were not ground down.

Maybe all this is completely insignificant and I should just bolt it on and forget about it. But, to mandrel bend this thing and leave so much crap on the interior surface, and seemingly misalignments does kinda seem counter productive. If any of you are interested I've got some small .jpgs of there areas you can check out. I'd appreciate any feedback you may have. Is all this acceptable? Should I contact them? Though it could be that there is no place for a perfectionist in the world of downpipe evaluation. Thanks alot.


Date: Sat, 27 Jun 1998 11:05:59 -0400
From: "Edward H. Kim"

I also noticed this when the Tripoint down pipe arrived but the ripples were minimal and barely noticeable. Now that it has been coated with JetHot 2000, the ripples are not noticeable at all.

On mine, the flanges and the the O2 sensor mount point are mild steel.

Mine is completely FLUSH between the pipe and the flange at the cat end.

Yes, I have a small amount of weld protruding through.

>The mount for the O2 sensor was also welded in cock-eye as well. The part
>near the opening sticks into the pipe 1/4", while the back region is
>flush. This seems unbelievable unless there is some good reason for it
>to be at that angle.

Mine is exactly as you describe.

I have some "slag" but minimal in my opinion.

I am not happy about the fact that the downpipe is not 100% stainless steel but I am satisfied with the overall quality of the pipe( Besides, it is already deramic coated). If I were you, I would get a replacement since the cat end of your downpipe is not as "perfect" as mine. I would like to see the JPG's. Good luck.


Date: Mon, 29 Jun 1998 14:30:00 -0600
From: "Scott C. Johnson"

I called Tri-Point today and spoke with Guy. I asked him about the issues I included in my original post, and he was extremely responsive. I told him I coudln't say for sure if all these things were significant, but he still insisted I send it back for his inspection. I'd really hate to send this thing out for ceramic coating only to get it back and find it doesn't fit properly.

In November Tri-Point contracted out the fabrication of these pipes to a large manufacturer. Tri-Point made the prototype and the jigs, but some of the attention to detail may have been lost.

I felt Guy really does want to check it out to see if something needs to be dealt with. With that type of customer service I have no problems taking the time and money to send it back. When I get a response from Guy I'll let you all know what his thoughts were.


Date: Tue, 7 Jul 1998 17:27:45 -0600
From: "Scott C. Johnson"

Guy gave me a call after he checked out the downpipe I returned to him and he agreed with all my claims. He was very disappointed in the pipe. Here is a summary of my observations and his comments:

The lower flange was not flush -- Tested the pipe and it did not fit on their jig. I'm glad I didn't have it ceramic coated and then find this out.

Wrinkles in the main bend -- Though not serious, shouldn't be there.

O2 sensor was crooked and protruded into the pipe rather far -- Not correct.

Pipe was a 2-piece unit -- Says they have never made a one-piece, and have even had 5-piece units. Someone told me they had a one-piece. Jim?

General quality of welds -- Agreed

Now the bad news. That was the last one they had, and due to its poor quality they are going to look for a different manufacturer. So, looks like I won't have a Tri-Point downpipe. Right now I'm leaning towards the ATR (or is it ART) pipe. As long as you're reading, someone send me their phone number so I don't have to dig for it. :-) Given all that has happened I can give Guy and the rest at Tri-Point a high recommendation. He listened to my concerns and when he found them to be valid refunded my money. I'd definately do business with them again. If you've got any questions or suggestions send em my way.

Date: Wed, 13 Aug 1997 09:41:03 -0400
From: "DeanColver"

Just to let everyone know the Petit Down pipe(stainless) is a very nice piece and he relocated the O2 sensor just a little further down..makes it a lot easier to get to...wonder how much HP is lost on that O2 sensor being there (hmmm).

Date: Thu, 14 May 1998 09:06:38 -0400
From: Tom Walsh

1)The kit is made by Applied Research and Technologies.

2)They do not have a web site that I am aware of.

3)The kit is available through JapTrix in West Palm Beach, FL. Their number is 561.963.8700 ask for David. It might be available through a local tuner as well but YMMV.

4)The kit cost ~$325 plus shipping. (I am not too sure about the price, but it is close)

5)I do not know if the pieces are available separately. Call David and ask him.

6)The pipe is made of T-304 Stainless Steel and the flanges are aluminized steel. (I checked my midpipe with a magnet.)

7)The pipe is mandrel bent.

8)It has a threaded hole for the O2 sensor for easy installation.

I am currently running the downpipe on my car awaiting my ECU upgrade to install my midpipe. I am pleased with its design and I also like the tone that it creates in the exhaust. It is not louder but it is a little more deeper overall.

Ryan Schlagheck is also running the same kit and I believe he is very pleased with the kit and the service he received from JapTrix.

Draw your own conclusions. I took my engine to be rebuilt by these guys and all I can say is that I have never had a major complaint.

From: Michel (

Those who read my original thread will remember that I had a significant increase in noise and fitment problems with the SR downpipe. I ended up taking it to a local shop which verified that it was indeed off enough to cause problems. I read another post where someone ovalized one of the bolt holes for the exhaust manifold flange. We didn't do that, but I did replace it with an HKS downpipe. With both off the car, there was a definite difference between them, but not by much. The SR pipe didn't "come around" in the rear as far as the HKS which caused it to be off by around 3" or so at the main cat area. The HKS went on without a single problem and bolted right in.

Comparing the two, (except for the fitment problem), the SR pipe was a better made unit overall, with slightly better finish internally. Now SR doesn't know about any other fitment problems so this may be related to my car somehow or a batch that was off spec slightly. It also turns out I managed to cross thread one of the bolts which helped create a larger exhaust leak, but even with it threaded correctly, the end of the downpipe (main cat end) rested against the body. So in went the HKS.

The Honda with a hole in the muffler sound is now gone and all that remains is the sound of the turbos spooling. I now must rate this as a mod you CAN sneak past the wife. The GReddy Power Extreme I ordered (for an exceptional price btw) may be another story altogether.

Date: Tue, 24 Nov 1998 23:50:06 -0500
From: Max Cooper

Stock pre-cat:  22.6 lbs (weighed with my $200 digital bathroom scale)
Bonez SS dp:     8.0 lbs (weighed with my $200 digital bathroom scale)
Bonez MS dp:    11   lbs (reported by list members)

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