Exhaust Gurus Needed

[Dhan]

A while back during some gas tank work, I noticed that the no name 2.5" cat-back exhaust that came with the car had rusted very badly. I hadn't ever noticed it, so it must've happened this winter. I removed it completely and it is not repairable.

After quite a bit of reading, I've learned that exhaust notes work in pulses and for a naturally aspired car such as my Laser, a 2.5" exhaust is a good compromise between low and top end power.
In the kind of racing I will be doing (rallyx in the dirt), low end power is important. Top speeds are around 30, maybe 40 mph. Your accelerating out of turns a lot, so would a 2.25" or 2.5" be appropriate?


I've found a lot of conflicting write-ups and thread discussions on this topic and am not quite sure how to proceed. I've narrowed it down to a few options.

1. Just locate a stock 2.25"(?) exhaust/muffler system from another n/t 1G
2. Get a stock 2.5" exhaust off of a 1G GS-T
3. Get an ebay exhaust system
4. Have a muffler shop fabricate something for me
5. Get the Pacesetter headers and 2.5" exhaust

I also plan on eliminating the catalytic completely and replacing it with a test pipe (it's not a street car).

So I'm asking anyone with experience with n/a exhaust applications to point me in the right direction and correct any misinformation I may have posted.


PS. Sorry this isn't in the n/t section, but it seemed like a ghost town.

 

[Bud92gsx]

1g's came with 2.25,2g's came with 2.5..Just to clear that up..CO has an emissions law, So I hope its not a street car if you plan on eleminating the cat..

 

[spooln4fun]

As far as your catback goes I'd suggest you have a shop (at least get a quote) do one up for you with your choice of muffler brand/design I know alot of mufflers on eBay have 2.5" inlet. I'm not sure how big of a problem locating aftermarket down pipes for the n/t is.
If your looking for something stock like Vibrant performance sells a dual tip oval muffler that is black or I believe comes in a stainless finish.

 

[Dhan]

Thanks for confirming that info Bud. The car will be strictly off-road on a dirt rallyx course, so emissions aren't a problem.

I was looking at something like this for a DP Dejon Tool EDP-2GA 2.5 inch Downpipe for the Mitsubishi Eclipse - DSMtuners.com. Into a test pipe (where the cat had been) then into a 2.5" cat-back, and some kind of muffler (or maybe no muffler).

However, if the stock GS-Ts had 2.5" piping all the way through, it might just make sense to pull one in a junkyard. Then find some inexpensive N/T headers (the stock one is cracked). I'll definitely get a quote from nearby muffler shops too.

I kind of just wanted to throw my idea out to everyone and see if anyone found any mistakes in my planning.

 

[Bud92gsx]

Most cast manifolds have cracks in them, my stock one did and did not leak..Make sure it don't leak, that's all you need to worry about..But If you want to get a new header and exhaust go for it..But some of those downpipes are longer and eliminate the cat in the first place..

 

[avenged5]

If it is the 4g N/A you're modding then I can tell you I have a full 2.5" exhaust and an OBX header. I didn't see much difference but it really comes alive between 3500-4000 RPM.

 

[Dhan]

Just about every 1G I've seen has a small crack developing in the manifold, so I know its weak spot . The blue Laser I have has a disaster for an engine, and the exhaust is no exception. Last autumn I hooked up the compressor and found numerous leaks in the head and manifold. If I find an OEM n/t mani, I'll probably just grab it.

avenged: I'm guessing by "comes alive", you mean it gets obnoxiously loud?

 

[avenged5]

Just about every 1G I've seen has a small crack developing in the manifold, so I know its weak spot . The blue Laser I have has a disaster for an engine, and the exhaust is no exception. Last autumn I hooked up the compressor and found numerous leaks in the head and manifold. If I find an OEM n/t mani, I'll probably just grab it.

avenged: I'm guessing by "comes alive", you mean it gets obnoxiously loud?

No by that I mean it upgrades from ungodly slow to to just plain slow. It only gets obnoxiously loud if I'm basically above 5k though, which doesn't happen in economy mode.

 

[Lofty]

I had an OBX mani on my NT with some Ebay catback I think.

I also had a magnaflow high flow cat.

The car sounded OK and it opened up a LITTLE bit of power.

However, it all depends if you believe in the "Exhaust scavenging theory" I do indeed believe in it (On turbo and NT cars).

Honestly, exhaust isn't going to give you much if any of a performance upgrade. I suggest polishing and porting the heck out of your head, as well as camming it.

(I assume your rallyx doesn't allow anything but natural aspiration)


An upgraded exhaust is only good if your engine can take full advantage of it and can pull in as much air as the exhaust can flow out.

 

[Dhan]

Yeah I've read up in the N/T section of this site a few times. One fella outlines his whole all-motor build process of porting, polishing, cams, etc. I found the article a little late though, as I've already started my build.

I do follow the various ideas of scavenging, pulses, etc., but I'm not looking for gobs of power out of this thing, just a sensible replacement exhaust for the garbage that rusted off this winter.

The rallyx I'm with follows normal SCCA guidelines, so anything is allowed- turbo or N/A.
It's pretty much dominated by Subarus, but there are some pretty fast FWD N/Ts. It really comes down to the driver in these races.

 

[Dhan]

Decided to revive this thread to see if I can get some answers, instead of starting a new one.....

1. I had to trash my OEM head because it was so warped. So I got a new head, but am not sure if it's originally from a turbo or N/T. Does it matter, are there differences?

2. What is supposed to go where the red circle is? It looks like some kind of oil reservoir or something. I just plugged the holes with some spare hardware to prevent the oil from leaking out for now.

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[9!'clipseDOHC]

Decided to revive this thread to see if I can get some answers, instead of starting a new one.....

1. I had to trash my OEM head because it was so warped. So I got a new head, but am not sure if it's originally from a turbo or N/T. Does it matter, are there differences?

2. What is supposed to go where the red circle is? It looks like some kind of oil reservoir or something. I just plugged the holes with some spare hardware to prevent the oil from leaking out for now.

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1. The turbo and N/T 4G63 cylinder heads are identical with the exception of the intake camshaft which has a 252 duration while the turbo has a 257. Both exhaust cams have 244 duration. The N/T intake cam also has 5* more overlap. Here is an in-depth explanation of 1g 4G63 camshafts:

Based on what I can tell from the service manual the 1G 2.0L cams differ as follows: (specifications pages, timing is in one place, lobe height in another)

Intake NT opens 26 BTDC close 46 ABDC lobe height 35.493 (34.993 limit)
Intake MT opens 21 BTDC close 51 ABDC lobe height 35.493 (34.993 limit)
Intake AT opens 21 BTDC close 51 ABDC lobe height 35.200 (34.700 limit)

Exhaust NT opens 55 BBDC close ATDC 9 lobe height 35.200 (34.700 limit)
Exhaust AT opens 55 BBDC close ATDC 9 lobe height 35.200 (34.700 limit)
Exhaust MT opens 55 BBDC close ATDC 9 lobe height 35.493 (34.993 limit)

From this I come up with the NT intake cam being 252 duration, the turbo intake at 257 and a duration of 244 for the exhaust. NT has 35 degrees overlap (26BTDC + 9ATDC) and turbos have 30 (21+9). These are seat timings. From the point where the valve first starts to move.

2. There are 2 ports in the red circle. The one on the front of the head should be blocked off with a set screw on both turbo and N/T heads. The one on the passenger side should be blocked off if it's a N/T and is the turbo oil supply for turbo models. The thread size is 10 mm x 1.25.

As far as your exhaust concerns, when my DSM was N/T I ran the fastest (16.1 ET) and it sounded the best with just a 2.5" Pacesetter cat-back. When I upgraded to headers and a high-flow cat, my car got ungodly loud without picking up any additional power. With that in mind, I would keep the front have of the exhaust stock and upgrade to a 2.5" cat-back and eliminate the cat if you want.

Hope this helps!

 

[Dhan]

Thank you sir! That was very helpful and interesting at the same time.

Now to find some exhaust manifold studs- I left the old ones in my trashed head

 

[9!'clipseDOHC]

Thank you sir! That was very helpful and interesting at the same time.

Now to find some exhaust manifold studs- I left the old ones in my trashed head

You are very welcome. Check out this site for the studs: www.ssstuds.com. They used to be a site sponsor and I've done business with them before.