Rally Exhaust?

[1990AWD]

If an exhaust is all your doing, you don't need a tune or wb, but you'll probably have boost creep. You start adding air and fuel as in bigger injectors, turning up the boost, etc, and then you need something to control everything and a wb to monitor how you're doing.

 

[Leonthefaded]

If an exhaust is all your doing, you don't need a tune or wb, but you'll probably have boost creep. You start adding air and fuel as in bigger injectors, turning up the boost, etc, and then you need something to control everything and a wb to monitor how you're doing.

Yes you are absolutly right, I wont be upgrading from my stock injectors or turbocharger for my build. All I'll be doing is the exhaust if I ever come close to what I'm aiming for.

Thats why I would really appreciate more sound clips from members exhaust systems and if possible photos of custom setups.

 

[Bud92gsx]

Actually I will buy you a rally exhuast If you fly me out there for a few weeks..

Oval muffler for least loudness.

 

[jtmcinder]

Well, it now seems to have sunk down to issues like "exhaust tone" so I don't think it's really a rally anything thread. Not to mention that the thread-starter has a 2G (so I won't mention it).

 

[knochgoon24]

How come this information isnt reflecting what is presented in the Stage 1 Upgrade Path for the 2G 46g3T?

It is currently being worked on. The staff has been busy with a few of these projects on the side, like getting a maintenance page updated.

DSM 4G63 Maintenance Guide - DSMtuners

The 2g Upgrade Path is right now under works, getting brought up to date with new tech, but it may be some time until it's live.

 

[Leonthefaded]

Well that's good to know. I'm trying to follow the upgrade path, and other tech guides I've been reading. Now link and gm maf is on my reading list.

Oval mufflers? Like the ones I see hondas using? Or like the therma r and d that was pictured recently?

Don't get me wrong. Exhaust tone is a very important aspect. The level of importance for my build concerning the exhaust is exactly like this: Tone, legality, performance.

In hawaii they are pretty strict about what you can and cannot put on cars. Concerning exhaust most police and county offcials do not take the time to get under your car and inspect it. They listen for it. Some depth in tone won't get you in trouble as much as the little honda bumble bees going down the road will.

A lot of you guys are in cali right? I've read a lot about passing emissions tests. Right now I don't have to deal with that. Just safety inspections and recons

 

[Tiki2777]

Well that's good to know. I'm trying to follow the upgrade path, and other tech guides I've been reading. Now link and gm maf is on my reading list.

Oval mufflers? Like the ones I see hondas using? Or like the therma r and d that was pictured recently?

Don't get me wrong. Exhaust tone is a very important aspect. The level of importance for my build concerning the exhaust is exactly like this: Tone, legality, performance.

In hawaii they are pretty strict about what you can and cannot put on cars. Concerning exhaust most police and county offcials do not take the time to get under your car and inspect it. They listen for it. Some depth in tone won't get you in trouble as much as the little honda bumble bees going down the road will.

A lot of you guys are in cali right? I've read a lot about passing emissions tests. Right now I don't have to deal with that. Just safety inspections and recons

You can only do so much with trying to keep your car legal.
The "legal" limit for dbs is 95 (in Nebraska, although most cops other than state patrol don't enforce it, we have enough Honduhs here with fart cannons that it wouldn't hurt; each state has their own rules, whether or not the cops enforce it is another thing) and most aftermarket catbacks will exceed it without a silencer.
This is not even considering the use of a catalytic converter. flex pipes most not knowing officers will assume it's a cat, while you could not risk anything and still get a good high performance/high flow cat.
If you want to keep your car legal, get custom 3 inch piping, a cat, and get your crappy stock muffler welded on.
Trying to get a good exhaust tone is much more difficult when trying to balance legality and emissions.



Don't talk shit about the Apexi N1 TB. It's amazing don't be jello

 

[jtmcinder]

The "legal" limit for dbs is 95

Really? Where? Or are you claiming this is a federal limit?

 

[Tiki2777]

Really? Where? Or are you claiming this is a federal limit?

In my state it is a law, but so is not coughing in church and spiting out bubblegum on the street. Each state varies, I don't know each and every state's law on it. Many of the emission testing states are really strict about it though. Nebraska couldn't really give a crap about it though... unless we're talking about the jerks that are the state patrol (they try to be dicks, just because they can).

I definitely didn't mean to make it seem like it was a federal law...

 

[jtmcinder]

I'm so tired of this stuff. It's so easy to check whether NE has a 95-dB limit. Why do you guys keep posting BS?

 

[Leonthefaded]

You can only do so much with trying to keep your car legal.
The "legal" limit for dbs is 95 (in Nebraska, although most cops other than state patrol don't enforce it, we have enough Honduhs here with fart cannons that it wouldn't hurt; each state has their own rules, whether or not the cops enforce it is another thing) and most aftermarket catbacks will exceed it without a silencer.
This is not even considering the use of a catalytic converter. flex pipes most not knowing officers will assume it's a cat, while you could not risk anything and still get a good high performance/high flow cat.
If you want to keep your car legal, get custom 3 inch piping, a cat, and get your crappy stock muffler welded on.
Trying to get a good exhaust tone is much more difficult when trying to balance legality and emissions.



Don't talk shit about the Apexi N1 TB. It's amazing don't be jello

Me using the word legality was wrong. Just like a private convo I was having about exhaust its not about being legal. Its about being less likly to be hassled by law and state officials about my exhaust compared to more annoying and louder systems.

I wasn't talking shit about the apexi. I was critizing it. But I am giving it another shot.

 

[PieEyedPiper]

I wasn't talking shit about the apexi. I was critizing it. But I am giving it another shot.

Don't talk shit about the Apexi N1 TB. It's amazing don't be jello

I'll happily talk shit about it, if you guys want to get down. The N1 is hands down one of the worst mainstream performance devices "designed" for our cars.

Your turn.

 

[Leonthefaded]

I have my doubts and opinions about the n1. It seems oversized, but for the price your getting quality work. Id rather use the dual n1.

 

[PieEyedPiper]

I have my doubts and opinions about the n1. It seems oversized, but for the price your getting quality work. Id rather use the dual n1.

That's the thing it isn't oversized, at all. Nor is anything about it "quality". The N1 is an exercise in cost savings by Apexi. There is photo proof that there are neckdowns throughout the exhaust, some of which are as narrow 2" or even less.

Stock is 2.25".


I'm not actually interested in debating the topic much, it's been done before and there are always those who can't live with the fact that their overpriced, aluminized-steel, rusting, and restrictive exhaust isn't god's gift to DSMs.

 

[gofer]

I just want to clear the air here since I've owned a GS-T and then converted it, the Apex'i N1 only has those restrictions on the FWD catback. I'm trying to dig up a picture of both, can't seem to find them though.

Anyone have shots of a Apex'i catback for a 2g GSX?

Here's a shot of one for a GS-T.

You must be logged in to view this image or video.

 

[Leonthefaded]

That's the thing it isn't oversized, at all. Nor is anything about it "quality". The N1 is an exercise in cost savings by Apexi. There is photo proof that there are neckdowns throughout the exhaust, some of which are as narrow 2" or even less.

Stock is 2.25".


I'm not actually interested in debating the topic much, it's been done before and there are always those who can't live with the fact that their overpriced, aluminized-steel, rusting, and restrictive exhaust isn't god's gift to DSMs.

Excercise in cost savings? Are you saying this is like a "economy" exhaust system? When I say oversized I'm not generally speaking of the whole cat back system they offer. I'm talking about just the muffler. I'm not a fan of the big mufflers for my own personal reasons.

My old red gsx I traded with my new friend joesph, he came by last night. He still has the full 3" straight pipe system with apexi n1 muffler and it didn't sound bad at idle at all.

 

[PieEyedPiper]

I just want to clear the air here since I've owned a GS-T and then converted it, the Apex'i N1 only has those restrictions on the FWD catback. I'm trying to dig up a picture of both, can't seem to find them though.

Anyone have shots of a Apex'i catback for a 2g GSX?

Here's a shot of one for a GS-T.

Very interesting information. I'm not sure that very many people have made that distinction. I hadn't.
Still interested in the picture, of course.

http://www.dsmtuners.com/forums/bolt-tech/396358-n1-restriction.html Ah, it seems I've come across this before. Need more memory...

EDIT: Just came across information that the 1g AWD N1 does neckdown like the 2g FWD. I've haven't found anything regarding the 2g awd yet. Sam to the rescue! http://www.dsm-addiction.com/4g63-specific-section/1497-apexi-n1-restrictions.html

Leon, when I say cost savings I mean that the materials used were used because they were cheap and did the job (sorta). Any sense of quality from Apexi will likely only be found in the GT series.
I just can't see spending as much or more on a skinny aluminized steel pipe that rusts when there are plenty of other, more affordable, or at least higher quality and higher performing equipment on the market.

When I hear "N1". I think of the catback exhaust Apexi sells. Not just the fart-can muffler portion.

 

[Leonthefaded]

Okay cause when i near N1 I think muffler, glad were all on the same page. I wouldnt be purchasing the catback system at all personally not when i get sweet deals on just the muffler!

 

[Leonthefaded]

Okay so I wanna try something, I was looking at another members GST and he had such a simple and awesome looking as well as sounding system on his car, I think I will try it first, it is also cheaper than anything I've thought of so far.

Straight pipe in place of cat, Muffler removed. Straight pipe resonated tips, using the factory tips. My O2 housing will be the stock one just to see the differences, if the difference is too far off I will go with a vender O2 housing, but the cheapest one to keep cost way down.

Remember the O2 housing will need to bolt on to the stock turbo and downpipe.

Check out DSMtuner member Jaime818 and his video too.

 

[gofer]

I'm going to be the douche and revive the thread, bringing in more information about exhaust theory,
of course!

Exhaust System Theory

"Howdy,

This thread was brought to my attention by a friend of mine in hopes of shedding some light on the issue of exhaust size selection for turbocharged vehicles. Most of the facts have been covered already. FWIW I'm an turbocharger development engineer for Garrett Engine Boosting Systems.

N/A cars: As most of you know, the design of turbo exhaust systems runs counter to exhaust design for n/a vehicles. N/A cars utilize exhaust velocity (not backpressure) in the collector to aid in scavenging other cylinders during the blowdown process. It just so happens that to get the appropriate velocity, you have to squeeze down the diameter of the discharge of the collector (aka the exhaust), which also induces backpressure. The backpressure is an undesirable byproduct of the desire to have a certain degree of exhaust velocity. Go too big, and you lose velocity and its associated beneficial scavenging effect. Too small and the backpressure skyrockets, more than offsetting any gain made by scavenging. There is a happy medium here.

For turbo cars, you throw all that out the window. You want the exhaust velocity to be high upstream of the turbine (i.e. in the header). You'll notice that primaries of turbo headers are smaller diameter than those of an n/a car of two-thirds the horsepower. The idea is to get the exhaust velocity up quickly, to get the turbo spooling as early as possible. Here, getting the boost up early is a much more effective way to torque than playing with tuned primary lengths and scavenging. The scavenging effects are small compared to what you'd get if you just got boost sooner instead. You have a turbo; you want boost. Just don't go so small on the header's primary diameter that you choke off the high end.

Downstream of the turbine (aka the turboback exhaust), you want the least backpressure possible. No ifs, ands, or buts. Stick a Hoover on the tailpipe if you can. The general rule of "larger is better" (to the point of diminishing returns) of turboback exhausts is valid. Here, the idea is to minimize the pressure downstream of the turbine in order to make the most effective use of the pressure that is being generated upstream of the turbine. Remember, a turbine operates via a pressure ratio. For a given turbine inlet pressure, you will get the highest pressure ratio across the turbine when you have the lowest possible discharge pressure. This means the turbine is able to do the most amount of work possible (i.e. drive the compressor and make boost) with the available inlet pressure.

Again, less pressure downstream of the turbine is goodness. This approach minimizes the time-to-boost (maximizes boost response) and will improve engine VE throughout the rev range.

As for 2.5" vs. 3.0", the "best" turboback exhaust depends on the amount of flow, or horsepower. At 250 hp, 2.5" is fine. Going to 3" at this power level won't get you much, if anything, other than a louder exhaust note. 300 hp and you're definitely suboptimal with 2.5". For 400-450 hp, even 3" is on the small side."

"As for the geometry of the exhaust at the turbine discharge, the most optimal configuration would be a gradual increase in diameter from the turbine's exducer to the desired exhaust diameter-- via a straight conical diffuser of 7-12° included angle (to minimize flow separation and skin friction losses) mounted right at the turbine discharge. Many turbochargers found in diesels have this diffuser section cast right into the turbine housing. A hyperbolic increase in diameter (like a trumpet snorkus) is theoretically ideal but I've never seen one in use (and doubt it would be measurably superior to a straight diffuser). The wastegate flow would be via a completely divorced (separated from the main turbine discharge flow) dumptube. Due the realities of packaging, cost, and emissions compliance this config is rarely possible on street cars. You will, however, see this type of layout on dedicated race vehicles.

A large "bellmouth" config which combines the turbine discharge and wastegate flow (without a divider between the two) is certainly better than the compromised stock routing, but not as effective as the above.

If an integrated exhaust (non-divorced wastegate flow) is required, keep the wastegate flow separate from the main turbine discharge flow for ~12-18" before reintroducing it. This will minimize the impact on turbine efficiency-- the introduction of the wastegate flow disrupts the flow field of the main turbine discharge flow.

Necking the exhaust down to a suboptimal diameter is never a good idea, but if it is necessary, doing it further downstream is better than doing it close to the turbine discharge since it will minimize the exhaust's contribution to backpressure. Better yet: don't neck down the exhaust at all.

Also, the temperature of the exhaust coming out of a cat is higher than the inlet temperature, due to the exothermic oxidation of unburned hydrocarbons in the cat. So the total heat loss (and density increase) of the gases as it travels down the exhaust is not as prominent as it seems.
Another thing to keep in mind is that cylinder scavenging takes place where the flows from separate cylinders merge (i.e. in the collector). There is no such thing as cylinder scavenging downstream of the turbine, and hence, no reason to desire high exhaust velocity here. You will only introduce unwanted backpressure.

Other things you can do (in addition to choosing an appropriate diameter) to minimize exhaust backpressure in a turboback exhaust are: avoid crush-bent tubes (use mandrel bends); avoid tight-radius turns (keep it as straight as possible); avoid step changes in diameter; avoid "cheated" radii (cuts that are non-perpendicular); use a high flow cat; use a straight-thru perforated core muffler... etc."

"Comparing the two bellmouth designs, I've never seen either one so I can only speculate. But based on your description, and assuming neither of them have a divider wall/tongue between the turbine discharge and wg dump, I'd venture that you'd be hard pressed to measure a difference between the two. The more gradual taper intuitively appears more desirable, but it's likely that it's beyond the point of diminishing returns. Either one sounds like it will improve the wastegate's discharge coefficient over the stock config, which will constitute the single biggest difference. This will allow more control over boost creep. Neither is as optimal as the divorced wastegate flow arrangement, however.

There's more to it, though-- if a larger bellmouth is excessively large right at the turbine discharge (a large step diameter increase), there will be an unrecoverable dump loss that will contribute to backpressure. This is why a gradual increase in diameter, like the conical diffuser mentioned earlier, is desirable at the turbine discharge.

As for primary lengths on turbo headers, it is advantageous to use equal-length primaries to time the arrival of the pulses at the turbine equally and to keep cylinder reversion balanced across all cylinders. This will improve boost response and the engine's VE. Equal-length is often difficult to achieve due to tight packaging, fabrication difficulty, and the desire to have runners of the shortest possible length."

"Here's a worked example (simplified) of how larger exhausts help turbo cars:

Say you have a turbo operating at a turbine pressure ratio (aka expansion ratio) of 1.8:1. You have a small turboback exhaust that contributes, say, 10 psig backpressure at the turbine discharge at redline. The total backpressure seen by the engine (upstream of the turbine) in this case is:

(14.5 +10)*1.8 = 44.1 psia = 29.6 psig total backpressure

o here, the turbine contributed 19.6 psig of backpressure to the total.

Now you slap on a proper low-backpressure, big turboback exhaust. Same turbo, same boost, etc. You measure 3 psig backpressure at the turbine discharge. In this case the engine sees just 17 psig total backpressure! And the turbine's contribution to the total backpressure is reduced to 14 psig (note: this is 5.6 psig lower than its contribution in the "small turboback" case).

So in the end, the engine saw a reduction in backpressure of 12.6 psig when you swapped turbobacks in this example. This reduction in backpressure is where all the engine's VE gains come from.

This is why larger exhausts make such big gains on nearly all stock turbo cars-- the turbine compounds the downstream backpressure via its expansion ratio. This is also why bigger turbos make more power at a given boost level-- they improve engine VE by operating at lower turbine expansion ratios for a given boost level.

As you can see, the backpressure penalty of running a too-small exhaust (like 2.5" for 350 hp) will vary depending on the match. At a given power level, a smaller turbo will generally be operating at a higher turbine pressure ratio and so will actually make the engine more sensitive to the backpressure downstream of the turbine than a larger turbine/turbo would.

 

[Chill Kill Kult]

Run a cat, but not a muffler. I don't think I've seen that too often. Haha.

SRT-4's didn't come with a muffler. that just popped in my head a month later and I thought I'd share.

 

[meliketoball]

I have the eBay tsudo cat-back system. It's cheap, and then you can spend the rest of the money on a highflow cat or something.

 

[PieEyedPiper]

I'm going to be the douche and revive the thread, bringing in more information about exhaust theory,
of course!

Exhaust System Theory

Thanks for posting this, good read.

There isn't much taper in a 3" dp to 2.5 catback. Sometimes there is none at all, only a raised lip that is more like a wall than anything else. 3" into 2.5" remains a bad idea in my books. But I'm glad that that
Garret article includes pretty much all of the main ideas that we've been discussing. Oooh, and as I read on they cover that stuff too. Dumping losses.

Don't add restriction.
-If you must, then taper down.
Don't taper down.
-If you must then do it gradually and towards the end.

Do go big.
-Taper towards big if you can.

2.5" into 3" will have dumping losses but allows room for upgrading at only $100.
Little to no account of the desire for mid-range torque has been made. Mating 3" and 2.5" parts isn't the way to do that. Again, dumping losses and it's opposite.

As for putting a hoover on the end of your exhaust, does anyone know the function of the strange looking cones/tips (factory parts, too) on the end of exhausts on big trucks? I asked a diesel buddy about it and he said it was for emissions. He said that the exhaust stream gets diluted with fresh air entering at the last 12" of exhaust and that's the purpose. I told him that if that's true, I think it's asinine because that's no way to lower emissions, only what the AFR rod sees.
So, whatever the story is with that device, I was thinking maybe it could be used to help pull air out from the exhaust. Let's just say that I can run faster with the wind than in windless conditions or conditions in which I would be pushing through while making considerable air resistance on myself. I guess you could just call that "into the wind". Similar to exhaust scavenging to get more vacuum in a crankcase or something.

And what about the dual muffler ideas? Where you have two mufflers in parallel but one of them capped off so it has no exit. The exhaust must enter or at least pass by the (full of exhaust gasses) secondary muffler and then out the primary. I've seen evidence that you can gain some very respectable torque at the cost of a small amount of peak hp.

 

[Leonthefaded]

I actually had time to read gofers post and even though alot of terms used I didnt understand and problably need to find out what they mean, I think I got some clear messages, as to what I should and should not be doing. So I think I know what I'll be doing