this may be my fav. thread on here. So much knowledge and open sharing and learning. love it <3 why can't college be cool like this.

 

In all actuality, SP2 is running the Descendant turbo kit with nothing but the axle back. I'd assume that I'd be fine with just a custom cat-back, but I want to play around with some stuff to see if it works or not. Just remedying my peaked curiosity.
My friend is running the full CX Racing 3" exhaust on his relatively stock 2AZFE. I say relatively because only other motor modification is the K&N Typhoon intake. That's it. Car still drives well, even in the lower RPMs. Picks up and goes like normal.
Once again, I'd assume he may have lost a bit of low end, but we hadn't put it on a dyno.
Sh*t's loud, though.

 

To start with, thanks for your genuine interest! I hope to better explain what I'm trying to say !

Simply, it's not a question of turbo, it's a question of what capability the exhaust supports! Turbo can do nothing the exhaust doesn't allow. And whatever capability the exhaust allows is available to N/A as well as turbo! As I said, there's nothing magical about turbo!

I don't pretend to be an expert, but I absolutely know that there's nothing special about turbo. Given appropriate intake capability, all it does is effectively multiply the capability of your N/A engine, presuming your engine is capable of that multiplication (generally speaking, it could break it.) My point is simply that if a 2" pipe following the CAT in my Eclipse is able to support much higher HP than my stock xB2, then the limitation we're looking at for the xB2 is not the post cat pipe but the combination of intake, engine, and pre-cat pipe.

The xB2 has a 2.4L engine whereas my Eclipse is 2.0L, no wonder the xB2 has the advantage over the turbo Eclipse with a dead turbo when it's allowed to breath (again, similar vehicle weight). What's interesting is just how much improvement is available with a good turbo. What this demonstrates is my Eclipse exhaust system supports a healthy throughput, I estimate somewhere in the neighborhood of 300HP. Given there's modest difference between the OE Eclipse exhaust system and the xB2, the question comes down to just what advantage is there in increasing the diameter of what portion of the xB2 exhaust. What I'm saying is a diameter of 1.8" immediately after the "scuba" is no big deal for our N/A engines. Obviously, we can obsess all we like, but what makes a genuine difference in real life doesn't necessarily have a whole lot to do with our obsessions. I submit that several feet of 2" in my Eclipse is a greater "liability" than a few inches of 1.8" in the xB2.

My own xB2 is running a 2.5" "S"-pipe and a Tsudo catback providing a 2.5" intermediate and divided 2.5" tail pipes. From the "scuba" on back, my xB2 clearly has the overall exhaust advantage over my Eclipse, but the road performance doesn't demonstrate that. So, the answer is the exhaust is just one component, and although not unimportant, the ability of the engine to utilize the provided exhaust is clearly the bigger issue. For N/A, the stock exhaust actually does a pretty good job, and I'm satisfied my W-R "S"-pipe "upgrade" is of dubious benefit.

As the exhaust gas temperature drops, the volume it requires shrinks, and hence the Toyota choice of 2.25" for the first half of the "S"-pipe and 2" for the remainder plus entry pipe to the "scuba" seems very reasonable to me. A lot of heat is dissipated in the 'scuba" and so a diameter of 1.8" at its exit strikes me as not in the least unreasonable given the reduction of exhaust gas volume. This doesn't mean there's no value at all in increasing the pipe diameter from this point on, but just that the value is severely limited. My Eclipse GSX several foot 2" tail end exhaust pipe clearly doesn't choke it relative to the xB2, and so it obviously wouldn't choke the xB2 either! Simply speaking, a modest N/A engine (like 2.4L) doesn't require a fire breathing exhaust to perform well!

 

That is hard to comprehend because it makes no sense at all. Just because you can make 300bhp from a turbocharged 2.0L engine using 2" exhaust doesn't mean that 2" exhaust is ideal any more than it means that 2" exhaust must therefore be big enough for a 200bhp 2.4L N/A engine. You're comparing apples to oranges here.

The concept of IHE performance mods is very simple: To get more air in and more air out. Forced induction does this by itself without the need for any accessory mods. FI supporting mods will add more power but are not actually necessary to acheive much more power than the same engine could ever acheive when N/A. OTOH, with N/A the only way to add power is to reduce restriction on both the intake and exhaust sides. A N/A engine relies solely on it's own vacuum and therefore can only breathe as well as the intake and exhaust restrictions permit.

I see your point about how a short 1.8" restriction in the middle of a N/A exhaust system doesn't necessarily result in a large increase in overall exhaust restriction however such a restriction is far from ideal. It causes turbulence, slows exhaust gas velocity, creates unwanted backpressure and loses both hp and tq. How much is pure guesswork without some dyno testing but the theory is sound.

Ideally a N/A exhaust should either taper down smoothly from front to back or remain constant with no sharp bends, restrictions or excess backpressure. Remember that backpressure is never desired but is an undesired result of maintaining enough exhaust gas velocity.

Rather than me going on trying to explain what others with better qualifications have already explained better than I can hope to, I'm going to post a link to an article that explains all of this in great detail. I hope this helps...

http://www.cobbtuning.com/info/?ID=3222

 

That is simply wrong on so many levels. A properly sized turbo can indeed increase exhaust gas volume and velocity hugely over what the same engine can flow when N/A through the same size exhaust piping.


Actually you do and what you claim to know "absolutely" is 100% wrong. You are very confused about some of the key differences between turbocharged and N/A engines.

Your Eclipse is turbocharged and therefore your comparison to the N/A XB2 is unfounded and your conclusions erroneous!

 

Whether or not 2" is ideal for my turbo Eclipse is totally beside the point. All that matters is that a 2" rear exhaust is easily enough to exceed the OE Eclipse power rating which is easily greater than the OE xB2 power rating! Yes, money can be spent on increasing the ID, but what is the realized value?

I went through your attached link and came up with this:

For max performance with a turbo it's critical to get max exhaust delivery to the turbine, however, that has little to do with what happens after the turbine. For a turbo engine, the back pressure is provided by the turbine itself, whereas for an N/A engine, it's provided by the exhaust system. Following the turbine, the rules are pretty much the same and if an exhaust setup doesn't flow, it doesn't flow! The turbine action doesn't force gasses through the exhaust, instead it depends on gas flow through the exhaust! Entirely true for both turbo and N/A!I don't see the support to these statements of yours in your link! For my part, I make the same claims about you!

PS. And I presume my misunderstanding is key to my lack of recognition of performance improvement due to a 2.5" "S"-pipe? Despite the reduction in exhaust gas volume, clearly my performance must be choking from a mere 1.8" exit pipe from the "scuba"?

 

We need dyno numbers to end this. Anyone got a spare dyno laying around? lol

 

You're still missing the point. The size of your turbo Eclipse exhaust has nothing to do with the optimal exhaust size for a N/A XB2.


Apparently you missed this part:

"One thing I do want to explain before I get too far into this is backpressure. I hear "You need backpressure to make torque." all the time. And it even comes from "tuners" as well as customers. This is flat out not true. Before I arrived into the company of true tuners I fell into the same trap myself. The reality is that backpressure is the enemy. You want to keep it as low as possible. What you do want is to keep velocity up. However doing the things that keep velocity high involves slightly more backpressure under some conditions. You want to keep the gasses moving as quickly as possible to make both good torque and top end power. The perfect exhaust system would keep the gasses moving as fast as they did coming out of the cylinder and have zero backpressure. However this is impossible to achieve in the real world."


What you seem to be either missing or refusing to understand is that when you force a larger volume of air into the engine with a turbo you also increase the exhaust gas volume. A turbo is not limited by exhaust gas flow the way you think it is. An undersized exhaust can make a turbo spool slower and choke at high rpm but it will still increase the volume of air ingested and exhausted by the engine hugely over what that same engine is capable of when N/A. How can I make this any clearer?



I never said that. I said that having a 1.8" restriction in the middle of your exhaust piping is not ideal and that all the other experts on exhaust design disagree with your "expert" opinion on this matter.

Look Trevor, you can do whatever you like with your XB but please stop and think before telling others that you've figured out the ideal exhaust sizing for a N/A 2AZ engine based on the exhaust size on your turbo Eclipse and the seat of your pants. It's just not that simple and I had hoped that you might have figured that out after reading that article from Cobb Tuning.

For the record I am not saying that there is a lot of hp/tq to be gained by replacing the scuba tank on a basic IHE XB2, just that leaving it is not as ideal as you claim it to be. I also very much question your assertion that since a 2" exhaust is big enough for your turbo Eclipse it must be big enough for a N/A XB2. IMHO 2.25" or 2.5" would work much better.

 

Who needs a dyno? Trevor claims to be able to feel as little as 2-3whp change with his butt dyno.

FYI for all:

According to Flowmaster, 2" ID single exhaust is good for 100bhp. 2.25" is good for 160bhp and 2.5" is good for 250bhp.

According to Magnaflow, 2"-2.25" ID single exhaust is good for 100-150bhp, 2.25"-2.5" is good for 100 - 200bhp.

According to another credible source, 2" is good for 144bhp, 2.25" is good for 185bhp and 2.5" is good for 232bhp.

Every expert source I've found says that when changing oem exhaust for more performance the exhaust pipe diameter should be increased between .25 and .5" for N/A street applications.

Using simple math we can deduce the following:

6250rpm x 147CI = 918750 /2 = 459375 * 0.000578703704 = 266 cfm

So now we know that at 100% volumetric efficiency our engines consume 266cfm of intake air. We also know that hot exhaust gasses occupy more space due to expansion. A known good ratio to convert intake air volume to exhaust gas volume is 1.467. So then:

266cfm * 1.467 = 390cfm

Now that we know our maximum exhaust gas volume we can make an educated decision regarding optimal pipe diameter for our exhaust system. Since round exhaust pipe flows ~115cfm per sq inch of area we can easily calculate the following:

1.80" = 240cfm
2.00" = 318cfm
2.25" = 408cfm
2.50" = 509cfm

Naturally there are other factors to consider such as pipe bends (mandrel or crush), mufflers, etc. but it should be fairly obvious that the oem exhaust sizing was designed to sacrfice maximum hp/tq in exchange for quietness and low rpm tq. Increasing the exhaust diameter will increase both tq and hp but at the expense of moving the tq curve a little higher in the rpm range. IMHO, 2.25" exhaust diameter would be as close to optimal for a N/A IHE 2AZ-FE as we can get without a lot of expermentation and dyno testing.

 

Of course higher intake volume results in higher exhaust volume -- what's not to understand about that? However, it's not so clear the engine will accelerate normally if the pipe is congested. In my examples, I've no reason to believe congestion was occurring.

Sure would be nice if you wouldn't keep making things up about what I've said!

Fred, the "rules" I'm talking about once the gases hit the down pipe are the mathematics of hot gas flow through the piping (blame my engineering background -- it's just the way I think). Hot gases flow in the same fashion from down pipe on regardless of being turbo or N/A sourced. I don't need you or your link to inform me of back pressure -- and that has nothing to do with anything I've been talking about (except the one caution I mentioned regarding ratcheting up the pipe diameter). And I'm not saying the way an automotive designer would choose exhaust piping for Turbo application is identical to that for N/A application. What I'm saying is simply that the pipe shown works!

You don't seem to comprehend that I'm not describing a theoretical comparison, but physical reality. Even if that estimated 300HP is only 250HP, it doesn't make any difference! My stock xB2 with CAI and AP pulley accelerates comfortably quicker than my stock '90 GSX with a dead turbo (no longer stock today, of course). You can say "False" all you like, but it doesn't repeal reality! The behavior of my '90 GSX with a collection of mods that are understood to achieve roughly 300HP together with the above pictured exhaust beats the pants of my xB2, and is definitely quicker than in stock form -- I was the owner and driver both before and after those mods and I am also the driver of my xB2. So, it's clearly demonstrated the pictured exhaust including several feet of 2" piping flows well enough to support that performance (be it 250HP or 300 or whatever). If you're saying the magic difference in the nature of N/A and turbo exhaust that results in turbo needing less exhaust flow than N/A for a given level of performance is pipe congestion, then fine, but that condition is both noticeable and atypical. So, it appears to me still that putting cost and trouble into a larger than 1.8" at the "scuba" exit for an N/A car is a dubious choice.

PS. I never claimed anything to be ideal, I merely pointed put some physical realities and drew reasonable conclusions about the value of replacing the 1.8" pipe.

 

So, clearly Toyota isn't expert since they use at least three different sized pipes in the xB2? Your experts don't concern themselves with the continually changing gas volume due to temperature drop -- their primary goal is to sell pipe!

BTW -- 2.25" is the first half of the OE "S"-pipe. Allowing for temp drop of the gases, looks to me like Toyota probably got it right.

 

Okay Trevor, I'll try one last time to explain this in a way that you might understand.

Just because your 2.0L turbocharged Eclipse can produce 250-300bhp with a very restrictive 2" exhaust does not in any way mean that 2" exhaust is optimal or even capable of permitting 200bhp on a 2.4L N/A 2AZ, much less 300bhp. There is no direct correlation between the two scenerios. It's as apples to oranges as you can get.

Were you to replace that 2" exhaust on your Eclipse with 2.5" you would acheive an instant increase in both hp and tq greater than the total hp/tq gains acheived by all the mods you've made to your XB.

BTW, you may want to check the exhaust sizing info I added to one of my previous posts while you were composing this reply.

 

If you truly believe that and further believe that Toyota designed the optimal exhaust system for maximum hp and tq from our 2AZ engine, you're beyond any help that I can offer. Have a nice day!


I was going to let this slide but... You've claimed many times over to be able to "feel" performance improvements from mods that are well known to add no more than 2-3whp at best. You are certainly the only man I know who can "feel" hp and tq gains from partially thermal wrapping a header and s-pipe! Then there's your wood block throttle body spacer and didn't you also claim to "feel" a big improvement from a lightweight crank pulley?




Actually Sp2 has a custom 2.5" exhaust from the turbo to the 2.5" axle-back making 298whp @10psi. Maybe you were thinking of Clean XB? He's running the Descendant kit with stock exhaust and a TRD axle-back.




...

 

I acknowledge you yourself are beyond any help, no wonder you have a few divorces to your credit (debit?). So, you're saying that exhaust volume doesn't reduce with reduction in exhaust temperature? You're the one that just specified 2.25"! Why are you criticizing Toyota's use of that very number? Looks to me like they are being responsible! You appear to be trying to just cover yourself!

Going to let it slide? Mostly what I've seen from you for a series of posts is a street fighter onslaught as opposed to a well reasoned discussion. I was careful to invite others to check out the possibility of the spacer and one did and agreed with my findings without even any prompting from me. So you choose to call us both idiots -- up to you I guess. As I've said before, high rpm HP means little to me (including with my Eclipse), what I care about is street performance and torque is readily apparent on the street. You question the value of wrapping? Hate to say this but there are plenty out there who'll disagree with you. You consider my partial wrap approach to be unintelligible? That's your problem, not mine.

Regarding the AP pulley, yes, it provided an improvement (I don't recall my saying "big"), but I gather your undersized pulley only provides an advantage because it's undersized? The reduced weight contributes nothing you'd personally notice? Whatever, yes, I found the AP pulley to make a definite difference when accelerating from a red light through an intersection.

 

Thing is, it's you that declares the 2" post cat pipe to be "very restrictive". Frankly, I don't detect it and the improvement in acceleration over stock is easily recognizable at the wheel. However, from the very beginning oif my stepping into this topic, my entire point has been that my Eclipse GSX with the pictured exhaust can run circles around the N/A xB2, and that's with CAI and pulley upgrades. So, ultimately what you're saying is I'm hopelessly incompetent? Fine, perhaps your audience will agree, or perhaps you'll conclude they're hopelessly incompetent as well. Maybe they'll simply accept whatever you say as gospel, the great Fred! The one thing that's especially clear to me is I completely misunderstood you and mistakenly promoted you to others. You have provided some good input to this forum (as per my sig), but your ego is a huge liability!

 

Trevor, despite spending a considerable amount of time on this forum, my time is still too valuable to me to waste it engaged in a long drawn out point by point flame fest with you. My only problems with you personally are that you pretend to know more than you do and refuse to admit even the possibility that you could be wrong about anything.

I may well be among the most arrogant and egotistical members of this forum but at least I can take some small comfort from knowing that I'm not the most arrogant, egotistical, know-it-all at SL.

Regards,

Fred

/threadjack and my apologies to the OP and other thread participants.

 

Come on now man that is totally uncalled for. We can have a civilized disagreement without any of that garbage. This is sounding like Honda-tech...

 

You call what I've had to put up with civil? No problem, I'm done banging my head against this wall that takes great pleasure in misrepresenting what I've said and ignoring the points of my own argument. It's not as if I have anything personally to gain by whatever choices people make. Do what you all will. As Fred says, I'm welcome to make my own choices and I'll continue to do that ! In the meantime, I'm done here.

 

Oh yeah. I forgot about that. Any which way... I'll have to work some more and buy some parts. See what happens. Good thing is, I have a couple local dynos I go to. The one is actually really good people.

 

Modern garage still in business in SLC?