evo1

That's exactly right .... the truth is, it is basically overkill to run a 3" dp unless ...

1. You upgrade the stock o2 housing to 3" as well (check out Vishnu & AMS new 3" dp kit) which is more pricey.

2. Or you plan to make allot of power in the future ... such as 350 whp maybe. I've called HKS on this one and they do not recommend going 3" on the dp until 400 whp on the evo. Actually, they don't even supply a 3" dp/dump tube in their 3037 T kit ... which is capable of 500hp!


Chris in HB is right, there are guys with BIG power running the RMR; however, don't mislead by that statement. If you are planning to make BIG power in the future, then a 3" dp with 3" o2 housing upgrade is the way to go. But if you are like most of us, that are looking to make good power without gutting out the stock turbo or stock o2 housing, then the HKS 2.6" dp will most likely produce more torque at lower RPM's. Sure the 3" RMR won't completely hurt you at this stage in the game either, but you may lose a little low end power while picking up a tic or two on the top end -- that's the comprmose.

At any rate, the HKS dp is working out great for me ... and as some of the other guys mentioned .... it's a very high quality dp.

losdog47

I saw that mag too. I was reading and was kinda suprised too. They did lose power from that one mod but gained it back just like hotrod2448 said with the rest of the exhaust set up. From what I understand if your going from big to small you're gonna choke up your engine a whole lot making more back pressure. Some is needed but too much is murder. I think thats whats happening in that situation.

.....................
-----------------...................................
-----------------..................................
.....................

A lil bit overexagerated but good to see my point. Periods are the pipes, dashes show gases. The exhaust is gonna have a harder time running out since the size is smaller. Like bottleneck traffic. Going from 4 lanes to 2 everyones got to merge in slowing down all traffic. Hope this helps.

Eric Lyublinsky

iTrader: (5)

I don't see how you would pick up TQ from having a 2.6in downpipe over a 3in downpipe. Can you prove it?

Here is my thoughts on this. There is a TQ loss because the Turbo Effency is bumped up witch in turn would yeld to knock sensor activaty witch would cause timing to be pulled and TQ to be lost. Being able to control all of this even with the stock 02 housing there would be a increase of HP and TQ from a 3in over a 2.6. (Not a lot but it's there ).

Downpipes and any exhaust just increase the Turbo Effency the more flow would mean more power. 3in have more follow then 2.6in.

Both are qulity products. with the RMR you will lose your Lower tie bars. With the hks you will be able to retain them.

I would suggest what ever you do just don't forget to wrap the downpipe with header wrap. This will keep the temps down near your oil pan.

My Very best
Eric

DrMerl

I seem to remember that putting a short dump pipe on a turbo was the way to go...

The turbo makes so much backpressure on its own that who cares about what an exhaust will add....just dump the hot gas cleanly - adjust piping/mufflers to ears need.

It's a sewer pipe.

evo1

Eric Eric; we meet again.

I was NOT making a claim that smaller dp's make more power, but it seems to be common knowledge that with a larger dp, the power will kick in a bit later (in higher RPM's), opposed to a smaller dp .... whether it really is or not, it is commonly perceived as low end TQ loss. And once again I emphasize 'low end.' Hell it might not even produce a negative effect to overall power, but as far as low end power .... it (larger dp) just seems to reduce it .... or it at least feels like less low end TQ.

You should know this from being around WRX's so often. I drove a REX Sunday night that just happened to have a 4" diam (?) downpipe, and the turbo LITERALLY did not kick in until over 5500 rpm (no low end power at all), and he's runnning the stock turbo. FWIW, the guy is not happy with it but he's in the process of upgrading to larger turbo anyway (most likely HKS 3037T).

How is one to benefit from a 3" downpipe when the o2 housing is only 2" diam anayway?


English please? So what u are telling us is that .... a larger 3" dp increases flow, which increases turbo effeciency. Meanwhile, the ECU (because of increased turbo effeciency), pulls timing; therefore, low end torque is reduced.

However, with a 2.65" dp (HKS), turbo effeciency is not increased quite as much, so the ECU does not pull timing as much .... which in turn, does not cause "as much" low end TQ loss as with a bigger dp, right?

Okay, so all we have to do is buy a 3" dp, advance timing with an Xede or E-Manage, and whaala that be fix eh. Nice theory Eric (if I'm correct).... I like it. But why not just leave at this & make it simple common sense?..

1. 2.65" dp = turbo (power) kicking in a little sooner (lower RPMs), and good top end power.

2. 3" dp = turbo kicking in a tad later, but a tic or two 'more' on the top end

Eric Lyublinsky

iTrader: (5)

""You should know this from being around WRX's so often. I drove a REX Sunday night that just happened to have a 4" diam (?) downpipe, and the turbo LITERALLY did not kick in until over 5500 rpm (no low end power at all), and he's runnning the stock turbo. FWIW, the guy is not happy with it but he's in the process of upgrading to larger turbo anyway (most likely HKS 3037T).""

Let me clear my throat here.

Let's just start with the WRX you drove (TurboXS down pipe???) 4 to 3 to 2.5 is not ideal that’s why a loss of TQ. About the turbo not coming on until 5500 on a stock td04 13g, tough to believe unless his wastgate door is open and can't close all the way. I have seen this with Twin Dump downpipes that have a tongue divider that catches the wastgate door and keeps it slightly open. So anyway you drove an un-healthy WRX. You can email me and I can help out with fixing it.

Bottom line is about proper exhaust piping for the application that you want to run is very important. For one you this is not a NA (with out turbo). NA cars need to have a little back pressure for TQ out but. But a Turbo Charged car does not need any restriction behind the turbo. The Turbo it self creates enough back pressure.


My Best
Eric

Z1 Performance

iTrader: (185)

There are no 4 inch downpipes offered for the WRX...the only one that is close is the Turbo XS, which as Eric said, starts at 4 inches, and taper to 2.5 inches. It is a very well designed piece that works as good as it looks, as it cures the most common problems on a WRX and the smaller turbos (IHI based or the stock unit) - boost creep. By having a nice wide bell mouth, it controls the creep very well - we have used this downpipe time and time again with great results. So I agree, you probably drove an unhealthy car.

As for diameter, I agree that the exhaust can only flow as much as the smallest opening. However, the mere fact that the 02 housing is 2 inches has nothing to do with downpipe diamter - since the downpipe fits after the 02 housing, not before (hence, its not a restriction. I agree that a 3 inch is complete overkill for the standard Evo turbo, and that is what most people will be sticking with. If you got to the point where you stepped up to a 20G, 3037, 3040, etc, then the 3 inch would be the way to go without a doubt.

I would disagree with Eric though about the turbo car not needing backpressure - you are assuming that the stock turbo is so efficient that it creates all the backpressure it needs. Take your downpipe and exhaust off your Evo and drive it - it will not spool till very late in the rev range (I have tried it), as the stock turbo is so small, it needs a bit of a restriction to make it work. SAame thing on a Subaru as well....

You will not pick up torque with the smaller downpipe, but your torque curve, in theory, should peak earlier than it would with the same turbo, same boost, same car, same dyno, same day, as it would with the 3 inch one on. A 3 inch can flow more than 2.6 inch yes, but with a 2.5 inch is more than enough exhaust for 400 hp.....there is less of an actual need for the 3 inch, though as I said above, it will work just fine, at the slight expense of some spool time (how much I could not tell you - way too many variables).

The other thing to consider is build quality - the HKS is one of the nicest downpipes I have seen for any car, period.

evo1

Great review Adam!

You guys are prob right about me driving an unhealthy REX ... but I'm glad you (Adam) agree with me on 3" being overkill in some applications.

Eric;

I think u need to rethink your cooments there bud .... by going with your logic, why not just throw a 10" diam dp on the car. Bigger the better right.

Eric Lyublinsky

iTrader: (5)

Oh yes I agree with Adam that the HKS pipe is made well.

Bottom line the 2in exhaust housing is the biggest restriction.

Pruven has taken the full exhaust off and has not seen the turbo to spool slower. I'm not about to try it my self to confirm. But hey if you saw that first hand I can't say that your wrong just that another source did not find the same findings as you.

Eric

Eric Lyublinsky

iTrader: (5)

Yep Bigger is better! If I could fit one with out dragging on the road I would! I don't need to rethink what I have seen on the dyno time and time again.

Noize

iTrader: (24)

His car is sick, period. The only DPs with a 4" bellmouth I'm aware are the original TXS system, and some other companies iterations of it. If its taking 5500 to spool the 13B, either his car is fried, or there is a hole the size of China in his uppipe. I've seen several TXS-2 cars (even owned one before I got a vf30), and the car will hit 16psi/1.1 bar fully by 3000rpm.

As someone said before, the turbo itself is all the back pressure you'd ever need, and I'd personally prefer a full 3" stainless TBE for when I have the supporting mods to flow someday. I could care less about losing a little low end torque in a 2.6 to gain a bit up top in a 3". As closely as this car is geared, you're landing at 4500rpm MINIMUM on upshifts. The Tq curve on the full 3" systems is flatter (because it sacs a couple ponies down low and raises it on top). When you're racing in any form, you want to extract every bit of power you can as close to redline as possible.




Why do you want low end (2800-3500) torque? To pass in 5th gear at 55mph? Moreover, I hope anyone who shells out for a TBE will eventually get some kind of fuel management, then you can override the ECU's default commands to get it to do what you want.

You're gonna see your tiny "kick" in the bottom of first (the shortest most ineffective gear for acceleration at duration), and in the top of every gear, the 3" is gonna land right in its kick on the upshift, pulling cleanly on you 98% of the run.

3">2.65" for autox, drag racing, road racing, or even street racing. I'll gladly sacrifice 7wtq at 3000rpm for 3whp from 5000-redline!

Mojo Powered

Hi Eric, this is Memed, I'm a friend of Mohammad's. We had met at a dyno at BM Tranny last spring, I had my black GTI with me that day, not sure if you remember me.

Anyway, I just wanted to say a few things since I have some experience on downpipe choice myself from my car. First of all, I have to say that my K03 turbo is as tiny as a turbo can get, running at 1.3bar. You can hear it whistling from inside the cabin with windows up. So it is running at full efficiency if not slightly over. My downpipe choice was to go with 2.5inch over a 3inch because of overspooling problems with the 3inch. When you're running that much pressure on such a tiny turbo, the last you want to have is overspooling.

However, I think evo's turbo is a decent size turbo compared to k03s or even k04s. Yes, you guys are right about the possibilityof losing low end torque with a 3" but I think the spoolup is much more abrupt and quicker with much less backpressure. So yes, the boost is not phased in smoothly or as smooth as it would be w/ a 2.65". But it will definitely help you to reach full boost easier. So in my mind, it'll make up for that roughness with added flow at higher rpms.

On the other hand, there's also the theory I was discussing with that Russian guy at the dyno (sorry can't remember his name) about accelerating exhaust gas flow. That could theoretically be achieved by a decreasing diameter catback. Actually, that theory even proved itself when Mohammad put down slightly more power with his 4" to 3" downpipe to a 2.5" setup. I remember as a comparison you had a 3" full turboback with pullies and you put down slightly less that day.

As a summary, although I am not be an expert, I'm all for a bigger diameter exhaust considering that evo is not a smooth car to start with. It's running 19.5 psi stock so in my mind, it makes more sense to me to go all out and go 3". Especially, if you get a full 3" downpipe like Vishnu or AMS. Matching that with a 2.5" or 3" catback should yield even better results.

In my mind, Mohammad's 4-3-2.5 setup is definitely ideal. I wish we had such a solution for the evo. Wouldn't you think that'd be the best setup to have accelerated exhaust gas flow with the least back pressure. Remember that these are turbo engines, we don't need that much of back pressure on high revving (6K+ rpm) high boost cars.... NA engines are a totally different story.

Memed

evo1

To each his own. Keep in mind that most of us are driving on the street more than we are racing .... so your 'racer' comments are basically irrelevant for most

Sorry dude but I think I'll trust a firm like HKS that has the money to do the R&D to form a 'real' conclusion as to which application works best on the evo .... opposed to one man's personal heuristics at evo-m. And don't even try to come back with that HKS marketing hype because then I'll know that you haven't even seen the quality & workmanship of this HKS downpipe.

My friends car just may be sick .... but for driving on the STREET, I'll personally choose low end power with a balanced power curve throughout the rest of the RPM range over the same with no low end. You are clearly DOWNPLAYING the amount of low end power that is nonexistent. However, racing is a different thing alltogether ... and unless u bought your car for 50% or more track use, then I suggest you think more about street use.

Bottom line, no need to argue any further about 5-10 whp increasing mod. Upgrading the dp is clearly less hp gain then the muffler or cat so lets get over it.

Eric Lyublinsky

iTrader: (5)

Yes I do remeber you!! I hope you have bin well. The other Russian guy Alex Amelnekov. Say hello to Moe, I have not see him for a while.

Oh buy the way I had the TXS exhaust on my own car and switching the exhaust to a HKS/Heilux full 3in exhaust I made 12 more then the TXS system. Yes I had the cat delete pipe and the TQ built up much fast at lower with the HKS system. Also The TXS system was cat less.

My Best
Eric

Noize

iTrader: (24)

One man's hueristics? How about several companies' dyno proven R&D work on this motor (since it has been out in the states since late 1989 with a lot smaller OEM turbochargers)?

You're kind of sounding a bit brand loyal to HKS at this point. Look at the Vishnu Signature exhaust. I can say with complete confidence that its fit and finish is superior to the quality piece HKS puts out. Of course, you pay for that quality.

Materials aside, we are arguing over like 7wtq! This is barely noticable on the ole butt dyno. On top of that, the highest torque surplus for the 2.65 over 3.0 is at a lackluster 3000rpm (interstate speed limits have me higher than that cruising in 5th), so it translates to a measley 4whp at that 3000rpm. Do you not rev your car when accelerating briskly on the street?

When you say a balanced power curve, a 3" DP has a LOT MORE of a "balanced" curve than a 2.6". What could be more balanced than a curve that is almost completely flat? You drop a **hair** (look at the dyno runs- there is no exxageration there) of torque at low RPM with the 3" (7wtq is 4whp at 3000). And you pick up less wtq with the 3" at the top... But wait... a measley 3wtq at redline is now 4whp in that spot. (This is mathematical proof btw, not hueristics or a hypothesis developed from study) All you're doing is moving the powerband up slightly and making the car faster in standing acceleration. This is at stock+TBE ratings, too. Get closer to the 450whp you're quoting and you'll see the 3" pull away much more convinvingly on the dyno in the midrange-up top. Moreover, the 3" gives you a good amount of more room to grow modwise. I know I plan to keep this car for a long time, and although I won't be making 400+whp this year, I hope to be someday not too far away.

I'm not putting your DP choice down at all, but I in no way find it to be superior to the RMR 3" unit, especially at the cost. The HKS unit looks A LOT better, but the finish on the RMR is quality construction that will last for several years and who ever sees the downpipe anyway? In the long run, with just a TBE and management on an Evo, you will barely notice the power difference between 2.6 and 3", but ESPECIALLY at the low RPM with the 2.63 where the torque multiplier is so much less.

Your DP is fine and well built, but my car does see high redline often, and room to grow is important to me. For others that feel and drive like that, a 3" unit is the logical choice. For any that doubt this, I challenge you to find a dyno run of an RMR unit on a 400whp car and then swap the HKS part on and run them back to back. The difference will surprise you.