Project Evo X , Testing The AMS Big Mouth Downpipe!

Project Evo X , Testing The AMS "Widemouth" Downpipe!

By Mike Kojima


When we last left off with Project Evo X we had tested the K&N Tsunami Intake and Greddy RS exhaust with good results.  Continuing with our testing of easy bolt on engine parts, the next step in uncorking our car was to go further upstream in the exhaust with an AMS Wide Mouth downpipe and test pipe.

Since we opened up the back part of our exhaust with Greddy’s 85mm in diameter RS catback exhaust system, it was natural to next look for a better downpipe.  After evaluating what was on the market, we decided to use the AMS Big Mouth because of several unique design features which we felt made it stand out above the rest.


Project Evo X , Testing The AMS Big Mouth Downpipe!
The AMS Widemouth downpipe is truly a work of art.  AMS used expensive investment casting tooling to build a thin wall cast stainless downpipe/turbine outlet to produce the freest flowing least restrictive downpipe on the market.  The downpipe is compatible with the stock heat shields and is actually better than OEM quality!


The turbine outlet on the stock Evo X turbo is a cast piece with a rather complex geometry.  It hugs the back of the turbo pretty tightly and has a small diameter outlet, necking down to around 2.25” before it enters the actual downpipe.  The discharge from the turbo’s internal wastegate is introduced right at the point where the exhaust flow exits the turbine and the entire gas flow is then forced to make a tight turn all in a small area.


Project Evo X , Testing The AMS Big Mouth Downpipe!
You can see how the stock turbine outlet makes a very sharp turn right at the turbine and wastegate discharge.  The AMS part uses smooth flowing bends with a much larger radius in this area.  The area where the turbine and wastegate flow comes together is very critical for overall flow.  Dumping all of this into a restrictive convoluted part is not the greatest for power.


This creates a lot of turbulence and if the exhaust gas volume is increased by running other power increasing mods, this juncture is an area where a lot of backpressure will be created.  Due to the space constraints, it is real hard to design a low backpressure fabricated part to fit in the area allowed that is actually better than stock.


Project Evo X , Testing The AMS Big Mouth Downpipe!
Looking down the throats of the stock part on the left and the AMS Widemouth on the right, it becomes painfully obvious which part is going to flow better.  You can see the complex geometry of the downpipe's inlet and how a casting is going to be able to make the most of the limited space here to make a good flowing part.


AMS came up with a solution to reduce backpressure and improve flow in this tight spot by designing the Widemouth downpipe as a one piece investment casting.  By making the turbine outlet section a casting, AMS was able to maximize what they could do in the area using three dimensions to make a higher volume, straighter path from the turbine housing to the downpipe itself.


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Monday, January 16, 2012 8:39 PM
I really hope this project continues with just adding one modification at a time followed with dyno results.
Monday, January 16, 2012 9:50 PM
Is there much of a diameter difference going from the test pipe to the Greddy cat-back? I'm curious about the tapering down at the cat most Japanese exhausts have.
Monday, January 16, 2012 11:04 PM
That's awesome. AMS does some serious R&D, and it shows.
With the upcoming new bolt ons, I'm sure you guys can break the 400 mark easily.
Keep it up!
Tuesday, January 17, 2012 4:19 AM
Nice results! Interested to see if you can make the magic 400whp.

Also I know I am nit picking but the X does not use the same compressor wheel as the IX, nor the same turbine wheel. While they may be mirror images of each other, they are not the "same".

Mike Kojima
Mike Kojimalink
Tuesday, January 17, 2012 6:53 AM
The wheels are the same design but flipped for conventional rotation. The turbine is the same size and contour and the compressor is smaller.
Dusty Duster
Dusty Dusterlink
Tuesday, January 17, 2012 7:04 AM
I'm surprised how much tuning is required even when something relatively small is changed on this motor. Is the stock EMS simply not very adaptable?
Tuesday, January 17, 2012 7:41 AM
@Dusty, it's not an adaptability issue with the hardware. It's the stock calibration which I believe is optimized for 93 octane, not the 91 octane we get in Cali.

On my 2005 Evo, I'd get 8-12 counts of knock completely stock and I had to take about 6 degrees of timing out on the top end. Dump in 93 octane, stock calibration, no knock. The OEMs also have to deal with emissions and fuel economy, so there are some 'interesting' tactics they use in the maps. I think more often then not, the maps are optimized for very specific emissions and fuel economy tests which are very rigid and standardized. That way, the OEMs get the best MPG and emissions numbers to put on the window sticker and meet CAFE regulations. It may cause some interestinng peaks and valleys in maps though.
Tuesday, January 17, 2012 7:44 AM
Oh yeah, the stock turbine outlet section has the super tight bend in it because of the right hand drive version of the car; I believe it's the steering rod that goes right by it. So I'm pretty sure the AMS, and pretty much every other downpipe designed in the US, won't work on RHD cars.
Tuesday, January 17, 2012 11:24 AM
Mike, are you considering going to an E85 blend in the future? A mere 2.5 gallons of E85 per tank has allowed my MS3 to run a full point leaner with about 9-10 more degrees of timing with absolutely no knock.
Mike Kojima
Mike Kojimalink
Tuesday, January 17, 2012 11:33 AM
No because in our area E85 isn't a practical fuel. There are only a handful of places that sell it and how do you control a mix when you are presumably blending it in your tank.

We also don't want the long term fuel system implications on a car that is driven every day. We know E85 is a real good turbo fuel but we are not out to break power records for bragging rights, just build a sweet no hassles all around car.
Tuesday, January 17, 2012 11:37 AM
Great article, but there's one thing I disagree about. A fabricated piece can and has been made to perform as well as AMS's cast piece. MAP and ETS both have fabricated downpipes that perform just as well as AMS's cast unit, one costs $100 less and the other $40 more. But I do like the other advantages that cast has over the fab'd downpipes... the only downside is that you can't get an open dump on cast downpipe.
Tuesday, January 17, 2012 11:42 AM
Dusty, I believe spdracer is right. I've added an intercooler and intake since my initial tune and I still have 0 knock. I've logged regular driving, driving like an asshole, and 3rd and 4th gear pulls. still 0 knock on washingtons 92 octane
Mike Kojima
Mike Kojimalink
Tuesday, January 17, 2012 11:52 AM
warm milk, it is would be really hard to fab a piece to be as good as the AMS in limited space but I agree with you that it is possible within the power potential of bolt in internal wastegate stuff. Casting gives total freedom of shape in this sort of space. Maybe I should have said better flowing instead of performing. In fact I will to mirror your suggestions and edit this.

We are going to switch to a GT3071 direct bolt in replacement turbo so we should be pushing the flow through it soon. I agree that a wastegate dump is better for power but it sounds like ass for a street car!

I had an Evo and a Turbo Sentra with dump and could not stand it.
Tuesday, January 17, 2012 12:02 PM
Both still perform pretty much the same on FPBlack turbo's also. In theory the AMS should flow better, but all the results I've seen there isn't much difference to them as far as making power goes. Not that I'm arguing against the AMS, I love the fact that its cast and it will probably be the downpipe I go with. The biggest advantage I see the AMS downpipe having is not giving off heat like a fabbed piece does...

Are you hard set on the GT3071? From the results I've seen it gives up alot of spool for not all that much power... If you're open to suggestions, look at MAPerformance's EF series turbo's.
Mike Kojima
Mike Kojimalink
Tuesday, January 17, 2012 12:17 PM
How well does the FP black work? Do you like it? We have the turbo so we are going to test it. It seems really responsive on other engines I have tried it on like a QR25 and a 4G63, like almost no lag responsive.

If the 4B11 is like a 4G63, a little slower response out of the turbo might be good, I am having trouble keeping our 4G63 out of surge.
Tuesday, January 17, 2012 1:08 PM
Mike, you have a GTX3071 with the 0.73 A/R turbine housing. Another advantage of the cast piece is durability over fabricated and welded pieces. Welding creates a Heat Affected Zone (HAZ) which has changes in material composition along with induced stress and possible cracks.

I'm not a fan of modified stock turbos as there are compromises involved as the design of the end housings are optimized for the original wheels. Start trying to cram bigger wheels and bearings where they aren't designed to go, and you end up with performance/durability compromises. I'm also weary of all compressor wheels that are non-engineered by one of the main turbo manufacturers. Read the MotoIQ article, An Inside Look at the New Garrett GTX Turbochargers as to why.
Tuesday, January 17, 2012 2:19 PM
definitely my favourite o2 housing/downpipe for the evo x. Although it sure is a pain in the ass to get the heatshields off the stock one, and things get even worse if one of the o2 housing to turbo bolts breaks.
Tuesday, January 17, 2012 4:02 PM
I may have missed it somewhere...but where previous dyno runs also done with a test pipe? Or was just this test done without a cat??
Dusty Duster
Dusty Dusterlink
Tuesday, January 17, 2012 4:13 PM
I guess I've been spoiled by access to high-quality 93-octane E10...
Tuesday, January 17, 2012 4:37 PM
We really are spoiled # Dusty Duster!

Here in the Midwest I can get every high-performance fuel imaginable. 94 octane ethanol-free street-legal gasoline, E85, premium diesel and even VP fuels 110 octane race gas straight from the pump! You can get it all from within 10 miles of my house.

Sometimes its great to be a redneck!
Tuesday, January 17, 2012 9:51 PM
I'm not sure this test should be "Certified MotoIQ Legit". From what I read, the baseline was done with the cats in place. Then the new downpipe was installed and ran on the dyno with the cats removed with the inclusion of the cat-less test pipe. Since the downpipe wasn't tested with any cats in place, there is no way to determine if the gains are from the test pipe or if the gains are from the downpipe..or both as a pair.

It seems as though a step was skipped. You are proclaiming the downpipe to be "legit" when it is entirely possible that the test pipe could have more to do with the gains.
Mike Kojima
Mike Kojimalink
Tuesday, January 17, 2012 10:38 PM
I did the test I declare it legit.:) I am rushing to meet a deadline in testing the turbo and had a major setback where a death in the family delayed the start of our testing by two weeks. I didn't deem it important enough to test both individually as I think most people will run them together. Blame me for not being picky enough but its my call.
Thursday, January 19, 2012 12:00 AM
Interesting choice of upcoming turbo.
If you are going the Garrett 3071 route, have you considered the GTX otpion?
I agree, for 91 octane there are probably better options out there with considerably more area under the curve and much better spool and response.
Thursday, January 19, 2012 12:47 AM
Aside from durability of the cast piece, what do you think of the "wide mouth" design vs separating the IWG & not dumping it to atmosphere, but rather re-routing it into the DP it's self? It seems that there are a couple companies that who fabricate a "split" DP. I think this & pretty much all AMS (Chicago) products are amazingly well crafted & exceptionally designed.
Thursday, January 19, 2012 6:37 PM
Due to the particular design of the Evo X turbo, I'm not sure there's much advantage to the separated IWG flow. I say this because in general, you don't want the wastegate flow impeding the flow out of the turbine wheel. In the case of the Evo X turbo, the turbine outlet flow has a good 2"-3" of clear flow before dumping into the downpipe. The wastegate flow also has a cavity that it dumps into, separate from the turbine exit flow, before dumping into the downpipe. On a turbo where the wastegate flow dumps out right where the turbine wheel flow also exits, then a more separated flow would be more benefical.
Wes Dumalski
Wes Dumalskilink
Monday, January 23, 2012 1:46 PM
More people ripping off designs. This time a HORRIBLE rip off but none the less something to watch out for.


Hopefully AMS will chime in.
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