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Many of you probably already saw this on Facebook, but for those lucky ones who haven't gotten sucked into that hell, here are the results of my latest 2GR improvement attempts.

The full writeup has been added to my blog here: https://wilhelmraceworks.com/blog/2gr-power-gains#Update 12-6-2019

The short version is that porting the lower intake runners and removing the protrusion around the injector is worth about 5hp: (Ignore the differences below 4800, those are unrelated to the manifold porting).


The X-pipe exhaust gives you a boat load of mid range torque and a little more top end:


And somehow adding a catalytic converter and muffler is worth 5hp on my setup compared to an open Y-pipe OR compared to the X-pipe muffler.

And yes, I broke the 300whp mark with the stock(ish) ECU and without cams or other engine internal modifications.
 

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Awesome work! It's nice to see people still looking to find ways to squeeze power out of these engines that are also willing to share that information.

In regards to the flywheel horsepower, since this type of transmission and orientation (transverse RWD) consistently generates a drivetrain loss of +-12% (referring to Lotus Elise/Exige/Evora, and Porsche Cayman/911) I believe the flywheel horsepower would be closer to 342hp.

Anyway, thanks for sharing this and all of the other great technical discoveries that you have made over the years. They have contributed greatly to my decision to acquire my MR2 in route to a future 2GR swap.

Lastly, do you have photos of your x-pipe setup? Those would be great to see.
 

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Thanks!

Here's a couple pictures of my current x-pipe setup, although I am now re-designing it to hopefully be a bit quieter, and hopefully pick up those 5hp that the y-pipe made vs the x-pipe. I think I will end up making my own X-pipe instead of using the muffler with the built in X, and running a pair of cats and a pair of separate mufflers. It won't be light weight any more, but if it ticks all of the other boxes that's a compromise I'm willing to make.
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As far as the WHP vs crank hp thing goes, I have always based it on old dyno reports that a stock good condition MR2 Turbo makes about 165whp on a DynoJet, and assuming the 200hp rating is correct that works out to about 17% loss. But at the end of the day a crank HP number is just for bragging rights, and not all that important.
 

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Add cat and muffler and get more power.

Add silencer inserts and get no difference (you tested this on dyno and I confirmed).

x-pipe really not gaining anything appreciable.

What is going on with this crazy engine? Ha ha. Ha ha ha ha.

On a lark I googled "resonance amplification of exhaust flow" and this is the top result.


This provides some interesting insights.

Big question is why is x-pipe somewhat disappointing compared to the y-pipe and the answer is that the location of the crossover (distance from exhaust ports) may play a part in the flow enhancement. Probably why the y-pipe seems to perform favorably is the location of the merge is enhancing scavenging. While the location of the x-pipe merge is not optimal. Could be that a small change one way or the other in the distance from the crossover to the ports could make a big difference. Or not. Ha ha. Ha ha ha ha.

Google "optimal location of x-pipe crossover" and the top result is this:

“The placement of X- or H-pipe is most effective when positioned somewhere around 8 to 18 inches from the end of the collectors,”
To be taken with this:

 

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Discussion Starter #5
x-pipe really not gaining anything appreciable.
Huh? The x-pipe gained a huge amount of mid-range torque. 20ft-lb at 3300rpm and 16ft-lb at 4000rpm (compared to the open y-pipe). I would say that's an appreciable gain! Plus 8hp at 7150rpm. I think it's well worth trying to optimize the x-pipe to figure out why all of a sudden my y-pipe with cat is beating it in the 5k-7k range.

As far as the position of the x-pipe, not much I can do about that, there are only so many places to put it. If I built a custom cross member I could move it a little closer by running the exhaust under the cross member, and maybe some day I will do that, but for now I'm also thinking in terms of making this whole mess potentially marketable, and the last thing I want to do is require a custom cross member for it to fit.

Here's my best guess so far as to why it's making more power with the catalytic converter:
The cat adds a bunch of heat. When a gas heats up it expands, so the exhaust increases in volume as it passes through the cat. Higher volume = higher flow velocity, AKA, the flow accelerates as it passes through the cat. This draws a vacuum on the piping up stream of the cat, creating a scavenging effect.

I'll admit it seems a bit weak, but it's all I have. All I know for sure is it made 295whp for 5 consecutive pulls, I attached the muffler section, and on the very next pull it made 300, then 301, then 300 again.

We will see, if I gain 5hp with my next iteration X-pipe (current concept model below), then I will believe it. It won't be light weight any more, but if it makes more power, and is quieter, I will give up on my lightweight exhaust quest.
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Alex,
In regards to the horsepower numbers I must say that it seems that the E153 is very inefficient because even the EA60 sees just a 12% loss. But like you said, it's quite irrelevant, all that matters is the power that gets to the wheels.

I think the x-pipe is showing great midrange gains because it has a larger flow capacity. Here is a link to an interesting chart that shows at what point various pipe diameters start to become a power restrictor. As you can see from the chart, dual 2.25 piping will outflow a single 3 inch pipe.

In regards to a lightweight, high horsepower capable system I've been fantasizing the combination of stepped (gouky-like) headers that go from 1 7/8 to 2 inch primaries with a 2.5 inch merge collector. This would then connect to a 2.5 inch y-pipe that merges into a 3.5 inch straight through or catted pipe that connects to this Vibrant muffler. If we use the numbers on that pipe restriction chart above as a general reference, we can see that this setup won't begin to become a restriction until power levels get up to about 468. It flows just as well as a true dual 2.5 inch setup so it will also save some weight. Of course, this power level is way beyond what this engine is capable of achieving with current off-the-shelf aftermarket parts but if the 3.5 inch pipe can fit with the stock crossmember it might be worth some consideration.
 

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Discussion Starter #8
Yes, dual 2.25" pipes has slightly more cross sectional area, but it also has a lot more surface area, and will probably have more of the total cross section taken up by boundary layer. Regardless, I highly doubt that flow area is the issue here. Especially consider that the X-pipe makes it's big gains at about 3500rpm where mass flow rate is only about 100g/s, compared to 7k rpm where it's more than 2x that. If flow area where the issue I would expect to see a top end restriction. And remember that my current power record is still with the y-pipe.

No, I really think there is some negative interaction caused by merging the streams in the Y-pipe that causes the big torque loss. And if you look at it, it really is a torque LOSS with the y-pipe, not a gain with the x-pipe. Looking at the shape of the curves, the torque curve with the x-pipe is pretty much a smooth arc from 2k to 7k rpm. Like that is the "natural" torque curve. Maybe longer secondary pipes before the merge would help eliminate that dip? Could run dual pipes up over the cross member and put the merge there maybe. As is the headers are about 18" long, and my y-pipe is 18.5" from the header flange to the merge. Putting the merge just behind the cross member would make the secondary pipes about twice that length (my dual system worked out to about 37.5" from the header to the v-band flanges at the muffler inlet).
 

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it really is a torque LOSS with the y-pipe, not a gain with the x-pipe.
This is an interesting way of looking at it. Maybe beyond a certain RPM the main restriction shifts up from the x-pipe/y-pipe to the headers and this is why the two perform roughly equally past this point. MWR sells long-tube headers and they claim a "massive" IIRC this is the word they used improvement in HP.

PS. I've checked the word they use is "huge" not "massive."
 

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Discussion Starter #10
Interesting, although I think now perhaps not correct. I think it is actually a very interesting example of the power of exhaust scavenging. If you remember, about a year ago I said that I tested an "open header" setup at the dyno. Just a pair of ~18" long pipes (a 90 and some straight pipe), 2.5" diameter, with o2 sensor bungs in them. I don't think I ever posted the dyno of that, but here it is. Green was the y-pipe with Berk muffler, blue is the open header setup. Slight gain in that mid range, and a tiny bit up top as well, but nothing even close to what the x-pipe gained.

68663
 

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Interesting, although I think now perhaps not correct. I think it is actually a very interesting example of the power of exhaust scavenging. If you remember, about a year ago I said that I tested an "open header" setup at the dyno. Just a pair of ~18" long pipes (a 90 and some straight pipe), 2.5" diameter, with o2 sensor bungs in them. I don't think I ever posted the dyno of that, but here it is. Green was the y-pipe with Berk muffler, blue is the open header setup. Slight gain in that mid range, and a tiny bit up top as well, but nothing even close to what the x-pipe gained.

View attachment 68663
just to add to this I have what I consider a very equal length Y pipe and bearing in mind my 2gr is supercharged my torque curve is pretty linear
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Discussion Starter #14
Interesting. The supercharger may well take that dip out of it, but it's also a bit of a different y-pipe design. That's certainly a nice compact merge. It looks like it might not flow as well, but maybe it's actually better, since it doesn't have as much of a "dumping into a large space" effect.
 

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Interesting. The supercharger may well take that dip out of it, but it's also a bit of a different y-pipe design. That's certainly a nice compact merge. It looks like it might not flow as well, but maybe it's actually better, since it doesn't have as much of a "dumping into a large space" effect.
This was my first ever attempt at welding so wasn’t sure what to expect, I was also thinking of doing an x over but decided there wasn’t enough space to do it well
 

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The DDPR y-pipe also merges into a 2.5-inch section that goes through a conical expansion to 3-inch above the cross-member right before the exhaust. So if you could get your hands on one for testing, it could shed some light on the high-velocity theory. From what I understood, this was Marc's original design.

 

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The DDPR y-pipe also merges into a 2.5-inch section that goes through a conical expansion to 3-inch above the cross-member right before the exhaust. So if you could get your hands on one for testing, it could shed some light on the high-velocity theory. From what I understood, this was Marc's original design.
True, although Dave Staba of DDPR is perhaps the leading champion of X-pipes over Y-pipes. Of course, he hasn't built an x-pipe for the MKII, but his general statements about the differences are that you see that big torque dip with the y-pipe. But, I'm not sure if his test experience is with a y-pipe similar to the one they build for the MKII or not.
 

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Hm yah well some people just like to push whatever makes them the most money. Nothing wrong with that. Last time I checked we are still in a capitalist system.
 

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Huh? The x-pipe gained a huge amount of mid-range torque. 20ft-lb at 3300rpm and 16ft-lb at 4000rpm (compared to the open y-pipe). I would say that's an appreciable gain! Plus 8hp at 7150rpm. I think it's well worth trying to optimize the x-pipe to figure out why all of a sudden my y-pipe with cat is beating it in the 5k-7k range.

As far as the position of the x-pipe, not much I can do about that, there are only so many places to put it. If I built a custom cross member I could move it a little closer by running the exhaust under the cross member, and maybe some day I will do that, but for now I'm also thinking in terms of making this whole mess potentially marketable, and the last thing I want to do is require a custom cross member for it to fit.

Here's my best guess so far as to why it's making more power with the catalytic converter:
The cat adds a bunch of heat. When a gas heats up it expands, so the exhaust increases in volume as it passes through the cat. Higher volume = higher flow velocity, AKA, the flow accelerates as it passes through the cat. This draws a vacuum on the piping up stream of the cat, creating a scavenging effect.

I'll admit it seems a bit weak, but it's all I have. All I know for sure is it made 295whp for 5 consecutive pulls, I attached the muffler section, and on the very next pull it made 300, then 301, then 300 again.

We will see, if I gain 5hp with my next iteration X-pipe (current concept model below), then I will believe it. It won't be light weight any more, but if it makes more power, and is quieter, I will give up on my lightweight exhaust quest.
View attachment 68652
Two cats plus 2 mufflers ought to quiet the beast down. Are you going with Vibrant or Magnaflow?
 

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Two cats plus 2 mufflers ought to quiet the beast down. Are you going with Vibrant or Magnaflow?
I considered Vibrant, but ended up sticking with Borla for now. The dimensions of the muffler should make it package just a tiny bit easier. But if it does end up still too loud or two drony I think I can fit a pair of Vibrants Ultra Quiet resonators in between the cats and the mufflers. Or at minimum a pair of "bottle style" resonators.

Started welding pipe today for the new design!
 
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