How much difference is there going to be between a full 3" catless tbe system and a 3" catless dp + 3" midpipe + 60mm (2.36") axle back on a stage 2 EJ25? searching has yielded very mixed results
Which axleback? The diameter of the pipe doesn't automatically dictate how well it'll flow. The chamber type will have a large impact on it, as well as other supporting mods. What TBE?
right now i have a JIC catback and an invidia dp. I'm considering switching to a turbo xs 3" midpipe with a 60mm axleback (brand is a secret right now :biggrin: but it is a straight through design)
If it's a straight through, I can't imagine it'd be that much of a hindrance, if at all...One theory is that an exhaust that necks down near the end helps keep velocity up, especially since as the air cools it's losing volume and you're already several feet behind the turbo. Like I said, that's one theory. It sounds like you're around a stage 2ish car, a 2.5 in axleback would probably not have much of an effect if it is a straight through.
yeah it's a "stage 2" STi. I won't be doing any crazy power mods for a while - this season is all about suspension. i could always add a cutout if needed
Very true. I would guess that until you are over that 4-450whp mark, a 2.5 axle back will not restrict you. After all, it is just a 2.5l 4 cylinder and even with the boost you still really don't flow the air needed for a full 3" exhaust. As long as you have a good flowing muffler that is all that is needed. Russ
ok what do you guys think - should i get this axle back? it's a L'aunsort p555 right now i have a JIC 505sus
Didn't you just say you were at Stage 2 and NOT doing any crazy power mods, and that this year was all about suspension? :roll: I think you just want the bling. Ask Soggy for some pointers... :biggrin:
yeah and? is going from a 3" exhaust to a 2.5" a power mod? no not really - that's why i posted this question. if i was doing a bigger turbo I would for sure stick with the 3" reading and comprehension > you
yea i'm marginally indecisive over this. I'll probably stick with the the JIC because I don't want to get this and then a midpipe which means added expense that could be better used on other stuff
You said this "season" is all about suspension, and then you ask for us to vote on how pretty a rectangular exhaust looks. I was pointing out the irony as a joke. I think your sense of humor < zero. I doubt anybody here has a PhD in aerodynamics, thermodynamics, fluids, etc. You can't do a flow calculation even though you know the difference in diameter of the different pipes because you don't know the exact cfm of the turbo on your car at peak horsepower. Any nobody knows the flow rates of the different mufflers. So we're all just guessing. But I am a scientific person. So to answer the question you posted at the top of the thread, I will chip in $10 towards a second set of pulls on a dyno day for you to measure 3" versus 2.36" exhausts.
hey sorry about that, i'm just very crabby because i'm working on all that stuff you just mentioned - particularily heat transfer and fluid flow. if i had more time i probably could run some fairly accurate simulations on ANSYS but I would need some egt and flow rate data, also convective coefficients for the exhaust and air
......... and they all said...... View attachment 2868 View attachment 2869 View attachment 2870 View attachment 2871 ......huh?!!?:eek3:
Easily understood. I bet you even had a Thursday morning meeting that was a complete waste of time and that prevented you from doing real work.
yea that was called philosophy :laugh: but then i had heat transfer lab which is pretty awesome actually
A muffler I picked up on ebay for my original exhaust plan had a three inch inlet and necked down to a 2.5. I thought it was pretty jank but for $45 what do you expect. So I asked one of my profs who was the fluids geek and he said the perforations in a straight through muffler are more of a restriction than the change in diameter, granted the change is smooth. food for thought
/lolz. i dont think so, i think kevin finally might have time :laugh: (now that i said this, he prolly wont :emo: )
And without those perforations, it's a pipe and not a muffler. So, what's more restricting? A baffled muffler or a straight through muffler? And now we're back to the beginning of the thread...
That's why I'd offer $10 to see the axleback swapped out in the parking lot on dyno day with a new pipe given three pulls. The layman's way of measuring... "Boy, them there engineers sure do make fine tools." :laugh:
that's why i posted hoping someone had real world results. figuring out an accurate simulation would take too much time
Well, I know back in the day, Riftswrx did some testing with his car. 02 wrx, 4eat, built 2.5 (might have been the 2.2) and he was running right around the 380 mark (so about 420 in a 5/6 speed) at the wheels. Between his txs magnaflow (2.5 inch pipe) and his stock muffler was about 20-25 whp. Like I said before, until you are up around the 400whp mark, I don't think you will notice a difference between a 2.5 and a 3". You want to keep the air volecity high and with a exhaust that tapers a bit at the end will help that out. Russ
I didn't say you shouldn't have the perforations. All I said is the they have more of an effect than the neck down in diameter, which is minimal. Please don't put words into my mouth :biggthumpup: Compressible fluids are a real biatch to simulate.
I've done it before. But even with FEA software it takes like 10-15min to iterate. And that's with just a 2D model of a strait pipe and laminar flow. It's fun and academic to model fluid flow, but anyone running a txs stealth-back with their stock muffler want to chime in on what their numbers are at stage 2? Can you even run stage 2? I'm thinking I want to go that route. Although zak also gave me a ride in his cobb tbe stage 2, and that was quite sex as well.
ANSYS is pretty good for modeling most anything lol. the main issue is coming up with all the constants and rates to input
Bingo! You telling me you want to crawl all over the place trying to inaccurately measure your entire exhaust geometry. Draw it up in cad, incorrectly guess at your boundary conditions, and incorrectly guess your fluid condions. To just in the end not even have enough nodes to even model it 2D. And then in the end, your simplified, not enough node havin' model ends up taking 4 hours to iterate. No thanks! Dyno pulls, swap, repeat. Even though I wanted to do that anyway when I was in school, you know, for fun. :roll:
Well here's a little test I did right after I got my '06. Stock everything with the exception of the addition of a Prodrive axelback.
Yeah. I just looked at the logs from these two pulls, and they were taken about 3 hours apart. Intake temps were about 2* cooler on the 2nd pull since it was later in the evening.
I'd like to know how he got such a perfect overlay on his graphs. I never get the same shape on mine. But to a previous question, I am running a TXS Stealthback with the stock muffler and a "Stage II" tune on my 2.0 Saabaru. Actually, I don't know what stage Tom would call it, but it's pretty strong. My MAF readings are 238. Consider that way back in the day with a Cobb Stage 2 map, we logged 188. But maybe I should order a Prodrive and then compare MAF readings. I still want to see 20 psi on the stock turbo...
I make all my road dyno pulls on the exact same stretch of road in the exact same spot. And with my current stage 1 tune, my road plots are showing ~260wtq. w00t.
There's too much traffic on the roads around here for me to stick with one spot. The one place I used to be able to get a good pull has been jammed with traffic the last three times.
