for the people who had a 2.25 and went to a 2.5 downpipe.... is there really any difference? i mean.... a quarter inch isnt all that much bigger, but could u notice the difference? boost go up at all? or just a little quicker spool up? just curious....



14.7 @ 93mph / 7psi 185hp/180tq

don't think of it as .25 more inches. it's more about the cross-sectional area that you're gaining.

2.25" gets you about 4 square inches in area.
2.5" gets you about 4.9 square inches.

that's almost a 25% increace in area. not bad for a 1/4 of an inch.

the thing that makes the most difference is that with the HRC downpipe, it's all fusterclucked to the OEM downpipe, which was designed with 140 BHP in mind. that OEM downpipe flows like poop. about a month and a half ago when i got my new 2.5" turbo-back setup i noticed a LOT of top end power. before it would just fall off after 5000 rpm's. then again, along with that ghetto downpipe i had the stock cat-back piping with a flowmaster muffler. it used to be an awful setup.

2016 WRX STi Limited (current)
2001 A4 1.8tqms (donated)
1991 GVR4 #1933 (sold)
old.dsmregistry.com/detail.php?carid=218 (dismantled)

Yea, here is a dyno graph of the difference between the HRC downpipe and a 2.5" that was done on my car at VT.

Matt
1995 Eclipse GS
2.0L, S16g Turbo, 8 Injectors, 26psi

1998 Eclipse GSX
2.3L Stroker, AEM EMS Converted to Speed Density, FP3065 Turbo, 35psi , and so on...

I dunno about the 2.5 pipes, but i went from the hrc 2.25 pipe into a 2.5 bend into a 3 inch pipe and cat into my apexi N1 and that made a whole freaking lot of difference.

See apexi has this theory they call "megaphone" you'll notice that, I think all their exhausts, start at a smaller diameter and get bigger. EG. the apexi N1 cat back for the gst starts at 3 inches then the middle section goes to about 3.1 inches and then last section is 3.3 inches into the muffler. This design greates a gas velocity drop which kind of creates a passive vaccum system like a scavenging effect. I have done calculations and given that the exhaust is in pulses say pulse 1 will have a scavenging effect on the next pulse therefore drawing it out to the muffler its basic thermodynamics.
When i made my downpipe i wanted to continue this theory all the way starting at the turbo. So my complete exhaust goes 2.25" at the output of the turbo, 2.5 inch from the HRC pipe under the oil pan into a 2.5 inch flex section, which is then connected to a 3 inch S-bend that bolts to a 3 inch hi flo cat into the 3 inch section of the N1 exhaust which goes to a 3.1 inch center section then finally into the 3.3 inch rear section into the muffler.
This totally made a difference in the power of the car. before my car would seem to drop off in power at the higher rpm's but now I can mash it and it will continue to pull HARD till redline. I hit the rev limiter alot now because I used to use the drop off in power as an indication to shift.
so, for the 180 bucks it cost me to make the downpipe i think it is totally worth it. I don't know about a 2.5 inch all the way, but i know the way i did it makes a world of difference

lates
james

Rest In Peace Heidi Doggy

hey matt - that 2.5 downpipe, was that a complete 2.5 pipe, or did u have the hrc pipe then 2.5 on that?



14.7 @ 93mph / 7psi 185hp/180tq

Matt- You gained from just the bigger DP almost 10whp and 13ft lb torque? :o That has got to be the best bang for the buck on a turbo car. Right?


http://www.cardomain.com/id/jasvbts2k2
"The ONLY Honda I'd mod would be ASIMO"

i believe thats the ert 2.5 vs. the hrc downpipe.

______________________________
Matt D.
'06 Evo IX SE
'98 RS-T 13.8 @ 106.1

so..... since the 2.5 did that, wouldnt a 3" be even better? or should i just shut up and buy motofools dp? haha



14.7 @ 93mph / 7psi 185hp/180tq

The downpipe that i had dynod was the ERT prototype. It is a full 2.5 inches back. It would be nearly impossible to get a 3" to work, but i suppose if you had lots of time and 3" pipe to spare, it may be possible. I don't think that having the hrc portion of the dp will make much of a difference since the turbine outlet is even smaller. It's the stock portion of the downpipe that really screws up the exhaust flow.

Matt
1995 Eclipse GS
2.0L, S16g Turbo, 8 Injectors, 26psi

1998 Eclipse GSX
2.3L Stroker, AEM EMS Converted to Speed Density, FP3065 Turbo, 35psi , and so on...

Yeah there really isn't room for a 3" bend coming out of the turbo, that's why ERT did the 2.5" as I recall. Which reminds me I have another e-mail to send to you Matt.

Yeah remember area is: pi x radius squared so a small increase in radius will give you a more noticeable increase in area.



15.9 @ 86.7mph

Smooth idle? We don't need no stinking smooth idle.

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