Welcome to Just Commodores, a site specifically designed for all people who share the same passion as yourself.

New Posts Contact us

Just Commodores Forum Community

It takes just a moment to join our fantastic community

Register

Limits of twin 2.25" exhaust

harrop.senator

Well-Known Member
Joined
Jan 26, 2017
Messages
1,376
Reaction score
342
Points
83
Age
28
Location
perth
Members Ride
vr senator 355, vu 5 speed l67
Hey guys I'm looking at expediting my ute to being finished and cutting some corners.

I'm looking at buying housed and finishing other projects so I don't think I'll be keeping it longer then six months once running again.

I can get a diff dump twin 2.25" exhaust for $80. Even me supplying the mufflers and hotdogs I was looking at $6-800 for press bent duals on my vs ute for header back.

I should be able to replace one length at a time with 2.5" on a diff dump if it's going to hold it back. But I don't want to start from scratch and definitely aren't making diff U bends in the drive way


The calculators say that 366 crank hp will be the max 2.25" dual will flow.

Only running 1.5" primarys and 2" outlets on the headers ( hoping to cut the collector down and fit a 2.5 or 2.25" collector extension on it)

I would be dissapointed with 300rwhp or less with the little pulley but don't wanna get my hopes up for 350 rwhp.

366 take 15-20% gets it right to 300rwhp.

Most theoretical calculations are for optimum in engineering and not that it straight won't do it. I'm hoping it's one of those things that it may go 325 and not 340 but can still go over 300 wheel. Or nope it just hits a wall.

Has anyone made over 300rwhp with a twin 2.25" system?
 

Attachments

_R_J_K_

Well-Known Member
Joined
Dec 20, 2008
Messages
5,427
Reaction score
883
Points
113
Members Ride
Zenki S14
What engine?
L67.

IMHO it would be fine (with me not knowing that much), but for $80 of pretty okay sized exhaust and something that you say you're not going to keep the answer should be pretty clear even if the calculators were wrong. Like in real world terms it's not close to being undersized or restrictive and any gains from a twin 2.5 will probably be marginal, like IDK anywhere from 1-10hp.
 
Last edited:

shane_3800

Well-Known Member
Joined
Aug 13, 2011
Messages
2,453
Reaction score
820
Points
113
Age
32
Location
places
Members Ride
vr commo
VE SS Commodores can make 250kw+ on 2.5" twin systems so I would think 2.25 will be fine for 300hp.
 

harrop.senator

Well-Known Member
Joined
Jan 26, 2017
Messages
1,376
Reaction score
342
Points
83
Age
28
Location
perth
Members Ride
vr senator 355, vu 5 speed l67
Cool couldn't see much real world answers out there. Everyone just saying twin 2.25" shouldn't even be used on a bolt on LS and going straight to dual 2.5". Every single thing I found was na needs a bigger exhaust then that.

I did an rpm calculation on swept volume and that's where the 366 HP came from. Really in a perfect world I'm hoping for 400-420 HP at the crank.

Rjk you have a point but even if I won't keep it I've already sunk 10k in to it. I still want it to be fairly impressive. That way I'll feel like all the money I've thrown down the pit wasn't such a bad idea.

The smart side of my brain says sell it , that with the money from the truck is a house deposit. Or sell it and buy a new turbo , manifold, fuel system when the 180sx gets back from paint and get the 215 panelled.

The other side of me says it's a 1400kg car wet. Throw a built box , 4k stall and radials at it and go run some 11's once I'm sick of killing five speeds

I'm honestly hoping for 250kw/350hp. But I don't like getting high hopes especially over dyno numbers. If I can go 110 mph in it I don't care about the dyno sheet. I've had 50rwhp differences in some cars I've owned pending the weather and who's rollers.
 

gtrboyy

Well-Known Member
Joined
Jan 25, 2006
Messages
2,661
Reaction score
1,126
Points
113
Members Ride
vt ss & lc gtr
Not keeping the car may as well slap it on for $80..if it strangles it a bit meh sell it.
 

harrop.senator

Well-Known Member
Joined
Jan 26, 2017
Messages
1,376
Reaction score
342
Points
83
Age
28
Location
perth
Members Ride
vr senator 355, vu 5 speed l67
Yeah I'm gonna go grab it Friday. Like I said I don't mind if I lose some potential gains.

Look I do want to sell it in theory. Be an adult , spend the money somewhere I can fit a hoist or on some cars that are cooler.

But after it being in pieces for a year. Me not having a running performance car for three. Spending all the money building it as wanted to keep it , may stick around for awhile.

I was just worried it'd make 210 on a 3.1" pulley , 290-300 on a 2.4" pulley and be told na it's the exhaust. It's capable of 350 but the 2.25's are killing it. If you want more go spend the $800 on exhaust and bring me another $500 to re tune it. Didn't know if it would just cost me more later on spend it now

If people are making 250+ rwkw on ve+s it'll be enough for me.
 

harrop.senator

Well-Known Member
Joined
Jan 26, 2017
Messages
1,376
Reaction score
342
Points
83
Age
28
Location
perth
Members Ride
vr senator 355, vu 5 speed l67
Was only twin 2" in the end going to give it a miss. I've got a really ghetto 1-2 dual 2.5" exhaust I might do some repairing on or I'll just pay the exhaust shop.
 

shane_3800

Well-Known Member
Joined
Aug 13, 2011
Messages
2,453
Reaction score
820
Points
113
Age
32
Location
places
Members Ride
vr commo
Do you have a mig? If yes just make it your self.
 

harrop.senator

Well-Known Member
Joined
Jan 26, 2017
Messages
1,376
Reaction score
342
Points
83
Age
28
Location
perth
Members Ride
vr senator 355, vu 5 speed l67
Yeah I do have a mig. But building a header back exhaust dual pipe with diff hoops on your back isn't my idea of fun.
 
Top