2.5" compared to 3"

[DID53]

Hey I have a stock vy ss ute an was just wondering if there would be any power/torque loss by goin 4into1 - high flow cats - twin 3inch as apose to tri ys - high flow - twin 2.5 inch . I might do cam down the track but for now is there any thing wrong with the 3inch system on a stock engine? Cheers dids

[blu ute]

IMO 3" not required unless going f/I. There will be no noticeable difference in power but will be much louder.

[Wonky]

The general consensus on a stock or bolt-on 5.7 is you'll definitely lose low down torque with either 4-1s compared to tri-ys and/or 3" compared to 2.5". Do both and it will be even worse.

On a 6.2 LS3 each actually improves the situation as proven by HPF in the video they did for TV. On a 6.0 litre like mine I wasn't worried about loss of low down torque and went 4-1 and 3" purely for the sound. :D

[pjk20m]

i put a 3inch system on my car after i did a haed and cam package and i noticed a few things noise lots louder, power a but not as much as i wanted, and a bit of drone

[V28VX37]

Hey I have a stock vy ss ute an was just wondering if there would be any power/torque loss by goin 4into1 - high flow cats - twin 3inch as apose to tri ys - high flow - twin 2.5 inch . I might do cam down the track but for now is there any thing wrong with the 3inch system on a stock engine? Cheers dids


IMO 3" not required unless going f/I. There will be no noticeable difference in power but will be much louder.
^^^ Good advice. I've got full DF twin 2.5" (inc. cats) with ported heads & mild cam, at around 290rwkw. If you're staying naturally aspirated there's little point in going twin 3" I reckon.

Edit: Also, no drone (M6 with 3.9 diff gears). Sounds sweet but It's not a particularly quiet system though.

[vassis]

Ive had a few combinations now

Had a duel 2.5" system with triys std cats on her when she ran a tuned stock ls1....Heaps of torque everywhere and feels good starts to die in power after 5500

Went to duel 3" with same headers and cats new mufflers same engine combo....Bottom end was deadend a fair bit but seemed to like going upto 6 grand sounded better had a nice crackle

Droped a stock L98 in the ls1's place same exhaust combo....Got the down lown back and even some more but didnt make good power above 5 grand

Cammed the L98 same exhaust combo.... Gained torque everywhere doesnt make much power after 5800-6000 RPM

Put a new set of genie 1 3/4, 4 into 1's and there cats same exhaust.... Lost the down low again.... Yet to be retuned driven once, and going back in a week to replace the 1 3/4" into 1 7/8" and hit the dyno again but she feels like she wants to rev to 7 grand now

In the end you need to loose some to gain somewhere else... Its proven by the accidental experiments and combo changes ive gone through. Might of lost down low torque with my last combo change but it feels way stronger up top without ringing her neck whilst running out of tune. If your going cam later on take it from me go straight to 1 7/8 incase you choose to do things later which most people do. The power loss still isnt as crutial as the power gained where the engine needs it most whilst on song. Ive also noticed that while the engine is deadened down low it is actualy using less fuel now using the 4 into 1 rather than the triy which is designed to help with vacuum at lower rpm. Its also running rich so when it gets leaned a bit down low she will be better again.

To answer your question in my opinion my car did feel better with the 2.5 inch in standard form but like you said if you cam definatly go a duel 3" and either 1 3/4 or 17/8 (1 7/8 if your doing other stuff like heads etc)

Good luck hope any info helps

[DID53]

hey guys this has been a great help :goodjob:, on my last set on my monaro i had tri y's - high flow - an twin 2.5'' xforce and it had great torque but not as much sound as i was after. im thinkn of going tri y's - high flow - twin 3'' an then to gain the torque back down low putting in 3.9 diff gears. would the torque loss down low be that noticeable comared to 2.5''? cheers dids

[stupotarnie]

Mate, I have 1 7/8 pacies, highflow cats and twin 3" exhaust. Lose of power was zero. Bigger pipes sound better to I reckon. At least if you go fairly big with exhaust it gives you some room for future mods without worrying about your exhaust being to restrictive. But as far as a drop in power, I dont think theres any, But there have been plenty of threads about it so maybe just read through some of them and draw your own conclusion. cheers.

[V28VX37]

hey guys this has been a great help :goodjob:, on my last set on my monaro i had tri y's - high flow - an twin 2.5'' xforce and it had great torque but not as much sound as i was after. im thinkn of going tri y's - high flow - twin 3'' an then to gain the torque back down low putting in 3.9 diff gears. would the torque loss down low be that noticeable comared to 2.5''? cheers dids

I'd hazard a guess that torque/power difference between twin 2.5" and twin 3" systems in a medium powered car (250-300 rwkw) would be pretty much negligible i.e. <5%. The only way to test is run the exact same car on the same dyno with the two different systems, of course.

I have DF 4-into-1 headers and DF high flow cats and good smooth power/torque curves. The car's tuned for response rather than peak power, very happy with it. It's definitely loud enough, in fact I'd prefer something quieter, I must be getting old...

One more thing to keep in mind with the 3" system is that you'll lose another 13mm or so ground clearance.

All in all and regardless of which system you pick you can't really go wrong with DF. Good luck.

[Lincoln87]

plus the DF 3 ONLY comes in S/S = $$$$$$



nothing wrong with the good ol' xforce. dont care what you say. both me and mates car/ute sound fantastic with them, sure do drone the tinest bit. But ive heard people complain about drone in anything and everything.
infact, his ute used to run the single 3.5 "drone free" and i was ready to do my head in on a 5hour + return trip to the entrance and back with it (to pick up the dual 3 lol)



from what ive gathered, there is SFA differenece performance wise with a bolt on car comparing a smaller system to an oversized system.
it also wont really increase in loudness, but will increase in deepness.



i orginally had a 2.5 system.


now wishing i went the 1 7/8s and dual 3 straight off the bat.

3inch with diff dumps
Calais Drive-Bys - YouTube

2.5inch with straight pipes (no rear resi)
Lincoln does another skidd - YouTube



**only just figured that that is an awesom comparison.
*cept for the fact that with the 2.5 i havent got the 4500 stall or the 3.73s

[Soopy]

Cut the pipe out of the xfarce system and it will sound a little better. They flow alright sound like ass imo though.