2" too restrictive!??

[Special K 81 0]

Ok guys,..have a 2" freeflow exhaust system,....very small mid box,plan was decat. I currently have looks like 3" scorpion, blowing in places till welded today. Anyway would 2" be too restrictive or would it increase backpressure and torque!!??

Surely 3" is a bit too much for n/a standard engine??

What is standard? 2", 2.25",2.5"....

[chief ka kar 0]

2.25 is standard i run a 2 1/2 straight tho on mine and a dont think am losing any torgue

[Special K 81 0]

2" too small?? may have wasted money!?!?lol

[cabrioman 6]

i ran a 3" on mine when it was N/A and had no power lose .....

[Special K 81 0]

Cheers Ka Kar!!

hey tony....i wouldnt say im suffering power lose tbh with what id say is 3", only changing because i dont like the twin dtm up turn tail pipe, plus till some welding yesterday was blowing at cat(which when i found it yesterday was ridiculous....blowing out of a bung i can only describe) and that stupid big mid box,cracked around pipe and around inside edge of box. Thought i'd just change a tired looking exhaust. Have a lovely small mid box...lovely welds...nice looking exhaust(is that some exhaust porn ha ha) and back box...was going to run a metre of s/s tube to a decat either resonated or none...but is 2"....wasting my time??

[gavinvr6 0]

i found with my 2.5 and straight through that you lose low down torque so around town it can feel a little boggy, BUT with a straight through and less back pressure the engine breaths better at higher rpm's where the vr makes its power. and if your giving it beans you'll always be at the higher rpm so need a free flowing zorst.

a 2" should be fine, it will help keep back pressure up to keep the torque low down, it would be better if you lost the mid box to allow a little less back pressure. but it's louder, i dont see the point in a 3" on an n/a engine. but thats just my 2 pence worth.

[Special K 81 0]

Ok gav cheers, like i just said to tony, apart from power loss through blowing my system befoe blowing doesnt seem to lose power....howeveeerrr, what do i compare it to.lol Just thought maybe a bit big for standard, great for gases getting out but with how much pressure. I obviously dont want to lose top end where the grunt is though, mate the mid box is small!!lol basically just takes some noise off i think,plus its a more direct route from cat, no god awful u bends to the mid box,lol So if i use decat pipe and keep mid box be the same as losing mid box and having resonated de cat pipe??? i dunno. I dont if im honest want stupid loud.

[gavinvr6 0]

i can only tell you what i found from my own experiance, i was running de-cat straight through to twin 2.5" tails from a single back box. it's great around town popping and banging on lift off but on a motorway the drone sound can get tiresome.

have you actually measurred the zorst? only ask as if a standard vr is 2.5 i cant think why anyone would deliberately make an after market one smaller than standard. unless it was to try and retain back pressure. a de-cat is a good addition, wont transform the car but does add a little bit of zing.

i tried everything with mine, cat back single box, double box even no box's, bt that was just daft, i ended up with a 2.5 inch de-cat back with a small mid box and free flowing back box, nice gains and not to loud about town with a healthy growl when you stomp in the go-go pedal

[Special K 81 0]

has wha i want and in fact good call gavin, i havent even actually measured myself...just taken a guys write up word for it, bit of a clown actually when i asked him a question he cam back with a answer which wasnt relevant.lol Says vr6 exhaust...but maybe really its just a mk3 one i shall have to measure..off top of head think it might be 52mm!!?

[p0u1 14]

your vr6 only turns one way right? mine only go round one way thats why back pressure wouldnt help mine atall, so backpressure is a myth sorry

[gavinvr6 0]

mine turns 2 way's, left way's and right way's.

what do you mean back pressure is a myth and your car does not need it?

someone tell me if im right here please. in the 15 yrs i been playing with car's i've always found that at lower rpm's a car with either no box's or a single box feel's less lively. and with a twin box system it feel's better.

my own car as an example was fine around town and nippy upto 3200rpm when it came to the power band of a typical vr6 when i was running a 2 box system but when running a single box i found it seemed less lively upto the power band but quicker past this point than with a twin box system so the additional back pressure caused by the twin box system aided in lower torque

[mike 6]

2inches is really small mate, may need to see a doctor

awsome thread title

[FishWick 21]

someone tell me if im right here please. in the 15 yrs i been playing with car's i've always found that at lower rpm's a car with either no box's or a single box feel's less lively. and with a twin box system it feel's better.

Agreed. Any gains with exhaust size on naturally aspirated engines would normally be found at full revs and full throttle.

It also depends on cam overlap too. Wild cams are good at creating a vacuum below atmospheric at max torque revs, which sucks out exhaust gases, but at lower revs, some exhaust gases can get pushed back into the cylinders, which dilutes the intake air/fuel mix, reducing power.

So exhaust tuning on NA ties closely with cam tuning.

And people who claim an exhaust is restrictive should really back it up with actual back pressure measurements (pressure sensor in the exhaust), rather than just assuming it's restrictive just because it's quiet ;-)

As for 2" bore, yes that is too small for a VR6. 2.25" suits stock. Nicely tuned with cams etc, a decent 2.5" system will see a few ponies released.