Brett928S2

Hi

If that question was for me...I didnt ,,,I bought mine in the UK from RITECH SYSTEMS ..and Richard Armstrong spent a lot of money and dyno time figuring that out...apparantly if you put the X in the wrong place it makes a HUGE difference to power ..also to increase the power more...you NEED 2 bullet boxes behind the X...

Hope this helps

All the best Brett

928 S2 AUTO V8 4.7 LTR 1986 IRIS METALLIC BLUE WITH X-PIPES ,RMB ,PROMAX CHIPS, KICKDOWN SWITCH.K&N.
PCGB UK 928 FORUM MODERATOR

hacker-pschorr

Bullet Boxes?

Brett928S2

Hi

Ummm... I am not quite sure what you call them in the US..



Trying to insert picture...or link for you to see them...

porsche link

Brett

Brett928S2

Hi

WOW i did it

Ok..the narrow boxes at the back end are what we call BULLET BOXES....they are "straight through"...etc...and they make a LOT of difference HP wise I am told....

All the best Brett

928 S2 AUTO V8 4.7 LTR 1986 IRIS METALLIC BLUE WITH X-PIPES ,RMB ,PROMAX CHIPS, KICKDOWN SWITCH.K&N.
PCGB UK 928 FORUM MODERATOR

inactiveuser92616

can someone explain why an X into a Y would provide more power than just a Y alone (Y placed where the X is now, and large single the rest of the way back)?
As I understand it, the power gain is from allowing the left and right cylinder bank streams to mix, promoting exhaust pulse scavenging. Also as I understand it, any niceley tapered pipe junction could do this well (X or Y). So why all the suggestions to mate a X and Y pipes.... seems like the extra bends would just create more minor-losses of the flow energy.

Brett928S2

Hi Pat

Ummm... as I understand the theory....you only got half this sentence correct....>>> "As I understand it, the power gain is from allowing the left and right cylinder bank streams to mix, promoting exhaust pulse scavenging."

The correct way to say the sentence ..I think...is this
>>>>As I understand it, the power gain is from allowing the left and right cylinder bank streams to CROSS, promoting exhaust pulse scavenging.

I changed the word MIX....which would do nothing,,,to CROSS....which creates the scavenging AND the PULSE effect needed...

I am sure some of the wiser brains here will correct me if I am wrong

All the best Brett


928 S2 AUTO V8 4.7 LTR 1986 IRIS METALLIC BLUE WITH X-PIPES ,RMB ,PROMAX CHIPS, KICKDOWN SWITCH.K&N.
PCGB UK 928 FORUM MODERATOR

FlyingDog

Those look like glasspacks.

Toofast seems to have done the X to Y because of resonance. Some people do it because you want the X or Y to be near the engine and ahead of the cats, but a single cat after a Y can be restrictive. If you do X then cats then Y you get the benefit of scavenging, higher flow through the cat(s), and a single exhaust at the rear.

toofast928

Yep Dog your right on. The benifits of an X pipe is more tq and HP in the lower RPM band. Mr Otto dynoed Y's and X's and my basic set up was based on his findings. 2" down pipes are just too small on any 928 engine.
The reason for the double Cats is less restrictive and more scavenging. More flow area in duel cats than a single 3". The goal is to keep the exhaust pulse flowing and not to bottle neck anywhere. The balance act is not to over scavenge, pull (or in my case blow) the intake charge out of the cylinder into exhaust. Crudly yet accurate we can measure the scavenge by amount of back pressure. I was shooting for 1-2 psi. ended up with 4 psi. I guess 3" duel cats would yeild 1-2 psi but I'm out of $$. Still I'm very happy with this set up, convinced the only HP left on the table is replacing the stock exhaust manifolds with headers.
The Y after the Cats allows me to connect to the already exising Borla exhaust.

Over the years I tried RMB, Cat, no cat, open exhaust. The trick to more power for the 16V is an X pipe. Single or duel exhaust after the cats your choice. Haven't dynoed yet but I'm telling ya wasn't able to break the rear tires loose in rolling second gear before the X.

slate blue

Hi Brett, thanks for posting that pic! As to our previous converstaion, did your car record those big Db numbers with those bullet boxs and the resonator? Or are the bullet boxes it and then just pipe?

Cheers Greg

Chuck Schreiber

Brett,

As Dog said, I'm pretty sure those are glasspacks. That's exactly what I want to do on the 79. X to duel glasspacks to a rear mounted muffler duel in and duel out, then run to the back with a nice set of polished extensions. Simple.

drnick

i will go with dave lomas take on this, that either the X or the Y achieve the same thing in allowing scavenging. im not sure why the UK made X has 'bullet boxes' though, can they really increase power??? btw the UK S and earlier S2 have a single exhaust as well, its only the late S2 that had dual pipes all the way.

Brett928S2

Hi Greg

My system is as follows...

The X with bullets you see in the picture....then 2 pipes to the standard middle boxes which are on both sides just in front of rear axle...then 2 pipes either side to the RMB at back...

Considering mine is 98 Db at tickover (700 revs) and goes up to 115 Db at 5000 revs... I dont really think the standard S2 middle boxes do much in the way of silencing lol....

All the best Brett

928 S2 AUTO V8 4.7 LTR 1986 IRIS METALLIC BLUE WITH X-PIPES ,RMB ,PROMAX CHIPS, KICKDOWN SWITCH.K&N.
PCGB UK 928 FORUM MODERATOR

Brett928S2

Hi Nick

Ummm...I spoke to Richard Armstrong for a long while about this and he says that those bullets make a BIG difference to HP gains and flow...and using them....I believe him
But it IS very loud...anyone ever run a 16 valve 928 on headers only and done a Db reading ??? as I doubt its very much louder than mine lol

All the best Brett

928 S2 AUTO V8 4.7 LTR 1986 IRIS METALLIC BLUE WITH X-PIPES ,RMB ,PROMAX CHIPS, KICKDOWN SWITCH.K&N.
PCGB UK 928 FORUM MODERATOR

FlyingDog

We ran Beerfish's car with manifolds and dual in/single out non-baffled muffler/Y-pipe and nothing after it. Idle was a fairly loud low pitched rumble which actually got quiet at higher revs. My full exhaust is much louder.

FlyingDog

I would use small round mufflers like Magnaflow or Borla 4, 5 or 6" rounds instead of glasspacks. Most glasspacks only have 1.75" or 2" cores. Some have 2.25" cores, but not many. They also have little clamshell shaped perforations that stick into the flow of exhaust. A straight through Magnaflow or Borla will be a single constant diameter pipe with round non-protruding perforations. That means you'll have a clean 2.25, 2.5, 3, or 3.5" path instead of a disrupted ~2" path. The glasspacks will be quieter, but also much more restrictive.