Exh size for Twins

[metal tech]

In recent weeks I've noticed several new threads by new people asking about twins. The info is concentrated on the turbos, what works good together. I have read very little about sizing the exh system for your power level. One post by someone that I feel has a solid knowledge background in this area says that "up to 570 HP a 4" system is ok". Another person wrote that "after 500 HP you need a 5" system. I know several of you guys have had twins for a long time and may have changed exh systems and noted improvements and/or no changes. Would you guys share your exp with the rest as to what is needed and what worked for you. FYI, I run a 4" dp then 5" straight pipe, no muffler, although loud and annoying on long drives, it sounds great ripping through the gears. My B2 is on order awaiting it's place below my 40.



Al

 

[SRadke]

A man very experienced on the subject said his 600+hp truck dynoed 12 hp more with 5" than 4" on the same day. Will this make a diffrence on a 400hp truck, I doubt it. The only thing that you need to know is that your new B2 has a 5" exhaust flange and clamp so just stick wiht it and run on out the back.



-Scott

 

[swankmetal]

fwiw, when i put the twins on and stepped up to 5", my exhaust note got MUCH quieter.



dave

 

[SRadke]

The second turbo will quiet things down significantly.

 

[lmills]

still runnning 4" on mine, but thinkning hard about going up to 5" very shortly.

 

[metal tech]

Thanks guys. Imills, it would be nice to hear how much of a difference the swap makes. Scott, I did know the B2 has a 5" outlet, I was told that one person doing twins uses a 5"-4" reducer to retain the typical 4" exh sys that most people upgrade to. Considering that at 600hp your source noticed a 12 hp diff, would seem that 4" will do a good job at 500 and slightly higher. BTW, this info isn't just for me, the new people asking about twins may benefit.

 

[SRadke]

FWIW mine is currently necked down to 4" to get shoved through my 4" Pacbrake but I'm hopeing to open it up a bit spring next year. If the turbo outlet is 5" the engineer of said turbo was obviously designing it to be used with 5".

 

[Todd T]

the only real measure would be to compare your drive pressures and see if freer flowing exhaust helps out on the drive pressures.



I started out with 5" all the way out the back and have since switched to a single 5" stack. I didnt notice a change with my SOP meter or EGT's.

 

[lmills]

I know what my numbers are with 4" I will try to get some with open 5".

 

[trqmnstr]

Todd T, do you have any pics of your single stack? Check out mine in my Reader's Rigs. I'd like to see some other singles. Clay

 

[Todd T]

pics are in this thread...

https://www.turbodieselregister.com/forums/showthread.php?t=133792