Outer Limits 4x4 Board

2.5" hi flow exhaust and hi flow muffler on a turbo diesel will that drop the rpm that the engine comes on boost , improve power and economy. Is there any point ?

Thanks for any help

Stop bagging the MIGHTLY RD28T its not that bad compared to the 4.2.
I did the Simpson including Big Red just as well as my mates 4.2 turbo GU and with better fuel economy.
I bet a 4.2turbo is a real slug compared to a chevy 6.5 turbo. :lol:

turbo will spool up faster, less back pressure


my 3" mandrel made a huge difference to my ZD30

i have a factory turbo 4.2 gu.
previous exhaust was stock system cut off just behind the cab....would go up the toowoomba range in 3rd at 400 revs at the top [did it just to see if it would make it in 3rd] but normally i would have to go back to 2nd as it would not hold third.

Beaudesert exhaust custom made me a 3"system [from back of turbo] that ended at the same spot.
neither exhaust had a muffler...nothing else has been done [fuel increase etc]

this time the truck held high revs in third and i could have gone fourth but it would not have held.

On another hill...
before: hit bottom at 100kmh and used 4th, went over the top at 90kmh.
after: hit bottom at 100kmh and used 5th, went over the top at 90 kmh.


so i guess you really could say the new exhaust made one gear difference.

i would expect similar improvement in your 2.8.

i have a factory turbo 4.2 gu.
previous exhaust was stock system cut off just behind the cab....would go up the toowoomba range in 3rd at 400 revs at the top [did it just to see if it would make it in 3rd] but normally i would have to go back to 2nd as it would not hold third.

Beaudesert exhaust custom made me a 3"system [from back of turbo] that ended at the same spot.
neither exhaust had a muffler...nothing else has been done [fuel increase etc]

this time the truck held high revs in third and i could have gone fourth but it would not have held.

On another hill...
before: hit bottom at 100kmh and used 4th, went over the top at 90kmh.
after: hit bottom at 100kmh and used 5th, went over the top at 90 kmh.


so i guess you really could say the new exhaust made one gear difference.

i would expect similar improvement in your 2.8.

I run a similar setup under my 260 (MQ) LWB with the RD28T and the turbo kicks in about 3-4 RPM earlier than before. Definitly worth it ! The sound is much deeper and throatier but not too loud.
BTW, the RD28T is not that bad. Mine is at 265k KM's and only needed a new cyl.head @ 260k because of excessive high-speed abuse here in Germany.