BJ42/3B WITH TURBO... what size exhaust (1 Viewer)

[kling-on]

almost done with parts collection on my Isuzu Turbo upgrade ... what size exhaust

tubing is everyone running??? are you running it to the rear tire or out that back and why ?? just looking for ideas ...post pick if you got them

 

[ToyRoverlander]

I've got a 2.5" exhaust on mine, exits all the way at the back to keep noise to a minimum. Got 1 silencer in it, it's nice and quiet. All stainless too. I used to have it exit on front of the rear wheel without a silencer, waaaaaaay to loud. Added a silencer very soon after. It was better but got worse as the silencer filled up with soot. I lenghtened the exhaust to the back of the truck and added a second silencer. This quiet it down a lot which I liked. That exhaust was made of mild steel and the first section, till under the footwell through the wheelwell, was wrapped to keep the heat of the footwell. Unfortunately that caused the metal to completely rot away in no time at all. As I didn't feel like making another exhaust and have it rot away I had a shop made the current one in stainless steel. Been on there for about a year now and I'm very pleased with it, money well spent.

Some pics, even if they are of no use to you as it's a Land Rover.

 

[RufusTheDufus]

I've done 2 exhausts for turbo 3Bs with 2.5" stainless. Jegs.com has a kit that's got all the bends and tubing you could want for a Cruiser exhaust. (I'm working on a 2.5" stainless exhaust for my HJ45 Troopy at the moment too.)

2.5" is plenty for the airflow of a turbo 3B. I'd recommend using mandrel bends, not the crushed tube bends. Your EGTs will be lower with a better flowing exhaust. A straight-through muffler or resonator should be all that's required to get the noise level to an acceptable level.

Some guys like to do 3" primarily for looks or sound but it will make almost no difference in performance on a 3B.

 

[gerg]

Id have to say that if you can fit a nice clean 2.5" its much better than a dirty 3". I put a 3" with a flow through aeroturbine but it dumps in front of the passenger rear tire. Really tuff to squirrel 3" through the frame and out the back. Its surprising how much easier a 2.5" is to fit vs 3". I used the 3" cus I had lots of room and all the materials.

Im a big fan of header wrap, but it will absolutely destroy mild steel in short order. Unless its like less than a foot off of the turbo it all stays wet for long periods and the metal gets hot enough to cook the oils out of it but the wrap holds in water for fairly long periods and its a perfect combo for rust. Conditions a lot like a BBQ.

 

[kling-on]

GREAT INFO GUY THANKS ... Keep it coming pics too are great thx

 

[jim land]

Is 2.5" exhaust too big for a NA 3b
I plan a turbo for next year probably. , but I need a new exhaust now and planning ahead
Currently have 2"

 

[RufusTheDufus]

2.5" is not too big for a normally aspirated 3B. It's overkill but won't hurt anything. It's not like these engines are high RPM, high HP with tuned intake and exhaust. Your engine will thank you for the 2.5" when you do your turbo.

 

[jim land]

Is 2.25" correct for turbo or 2.5" is the minimum

 

[Dougal]

Is 2.25" correct for turbo or 2.5" is the minimum

It'll do.

 

[RufusTheDufus]

Some of the older stock Saab turbo setups would have a dump pipe of 3" and transition to 2.5" a few feet away from the turbo. (These are gasoline engines that move a lot more air, don't pay attention to the sizes.) You could do something along these lines when you add a turbo but a 2.5" stepping down to 2.25". Exhaust gases cool quickly as they leave the turbo. Cooler exhaust takes up less volume and doesn't require as large of a pipe.

2.25" is more than enough to handle the roughly 350CFM of air your engine will be pumping when you add a turbo. (3.4 liters @15psi boost is 350CFM) I found this handy chart that estimates how much air different pipes can handle. 2.25" should be able to handle up to ~400CFM without becoming a significant restriction.

Try to install a free flowing muffler if you can. Otherwise exhaust sizing isn't really that important.

 

[jim land]

Thank you @RufusTheDufus for those good advice.