3" vs 2 3/4" Exhausts

[birdboy Junior Member Find all posts View Profile Close birdboy]

Given my experience going from a 3" to a 2.75" recently i would back this comment 100%

I've just had a 3" Scotts Rods fitted and it was brilliant - turbo spooled up quickly and engine felt like it was breathing alot better. Only problem was that it is such a tight fit over the diff/chassis that it rattled badly on start up etc. My mechanic told me to drive it for a week so that it heated/cooled a number of times before trying to rectify it. In the end the only way he could solve it was to crush it down a bit in the tight spot.
Now it doesn't rattle but i have lost a significant amount of the initial gain. Especially at low rpm but also throughout. It is still better than standard but had i not experienced the full deal i would have been disappointed.
So two thoughts here:
1. Is there a chance that those with 3" that went to 2 3/4" had pipes that were crushed a bit in order to fit? I'm thinking that a straight 2 3/4 not crushed would yield a better result due to no disruption in the gas flow.
2. Anyone else have this problem with the Scotts Rods or any 3" system? I just can't see that in my vehicle it is going to fit?
Any suggestions? I don't really want to do a body lift but it might be the only option?
Love to hear peoples thoughts

I must also say that i have been in communication with Scott and he is sending me another part. Very happy with their customer service! I'm super keen to get the full 3" as it was fantastic. Obviously didn't transform it into a rocketship but it was all the extra oomph i need.

[shodown Senior Member Find all posts View Profile Close shodown]

Only problem was that it is such a tight fit over the diff/chassis that it rattled badly on start up etc. My mechanic told me to drive it for a week so that it heated/cooled a number of times before trying to rectify it. In the end the only way he could solve it was to crush it down a bit in the tight spot.

I had a rattle on the 2.75" Beaudesert fitted to my 150 - turns out one of the exhaust hanger bolts protruded too far from the underside and the exhaust would rattle against it.

They had to take back section off and cut back the excess bolt

[ScoticusMaximus Member Find all posts View Profile Close ScoticusMaximus]

I've just had a 3" Scotts Rods fitted and it was brilliant - turbo spooled up quickly and engine felt like it was breathing alot better. Only problem was that it is such a tight fit over the diff/chassis that it rattled badly on start up etc. My mechanic told me to drive it for a week so that it heated/cooled a number of times before trying to rectify it. In the end the only way he could solve it was to crush it down a bit in the tight spot.
Now it doesn't rattle but i have lost a significant amount of the initial gain. Especially at low rpm but also throughout. It is still better than standard but had i not experienced the full deal i would have been disappointed.
So two thoughts here:
1. Is there a chance that those with 3" that went to 2 3/4" had pipes that were crushed a bit in order to fit? I'm thinking that a straight 2 3/4 not crushed would yield a better result due to no disruption in the gas flow.
2. Anyone else have this problem with the Scotts Rods or any 3" system? I just can't see that in my vehicle it is going to fit?
Any suggestions? I don't really want to do a body lift but it might be the only option?
Love to hear peoples thoughts

I must also say that i have been in communication with Scott and he is sending me another part. Very happy with their customer service! I'm super keen to get the full 3" as it was fantastic. Obviously didn't transform it into a rocketship but it was all the extra oomph i need.

i had dramas with my 3" in the early days rattling, it was actually hitting the floor in the back of the car as it went over the axle, it would only rattle over bumps or awkward angles, went back to the shop i got it about 4 times before i got it sorted (mine was due to a dodgy flex joint, and it didnt get crushed). have never had a problem with the 2 3/4".

Cheers,
Scott.

[birdboy Junior Member Find all posts View Profile Close birdboy]

Thanks Scott. Yes mine was hitting the underside of the body too.

[BlakMoth Avid PP Poster! Find all posts View Profile Close BlakMoth]

Sounds more and more like 2.75" is the way to go.
What's with the aluminised steel they use? Is that just a fancy word for mild steel? Apart from longevity what other benefits are there for stainless?


Sent from my iPad using Tapatalk

[clarkie383 Member Find all posts View Profile Close clarkie383]

The only problem i had was the Scoots Rods system hitting the top diff mount on bad bumps when loaded up.
This was more to do with having to tweak the rear exhaust to one side because of towbar bolts.
I moved it back closer to the bolts and no more problem.
Since then have fitted a lift kit so now huge clearance.

[djnapkin Junior Member Find all posts View Profile Close djnapkin]

Thinking about a Scott's rod for myself. Are other folks having these problems with it hitting the body running any lift or just stock height?

[74Damo Junior Member Find all posts View Profile Close 74Damo]

3 inch drone so much with auto's so I went 2 inch spools up quicker no difference in egt from 2 and 3/4

[DJD120GXL Senior Member Find all posts View Profile Close DJD120GXL]

how was the fitting? worth the hassle?

Beaudesert. 2 3/4inch. Delivered to your door. Prado 150 with ceramic dump pipe option as well.

[birdboy Junior Member Find all posts View Profile Close birdboy]

Got replacement section sent from Scott's Rods and it's perfect. No more rattles.
Djnapkin where it hits the only help would have been a body lift

[Bennyc2003 Lurker Find all posts View Profile Close Bennyc2003]

Hey guys. I also went through beaudesert exhaust and was told the 2.75 is alot better then the 3 inch for the 120 d4d. So I went with it. And its great. I didnt notice a great change but there was definitely a change. The only thing I wasnt happy with was the rattle in the tip. When the car revs low the tip rattles alot. Enough to hear it in the drivers seat. Does anyone have a solution for this cheers blokes

[cameronsch Junior Member Find all posts View Profile Close cameronsch]

Just thought Id update. I have upgraded my exhaust with a 2 3/4" stainless steel dump pipe back system on my 1KZ. Sounds awesome (rumble and turbo whistle), drives even better. Put this with my DP chip and it really gets going. Great off the line, massively improved drivability, and pulls like a train. I drive her nice and easy too, always have. Would recommend.

[mybo Member Find all posts View Profile Close mybo]

Just thought Id update. I have upgraded my exhaust with a 2 3/4" stainless steel dump pipe back system on my 1KZ. Sounds awesome (rumble and turbo whistle), drives even better. Put this with my DP chip and it really gets going. Great off the line, massively improved drivability, and pulls like a train. I drive her nice and easy too, always have. Would recommend.

Thanks for the feedback cameron, always good to hear people's actual experience from putting their money where their mouth is

I've been researching exhausts myself, and probably the best explanation of the effect of increasing exhaust size I've come across is on this page:
http://www.nsxprime.com/nsx-faq/exhaust-theory/

There's a lot there, but I encourage people to read it all - you'll learn a lot.

For our turbo diesel prados, the main thing I got from this is that we want to get the exhaust gases out of the system as fast as possible. Achieving this means removing sources of restriction (straight through muffler and mandrel bends), and maintaining exhaust gas velocity. If you go too big in terms of pipe diameter, you can actually slow down the exhaust gases because as they expand, they cool and become more dense and move more slowly (read the "Exhaust Pulse" and "Pipe Sizing" sections on the linked page). So what is the best pipe size for the prado? I dunno - but I'm seriously considering just using a 2.5 inch cat-back system on mine...

[cameronsch Junior Member Find all posts View Profile Close cameronsch]

Thanks for the feedback cameron, always good to hear people's actual experience from putting their money where their mouth is

I've been researching exhausts myself, and probably the best explanation of the effect of increasing exhaust size I've come across is on this page:
http://www.nsxprime.com/nsx-faq/exhaust-theory/

There's a lot there, but I encourage people to read it all - you'll learn a lot.

For our turbo diesel prados, the main thing I got from this is that we want to get the exhaust gases out of the system as fast as possible. Achieving this means removing sources of restriction (straight through muffler and mandrel bends), and maintaining exhaust gas velocity. If you go too big in terms of pipe diameter, you can actually slow down the exhaust gases because as they expand, they cool and become more dense and move more slowly (read the "Exhaust Pulse" and "Pipe Sizing" sections on the linked page). So what is the best pipe size for the prado? I dunno - but I'm seriously considering just using a 2.5 inch cat-back system on mine...

No worries.
I ended up going 2 3/4" Outlaw stainless through Right price exhaust at Slacks Creek Brisbane, and would highly recommend them. The manager there was awesome, and from what I told me, you're on the money.
Outlaw test different size exhausts on each car - 2 3/4" came out best performance wise for the Prado. He said keeping a bit of that back pressure allows for more torque. Outlaw do their exhausts in 409 grade stainless, which he told me is better as some of the 304 grade (other brands) come back to his shop due to cracks and the like since a turbo diesel shakes so much. 409 is much more maleable, only downside he mentioned was, 409 isn't as pretty .

[Regan Lurker Find all posts View Profile Close Regan]

some great info guys its helped me decide what exhaust i want im thinking 2 3/4 sounds like the one.