Comparison between 2.5" and 3" exhaust

**steveG** · 9th December 2012, 08:33 PM

This week I finally got off my butt and finished the rest of my 3" exhaust as it was still the old 2.5" system from around the transfer case rearwards.
It was more time consuming than I thought doing it out of mandrel bends and straight tube but I was pretty happy with how it came out. Used a single muffler with offset inlet/outlet under the rear passengers feet.

Thought some of you might be interested in before and after readings from driving my test hill. Its not a particularly long hill (about 1km), but has a steady climb with a steeper section just before the top. I can do the bottom section flat to the floor in 3rd at 3000rpm, but the revs slowly drop until you're sitting at about 2000rpm (~60km/h) on the steep section and can then hold that to the top.

Enough words - here's the figures from the top of the steep section:

Before:
Ambient temp: 25*C
Boost: 12psi
Max EGT (pre-turbo): 725*C and climbing
RPM: 2000

After:
Ambient temp: 20*C
Boost: 12psi
Max EGT: 675*C steady
RPM: 2000
Carrying an extra ~120kg

Engine is a '82 NA 4bd1 with a Garrett T25G, wastegate wired shut, and no intercooler.

I'm pretty pleased with the 50*C drop in EGT, and it seems to build boost a bit more quickly in the 2-3000rpm range if you give it a boot full.

Steve

lokka · 9th December 2012, 08:50 PM

So they do breathe better with the bigger pipe good to see a simple test to prove it

Now you need to fit the intercooler and see how much better it goes

**c.h.i.e.f** · 9th December 2012, 09:32 PM

Nice findings Steve!
Exhausts are such a PITA to make

**steveG** · 9th December 2012, 09:52 PM

Originally Posted by c.h.i.e.f

Nice findings Steve!
Exhausts are such a PITA to make

At least I had a cutoff saw for this one. I've done a couple of 3" snorkels with just a 4" angle grinder and cutoff disks and that really sucks

Before I get the intercooler on I want to have a play with turning up the fueling a bit more. Currently I'm seeing 15psi sometimes, but only maintaining 12psi in most conditions.
Now that the exhaust is a bit more free flowing, I'm interested to see if I can up the fuel, get more boost, and maybe even drop the EGT's a bit more.

Steve

**c.h.i.e.f** · 10th December 2012, 04:30 AM

Beautiful I am not the only one then that struggled with doing it with a 4" grinder

I ended up converting to the drop saw too after almost loosing a finger by running a 5" disc on the 4" grinder for some more depth

Good simple testing is showing some clear results by what you've said...will be good to see what happens with your suggested plans..

**Dougal** · 11th December 2012, 03:40 PM

Great results, shame you didn't get a before measurement for min rpm to deliver 10psi boost.

Now we all know that a 3" pipe is a waste of time with 12psi boost. Better go sort that out now.

**steveG** · 11th December 2012, 05:54 PM

Originally Posted by Dougal

Great results, shame you didn't get a before measurement for min rpm to deliver 10psi boost.

Now we all know that a 3" pipe is a waste of time with 12psi boost. Better go sort that out now.

Didn't even think about recording the lower end of things Dougal, but I can check what it is now. Whats the best way - eg rolling in 3rd?

What max boost do you reckon the T25G will be comfortable with?

I also have to confess to taking it for a quick spin with just the dump pipe on (back to the g/box crossmember). Sounded pretty "choice bro" but I'd be over the drone in half an hour I reckon. Would have been interesting to be able to run it on my test hill in that configuration. Just have to get all the soot off the transfer case now

**Dougal** · 11th December 2012, 06:11 PM

I don't have a map for the T25G, but I'd expect it to handle most of 20. Hell I ran the little T25 to 20 and it survived.

The highest gear you can pull is best for measuring boost onset.

What muffler did you use and how quiet is it?

**c.h.i.e.f** · 11th December 2012, 08:16 PM

Larger the turbine AR the more raspy it is so I'd take a guess and say a 3" straight pipe full length wouldn't be to loud for your comfort with the turbo you are running

**steveG** · 11th December 2012, 09:34 PM

The muffler is an oval offset-offset configuration. Both tubes run straight into an open central chamber which is approximately the middle third of the muffler. The tubes overlap in that chamber.
I bought it from a local "old school" muffler shop (they do more bending and fabrication than bling) and explained to the guy that I was after something free flowing and it didn't have to do much silencing.

My wife couldn't detect any increase in noise level over the 2.5" system with similar muffler in the same location. Running just the dump pipe the exhaust noise was obvious (as was the increased turbo whine), but with the full pipe and muffler you're not really aware of any exhaust noise from inside the vehicle.

Chief - I thought about just running a straight pipe, but the County is set up mainly for touring and I was concerned about getting a couple of hours down the road and finding that the drone was getting to me. There's already enough sources of noise/vibration without adding the exhaust to the mix

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