exhaust back pressure

G'day Scott,
I suppose it was an exhaust bloke who told you the exhaust system needed replacing.
First thing I'd be doing is getting it checked over by a reputable place (I had my Nissan tuned up by HiTech Diesel in Adelaide last October).
Mind you, they charged about $800- to do the injectors, tappets and adjust fuel pump. I already have a 3" exhaust system with a small muffler on my 4.2TD Patrol. After they tuned it they stuck it on the dyno and it showed 91kw at the rear wheels.
If yours is naturally aspirated and you don't want to add a turbo, the next best thing would be set of extractors and a free-flowing exhaust (2.5" or 3").
I haven't heard of exhaust back pressure being measured before, but that doesn't mean it isn't a legitimate way of looking at performance etc.
I'm not a mechanics backside, so what I've said here is just what I've learnt along the way.
Good luck mate.

I have a GQ Patrol Diesel, which develops 65 kw at the back wheels, its standard non turbo, But ive Fitted Extractors, 2 1/2" exhaust with a sports Muffler, I Must admit it Hangs on a lot more on a hill!! Money well spent you will notice a Difference!

Go with a set of pacemaker extractors and a free flow 2 1/2 inch exhaust and you will be surprised at the power and economy difference. Mate that lives at Golden Grove was happy with his job on ihz 75 tray, so I could find out where he had it done if you like, I had mine done at Balaklava. Blocked Exhaust could be possible with a deisel and there is no difference with materials used. The exhaust will still be black.

Hi Scott,
I have a 4.2EFI GQ with Genie extractors, 2.5" ehaust with hiflow muffler and resonator so it only burbles lowdly between 1600-2000RPM. puts out 100kw at the rear wheels with 95% of max torque from 1400rpm..
The back pressure is an interesting one that no exhaust place said the same thing to me when I was asking around before changing the rusted muffler out. Some places said engines need a little bit of back preasure and some said you dont want any..... So Im not sure who is correct.. however I have dropped fuel economy slightly when I removed my old blocked muffler and put on the hiflow system with extractors,, basicly removing any back pressure.. so maybe engines should have a little there to assist with the combusion process????

Having said all that, my mate has a 4.2TD GQ naturally aspirated with pacemaker extractors and 2.5" exhaust with a truck muffler.. he had his all retuned and puts out 73kw at the rear wheels from memory.. he is very happy with that setup, but without the resonator it does make more noice which may get annoying on a long trip as it resonates thru the cabin..

regards
Bryan

Scott,
Back pressure as far as I know makes a difference to performance and economy. Some engines are designed to operate with a certain amount of back pressure, too much back pressure doesn't allow the gas to flow freely so more unburnt fuel AKA smoke remains in the engine, you don't get the performance so you put more hoof into it, more fuel more smoke and little improvement in forward momentum. Some times when I've done a lot of city driving I put my hoof into it in third and red line the motor near enough, or whatever I'm comfortable with, if I look in the rear view mirror the people following have their lights on you would be amazed at the amount of crap that comes out of the pipe. After I've cleared the pipes out the vehicle seems to perform better. Extractors work well and make an improvement so does a bigger pipe, reducing the amount of sharp bends helps if your getting a custom made jobbie. I've gone to a 3 inch system on my GU, works even better than it did before. My opinions and findings as usual. I'm in Perth so I can't help you with a muffler center. Please make note about my comment about red lining the motor, just rev too where you are comfortable, I don't want your next post to be about an engine rebuild. Hope this helps a bit.

Hi Scott,

I've just sold my GQ Patrol TD 4.2 but I went through the same debacle when I turboed mine.

So many people tell you different things. Go to 3 or 4 different exhaust shops and they will tell you different things ie. size of muffler, type, brand, and size of exhaust.

I finally went to Brisbane Turbos and Tuning and basically told them not to B.S. me about what I needed. Make sure you tell them what you want ie. do you want noise from the exhaust or a really quiet system, what do you use the vehicle for, if it gets used regularly on the beach etc.

In my own experience most exhaust systems need replacing when the entire system is visibly knackered or you want a little more power. I went for a 3 inch mandrell bent system with flex joints, however a larger muffler was put on to obviously reduce noise. My turbo was putting out 12psi and the boys from Brisbane Turbos modified my pump to cope with the extra fuel requirements. I had 165 horsies at the rear wheels or 124 kw. I miss the truck as I test drove a 4.2TDI GU yesterday and it was a slug in comparison.

So you can get great performance with the right guy with the right know how. Probably worth a Saturday morning tripping around to different places and having a chat for half an hour with each shopp so you can get a feel for whose spinning a yarn and for those who really know there stuff.

Have fun!

Trol.

I have a 100 series diesel standard cruiser and have just fitted a Dynamic turbo charger kit.

I still have the standard exhaust system and mine put out 86kw on the dyno after the turbo was fitted. The mob who fitted said that I have now got a 45% increase in power over a standard non turbo 1hz.

Craig

Scott,
I also have an 80 series normally aspirated diesel. Got a new exhaust pipe recently. I tried to minimise the bends in it so had it run straight backwards between the chassis rails getting rid of the muffler under the drivers seat. Had the original round muffler replaced with one that was able to be placed a little higher thus reducing the chance of it being bashed (somethig that happens pretty regularly with the original). So now I have only one muffler. Hardly any more noise and certaily no more inside the cabin. There is also a nice free space under the driver's seat for something. Haven't worked out what to put there yet.
As for backpressure it was sugested to me that a lack of backpressure may reduce the pickup from stationary but should be reflected in better acceleration and economy at higher speeds. This may well be the case but not sure if my seat-of-the-pants sensations are sensitive enough to confirm this. Anyway economy has improved a little I think (about 0.5l/100km)
Doesn't need to be mandrel bent unless turboed.
Good luck