Back pressure and our diesels

[jtisdale]

How much back pressure do our diesels really need? Is it possible to have too little back pressure so that the engine will not run properly? Doesn't the waste gate "control" the amt of pressure in the engine. What I am getting at is. . Will taking the muffler and/or resonator off make the engine not run "correctly"? Is it possible to have an exhaust system that flows too freely?

 

[Chipstien]

From what I have learned here on TDR, the less restrictions on the exhaust the better. Besides, if backpressure was an issue than the turbo should cover that problem.

 

[THancock]

The wastegate controls how much pressure enters the engine as boost, not the amount of back pressure in the exhaust. With a turbo stuck right smack in the middle of the exhaust flow, you'll never not have enough back pressure. Back pressure isn't really needed in an engine anyway. The less restriction the better.

 

[K_Arts]

Originally posted by jtisdale

How much back pressure do our diesels really need? Is it possible to have too little back pressure so that the engine will not run properly? Doesn't the waste gate "control" the amt of pressure in the engine. What I am getting at is. . Will taking the muffler and/or resonator off make the engine not run "correctly"? Is it possible to have an exhaust system that flows too freely?

It all depends on elevation. I live at about 5200 feet and backpressure is an issue.



When I put on a full 4 inch exhaust with a straight through muffler, I actually lost power. My turbo took a lot longer to spool up, my EGT's went up and my truck was a dog... . all it did was puff black smoke. Now that I've added around another 100 HP I am fine. Though I am still not impressed. So yes you can have a system that flow's too freely.



In higher altitude you need some back pressure to help the turbo spool up. I can also say that JKloppe here in CO has complained of the same problems that I have... . so I know it is not just my truck.



Hope this helps. .



Kev

 

[Fireman Dave]

Jim,



No high altitude here in the land of 10,000 cheeses. Just open her up! Oo.



You won't regret it!

 

[TREEMAN]

I,d have to agree with K,Arts,I replaced my hy turbo with Piers hx with the stock exhaust still in & noticed very little difference in spool up . I then installed a 4"exhaust & noticed a big difference in spool up. Couldnt handle that ,so off came the exhaust & I put back the 3" downpipe & flared it out to the 4" which helped the lag quite a bit. I,m at sea level by the way.

 

[dthorkelson]

Backpressure

I disagree with K Arts assessment of the backpressure issue. I had my 4" installed at Jardine in Dubois Wy and noticed an immediate improvement in performance a lower exhaust temperatures as well as faster turbo spool up. My EZ is set at tne middle position . By the way, the altitude at Jardine is nearly 9,000 ft. Go for it

 

[Mark_Kendrick]

I'm gonna have to disagree w/ K_arts too. A turbo works on differential pressure. You increase the pressure brefore the turbo and the act of releasing that pressure throught the turbo is what is used to drive the turbine to power the compressor. As the pressure drops energy is released so. . the greater the drop the greater the energy.



At high altitude the air is thinner. Turbos don't reallt work on a PSI scale they work on percentages. If abient pressure is 14psi(near sea level) and boos pressure is 40psi then you are getting a 285% increase in pressure.



If ambient pressure is more like 13psi you will only get 37 psi at the same efficiency. the problem is that at the higher altitude you get less O2 in the intake stream which burns the fuel less efficiently making more smoke and less drive pressure. the lack of drive pressure results in a lower drop across the turbo leaving less energy to drive the turbine.



Granted this is a simple view of the turbo setup but it is essentially correct.



Later,

Mark

 

[K_Arts]

All that I can say is that I did some testing with both systems and the dyno showed a loss of 32 hp with the 4" Jardine exhaust. Boost dropped from 32lb's to about 25-26 lbs of boost and EGT's rose a tad over 200 degrees pre turbo and I lost tons of throttle response.



I then in return spoke to some exhaust shops around town, including Cummins and they all told me the same thing. Less back pressure is better, but you still have to have a certain amount of back pressure. I am actually going to have one of the local exhaust shops make me a 3 1/2" setup once money permits.



After talking to JKloppe at our last meeting, he was complaining about the same things that I complained about. So all I can say is that in our altitude here in Colorado a 4" is really a waste of money. You'd be better off trying out a 3 1/2" pipe, or a less restrictive muffer.



Kev

 

[EShaw]

K_Arts,

It sounds like you've got a leak downstream of your turbo. Could this be possible? Hope this is just a fluke... ... . Everyone should be able to BOMB their Cummins WITHOUT discrimination! Regardless of elevation... ... ... ... ... Oo. :{

Eric

 

[K_Arts]

We did check for leaks and couldn't find any... but of course that doesn't certify that there isn't any.



Before the pipes got warm we did the soap water truck... and everything looked good. Since then the pipes have seemed to seize together, so I beleive everything is ok.



But as I said before, I am not the only person having this problem in our altitude.



Hope this helps. .



Kev

 

[R.ebel]

Backpressure?

I'm at 6000 ft. My finding are completely opposite to K_arts. (Not my intention to flame you K_arts) After installing a Jardine 4" exhaust my egts went down and the turbo spooled noticably faster



Question for K_arts, I find your dyno testing results very interesting, were all the dyno runs performed on the same dyno?



I'm having a tough time trying to understand from a theoretical standpoint how back-pressure can give more power.



Someone please enlighten me.

 

[EShaw]

Boost leak

K_Arts,

I think you have a boost leak... ... . not exhaust leak... ... with the new turbo and the exhaust... ... more boost... ... ... I think you're leaking somewhere and you're not the only one. Other guys out there are not boosting to max potential either... ... ... ... . Good Luck

Eric

 

[K_Arts]

To answer the question about the dyno... yes, the runs were all on the same dyno.



As for the boost leak. I have checked my truck over and over again... and I sure can't find any leaks. After completely plugging the wastegate, I can peg 32 lbs of boost. Whichs sounds pretty reasonable to me.



I have gone through and tightened all of the clamps. I've taken my gauge in and out several times checking it. My turbo is torqued down properly... I dunno what else I can check. .



Kev