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silly question about muffler versus straight stack

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NE1

02-21-2007 21:07:25

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Kind of a silly question, but need to know the truth. You see some more modern tractors with a chrome stack. For example an IH 1066, with factory turbo. I"ve heard you can"t put a straight stack on a diesel with naturally aspirated engine, only on those with a turbo, because it will be louder than those with a turbo and you also need some back pressure. Is this true?

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bcPA

02-22-2007 19:44:57

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Re: silly question about muffler versus straight s in reply to NE1, 02-21-2007 21:07:25

My 855 cu in cummins lost the muffler and I put on a st pipe the neighbor found on the highway. I went to kansas city and when I got back to ne pa I could not wait to buy and install a muffler. In the 70 and eighties many macks did not have mufflers from the factory. These were the ones with the mack engines.

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02-22-2007 17:31:32

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Re: silly question about muffler versus straight s in reply to NE1, 02-21-2007 21:07:25

KEEP IT STOCK.

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matthies

02-22-2007 10:21:10

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Re: silly question about muffler versus straight s in reply to NE1, 02-21-2007 21:07:25

Engines also run cooler with a straight pipe cause of less resistance. Of course they had the screw turned on the pump.

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ken in texas

02-22-2007 07:51:18

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Re: silly question about muffler versus straight s in reply to NE1, 02-21-2007 21:07:25

my 4020 jd with turbo and 1370 case with turbo ,both were quiet enough without mufflers.

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NEsota

02-22-2007 07:37:43

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Re: silly question about muffler versus straight s in reply to NE1, 02-21-2007 21:07:25

Hendrik or anyone else, "IMHO back pressure", what is it please?

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Allan In NE

02-22-2007 07:55:48

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Re: silly question about muffler versus straight s in reply to NEsota, 02-22-2007 07:37:43

In My Humble Opinion.

Allan

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Hendrik

02-22-2007 12:31:11

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Re: silly question about muffler versus straight s in reply to Allan In NE, 02-22-2007 07:55:48

Thanks, Allan, for answering this question for me ;-)

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Fixerupper

02-22-2007 06:37:10

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Re: silly question about muffler versus straight s in reply to NE1, 02-21-2007 21:07:25

Back in the 70's I had a neighbor who always took the muffler off his John Deeres and stuck a straight pipe on them because he liked to listen to them, not because he thought he was getting more power. He once did a dyno test on his 4520 with a muffler and then with a straight pipe and he gained one horsepower with the pipe. Then there's the old time IH mechanic who claimed all 806's needed a straight pipe because the factory muffler strangled them. My answer to that is, why would the factory spend hundreds of thousands of dollars developing and perfecting an engine and then strangle it with a 20 dollar muffler? I tend to think they are smarter than that.Jim

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nickg

02-22-2007 06:24:50

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Re: silly question about muffler versus straight s in reply to NE1, 02-21-2007 21:07:25

I am not sure how new tractors your talking about, but I know that alot of newer tractors only look like they have straight pipes. for whaat ever reason some of the companies are putting the muffler under the hood.

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Hendrik

02-21-2007 23:46:10

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Re: silly question about muffler versus straight s in reply to NE1, 02-21-2007 21:07:25

KB and Vegas pretty well summed it up. IMHO back pressure is only beneficial to carbureted two stroke engines (with ports rather than valves). Other opinions on this?
My 2c, Hendrik

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B-maniac

02-22-2007 14:32:01

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Re: silly question about muffler versus straight s in reply to Hendrik, 02-21-2007 23:46:10

You are right about the 2 stroke thing but only to a point. That point being that the only back pressure that is of any bennefit is PROPERLY TIMED back pressure. This is why a 2 stroke uses a tuned expansion chamber instead of a muffler to achieve max hp and torque. Exhaust pulses bounce back and forth to provide scavenging when needed and back pressure when needed. Diesel..no need. Gas engines(4 stroke) don't need back pressure , BUT they do need the fuel mixture richened up to make up for no back pressure or they will run lean and we all know what that does to an angine.Run hot,burn pistons,and valves and less power. Tuned headers actually "draw" the exhaust out in a timed manner which is even better than 0 back pressure BUT only if you add fuel at the other end.

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K.B.-826

02-21-2007 21:52:15

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Re: silly question about muffler versus straight s in reply to NE1, 02-21-2007 21:07:25

All backpressure does for a diesel engine is rob power. A diesel engine textbook I have states that for an average heavy-duty diesel engine, a 2 psi increase in backpressure will cause a loss of 4 horsepower. As far as noise goes, a naturally asperated diesel with a straightpipe under load is just too loud for a person to tolerate for more than a few minutes without some sort of ear protection. The noise level of most smaller turbocharged diesels when straightpiped is pretty reasonable. The spinning turbine cancels out the harsh sound impulses. IH had a straightpipe on the 1206 from the factory, and the muffler was replaced with a straightpipe on the thousands of tractors that had M&W turbo kits installed. Larger turbocharged diesels have quite a bit of "bark" when straightpiped, which is why the guys who have to run them in the field 10 hours a day prefer to have a muffler, but they are still noticably quieter than a natually asperated straightpiped engine.

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las vegas

02-21-2007 21:28:32

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Re: silly question about muffler versus straight s in reply to NE1, 02-21-2007 21:07:25

as far as the backpressure thing goes, it"s a joke. Backpressure is only a damper to limit the horsepower. Now as for the noise, i would think the TURBO would be noisier????? ??

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Don-Wi

02-22-2007 00:04:00

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Re: silly question about muffler versus straight s in reply to las vegas, 02-21-2007 21:28:32

We had to run a straight pipe on our 1855 Oliver for a week or 2 before I could fix the manifold, and I really couldn't tell the difference once the pipe put it above my head. Kinda temped to go back to a straight pipe some time if the muffler ever rots out.

With a straight pipe it may have a little extra bark, but not much...

Donovan from Wisconsin

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Ken Macfarlane

02-22-2007 12:55:28

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Re: silly question about muffler versus straight s in reply to Don-Wi, 02-22-2007 00:04:00

On a non turbo diesel the backpressure plays almost no role in power and it only affects the very top end of your dyno chart. BTW it would be a heck of an exhaust to cause 2 psi backpressure.

On a turbo'ed diesel the backpressure plays a bigger role as it can reduce the peak intake pressure which really can affect hp.

The reason exhaust backpressure has such little effect on naturally aspirated engines is there is such an excess of pressure in the cylinder when the exhaust valve opens, say 100 psi vs the 14.7 psi atmosphere, if the backpressure causes 16.7 psi, it is still gonna scavenge the cylinder quite well.

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