Muffler back pressure.

Fernando Mendes · Post by **Fernando Mendes** » Sun Aug 31, 2008 10:18 am

"The muffler is designed for straight through exhaust to MINIMIZE BACK PRESSURE".Would like to see an explain about this.Thanks.

dr deuce · Post by **dr deuce** » Sun Aug 31, 2008 11:00 am

Back pressure puts stress/pressure on the manifold to head gaskets causing them to want to blow out. Same with the inter-manifold gasket.

Karoshi · Post by **Karoshi** » Sun Aug 31, 2008 11:51 am

Exhaust "Back Pressure" can be a bad thing. On the exhaust stroke the burnt gas needs to escape as quickly as possible to purge the cylinder ready for the next intake of gas/air mix, on the down stroke of the piston.

A poorly designed exhaust that prevents a quick scavenge, impeeds refil gas and hence lowers power output.

Many modern engines have duel exhaust valves to ensure that the burnt gas is moved away in good time.

However Exhaust systems do not have to be of the "straight thro" type to efficient. Pipe diameter, length, number of bends, gas tempertaure etc all have to be considered in design.

SpookyDad · Post by **SpookyDad** » Sun Aug 31, 2008 12:07 pm

The German vehicle I am converting to has the exhaust at the rear. Would extending the pipe all the way to the back, increase or decrease the exhaust pressure?

Neil

Karoshi · Post by **Karoshi** » Sun Aug 31, 2008 12:41 pm

Same size pipe would increase back pressure, in reality a couple of meters isnt gonna make a difference, that you'd notice. Remember the exhaust system is designed for the worst condition. At less than full rpm and not hauling a full load there is plenty of spare capacity.

Fernando Mendes · Post by **Fernando Mendes** » Sun Aug 31, 2008 1:05 pm

Karoshi and Dr. Deuce what kind of damage in my engine Continental can be occurred for example:"my Jeep Willys MB 1942 was with its number 4 cylinder exhaust valve not opening.Its tappet wasn't touching the valve stem,than it didn't open.

Karoshi · Post by **Karoshi** » Sun Aug 31, 2008 1:20 pm

Little would have happened to the "lower end" of the engine, but you will need to check out the "top end" to see it the push rod is worn or bent , or if the rocker arm is worn or damaged, or even if the rocker shaft is worn.

Is the "tappet" bucket free to move up and down with the camshaft lobe ? For this you will have to take the Side Chest plates off, to enable you to see.

Fernando Mendes · Post by **Fernando Mendes** » Sun Aug 31, 2008 2:13 pm

.The Continental Go Devil L-4head don't have rocker arm..Yes,the tappet clearance was more or less 1".Do you think that the cylinder head gasket can be damaged and the oil pan gasket?

Karoshi · Post by **Karoshi** » Sun Aug 31, 2008 2:16 pm

Ah yes of course, side valve. Wasnt thinking, being a CCKW forum !!

The only way you're going to solve this mystery is to get in there and have a look.

dr deuce · Post by **dr deuce** » Sun Aug 31, 2008 5:20 pm

You really can't have 1" clearance with a flathead engine unless:

The valve is stuck open
The cam lobe is worn off
The valve stem is broken off
etc

Fernando Mendes · Post by **Fernando Mendes** » Mon Sep 01, 2008 12:30 pm

Dr.Deuce the tappet adjusting screw(only this) was all turned in clockwise.Now it is already turned in counterclockwise(clearance 0.014" cold) and I can see this tappet working well in valve stem.I can see this valve opening normally.Did you understand?I think that my mechanic forgot(didn't see) to adjust only this exhaust valve.Thanks for your help.

The GMC CCKW

Muffler back pressure.

Muffler back pressure.

Kind of damage can be occured.

Damages.

Tappet adjusting screw.