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Exhaust pressure extremely different between pipes?

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J

John Fautz

Freshman Member
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I have notice that the exhaust pressure is considerably more from one tail pipe than the other. That can't be right. Do you know what that could be a symptom of? I would think that the rear SU is maybe too lean? It's running great but I know that's not right.
FYI; Apparently my HD SUs require the slow running jets to be turned off when the carb is equip with throttle adjusting screws on the shaft. Who knew... I discovered that information buried in the body copy in a "SU carb tuning tips, etc." manual.
Anyway, if you have any ideas about my exhaust discrepancy issue please rush it to me. I should know this but I don't. I'm on a roll but the exhaust thing concerns me.


Any help would be appreciated,
John

 
John, you have posted in the section for help on the forum itself, not help on cars.
I suggest you re-post in the appropriate car section.
Cheers!
 
THREAD MOVED

John, as Roger said, you have posted in the forum for getting help with navigating the forum. You did not mention in your post what car you are talking about, but I see from your profile you have an Austin Healey 3000 so I'm taking a guess that's the car in question so I have moved your post to the Austin Healey forum. If you are raging this you are in the A-H forum.

Basil
 
The pressure disparity can only be one of two things: a blockage or leak in one of the pipes, or one or more cylinders is not producing as well as the others. My BJ8 had such a disparity, and when I finally did a compression check I found the #2 cylinder had only 60psi. Still, the car ran fine and I put many, many miles on it.
 
This can be normal where dual pipes are used without the benefit of a Ballance pipe also called crossover pipes.

My Damler 250 utilizes one
 
Bob_Spidell said:
The pressure disparity can only be one of two things: a blockage or leak in one of the pipes, or one or more cylinders is not producing as well as the others. My BJ8 had such a disparity, and when I finally did a compression check I found the #2 cylinder had only 60psi. Still, the car ran fine and I put many, many miles on it.
Click to expand...

I agree with Bob. I'd first do a visual inspection of your exhaust system to make sure one of the pipes hasn't been crushed on a speedbump or such. If everything looks good, go to a compression check and make sure all the cylinders are close to equal. If all is good there and depending on the age of your exhaust system, I'd suspect a blockage in your muffler or the rear resonator (saw you had a MK III) that occurred as the interior of the muffler or resonator deteriorated over time.

Keoke said:
This can be normal where dual pipes are used without the benefit of a Ballance pipe also called crossover pipes.

My Damler 250 utilizes one
Click to expand...

I don't see how the lack a of a balance pipe would change the disparity in power output of the two pipes. In the Healey six with a split manifold, each pipe is serviced by three cylinders. If one pipe doesn't have the same output as the other, it stands to reason that the power in one, two or three of those cylinders aren't producing up to snuff or there is an obstruction. Same with a Daimler, except lesser power in one pipe would mean one bank of the V8 is down on power. All the addition of a crossover pipe will do is mask which bank is down on power by more evenly distributing exhaust output.
 
I'm curious, does the muffler co-mingle the output of the two pipes. I think we discussed this some time ago but I forget what the answer was. If the muffler co-mingles the out put of the two pipes then maybe the problem is in the muffler or in the pipes aft of the muffler.
 
vette said:
I'm curious, does the muffler co-mingle the output of the two pipes. I think we discussed this some time ago but I forget what the answer was. If the muffler co-mingles the out put of the two pipes then maybe the problem is in the muffler or in the pipes aft of the muffler.
Click to expand...

The ANSA exhaust my BJ8 used to have had two perforated pipes in both the resonator and the front muffler, both in one housing packed with glass. I hacked in a couple Heartthrob glasspacks for each to replace them when they went south.
 
vette said:
I'm curious, does the muffler co-mingle the output of the two pipes. I think we discussed this some time ago but I forget what the answer was. If the muffler co-mingles the out put of the two pipes then maybe the problem is in the muffler or in the pipes aft of the muffler.
Click to expand...

John has a BJ8, which has an individual muffler and resonator for each pipe, unlike the earlier cars where both pipes go into a single muffler with dual inlets and outlets.
 
Bob_Spidell said:
FWIW, my BJ8 has a balance pipe.
Click to expand...

Good:

Balance / Crossover pipes rely on exhaust expansion to balance the cylinder banks. A small section of tubing in between the main pipes provides an area for gases to expand into during exhaust pulses. Only a small amount of exhaust flows from one stream to the other as both sides push back and forth in the center section., so gains in performance are noticed from low rpm and give the exhaust a deeper, muscle car-like tone.

When you pull in to a Jaguar meet in a Daimler 250, them folks think you got a modified.---LOL
 
"John has a BJ8, which has an individual muffler and resonator for each pipe."

ME TOO!

Cept I did not like the Healey OEM mufflers so I use Volvo P1800 series mufflers, last forever.
 
Slightly off topic but the HDs fitted to Healeys did not have throttle adjusting screws. This often confuses people reading the Burlen instruction manual, which has poor illustrations.
 
DerekJ said:
Slightly off topic but the HDs fitted to Healeys did not have throttle adjusting screws. This often confuses people reading the Burlen instruction manual, which has poor illustrations.
Click to expand...

Technically true, but the HD8s in my BJ8 have screws which open the throttles when the choke is pulled out a bit. I think they're called 'fast idle' screws.
 
Keoke said:
Good:

Balance / Crossover pipes rely on exhaust expansion to balance the cylinder banks. A small section of tubing in between the main pipes provides an area for gases to expand into during exhaust pulses. Only a small amount of exhaust flows from one stream to the other as both sides push back and forth in the center section., so gains in performance are noticed from low rpm and give the exhaust a deeper, muscle car-like tone.

When you pull in to a Jaguar meet in a Daimler 250, them folks think you got a modified.---LOL
Click to expand...
The crossover pipe idea was first used by NASCAR guy Smoky Yunik I believe. He was always doing things for more horsepower and NASCAR had to keep rewriting the Rules to keep,up with him. I hope I got the correct name.
 
Duane_Rhynard said:
Interesting!


https://www.smokeyyunick.com/
Click to expand...

Wow. Gotta respect someone who flew B-17s over Europe in WWII. I've heard that was the riskiest job in the war, at least before P-51s could escort them to Berlin and back. I believe the Brits thought we were crazy for flying in the daytime (Curtis LeMay probably was crazy). Got his book 'Power Secrets' on my bookshelf.

Don't know if it's the crossover pipe or the glasspack mufflers or both, but people sometimes think I have a V8 in my BJ8.
 
Patrick67BJ8 said:
The crossover pipe idea was first used by NASCAR guy Smoky Yunik I believe. He was always doing things for more horsepower and NASCAR had to keep rewriting the Rules to keep,up with him. I hope I got the correct name.
Click to expand...

Smokey was a true automotive genius and came up with all kinds of performance improvements. He was even more of a genius at interpreting the rule book, which some might ungraciously call "cheating". Smokey cheating stories are legendary in NASCAR, but Smokey always denied he cheated, insisting he just did what the rulebook only said what he couldn't do, not what he could do. Here are some of his better interpretations of the rules: https://www.hotrod.com/articles/ctrp-0801-smokey-yunick/
 
Rick, From checking out the "smokeyyunick.com" link above, I then found that same article you referenced. I liked it so much, I shared it with with the Hudson Hornet auction on Bat. I'm coveting that car as well, but I have a feeling that it may bring crazy money.

That article is a great read, and I'm totally in awe of that guy! Dad was a fan of his - and Fireball Roberts - back when NASCAR ran actual cars...

Sorry to get off-topic, but I really enjoyed it.

Jim
 
Jim 58 BN6 said:
Rick, From the "smokeyyunick.com" link above, I found that same article a couple of hours ago. I liked it so much, I shared it with with the Hudson Hornet auction on Bat. I'm coveting that car as well, but I have a feeling that it may bring crazy money.

That article is a great read, and I'm totally in awe of that guy! Dad was a fan of his - and Fireball Roberts - back when NASCAR ran actual cars...

Sorry to get off-topic, but I really enjoyed it.

Jim
Click to expand...

I used to read Smokey's column in Popular Science as a kid. He wrote an autobiography called "The Best ****ed Garage in Town" I'd love to read, but copies are about $350 now. The stories in the Hot Rod article aren't even some of the most famous ones, like filling the empty tubes of the rollbar with fuel to get some more laps out on the track. Supposedly, [FONT=&quot] before the Daytona 500, tech inspectors found a bunch of Smokey's cheats that had to be fixed before his car would pass inspection. In the process, they removed the fuel tank. Frustrated, the inspectors told Yunick to get his car out of there. Yunick climbed into the car, fired the engine, and drove away with the fuel tank still lying on the floor of the garage.

[/FONT]That Hudson on BaT his pretty cool. A guy at our local show has one is similar condition with Twin-H power. Good luck if you bid.
 
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