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MG MGB GT V8 Factory Originals Technical - Dual Exhaust System Input Requested

Gentlemen,
An advanced thank you for this fine BBS and any answers I may receive to the following questions:
If I do not use a crossover pipe on a dual exhaust system, will my idle be any more lumpy than with a crossover? and-----Will there be a significant power loss? Will the system be noisier?
James Johanski

The experts say that the crossover pipe is worth a few bhp, but when you have so many to play with, would you notice? It will make no difference to the sound - that depends on the type of silencers (mufflers) you use. All V8s idle in a lumpy fashion and I don't think a crossover pipe will make one jot of difference. That's my take on the subject.
Mike
Mike Howlett


IMHO, how "lumpy" or smooth your idle is will be determined largely by cam selection. After that, carb/intake selection and carb tuning will have more impact than exhaust.

Will a crossover add power? Without knowing anything at all about your engine or the rest of your exhaust system, I don't think anyone can possibly answer that. There are lots of variables, and all exhaust systems are compromises. My advice would be to build the car without a crossover, test it, and then add a crossover. Then, you can tell us whether it helped on your specific car. If it doesn't help, you can always remove it.
Curtis Jacobson

They do reduce exhaust "droan", that can occur at certain RPMs.
bill jacobson

James:
I built a custom X pipe in my system. Check the article by David Vizard in this link, particularly page 10, where he deals with balance pipes. They do reduce noise and increase power.

http://www.geocities.com/motorcity/track/6992/vizard.html
Phil O

James,

Summit make a very nice universal X pipe set up.

http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM%2D642122&N=700+400304+115&autoview=sku

I have installed it in a few V8 conversions.

Cheers

Pete
Pete Mantell

Rather than make a crossover, why not use the same muffler I did? 2 inlets and 2 outlest. Inside the muffler, both sides can do the crossover thing. It sounds very nice

http://store.summitracing.com/partdetail.asp?autofilter=1&part=MPE%2D11378&N=700+115&autoview=sku is the one I used and it will fit in the same space the rear resonator did. (and it is stainless steel)

Richard
Richard Morris

Richard,
Where did you place the muffler? I looked at the same one and wondered if it would fit vertically beside the tank.
David

Richard's muffler/exhaust can be seen here: http://www.britishv8.org/MG/RichardMorris.htm

Curtis Jacobson

It fits between the tank and leaf spring. It's the right height for the rubber bumper, but when I get the chrome bumper on the back, I may raise it up a little.
I intially had the V8 running into just the MGB rear resonator, but it was too restrictive. I was a little suprised that this muffler is more quiet than the B resonator. Much deeper sound now.
Richard Morris

It would help if you stated what engine you are talking about
Bill Spohn

Bill,
A Rover 3.5 V8.
James Johanski

I have a twin system made as per photo (if the link works).
It sounds great and the cross over pipe stiffens the system considerably, helping to stop the rear silencers from hitting the fuel tank.
http://i138.photobucket.com/albums/q279/davidtetlow/Exhaust001.jpg
Dave
D M Tetlow

Jim, I just put a cross over in last winter, didn't notice and difference in power or sound st idle.

Steve
Steve Carrick

James,
The "lumpiness" factor is determined mainly by the angle between the inlet side and the exhaust side on the camshaft. This is normally refered to as the lobe displacement angle.

A crossover pipe will help noise reduction since both mufflers share the muffling duties instead of just one. I am assuuming here the mufflers are aft of the crossover pipe.

The power and torque values are normally unaffected BUT the range and sometimes the peak location can be changed.

There is an extremely rough rule of thumb which says the greater the distance from the engine the crossover pipe is located the lower down the rev range the torque will occur.
This is , as you can probably imagine , a very broad statement and there are so many other factors coming into play.
Carb (or efi) selection , manifold choice , cam choice , exhaust header type and size, etc etc.

There is also the "dollar factor". This is where someone spends an amount of money on whatever it is and therefore the benfits are there. End of discussion.

Ths suggestion to read all you can of David Vizard is a n excellent one.

Personally I would start there and make your own decision .

Cheers , Pete.
Peter Thomas

James , forgot to add:

The term "Lobe displacement angle" is also known as "Lobe separation angle (LSA)" by some people.

Pete.
Peter Thomas

In an story in one of my street rod mags the way to determine where to put the cross over is to draw a crayon line on the exhaust pipe and run engine. After the system warms up look to see where the crayon stopped melting and install cross over at this point.
Steve

Then I have a natural crossover! I'm pretty sure the side exhaust tips get hot enough to melt crayon.

Jim
Jim Blackwood

This thread was discussed between 06/02/2007 and 27/02/2007

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