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MG MGB GT V8 Factory Originals Technical - Single or Twin Exhaust?

Hi All,

I'm at the stage of restoration/conversion where I can move the fuel tank to accommodate twin exhausts if required. Problem is...I have already got stainless RV8 headers and a full stainless single system (with single rear muffler) from the BHive. I was wondering if there was a big difference in performance or exhaust note between the two, bearing in mind I probably have to use a balance pipe with the twin system anyway. I know it seems silly changing my mind now, but I'd rather take the pain and do it now if it has huge benefits, rather than trying to do it later after the car is finished.
If the single system puts out more power then I think I can live with a slighly less mouth watering exhaust note..if you know what I mean.


Kind regards,

David Staines

I just have a single on a pretty hot 4.2L. Works good and sounds good. But I marvel at the guys who run dual setups, because they look cool and sound cool but it's just gotta be an *unearthly* amount of work, by the time you move the gas tank, move the wire loom, cut the rear valance, etc.!!! I read somewhere that guru Glen Towery does not advise twin setups, but I don't really understand. It would seem to me that with a dualie setup you'd have less back pressure. All I can say is, if I had an unlimited amount of time and I were 100% sure I'd never crash the car, I'd put in a twin setup.

I have centered my tank and have only run into one problem. That is what mufflers to use. You are limited by space. If you are running chrome bumper heith or lower{I lowered my 67 1 inch} you can not put them under the seats.
I went with 14 inch glass packs on each side of the gas tank with monza tips to soften them up. I then had the mufflers ceramic coated to reduce the heat and I will still put in a heat sheild to protect the tank. I realize its a lot of work but they do look good.

You will find Exhaust is a very personal situation. Some like a soft burbble, Some want noise at WOT, some like it to crackle and roar acrost the RPM range. Even when comparing single or duals to same type of sysem you can get a wide range of sounds.

I have custom 1.5" full length headers, into dual 2.5" exh with no crossover. It is fairly quiet at idle, and roars when I jump on it, but I am not happy with it, I want a deeper stronger tone. MUFLERS make a huge difference. Mine are cheapy turbos, If I drop flowmasters on there It will get more rumbly and impressive. Glasspacks are known to sound "ratty" as they do not offer much sound deadening, but the tips mentioned change that.

Clearance like mentioned is also something to think about.

Go listen to other MG V8's if possible, that will help you decide what you want.
Larry Embrey

I'm in about the same stage of my build...just put up photos & write-up of my tank can see it at
...will be adding more photos & thoughts as the project moves along...I'm keeping a running account of the entire project on the website...&, Glenn is trying to talk me out of the duals but I'm standing pat.......
.........I'm gonna go with RV8 headers & duals hopefully using Flowmasters turned sideways next to tank (if they'll fit) out to dual tips on each pipe...
Tony Barnhill

I'm just curious: what is the reason that Glenn cites for not doing dual exhausts? Is he jealous or something? I just don't get it. I'd have done it if I had significantly more time, skill and courage. First thing all the hot rod guys say to me is, nice installation, too bad you don't have dual exhausts.

A good single exhaust with the same cross-sectional area as a dual exhaust will have less inside surface area than the dual pipes - so should be less restrictive. If you do the math, a 2-1/2 inch dual exhaust works out to be (about) 3-1/2 inch single. A 3 inch dual exh. is about 4-1/4 inch single. That's a lot of tubing hanging under the car, ...and imagine the muffler!

Wayne Pearson

I see where Flowmaster makes a very shallow, oval shaped muffler now, with 3" oval outlet and inlet; these should help with clearance. Shouldn't be too hard to go from round to oval exhaust pipe. I do have Flowmaster mufflers on my pickup, and they made a noticeable difference in drivability. A little louder, but I no longer have to downshift to 4th when climbing a grade on the highway. I'm gonna look into them for my conversion. Joe
Joe Ullman

I've got a single flowmaster under my drivers side floor pan and the thing sounds like a 5 liter mustang with dual exhausts... it's REAL aggressive when you lay down the gas! At idle it has that nice dual exhaust v8 burble, but it's only 1 single pipe! Everywhere I go heads turn when they hear it because it sounds SO powerful!

I'll be driving over to the V8 convention in Grand Rapids next weekend so people can hear it there.


<<You will find Exhaust is a very personal situation. Some like a soft burbble, Some want noise at WOT, some like it to crackle and roar acrost the RPM range. Even when comparing single or duals to same type of sysem you can get a wide range of sounds.>>

I'm with Larry. It's a personal touch and highly subjective as to what sounds good. Some want a nice tone and some want loud. I think the exhaust tone of an Austin Healey 3000 is about as sweet as it gets. Can I get my MGB V8 to sound like that? I doubt it.

Flowmasters do what their name implies, but I have never been a fan of the tone. I have dual 3" double chamber Flowmasters on my '68 Camaro. The cold-rolled steel Cherry Bomb header mufflers sounded much better.

The round turbo muffler on my MG sounds raspy when you stand on the gas. You know, like those annoying slammed Hondas. Back to the muffler shop for me. If it takes duals to get it to sound right, then I may have to bite the bullet. I prefer stealth mode, though.

I'll be listening in Grand Rapids.

I have a dual system using Streetmaster mufflers, because I wanted a quiet system. Noise is fun once in a while, but not for hours at a time or in every day driving. If it was a weekend car, well, it might be a little louder.

Moving the gas tank to center is not all that difficult, takes about an hour to drop the tank, do the measuring, cut a chunk out of the trunk floor & bolt it up. What takes time is making a proper repair of the original hole.

I shielded the gas line with some high temp insulating sleeve & relocated the line somewhat, but did not move the sender. It has been fine with over a years driving and over 30,000 miles. Brake lines were also moved slightly with no problems. The Street Rod guys figure that if you have 1 1/2" clearance, you are OK & that seems right to me, except I would want more room at the collector. By the time the exhaust gasses get to the rear of the car, they have cooled significantly.

Thanks everybody,

I should have realised before posting this thread that everybody's taste would be different, it has helped me nonetheless.

My four cylinder had a very loud exhaust and when I had it fitted originally (about ten years ago), the receipt from the muffler shop said 'muffler fitted at owners request, exceeds legal limit - 96dB'. I can certainly vouch for the noise level, over a ten hour drive with the top down, I would be numb with noise fatigue.

For the V8 I'm leaning towards the single system with single muffler at the back as it's cheaper and also if I don't get on with this project the Earth will have run out of fossil fuels by the time it's finished.

Thanks again,

David Staines

Quite honestly puting in your own is not rocket science. If you know how to weld, then you can do it yourself is you want a simple system.

If you want one that curves and follows teh contour of the bottom of the car then it is a pain, but if you want a nice simple straight tube system, then do it yourself.

Begining of Feb I had never touched welder, by end of month I was done, headers and all. My collectors are under my feet, with 2 straight 2.5" tubes back to mufflers under my seats. If you still have a shop do it make sure they put in what YOU want for the price quoted, I have seen my sahe of hack exh jobs, my truck included..

Check my site, I have side side shots of my exh.
Larry Embrey

OH, just for some more info, I only spent around $520 for my system and that include $350 for the welder.

$100 for two used sets of full length truck headers off Ebay
$20 for 20ft of 2.5" alum exh tubing
$17.99/ea for some cheap turbo mufflers
$10-15 for misc clamps and mounts

Larry Embrey

Does anyone know a source for the "chambered pipe" that used to be sold by Walker? This was used on some GM muscle cars and the side-pipes on the early Corvettes.
I had planned to use the pipe on my conversion but I'm told it is no longer available.

Phil look at they even have one that they say will replace 5.0 mustang mufflers.

Steve Nightingale

I bought some several years ago from JC Whitney

Larry Diede

I have duals exiting on the same side. Stock gas tank position. I dout that there is much of a performance issue, one way or another. If you like the even rythem of the V8 (duals are slightly odd sounding at idle) put a balence pipe in.

Has anyone used oval exhaust pipe? I've seen it for sale but I've never heard of anyone using it. Any odd back pressure issues?

Yobi mentions that a balance pipe will smooth out the sound of the V8. Is there any other good reason for using a balance pipe? The MG Owners Club Supersports MGBV8 uses twin pipes with no balance.
Mike Howlett

Some say that the cross-over allows both exhaust 'pipes' to be used by both cylinders increasing the flow capacity, thereby decreasing the resistance to flow (and therefore is less restrictive), increasing the top-end (high rpm) power that the engine can deliver.....Others say that the cross-over somehow allows the energy pulse of one cylinder to reach the other, thereby increasing the low-end (low rpm) power which the engine can develop....

...proper placement of the cross-over (or "H" pipe) pipe is to paint the exhaust pipes from collector back about 2 feet...then, drive the car until the pipes are hot enough to burn the paint off (it'll burn an almost perfect circle around the diameter of the pipe)...weld the pipe where the paint is burned....

...I'm going with an "X" pipe can buyy them...what they do is "X" the exhaust ppes so the right goes out the left side of the car, etc...better balancing I'm told plus it eliminates the gurgle of a V8 & gives a more solid sound
Tony Barnhill

This thread was discussed between 08/08/2002 and 14/08/2002

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