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Has anyone put on a dual exhaust system on a TR7? I saw a TR7 Monza dual exhaust on part shop forum. I have a Falcon single waiting to go on when I get that far, but after seeing the dual system, I wonder if the reduced backflow of duals would be of any help.

Please your comments.

Not really, I just fitted a dual (the TR8 system) on a 16V Sprint for the looks

Is this the sort of thing? http://www.thewedgeshopstore.com/produc ... m-TR7.html

Looks quite nice, but I can't seem to see anywhere in the UK that stocks this.

regards

Graham

That's what I'm looking for.

What did you do; add a Y-Pipe and cross over? Do you have any pictures of underneath? Any improvement in flow-through?

The one from the Wedge Shop is a Monza. I have a Falcon system ready to install when it is time.

Thanks,

Larry

I used a 'y' piece. The better the design, the better the flow. Removing the H piece of a TR8 system would be advisable.

Can't remember the details now (age thing) but I have read that a naturally aspirated engine needs some backpressure to work well. Boy racer large bore exhaust systems often lose power compared to standard ones if they are too large. Turbo engines benefit from reduced backpressure as it allows the turbo to work better. You could just bolt the rear part on for the appearance of a twin tailpipe outlet .

Agreed. You'll lose performance with a modification like that.

John_C wrote:Agreed. You'll lose performance with a modification like that.

Racing engines like old Ford Cosworth DFV V8 have little or no exhaust restriction.

A paraphrased quote from Vizard: "I have heard (more than once) that any conventional 4 cycle engine needs some exhaust back pressure but I have found that reducing back pressure always improves efficiency and performance - timing and fuel mixture being setup to suit.

Waste of money. Reduced back pressure only works up to a point. What does work is a tuned exhaust. How does a tuned exhaust work? There is a pressure wave front that moves from exhaust port down the pipe to the collector where it bounces back to exhaust port and returns. The returning helps scavenge
the next time the exhaust valve opens. The way to get this is equal length pipes from each exhaust. As they (exhaust ports) are in a row and the pipes exit out the rear they have to be shaped like a bowl of spaghetti, not only to clear frame etc. but to maintain their equal length. Even where frame clearance isn't an issue they still have to twist and turn (see F1 exhausts). As they are of constant length they work best at a specific RPM range, that range being dependent on length. For a road going car that uses a wide RPM range they are of limited use. I use the stock resonator to take care of some sound frequencies, a low restriction SS Magnaflo muffler for the rest and a Thrush muffled dual tip (for looks and because it came with the car). I don't use header because of cost but if I did have money to throw at the car would use a tuned SS header.

Fancy tuned headers look nice but.....check this out:

https://www.youtube.com/watch?v=azPKIjxmmdU

Brings up something. I've often read that people have had to dent their headers to clear the frame but a friend had a set from S&S on his converted Sprint engine and they fit fine with no denting. Close but no denting needed. I guess because they are basically hand made there would be differences from one to another, you just have to pay your money and take your chances. Whether makes any difference or not bashed header just doesn't look pretty.

I think if just adding back pressure increased the power of an engine, the Merlin in the Spits, Hurricanes & Mustangs of WW11 fame, along with the hugely powerful Yank radials would have had different exhaust systems other than 6" stubs.

I raced more than a few 4 pot Cosworth engines, & have some real experience of sudden changes to an exhaust.

The exhausts on all these had no back pressure. They were a 4 into 2 in the extractor, which terminated about 6" from the back of the car, & a 2 into one, which was a trombone shape, [like motor bike exhausts] projecting out the back of the car about 18". This trombone was not just easy flow, but a tuned length & shape extractor, helping to scavenge the exhaust gas from the engine.

This trombone 2 into 1 section was easily removable, usually held on by a couple of tension springs. They had to be removed to minimise the length of the car to fit it into a trailer.

These were all Weber carb engines, with tuned length ram type inlet pipes on them. They had absolutely nothing under about 5500 RPM, & still only chicken power before about 6400 RPM, coming on strong at about 6700. They then ran out of puff at around 8000, & many actually cut out at about 8300, due to point bounce destroying the ignition timing & output.

Now the experience. In one race in which I was comfortably leading the formula 2 class, & in front of half the F1s, I had the trombone section of the exhaust fall off. The cars performance changed so dramatically I thought I had a major engine problem, & almost retired. Then I noticed the difference in the exhaust note, not easy with helmet & ear plugs, & kept going.

The thing dropped the lower half of it's power band quite dramatically. It suddenly had nothing below 7200 RPM, but was not effected that I could feel above that. Surprisingly it had more power below 7200 on about 2/3 throttle than full throttle, after loosing the tail pipe. This cost me about a second a lap at the old Sydney Warwick Farm circuit.

The cars owner spent some hours on the dyno experimenting with replacement tail pipes, both straight & sort of trombone shaped. The top end power was down a little, but they could not get near it's previous power on the same dyno in the under 7000 range.

Then fortunately the tail pipe appeared. A spectator had picked up, & finally took it to the race organisers, who returned it to the owner. With it fitted the engine was back to previous performance figures on the dyno.

This brought home how important exhaust extractors, & the shape of that trombone was to these little engines. Every one measured the trombone & some copied it to fit to 1100cc versions of those little Fords as used in Formula Junior. Sadly that shape did not work on the smaller engines. Obviously Cosworth had done a lot of work on those exhausts, matching them to their cam profile, & engine output. The whole thing from inlet ram to tailpipe was a package, not changeable by most people.

Hasbeen

Has anyone tried using chambered exhausts like on the old Corvette side mounted mufflers?

Wow!!! That You Tube video is insane. I've got a 4 into 1 Falcon header and I think I'll go beat on it with a sledge and increase HP.

Hasbeen wrote:I think if just adding back pressure ...

Interesting write up