Exhaust tuning

Bobbieslandy · Postby **Bobbieslandy** » 09 Dec 2010 18:35

Can my 4 into 2 into 1 straight through exhaust with a sports back box have a detrimental effect on performance? if so can the rest of the engine be "tuned" to turn the negative effect of the exhaust into a positive one?

I did use a basic exhaust calculator which recommended a 2" internal dia throughout including the bends. This is what i've got but there was nothing there about length though.

Just getting some ideas together for the spring[:D]

Rob.

Beans · Postby **Beans** » 09 Dec 2010 19:22

Most important on an exhaust system are the primaries they should be equal.
To be more precise the volume of the primaries should be equal.

As an afterthought (and some blasphemy [}:)]) have a look at the CT/Forum/TR7-8, search for Sprint camshaft and Sprint engine advice

<center>

1980 TR7 DHC (my first car, now restored and back on the road)
1981 TR7 FHC Sprint (better known as 't Kreng)
[url="http://www.tr7beans.blogspot.com/"]My Weblog[/url]</center>

Bobbieslandy · Postby **Bobbieslandy** » 09 Dec 2010 19:46

Cheers Beans, the primaries are equal. Well as equal as this shoddily thrown together manifold can be i guess. Actually, looking at it now they don't look equal at all!

richards · Postby **richards** » 10 Dec 2010 09:39

I am not even remotely an exhaust expert but what little I do know is that back pressure can change the torque curve of a car, iff you have too little BP you loose midrange and low down torque but you can achieve higher BHP at the top end ( think drag racing ). maybey you need to consider a different tail box.

Get a lifestyle
Get a TR7!

www.ttr7.co.uk

FI Spyder · Postby **FI Spyder** » 10 Dec 2010 15:23

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Bobbieslandy

Cheers Beans, the primaries are equal. Well as equal as this shoddily thrown together manifold can be i guess. Actually, looking at it now they don't look equal at all!
<hr height="1" noshade id="quote"></blockquote id="quote">

They are pretty staight when compared to S&S's tuned exhaust which has some pretty curved parts to get the volumes equal. The length determines the timing of the pressure fronts which help suck out (have less back pressure to) the exhaust gases at a certain RPM. 4-2-1 exhausts help more in mid range (street) whereas 4-1 exhausts have higher range advantage (racing). The design is not something you do by trying to make it look nice or make it fit easily. Something best left to the professionals. Just look at the spagetti exhausts of F1, you know they've done it right (for their application).

TR7 Spider - 1978 Spitfire - 1976 Spitfire - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra - Yellow TCT

Bobbieslandy · Postby **Bobbieslandy** » 10 Dec 2010 15:35

I wasn't trying to design the exhaust, it was more a case of using what i had available without spending any money! The bag of snakes exhaust of the GT40 springs to mind. I was just wondering if that exhaust on the sprint engine with standard cams + carbs could cause any issues. A different tail pipe is definately on the adgenda, the one i have now sticks out so far you can actually trip up when walking behind the car. The thing is i haven't seen a tailpipe which suits the TR7 more than the single straight pipe, or twin on the V8. All the aftermarket ones seem to be a bit OTT. Pics of any aftermarket back boxes on TR7s would be good!

Rob.

jeffremj · Postby **jeffremj** » 10 Dec 2010 16:33

<blockquote id="quote">quote:<hr height="1" noshade id="quote">A different tail pipe is definately on the adgenda, the one i have now sticks out so far you can actually trip up when walking behind the car.<hr height="1" noshade id="quote"></blockquote id="quote">Which is, IIRC, illegal [:0].<blockquote id="quote">quote:<hr height="1" noshade id="quote">The thing is i haven't seen a tailpipe which suits the TR7 more than the single straight pipe, or twin on the V8.<hr height="1" noshade id="quote"></blockquote id="quote">I used the TR8 system on my 16V. The standard twins look great:

A person with your skill should be able to fabricate a better Y piece than mine. Just make sure the exhaust goes into one before you split it out again. You may lose a bit of power with this option, but not much IME:

FI Spyder · Postby **FI Spyder** » 10 Dec 2010 16:36

The dual pipe a la Monza exhaust is the best I've seen. They have yellow stripes around it and although you can't see it here I've put red stripes atound mine to match the red striping on the Spider. Mine was attached to an oval Thrush muffler which has to be replaced this winter. I'm going to replace it with same sized flow through as I can get using the same chrome tail pipe.

The stock round muffler with plain tail pipe is just too plain jane.

TR7 Spider - 1978 Spitfire - 1976 Spitfire - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra - Yellow TCT

Beans · Postby **Beans** » 10 Dec 2010 18:06

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Bobbieslandy

... I the one i have now sticks out so far you can actually trip up when walking behind the car ... <hr height="1" noshade id="quote"></blockquote id="quote">
Put an American style rear bumper on the car and it will be legal [:D]

<center>

1980 TR7 DHC (my first car, now restored and back on the road)
1981 TR7 FHC Sprint (better known as 't Kreng)
[url="http://www.tr7beans.blogspot.com/"]My Weblog[/url]</center>

Bobbieslandy · Postby **Bobbieslandy** » 12 Dec 2010 08:59

The weird thing about my tail pipe is that it is a standard aftermarket part, i just fabricated the bit between the manifold and the back of the tailpipe. That's an interesting idea, i didn't think to make my own. I'll reuse the backbox but make my own tailpipe as you've done, good idea that!

I do like those american bumpers, especially when colour coded but my money has to go on making it quicker!

Thanks chaps.

Rob.

Bobbieslandy · Postby **Bobbieslandy** » 22 Dec 2010 23:13

Right, i finally got round to making a tail pipe. in hindsight i should of really made a "Y" section but got carried away, besides, it's purely cosmetic anyway..........

A mate's letting me borrow his polishing wheel so i'll give it a good going over at the weekend. My only fear is that the way i've done will cause it to bloody whistle!!! Fingers crossed eh.

Rob.

Marsu · Postby **Marsu** » 23 Dec 2010 02:36

Rob,

I am curious about what affect this tail pipe may have.

It seems a bit of effort for what may be minimal gain.

Thinking about the laminar flow the approach seems analguous to punching a hole in a sail and putting an exhaust vent on the leeward. Not something I've ever seen work.

It seems, to me, that the flow will become more chaotic as it passes the side aperature. This will increase pressure in the preceeding flow, thus increasing back-pressure on the pulse. But it will also slow the flow. I wonder if this is the right place to do this?

Looking at the pics I wonder what difference a tongue from the branch into leading pipe may have made. Could splitting the flow and causing an acceleration may have made a big difference?

Do you know anyone with a flow bench? Or can you put it on the dyno with the old and the new?

Shauniedawn · Postby **Shauniedawn** » 23 Dec 2010 11:15

Hiya Rob.

My question is much more basic!

The pipes seem to be a lot closer together in the final pic than in the one preceeding it - any reason?

And here's a hindsight observation. It might have been easier to polish both individual pipes, and then weld them together, if you see what I mean?

Nice little project [:)]

Shaun

Bobbieslandy · Postby **Bobbieslandy** » 23 Dec 2010 12:11

Marsu,

This will hopefully have NO effect whatsoever! It's purely cosmetic. There was a bit of a tangent on this thread, i was concerned about my free flow exhaust having a negative effect on performance but came to the conclusion it'll probably harm low and middle range performance but help at the higher revs. Something i'm more than happy with.

Shaun,

I didn't have a hole cutter big enough to "fishmouth" the 90 deg bend, i had to use a hacksaw, band saw and file so the end result was less than perfect. Because of this there were large gaps around the join between the straight through pipe and the bend once the pipe had been placed end down on the bench to level everything up. The first pic where the pipes have a gap between them was only because they weren't welded up together and were just loosly assembled. The reason for there not being a gap now is so that the person driving behind can't see how they're joined together[:D]

The polishing wheel is thin enough to go between the pipes so i'll have no probs getting it all shiny.

My first thought about the flow of this tail pipe is that it may cause a venturi effect, sucking air through the branched tail pipe and exhausting it out the other, or that it will whistle! if i notice any of the two then i'll take it off and make another with a "Y" section.

Trust me, it was no effort, it was just some welding practise.

Rob.

Beans · Postby **Beans** » 23 Dec 2010 12:46

Would have been better if you made the end pipe into a "Y"
instead of an "h".
But should look good ones under the car, though doubtful about the effects [;)]
Just make sure it is aligned properly otherwise it will look sloppy [:D]

B.t.w. to show how an exhaust can influence an engine ...

I spoke to a friend, who owns a TR7-V8, a few weeks ago at the start of a navigational rally.
He told me he just made one of the best changes to his car ever.
He ditched the standard twin rear exhaust TR8 set up (the ones that are for sale through the normal TR7 specialists) for a single one.
The engine ran much smoother after that ...

<center>

1980 TR7 DHC (my first car, now restored and back on the road)
1981 TR7 FHC Sprint (better known as 't Kreng)
[url="http://www.tr7beans.blogspot.com/"]My Weblog[/url]</center>

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