Oval/Flat Exhaust Systems and Mufflers

[toyo-al]

Hi guys,

I've been doing a bit of reading into designs and fabrication of oval/flat exhausts, not dissimilar to those used in certain forms of motorsport, etc where space is a restriction.

I currently have a 3" exhaust system in my TA22 from the turbo back to the diff, where it is reduced down to 2.5" over the diff and out the rear. Because of the lack of room (mainly under the gearbox cross-member) the exhaust sits quite low, and to get my car engineered required the front of the car to be raised enough to clear the minimum 100mm of clearance from the lowest point of the car to the ground. The rear of the car is sitting exactly where I want it, though the front needs to be lowered as it's destroying the geometry of the front suspension (can fit 2 fists between the guard and the top of the tyre... Not a good look haha).

With the suspension height as-is, the 100mm rule is satisfied, but the muffler just behind the gearbox cross-member scrapes on everything from driveways to speed bumps and the diff taps the exhaust over most bumps.

The following is a list of modifications in the pipeline will most likely effect what I do with the exhaust in some way or form:
- Fit 15" SSR Long Champs and suitable tyre
- A coil over conversion in the front; lower the height around 2"

Taking into account the planned mods, without reducing the exhaust down to 2.5" and raising my car, I feel a good option is to scope of a oval or flat type exhaust system.

Has anyone on here done this or seen the results of it? Has anyone got any pointers, experience, stories, etc relating to such a system?

I've seen it used on side-exiting exhausts, race cars, etc.. But never seen it on a street car.

Buying the bends and straights seems cheap enough to me. Would love to give it a go!

Cheers,
Al

[LeeRoy]

I had a bit of pipe made for this purpose but haven't used it yet. Just got a 2 1/2" pipe and cut it down the middle, spread it apart, then put a strip of flat steel down the guts. You need to work out the cross sectional area of the 3" pipe and then see how wide it needs to be for the smaller pipe.

a 3" pipe has a cross sectional area of 4536mm2
a 2.5" pipe has a cross sectional area of 3216mm2
a 2" pipe has across sectional area of 2042mm2

To retain the same cross sectional area as a 3" pipe a;
2.5" would need to be widened by 50.25mm
2" would need to be widened by 63mm

Hope that helps.

[Valkyrie]

Why don't you just run 3" to 2 x 2.25" the length of your car? You could even merge the 2 x 2.25" after the diff into a 3" if required/wanted. This just seems a lot easier to me.

I'm looking at this due to ripple strip damage to my current exhaust.

[toyo-al]

Thanks for the numbers LeeRoy, appreciate it! I know you can buy lengths of similar stuff (cut and welded with flat top and bottom) for a decent price. And I'm sure I've seen bends too, which would help me over the diff!

The thought of dual 2.25" has crossed my mind also, though I still need to get mufflers in there somewhere to quieten it down. I could even go dual 2.25" with a flat/oval muffler design on each pipe after the gearbox cross-member. Then merge after the diff at the rear muffler. On that note, what sized muffler are TA22 guys using. There's not much room to play with, and I don't like/need really loud exhausts for my daily. Currently the muffler is on an angle to actually fit up under the car! I don't like this..

[Valkyrie]

This is under my TA22 with a 2.5" mandrel bent system. I only have a Genie 2.5" muffler after the diff. There is no tailshaft in the picture, so I don't know if the exhaust could go higher. Looking at the picture, I think even 2x2.25" may not even be enough to lower your car to the height you desire You'd lose a little flow with 2x2", but that might be enough to get the nose down?

[88cameron88]

we can put a smaller muffler at the back man to make it not on an angle but it will obviously make the car a bit louder then it is now, we went a muffler that big to get you through your noise test. do remember if we put a tri flow or chambered muffler in it???

[toyo-al]

we can put a smaller muffler at the back man to make it not on an angle but it will obviously make the car a bit louder then it is now, we went a muffler that big to get you through your noise test. do remember if we put a tri flow or chambered muffler in it???

I think (hope) it was a chambered muffler, though I don't remember seeing it written anywhere. I'll grab the receipt out when I'm home next!

Here are a few links:
Dr. Gas Exhaust - Oval Tubing, Oval Tubes, Oval Bends
BoomTubes.Com - Boom Tube Exhaust, Flat Exhaust, Stock Car Boom Tube
BoomTubes.Com - Boom Tube Exhaust, Flat Exhaust, Stock Car Boom Tube
BoomTubes.Com - Boom Tube Exhaust, Flat Exhaust, Stock Car Boom Tube

This one might help solve the gearbox cross-member issue:
Frame Clearance Sections

I know why the muffler is angled like that, but with this next exhaust system I'm hoping to rectify it I think my best bet is the run 2.5 into 3" OR 3" off the turbo, then at the bottom of the dump pipe merge it into a boom tube/flat tube with either 2 (flat) mufflers here or 1 (flat) here and one after the diff. I don't know whether to try and squeeze the 2.5" or 3" equivalent flat tube over the diff. I'm currently running with 2.5" over the diff with a 2.5" muffler - this is said to increase mid-range torque, which is good considering it'll be mainly street driven and it's only a 1.8L so needs all the torque it can get!

This will all be behind a hi-flowed CT26 turbo, so it's not going to be making full boost as early as the wee little CT20

I'll try and get some pics of the system, might still have some from when it was up on the lift at your work Cameron. It can't come up any closer to the body or the gearbox cross-member, and was always going to be tight over the diff, though having a live rear end means can't go under it (with any reasonable ground clearance).

Cheers guys!

[toyo-al]

This build thread here pretty much details the exact system I am keen on making. Similar concepts anyway!

Audi sport quattro - Page 5 - Mitsubishi Lancer Register Forum

[mattysshop]

few options spring to mind, just wanted to see if any apply..

first - fabricate a new cross member to accomodate a larger system?

b - for the diff - can you go under?? the height you want at the back - using turned down seirra or similar shocks that won't extend to let the diff hang on the exhaust

3 - why do you have to run 3"? example 2.5" system on sr20 with a GT30 just to name one that springs to mind - can't remember a power figure, but it's pretty stout! in a datto 1600, it has a section welded into the crossmember for the system to tuck in (pretty sure it was an off the shelf cross member from datsport).. and also who is making the exhaust?? here is something that they can learn from.. or you could just bring it up here and have Craig at Extreme do one

Project 510 - 1972 Datsun 1600, SR20DET Conversion - Under Construction - Page 6 - fullBOOST

check the exhaust Craig did on this (have a look through the pages for pictures)

lastley - assuming XX engine with a CT26 won't be infront of a T series diff - can you tastefully modify the over diff section to allow more room? or is modifying the car out of the question?

[JustenGT8]

Check out the spintech site, lots of low profile options there.

I have a few of their mufflers in the shed....well made. no idea how well they actually muffle as yet

[toyo-al]

few options spring to mind, just wanted to see if any apply..

first - fabricate a new cross member to accomodate a larger system?

A new cross-member is a last resort. I'd rather try the flat tube under (or even over if there's room) it. It's already got a section for the exhaust, though I'm sure it would have been 1.25" or similar with the ol' single cam 2t

b - for the diff - can you go under?? the height you want at the back - using turned down seirra or similar shocks that won't extend to let the diff hang on the exhaust

I've seen pictures of systems that go under the centre of the live rear axle - it looks to be too low (<100mm) for legality reasons and I generally don't like the look of it hanging down like that. I think over the diff is my only option for the rear.

3 - why do you have to run 3"? example 2.5" system on sr20 with a GT30 just to name one that springs to mind - can't remember a power figure, but it's pretty stout! in a datto 1600, it has a section welded into the crossmember for the system to tuck in (pretty sure it was an off the shelf cross member from datsport).. and also who is making the exhaust?? here is something that they can learn from.. or you could just bring it up here and have Craig at Extreme do one

Project 510 - 1972 Datsun 1600, SR20DET Conversion - Under Construction - Page 6 - fullBOOST

check the exhaust Craig did on this (have a look through the pages for pictures)

That 1600 looks amazing. The pipe work there is very nicely/tastefully done. I'm guessing work like that does come at a high price though!?

lastley - assuming XX engine with a CT26 won't be infront of a T series diff - can you tastefully modify the over diff section to allow more room? or is modifying the car out of the question?

The little T series is still back there at the moment. I'm still deciding on which diff to put back there when the time comes to upgrade it. There really isn't much room over the diff, and it's hitting the exhaust on big bumps already..

I stumbled across pics of Toyman's TA22 (I think it was his..) which had a 3" system that was tucked up so neatly that you can hardly see it from a profile view. I'll have to ask where he got that done.
**EDIT** Looks like his gearbox cross member is different to mine (no cut out to allow the exhaust to go under), allowing the exhaust to sit above the cross member:
rear on truck.JPG
exhaust 005 (2).jpg
Looks so tidy!!

Thanks for the heads-up Justen - had a quick look over their items and already have a mental shopping list going

[mattysshop]

work like that is part of Extreme Custom Engineering's every day quality, and it's not as expensive as you think more than half the cost of that exhaust was in the matarials..

did the dash, tank, cooler piping, air box, dump pipe, exhaust, just to name a few things on that car..