333pg333

Went over to the workshop where my car is sitting, still not touched since the crash. Got to talking about this and that with the shop owner, Paul. Currently he has this pretty heavily modified Time Attack Evo in the shop which he's doing a bunch of stuff to. We were looking at it and I commented that it made my car look like a shopping trolley. Apparently it has circa 700hp to all 4 wheels. I'm not sure of the engine spec and what boost it's running but it would be at least 30psi. Paul was fixing the exhaust and noticed that the downpipe was 2.75" and even less where there is a flex joint. The whole exhaust is only 3" after that. It runs a detachable flat bottom and we were looking at my car and exhaust and he suggested that we make a new exhaust that is smaller and ovalised which he felt would serve 2 purposes. Firstly it would make more room underneath and he feels that my current exhaust is potentially too big. Certainly for the current 2.5L motor it's over-kill....but something arrived in the post the other day, and well I wonder if 3" is enough? His take was that no matter the output of the new package, we aren't going to have 700whp and it works on the Evo so why not on mine?

So I guess there is a case of diminishing returns on exhausts. On one hand we are told that the less restriction after the turbo the better, yet if you keep going bigger and bigger aren't you going to eventually lose velocity? So how much is too much? Would I lose something by going back to a 3" exhaust? Would we gain spool or doesn't that get affected by post turbo exhaust? (Note the current exhaust is an SFR creation that is essentially a 3" V-band straight into a 3.5" downpipe running into a 4" oval section and 5" muffler back.) By comparison, not that our motors have been too similar for some time, but Sean's 2.5L motor has always shown power earlier than mine and his is a 3" system. To add to the mix the new package has large equal length 4-1 headers which I think will shift the curve a little to the rhs? Of course the only way of really knowing is doing dyno comparisons. Might even try this. Btw, can you get really flat exhaust tubing? Such as 2" x 6" or whatever would have the equivalent flow of various round tubing? Seems like there would be plenty of calls for this sort of stuff in the Automotive industry?

There also seems to be a trend for building virtual n/a motors and putting turbos on them. People are running 11-13:1 c/r and pumping boost through them for racecars. Seems amazing, especially when most of us are running around on 8:1 but I guess with better control via ECUs etc and fuels such as E85 more options are becoming available. In which case I assume headers and exhausts are becoming more important to forced induction cars also. Pulsing and reversion which seemed virtually undiscussed with old school turbo cars are now topics written about in various forums.

Another thing I'd like to discuss is that of intakes. I know again that there is a school of thought that intakes and heads don't make that much difference with forced induction. Just stuff more in there via boost. But of course everything can have an influence on the outcome of our motors. The thing in the wooden crate has a modified stock intake. It's been extruded honed and had some steps welded in to help balance the runners. However this would seem a compromise. I wish there was more quantifiable results on the LR intake as it's seemed to have had a few question marks raised over it from time to time. Some have suggested that it's really for a race motor as it shifts the torque across to the rhs with it's short runners. Others have hinted that it flows even worse that the stock intake. I discussed the stock intake briefly with the guy that installed the Motec etc on my car and he felt that the factory would have spent a lot of time and money on the stock one and it should by rights be fine. There just seems not to be much info or choice out there on intakes for our cars. SFR has clouds hanging over them too. Hopefully DNovak / Dave puts some of his together and flows them as he mentioned some time ago. It would be great if someone did some back to back tests of the options out there. Unlikely to happen but one can only dream.

DDP

You finally got it?!

333pg333

Yeah. Not sure if we'll install it now or wait to sort out the chassis with the existing low hp motor.
Just to clarify, I'm only using my circumstances as an example. The questions are more of a general nature.

thingo

I think with the exhaust you should try swapping in something a bit smaller and see how it drives, if you notice it on the way to the dyno I think you will have most of the answer. Evos don't go above 3" as there are no gains, I think with our cars there can be gains with kkk turbine housings, but no so much with gt turbos, but the only real way to know is to try it.

Oval tube is not to hard to find, eg mandrel bending solutions or burns stainless.

With the intake I think a bigger throttle body would be an improvement, but you need a new intake for that

blade7

Track or road ?, my brief experiment with barely any silencing on my road car seemed to lose bottom and mid range but came on stronger at high revs, it wasn't optimised for the straight through exhaust though, maybe a bike type exhaust valve would work, restricting dia at low revs/throttle position then opening fully with revs/full throttle ?.

Paulyy

Very interesting Patrick,
if you go on LR website you can see a difference from their 3" to their 4" exhaust but that was done on a k26/8 which we all know suffer from high back pressure, un like our turbos, we have TiAL hot housing which flow the same as a garrett, but the design with that and the wheel has a lot less back pressure so i doubt you would gain much with a larger exhaust.

when i think about exhaust, Dukes 514 rwhp motor, he ran a 4" exhaust, i always wonder if he ran a 3" if there would be a much loss in power.

a guy i know, His VL Turbo (RB30ET) when it was running a T51R on 26psi, it made 470 rwhp with a 3" straight exhaust... Its on LPG

V2Rocket

An oval tube should flow pretty much the same as a round one of equivalent area.

Where a circle is pi*r^2, an oval is pi*r1*r2. A 6x2" oval pipe would be about the same area as a 3.5" round.

I am going to "make" some oval tubing soon to fit in the space I have in my front end for an IC. Basically putting a flat piece of steel on top of a 2.5" pipe and cranking the 12-ton press down...

333pg333

So I assume that no gains for Evos over 3" has been tested Rod? You'd have to think that someone's tried. The reason we are thinking of going down in size is for both clearance and performance. The t-body in that pic is larger and the intake has been modified to fit it.

This is for the track. Not so worried about the noise. This car so far is pretty quiet. Benefit of turbo. Maybe with smaller exhaust it might be louder?

The turbo on the new motor is a Borg Warner E.T.T. S362. I don't know much about it's characteristics. I'm told it's loud on the dyno. This is as close to the specs as I have. Turbocharger Name - S362
Compressor Wheel Part # - 300100-1
Compressor Wheel Inducer - 62mm
Compressor Wheel Exducer - 80.6mm
Compressor Wheel Trim - 54
Turbine Wheel Inducer - 76.3mm
Turbine Wheel Exducer - 67.6mm
Turbine Wheel Trim - 79
Turbine Wheel Part # - 310100-7
Turbine Option - Outlet - V-Band
Turbine Option - Inlet - T3
Turbine Option - A/R - 0.70
Horsepower Rating - 350-680

I wonder if that formula is basically saying if you measured the outside of a e.g. 3" pipe and came up with 10" (Just a guess), would the flow be the same if you flattened that 3" pipe to say 1/2" x 8" wide (again, guess) ? Would the same amount of air pass through it at the same speed under the same force? If so, I would like to consider something like this which might make affixing a flat bottom to the car in the future more viable. This is all theoretical at this point and I'm not thinking of doing this now. Just wondering for the future.

V2Rocket

To get a 1/2" tall pipe with the same area as a 3" it would have to be 18" wide...lol. I would think there would be a point where one dimension gets too small for airflow - starts to develop a corner rather than a curve and airflow gets messy there. Sort of related, but one of the big problems Ford had with the 6.0 Powerstroke diesel engine was the EGR system - early ones (2003, maybe 2004) had a round housing whereas later ones had a square one. Soot and stuff would collect in the corners which would cause the system to fail.

Not to mention the smaller diameter means there would be less space between the laminar/boundary/whatever layers running on the pipe walls.

I would think you could get a 5" wide oval pipe in the stock tunnel. I don't remember how wide it is but there is plenty of clearance around the 3.25-ish inch torque tube. Using the 6x2 vs 3.5" reference from before, to get the same area you could use a 5x2.5" oval tube. That should be about right to get the flat floor...

74goldtarga

Been a while since fluid mechanics but basically an oval pipe with the same cross-sectional area as an round pipe would have lower flow, flow velocity will increase proportional to the distance from the pipe wall roughly. In the oval pipe you are collapsing the walls inward, slightly reducing flow (assuming laminar flow which I realize this is not). Bottom line, I think you'd need a slightly larger cross-sectional area pipe in an oval shape to get flow equal to a round pipe of a given size - the more out of round you get, the bigger the increase in area you'd need with the extreme example being a slit about a mile wide.

333pg333

Ha, well we won't be going a mile wide under there. Hell, perhaps we can get a decent 3" pipe up into the stock exhaust 'groove' that will also give us good clearance. Still wonder if it won't cause backpressure but it doesn't sound like it from other cars.

blown 944

I know I repeatedly measured for exhaust pressure and I didn't see much unless I went absolutely crazy with the boost. I do have a vented wg though, so that will play a huge role. We'll be doing a new exhaust soon with it tied back in in 3.5 @ and I'll measure again to see. I doubt it'll register much.

333pg333

Thanks for that Sid, be definitely interested to know your findings.
What are your thoughts on the intake questions I raised last paragraph-opening post Sid? Is Dave continuing with his or just too busy at the moment?

blown 944

Dave is busy building a shop at the moment. I know because my newly liscensed son has been helping him. I'm sure he'll get some data asap

Dave W.

FYI you can get oval exhaust piping at Vibrant. It cost a little more but it looks like it'll fit better.
http://vibrantperformance.com/catalo...Path=1022_1243