Jump to content
SAU Community

Recommended Posts

Restriction found...

Why would you run a 3" pipe, at the point where the gasses are their hottest, and most turbulent (IE, when they need the biggest area to flow)?

Drop the dump, and I bet power climbs. Or are you still on the screamer?

Adam told me the dump is fine for 400+. But that will be one of the things ill be changing.

Most of the dumps I've seen for 400+ have been 3.5" - 4"

And the outlet may be 3", but take a look at the big power builds, they all mouth out nearly instantly

Increasing the diameter of the exhaust at any point isnt the magic bullet unfortunately. As soon as you exceed the the most efficient diameter you start to detriment the system. 'The most efficient diameter' is the $64m question though, and obviously pretty variable.

Hot gas is less dense, so the engine doesnt have to work as hard to 'push' it out. Increasing exhaust diameter makes the gas expand quickly, cool quickly, and become dense. Obviously dense air at the beginning of the exhaust process is bad news.. it equals resistance. Think about the reasons for heat-wrapping exhaust headers - it's definitely not meant to protect intake temps.. the hotter the temperature of the exhaust gas, the 'easier' it's expelled. Increasing exhaust diameter too far decreases temperature, and therefore is inefficient.

What you've seen in real life Matt, is probably a system which is close to the most efficient diameter for the dump pipe - but I guess it depends on whether they've tested it side by side with a dump with a smaller diameter (or matching) outlet size to the turbo too! :cool:

Someone correct me if I'm talking shit, this is just my understanding :blink:

Increasing the diameter of the exhaust at any point isnt the magic bullet unfortunately. As soon as you exceed the the most efficient diameter you start to detriment the system. 'The most efficient diameter' is the $64m question though, and obviously pretty variable.

Hot gas is less dense, so the engine doesnt have to work as hard to 'push' it out. Increasing exhaust diameter makes the gas expand quickly, cool quickly, and become dense. Obviously dense air at the beginning of the exhaust process is bad news.. it equals resistance. Think about the reasons for heat-wrapping exhaust headers - it's definitely not meant to protect intake temps.. the hotter the temperature of the exhaust gas, the 'easier' it's expelled. Increasing exhaust diameter too far decreases temperature, and therefore is inefficient.

What you've seen in real life Matt, is probably a system which is close to the most efficient diameter for the dump pipe - but I guess it depends on whether they've tested it side by side with a dump with a smaller diameter (or matching) outlet size to the turbo too! :cool:

Someone correct me if I'm talking shit, this is just my understanding :blink:

You're sort of on the right track, but you also have to consider Bernoulli's theorem, which roughly states that as velocity increases, pressure decreases. (this is the basis behind the lift equation in aircraft etc). The same works in reverse, so if the velocity of the exhaust gasses decreases (due to a sudden increase in pipe diameter) the pressure will increase and impede exhaust flow.

The trick in making a perfect exhaust would be to have the pipe diameter increasing at the same rate as the exhaust is cooling, to keep the flow the same, and hence no pressure change.

Just a thought, heat wrapping your 3 inch dump may be a "band aid" fix to the problem, as you would be retaining more heat in the exhaust, which would keep the flow faster in that section. But the Ideal solution would probably be a nice transition from the 3 inch output of your turbo, to a dump that matches the rest of your exhaust.

The easiest test to find out if the dump/exhaust is being a restriction, is quite simply to drop it.

But can anyone find a car make 400RWKW with a 3" dump? Most I know of from experience run 3.5" - 4" dumps, and then a 3.5" system.

While you're say going to a smaller pipe increases speed, decreases pressure. You also have to know for a fact, that whilst you go really small, the speed of the gas might be super quick, and low pressure in that section, but the section before has been restricted down basically, and it now has a huge pressure build up.

Run too small of a dump, the pressure in the turbo / exhaust manifold starts to build up, and counteract the pressure going INTO the motor.

It's not like I said go and put a 6" dump as from experience, everyone knows that it will become detrimental to the exhaust flow.

Whilst the hotter gas is less dense, it also takes up more area. And that's the big problem, as it's exitting the turbo, exhaust gas can be as hot as 850degrees, by the time it reaches that tail pipe, a mere 200 - 400 degrees.

Half the temperature, half the density... So you need half the area for the cooler gas...

I agree, there is an art to building exhausts, bigger is not always better, but experience tells me, for 400KW, a 3" dump is too small.

no...

simply no, you are wrong

From his list, the only differences to my pos are the 3" dump (3.5), 76mm china cooler (100mm) and obv the 26 head. I'm not sure about simmo but most of the guys I know making over 400rwkw are running 3.5 or 4" drain pipes.

Edited by DCIEVE

i made 430rwkw with a 3" dump

brockas just made nearly 440rwkw with a 3" dump

rr84wa made about 420rwkw with a 3" dump

nattalotto made nearly 470rwkw with a 3" dump

thats a quick list off the top of my head...

dont forgot a shit load of exhaust flow is going through the gate at high rpm!!!

i made 430rwkw with a 3" dump

brockas just made nearly 440rwkw with a 3" dump

rr84wa made about 420rwkw with a 3" dump

nattalotto made nearly 470rwkw with a 3" dump

thats a quick list off the top of my head...

dont forgot a shit load of exhaust flow is going through the gate at high rpm!!!

all running screamers?

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now



  • Similar Content

  • Latest Posts

    • This looks great! Awesome to have the 5 speed with an LSD in this. The Recaro's look like SR2's or SR3's. It's a shame they've been retrimmed as they would have looked sweet in their original colours. I think I'd want my agent to be a little more up front and informative too. I've never imported but I reckon it would make me a little nervous, so the more info the better.
    • Thanks for doing that Duncan! Makes you a good person in my books. We don't get kangaroos or wombats here. But we have bats and it's similar. AFAIK it's often the mums with a baby attached that get hit because they drop lower when starting from a tree. If you hit an animal, check on it. https://www.ifaw.org/au/resources/wildlife-rescue-app An app to get the closest wildlife rescue contact.
    • My dream is also to have a proper hoist, but I don't think it will ever happen. My quickjack is probably as close as I'll ever get, it really is very good though. 
    • Yeah we keep on in the dailies, it is pretty poor how many animals get hit and the driver leaves without checking....have saved a couple of little ones over the years. Bit of a gruesome job though, pouches generally need to be cut open because they are so tight and often the joey doesn't realise mum is gone so they are still locked onto the teat. I checked the modules in front of the DS wheel where an oil cooler should go.... There is the radar unit - that can go for race use) One of the 2 HX water pumps, the silver cylinder. That needs to be kept but might be able to be relocated But the bad news, the big computer mounted vertically in front of the wheel (blocking any potential air exit) is the electric steering computer. That is required until/unless i do a hydraulic steering conversion, and in CAD based modern car design it is not like I can just pop a big unit like that somewhere else (plus the loom would be too short anywhere else too). So, the passenger side is OK to clear out (just use a smaller washer reservoir, potentially elsewhere), but the DS no beuno
    • Well, all the best with the new camry It was interesting to hear about the UK process, it is generally a lot more streamlined here with a shipping agent looking after all the import side (noting the exact final price can still be a surprise.....) and I've used a few different brokers on the japan (or US) side, and never had any trouble with any of them....luck of the draw I guess. You mentioned you didn't get the auction sheet (understandable since you bought it from a dealer, not auction), but I always try and get hold of that because they are pretty thorough. I've imported 2x R grade vehicles over the years and both were fine, repairs in Japan are pretty thorough compared to here in Oz.
×
×
  • Create New...