Dump Pipe Questions

[bugster70]

I know dump pipes have been done to death before, but I can't seem to find comprehensive answers to the questions floating around my head.

First up, I understand that, for a stock unit anyway, the factory dump pipe on the XR6Ts is very good. That's fine, but to what sort of power level? And, even if you're looking at relatively low power levels, is there any advantage to changing it for an aftermarket item? Let's say we're looking at around the 300rwkw mark (and we can assume that there is already a better/higher flowing cat as part of the overall system).

So, at 300rwkw, do you think it's worth the money changing the dump pipe?

If so, what pros and cons are there for, say, a twin 3 1/2" dump and a single 4" dump? For that matter, why do we have single and twin versions? Is the single only really beneficial when you're talking really big numbers or are there other considerations?

Thanks for your help/advice guys!

[F6 RAPID]

For 300rwkw's, save your money.

[RAPHOON]

Bugster,

Are you planning over 300? If not, you can use the money to greater benefit elsewhere.

[bugster70]

Thanks guys. The answer is no, I'm not planning for over 300 at the treads.

But, purely out of interest then, when DOES it become worthwhile? And what about single vs twin dumps?

[gogo]

hi Bugster!

I would look at it like this - most changes that will make the car breath better - whether they be exhaust or induction will have some benefit, particularly in top end performance - but also with things like fuel economy.

So from this point of view - a better dump such as the smb will enhance performance, however you could probably chase up to in the order of 350rwkw using the standard dump arangement. More than this might be acheivable, but suspect losses will start to become unacceptable...

As to the arrangement - twin versus single - this really probably depends on the wastegate arrangement. If you are retaining the standard turbocharger with the integral wastegate, then you would only be looking at a single larger diameter dump pipe. The dumps like mine that Nizpro make with the seperate waste gate pipe, are mostly done that way to get maximum flow through the physicaly space available.

Key is that the dump arrangement has the capacily to flow both the total volume of gas, and if a twin, the maximum flow rate for wastegate so boost can be controlled, and for the main part of the dump high enough flow so back pressure on the turbo is minimised... The arrangement which acheives these two the best (and fits) will be the best regardless of configuration IMHO

hope that makes sense....

cheers,

Ben.

[bugster70]

Hi Ben! And thanks for the reply mate, comprehensive as usual.

Okay, starting to make sense now. I do recall seeing photos of the turbo off a car, and think I recall the 'output' end (excuse all my technical jargon, won't you ) being just one big opening. I also understand that the 4" SMB dump is perfectly matched to that opening, thus confirming your advice re the single larger opening being best for a stock turbo/wastegate setup.

So then, why would a company like Exotic Exhaust in Brisvegas be offering a twin dump pipe as part of their upgrade for a stock setup (I'm just using them as an example as I rang them asking about this stuff - I'm sure they wouldn't be the only ones)? If what you are saying is true, I would imagine that the vast majority of people would be after a single pipe, not one with a separate wastegate pipe?

Also, is there any truth in the theory that a larger dump allows the turbo to spool up faster, therefore bringing the power on earlier in the rev range?

[boosted_sa]

there would be truth to that, due to the fact that there isn't as much backpressure restricting the turbine from spooling up.

[quigebo]

Hi Ben! And thanks for the reply mate, comprehensive as usual. 

Okay, starting to make sense now. I do recall seeing photos of the turbo off a car, and think I recall the 'output' end (excuse all my technical jargon, won't you    ) being just one big opening. I also understand that the 4" SMB dump is perfectly matched to that opening, thus confirming your advice re the single larger opening being best for a stock turbo/wastegate setup.

So then, why would a company like Exotic Exhaust in Brisvegas be offering a twin dump pipe as part of their upgrade for a stock setup (I'm just using them as an example as I rang them asking about this stuff - I'm sure they wouldn't be the only ones)? If what you are saying is true, I would imagine that the vast majority of people would be after a single pipe, not one with a separate wastegate pipe? 

Also, is there any truth in the theory that a larger dump allows the turbo to spool up faster, therefore bringing the power on earlier in the rev range? 

←

yep spool up is correct if the rest of the system flows good.. like the cat..

ive heard and read that the only diff between single 4" and twin dumps is the 4" has a bit more 'turbine' spool-up noise.. ive got a 4" and it whines when it spools up.. u get used to it

id say any need a custom tune to match..

[gogo]

Bugster -

it is not so much that the single larger system is natively better - it is just that for the space in the falcon, I would think it is easier to get a single, higher flowing pipe through, than two smaller pipes that will flow the same amount. There are also penalties for spliting the flow just as there are for making flow go around a bend, or any other change in direction, shape, crossection etc....

Based on experience with WATER flow (which will have different boundary effects and so behave differently to the compressible flows of cooling exhaust gases) I would expect a single 4" to flow a similar amount to twin 3" pipes... since I think unlikely that you would fit twin 3" pipes through the space, I would expect a single 4" to be a better option for an integral waste gate arrangement...

And yes - a freer flowing exhaust will allow the turbo to spool a little earlier and a little quicker - but the key to this is the back pressure on the turbo resulting from flow through the whole exhaust - the lower the back pressure, the earlier, and greater the pressure drop across the turbine wheel - meaning the greater the amount of work the exhaust gasses are doing earlier...

dump pipe is only one part of this equation (although being closest to the turbo - agruably one of the more important bits or pipe), and I suspect that if you were spending money, CAT would be the No. 1 choice for cash, as I would expect the cat to offer the greatest resistance...

again - hope this helps...

cheers,

Ben.