Interesting dump pipe/ex system size specs for Optimum flow

CETFLY · Post by **CETFLY** » Thu Jul 22, 2010 4:18 pm

Ive been concerned that my bendy dump could be restricting flow at high rpm compared to a smoother 3" bend. Ive been re-reading a lot of Maximum Boost (breaks down in terrific detail how to engineer a turbo engine and complete setup) and the info below the pics is interesting.

Heres mine:

In the book Maximum boost it states that with turbo setups the "dump and exhaust should be approx 10% larger than the turbine outlet diameter."
This is to maintain an exhaust gas velocity 250ft/sec. This should not be exceeded as it has detrimental effects.

My turbine wheel is just over 48mm. Lets call it 48.50mm.
48.50 x 10% = 53.35mm dump and exhaust.
I know that seems tiny - 2.10" dump and exhaust- but for FLOW it should be far greater and allow much more HP and top end, spool up, the works.
Would be interesting to try it actually.

In the book he has a chart with HP verses Pipe diameter needed.
Roughly 300HP (at engine) would be just under 2.25" dump and system.
Sure, as he states, the best system is none at all, but for flow, its more the figures Ive listed above than the 3" pipe we all commonly do (as I have too).

Food for thought.......

Andjeti · Post by **Andjeti** » Thu Jul 22, 2010 4:32 pm

Does the book make mention of Mufflers/Baffles (and or cats). It may just be my mind being absolutely hammered after a week of exams, but wouldn't the addition of a muffler or baffle cause more back-pressure, therefore requiring a larger diameter of pipe to be required to get the same flow up to that point?

EDIT: I found a copy of this book in PDF if anyone is interested

CETFLY · Post by **CETFLY** » Thu Jul 22, 2010 4:42 pm

Hey mate
Youve got there that you've found a pdf version of the book. Have a read of the next few pages, namely page 136 under the heading
"Muffler styles, sizes and numbers"

CETFLY · Post by **CETFLY** » Thu Jul 22, 2010 5:39 pm

I think I'll make up a new, simple dump anyway. Same size as this atm. I have to relocate the O2 sensor anyway as its too far from the turbine. The closer to the manifold the more accurate the readings

BADET-4 · Post by **BADET-4** » Thu Jul 22, 2010 6:00 pm

Andjeti wrote:
EDIT: I found a copy of this book in PDF if anyone is interested

Im interested!!!!!!

Andjeti · Post by **Andjeti** » Thu Jul 22, 2010 6:20 pm

http://uploading.com/files/CSWDZ7CQ/0837601606.rar.html

I found it by doing a google search for the ISBN of the Book.

Panda_ET · Post by **Panda_ET** » Thu Jul 22, 2010 6:57 pm

I wouldnt worry too much about what a book tells you if it works its works, there are so many different views on it all and really unless your willing to test them all back to back its not worth worrying about don't get lost in the magical numbers wes...just remember its magic not reality

Post by **tassuperkart** » Thu Jul 22, 2010 7:35 pm

Couldnt have said it any better myself Panda.
Wes, you have to look at the flowrate increase v's pipe diameter. You cold happily add sharp 90 degree bends to a 3" pipe and NEVER realise it as a restriction on such a pissant motor and turbo.

And adjeti. No you cannot account for and compensate for a restriction further down the system by increasing the flow capacity of a dump pipe, or any othe rpart of the system for that fact.
A restriction is a restriction no matter where it is and in order to realise the potential of a given system you have to view THAT restriction as the limiting factor. Only way to better it is to REMOVE that restriction, not try and increase flow somewhere else.

l8r
E

Andjeti · Post by **Andjeti** » Thu Jul 22, 2010 8:50 pm

Kinda what I figured Tas. But my theory behind it was that say a 3" inlet and outlet muffler would restrict as much as a 2.25" straight through. Meh, I don't know what I mean anymore, need sleep.

Post by **tassuperkart** » Thu Jul 22, 2010 9:33 pm

CETFLY wrote:I think I'll make up a new, simple dump anyway. Same size as this atm. I have to relocate the O2 sensor anyway as its too far from the turbine. The closer to the manifold the more accurate the readings

Actually no. o2 sensors work just fine right at the tip of the tailpipe!.
The distance simply adds a slight dampening effect to the readings which is good and also reduces the temps the sensor tip is subjected to.

Mine is well over 1 meter away. Dont sweat it.

The ONLY changes you need to make are to accomodate your AC pump.
THATS IT!
Dont get too dazzled in science Wes. Its not all that clear cut as it may seem.

L8r
E

CETFLY · Post by **CETFLY** » Thu Jul 22, 2010 10:29 pm

tassuperkart wrote:
CETFLY wrote:I think I'll make up a new, simple dump anyway. Same size as this atm. I have to relocate the O2 sensor anyway as its too far from the turbine. The closer to the manifold the more accurate the readings
Actually no. o2 sensors work just fine right at the tip of the tailpipe!.
The distance simply adds a slight dampening effect to the readings which is good and also reduces the temps the sensor tip is subjected to.

Mine is well over 1 meter away. Dont sweat it.

The ONLY changes you need to make are to accomodate your AC pump.
THATS IT!
Dont get too dazzled in science Wes. Its not all that clear cut as it may seem.

L8r
E

Yeah mate, I realise that, but tell that to an F1 team.
Now, clearly I know our cars arent F1's and are nowhere near it.
However, due to their age and lack of technological refinement etc each and every bit of help really does make a big big difference.
I was on these forums when they very began, back in 1997.
The amount of money we were throwing at the cars hasnt changed. The amount of progress by the older lads like us on here doing things by trial and error and warning/educating/sharing the lessons learned has benefited the entire group by bringing the 1/4 mile times from the 14's well into the 12's and even 11's.
This has only happened by people getting their tuning finer and finer and not putting up with "little things" that people advise you to overlook or not worry about.
All these little things add up to holding you back.
If youve got the chance to do things the best you can, then why not try and do it.
This is where Im coming from and why im trying to get as much of the car as best as I can for the current build

Callumgw · Post by **Callumgw** » Fri Jul 23, 2010 8:04 am

Wes,
I've had rally guys tell me similar things to whats in this book, 15 years ago!
I know there a lot of disagreement. But from personal experience the worse system I've had on turbo car was none.
I had heat wrapped dump pipe on my Starion, it ran for about 4 years like that, then at an event in East Sale the dump pipe failed. By that I mean the metal had crystallised and shattered like glass. You could poke it and it would fall apart like a old shatter front windscreen. Which left me with no dump pipe and 350km to get home.

The car was sluggish and extremely loud. It had much worse performance than standard.

C

Timmzy · Post by **Timmzy** » Fri Jul 23, 2010 1:31 pm

There are some really good points in this discussion for both sides.

The way I view it is like this:

Given the dollar value of our chosen chariots:

- Its a fucking expensive experiment to get wrong so if you can do some basic calculations to get it as close as possible before shelling the $$ its a good thing.
- If you walk into an exhaust shop and ask for a 3inch mandrel bent system they are going to sting you with the "performance" tax
- If you walk into an exhaust shop asking for a 2.5inch press bent "best price for cash" exhaust you may pay less. 2.5inch press bent may have min. diameters of 2.25inch.

The above is not considering mufflers though - and everyone needs one of those to get roadworthy - so in the end mufflers are probably the biggest obstacle to flow anyway.

discuss

Darren.

CETFLY · Post by **CETFLY** » Fri Jul 23, 2010 1:36 pm

Callumgw wrote:Wes,
I've had rally guys tell me similar things to whats in this book, 15 years ago!
I know there a lot of disagreement. But from personal experience the worse system I've had on turbo car was none.
I had heat wrapped dump pipe on my Starion, it ran for about 4 years like that, then at an event in East Sale the dump pipe failed. By that I mean the metal had crystallised and shattered like glass. You could poke it and it would fall apart like a old shatter front windscreen. Which left me with no dump pipe and 350km to get home.

The car was sluggish and extremely loud. It had much worse performance than standard.

C

It mustve been the thinking back then. Ive heard this my entire car-working life. The best exhaust for a turbo is none at all. I still believe that as the turbo is the biggest backpressure/restriction in the system. If that can vent to atmosphere, then it would be in-theory, ideal.
True, this doesnt always work, but think about it. If you had to remove the dump, that means the O2 sensor wouldve been out of the system too. It wouldve been chasing its tail trying to work out the afr's without it.
Ideally for a turbo with no exhaust, would be to mount an open pipe off the side of the turbo with an 02 sensor in there, then have it tuned.

Its a funny thing though.....for me, when the exhaust gets louder or noisier, you feel like youre going slower. When its a very quiet, yet efficient system, it feels to me like Im accelerating much faster.

Callumgw · Post by **Callumgw** » Fri Jul 23, 2010 2:04 pm

CETFLY wrote: that means the O2 sensor wouldve been out of the system too.

Starion is per O2, so doesn't feature...

I suspect there's something like a chimney at play here, that actually helps to draw gasses away. F1 cars still run exhausts and they still run collectors and such, so.....?

C