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Author: Subject: Sizing of Turbo Header Tubes?
Rallye_Mark

posted on 28/2/11 at 02:50 PM Reply With Quote
Sizing of Turbo Header Tubes?

I have just received my flange from the states and going to buy some welding elbows, the ones im looking at are either 42.4mm or 48.3mm OD with a wall thickness of 2.6mm, therefore ID's of 32mm and 40mm respectively.

I have done some calculations for the area of the exhaust port flange, the inner pipe area for both, and the area of the T3 turbo flange. I would like to make the system responsive so I think I need fast flowing gasses but not too small that it will restrict flow. My calculations are below...

Exhaust Port Outlet
1306mm squared

T3 Flange
3303mm squared

48.3mm Pipe
1256mm squared and therefore 4x = 5026mm squared

42.4mm Pipe
804mm squared and therefore 4x = 3216mm squared.

So what would be the best pipe to use, the smaller diameter one has less of a bend radius so can be made smaller which is better, however I do no want it to loose flow or restrict it however it has almost the same area as the T3 flange area. On the other hand the larger pipe has nearly the same area as the Exhaust Port but much larger than the T3 flange so this might cause it to restrict flow.

Any input would be great as I plan to build it shortly.

Cheers Mark

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Bare

posted on 28/2/11 at 06:02 PM Reply With Quote
manifolding

Interjecting a bit of real life info :the venerable Saab cast iron turbo ex manifold,as found on an old Saab 9000, looks to be a compact, unpretentious thing.
Yet it has proven to allow the 2.3 engine to 480 hp.. before.. it becomes a bottleneck to performance.
Don't need to overthink yer design :-)

[Edited on 28/2/11 by Bare]

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Volvorsport

posted on 28/2/11 at 06:20 PM Reply With Quote
the one i built is 38mm ID .

i supose youve had to order all your flanges ? just couldnt get the time to repair the dxf!!





www.dbsmotorsport.co.uk
getting dirty under a bus

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Rallye_Mark

posted on 28/2/11 at 07:39 PM Reply With Quote
quote:
Originally posted by Volvorsport
the one i built is 38mm ID .

i supose youve had to order all your flanges ? just couldnt get the time to repair the dxf!!


Yeah I ordered one from RSII in America and they arrived this morning, the T3 flange looks quite small and doesn't look like it will seal well, but can check next time i work on the car.

After thinking things through i think i'll make a LOG manifold to save on space, means I can have a shorter inlet track to teh intercooler, but will need to wait and see lol.

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Ivan

posted on 28/2/11 at 07:57 PM Reply With Quote
Don't know if I have understood what you are saying properly but if I where designing my exhaust manifold I would get the flange cut to match the head runner as closely as possible then choose the smallest ID pipe that just fits the whole area in the circle so that assuming that the runner is square there is a little overlap on the downstream face of the pipe to flange joint in places - this helps stop reversion so if your cam is slightly on the hot side you have less reversion when boosting.

The above notwithstanding - smaller is better.

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atspeed racing

posted on 1/3/11 at 02:17 PM Reply With Quote
what turbo are you planning to run?

what are your power goals?

here are some dp-engineering in holland have done for volvo engines.

http://www.dp-engineering.nl/EN/products/exhaust_manifolds/dp/volvo/

dependant on your requirements, you may find exhaust gas velocity is far more important, so keep it small and get the turbo wound up. exhaust system diamter, usually 2.5" is sufficient for just over 400bhp. but depends on the cc of the engine. as a rough idea, if the turbo makes 1 bar boost pressure, it should have around 1 bar of exhaust pressure in the exhaust system.

measuring one of the DP manifolds we use for the peugeot TU engines, these measure 42mm OD (unfortunately i cant get an ID measurement, but wall must be a good 1.5-2mm thick) we have one of these manifolds on a 420 whp engine - 1800cc, 35psi boost.

- colin.

[Edited on 1/3/11 by atspeed racing]

[Edited on 1/3/11 by atspeed racing]

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Bare

posted on 1/3/11 at 05:39 PM Reply With Quote
back pressure

Ad hoc testing has found that an a OEM Saab 2.3 ex backpressure can reach tio 45PSI (oem boost is approx 1.4 bar :-)
That seems *somewhat* different than the 1psi ex= 1psi boost ?

Rather than build some poorly conceived item out of pure expediency?
Could you not take a Cast manifold and 'alter/adapt' it to your needs?
Cast Iron ex manifolds Can be reliably brazed (by a genuinely skilled welder :-)
Just a thought.

[Edited on 1/3/11 by Bare]

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atspeed racing

posted on 2/3/11 at 12:33 PM Reply With Quote
sorry perhaps i was not clear.

thats pressure in the exhaust AFTER the turbo.

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coyoteboy

posted on 2/3/11 at 01:27 PM Reply With Quote
Tubby exhaust manifolds tend to be narrower than their NA counterparts I find, and possibly due to the fact that you want to keep a nice, narrow, hot flow of gas - any expansion is cooling and loss of energy that drives the turbine. I know many people who have changed to a stainless, larger bore manifold and found a drop in performance (for several reasons, not least due to heat bleeding into the bay) but rarely a gain. Again, it's fairly well known with 3S-GTE's that the stock cast manifold is good to ~400 (over the stock 200) quite happily - I'd be trying to match the port area quite closely.

colin - with respect I'm finding myself questioning your statement about 1 bar of exhaust pressure - are you suggesting it is optimal to have exhaust pressure after the turbo? All my studies on turbomachinery have suggested it's optimal to have the absolute minimum possible pressure after the turbine. The best exhaust for a turbo is no exhaust, and the best manifold/headers would be about the same as the ports to reduce flow rate changes.

[Edited on 2/3/11 by coyoteboy]

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atspeed racing

posted on 2/3/11 at 05:12 PM Reply With Quote
im only repeating back information from a recent telephone conversation with Owen Developments.

i was always under the impression that you want little to no restriction also, but after after speaking to owens they said to work correctly it needs resistance on both sides of the turbocharger.

it doesnt create much exhaust gas in a system to create pressure, put your hand over the tail pipe at idle rpm... so a bar is not much at all at say 5000rpm.

an open pipe may be better for top end power, but not best for all round performance like is required on a street or track car. even on the dyno when we have run turbo cars with open downpipe on the dyno, with a properly designed system the power gain is minimal, but turbo response is slower.

- colin.

[Edited on 2/3/11 by atspeed racing]

[Edited on 2/3/11 by atspeed racing]

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Rallye_Mark

posted on 3/3/11 at 07:19 PM Reply With Quote
I will be aiming for about 250bhp initially, however I want room to upgrade this so perhaps 300bhp or something like that?

I have a flange cut already to match the head ports so just a case of picking the correct tubing with suitable ID, bend radius and thickness. Whats a good thickness to have on a turbo manifold?

I will be running the standard turbo initally as it can go to 250bhp by upping the boost to about 1bar.

Also due to little room between the engine and chassis rail I think i will construct a type of SPLOG manifold, a basic LOG manifold which has 2 collectors before the turbo flange which gives better flow than the standard LOG style. A splog looks like the following:-




No I need to find a pipe and do some drawings for different bend radius of pipe to make sure it will all go together

Thanks For your replies, Mark.

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coyoteboy

posted on 3/3/11 at 09:59 PM Reply With Quote
quote:
it doesnt create much exhaust gas in a system to create pressure, put your hand over the tail pipe at idle rpm... so a bar is not much at all at say 5000rpm.


Well of course there's pressure with your hand over the pipe, it's a massive restriction so the volumetric flow rate throttled through the hand will generate a high pressure. But when there's just a high-flow exhaust system it should be sweet FA restriction.

quote:

an open pipe may be better for top end power, but not best for all round performance like is required on a street or track car. even on the dyno when we have run turbo cars with open downpipe on the dyno, with a properly designed system the power gain is minimal, but turbo response is slower.




Again, that makes little sense to my experience/understanding of the fluid dynamics going on. On a naturally aspirated car a nicely tuned system will aid gas extraction, but when you drop a turbine in the way you lose the benefits of tuned pipes. Turbine energy extraction increases with the pressure difference across the turbine - the higher the exhaust pressure after the turbine the less energy can be extracted and the slower the turbo will spool. Your comments are counter to everything I know about turbines and turbos!

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coyoteboy

posted on 3/3/11 at 10:05 PM Reply With Quote
Further reading to confirm my points, info from a garrett employee:

http://www.tercelreference.com/tercel_info/turbo_exhaust_theory/turbo_exhaust_theory.html

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