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
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]
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!!
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!!
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.
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]
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]
sorry perhaps i was not clear.
thats pressure in the exhaust AFTER the turbo.
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]
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]
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.
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.
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.
Further reading to confirm my points, info from a garrett employee:
http://www.tercelreference.com/tercel_info/turbo_exhaust_theory/turbo_exhaust_theory.html