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I think what we have discovered is that it is smaller, but its exactly the right size. The OEM ones are over sized.
Or something.
Or something.
ian_cupra
Guest
no worries alec, prob wont be fitting it tomorrow, as working, and need to have it running ok for weekend as got a rolling road day and a trackday on
think the oem ones actually get smaller near middle which creates more resistance, where as these jbs ones are same size all way through which are best for the air flow
think the oem ones actually get smaller near middle which creates more resistance, where as these jbs ones are same size all way through which are best for the air flow
OEM is not constant sized or constant geometry. larger initial intake then the port runners change and shrink.
not oversized, its not that simple... internally they choke down severely and where they merge.
ian_cupra
Guest
from what Alec is saying as i read it, there will be less step from cylinder head port to manifold than OE on their JBS mani as the pipe size (although smaller ID) is consistent with the cylinder head port feeding it.
Now whether a 1.25" vs 1.5" pipe size will out perform each other or at all, remains unknown, with no evidence to the contrary.
within the stock mani yes, it changes geometry and also shrinks in cross section severely. tube fitting type mani by nature of it being pieced together with sch pipe and fittings is constant internal geometry. the outlet collector on the pipe version is much deeper and open in the pictures compared to stock, keeping the flow going.
ian_cupra
Guest
ian_cupra
Guest
well i got a rolling road tomorrow, so might go back after its been fitted and see the difference there too
JBS Alec
Guest
Am I correct in saying that if the runner sizes are similar to the exhaust ports, the pressure will not drop when the gas goes into the runners, so the temperature will not drop. Therefore the runners are more likely to be at equal temperatures, leading to less chance of distortion?
You'll get i small amount of pressure drop per unit distance anyway due to friction with the side walls. Obviously this is negligable with small distances!
internal diameter, length, surface finish, temperature of the hot gas stream, changes in section, changes in direction, merge collector chape and design all combine to make for losses & effect on flow.
In the context of the turbo providing the airflow however, the sized to suit comes to play.
you wont find a BT manifold with 1.25" sch fittings for example. Its not a linear relationship between flowrate and frictional losses.... there will be a crossover where 1.25" fitting internal bore will be a restriction to ultimate flow.
much like an R32 throttlebody allowing more airflow for same boost over a stock one. Whether you have enough airflow to benefit from larger is down to turbo size.
In the context of the turbo providing the airflow however, the sized to suit comes to play.
you wont find a BT manifold with 1.25" sch fittings for example. Its not a linear relationship between flowrate and frictional losses.... there will be a crossover where 1.25" fitting internal bore will be a restriction to ultimate flow.
much like an R32 throttlebody allowing more airflow for same boost over a stock one. Whether you have enough airflow to benefit from larger is down to turbo size.
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