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Probably is still aplicable for the stock cams / engine designs, like some toyota supra engines which tolerate very high backpressure because of cams designs . For drag / race the ideal i think is around 1:1 , even so if i understood right, eklund's engine for example has lower exhaust pressure than intake.
edit: I don't measure backpressure, as I know no one on this forum actually knows how to measure it correctly, not to mention what it means. I stopped measuring it, when I realised, moving the measuring point by two inches I managed to lower the backpressure by 7 psi.
is written by a very reputable tuner (Repo), i get the point about placement, or the way is ussualy measuring, but how can you get away with even measuring it, ok you may check egt's , but that is not all ? if you bost and you gain power is ok, if not , not ?
I'm not sure there is a difinitive answer to this question?
My tuner has always maintained that some backpressure in the EM helps with early spool up of the turbo. This theory is backed up by Repo. When replacing my knackered EM, he used narrower tubing slightly restricting flow, thus introducing more back pressure. However, restricting that flow has a detrimental affect higher up the power range.
Therefore, how much is needed will no doubt vary by the application it is intended for. This is where it is hoped the knowledge and experience of a good tuner will get it just right.
Andy, for before the turbo, which is the one that matters. You would need to drill and tap a thread in your exhaust manifold, screw in something like a length of brake pipe which is long enough to get rid of the heat and push some rubber hose on the end and connect it to a boost gauge.
My understanding is the manifold wants to be circa 14psi higher than the inlet pressure, any higher creates surge any lower and you wont get boost.
The hot side has always got to be higher than the cold side or the turbo wont be a turbo...
I'm not sure there is a difinitive answer to this question?
My tuner has always maintained that some backpressure in the EM helps with early spool up of the turbo. This theory is backed up by Repo. When replacing my knackered EM, he used narrower tubing slightly restricting flow, thus introducing more back pressure. However, restricting that flow has a detrimental affect higher up the power range.
Therefore, how much is needed will no doubt vary by the application it is intended for. This is where it is hoped the knowledge and experience of a good tuner will get it just right.
I would think the narrower tubing increases the exhaust speed, which will hit the vanes harder and the turbine will accelerate faster. And that this has a downside/secondary negative effect in the increased backpressure, most significant at high boost/rpms.
Leif-Helge
-91 S2 VEMS and Comp Turbo
-12 B** 530XD Touring "S2 parts transporter, and daily driver"
I would think the narrower tubing increases the exhaust speed, which will hit the vanes harder and the turbine will accelerate faster. And that this has a downside/secondary negative effect in the increased backpressure, most significant at high boost/rpms.
It is possible to have a lower turbine drive pressure than compressor outlet pressure. A 110 vw tdi operates in this mode upto 3500 rpm. I no I measured it. Higher turbine pressures than compressor means you turbine wheel is too small or ar too tight. Very important on big diesels as they operate at fill load and need to be efficient.
On our engines a higher turbine than compressor pressure will give better response.
well, the target is 1/1, is there any rule of thumb or something from which you aproximate the bakpressure decrease as you increase a/r ? also how much is cam timing / overlap affects backpressure ?
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