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Turbo Myths

Fredrik_Steen

By Fredrik_Steen
in Forced Induction

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Arttu

Arttu

Posted
Posted

Here goes a pair of very common opposite statements or beliefs:

  • Boost equals power - more boost always means more power.
  • Boost is only measure of restriction - air flow is what makes the power and these have no connection to boost pressure.

While both have good amount of thruth in them they are usually used as overly simplified statements which makes them quite misleading.

  • Like 1
Gixer1460

Gixer1460

Posted
Posted

Could you pls explain the 2nd one as in my experience the first bit is true, in that without restriction or constriction, you can't measure pressure? ie. if a boost pipe blows off the manifold there is no measurable boost although the turbo is still spooled and blowing air. And the second part is confusing as, if two turbo's are run side by side, one flows 600cfm and the other 300cfm, both at a pressure of 1bar, and both fueled correctly for the air volume - which makes more power? I respect your thinking, I just don't understand it this time LOL!

Arttu

Arttu

Posted
Posted
10 hours ago, Gixer1460 said:

Could you pls explain the 2nd one as in my experience the first bit is true, in that without restriction or constriction, you can't measure pressure? ie. if a boost pipe blows off the manifold there is no measurable boost although the turbo is still spooled and blowing air. And the second part is confusing as, if two turbo's are run side by side, one flows 600cfm and the other 300cfm, both at a pressure of 1bar, and both fueled correctly for the air volume - which makes more power? I respect your thinking, I just don't understand it this time LOL!

Ok, let's take a closer look on that.

"Boost is only measure of restriction" Well, sort of true. Boost pressure is result of air flow produced by the turbo and restriction of caused by engine. But while it's true it isn't actually telling anything, just stating the obvious.

Also it's true that the air mass flow is what dictates the power that the engine can produce. But the catch is that you can't increase the air flow indefinitely without adding pressure. The engine shifts roughly its displacement of air volume at every cycle. Sure you can improve that by tuning cams, ports and so on, but even at the best case you will hit the limit somewhere around 110% of displacement. So if you want more air mass flow through the engine you have to increase the pressure. And the engine doesn't care how the pressure at intake has been generated. It just gasps in that volume of air at given pressure. So it doesn't really matter if the turbo producing the air pressure is capable of flowing 300cfm or 600cfm or whatever. As long as the engine demand doesn't exceed capacity of the turbo.

Ok, in reality size of the turbo has some effect on the air flow. A bigger turbo MAY have better efficiency at required pressure / flow point which then results lower intake air temp exhaust back pressure. And those help to get more air flow through the engine at the same boost pressure. But even that can get you only so far. Eventually you just have to increase the pressure to get more flow and power.

  • Like 2
  • 2 weeks later...
Reinhoud

Reinhoud

Posted
Posted
19 hours ago, Wagola said:

ALOOMINUM................that's the one that gets me !>:(

Me too, but I learnt not too long ago that the Americans pronounce it actually pretty close as what aluminium was called whwen it was invented/discovered/made.

  • Like 1
no class

no class

Posted
Posted

… boy… this topic has drifted off course….who gives a fuck about how we all describe shit …. allooominum, aluminium …. lol …. fags = (cigarettes) ( homosexuals) 

  • 2 weeks later...
Joseph

Joseph

Posted
Posted (edited)

Also, maybe everyone knows this page, but i found this the other day, which is on topic of this topic :

http://www.spartgsxrspecials.com/turbo%20do%20and%20dont.htm

Seems interesting for info ?

Edited by Joseph
  • Like 1
Joseph

Joseph

Posted
Posted

Ah damn, i think its a case of copy paste, can't seem to get it to be clickable :(

As for Flats and turbos inded i noted i had never seen any in any setup, whats the theory behind it ? The vacuum system on CVs is mandatory ?

Asking out of technical curiosity

Arttu

Arttu

Posted
Posted
2 hours ago, Joseph said:

Also, maybe everyone knows this page, but i found this the other day, which is on topic of this topic :

http://www.spartgsxrspecials.com/turbo%20do%20and%20dont.htm

Seems interesting for info ?

That looks like good basic info package. There isn't much that I can't agree with. Although the focus seems to be on relatively basic turbo installations on carbed bikes. Not really a fault but good to keep in mind when weighing the advice.

This link should work:

http://www.spartgsxrspecials.com/turbo do and dont.htm

  • Like 1
Gixer1460

Gixer1460

Posted
Posted
22 minutes ago, Joseph said:

As for Flats and turbos indeed i noted i had never seen any in any setup, whats the theory behind it ? The vacuum system on CVs is mandatory ?

Asking out of technical curiosity

Its as simple as air pressure / volume acting on the slides. When under boost, the amount of air passing through the carb is staggering and has considerable force behind it. Trying to close a slide carb against that pressure is nigh on impossible, therefore its almost a engine runaway condition - engine draws air & fuel,  makes boost, more boost = more air etc. With a CV carb the fuel delivery is independent of the throttle blade position and due to the rotary operation its easier to close even with huge air pressure. But pair an HSR42/45/48/50 with a suck through turbo - match made in Heaven!

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