Boost vs. Flow
Boost vs. Flow
I have done a search on this topic and cannot find anything about it or even archived. I am still learning how the whole turbo deal works and I am hoping some of you guys with some experience can help. I have another current post about a setup I am thinking of running and I need some information. Which is more important to a proper turbo setup: Pressure boost or actual flow. I know that a turbo can have actual internal compression, unlike most superchargers, so that when a blower makes boost it is because there is simply a backup of air in the manifold. But I know that air is actually compressed in the turbo, so it can technically be boosted even though there may not be any air in the manifold. Also, I know flow is rated as what enters the compressor, so I assume that the actual air flow leaving the compressor is smaller but under pressure. My question is when selecting a turbo for my car, do I use the info about the flow of the compressor versus what the engine can hold at 100% VE or do I concern myself with boost to emulate compression in the motor. It may also be worth noting that since I am using a mostly stock block KA, I will want a mild setup so I do not need to worry about detonation. So, what do I need to worry more about Boost or Flow?
Re: Boost vs. Flow (Chezedik)
You should worry more about flow. Boost is generally measured at the intake manifold and just shows the relation of how much more air you're pushing in than you would if it was NA. The best way is to get a compressor map for your turbo and find the flow numbers for the engine. That way you can plot out how much flow the turbo can handle in different efficiency ranges. Going by boost is usually misleading unless talking about the same turbo on the same engine. 10psi on a 5L is nowhere near equal to the amount of flow as 10psi on a 2L. The turbo on the 5L will have to push way more air to make the equavilent boost.
4L = 400cfm (made up numbers)14.7 psi = 800cfm on 4L
2L = 200cfm14.7 psi = 400cfm on 4L
So obviously both engines are running the same boost but the 4L needs a way bigger turbo because it's pulling in twice the amount of air.
4L = 400cfm (made up numbers)14.7 psi = 800cfm on 4L
2L = 200cfm14.7 psi = 400cfm on 4L
So obviously both engines are running the same boost but the 4L needs a way bigger turbo because it's pulling in twice the amount of air.
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:: orion ::
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You should worry about the MASS of air entering the motor...so, to relate it to your question...you want flow.
Check out that other thread with "Mustangs_Suck"'s dyno chart...he was moving enough MASS of air to make ~200rwhp. His little T25 needed 7psi to move that much air. My T04E compressor moved the same MASS of air with only ~4.5psi...
This has a lot to do with compressor efficiency.
Hope that helps - Brian
Check out that other thread with "Mustangs_Suck"'s dyno chart...he was moving enough MASS of air to make ~200rwhp. His little T25 needed 7psi to move that much air. My T04E compressor moved the same MASS of air with only ~4.5psi...
This has a lot to do with compressor efficiency.
Hope that helps - Brian
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WDRacing
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Straight T3 with a .48 AR, good for 12-15 psi with no lag problems. But not good for much more then that. So if you stay below 10 psi, get one of those.
The thing about turbo's is this, the compressor maps will only tell you 1/2 of the equation, flow and whatnot is great, but the exhaust side is very important, when it comes down to power production.
A typical T3 exhaust housing with a .48 AR is great for almost instant boost when matched correctly with a good compressor. But the .48 AR is to small to make big numbers without turning into a total heat pump. Now the .63 AR is almost perfect for the KA24. Plenty of flow and almost no lag. This is the exhaust housing that almost everyone ends up with, even if they started with a smallish T3 with a .48 AR.
The best turbo for the KA is definitly the T3/TO4E in 50 trim with a .63 AR exhaust housing. It has very little lag and will flow enough volume for 450WHP or so.
Search around, Like I said in your other post thread. The info is already here. You just need to read through a couple threads to find it.
The answer to your question is you need to worry about boost and flow.
The thing about turbo's is this, the compressor maps will only tell you 1/2 of the equation, flow and whatnot is great, but the exhaust side is very important, when it comes down to power production.
A typical T3 exhaust housing with a .48 AR is great for almost instant boost when matched correctly with a good compressor. But the .48 AR is to small to make big numbers without turning into a total heat pump. Now the .63 AR is almost perfect for the KA24. Plenty of flow and almost no lag. This is the exhaust housing that almost everyone ends up with, even if they started with a smallish T3 with a .48 AR.
The best turbo for the KA is definitly the T3/TO4E in 50 trim with a .63 AR exhaust housing. It has very little lag and will flow enough volume for 450WHP or so.
Search around, Like I said in your other post thread. The info is already here. You just need to read through a couple threads to find it.
The answer to your question is you need to worry about boost and flow.
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:: orion ::
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You don't need to solve for mass...
What you need to do is plot compressor efficiency on a compressor map...and determine turbo choice form there.
But as WD said...it';s been done, over and over and over for the KA...tried and trued.
You want a simple, ~240rwhp setup with no lag? T3 Super 60 with a .63 A/R (has Stage I wheel).
Looking for more power, like ~300rwhp and up? T3/T4 50-trim, .63 A/R (with Stage III wheel).
Mass flow is what's important, and choosing an efficient turbo (proper compressor and trim, plus the matching exhaust side) will get you moving a good mass of air = big power.
- Brian
What you need to do is plot compressor efficiency on a compressor map...and determine turbo choice form there.
But as WD said...it';s been done, over and over and over for the KA...tried and trued.
You want a simple, ~240rwhp setup with no lag? T3 Super 60 with a .63 A/R (has Stage I wheel).
Looking for more power, like ~300rwhp and up? T3/T4 50-trim, .63 A/R (with Stage III wheel).
Mass flow is what's important, and choosing an efficient turbo (proper compressor and trim, plus the matching exhaust side) will get you moving a good mass of air = big power.
- Brian