Quick question about turbo maps

Wesman07

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What happens if you limit boost to say 3-5psi? Most of the time your plots would fall off the map, but you would not be into surge or choke.
 
Sorry i cant realy help you with your turbo question, but i have a quick question for you. What do you gain from advancing your stock cam? And by how many degrees did you advance it?
 
Wesman07":t3ji8wrk said:
What happens if you limit boost to say 3-5psi? Most of the time your plots would fall off the map, but you would not be into surge or choke.
They will still run there with the surge and choke lines extrapolated downward.
Most turbo compressors are not very efficient at those low pressure ratios unless the compressor housing has a larger A/R ratio being .70 or above.
As you can see the power bandwidth is short that low on the map.
A positive displacement supercharger works much better at low boost and will have a much wider rpm power band.
 
So by limiting boost, you could run into the choke zone?

I never even thought to look at the compressor a/r.

I don’t think a super charger is what I want. I’m just doing some homework on general set up. Finding out the limitations is part of that.

Thank you.
 
Wesman07":1nxj5av1 said:
So by limiting boost, you could run into the choke zone?
Yes but it requires an explanation.
A tubocharger manufacturer defines the choke line by the point where efficiency drops below a certain percentage.
Looking at different maps it is typically below 58% to 60%.

Notice the RPM lines that dissect the map and how they turn downward after the center efficiency island.
As you try to maintain the same boost level past the center island the rpm required to do so increases. Thats normal.
When you cross over into the choke zone the compressor effciency drops quickly and the rpm heads for the limit and possible destruction.
At 5 lbs of boost it has further to go to get to the rpm limit and since the compressors pumping efficiency drops off so does the engines exhaust pressure and the engine may simply stall at a certain rpm depending on the engine load.

One thing for sure is as the compressors efficiency drops the outlet air temps rise drastically to the point where boost pressure is more of a matter of expanding air rather than additional air being pumped.

Hope this makes sense
 
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