Compressor Maps and Surge Limit - Ford Mustang Forums : Mustang Forum
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post #1 of 3 Old 10-23-2007, 01:41 AM Thread Starter
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Compressor Maps and Surge Limit

Ok so I've been trying to learn a lot about turbos ever since coming here and seeing the Quicktime kit. I pretty much have the idea of most of the stuff down except for the compressor maps/surge limit.

I plotted my "points" on a compressor map to a T76 turbo and came out with great efficiency at ~10psi from around 4500-6000rpm which I'm thinking will be my operating range. It stays on the right side of the surge line till around 2500rpm and lower, and I imagine I would be cruising the freeway at around 1500-2000rpm.

So my question is do I have to be on the right side of the surge line at all times even though I won't be into boost at that RPM?

Also I think a T76 seems a bit on the big side for what kind of numbers I'm looking to run (ie stock block 302, ~500 or less) but I decided on the T76 purely from the efficiency range of the turbo and where I am wanting to run it. Would it be better to go with a smaller turbo even though the efficiency range isn't as good.



If info is needed on my combo, I can add that too. As of right now my numbers are 290hp 315ft-lbs.

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post #2 of 3 Old 10-23-2007, 08:53 AM
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This link helped. There are compressor maps in here for about every turbo.

I would say that yes a t76 is to big for what you are wanting. I would say a 60mm or 66mm turbo would be about what you want.

Last edited by fred50stang; 10-23-2007 at 08:55 AM.
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post #3 of 3 Old 10-23-2007, 08:30 PM Thread Starter
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Yes that is the site I was reading before I asked my question, it was a big help and thanks.

But here, I'll show you what was looking at. I can't post the graphs and plot points on here because I haven't been here long enough to post URLs. But this is based off of 5.0L air consumption table and at 10psi (1.68PR)

3400rpm 65%
4000rpm 70%
4500rpm 78%
5000rpm 78%
5500rpm 78%
6000rpm 78%

3400rpm 74%
4000rpm 76%
4500rpm 74%
5000rpm 74%
5500rpm 72%
6000rpm 70%

This is assuming that I am making 10psi from 3400rpm on. With the T76 I'm basically right at the surge limit at that point But at 4500, where I am making my peak torque numbers it is in the 78% efficiency area and continues there all the way through till 6000rpm.

With the T66 I start out at 74% efficiency at 3400rpm and peak at 76% at 4000rpm and gradually drop from there to 70% at 6000rpm

Now that I compare the 2 side by side I see that the T66 is probably a better choice, since I was thinking I was going to have to purposely make the T76 lag till I got to a certain RPM because of the surge limit, but with the T66 I can have it fully spooled to 10psi before 3000rpm I would guess.
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