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Help with compressor maps?
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morghen  



Joined: 21 Jan 2005
Posts: 7871
Location: Romania

PostPosted: Fri Jun 12, 2015 6:50 pm    Post subject: Reply with quote

There is no point in planning to run more than 1.1bar with factory 924 turbo pistons and rings. It seems they wont hold for much abuse above that limit.
Anyway, with those compressors you will heat up the air a lot 4500RPM upwards.

Remember, these plots are just to give you a perspective on compressor efficiency vs what power and boost you want to run...not to tell you if you can actually make that power at those boost levels.

Here are two quick plots of the K26 compressor and below that K27 plot i did for my car, notice how the K26 efficiency drops below 60% at 400CFM, thats roughly 250hp. Also notice how fast that K26 will be spinning to flow that much on the 924 engine. Now compare to how efficient the K27 is at those power levels and how fast it spins...much more relaxed i would say.
So basically, on the 924 turbo engine the K26 will run out of puff at around 220-230hp while the K27 will be most efficient at around 300.
Plot points start at 2000RPM and have 500RPM intervals until 7000RPM

K26 2664 at 1.2bar, 924 turbo engine.



K26 2664 at 1bar, 924 turbo engine.


k27 at 1bar, 924 turbo engine with k26 turbine

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morghen  



Joined: 21 Jan 2005
Posts: 7871
Location: Romania

PostPosted: Fri Jun 12, 2015 7:18 pm    Post subject: Reply with quote

Now to try to link the plots with seat of the pants experience.
I had the K26 before the K27 ofcourse, i remember running 1 bar or even a bit more on the old setup too...after 4000RPM the GO faded away. I remember hearing detonation going on. I had an intercooler calculated by me to be good for @250hp if i remember correctly...but i think the intake temps were quite high.

Now i use the K27 compressor i showed you earlier, it starts to go pretty strong at about 3000RPM and keeps getting stronger.
At 4000RPM its already much more than at 3000RPM and thats where it starts to get dramatic, rear end of the car squats down and engine sound changes completely. The GO never fades away, it pulls harder and harder. I never had the balls to rev it to 7K, the fastest i've been is about 6500RPM in 5th(944S2 gearbox) at night on a highway in Germany ofcourse. It held with a 991 until whatever the speed was..and then i had no more gears and the 991 just walked away

To be mentioned is that my car is an S2, with CGT DITC, so it runs more advance than the normal 924 turbo, and it only backs off the advance if intake temps climb too much.
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 1556
Location: MI

PostPosted: Sat Jun 13, 2015 2:27 am    Post subject: Reply with quote

Morghen I think your k27 map looks the best of them so far, still a lot of room after 1 bar too.. Wish I knew what "standard" k27 compressor that map is for..

Your maps red X axis in CFM correct?

I am not looking for more than 1 Bar really on the stock engine and your maps on the 2664 look much worse than what the garrett calc gave me, yours if probably the more accurate one...

Not to knock anyone else's IC but I feel mine will be quite optimally efficient, fill weld the outside for meat and port the lower charge tube, I'm thinking header wrap from the TB to the sway bar...

I would like to go non-interference with VW flat tops some day..

You think me having low US S1 7.5:1 compression, and non-DITC ignition so I can actually retard my own timing if I want, would be even safer pushing the boost no?

Maybe retard my timing 5-10 degrees before raising boost and then bring it back later if its good?

Isn't the overboost switch 1 bar cutoff? Could I just raise boost untill I bounce off it and then back some and be quite safe with a good IC? Thaught about hooking the overboost switch to the ignition rather than the fuel either to its ground or with a relay in its power, would that be bad for the ignition in any way to cut while its operating?
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Last edited by Fasteddie313 on Sat Jun 13, 2015 2:57 am; edited 1 time in total
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 1556
Location: MI

PostPosted: Sat Jun 13, 2015 2:48 am    Post subject: Reply with quote

In theory couldn't I hook a junkyard hot wire type MAF to my airbox , and to a multimeter in the car, take some runs at different boost levels with a passenger noting the max value on the multimeter, and get a CFM @ atmospheric vs boost@Xrpm calculation out of it in the real world?

Same with an IAT intake air temp sensor?
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morghen  



Joined: 21 Jan 2005
Posts: 7871
Location: Romania

PostPosted: Sat Jun 13, 2015 4:25 am    Post subject: Reply with quote

Many things can be doe, take one at the time.
But dont hook up the boost switch to the ignition.
The fuel will still run and when the spatk is back you will light it up while its exiting the cyls..not what you want.
But i think the switch is set at 1.5bar not at 1...i run 1.1 with no mods.
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Carrera RSR  



Joined: 08 Jan 2010
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Location: Somerset, UK

PostPosted: Thu Sep 27, 2018 5:14 am    Post subject: Reply with quote

Looking forward to installing Ciprian's K27 turbo into my car very soon.....
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