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Boost and octane

 
Old 12-11-2001, 09:08 PM
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86944turbo
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Post Boost and octane

I noticed that a lot of 944 turbo owners are using significant amounts of boost. For those that run more than 13 lbs. of boost. I have a couple of questions:
1) What type of fuel and octane do you use?
Along with the boost you use.
2) Since some turbos (some K-27's too) are not able to hold boost at higher RPM's. What is your boost at redline?
3) What is your redline?
I'm asking this 'cause with the octane in pump fuel dropping, the only "safe" solution that I've found is racing fuel. Thank You
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Old 12-11-2001, 10:13 PM
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DanD
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I run 15-18psi. Usually 91 octane unless I want to drive to Manteca. (is that where you're getting your racing gas?). However, I'm running a stock k26 turbo, and for some reason I'm not having a problem with pinging/knocking. (not that I'm complaining). I do drop off at higher RPMs to about 13psi. I suspect that as I move to a larger turbo I'll have to bump up the fuel pressure and possibly injectors to keep things from imploding.
My choice in a maxed machine would be water-alcohol injection. "Other makes" are running up to 30-40psi with a healthy dose of mist. Ours should be able to take more than 20psi with the correct mix.
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Old 12-11-2001, 10:19 PM
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Paul Bloomberg
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I have a 2.5ltr and have run 19-20psi for the last year or more. I have ran 100(at the pump) or 110 octane exclusively since modifying the car. I believe the o-ringed head may help. It's a weekend driver. I my pwr band is 4500-6500 or so.
Have you ran your 3.1ltr monster on a dynojet?RWHP?
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Old 12-11-2001, 10:22 PM
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Luke
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I run 15lbs on stock chips. (93 octane)
and @ around 5900rpm i am holding 14-15lbs.

With a stock k26/6 (pretty sure its original too)
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Old 12-11-2001, 11:06 PM
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adrial
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15psi autothority stage 2 chips...
usually run 93 or 94 octane
I still have the stock gauge, so I really haven't been able to see how much boost falls off..
I used to think I got full boost at 3500...this may still be true...but at about 3200-3300 I get full boost on the gauge...I -feel- full boost at about 3500rpm.

Rev limiter is I believe 6800rpm, but I never take it past 6k (purposely), no reason to on the street...all the power is below there.

Another solution for you may be Toluene...search the archives (on the 924/944 list I believe) and you'll find plenty of info. I think toluene has an octane rating of 105 or higher...a gallon or two per tank should get your octane rating high enough.
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Old 12-12-2001, 02:19 AM
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Toulene is 114 octane. So it will take 2 gallons per 18 gallons to get 91 pump to 93.3. Trick is to find cheap toulene in bulk.
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Old 12-12-2001, 11:14 AM
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Russ Murphy
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Wow! These are all pretty signifigant boost levels on (mostly) pump gas. I read something pretty interesting here(I hope I get this right)SDS Tech Pages. It seems like the way to big gains might be using octane to run these high boost levels and advance timing.
I doubt that other makes running 30-40 psi have anywhere near optimal (32-35 degree)
timing at peak boost and rpm. Whad'ya think?
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Old 12-12-2001, 11:18 AM
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I had similar questions in the past and found the octane requirements for a given boost is quite high. Here are the requirements

Boost Octane
12 99.01
13 100.16
14 101.3
15 102.44
16 103.59
17 104.73
18 105.87

These values represent the requirement for ZERO detonation. I run 17 psi with a k27 and I mix 1/3 tank of 93 with a 2/3 tank of 110.
If you are running lower octane than the figures listed for a given boost you are detonating for sure ! and will eventually result in reduced reliability. At redline I am about 16 psi.

Good luck
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Old 12-12-2001, 01:28 PM
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Russ Murphy
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Those values represent zero detenation at what advance? All our cars have timing values
retarded at peak boost from the maximum advance. Boost related retard is the primary
detonation preventing strategy employed by the(any) engine management system. That's the problem with piling-on more boost. The hp gains of denser charge are offset by the fact that the controlled burn of the cylinder firing is taking place after the best leverage is availible on the crank. It would be neat to see some dyno results trading advance with boost.
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Old 12-12-2001, 08:22 PM
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Paul Bloomberg
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Turboguy where did you get the chart? Was it based on the 951? It seems that the requirements for 1 bar (14.7psi)are high as is the whole chart. What is the stock boost level for 951/952's? I thought that one of the main concerns when running more boost is making sure that you have a proper a/f ratio.
I really didn't think that I was running that much boost 19-20psi(compared to some) for 100-110 octane with the rest of the bolt on stuff that you should have so you don't lean out.(K27#8,3 bar reg.,exhaust,o-ringed head,ect..)I hope this doesn't jinx my head gasket!
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Old 12-12-2001, 09:07 PM
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adrial
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Stock boost is I believe about 11.5psi or thereabouts...So according to that chart Porsche should have recommended 98octane

Is it possible that chart is measuring octane/fuel in RON rather than the US standard?

--Adrial
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Old 12-12-2001, 09:50 PM
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This motor has not been on a rear whell dyno. My 2.5L was and recorded 392 H/P. On the engine dyno it recorded 434 H/P. I use Sunoco GT-Plus 104 octane, unleaded. It is rated for use in up to 14.5:1 compression. Realizing that the 20 lbs. of boost that I've recorded is closer to a 20:1 compression ratio, I asked the engine builder if the secret to preventing detonation was in the timing of the motor. He said, yes, timing is reduced to prevent detonation. Mine is in the order of 23-24 degrees BTDC @ 6400 RPM. In addition, the J&E pistons have some anti-detonation properties built into them. Interesting that one of the main ingredients in the fuel I use is Toulene (or so I'm told). It stanks. If I'm at a stop light and have a motorcycle behind me, the rider usually is either shaking his head or opening the visor and caughing, squinting, etc. But I'm told of 951 turbos back east running 26 lbs. of boost using this stuff w/o detonation. I have run 20 lb. of boost right up to redline, 6980 RPM. Another key in preventing dettonation is plenty of fuel at the higher boost. The downloads I pull show .83 Lambda at 240kpa @6800 RPM. The higher the RPM, the richer the mixture, as well as with higher boost. The west coast distributor of this is in Oakdale CA.; Paul Oil Co., they deliver.
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Old 12-12-2001, 09:58 PM
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Running, 93 Octane, with:
Stage II chips
LR wastegate
LR stage I intercooler
Kokeln intake.

Best boost is between 3000-5800, holding 14 psi, droping a bit after that. I've got the manual controller a bit lower until after the holidays; new head, turbo, injectors, and chips.

In relation to the fuel and timing advance and retard, has anyone been on the dyno and changed the rotary switch settings on the DME?
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Old 12-13-2001, 11:30 AM
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Paul the chart is based off of calculations from a software program named "TurboCalc" and is based on our 951 engine parameters. The only fudge factor that I assumed was a engine VE volumetric efficiency value of 80% all other inputs are accurate ie bore, stroke, boost, displacement, compression ratio, etc...Ski I have changed my DME switch setting to 1 ie + 3% fuel.
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Old 12-13-2001, 03:42 PM
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Russ Murphy
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Ski,
No dyno time, but I've done some extended 3rd gear pulls on a 1k 6% grade and the 2nd DME switch setting of +%5-%7 seemed to be significantly stronger at my measly 13psi
with stock software.
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