fuel /boost query

[Alan L]

I've just fitted a zork to my stock 930 engine - which I only use on track.
Stock turbo (3LDZ).
My boost has raised from 0.8 to 0.95 with the zork (the car feels awesome).
I dont want to melt down. Stock IC.
Am I safe to run the 0.95, or should I go back to 0.8. I can use av gas, will this help.
Should I run av gas at 0.8 for better luck.
If I ran 0.95 should I knock timing back. I'm at 26 deg, and stock dizzy.
I'm quite happy to dial it back to 0.8, I've been running at this no problem on pump gas (98 here which I think is around your 93).
Any suggestions.
Basically, if I can tweek a bit more with out loss of engine safety, I'll take it.
If I am pushing the margins, I'll go back to where I was. But the Zork stays. Definitely.
Thanks
Alan

[DDDD]

Aviation fuel has a different specific gravity. My understanding is that you would use a wide band O2 sensor and check all your AFRs with the aviation fuel since it will simply require a slightly richer (?) adjustment than regular gas, after which you are good to go and the extra octane is good for track use.

Timing adjustments I don't know about.

People run 1 bar all the time on normal gas but with aviation fuel it is even safer if tuned right.

I am curious about aviation fuel as well.

[Alan L]

I have AFR and digiWUR, so tweeking fuel is not a problem.
But I really dont understand enough about octane/antiknock/timing to make a guess on this stuff. I have read plenty on this forum that fairly goes over my head on that subject.
Av Gas is about 120 octane as far as I know, but is also slow burning as far as I know.
(And used in low compression air cooled engines). So, how this all relates to running higher boost safely, I'm not sure. I presume higher octane = higher anti knock = less detonation = allows more boost. But slower burning = less power?
I'm lost here.
Alan

[DDDD]

I read something about that and can't remember. I think you might be able to advance your timing actually to compensate for slower burn. I don't think it has to be less power, it just is not MORE power. People assume octane makes more power but really it retards your burn and allows you to run more boost.

Anybody???

[RarlyL8]

Octane facilitates power by allowing additional timing and/or compression before the onset of detonation.
Generally speaking the higher the octane the hotter the burn. Too high of an octane rating for your application is detrimental.
Given the heat produced by racing, which promotes detonation, I would back off to 0.8bar and run 91 octane fuel. This combination should give the correct burn rate and burn temperature for longevity while being below the detonation barrier.
Having a stock intercooler is a significant handicap.
Racers need to chime in here as this type of tuning on a 930 is beyond my scope. 930Rocket?

[Alan L]

OK. Thats what I am going to do for now.
Back to my previous settings. Until I get a better idea of where to go.
So, running avgas with my standard settings may also be detrimental?
Brian, the zork is great.
Regards
Alan

[Ronnie's.930]

Regarding avgas - I won't be able to find the post, but I am almost certain that in a previous avgas thread, Goran (BeepBeep) said that the lead in avgas will quickly destroy oxygen sensors . . .

[356-930]

A former street-rod racer chiming in.

I respectfully disagree with the premise, “the higher the octane the hotter the burn.”

Octane rating does not relate to the energy content (ability to produce heat) of fuel. It is only a measure of the fuel's tendency to burn in a controlled manner, rather than exploding in an uncontrolled manner.

Indeed, today’s racing fuels, some rated up to 130 octane and compounded to inhibit flame front propagation, would not be appropriate for an air cooled 930. However, 100/130 avgas as sold in NZ and the US would serve to assure longevity of the reported stock 930 if the engine were tuned with this fuel at factory specified timing.

Because of the high cylinder head temperatures associated with sustained boost on the track, detonation has to be a major concern and if a bump in detonation insurance can be achieved through 100/130 avgas use, I believe it's a good thing.

On the downside, tetra-ethyl lead (ah, the good-old-days of Ethyl) in avgas will eat an oxy sensor in short order.

And, if a racing sanction body permits such modification, I suggest use of water/methanol injection. Yes, this scheme can be used to get more power through aggressive timing. However, IMO, for a track car, Not a good idea. With timing left alone, it provides a means of reducing intake air temperature and thus lower combustion/cylinder head temperatures.

If someone is willing to spend the $100 for a set of specifications for avgas and motorgas so we could all know the true differences, they are available from ASTM International www.astm.org as:
D910-07a, Standard Specification for Aviation Gasolines
D4814-09, Standard Specification for Automotive Spark-Ignition Engine Fuel

[Alan L]

Our track air temp will be very cold (winter here - hailed today). Air temp will probably be around 50F.
I presume that is helpful to an engine on full boost - keeping the charge cooler?
I have dialled the wgate back as far as I can - removed all shims that were in there. Hopefully that will get me around 0.85- 0.9 bar.
My lesser spring gave me 0.7. I took it out.
I read somewhere recently that factory boost was actually 0.85, not 0.80.
Alan

[beepbeep]

Stock 930 euro boost was 0.7 bar, as far as I know. Adjusting boost by changing springs is very cumbersone, just install the softest spring you got (for example one that gives you 0.7 bar with zork) and you can gain whatever additional boost you want by bleeding the wastegate pressure line (by any means you fancy: adjustable knob, EBC etc.)

Regarding boost, 0.9 is somewhat OK on stock 930 intercooler as long as you have good quality fuel and ambient temp isn't too high. Some people run up to 1.0 bar on stock engine but you run into diminishing returns above 0.8-0.9 bar: you just produce bore boost and more heat, power doesn't climb linearly to it. Running more power means increased risk of shattered piston rings. YMMV.

I recommend installing 0.7 bar spring and then adjusting it upwards with bleed to whatever you find comfortable (I believe 0.85 would be prudent on track, if AFR's are in check).

Regarding AV-gas, it's leaded. It destroy WBO2 in couple of hours. It's also somewhat hard to come by (at least here). So I would stay away from running it.

Regarding octane: higher octane doesn't necessarily mean it burns quicker or slower or hotter or anything. It just mean it won't detonate as easy as lower-octane product. 104 octane E85 will for example burn cooler, and combust quicker (for certain loads). Nitro will burn slower etc.

If you want more power and reliability, I recommend using bigger and more efficient turbo and bigger intercooler. It will allow you more power with same amount of boost by virtue of higher efficiency = lower intake temps = more oxygen = more power.

Regards,

[Alan L]

I have a spare WG, so have shimmed the 0.7 spring as far as I can, and will use that if need be. Must say, the extra oomph is pretty addictive. Glad I took the EBC out of the car. I think we would have come apart long ago.
Thanks
Alan

[Alan L]

Hi Goran, our posts crossed.
Thanks.
I have to have the car finished tonight- commitments - so am taking two WGs.
Yes the AFR supplier mentioned high lead fuel no good. Avgas common here - 5 mins down road. As much as you want. Smells great.
I am running 98 pump gas, unleaded. I think that is about 93 US.
Regards
Alan

[RarlyL8]

Burn temperatures are a characteristic of the cocktail providing increased octane. That is why I said "generally speaking". Any alcohol blend will lower head temperatures while something like nitro methane has the capacity to melt an aluminum head.

[beepbeep]

Well if AV-gas is easy to come by, then it's probably a good alternative. In case you shose to run on AV-gas, I recommend doing a quick run with WBO2 just to make sure AFR's are OK, then removing it.

Here is info on Bosch LSU4 sensor lifespan vs. lead content:

http://wbo2.com/lsu/lsu4.htm

AvGas 100LL has 0.56 g/l Pb, suggesting a sensor life of 200 hours

[RarlyL8]

Interesting topic as race applications test the limits normally not seen in a steet car.
One of the Pelicanite engineers should do some calculations to see what octane rating you actually need for your setup. It would be wasted money on expensive avgas if typical 91 or 93 octane fuel will work for your application.
If the car is only tracked occasionally and needs more octane than standard fuel you could also look into blending your own fuel by adding the appropriate amount of toluene to the gas you currently use. No lead issues there. The feasibility of that depends on what octane level you need. Running too much touene is not good either as it burns hot. Alcohols burn cool but are hard on the CIS components due to their corrosive nature and hydrophilic tendancies.

[Thierry25]

Originally Posted by Alan L

I've just fitted a zork to my stock 930 engine - which I only use on track.
Stock turbo (3LDZ).
My boost has raised from 0.8 to 0.95 with the zork (the car feels awesome).
I dont want to melt down. Stock IC.
Am I safe to run the 0.95, or should I go back to 0.8. I can use av gas, will this help.
Should I run av gas at 0.8 for better luck.
If I ran 0.95 should I knock timing back. I'm at 26 deg, and stock dizzy.
I'm quite happy to dial it back to 0.8, I've been running at this no problem on pump gas (98 here which I think is around your 93).
Any suggestions.
Basically, if I can tweek a bit more with out loss of engine safety, I'll take it.
If I am pushing the margins, I'll go back to where I was. But the Zork stays. Definitely.
Thanks
Alan

Hello Alan

There is an important part of the equation that you do not mentionned.... what camshafts do you use ?

So far it is not the same thing to run 0.9 bar with stock cams ( small air filling) than to run the same pressure (0.9) with racing cams and opened ports ( high air filling) !

Personnaly, with stock ports and CIS , I think the 0.95 bar is still safe with stock , SC or 964 cams since it is still away from the knocking... as you have the tools to adjust the right AFR , there is no problem.

[drmatera]

av gas is typically called "low-lead", I ran it in my turbocharged mustang for well over a year with no sensor damage or degraded metering. Atleast it is here in the USA, not sure what you guys consider av gas over there.. Here it's generally 100 -101 octane

[911st]

I was told by a major tuner to always run some race fuel on the track as 930's like to eat a piston on the track.

Thus, I would run the best safe gas you can find, keep boost at .8 bar and check your AFR's.

Your stock turbo will probably run out of efficiency and boost before your AFR's run lean but you never know and they should be verified.

However, cool can pack a lot of air in a motor and CIS dose not adjust for this very well automatically so again, check AFR's and I would want in the low 11's to 1 at TQ and HP peaks.

I would short shift at 6000rpm and not over do it until you get a more efficient turbo and inter-cooler.

I am also a big believer checking the balance of the fuel head at the injectors and would never run a 930 on the track unless I felt good about it.

If staying at .8 bar the timing is not an issue. Heat and AFR's are.

It might be worth picking up a copy of Bruce Anderson's book on modifying Porsche's as he has a good section on the limitations and what should be done to run a 930 on the track. Many push past his recommendations these days but his info is well thought out and well tested.

Just my two cents.

[Thierry25]

Originally Posted by 911st

I was told by a major tuner to always run some race fuel on the track as 930's like to eat a piston on the track.

Thus, I would run the best safe gas you can find, keep boost at .8 bar and check your AFR's.

Your stock turbo will probably run out of efficiency and boost before your AFR's run lean but you never know and they should be verified.

However, cool can pack a lot of air in a motor and CIS dose not adjust for this very well automatically so again, check AFR's and I would want in the low 11's to 1 at TQ and HP peaks.

I would short shift at 6000rpm and not over do it until you get a more efficient turbo and inter-cooler.

I am also a big believer checking the balance of the fuel head at the injectors and would never run a 930 on the track unless I felt good about it.

If staying at .8 bar the timing is not an issue. Heat and AFR's are.

It might be worth picking up a copy of Bruce Anderson's book on modifying Porsche's as he has a good section on the limitations and what should be done to run a 930 on the track. Many push past his recommendations these days but his info is well thought out and well tested.

Just my two cents.

Keith

His car is 95% close to stock setup..................... this car was designed to be driven at high speed ( higwhay) and during long period.........so far it is much more painfull for the engine than many kinds of tracks which have much shorter duration !!!

Agree to shift at 6000 rpm since the engine is no more efficient at this RPM . Of course , also agree with AFR recommandation.

Just my 2 cents too...

[spuggy]

Originally Posted by beepbeep

Stock 930 euro boost was 0.7 bar, as far as I know.

I've read the 0.7 bar figure several times, and don't know where it comes from. I suspect it may be a minimum figure.

I've run two factory wastegates on my car, both, as far as I know, stock and unmodified; one with a 3DLZ (which the factory spec book says should provide "0.70 to 0.85" bar boost) with factory headers and open pipe post-turbo, the other with GHL headers and a K27/HF and a factory muffler.

Both wastegates regulate boost at 12.5 PSI according to my VDO mechanical gauge, which I calculate as rather more than 0.70 bar.