Which race gas to diagnose knock ?

ManBearPig said:

I see some intermittent knock at throttle tip-in and am trying to determine if it's real or false. I've mixed in some vp octanium and saw no change but would like to try some actual race gas as well. I know that certain oxygenated fuels have a different stoich than the standard e10 the car is tuned for. What fuel is best to use when strictly trying to troubleshoot s potential knock? I see ms109 is the most commonly discussed but if I'm not mistaken it really needs a specific tune otherwise the car will lean out.

Thanks

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https://vpracingfuels.com/product/motorsport-109-ms109/

You are mistaken, ms109 is a direct replacement for premium unleaded.

ManBearPig said:

I don't think it's false either. But if it's not from low octane and it's not false....wtf is it from?

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Things are changing rapidly on tip in, when you're on and off throttle quickly. They can pull some timing out on tip in or add fuel.

markmurfie said:

https://vpracingfuels.com/product/motorsport-109-ms109/

You are mistaken, ms109 is a direct replacement for premium unleaded.

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According to this link the stoich is different from pump 93 and it is oxygenated. This review says they got a tune specific for the fuel, too.

Basically, How will ms109 react in a car tuned for 93?

PRODUCT DESCRIPTION
In engines that can run on pump gas, MS109 is a direct replacement that produces more power than any other unleaded fuel – up to 5% more than premium unleaded. Recommended for applications with up to 25 lbs of boost and naturally aspirated engines with CRs up to 15:1. Compared to other unleaded fuels, MS109 offers better detonation protection_as well. Excellent in crate engine applications.

And if you download the spec sheet of the fuel it is unleaded.

MS109E is oxygenated, not MS109. MS109 is high octane non leaded fuel used for motor sports.

I was basing my understanding of the fuel from the review page where they mention a new tune was used for the fuel due to its oxygenation. Are they talking about the ms09e here?

"Using a Lund Racing N-Gauge, he and the folks at Wicked Motorsports logged the baseline run. After emailing Dakota Deck of Lund Racing the baseline logs, Bittel added in VP Racing Fuels MS109 unleaded fuel as he waited for the return email. “For MS109, I simply changed the stoich point to account for the oxygenation that MS109 contains,” explained Deck. He continued, “then I added 2 degrees of spark advance over where it was on pump gas.”

I used to run non oxygenated race gas in my two stroke dirt bike, and had to jet richer for it. Maybe this same logic doesn't carry over to the car like I'd expect it to.

Technically pump gas E10 is oxygenated. Thats why the stoich point is 14.08 instead of what older cars used as 14.7.
They claim its a pump gas replacement. That to me means It would falls with in a few percent of E10 stoich. and can put put into any car with out a re tune. The stock tune is capable of 0-15% ethanol. I think it says it right on the back of the gas cap cover.

I sent them an email to see what they say the stoich of the two fuels are.

MS-109 13.43 to 1 that's 5% richer
MS-109E 13.14 to 1 that's 7% richer

Sure a tune change could get everything closer. If it is being mixed into a tank of pump, the fuel trims would easily take care of that much leaner.

Use 2 cans of torco

Running MS109 on a pump gas tune will make the engine run leaner, not richer.

Need4Speed15 said:

Running MS109 on a pump gas tune will make the engine run leaner, not richer.

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I was comparing stoic to stoic, not what the engine would show.

Below that I said fuel trims could easily take care of the lean difference.

1.05-1.07 or 5-7% positive fuel trims indicate lean. The 5-7% is actually added fuel, so technically the engine is going to be running the fuels stoic value with out any tune change. With adaptive trims at WOT it would even be running the same targeted wot lambda value. Measured lambda would show very little difference from pump gas.

All this would eventually be learned in the LTFTs. Which a lot of tuners rely on instead of actually getting fuel dialed in closer. It's usually a few percent rich "safety margin" that the car learns out. Everyone says their car gets better after it learns. Running MS109 would have the opposite effect, it would start out feeling better then as it learned feel weaker.

All I want to do is run a few gallons for 100 miles or so and see if the intermittent knock goes away. If the fuels stoich values are that close I think I should be fine to run 3-4 gallons of ms109 mixed with whatever residual amount of pump 93 is in the tank by the time I get there. Right?

ManBearPig said:

All I want to do is run a few gallons for 100 miles or so and see if the intermittent knock goes away. If the fuels stoich values are that close I think I should be fine to run 3-4 gallons of ms109 mixed with whatever residual amount of pump 93 is in the tank by the time I get there. Right?

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Are you going to a VP station? If so check out MS103, similar stoich to pump 93. My local VP let’s you pump the MS103 in directly and only sells the MS109 in 5 gallon drums. Lots of guys down here use the MS103 and I’ve used it a lot in my 2012 nitrous car.

https://vpracingfuels.com/product/motorsport-103-ms103/

ManBearPig said:

According to Sunocos website the closest location 260 GTX is sold is 118 miles a away.

There is a station that sells Sunoco "standard" leaded 110 about 50 miles away though.

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your local drag strip probably sells it