Given its 117 octane rating, and other attributes, I had always assumed that C16 fuel was the best alternative for making big power in a 996TT. Then, after running C16 in my car for a few months, my engine was developing significant deposits in every cylinder. I assumed these deposits were caused by an excessively rich tune (in conjunction with the presence of lead), and a different tune would eliminate the condition (or at least reduce it). I recently spoke at length with the national technical advisor for VP Racing Fuel (Jay). Needless to say, Jay knows fuel.

Jay told me that C16 has an incredibly slow burn rate, combined with a huge lead content, and C16 is therefore not appropriate for many engines, including mine. According to Jay, the deposit build up I encountered is not a function of my tuning and cannot be tuned out. Rather, according to Jay, the deposits were caused by the particularly slow burn rate of C16, which resulted in significant unburnt fuel in my cylinder, and I must switch to a fuel with a faster burn rate.

Jay recommended C12 for my car. He observed that C12 burns much faster than C16. Moreover, C12 has 33% less lead than C16. C12 also has an additive to cool the charge. Although C12 has less octane than C16, Jay reports that my car will run better with C12 and I will not build up deposits in the cylinders. Jay has encountered the identical phenomenon on many other cars.

I spoke with my fuel distributor today and he introduced another alternative – Sunoco 112 – which, according to him, has a burn rate comparable to C12, less lead than C12, and a higher octane rating. He is faxing me data as I type this post.

My car is being retuned for approximately 110 octane fuel (yesterday and today).

I am sharing this data for those of you out there who are running C16 (I don’t think there are many). Be careful, as it may actually be counter-productive. Take a look at your fuel filters.

Finally, please remember that I understand only a small fraction of these issues, and only at the most superficial level, so I almost certainly have misstated a myriad of facts and scientific principles as I feebly attempt to repeat that which others have told me.

Regards,

Craig

 

do you keep barrels of this stuff in your garage?

 

Good info Craig. I was mixing C16 with 103 for the extra octane, but I'll try C12.

I think I have 6 drums now in my garage

 

What do you do about the O2 sensors with the leaded fuel? Won't it give you a CEL, also?

 

craig that was one of the best posts i read in a while .. as i am running c16 and was actually advise to run.. VP import.. do u know anything about that?

 

I built a storage container adjacent to my garage where I store two 55 gallon barrels and I have a full electric pump (similar to that found in gas stations), with auto shot off, that reaches to the front of my garage.

Craig

 

I have several things that give me CELs, including no cats. I have a tool to reset my CEL whenever I am so inclined (which is rare).

I am told that the O2 sensors will eventually fail, at which time I will replace them. However, the Porsche O2 sensors are remarkably hardly and have been fine so far.

Craig

 

Thanks. I do not know anything about VP Import beyond what is on VP's website. I think C16 works fine for many engines that can accomodate the slow burn rate (VP Import as well), so if your Skyline was running well on the C16, without building deposits, you may well do even better with VP Import.

Craig

 

Very interesting post, Craig. Thanks for the great information. I may need to rethink my high boost fuel choice.

 

now that is bad ***

 

We use VP import whenever possible on the Evo 8 cars...
its better then c16 for sure... Its very very expensive.....
markski

 

In my continuing research, I was provided with the following Tech Bulletin from VP Racing concerning C12: http://www.vpracingfuels.com/spec/TechBulletin-c12.doc

The following quote was of particular interest to me:

"C12 was the first racing fuel to prove that burning speed, vaporization and BTU value were as important as octane. This allowed C12 to be the first racing fuel to make more power than other fuels that just concentrated on octane." (Emphasis in original).

Moreover:

"You can't make a racing fuel that has the best of everything, but you can produce one that will give your engine the most power. This is why we produce different fuels for different applications. The key to getting the best racing gasoline is not necessarily buying the fuel with the highest octane, but getting one that is best suited for your engine."

I also did some comparisons of initial boiling points as between C16 and C12. Whereas C12 will experience 10% distillation/evaporation at 131 degrees, C16 requires 211.5 degrees to achieve the same result. That is a huge difference. Likewise, C12 will experience 50% distillation/evaporation at 194 degrees, whereas C16 requires 213.1 degrees.

I also spoke with another fuel industry technical advisor who concurred that the excessively slow burn rate of C16 was the likely cause of my deposit build up, and he agreed that I should switch to a faster burning fuel.

Interestingly, C12 is VP's most popular fuel, precisely because it strikes a balance between these various factors and is compatible with most engines (whereas C16 is not always compatible).

Craig

 

VP import is also a VERY slow burning fuel, although it has a completely different curve than C16. It begins to burn at a lower temperature, but takes FAR more heat to acheive a complete burn. On the other hand, VP Import is oxygenated, which helps to reduce/eliminate deposits (Qwkr, I just learned this in the last hour).

Given that I use this fuel every day, I need to error on the side of a faster burning fuel. That is why I am going with C12 as my daily fuel.

Craig

 

Craig,

cool stuff!

Cost:

C12 purchased by the barrel per gallon ==
what is there next fuel down from C12?

On a side note I have Shell 100 Octane Unleaded available 10 miles from
my house but I also may supplement by the barrel (with C12) and am building a new
garage which will allow my to acommodate this.

Marty K.

 

Thanks Marty. I have been quoted $7.50 per gallon for C12. VP sells several leaded fuels below C12. You might also want to consider VP 109, which is unleaded.

Craig