Pump gas vs. race gas question
 

Hello.

I have a sbf Mustang bracket car with a 312 ci normally aspirated engine with a 750 hp carb and 9.5 to 1 flat-top pistons. It runs high 11's at 112 mph in the summer heat and mid to high 60's in good air. I have been running Sunoco 93 octane pump gas for quite some time but have noticed that the fuel lately seems to be a little bit inconsistent in the way it appears and smells.

Sometimes it is very cloudy and does not have much of a strong gas smell to it while other times it is very clear and has that strong gas smell that gas should have. I know that Sunoco mixes a small amount of ethanol in it and maybe the way they mix it is what is causing the cloudy appearance but I don't know for sure.

My main question is do you think that my combo will run better and maybe a little quicker with the Sunoco 100 octane unleaded race fuel? A few guys on other sites feel that it won't do a thing but I believe otherwise. I do agree that 110 or 114 leaded race gas is way overkill for this combo but I really think the car will like the 100 Sunoco race unleaded. Also, what type of pump gas would you guys recommend other than Sunoco if I decide to stay with pump gas?

Thanks for the help,

John Hedenburg

Re: Pump gas vs. race gas question
 

John,
I deal with your situation with quie a few engine customers. I can say that with out a doubt the low octane race fuel will be more consistant. The ethanol mix is never the same. It is mixed by vol. When tuned (jet & timing) correctly for the race fuel the engine will like it and will usually make your car more consistant. I can also tell you that after many years of refreshing my customers engines the engines run with race gas will show less wear, esp. in the cylinder and valve/guide areas.You are absolutely right about the higher octane not showing you anything. Your cylider pressure is too low for octane to be a real issue.
One recent example of the difference in pump gas and race gas was a 540 I built and had on my dyno. It was built for a Velocity 42 ft I/O boat. It had to idle at a low rpm to be docked and run in no wake areas. It was a 9.5-1, hyd roller, Brodix head with an 850 carb. It only had 155 lbs cranking pressure. I broke it in on VP C-12. (nice to have a little lead on new parts) I also did a Jet and timing loop while on the C-12. Then I dropped in some Shell 93. It dropped 25 hp. After a jet & timing change I got it to be only 13 HP less than the C-12.
It ended up making 650 lbs ft of torque and 625 HP. The torque curve carried 600 lbs ft from 2,800 to 5,600.
I don't think that was too bad for pump gas in a less than 6,000 RPM engine that will push the big boat over 80 mph and will have good driving manners. This was the third engine the customer had built for this boat. The others expired because their builders didn't take into account the use of pump gas and the way the boat was used. (stuck on selling big HP numbers)
Your combination can run the low octane fuel. good luck with it

Re: Pump gas vs. race gas question
 

Adger I was curious what the Timing and Jet was with the VP C-12 and with the Shell 93

Re: Pump gas vs. race gas question
 

68,
You have a PM

Deleted

Re: Pump gas vs. race gas question
 

Adger,

I have the same questions about the timing loop info VP C-12 vs Shell 93. (Long night) My Olds is a '71 low-compression 455 in , so higher octane probably won't help, but NHRA Div and Nats Stock eliminator approved fuels don't include the unleaded race fuels so I can't use the 100 stuff.

In addition, have you done any testing on Rockett 111 and/or 114?


Thanx, Marvin

Re: Pump gas vs. race gas question
 

Marvin,
Yes, I've had the Rocket 114 in a couple of customers engines. I like to tune with the fuel the customer can get in his area of the country. I have done back to back with VP C-14 & C-12 and rocket 114 in one of my customers (Chicago area) 385 fast burn crate engines. The tune up (jet and timing ) was different to get the best power and torque avg's. Keep an open mind about tuneups. What works for engine X may not work for engine Y.
Sometimes a customer will think his fuel is the best, but testing different fuels can prove them right or wrong. I'm not an advocate of any particular fuel as "The Best" . There are too many engine combinations that have different needs from the fuel for one brand or blend to fit all. Last time I checked VP made 52 different blends. That should tell you something about the needs in the fuel market. I know there are companies that just sell 3 or 4 blends. I don't think that covers ever need for every engine. I think that they are just working their slice of the market, or market share if you want to call it that. Low compression engines have different problems with fuel than extreme cylinder pressure engines. The burn rate to RPM and combustion chamber shape should be considered. I might add one thing. the heat range & type plug you use can have an effect on how the fuel burns.
Take your engine:
Low compression, probably low cylinder pressure too. Spark plug location is not in the best place and it has a very bad quench to bore ratio. (chamber is not real active) Piston speed & stroke should be considered too. I would try to find a low octane fast burn rate fuel that gets along with the extra heat a low compression large combustion chamber engine has. Then start testing what it likes as to timing and jetting to get the best power avg and BSFC's. Call around and talk to the fuel MFG's that are available in your area of the country. Listen to what they say & try to get past the sales pitch. :~)
Good luck,

Re: Pump gas vs. race gas question
 

I have the same problem. My car is pretty inconsistent on Sunoco 93...But I can't just stick race gas in it because I still street drive it a lot and mixing fuels will really throw the air/fuel off...

Re: Pump gas vs. race gas question
 

Marvin , VP C-10 is on the S/SS approved race fuels list and that IS unleaded.

Re: Pump gas vs. race gas question
 

I just got through a weekend using Chevron-Phillips 111. LT-1 ran better than it did on C12, ET-wise. Also came back to pits cooler.
Is it the best? Not sure but at $5.70 a gallon I like it better than $10.50 for C12 at LODRS events.

See ya at the stripe,

Jok