Blower Octane Requirements

[HTWOODS]

Hello T Bucketeers,


I'm new to this forum. While in the process of building my "Blown," Buick Nailhead Powered, T Bucket, I came across some information, that may be useful, for those building Blown Engines, for high performance street use.

I hope this serves as a guideline in determing the minimum octane required for your engine. It helped me! Good Luck!

HTWOODS



Final Compression Ratio (FCR) = ((Boost/ 14.7)+1) x CR

Boost= Maximum Blower Boost

14.7= psi at sea level

CR=engine compression ratio

Corrected Compression Ratio= FCR- ((altitude/1000) x 0.2)


Use the above formulas, and the attached information, as a guideline, to help determine the “minimum” octane required, for a “Blown,” “high-Performance,” “Street Engine.”

Use the static compression ratio of the engine, and the maximum blower boost from the blower system, to determine you Final Compression Ratio. Altitude plays an important role in determining compression ratios.

Final Compression Ratios in excess of 12.4:1 are not recommended for use with “pump gas.” The higher the final compression ratio; the higher the octane rating of the fuel must be, to avoid, engine damaging, detonation.

 

[MRYoung]

Handy... very handy... I'm writin that down. Thanks.

 

[RexRod]

Thanks for the post. That's some good info.

I learned recently that E85 has an octane rating of between 100 and 105 depending on the blend. Here in Fort Collins, E85 is available all over town for about 30% on average below the price of unleaded premium. Might be a good fuel for high compression engines.

Just thinking out loud.

David

 

[LumenAl]

... I learned recently that E85 has an octane rating of between 100 and 105 depending on the blend. Here in Fort Collins, E85 is available all over town for about 30% on average below the price of unleaded premium. Might be a good fuel for high compression engines.

Just thinking out loud.

David

That fuel is designed for flex-fuel engines as it's 85 alcohol (and absorbs water like a sponge)...

here is a good article on E85 - Wikipedia, the free encyclopedia

 

[Wild Mango]

Yes also keep in mind that with that much % alcohol you need about 40% more fuel for the same volume of air compared with gasoline, so your mileage will suffer to the same extent.
The main problem with alcohols is they are corrosive, attacking ally and rubber, and also conductive, so any brass fuel line fittings (for example)will have the zinc leach out as a white crystalline residue, evidence of galvanic corrosion.

I have burned alky in a variety of Midget engines over the years. Fuel goes in the car 15 mins before warm up and comes out straight after the feature ends, at which time the fuel system is flushed with 50/50 gasoline and ATF. Plugs come out and the engine internals given a good coat of WD40 sprayed down the stacks. Always.

 

[Screaming Metal]

Yes also keep in mind that with that much % alcohol you need about 40% more fuel for the same volume of air compared with gasoline, so your mileage will suffer to the same extent.
The main problem with alcohols is they are corrosive, attacking ally and rubber, and also conductive, so any brass fuel line fittings (for example)will have the zinc leach out as a white crystalline residue, evidence of galvanic corrosion.

I have burned alky in a variety of Midget engines over the years. Fuel goes in the car 15 mins before warm up and comes out straight after the feature ends, at which time the fuel system is flushed with 50/50 gasoline and ATF. Plugs come out and the engine internals given a good coat of WD40 sprayed down the stacks. Always.

Yep....the more alky ya got, the more fuel it takes. Thats like when you alky on carbs....replace the rubber gasketsl, use metal floats, which need to be set higher.......and bigger jets....alky is really dry and has a tendency to wash the oil off your cylinder walls....with the ethanol laced fuel we have now, on a blown engine....it doesn't hurt to mix a little green/blue av. gas in or something to jump the octane rating up and some lube. They do have the additives but they're getting outrageous, too