Fuel Octane Test - Project Pure Poncho

Do 9.1:1 engines need high-octane fuel to make power?

From the September, 2012 issue of High Performance Pontiac

By Ray T. Bohacz

Photography by Ray T. Bohacz

With Project Pure Poncho fully broken-in and its power documented (491.8 hp/551 lb-ft), it was now time to begin our research and development work.

As a review to those who may not have followed the build-up, our test engine is a 467ci mill with ported 6X cylinder heads, a hydraulic roller camshaft, and a street-friendly 9.1:1 compression ratio. It was built by RaceKrafters Automotive Machine with components supplied by Summit Racing and Butler Performance. Its purpose is to test parts and combinations, along with engine theory so that when the time comes to modify your engine, real, hard data has been established.

Over time, the gamut of testing will be quite broad, so HPP felt the best place to start would be to determine the engine’s octane tolerance in its current form. There has been much written and discussed on all levels about the octane requirements of a Pontiac engine. Some is rooted in truth, while some is simply opinion. We will test for octane appetite using a quasi-scientific method.

Octane Demand

The Sept. ’11 issue of HPP features an in-depth primer about gasoline (“Give It the Gas”) so it’s a good idea to reference that before fully digesting our octane testing.

Octane by definition is not complex—it’s simply the fuel’s ability to withstand pressure and heat without reverting to auto ignition. The fuel needs to wait for the arcing of the spark plug to begin its burn and expansion across the bore. When this doesn’t occur and the fuel ignites independently of a spark, it’s referred to as abnormal combustion. When fuel waits for the arcing of the plug electrode, it’s called normal combustion.

Both the oxygen and ethanol...

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Best Dyno Pulls

88-Octane Rockett Brand Fuel
RPM	TQ	HP	BSFC
3,300	545.3	342.6	0.37
3,400	548.7	355.2	0.36
3,500	551.0	367.2	0.37
3,600	551.0	377.7	0.37
3,700	550.1	387.5	0.38
3,800	549.2	397.3	0.37
3,900	543.7	403.7	0.37
4,000	544.0	414.3	0.37
4,100	547.0	427.0	0.36
4,200	546.4	437.0	0.36
4,300	545.0	446.2	0.36
4,400	543.9	455.6	0.36
4,500	537.2	460.3	0.37
4,600	535.1	468.6	0.37
4,700	531.1	475.3	0.38
4,800	526.0	480.7	0.39
4,900	519.8	485.0	0.39
5,000	508.6	484.2	0.40
5,100	503.1	488.6	0.41
5,200	491.7	486.8	0.41
5,300	482.0	486.4	0.42
#73/#73 jets, 32 degrees timing

94-Octane Rockett Brand Fuel
RPM	TQ	HP	BSFC
3,300	547.5	344.0	0.39
3,400	551.8	357.2	0.38
3,500	553.4	368.8	0.39
3,600	554.2	379.8	0.38
3,700	551.4	388.5	0.39
3,800	552.2	399.5	0.40
3,900	552.6	410.3	0.40
4,000	551.7	420.2	0.39
4,100	551.0	430.1	0.38
4,200	546.5	437.0	0.40
4,300	548.3	448.9	0.39
4,400	546.1	457.5	0.39
4,500	543.3	465.5	0.40
4,600	538.6	471.8	0.41
4,700	534.8	478.6	0.42
4,800	527.8	482.4	0.41
4,900	521.1	486.1	0.41
5,000	513.0	489.1	0.42
5,100	500.2	485.7	0.44
5,200	493.2	488.3	0.45
5,300	480.9	485.3	0.46
#79/#79 jets, 32-degrees timing The different chemical composition is the reason this fuel wanted more jet than the others.

100-Octane Rockett Brand fuel
RPM	TQ	HP	BSFC
3,300	544.2	341.9	0.39
3,400	548.7	355.2	0.39
3,500	552.0	367.9	0.39
3,600	550.8	377.5	0.40
3,700	550.7	387.9	0.40
3,800	548.0	396.5	0.40
3,900	549.0	407.7	0.39
4,000	549.0	418.1	0.39
4,100	546.9	426.9	0.39
4,200	550.8	440.5	0.38
4,300	549.0	449.5	0.38
4,400	546.4	457.8	0.38
4,500	543.4	465.6	0.39
4,600	541.2	474.0	0.39
4,700	534.9	478.7	0.40
4,800	530.4	484.8	0.41
4,900	525.3	490.1	0.42
5,000	516.6	491.8	0.41
5,100	507.4	492.7	0.41
5,200	498.0	493.0	0.44
5,300	488.3	492.7	0.46
#73/#73 jets, 34 degrees timing

The Rockett Brand 100 octane is considered a race fuel that is street legal. For this reason, the full specifications are supplied. Note that it had no ethanol and the oxygen content was slightly lower. The RON is 105 while the MON is 97, which would put the AKI at around 101 octane--an excellent fuel for race day with a street/strip Pontiac.

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