World Champ Pro Street
In this section, we focus on turbocharging that is discussed in over 40 pages of our methanol racing fuels manual. At the SEMA show, we met Larry Larson. He is world champ in street car racing in the quarter mile at 6.16 seconds, 219 MPH. LATEST UPDATE AS OF 11/24/2014: Larson just ran 5.95 sec. ET, 244 MPH!
Larry shared a few added specs from the Chevy S10 Pro Street truck engine combination built at Larson Race Cars for this unique street legal competition. It is powered by a twin turbocharged big block V-8. Note the following specs: estimated HP @ 3,000+; air to fuel ratio @ 3.3 to 1 for straight methanol racing fuel; size of turbochargers @ 98 mm; engine size @ 620 ci; cylinder head flow @ 535 CFM @ 0.900 lift; intake boost @ 40 psi; shift point for his race prepared Turbo 400 transmission for 1-2 @ 7,000 RPM; for 2-3 @ 7,800 RPM; hitting 9,000 RPM at the quarter mile racing finish line!
Larry was present in the Gear Vendors Under/Overdrive booth during most of the show. His spectaculer hot rod is equipped with a Gear Vendors overdrive for street driving. He was one of the most personable racers I ever met, and his inside information is very well appreciated. Larry’s hot rod is the cover car on Hot Rod Magazine, Issue 0115.
Turbo Methanol & Intercooling
One of our methanol book customers talked about a twin turbo Pro Mod methanol engine that he just built. Dynamometer tests revealed that his combination would make 3,000 HP at about 30 psi boost. Intercooling provided horsepower at lower boost values than racing engines without intercooling such as the previous street car world champ setup. However intercooling for a high horsepower engine can add 100+ pounds of weight and occupy a lot of space. It becomes a builder/tuner’s tough decision whether to add an intercooler to gain more horsepower for the weight & space that it takes. If there are race vehicle weight & space requirements that can be maintained even with an intercooler, then the intercooler is a good choice. However, if there is no minimum weight or the weight & space limit is exceeded with an intercooler, then the absence of one may be a better choice. That is the application Larry said he was facing.
Intercooling with Methanol
With alcohol fuels, combustion chamber cooling can be done with fuel enrichment when an intercooler is not used. There are limits to the amount of fuel that should be added. Excess fuel will cut power. Inadequate fuel volume will not inhibit detonation or pre-ignition. According to engineering data in our methanol racing fuels manual, the stoichiometric air to fuel ratio of methanol is approximately equivalent to gasoline with an octane rating of only 99. That is, if methanol is leaned out to an air to fuel ratio suitable for highway use, it is similar to 99 octane gasoline for detonation resistance. Proper enrichment is necessary to increase its detonation resistance to higher values necessary for high output racing engines.
Air to fuel ratio control such as what is described throughout our publications & jetting calculator is a good method to achieve that proper fuel amount and to maintain it. I would expect AFRs with numbers much less than 2.8 to 1 are power reducers in high boost applications. We analyzed some drag racing Top Alcohol Screw blower engines that pulled boost values up to 60 psi. The AFRs were at 2.9 to 1 although those were the richest I ever saw that were competitive. AFRs with numbers much more than 3.5 to 1 may be prone to detonation in 30 psi boost applications. Note that the boost level is the key. More boost needs more enrichment in applications without an air-to-air or air-to-water intercooler.
Enrichment Blown vs Unblown (Normally Aspirated)
In a recent drag race track test of a normally aspirated methanol engine, best performance was achieved at an AFR of 5.2 to 1. A richer AFR (smaller number) dramatically reduced power. That AFR would destroy a typical blown racing methanol engine. In comparison, best performance in a moderate boost, blown methanol Hemi racing engine of a similar size was achieved at a much richer AFR of 3.5 to 1. Any AFR that was leaner (numerically bigger number) would melt pistons in the blown Hemi application while it is dead rich in the unblown application.
Enrichment Effects Blown Engine Power
Although both engines were of similar size, the blown engine made about 50% more power than the normally aspirated racing engine. That did take about 2 atmospheres of boost. It is interesting that although power was up it was not double, even though there was twice the amount of air going through the blown engine. While enrichment is not all of the inefficiency, the amount of enrichment costs a considerable limit to the power increase. Cool excess fuel is going through the entire combustion process as described in detail in our methanol racing fuels manual. It occupies space in the intake, combustion chamber, and exhaust. It takes heat energy from the combustion process. That is the trade-off for the increase in detonation tolerance from a rich mixture for high compression, blown engines.