By Dave Hagen, Steve Fox and Mike Caruso with Rob Munro and Jay Ryan
A great effort has been made to clean up exhaust emissions. Those efforts and the increased need for alternative fuels have resulted in renewed interest for use of LPG (Liquefied Petroleum Gas) or CNG (Compressed Natural Gas) as an engine fuel. AERA has learned that if a car/truck is manufactured as a Flex Fuel vehicle, they are built using hard valve seats and higher temperature material for intake valves. Increased heat production from LPG and CNG necessitate that intake valves be made of harder than normal material. Generally, this material is found in stock gasoline exhaust valves. Exhaust valves require more durable material than standard so Inconel or other OEM/aftermarket material indicated for LPG or CNG use is advised.
LPG and CNG have about the same BTU/H.P. value but CNG operates using a very high pressure fuel tank. Whereas LPG operates at a much lower pressure fuel tank, making it safer to refill. In Europe, LPG is known as Autogas or GPL (no lead or carbon deposits). LPG is extremely popular in the Netherlands, Serbia, Italy, Poland, Australia, Korea and Hong Kong. Armenia might be the greatest user of Autogas.
Another word of note is late model OEM Flex Fuel engines that are set up to burn gasoline or E85 may also use LPG and CNG without modification to basic internal engine components. As OEMs constantly advance engine design, more and more engines will be produced to use a variety of alternative fuels.
Seats, Valves, Rings and Materials
More vehicles are being offered by the OEMs called Flex Fuel that are already converted to run on E85 fuel. Other vehicles are set up from the OEMs to be run as a dual fuel gasoline and LPG fuel. What does this mean for cylinder head engine builders today? There are great opportunities out there for the shop that does the work right the first time. Let’s look at this fuel and what its use means to the engine builder.
Gaseous fuels burn with an almost complete absence of ashy deposits. These deposits in gasoline engines protect the valve and seat faces from wear. Their absence gives rise to the name “ Cold, Dry Fuel” commonly used to describe LPG and CNG fuels. The lack of these deposits allows direct contact between the valve and seat mating surfaces in the combustion chamber. This direct contact causes micro welding to occur with metal from the valve seat or valve face surface transferring (micro welding) to the other.
During the next open-close cycle, the deposits heat up and oxidize. These oxides are both corrosive and abrasive and explain why some non-OEM converted engines suffer severe and rapid valve and seat wear. Another cause of rapid seat wear is that valve heads flex under combustion pressures. In some applications this can accelerate a wear problem and lead to early failure. To combat this wear, various techniques should be used. The first plan of attack is to widen the seat contact point to around 0.100” . Remember that a full 76% of the heat transferred out of the valve goes out through the valve face to seat contact point. Widening the valve seat contact area allows more heat transfer and spreads the compressive load over a larger area. This helps prevent the welding process. Also you do not have to worry about carbon being trapped between the valve face and valve seat. These fuels burn very clean due to the lack of carbon content.
The next concern is to ensure ample contact between valve and seat faces. It is not recommended to machine an interference angle between these faces and is particularly important for LPG heads. It is also good practice to “ blue” the contact area and hand lap if necessary. Valve rotators should be replaced with standard type retainers. Some shops have welded rotators solid to prevent excessive face wear.
The most immediate action is to upgrade valve and seat materials. Exhaust material is used to make both intake and exhaust valves for LPG and CNG engines which are specifically designed to withstand the extra wear experienced with the use of LPG and CNG fuels.
Valve faces need added heat protection as do the seat contact surfaces. In the case of valves, addition of hard facing materials, usually Stellite is considered essential in preventing valve failures. In some cases the valve head can be made from Cobalt based super alloy such as Inconel. This alloy flexes less than regular exhaust material thus preventing wear due to valve head bending. In some cases, 454 GM for example, both Stellite seats and Inconel exhaust valves are required to provide acceptable service life. The valve can also be internally cooled with sodium if required and available.
Valve seats also need attention. If the head was not designed to run on LPG or CNG, hard corrosion resistant valve seats need to be inserted with a material specifically designed for gaseous fuel use. These seats are very hard and are indicated for high heat operating conditions. These seats are made from special materials with high Nickel, and / or Stellite content to withstand corrosive and abrasive actions present in LPG and CNG fueled engines. Ever wonder why we use black instead of common grey pipe in our homes when using Natural Gas to fuel our heating systems? Corrosion resistance is right at the top of the list.
The valve guides of choice are Manganese-Bronze with special bronze alloys which utilize hard filament shaped wear particles that are evenly distributed throughout the material and aligned along the length of the finished valve guide. This combination of materials provides good thermal transfer of heat from the valve stem into the valve guide.
Manganese-Bronze alloy has the highest heat transfer rate of any bronze valve guide alloy.
- More than 200% of nickel-aluminum bronze guides.
- More than 200% of aluminum-silicon bronze guides.
- Exceeds phosphor bronze alloys with 88% copper.
Ring packs are pretty standard for LPG and CNG engines. Much like turbocharged engines that must also contend with heat issues, LPG and CNG fueled engines use Moly rings with great result. If additional protection is deemed necessary, it may be well worth time spent calling your favorite ring manufacturer and see what other ring application they may recommend.
Gaskets for these engines are no different than their gasoline counterparts unless there is coolant or exhaust contained within the intake manifold. In those older engines, you may want to consider blocking off coolant or exhaust flow within the intake manifold. This can be accomplished in various ways such as a block off plate within the intake gasket or physically sealing the opening with a metal pipe plug. Consider doing this only after careful thought as some engines may not respond favorably to this modification.
Related Areas of Concern
Often, after the sale service can make a big difference to ensure engine survival. When an engine has been converted to LPG or CNG use and the cylinder head has been built specifically for the fuel, it can still fail without attention to both the ignition system and the fuel mixture. The distributor must be re-curved to provide total advance of 36° at 1000 RPM (15” of vacuum) and total advance of no more than 42° at 3000 RPM. Initial timing can be advanced about 10% but if this is done, an equal amount must be removed from the total advance curve. The fuel delivery system is also important. Most LPG systems require a 2% oxygen exhaust content to ensure adequate cooling in the combustion chamber.
When it comes to arriving at a reliable compression ratio, the best results have been achieved with ratios from 9.5:1 up to 10.0:1. For some performance applications they will go a little above the 10.1:1. But for any heavy duty application it is best to stay below that figure.
As mentioned earlier, propane is a “cold” fuel and it is best to keep it that way by eliminating any intake manifold preheating done either through an exhaust crossover or engine coolant. Many engine builders also use a lower temperature engine coolant thermostat, somewhere around 180°F if available. It is not recommended to use LPG on V-10 style engines unless a dual feed intake manifold is comprised. A single feed mixer has the tendency to lean out the cylinders on the ends under heavy loads.
Unlike gasoline engines, a rich LPG mixture overheats the valves and seats causing seat recession. Failures witnessed in engines that have been in service a long time are generally from inadequate maintenance of the fuel mixer or ignition system. LPG engines do not like lean or rich mixtures of fuel and offer no tell tale signs of over fueling like gasoline with black smoke coming out the tail pipe. As a general tuning practice, keeping total ignition advance to 30° BTDC seems to keep them together while providing appropriate power. The only way to ensure correct fuel mixture is to use an exhaust gas analyzer. There are many sources for these tools but one is Honeywell Analytics in Lincolnshire, IL (1-800-538-0363). Another method would be to use a Wide Band 02 (LM1 or similar) sensor which is available from Innovate Technology, Inc. Irvine, California (949-502-8400) among others.
Summary of Parts Required to Retro Fit for LPG and CNG use
- High temperature intake valves are made from exhaust valve material.
- Exhaust valves made from high temp materials such as Inconel.
- Sodium filled valves for extra protection.
- Harder valve seats installed into cylinder heads reducing erosion.
- High lubricity valve guides.
- Special valve stem seals if made for your engine.
- Eliminate valve rotators; some people weld while others replace retainers.
- Moly ring packs are recommended.
Advantages of LPG and CNG over Gasoline
These fuels offer abundant local supplies with vast reserves without relying on imported crude oil. LPG and CNG are less expensive than the cost of gasoline and diesel fuels. They are readily available with an excellent infrastructure. They continue to expand from remote areas into the city.
LPG is stored as a liquid under pressure in safe extremely strong storage tanks or vessels. LPG is a liquid and turns into a gaseous fuel which disperses and diffuses quickly when released from its pressured tank. LPG has an auto-ignition temperature point of 878°F (470°C). When that temperature is compared to gasoline’s auto-ignition temperature points of 572-752°F (300 – 400°C) LPG seems safer to store and handle. The cleaner burning LPG fuel produces less harmful CO (carbon monoxide) gasses and less HC (hydrocarbon) and NOX (oxides of nitrogen) emissions than gasoline.
- Does not produce fine particulates dangerous to people with respiratory problems.
- Have lower emissions during cold starts because no choke enrichment required.
- Produces less Greenhouse Gas (GHG) emissions carbon dioxide.
- Helps prevents detonation; stops the pinging or knocking noises.
- Offers longer spark-plug life vital for emergency service vehicles. (No fouling)
- Offers longer engine life producing no abrasives in oil or oil dilution by fuel.
- Does not get trapped in piston ring grooves to form hydrocarbons.
- Gaseous fuel does not wash lubricating oil off cylinder bores that normally cause excessive bore wear.
- Does not form smoke even if the mixture is very rich air/fuel ratios.
- No fuel line freeze-up in cold weather; no water in fuel system.
- Mixes evenly and quickly with the induction air in very even air/fuel ratios.
- More tolerant to very lean mixtures.
- Simple fuel system reliable and very easy to diagnose and service.
- Engines which are Normally Aspirated (N/A) are perfect to run a higher Dynamic Compression Ratio making more power for the same amount of fuel flow.
These fuels when used in a Turbo or Supercharged engine can make more power by addition of ignition advance. Even more power can be obtained by raising the slope of the boost curve and adjusting the maximum boost level higher without any internal engine modifications.
E-85: Fuel for the ages or more trouble than it’s worth?
By Marty Brown
E-85 seems to stay front and center in the news. Often blamed for the run up of corn and grain prices thereby driving up the price of virtually every grocery item worldwide, it has it share of supporters and detractors.
Leaving politics and the environmental elitists out of the equation for the moment, it would appear that at least for the next several years the E-85 fuel program is going to continue to receive subsidies from Federal and State Governments to expand the production of this alternative fuel. That means more production and, at least for now, a lower price per gallon contrary to the cost of the raw materials.
Boiled down to the simplest elements, E-85 describes the fuel content 85% Ethanol, 15% Gasoline. A common misconception however is that is the normal ratio. E-85 indicates the maximum Ethanol percentage at 85. It can be lower, in some cases much a much lower percentage than the stated 85%. The percent of gasoline can increase for any number of reasons most often cited is better starting during cold weather but there does seem to be quite a bit of variation in blend percentages (as monitored at retail pump locations) and that would suggest at least for now there are likely some transportation and distribution issues keeping the mix ratio between the Ethanol and gasoline in the correct relationship.
Shortly several companies will have inexpensive monitoring systems that will enable an individual to determine what the Ethanol/Gasoline ratio actually is to take some of the potential guess work out of using this fuel full time for a specific application.
When everything is correct, E-85 simply using conventional unleaded pump gas has an octane rating of 105. That’s music to any performance enthusiast’s ears. It’s been a long, long time since you could drive into a gas station and actually pump a product that contains 105 octane directly into your tank. I would guess the last hold out was probably Sunoco 260 which vanished around 1975. So now that we have this new high octane fuel available what can we do with it?
For specialty applications that require more compression like pre-73 muscle cars, street performance cars with modified engines or local racing classes it looks inviting. E-85 is a low cost alternative to increasingly more expensive racing fuel or at the very least a host of additives necessary to keep the octane level high enough to keep the engine parts happy. As any engine builder knows, compression is the way to make horsepower. While it is possible to make very impressive horsepower numbers with low compression that is compatible with today’s pump gas, it is usually far more cost effective to increase the compression ratio that a high octane fuel allows.
As with any alcohol fuels there are some issues to deal with. First, the engine will consume approximately 30% more fuel than with gasoline. This requires that all the components in the fuel delivery system must be equal to the higher fuel volume demand. Second all the internal fuel passages within the carburetor must be larger not to mention some things you might not usually think about like large needle and seats with a stainless steel needle tip as the normal Viton® won’t hold up with prolonged exposure to E-85. Likewise, the Nitrophyl (black cellular construction) floats will eventually absorb fuel, then sink resulting in flooding. Any of the accelerator pump diaphragms should be exchanged discarding the black rubber diaphragms in favor of the green G.F.L.T. diaphragm material that holds up far better to alcohol based fuels. Finally, never use a paper filter in the fuel system — the Ethanol will destroy it in short order, plugging up the whole system.
At Quick Fuel Technology we offer a variety of options to address the carburetor part of the equation. We have a couple conversion kits (one specifically designed for race only carburetors) and we also offer a pair of metering blocks that can be used as the foundation for converting existing gasoline carburetors if an individual is so inclined. We offer the other required parts to complete the conversion. In addition, we offer a range of carburetor sizes to suit most applications although the majority have a race bred calibration. We do offer a 650 CFM street version that would work extremely well on most low compression run of the mill small block engine found in a large percent of “ drivers” . As the horsepower increases so too does the expectations of the carburetor. Our Q-Series carburetors are certainly capable of meeting the requirements of engine packages approaching 900 Horsepower.
Obviously it is difficult to cover both the fuel and the parts needed to take advantage but clearly there is a great deal of information available on E-85 and the flow of new information seems endless. With a little research and some practical experience with this new fuel it shouldn’t take too long for you to become the resident expert. If we can be of any assistance on the carburetor or fuel delivery system certainly feel free to call us we would be more than happy to try to assist you where ever we can.
E-85 offers the win-win situation, we can increase the power of our engines and get an environment thumbs up for doing so. I can’t think of any scenario better than that for our industry!
FAST™ offers many options for E85 users
BY Jay Rohrback
We at FAST™ have done extensive testing with alternative fuels, especially E85. Anyone doing business with customers in the Midwest should certainly be looking at how they can help their customers utilize the benefits of this fuel if they haven’t already. As I sit here writing this I’m listening to a local southern Michigan radio station report on several new manufacturing facilities for this fuel being built in the Michigan/Ohio/Indiana area. It’s here and it does offer benefits to the performance enthusiast.
In our dyno and in-vehicle testing we’ve found that the higher octane rating does (in most cases) allow for a few more degrees of timing to be applied over standard gasoline, as well as an obvious increase in compression ratio. This is also very good news to the muscle car owner that has an original, higher compression V8. He now has more options than just knocking the compression down in the next rebuild, or dropping the timing back to get away from detonation, or dumping a bottle of octane boost in the tank with every fill-up. How would it be to pull up to the pump in a Mustang, Cuda, Camaro, GTO, or 442 like the old days out on Woodward Ave. here in Detroit or the local cruise in your area. That’s actually becoming possible again with the availability of E85.
We’ve been known in the past as an EFI company, but with the addition of our Wide-Band Air Fuel Meters a few years ago that can easily be used for both carbureted or EFI applications, we’ve really transformed FAST into an electronic tuning company. That’s really what our stand alone XFI™ system is, a tuning tool. It allows the user to easily tune an engine in many ways he couldn’t possibly do before with a carburetor.
In the testing I mentioned before we’ve worked diligently to come up with easy to use electronic tuning tools to help you take advantage of E85. For the carbureted user and those that are re-tuning factory EFI engines, we’ve added E85/E98/Methanol capable Wide Band Air Fuel Meters in both single (part# 170590) and dual (part# 170608) sensor versions. These, along with just released free software called FASTView™ allow the user to not only tune, but download, save, view, and compare air/fuel data logs to get that engine exactly where you need it to be. It’s our most inexpensive tuning tool and a must have for any tuner, novice to professional. We’ve also come up with a unique feature to utilize E85 with our XFI™ EFI system (part# 30-1000). The Fuel Energy Constant feature allows the user to input a numeric value that corresponds to the type of fuel being used. For example, gasoline is a 1.00 constant, where E85 is a .680 constant. All fuel type constants can be found in a handy chart in our software (a sample of this chart is shown on page 21).
What the XFI™ does with this constant is modify the Target Air/Fuel Ratio table so that fueling is adjusted properly for the fuel type you’re using. In other words, it allows you to tune an engine on gasoline, and then just by changing one simple number in the software you can switch to using E85 without needing to re-tune the engine. The XFI™ also has our Qwik Tune™ Technology, which allows the user to save 4 separate tune-ups in memory of the XFI™, and with the use of a simple 4 position switch choose any of the 4 tune-ups without having to plug in a laptop. That way you can have one tune-up for gasoline and one tune-up for E85. Or, with the price of gasoline going up as much as it has lately you could have an economy tune-up for each and a performance tune-up for each with the simple flick of a switch. If you want to take it even further, with the addition of a Flex Fuel Sensor available at your local GM dealer parts counter, it can very easily be wired into the XFI™ so that the constant can be controlled by the Flex Fuel Sensor automatically. When the sensor senses a different type of fuel, it sends a signal to the XFI™ and the XFI™ will switch the Target Air/Fuel Ratio table to match that fuel type without the user doing anything but driving.
We’ve been hard at work adding things that can help you utilize alternative fuels. For more information, go online to www.fuelairspark.com or call 877-334-8355.
The AERA Tech Team – Dave Hagen, Senior Technician, has over 36 years of experience in our industry. An ASE-certified Master Machinist, Dave specialized in cylinder head work and complete engine assembly for the first 17 years of his career. Steve Fox has over 20 years experience in the engine building industry with eight of those years spent working in the machine shop. Steve is an ASE-certified Master Machinist, as well as a longtime member of the drag racing circuit.
Mike Caruso brings over 42 years of rebuilding and high-performance experience to AERA. An ASE-certified Master Machinist, Mike came to us from FEL-PRO’s high-performance R&D and tech line, where he worked for 11 years.
Rob Munro is President of Valley Speed Machine Shop in Kamloops, British Columbia, Canada. Rob is a former AERA Chairman. He also served as first and second chairman, treasurer, as well as a board director for three years. Jay Ryan is with S.B. International in Nashville, TN. Call 800-843-7348 or go online, www.sbintl.com. Marty Brown is with Quick Fuel Technologies in Bowling Green, KY 42101. Call 270-793-0900 or go online, www.fuelairspark.com. Jay Rohrback is with Comp Performance Group. Call 734-341-6307 or go online, www.compperformancegroup.com.
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