We continually get asked by customers and other engine builders plenty of questions about oil. From how much, to how often, to what brand. While we are not in the business of "promoting" any particular brands of oil, as engine builders, we certainly do have our preferences. All oils are not created equal. It's more than a sales pitch, it's a simple fact. Also, what may work best in a nitro funny car, most likely will not be the best choice for your kart engine. For the most part, whatever brand of oil you use is ultimately up to you. How well it performs in your engine though is up to the oil manufacturer, and also up to your engine builder. Engine builders of air cooled small engines like we use in junior drag and kart racing, prefer a lighter weight, (ie less viscuous) oil. Your engine builder likely has years of experience under his belt and can recommend an oil that will work best for your application. If you have any doubts or questions, be sure to check with him before pouring it in. After all, it's your investment. Most oil manufacturers offer a lightweight oil for air cooled engines and tighter tolerance race engines. For several reasons, a full synthetic oil is the oil of choice for racing. I could go into a myriad of reasons, including but not limited to: less carbon buildup on top of the piston and in the combustion chamber, (too much build-up not only hurts performance, but could cause a rules infraction in post-race tech), lighter weight possibilities and less affect or breaking down due to heat, ease of oil flow in a splasher type oil system. Keep in mind that the oil in your kart race engine is not pressurized like it is in your automobile. Oil crankcases that are pressurized, whether wet or dry sump, can utilize much heavier weight oils to "cushion" the effect of combustion on the rotating assembly. When using heavier weight oils, it is necessary to have more clearance machined into the parts so that the heavier oil can flow easily to all the parts needing lubrication. Also, certain fuels make a larger "bang" in the combustion chamber, and thus load bearings much harder than say a high rev, low compression applicaton. Bottom line: Choosing the right oil is critical in protecting your engine. Either you need to use an oil that is compatible with your engine builder's machine work clearances and tolerances, or you need to have your engine built to the capability of the oil you have chosen to use. Let me just say that aside from a big dollar sponsor offering cash and product to use their brand of oil, it is always best to use an oil that is compatible with your engine and follow your engine builder's advice.
More specifically, when we build a kart racing engine at Carlson Racing Engines, the machinework is done very precisely and it is of utmost importance that the proper oil viscosity be used. For instance, we tend to build our Briggs flathead race engines with very tight cylinder clearances, and we're definitely tighter than most on the valve guides. For this reason it is important that you use a 0 wt. or lighter oil. While some customers have had success with "qualifying" oils, or lighter than 0 weight, we recommend 0 weight for all of our stock class flatheads. This is most critical when the engine is fresh or nearly fresh. As the engine gets more laps on it, (say after 250 laps), you may choose to go to a heavier weight oil such as a 5 wt. While we don't recommend racing with a 5 wt. oil in the flathead classes, it will work for a few races if you need before you get your engine in for a freshen-up. The Animal engine requires a bit heavier oil and we've found that a 5 wt. is our preference for racing. Again, some customers may choose to use lighter weight oils, but 5 wt. is what your Animal race engine has been built for.
Motor mounts: We get asked quite often what is the correct "angle" of motor mount to be using with your engine and chassis combination. Let me answer this in two parts: First, through countless hours of dyno testing, we have confirmed that the best acceleration and performance in a flathead continues to be on a 15* engine mount. That is, with the base of the block tilted forward by fifteen degrees. There's a couple of reasons for this. Really it has nothing to do with the entry angle of the carburetor or fuel load at the intake port, rather, it has everything to do with the weight of excess oil and parasitic drag on the rotating assembly in your engine. While chassis manufacturers understandably argue that a flat motor mount will lower the vertical center of gravity of the kart on the track, I honestly believe this additional benefit of having your 34 pound motor dropped a total of less than one inch is negligable compared to the proven benefits found by using a 15* mount on the dyno. It's six of one and likely two dozen of the other in my opinion.
How much oil? Again, I'll address this in parts as it does matter a bit on the application.:
Break-in oil: When using a pure synthetic oil for racing, it is important that you follow your engine builder's engine break-in procedure to the "T". If you have had your engine broken in on a dyno, this step may not be necessary. Again, please be sure to check with your engine builder. Don't be afraid to ask questions. A lot of times, even if we do get an engine on the dyno after being built, we may still recommend that you follow a break-in procedure that will better allow the rings and other moving parts to wear or "break in." When breaking in an engine, NEVER use a full synthetic oil. In fact we offer special break-in oils that are castor or petroleum based and fortified with zinc additives to better promote the break in procedure. Again, follow your engine builder's break-in procedure exactly, never allowing the engine to run with no load. If you cannot consult with your engine builder on his recommendations for break-in, might I first suggest that you look for another engine builder, or at the very least follow our procedure, (found elsewhere on this website.)
How often should oil be changed? This is a no brainer to me. If you remember the old auto parts commercial saying, "You can pay me now, or you can pay me later", I think you'll get where I'm coming from on this. If you break down the cost of oil per oil change, you will get about $2.50 per oil change even with my rough math. Considering that flathead cranks cost upwards of $125, the expense of more frequent oil changes is pretty cheap insurance. There are several reasons why we change oil so often. The single biggest reason is because our engines do not have a filtration system. Keeping the crankcase flushed regularly is our only means of keeping out the contaminants. It is also convenient to check the oil level. Some engines will burn a little bit of oil, and some will push oil into the catch tank, and constant changing insures us we have enough oil to prevent damage. It is a good idea to drain your oil when it is warm. This helps make sure all the settled particles and contaminants are flushed from the system.Other than filtering and obvious oil level, the biggest problem with oils necesitating being changed, is oil dilution with fuel, or more specifically, alcohol. While alcohol is the mandatory fuel for competitive kart racing, it is water based and plays havoc with your oil, (ie oil and water don't mix.) If there is any alcohol in the oil, it will likely displace oil and cause undue damage. While some oils have rust inhibitors added to the base oil stock, the chance for rust due to fuel contamination still exists as the engine sits idle during the week. For this reason alone, it's worth while to change the oil at the end of every racing night.
While each engine builder will likely have their own preference for oil brand in their engines, I am not different in that respect. The following recommendations come with 35+ years of experience in kart racing and engine building. While performance of an oil can be measured on a dynamometer, that is not the final draw on oil quality. I see the insides of engines every single day here in the shop, and I can tell what oils work and what oils do not when it comes to protecting moving parts. While I generally haven't had any bad experiences with particular brands of oil, I tend to steer customers away from oils with molybdenum in them. While moly lube is a great extreme pressure additive for oil, my personal belief is that it has no business in a splasher style oil system with no pressurization or high load characteristics. It might work great in a differential, but it has no business in a kart racing engine. Again, there are specific oils for specific uses. For kart and junior drag racing engines, I certainly do have my favorites. I'll take a moment to list them here. Disclaimer: This is by no means a definitive list of all good oils, simply brands that I have had personal success with and heartily recommend to our engine customers.
Cool Power Green Light by Morgan Fuels. Cool Power has been around karting for as long as I care to remember. I have used their oil almost exclusively for over 20 years in my own personal race engines. I have never traced an engine failure to Cool Power and the performance and price make this an obvious choice for any kart racer or retailer.
Thor Oil. While my experience with Thor has been somewhat limited to the past few years, I have been surprisingly impressed. That says alot, trust me. Retail pricing is right in line with other popular brands and it is a great quality oil.
Red-E. While Red-E is certainly not as popular in most retail shops, most engine builders recognize the name. Red-E makes a top of the line product and lives up to their claims of reduced oil temperatures and quicker revs. While Red-E is considerably higher priced than the other two forementioned oils, it is still very popular among the most serious racers. While the company uses the cost argument that you can leave the oil in longer between change outs, most racers are more comfortable following the normal routine of dropping the oil after each time on the track.