Dirttrack510 Posted July 1, 2015 Report Share Posted July 1, 2015 Does anyone know much about octane needed for a given compression ratio in a L series engine? My race motor is 11:1 and I was curious if I can run 92/93 octane pump gas workout damaging the motor? I run a lot of advance. About 38 degrees and a huge cam. Full port and polished head, 280 z stainless valves. Single downdraft weber 38mm carb. This is an L16 engine. Quote Link to comment
Z-train Posted July 1, 2015 Report Share Posted July 1, 2015 "My race motor is 11:1 and I was curious if I can run 92/93 octane pump gas workout damaging the motor? " No. 2 Quote Link to comment
datzenmike Posted July 1, 2015 Report Share Posted July 1, 2015 Too many variables to be exact. Some generalities could be made though. Improper octane to compression results in pinging and at worse detonation, the uncontrolled exploding of the fuel in the combustion chamber that very quickly beaks the pistons or melts them or the head. Basically the heat of compression turns your gas engine into a diesel just before it destroys itself. The following other factors also affect the point where more octane will be needed Heat is the enemy of all gas engines. Hotter days, higher compression, hotter running engines all will require more octane. Too high a heat range spark plug (added to the compression) can be the ignition point needed to start the detonation process. Too lean a fuel mixture will run hotter than richer which absorbs heat by evaporation. You can eliminate heat better by running a larger rad, an oil cooler, cold air intake, fuel return line to keep fuel cooler, heat shields around carb, header wrap or keep stock exhaust manifolds. High humidity lowers the need for octane. Higher altitude (less air = less heat of compression) lessens the need for more octane. Generally a closed chamber head used with flattop pistons can run more compression than an open chamber head with the same compression without pinging. The large quench area generates beneficial turbulence and swirl in the combustion chamber. This eliminated lean mixture areas that are not cooled properly by the in rushing air and rich areas that carbon up and become glowing hot spots than can cause auto ignition. Different fuel providers with the same octane ratings can run differently also. Chevron 92 may run better than 92 from Exxon. Find what works best. 2 Quote Link to comment
Stoffregen Motorsports Posted July 1, 2015 Report Share Posted July 1, 2015 You can have an engine with very high compression and run it on pump gas, but you may need to de-tune it a bit. What octane is required for a specific compression ratio? That question has no simple answer. Combustion chamber shape, cam lift and duration, fuel mixture, spark plugs, timing advance and curve, material of cylinder head. All of these are variables in determining when an engine will preignite the air/fuel mixture. I drove a 12:1 2200 L series on the street for years. I had a monster cam and it was very well tuned, but I had no problems. Eventually I dropped the compression ratio down with a new set of slugs, but I didn't need to. Quote Link to comment
Dirttrack510 Posted July 1, 2015 Author Report Share Posted July 1, 2015 I've always run 110 octane, just didn't know if it was nessesary. Quote Link to comment
DaBlist Posted July 1, 2015 Report Share Posted July 1, 2015 11:1 is your mechanical compression ratio based the space in your cylinder being 11 times smaller when the piston is at the top verses when at the bottom but a running engine only builds compression after both the intake and exhaust valves are closed. Large cams that hold the valves open longer can actually lesson the compression allowing an engine to have a higher mechanical compression ratio without requiring race fuel. As stated ignition timing and many other things have a big effect on fuel requirements too. 1 Quote Link to comment
scooter Posted July 2, 2015 Report Share Posted July 2, 2015 If your 110 octane is pump gas im jealous! And yeah keep running 110, or you can try 100LL avgas. I also think you should pull your timing back to 32-35, 38 is a fuck ton of timing unless a set of rollers told you it made more power with 38 degrees. 1 Quote Link to comment
paradime Posted July 2, 2015 Report Share Posted July 2, 2015 Your 11:1 race motor is a high strung little monkey. Sure you can run it on 92 octane bananas, but you'd have to castrate it to do that. Pull timing and run it super rich and you'd be safe, but you'd have a sloppy ass drunk money instead of a race motor. Be kind to your monkey and feed it high octane bananas. 4 Quote Link to comment
datsunaholic Posted July 2, 2015 Report Share Posted July 2, 2015 My race motor is 11:1 and I was curious if I can run 92/93 octane pump gas workout damaging the motor? Sure. At idle. At full song... probably not. Possibly. Not with that much timing, but possibly. Not sure I'd want to try it and find out it didn't work by blowing holes through the pistons. 38 degrees... that's a lot, even if it's a statically locked dist.. We don't run that much with our "race" engines, and we have a 5 1/2" bore. 28 degrees there. Takes a while for the flame front to progress on a bore that big. 1 Quote Link to comment
Dirttrack510 Posted July 2, 2015 Author Report Share Posted July 2, 2015 On the timing, I agree 38 is a bunch, but this motor likes it for some reason. I've tried running it with less timing and my throttle response dropped off significantly. This is a locked distributer by the way. I buy the 110 at the race track normally, but we have a few gas stations that sell it too. You have to put it in gas cans though, it's illegal to pump it straight into a car, because it's still got lead in it. Quote Link to comment
Stoffregen Motorsports Posted July 2, 2015 Report Share Posted July 2, 2015 Do you know how to tune a race engine? If you do, then go to the track one day with pum gas and tune it for that. You may not be able to, but with a large cam, I suspect you could get away with it. I bet the only changes you'd have to make would be the jetting, timing and spark plugs. Back the timing down to 28-32 and get some NGK plugs (you're probably running Champion right now?) and go run a few laps. Stay away from projected tip spark plugs on the L series motor. Quote Link to comment
620Turbo4X4 Posted July 2, 2015 Report Share Posted July 2, 2015 Stay away from projected tip spark plugs on the L series motor. Curious, Why? I'm running BP8ES plugs in my 11.2:1 L20b DD 620 4X4. My engine seems to like these the best. Tried B7ES, and B8ES, but it likes and runs best with the projected tips with 26-28 degrees total advance. W/ 92 octane. But, This is no race truck. Engine was built for torque and low end power. Running the small Isky 270 cam. Might hit 6k once or twice a week.... Been running the projected 3 years and aprox 30k miles now. No problems with fouling or preignition.... Nice light tan color on insulator and color transition on ground strap right where it should be. The closer you can get plug to center of chamber the faster the burn, and less advance you'll need, and the less advance is less likely to have detonation problems. This article from hotrod.com explains what I'm getting on about... "Electrode and Gap Design When selecting the spark plug “nose” configuration, the simple rule to remember is: The more the spark plug is exposed to the air/fuel mixture, the easier it is to initiate combustion. Many specialized plugs have been developed for high-end race cars, but for most dual-purpose vehicles the choice typically boils down to either regular-gap (conventional) or projected-nose styles. The regular-gap plug is the traditional configuration factory-installed on many classic musclecars. For modern high-performance work, it should only be used if there isn’t enough clearance for a projected-nose plug. The latter style “projects” the spark further into the chamber than a standard plug, and will nearly always offer improved performance if there is sufficient valve and piston clearance, although many nitrous oxide users prefer to stay away from them because of excessive heat buildup in the tip that can cause detonation. Projected plugs initiate the flame-front closer to the center of the combustion chamber, which has an effect similar to advancing the timing. This lets the total ignition advance be reduced, decreasing the chances of detonation while providing superior throttle response. A projected plug’s longer core nose provides a hotter plug at low speed to help prevent fouling. As engine speed increases, the incoming air/fuel mixture flows across the core nose tip, providing charge cooling that effectively reduces the heat range for increased top-end detonation resistance. Today many race cars also used projected-nose plugs, albeit in highly modified form from the “civilian” versions—the ground electrodes are often cut back to help improve the flame kernel and reduce the voltage amount needed to fire the plug. Read more: http://www.hotrod.com/how-to/engine/spark-plugs-tips/#ixzz3elU1m25U Follow us: @HotRodMagazine on Twitter | HotRodMag on Facebook Back to the original question... I don't see why not, as long as your not running an open head and or, pop up pistons, obscuring or delaying the flame front. With a closed head/flat top piston combo it should be fine with proper tuning. The difference in power might not be all that much since 11:1 is not really taking full advantage of 110 octane fuel... 2 Quote Link to comment
Stoffregen Motorsports Posted July 3, 2015 Report Share Posted July 3, 2015 The projected tip plugs encourage detonation on L series motors. I don't know why, but dyno testing and general tuning prove that they are no good for this particular application. Before you jump all over me and explain why they should work, understand I am coming from personal experience. If you want to try them, be my guest. 620Turbo4x4, this defensiveness is not directed at you specifically. Check out this link: http://www.ngksparkplugs.com/docs/tech/racing_spark_plugs_performance_applications.pdf 1 Quote Link to comment
620Turbo4X4 Posted July 3, 2015 Report Share Posted July 3, 2015 No need to be all defensive, and no, I'm not going to jump all over anyone and explain why they should work. Now that would be foolish... There are many different factors in determining the correct plugs for any engine, including the driver... Was just curious your reason why not to use on a L series, and if it's something I should be concerned about with the CR i'm running... My dirt bike runs a $30 plug with an extra thick insulator, cause if was found that engine harmonics would break the standard plug insulators... The projected plugs were actually my last choice. I had the same thoughts of pre-ignition, leading to detonation. The B7's I tried got too hot under load and the B8's had trouble staying clean. The BP8's, properly indexed and timed, turned out to be the happy medium in my case. To me, the hotrod article makes perfect sense and is what I experienced.. The NGK application guide doesn't really explain what to look for when choosing plugs besides the insulator color. Reading the ground strap can tell a person if engine is happy with the timing, and threads can indicate whether or not the heat range is correct. These articles aren't bad, http://www.4secondsflat.com/Spark_plug_reading.html http://www.dragstuff.com/techarticles/reading-spark-plugs.html Thanks for the reply. Now, back to the subject... 3 Quote Link to comment
Stoffregen Motorsports Posted July 3, 2015 Report Share Posted July 3, 2015 You're right. I should pull my panties out of my sandy vagina. NGK does offer tech support. On the link somewhere there is a tech number you can call and they will help you chose a plug based on a variety of questions they ask. I would be curious to find out what plug they would suggest. Quote Link to comment
Z-train Posted July 4, 2015 Report Share Posted July 4, 2015 Do you know how to tune a race engine? If you do, then go to the track one day with pum gas and tune it for that. You may not be able to, but with a large cam, I suspect you could get away with it. I bet the only changes you'd have to make would be the jetting, timing and spark plugs. Back the timing down to 28-32 and get some NGK plugs (you're probably running Champion right now?) and go run a few laps. Stay away from projected tip spark plugs on the L series motor. ^^^^^^ Quote Link to comment
Dirttrack510 Posted July 5, 2015 Author Report Share Posted July 5, 2015 My engine is tuned just fine, The only reason I was wondering is this... I'm working on a new car (SCCA type) and was considering using my race engine for some street duty, just for fun. Not a daily driver, but the occasional trip to a car show or cruise or sumpin'. :D I'll probably end up just slapping in a good L18 I have lying around and swap in the L16 for races, as it only takes a few hours. :P No build page, cuz I'm working extremely slow on this one and figure i'll post most of it when the car is done. Quote Link to comment
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