Alki Kits
Race Director
Joined: Jan 2003
Posts: 19,802
Likes: 0
From: San Antonio Texas
St. Jude Donor '05-'06-'08
Alky
In gasoline engines, as with any intercooler, this suppresses detonation so more power producing boost and timing can be utilized. Water, with its high latent heat of vaporization cools the intake charge and combustion. Methanol cools the charge and combustion but also acts like an extremely high octane fuel (some researchers claim as high as 120 octane) as well as adding more oxygen to combustion.The latent heat absorption of water, in conjunction with energy-consuming phase-change processes will reduce the temperatures of the intake's charge. What benefits are there in having a cooler intake charge? Just saying more power would be an oversimplification, but it really depends on myriad other factors. I will touch on a few that come to mind, but this is a topic that runs into heady thermodynamics I am neither inclined nor qualified to delve into.
Having used water injection since the late '70s/early '80s, I admit a long-time fascination that began after having read about P-51 Mustang racing airplanes. Termed "detonation suppressant" in the P-51 ranks, I saw water injection as a natural to internal combustion engines exposed to stress. Especially engines whose dynamic compression ratios extend to 17:1, & beyond. Libary reading of [names-forgotten] library books showed that varied methods of application altered the results of injecting water. Allowing phase change to occur closer to the combustion process, serves more as a detonation suppressant; while futher away, earlier in the intake tract, serves more in reducing intake charge temperatures. Both yield positive benefits, but are divergent in effects on combustion, requiring the tuning approach to take this divergence into consideration.
More than one time I've read that X° of temperature reduction equates to a power increase of Y horsepower. Most often I see that a 10°F drop to intake temps equals 1 horsepower. In & of itself, increasing horsepower by reducing temps based on this formula would not yield a significant performance improvement. Perhaps more important than making visceral power is the new set of conditions that are presented to the combustion process. A cooler, denser intake charge is more conducive to controlling combustion, wherein enhanced reliability is realized.
Controlling combustion, ha! LOL, Who am I kidding? No one. Detonation, pre-ignition, audible & inaudible knock, are all terms relating to critical threshold values that a successful performance engine will respect. They are the line drawn in the sand, where life or death is decided. I hope this metaphor does not go unappreciated. Mechanisms to reduce or eliminate detonation include ignition timing, robust ignition, cam timing, fuel quantity, fuel octane, compression ratio, piston design, combustion chamber design, spark plug selection/gap, & others that don't occur to me at the moment...except for water, methanol-water, or methanol injection. Yes my friends, these near mystical methods of auxilliary injection provide one of the most tractible means of controlling the demon detonation.
Adding more ignition timing is likely the most common by-product of implementing this form of injection. Advancing base timing, & seeing the ECU still not pull back timing under high boost is a sight to behold. It is a pleasure usually reserved for the use of racing gasolines. Coincidentally, reliance on gasoline as a coolant to stave off detonation is a major benefit, thus allowing lower injector duties for a given power output. Running the fuel system at moderate injector duties serves as another reliability enhancement. That factored-in overhead combined with an -aware ECU [EG, EMS] can provide contingency-based fallback maps. Using wideband oxygen sensors, amp; EGT data, or multi-gas analyzers in either realtime on the dyno, or datalogging on the street, full advantage of the detonation-suppressant nature of injection can be taken. So much fun. AFs change with timing changes, too...so, as I may have said elsewhere many times, it can be tedious!
The mixture responsible for this dense, cool intake charge also causes lost volume in the combustion chamber, which serves the premise of combining a high octane component like methanol, or other long chain alkane alcohols. Providing a participatory component to the combustion process helps compensate for the space occupied by the water/water vapor, & a more ignition-friendly mixture is created. Additional value of alcohols is found in high latent heat absorption values. The actual BTUs of absorption are lower than water, but remain a significant contribution to intake charge cooling.
On the last dyno using plain water, AFs were found @ ~12.5:1 thru the meat of 4000-4700rpms, yet EGTs ran ~100F lower than previous runs @ ~12.3:1. Leaning AFs beyond 12.5:1, made power begin to drop, though no audible knock was noted. Likely the knock sensors in action. Keep in mind lambda values when methanol is used. The Methanol-Water Mix section of this page may provide some additional insight if you plan to use it.
Previous to the water injection, 11.8:1 was deemed the best compromise for power/safety- so there was a measurable change in AF requirement to obtain the highest output/safety margin for that day. Disclaimer: By endorsing H2O injection, I cannot stress enough the need for a properly tuned fuel curve, timing curve if you have access, or a reliable knock sensing system if you don't have timing control. It's OK to play, but decide in advance how far you want to go- like choosing your boost level. Keep the ECU/Knock sensors' max threshold[s] in mind, & AFs safe enough to not blow rings/ringlands if the injection happens to take a dump. Use a programmable ECU, & set safeguard thresholds, alternative safe-mode maps, etc.
When elevated boost pressures are targeted, spark plug gaps oftentimes require reduction to ensure combustion. This is a fixed parameter decided upon by analyzing the specific results of using various gaps, as well as considering common use of cooler temperature spark plugs. Trial & error does not take long to find the right temp plug, & sweet spot gap where idle has as few bumps as possible, & boosting to 25psi exhibits no misfire. I start by gapping high to the point of misfire, then backing off a big notch. On my engine, a 0.034" gap had trouble above ~1.5 Kg/cm² on the TO-4E. A 0.026" gap was tried next, which gave back a crappy idle- sort of expected. Power was off across the board, too. A move to OEM spec of 0.031" gap gave good idle & no misfire to ~2 Kg/cm² boost, injection at full gallop.
Testing will tell you what you can get away with. Heh, I use Autolite 3923 copper spark plugs, one step cooler yet still manage OEM gap on them under full boost, without any misfire under load. No, I'm not lucky. A perfectly in-spec OEM ignition system on the 7M-GTE is an engineering marvel; so be sure to have one if you're modding the 7M-GTE, with or without injection. Spare the "but it's a wasted-spark setup," crap. It lights up just fine, BTDT...with injection.
More timing? More boost? Injection yes, but where, when, & how much? Dyno time is invaluable to determining what combination works best, given your unique engine setup. The process is tedious, yet exciting doing have gotten me doing this ~30 years later. More boost, more power. And when each engine disassembly invariably arrives, the very clean intake tract, head, & combustion chambers are exposed, & a retrospective smile will overtake me.
Water injection is relatively easy to install, & calibrate; while inexpensive to maintain. If you only use water, it's just the cost of de-ionized water at your local market. Don't us tap water, please. Methanol/alcohol will increase the cost, depending on what is chosen; but is worth the cost. Literate modders will not find this mod difficult, & will usually yield positive results without too much fuss. The early Buick GN modders used to do it with hardware store parts, while current kits offered by GN enthusiasts can be quite elaborate. The oft-mentioned ERL's 3-D mapped system is quite the techno-marvel. Given the pricepoints of their systems, they sure do think highly of them. Neat stuff, but finding a happy medium is probably the best approach, as the benefits of one system over the other are often touted, but ask yourself: Are they worth the difference in cost? How much of the 'kit' am I going to have to modify to make it work for my engine anyway?
Another price of sorts is an additional maintenance item on the 'frequent fill' list, as well as an occasional adjustment, based on anticipated macro changes to ambient temp/altitude/boost level. Running steep graded, high elevation summits to reach Death Valley in 104°F ambients, to arrive there below sea level at 114° has been done by OldSchool Supra...windows up, AC on. With lots of hill-climbing boost-on, low-pressure injection points were selected, & the engine ran so happily that any maintenance issues melted away. :-)
Having used water injection since the late '70s/early '80s, I admit a long-time fascination that began after having read about P-51 Mustang racing airplanes. Termed "detonation suppressant" in the P-51 ranks, I saw water injection as a natural to internal combustion engines exposed to stress. Especially engines whose dynamic compression ratios extend to 17:1, & beyond. Libary reading of [names-forgotten] library books showed that varied methods of application altered the results of injecting water. Allowing phase change to occur closer to the combustion process, serves more as a detonation suppressant; while futher away, earlier in the intake tract, serves more in reducing intake charge temperatures. Both yield positive benefits, but are divergent in effects on combustion, requiring the tuning approach to take this divergence into consideration.
More than one time I've read that X° of temperature reduction equates to a power increase of Y horsepower. Most often I see that a 10°F drop to intake temps equals 1 horsepower. In & of itself, increasing horsepower by reducing temps based on this formula would not yield a significant performance improvement. Perhaps more important than making visceral power is the new set of conditions that are presented to the combustion process. A cooler, denser intake charge is more conducive to controlling combustion, wherein enhanced reliability is realized.
Controlling combustion, ha! LOL, Who am I kidding? No one. Detonation, pre-ignition, audible & inaudible knock, are all terms relating to critical threshold values that a successful performance engine will respect. They are the line drawn in the sand, where life or death is decided. I hope this metaphor does not go unappreciated. Mechanisms to reduce or eliminate detonation include ignition timing, robust ignition, cam timing, fuel quantity, fuel octane, compression ratio, piston design, combustion chamber design, spark plug selection/gap, & others that don't occur to me at the moment...except for water, methanol-water, or methanol injection. Yes my friends, these near mystical methods of auxilliary injection provide one of the most tractible means of controlling the demon detonation.
Adding more ignition timing is likely the most common by-product of implementing this form of injection. Advancing base timing, & seeing the ECU still not pull back timing under high boost is a sight to behold. It is a pleasure usually reserved for the use of racing gasolines. Coincidentally, reliance on gasoline as a coolant to stave off detonation is a major benefit, thus allowing lower injector duties for a given power output. Running the fuel system at moderate injector duties serves as another reliability enhancement. That factored-in overhead combined with an -aware ECU [EG, EMS] can provide contingency-based fallback maps. Using wideband oxygen sensors, amp; EGT data, or multi-gas analyzers in either realtime on the dyno, or datalogging on the street, full advantage of the detonation-suppressant nature of injection can be taken. So much fun. AFs change with timing changes, too...so, as I may have said elsewhere many times, it can be tedious!
The mixture responsible for this dense, cool intake charge also causes lost volume in the combustion chamber, which serves the premise of combining a high octane component like methanol, or other long chain alkane alcohols. Providing a participatory component to the combustion process helps compensate for the space occupied by the water/water vapor, & a more ignition-friendly mixture is created. Additional value of alcohols is found in high latent heat absorption values. The actual BTUs of absorption are lower than water, but remain a significant contribution to intake charge cooling.
On the last dyno using plain water, AFs were found @ ~12.5:1 thru the meat of 4000-4700rpms, yet EGTs ran ~100F lower than previous runs @ ~12.3:1. Leaning AFs beyond 12.5:1, made power begin to drop, though no audible knock was noted. Likely the knock sensors in action. Keep in mind lambda values when methanol is used. The Methanol-Water Mix section of this page may provide some additional insight if you plan to use it.
Previous to the water injection, 11.8:1 was deemed the best compromise for power/safety- so there was a measurable change in AF requirement to obtain the highest output/safety margin for that day. Disclaimer: By endorsing H2O injection, I cannot stress enough the need for a properly tuned fuel curve, timing curve if you have access, or a reliable knock sensing system if you don't have timing control. It's OK to play, but decide in advance how far you want to go- like choosing your boost level. Keep the ECU/Knock sensors' max threshold[s] in mind, & AFs safe enough to not blow rings/ringlands if the injection happens to take a dump. Use a programmable ECU, & set safeguard thresholds, alternative safe-mode maps, etc.
When elevated boost pressures are targeted, spark plug gaps oftentimes require reduction to ensure combustion. This is a fixed parameter decided upon by analyzing the specific results of using various gaps, as well as considering common use of cooler temperature spark plugs. Trial & error does not take long to find the right temp plug, & sweet spot gap where idle has as few bumps as possible, & boosting to 25psi exhibits no misfire. I start by gapping high to the point of misfire, then backing off a big notch. On my engine, a 0.034" gap had trouble above ~1.5 Kg/cm² on the TO-4E. A 0.026" gap was tried next, which gave back a crappy idle- sort of expected. Power was off across the board, too. A move to OEM spec of 0.031" gap gave good idle & no misfire to ~2 Kg/cm² boost, injection at full gallop.
Testing will tell you what you can get away with. Heh, I use Autolite 3923 copper spark plugs, one step cooler yet still manage OEM gap on them under full boost, without any misfire under load. No, I'm not lucky. A perfectly in-spec OEM ignition system on the 7M-GTE is an engineering marvel; so be sure to have one if you're modding the 7M-GTE, with or without injection. Spare the "but it's a wasted-spark setup," crap. It lights up just fine, BTDT...with injection.
More timing? More boost? Injection yes, but where, when, & how much? Dyno time is invaluable to determining what combination works best, given your unique engine setup. The process is tedious, yet exciting doing have gotten me doing this ~30 years later. More boost, more power. And when each engine disassembly invariably arrives, the very clean intake tract, head, & combustion chambers are exposed, & a retrospective smile will overtake me.
Water injection is relatively easy to install, & calibrate; while inexpensive to maintain. If you only use water, it's just the cost of de-ionized water at your local market. Don't us tap water, please. Methanol/alcohol will increase the cost, depending on what is chosen; but is worth the cost. Literate modders will not find this mod difficult, & will usually yield positive results without too much fuss. The early Buick GN modders used to do it with hardware store parts, while current kits offered by GN enthusiasts can be quite elaborate. The oft-mentioned ERL's 3-D mapped system is quite the techno-marvel. Given the pricepoints of their systems, they sure do think highly of them. Neat stuff, but finding a happy medium is probably the best approach, as the benefits of one system over the other are often touted, but ask yourself: Are they worth the difference in cost? How much of the 'kit' am I going to have to modify to make it work for my engine anyway?
Another price of sorts is an additional maintenance item on the 'frequent fill' list, as well as an occasional adjustment, based on anticipated macro changes to ambient temp/altitude/boost level. Running steep graded, high elevation summits to reach Death Valley in 104°F ambients, to arrive there below sea level at 114° has been done by OldSchool Supra...windows up, AC on. With lots of hill-climbing boost-on, low-pressure injection points were selected, & the engine ran so happily that any maintenance issues melted away. :-)
