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Help: Question Repository
- Get 300 hp more using nitro
- Higher idle checks
- Weather standard for baseline
- Fuel pump pressure for gasoline
- Does Pro-calc support E85?
- Can I save run data?
- Adding low percentages of nitro
-Jetting for a gas lakester at Bonneville
- Getting nan results
- I'm unsure of my blower size
- AFR compared to stoich point
- My engine is still running fat
-Tuning turbo engines wih mfi
Below are responses we've provided to racers who've sent in questions over the years. Some of these may be specific to their engine setup but we hope you can get something out of them as well. Also keep in mind, sometimes these reference the books at racecarbook.com. Purchasing these books would help you but should not be necessary to to get use out of the answers provided here.
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How much Nitro would we need to get 300 HP more in the engine?
With reference to nitro HP, take the horsepower that the engine is making and determine the percentage of power increase for your 300 hp goal. For example, if the engine makes 600 hp on methanol, then 300 hp increase / 600 hp = 0.5 or 50% power increase. Check out p. 92 & 147 of the blown nitro book for the amount of btu's increase with different amounts of nitro. Those btu values would be close to the power increase for the various percentages of nitro. Using the example for a 50% power increase, that would be about 45% nitro amount (by weight) from the table on page 147. Page 87 & 147 have stoichiometric air to fuel ratios for different amounts of nitro. For enrichment amounts of 70% (or more for greater amounts of nitro shown for blown engines in those tables), the revised air to fuel ratios are shown as well. Those values would be the air to fuel ratio target for jetting in the ProCalc (instead of 5 to 1 for straight methanol). For 30% more fuel for enrichment amount for a normally aspirated engine, the revised AFR would be 3.6 / 1.3 = 2.8 That would be an AFR of 2.8 to 1. That would be the AFR target for jetting in ProCalc, (again instead of the 5 to 1 for straight methanol). In addition, in ProCalc, you would enter 45% nitro by weight for the fuel mixture. ProCalc will adjust the weight of fuel for the nitro addition. A combination of nozzles and main bypass to keep fuel pressure over 50 psi at the low engine range would be a reasonable goal as well. Your engine may need an enrichment of a little more or a little less than 30%. That is an AFR of a little less numerical AFR of 2.8 to 1 or a little more numerical AFR or 2.8 to 1. That would be revealed by the spark plug reading and the performance. Somewhere around that value, one or two spark plug threads will be discolored and the engine should run the best. You may also need a few more degrees of spark advance over your best value for straight methanol. For example, if you are running 38 deg of spark advance for methanol, a spark advance for 45% nitro may be around 42 to 45 degrees. Writings are in the books about the spark advance issue from nitro. It is harder to start to ignite the mixture. After it gets past first stage combustion, it continues to ignite faster. The relation is complex but written about in the books. FYI 1: At lower percentages of nitro, less enrichment may make more power. The fuel acts more like methanol. FYI 2: However, for higher percentages of nitro, more enrichment (up to a point) may make more power. That would be from monopropellant combustion of the extra nitro beyond the stoichiometric ratio. That would occur only if the mixture is well ignited by the amount of ignition that is present, the engine temperature, the compression ratio, the ignition advance, and the best working air to fuel ratio. There is info in the nitro book and the hi HP tuning book about monopropellant combustion as well as the other values. The key to making good performance from nitro is a good combination of all of those. The methanol book, p. 202, has a table on the temperature ranges for fuels including temperature for vaporization and self ignition limit. That is the range to operate an engine. The combination of compression ratio, spark advance, nitro percentage, fuel enrichment, and AFR detemine if you stay below the self ignition temperature or not. The methanol book has a lot more info throughout.return to top
For those that run higher idle checks, where do you end up at with the BV?
I upped the idle to 12#. It was huffing fuel out at idle, barrel at 80%. Instant iced injector and cold pipes loading up in gear, etc. Spun the quick-Adjuster (Ray Hadford's deal) until we ran out of adj and it was 'better'. not right, still wanted to load up. I haven't flowed it to see where it is, but i will tomorrow. gotta be in the LOW 70%'s (or high 60's).
OUR HIGH PRESSURE SETUP We ran 12# and various idle leak downs depending on the outside temp; in the FI book; from 65 to 75% on our KB leak down meter. IDLE FUEL CAN BE THE SAME BUT BV PHASING DIFFERENT The idle fuel ends up the same. That can be determined by idle oil temp with a heat gun. Set low idle pressure/high leak down and high idl pressure/low leak down to heat the oil at the same rate at idle. You want 150+ oil temp. Probably not more than 180 on the starting line, after the burnout. The idle bypass hole (and pump relief bypass hole in K valve) and idle slot end up in different locations at the two idle position; phased a bit different with the throttle plates. HIGH PRESSURE IDLE For the high pressure low leak idle, the bv is rotated against the throttle direction at idle. Bypass holes are disabled later only after greater throttle opening. That would make the mid throttle leaner. LOW PRESSURE IDLE For the low pressure high leak idle, the bv is rotated in the direction of throttle opening at idle to reproduce your idle enrichment characteristic. Idle and pump relief bypass holes are closed down sooner with less throttle movement that would make mid throttle richer. CONSIDERATIONS Those relationships may be important to throttle response off idle and burnout power. If burnout power is limited due to excessive enrichment, then the high pressure idle may lean it out more at mid throttle and pick up power. We reduced our pump relief poppet from about 125 psi, as received from the MFI supplier, down to 100 psi. Burnout power picked up a bunch. Our off idle response and low end power was real good. Watch our videos of idle launch or low RPM launch all with a pedal clutch at 1500 pounds static. SQUARE BV For the square valve, there would be no pump relief port. SQUARE BV OVERCENTER CHECK For the square barrel valve, if you change the combo, put a leak down meter on the idle secondary bypass output and rotate to full throttle to make sure you do not go overcenter if you are advancing the bv with more leak down and less pressure. If you are overcenter, the leak down meter will stop flowing at mid throttle then start at full throttle. That is bad. LEAK DOWN METER ADDED CHECK You can also use the leak down meter to determine what throttle position the idle secondary bypass power is shut down. That would be for the square or K valve. The important issue is the amount of throttle blade opening. You can check it for the low pressure and high pressure idle. See how much throttle opening differs with the two setups. That will give an idea of off idle and mid throttle burnout power characterisitics. Or try both and see what one feels better. K VALVE LEAK DOWN METER ADDED CHECK For the K valve, you can use the leak down meter to determine what throttle opening that bypass is shut down as well. It will be at a phase that is different then the idle bypass output port As well as an overcenter check also.return to top
Would it be correct to also use the Baseline profile to determine AFR 5.2:1 @ 85% VE for a 360CI to find M O.OO" & HS O.OO" jets using 60 degrees F, 0% H, and 29.92" Hg as weather?
That is a great question with a difficult answer. I often use 100% air density from those weather values in computations featured throughout the jetting books and in our other books to illustrate different tuning principles. For my consultation & tuning with local racers in Sacramento, CA, I use temp 80, humidity 30, and (uncorrected) barometer 29.9. That provides and AD of about 96%. Those are the frequent local weather values and a common local weather AD. One strategy for a baseline is to determine the range of weather variables that you intend to race in. Determine the worst and the best. Then pick a combination of weather values to get an AD in the middle or an average for weather entries. There may be a different between the middle and the average. That is a decisioin. Then, use that value for the baselines. Then the jetting moves from the baseline should be the smallest values. Unfortunately that is not always easy. I often saw mixtures of good and bad temp, good & bad humid, and good & bad baro that made the determination of an average AD difficult. Especially when multiple racing locations with dramatic elevation changes are envolved. Studying the weather values is a good tuning exercise to get in the middle if that is possible. Most of the racers I encounter do not do that for planning. They setup and tune in a serial fassion. Just tune for the new condition without good planning. Most MFI tuners do not do a real good job of air to fuel ratio control without some method of air to fuel ratio management. Some have great tuneups from a lot of testing, but are real fragile to extreme weather or location changes without air to fuel ratio management. A good indication is the frequency of engine failures at most racing events. At the local drag racing events, banged blowers and melted head gaskets or pistons are quite common as are poor performance from overly rich mixtures. Not too long ago, one of the top ProMod local racers ran so rich, that he had to change oil every round. It was completely contaminated with methanol. In our last test program on nitro, we ran the same oil all year. We added oil to make up for consumption, but never changed the remaining oil. We had good air to fuel ratio control with good engine temperature control. The engine was amazingly reliable, even on nitro with a blower. The oil looked like new at the end of the season. FYI: we did drain it every outing and inspect. And always put the remainder back in. We also check our oil filter every round. Experiences like that sold me on good tuning with air to fuel ratio.return to top
Looking through your book, I can't find a recommended fuel pump pressure for gasoline. All I find is 50+ lbs for alcohol. What is the recommended fuel pump pressure for gasoline?
Which book are your referring to? We have several. Do you have our new book High Horsepower Tuning for Mechanical Fuel Injection For Normally Aspirated Racing Engines. If not, look at the index of terms and index of names in the book description on www.racecarbook.com to get an idea of what is in it: info specific to gas including a section for gas on the street, recommended gas jetting combos, gas fuel pressure info, & the effect of fuel weight differences in gasoline on air to fuel ratio. Hilborn says keep fuel pressure below 50 psi for gas. Kinsler recommends around 50 psi for the cruising range. The proper fuel curve is vital for gas because of the narrow tuning window. Compensation for changes in the weight of the fuel are vital.return to top
Does this program support the use of E85 blended fuels? if I plug in the AFR I'm after, is that calculation in the ballpark?
Yes it is can be used to support ethanol blends. Air to fuel ratio computations for air to fuel ratio are good for the 85-15 mixture ratio. ETHANOL-GAS MIXTURE CHANGES However, E85 at the pump can vary quite a bit from the 85-15 label. For different mixtures, the fuel weight will change. That can be compensated for in the calculator to produce good air to fuel ratio determinations for those blends as well. TWO TUNING TASKS FOR DIFFERENT MIXTURES We found that it is important to know the mixture ratio and adjust for it in tuning. We saw ethanol-gas mixture ratios vary from 70-20 to 90-10 from pump blends. Two vital tuning tasks result from that change: -- one is tuning adjustment for the weight difference in the fuel that can be done quite easily with the calculator -- two is tuning adjustment for the target air to fuel ratio; mixtures with higher amounts of ethanol would need to be run richer than those with lower amounts of ethanol; however, the calculator is a good tool to help determine those AFRs for the different mixtures. THIRD TUNING TASK FOR AIR DENSITY Jetting adjustments for air density from weather or altitude changes is a third tuning task for mechanical fuel injection. The calculator can determine main bypass, nozzles, or a combination for the numerical air to fuel ratio. MAINTAINING FUEL PRESSURE The calculator also determines the fuel pressure. Engine response from adequate fuel pressure can be maintained in the jetting size profiling for all the different conditions. Note that the appropriate jetting change for different mixtures with different AFR needs in different air densities with good fuel pressure is almost impossible to trial-and-error find in a reasonable time without a shortcut tool like the calculator. Most of that task can be done in virtual reality, ahead of time, without the expense of testing. TIP: STANDARDIZE AN ETHANOL-GAS BLEND One tip is to standardize the ethanol blend to a specific mixture that is most common or easiest to achieve such as 80-20. That is easy to do by adding gas to ethanol rich mixtures, then jetting for air density changes for a constant ethanol-gas mixture. SUMMARY With a little discipline, ethanol fuel blends become a great source for power, and tuning using the calculator is very repeatable. With the ability to numerically determine air to fuel ratio from jetting and air density, you can very carefully lean down to the best power with less risk of engine damage. The calculator allows you to maintain a repeatable air to fuel ratio and fuel pressure in changing air densities. In effect, the calculator acts like the computer in EFI. We did some full throttle fuel maps with the calculator for mechanical fuel injection. We are now studying idle air to fuel ratio and AFR at launch with various launch controls and throttle positions.return to top
Can I save my run data?
Fuel injection jetting & tuning info is throughout our books based on math. My daughter put all of that math together into a fuel injection jetting calculator called ProCalc. It also is equipped with a data output function for recording and analysis in a spread sheet program such as MS Excel. It is a tool for checking your previous setups or determining a new setup.
Here is a snapshot of one of the calculators -- AFR calc for a 469 ci normally aspirated engine. It was selected from a custom baseline profile that was previously setup to determine jetting and fuel pressure for a high altitude racing location (low uncorrected barometer):
Each of the calculators has a comma separated value output for fuel injection data. That will open in a spread sheet program like MS Excel. Jetting records are made that include air density data, air to fuel ratio, fuel pressure, and any jetting changes (or blower overdrive changes if so equipped; blown engines are set up with a different format in ProCalc showing blower size, overdrive, and efficiency).
Here is a sample MS Excel spread sheet that was constructed for a normally aspirated 383 engine with mechanical fuel injection. It was constructed from exporting data over several calculations. The tuning air to fuel ratio is examined for three different temperatures to show low end (torque peak) and high end (HP peak) jetting. Columns of numbers from different tryouts were imported into a single spread sheet file. Here is that file:
The first three columns would be torque peak setups typically running at 100% volumetric efficiency; without a high speed bypass.
The second three columns would be horsepower peak setups typically running at 80% volumetric efficiency; with a high speed bypass to lean out the high end. A reduction in volumetric efficiency is common in normally aspirated engines at engine speeds above the torque peak.
Temperature, humidity, and barometer are part of the record.
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How much nitro can I add to my blown altered to get below 7.5 seconds ET
This was originally posted on racecarbook.com. View the original post. At a local drag racing event recently, we helped one of the racers chop 0.3 seconds off his ET slip with a correct addition of a low percentage of nitro. The racecar was an early model, low compression Hemi drag car with a small 6 GPM fuel pump. It ran solid 7.6 seconds in the quarter mile. The owner / driver said it was close to the limit on methanol. He had a few gallons of nitro to pump up the power. Rather than guess how much to run, we did an analysis using our resources. Engine Analysis: His combination was entered into our ProCalc jetting calculator. His air to fuel ratio on methanol in this low compression, 6-71 blown Hemi was at 4.3 to 1. That would be lean for a higher compression blown engine, according to our new nitro book. The main bypass jet was removed from his jetting profile in the calculator. That was done to determine how much more fuel could be put into the engine. With more fuel into the engine, enrichment from some amount of nitro could be done. ProCalc was used to determined the air to fuel ratio (AFR) for various percentages of nitro. That took only a few minutes. Nitro Addition Analysis: The AFR requirements for different percentages of nitro were determined from our new nitro book. I asked if he preferred measuring the nitro by weight or by volume. He preferred measuring it by volume. At 10% by volume, info from our nitro book indicated a 3.8 to 1 air to fuel ratio ‘on the pump’ for his combination. That took a few more minutes. Good Combination: With 10% by volume nitro entered into ProCalc with all the fuel to the motor, his air to fuel ratio was 3.8 to 1 from his fuel system. That was the cross over point. If he ran more nitro, his engine would be out of fuel pump and too lean. If he ran less nitro, his engine would be too rich. That could cause a power reduction over straight methanol. All total, we spent about a half hour sorting that out. Fuel Pressure Analysis: ProCalc was also used to check the fuel pressure increase with the removal of the bypass. This check determined that the pressure increase would be about 10 psi more than the straight methanol setup with the main bypass. That was still within the fuel pump rating. Successful Result: He removed the bypass jet, added the the correct amount of fuel mixture, and ran effortless 7.3 sec ETs with no reported damage. Cost data in our nitro book revealed an increase of $45 in added fuel costs per round. Not bad for a 0.3 second drop in ET! Even More Power: Using ProCalc, we examined how to turn the power up if necessary. To do this, we looked at dropping the blower overdrive. That would allow an increase in nitro percentage. With 24% less blower overdrive ratio, 15% more nitro could be run on a safe air to fuel ratio at a different cross over point, within the limits of the fuel pump that was installed. The power would be down from a slower blower. However, it would be up from more nitro. Using our BTU’s table in our nitro book and adjusting for a slower blower, the power would still be increased further by about 7% over the previous lower percentage of nitro that was successfully run. Although the owner / driver did not have to run this combination, that would drop the ET another tenth or two if needed. That took less than a half hour to determine. It demonstrates that blower overdrive and nitro percentage can be juggled in virtual reality with ProCalc to get the most power within the limits of the fuel pump and the fuel injection jetting setup. This combination represents almost a half second drop in ET. According to a cost table in our nitro book, that percentage would be about $62 more in added fuel costs. Where can you go anywhere on earth for $62 a run and get a half second drop in ET? Try “Blown Nitro on a Budget”.return to top
I am trying to figure out the jetting for a gas lakester at Bonneville. My problem is, at speed, 250 to 300mph, I will have up to 1.5 lbs of boost on a normally aspirated engine due to ram air entering the intake. I do have an enrichment valve because I will be running @6500 rpm, right at the torque peak. Is there any way to calculate the enrichment?
Regarding ram air boost, you can modify the engine size or the volumetric efficiency in ProCalc based on the amount of ram air boost. Then compute jetting for that weight of air going into the engine. In this case, I did the following for VE modification instead of an engine size change: Sea level dyno:- assume ambient psi: 14.7 psi
- boost pressure: 1.5 psi
- VE correction for ram air: (amb psi + boost psi)/amb psi
- VE correction for ram air: (14.7 + 1.5)/14.7
- VE correction for ram air: 16.2 / 14.7
- VE correction for ram air: 1.10
- air pressure at elevation = barometer at elevation / 29.92 x 14.7
- assume barometer at elevation = 24.5 inches HG
- air pressure at elevation = 24.5 / 29.92 x 14.7
- air pressure at elevation = 0.819 x 14.7
- air pressure at elevation = 12 psi
- VE correction for ram air at Bonneville = (12 + 1.5) / 12
- VE correction for ram air at Bonneville = 1.13
- assume 6 pound per gal (PPG) gas
- assume a fuel pump rated at 3.8 GPM at 4,000 pump RPM / 8,000 engine RPM
- derated pump entry = 3.8 x gas weight / 6.6
- derated pump entry = 3.8 x 6 / 6.6
- derated pump entry = 3.8 x 0.91
- derated pump entry = 3.45
- fuel pressure around 50 psi with the 3.8 pump entry and
- AFR around 12.5 to 1 at torque peak & HP peak with a 3.45 pump entry, at altitude.
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Keep getting a NAN IN for main jet size. What does this mean and how do I get the correct jetting?
A nan is usually a result of a combination of jetting entries that do not compute. That is commonly a result of an entry error. Throughout the baseline screen are references to instructions that provide information on entry numerical formats. Typical entry mistakes are jet or nozzle number such as 14 instead of the jet or nozzle diameter such as 29 or 0.029. The diameter is necessary for the entry. It can be put in as a whole number or a decimal. In blown engines, I have seen entries like 1471 instead of 550 from the instructions that are referenced. The displacement of the blower is needed. Not the blower number. For blower overdrive, I saw an entry of 20 instead of 1.2. An overdrive of 20% over is 1.2, not 20. Another possibility is extra digits in an entry from overwriting oversites. I saw extra digits that do not appear in a field. For example, a nozzle entry of 0.270.29 may not show the .029 on the screen. It would not not compute. I saw problems with weather entries (temp, humidity, & barometer) as well. It is important to enter either an uncorrected barometer with no altitude entry or a corrected barometer with an altitude entry. That is explained in the instructions. A nan is also possible, in some combinations with no mainbypass in the baseline profile for example. Data pulled from the baseline will not compute in the jetting calcs, and a nan may be the jetting calc result. Roundoff error in the math in the various calculators may not compute very well and cause a nan in the answer. With no mainbypass entry, for example, the jetting calcs -- mbp, nozzles, and jetting from pressure may generate a nan for the answer. That is a result if a zero mbp entry that is pulled from the baseline that may not compute from a different direction in the math. With 4 different calculators, some jetting combinations result in a nan answer. It is like trying to divide by zero in a hand held calculator. That faults out from the entry combination. Each of the calcs compute from a different direction. In some baseline combinations, a change in one of the calcs just don't compute from that direction. It became apparent to me, as I investigated different combinations on the calculators that trial and error jetting in the field can be a crap shoot.return to top
I'm want to set up my baseline but I'm unsure of my blower size.
I entered your profile and set up a combination for a 14-71 at 60% over. That is a blower overdrive of 1.6. Then I entered two rows of nozzles at 0.050 each. I put in local weather. I changed the main bypass for an AFR close to 3.4 to 1. That took a 0.020 inch dia Main bypass. At that size identified by ProCalc, there may be none or zero for a main bypass with all fuel going to the motor. A blower OD of 1.6 is very high. That is normally only used in max effort engine that is run a lower engine speed such as less than 7,000 RPM. FYI: Roots blower speed over about 9,500 RPM becomes much less efficient. Blower belt drag is significant and blower belt life would be low. Most Roots blowers over about 12,000 blower RPM stall and power is not gained from higher blower speeds. As we discussed, the blower size needs to be confirmed. The main bypass that was run needs to be determined. Then you can determine what AFR was run with the combination that was set up. Regarding the inlet fitting, that right angle fitting would lead to inlet suction problems that may cause a lean out at higher flows (engine speeds). If that is how this engine was run, then high end leanout would be a good possibility with the previous setup. As we discussed, a gentle inlet bend is needed.Thanks again for spending do much time explaining things yesterday, I really appreciate it! I did pull the hat off last night and measure the rotors, it is indeed a 1071 blower. The jet/pill is a 70. There was a 55 jet/pill above the pump I believe you call that a "high-speed bypass"
REVISE PROCALC ENTRIES: After you revise the baseline that I set up in the jetting calculator, you can determine your high speed air to fuel ratio displayed in the baseline summary. Then run the AFR calculator to get fuel pressure. When you enter any one of the calculators such as the AFR calculator, you will have to re-enter the weather. After that, get a run through of the AFR calculator with that high speed bypass. That will tell you the fuel pressure with the high speed open. Note the air to fuel ratio. If it is numerically less than 3.4 to 1, it is rich. If it is numerically less than 3.5 to 1, it may be too lean. HIGH SPEED POPPET SETTING: You should check the poppet attached to the high speed coming out of the pump. If it is around 50 psi or more, that is probably a high speed bypass that is suppose to open at higher RPM. If it is set to a real low pressure such as 20 psi or less, it may be what is called a pump sizer or pump saver. It would be open at any pressure above that low setting and that would be the air to fuel ratio from that RPM up. HIGH SPEED BYPASS OPENING RPM: Next, remove the 55 high speed from the baseline or in the AFR calc and run the AFR calc. That will give you the low speed air to fuel ratio before the high speed bypass opens. Again, that would only be the case if that is used as a high speed leanout at higher RPM (poppet pressure around 50 psi or more). It will also give you the fuel pressure that occurs at full throttle before the high speed opens. You can vary the target RPM entry in the AFR calc to get the fuel pressure that matches the high speed poppet opening point. That determines the engine speed where the high speed opens and the engine goes from the low end AFR to the high end AFR. FYI: You will read about our high speed. We determined that on methanol, a high speed bigger then 0.040 inches was too large. MORE ON THE CALC: There is a bunch of instruction about varying the target RPM with and without different jetting to get the fuel pressure without various bypasses or jets. REGARDING PORT NOZZLES: For example, see if there is a poppet in the feed line of the port nozzles. If there is, check the pressure that it is set at. When we ran port nozzles (nitro book data), we set our port nozzle poppet to a low value so that the engine would idle on the port nozzles. Some tuners set it to a fuel pressure above the idle pressure so that the engine will not idle on the port nozzles. You will just be unraveling the setup. NOZZLE SIZE: I think those 0.050 nozzles in the hat and ports will show up to be too big. I expect your fuel pressure may be real low. If your 8000 RPM fuel pressure is below 50 psi, there is some power and a lot of response to gain by shrinking down those nozzles. HAT NOZZLES ONLY: In fact, for the low blower speed to start, you may want to disconnect your port nozzles. Those hat nozzles only will probably get your over 100 psie pressure for and 8000 RPM value. You will read about our experience with nozzle size and fuel pressure throughout the racing secrets book and the nitro book.return to top
According to the AFR calculations my engines are running at 3.46:1 on methanol. The stoich point of methanol is 6.4:1. Am I running way too rich? Or am I confused?
Our blown methanol drag hemi ran 3.4 to 1 as the center of the operating window. At 3.8 to 1, it melted pistons. It had 12 to 1 cr and 2+ atm of boost. We ran a drag racing test program for a lower compression, blown alcohol combo that was best around 3.7 to 1. At the lower compression, the center of the afr window was much different that for the high compression engine. So engine compression for blown engines is a significant issue for the best air to fuel ratio. Blown methanol wedge engines with high compression run best a little less rich at around 4 to 1. Normally aspirated engines run around 5 to 1. One recent dyno test of a sprint car engine made the best power at around 6 to 1. However, it is doubtful whether that would work in racing with a light weight cooling system. Yet we saw a sprint car engine running as rich as 3.6 to one at the torque peak, getting less rich at 4.6 to 1 at the horsepower peak. Not sure of the condition of the cooling system. Enrichment was needed in this case to keep engine temperature down over the many rounds. Methanol is a form of fuel intercooling. We present NASA data in our methanol tech book that shows the potential temperature of various engine fuels around stoiciometeric combustion. For most fuels, it is way high, beyond the melting point of steel, without some type of suitable heat sink or fuel volume limitation, or reduction if flame speed from the nitrogen in the air. We go far into air to fuel ratio throughout our publications at www.racecarbook.com You can browse the store for various books and check index of terms for the extent of afr in the various books. Our methanol book is 300 pages, all centered around the proper afr. FYI: once a good afr is deternined for a particular engine combo, it can be reproduced with proper jetting info from ProCalc for different air densities and altitudes. For blown engines, the blower can be changed. ProCalc can be used to determine revised jetting to maintain that same afr or the revised blower overdrive to maintain the same jetting and power. Plug readings will be maintained. At 3.46 to1, that sounds like a good value for a blown hemi engine with high compression. It may also be a good value for a blown alcohol wedge engine with really high compression. One of the local racers was running 14.5 to 1 cr with a high overdrive 1471 blower. His afr was in the low 3's His did scatter the engine at that cr and did not maintain good afr control. He did tuning by the seat of his pants. Screw blown engines with 60 psi manifold boost run around 3 to 1. I analyzes some as fat at 2.6 to 1. Not sure they were optimum although they did run in the 5s ETs for drag racing. On our web site is a lot of free info on a blog, news letters, and freebies about afr enrichment. Also we have a nitro book that provides afr's for different percentages of nitro. All determined accurately with chemistry analysis and confirmed with many setups from actual racecars. In fact your nitro book does an extensive analysis for low percentages with a blower. Our methanol book has afr info for many different fuels. Our fuel injection secrets book has afr's from several running racecars. Our high HP tuning book has a ton of afr info for normally aspirated engines.return to top
My best was 770 @ 174mph. It was still really fat. I need you to help me get this thing to run 750 @ 185 mph
That would make sense. At a 3.4 AFR, that is very rich for a blown BB. it should be closer to 4 to 1 with 8,000 RPM fuel pressure closer to 100 psi. One intermediate step you can do is remove hot nozzle 3,4,7,8. Install blanks and plugs. Put them at zero in the calc. That will reduce your nozzle area. Then rerun the AFR calc changing the main bypass or the high speed entry until you get closer to 4 to 1. Then examine your pressure. If your 8,000 RPM pressure is over 65 psi, you should be all right for your next outing. If not, you should look at changing nozzle sizes. Another step it to block off your port nozzles. If the nozzle holders are the same as your hat nozzles, then put a couple of the large port nozzles in the front of the hat. That should bring up your fuel pressure over 100 psi. Then adjust your main with no high speed for the 4 to 1 AFR. You should not need a pump saver high speed. Block that off as well. If the port nozzles are different, then you may need to get some larger hat nozzles. If you have our racing secrets book or our nitro book, you can look up our hat nozzle jetting from our various runs. i think is was around 46 to 50, larger in the front in 0.002 inch increments. With hat only nozzles and a conventional blower lower opening, you should staggar the nozzle size in 0.002 inch increments starting with larger ones in the front.return to top
What procedure is there for turbo engine wih mfi?
TURBOCHARGED MECHANICAL FUEL INJECTION ENGINES The calculator can be used to determine jetting for a mechanical fuel injection with one or two turbochargers & boost controlled waste gate. (Series turbo charging or series turbocharging with a mechanical supercharger can be done as well). The recommended setup for turbocharging uses two nozzles per cylinder. The first nozzle is sized for the normally aspirated mode. The second nozzle is sized to provide added fuel necessary for boost. Two different setups are done in the calculator: One is the normally aspirated mode with one set of nozzles and two main bypasses. Jetting is adjusted for an air to fuel ratio of about 5 to 1 for methanol fuel.- The weight of air for the air to fuel ratio is determined by the calculator for the normally aspirated engine size, volumetric efficiency, and air density.
- The weight of the fuel is determined by the calculator for the amount of fuel flow through the one set of nozzles with the two main bypasses.
- The weight of air for the air to fuel ratio is determined by the calculator for the engine size x the boost in atomospheres.
- The weight of fuel is determined by the calculator for the amount of fuel flow through the two sets of nozzles (added set enabled with boost) and the one main bypass (other bypass shut down with boost).
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