cygnusx1 Posted August 17, 2011 Share Posted August 17, 2011 (edited) I am thinking about installing a new FPR to run a little more fuel pressure than the factory ZXT regulator does. Back when I ran the stock ZXT injectors, I ramped up (RRFPR) to 65psi of fuel pressure on boost to keep the AFR's in check. Now I have 440cc injectors and run stock pressures. I am thinking that a higher base pressure will do two things. It will keep the fuel further away from vaporizing point, and it may improve the atomization through the nozzle. Of course I will need to adjust the fuel map in Megasquirt to compensate. I am thinking 45-50 psi. Thoughts? Edited August 17, 2011 by cygnusx1 Quote Link to comment Share on other sites More sharing options...
stprasinz Posted August 17, 2011 Share Posted August 17, 2011 As long as the fuel pump can keep up at full boost (every psi of boost is 1 psi of additional fuel pressure) so, add the amount of boost you are running to know the maximum fuel pressure you are running. And as far as negatves, other than I just listed, until the point your running so much pressure you slow the injector opening time, or worse even yet, lock the injector entirely, there are only positives... When I install the 2 parralel walboros I'm gonna run about 55-58 psi of base out of 440 injectors... should result in better idle from the atomozation, and more hp potential from more fuel... and i think base pressure of factory is 44 psi... so 45 would be negligable, and 50 would be slight improvement, and should be simple to tune it back. And may even benefiet from better idle, but you'll have to retune the idle, not just by math, but a basic start over for it. good luck, and you should be happy with the final results! Quote Link to comment Share on other sites More sharing options...
Tony D Posted August 20, 2011 Share Posted August 20, 2011 That's it, as long as the fuel pump has the flow at the pressure, there should be no problems. You will effectively have 500CC injectors++ with the higher pressure (4 bar VS 3 Bar), so you will have to re-tune accordingly. The only practical advantage will be the vapor point increase in the rail. As I mentioned previously, there IS a SARD Fuel Cooler available now to keep the temperatures under control on the fuel side. Just realize 4-5 psi isn't going to do much for you, on suppression that is. It's not really doing anything for you from the 'atomization' standpoint. JeffP was running a 4 Bar base pressure (60psi) to get higher capacity from existing 450CC Mercedes Injectors. This is the most common reason for doing it, as you stated. Even with the higher pressure, the phenomenon of changing AFR's still occurred. It's not changing state, the BTU content changes due to less dense fuel. THIS is the root of the problem, not 'vaporization'... You are heating the entire fuel tank (exacerbated below 1/4 tank for sure!) This is why newer cars with tighter emissions standards incorporate fuel temperature sensors (this is on the Z31 box, and usually jumpered high on conversions.) Quote Link to comment Share on other sites More sharing options...
Chemicalblue Posted August 21, 2011 Share Posted August 21, 2011 Most injectors have a min and max pressure, they also have a recommended pressure that they should be set at to get the listed ???cc. Raising the fuel pressure beyond that point has a negative effect on the injector and spray pattern and hurts the injector. I would never (from a tuning stand point) raise the fuel pressure to compensate for "keeping AFR in check", that's what the ecu is for. A RRFPR is an old school way of doing things that's not very reliable and needs to be checked constantly. If your tune in MS is correct you should be able to run as high of a boost pressure that you want, until you run out of injector flow capacity. If you are out of injector flow capacity and are set at the factory pressure, sure, bump it up till you hit the max recommended pressure. Just adjust the entire map to compensate for the change, and expect a low injector life. My 2 cents Quote Link to comment Share on other sites More sharing options...
Tony D Posted August 21, 2011 Share Posted August 21, 2011 The key to this is that the change in AFR is NOT due to 'vapor state change'---it is due to Density of the fuel changing. Less dense fuel (hot) has less heating content (BTU's) per volume injected. This is why the pulsewidth stays the same, yet the AFR goes 'lean'... This is why drag racers run a 'cool can'---your fuel being close to 0C has a constant, and relatively constant heating content for the whole run. If you ran your fuel through your A/C line to cool it to sub-zero you would get more fuel heating value to the engine than when it's 45C (typical temperature on half a tank or less running in the summer...) Points on proper operation of the injectors are also correct as mentioned. The problem is heat in the fuel, not to a vaporization point...but enough to change the density and heating value of the fuel making it go lean. Cool that fuel, or keep it at a constant temperature (relatively) and you will cease having these issues. SARD Fuel Cooler Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted August 22, 2011 Author Share Posted August 22, 2011 (edited) Very interesting Tony. I used to run a RRFPR with the stock turbo injectors, ramped to 65psi of fuel pressure on 14psi of boost. It was very repeatable. I used to check it with a bike pump on the regulator with a gauge, while watching the fuel pressure gauge. On a hot day in Syracuse, at the convention, I pumped out 265 RWHP with the stock motor and ECCS in place. However, I have no clue (lol) looking back, if the AFR's were anywhere near OK. It ran great, hit Watkins Glen International, and drove us home with the A/C on. Nowadays, I have more info and can see the fine detail of what goes on behind the scene thanks to Megasquirt. I have my tune really close and rarely see my EGO corrections go much over +/- 5%. However, when the system gets hot, you can see the EGO corrections pinning in the +20% realm (only at idle and very low revs), where I limited WBO2 authority. Therefore, I know I am dealing with a hot AND fuel variable condition. I will install the new regulator anyhow, and play with the pressures a bit...experimentation and learning. I may end up sending the injectors out to get blueprinted again, for shits and grins. Back when I had the rail dead-headed, I had a nice cool fuel tank. I had the regulator over on the passenger fuel rail where the fuel came up, and went back to the tank with minimal heat exposure. Now, I recirculate the fuel, so it stays OK for a longer period, but eventually still gets into the "leanies" as the tank heats up. I am a sucker for blue anodized stuff, but right now, I can't find to many spare yen hanging around. Fall and Winter are near. Nothing like the feel of a turbo Z, in the cool air. I still think my system would like some additional fuel pressure so I will give it a try. I always learn the hard way. Edited August 22, 2011 by cygnusx1 Quote Link to comment Share on other sites More sharing options...
Tony D Posted August 22, 2011 Share Posted August 22, 2011 "On a hot day in Syracuse, at the convention, I pumped out 265 RWHP with the stock motor and ECCS in place." That was on that neat all-wheel dyno brake setup that guy brought in the van, right? That almost had me change careers into "Portable Dyno Owner Business"! JeffP is an inveterate cheapskate, and I can't get him to buy a whole ZX Tankfull of C16 Racing Fuel, so he miserly pours it into the tank 5 gallons at a time, and it wasn't long before I realized we had a 'perfect tune' on our first three pulls, then foudn issues after letting the engine cool and making another pass where the AFR's went all over the place. Exactly the same thing you are seeing at idle! And that carries on. More sophisticated systems (Z31) have that fuel temp sensor, I don't see why MS couldn't incorporate the same sensor and stop all this BS, it's the same basic coding chart as for battery compensation or CLT compensation (run it Inverse to CLT, for instance hotter fuel gets more pulsewidth instead of colder) and this would cease to be a problem. There, now have your codewriter guys do this for you and we are all better off! Frankly this just came to me and I'm shocked that it could actually be that easy to implement and would really help with the situation on the MS. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted August 22, 2011 Author Share Posted August 22, 2011 (edited) Great time to hit up Matt Cramer! ring-ring.... Holyrollerdyno was the outfit. They went to a better place. http://holyrollerdyn...me/Welcome.html Edited August 22, 2011 by cygnusx1 Quote Link to comment Share on other sites More sharing options...
Tony D Posted August 23, 2011 Share Posted August 23, 2011 Another John Galt conversion... Quote Link to comment Share on other sites More sharing options...
randy 77zt Posted August 24, 2011 Share Posted August 24, 2011 (edited) I will probably be at the limit of my 440cc injectors when my car gets dyno tuned some day and i am thinking of running up the base pressure of my efi system to 4 or 5 bar with a new regulator.i had problems with walbro fuel pumps and switched to a single bosch 044 .Supply side is all -8.Lots of earl's push-loc fittings used.The pump is mounted where the original 280zx pump was mounted and the hard line was replaced with 3/8 aluminum line.I have had tuning problems with fuel heating after idling and fiddling on the laptop .Maybe my nice home-made fuel rail needs to have some insulation put on it .i suspect it was vaporizing the fuel between the pump and the tank after the fuel got hot-idling on a 95f degree day while on a laptop for 20+ minutes.I might put a surge tank in the spare tire well so I can be sure the 044 is correctly fed.Some clear fuel line in a few places would help check for airation of the fuel.Getting sent home from the dyno with problems to fix is not good.On the RC Engineering website there are math formulas for the injector size/pressure calculations. Edited August 24, 2011 by randy 77zt Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted August 24, 2011 Author Share Posted August 24, 2011 Like Tony says, fuel is injected on a time-pressure meter. When it expands from heat, there is less of it getting to the cylinders. I should have figured that out myself since I used to design time-pressure filling equipment for hot liquids. I used volumetric designs for stuff that was slightly variable in density, and when fill volume was more critical than mass. Quote Link to comment Share on other sites More sharing options...
Nigel Posted August 24, 2011 Share Posted August 24, 2011 (edited) I had the same lean out at idle on hot days with a 1/4 tank of fuel. So, a couple of years ago, I added a Flex-a-lite fuel cooler after the pump (based on instructions for a Barry Grant cooler), and insulated all of my fuel lines in the transmission tunnel (3/8" lines that ended up close to the exhaust). This made a significant improvement. It's not 100% better, but far more stable than it used to be. At some point, I'm also planning on installing an Aeromotive fuel pump speed controller... My lihttp://aeromotiveinc.com/products-page/accessories-electronics/16306-billet-fuel-pump-speed-controller/nk This would reduce the heat pickup by slowing down the fuel circulation, and reduce wear and tear on the pump. I've already sourced a pressure switch to wire into the controller to automatically switch the controller to full speed when boosting. I still have problems with hot starts. I tried insulating the fuel rail, but it made no difference. I'd put my finger under the insulation, and the rail would still be boiling hot. I think the heat is coming up through the injectors. I was thinking about making a fuel rail with another passage to run coolant through, powered by a small PC liquid cooled CPU radiator with a pump (I originally said fan by mistake). But I've also found that letting the electric rad fan run for several minutes after shutting the car down helps a bit too. I'm also going to try adding a toggle switch to let the fuel pump run for a bit to flush out the rail before starting. Nigel '73 240ZT Edited August 24, 2011 by Nigel Quote Link to comment Share on other sites More sharing options...
Tony D Posted August 24, 2011 Share Posted August 24, 2011 What you both need to realize ESPECIALLY with high-flow pumps, is that when the fuel is heated it looses vapor pressure. It turns to gasseous state easier. If you are NOT running a carbon cannister on your car, with the proper pressure blanket on the fuel in the tank (it's several inches H2O before it relieves to the carbon tank, or the crankcase/air filter) then you can CAVITATE the inlet of the pump. This makes your fuel pressure drop, or you have delivery problems. It can be severe enough to damage the pump. NPSH is not something to screw with, but everybody pulls these 'emissions' items off their cars without understanding that there IS some other engineered practical functions they also perform. When you remove them, you take the perceived bad out with all the imperceptible good...then wonder why the problems arise! The state change WILL NOT HAPPEN between the pump and the engine compartment. It can happen as the system COOLS after the fuel expands and the FPR relieves pressure...then as it cools and contracts pressure drops to the point where it flashes (making pressure rise and FPR to relieve...) and before long you only have gasseous fuel in the line. But if the engine is running, the process should never occur on that pressurized part of the system unless you are getting temperatures above the pressure-point boiling temperature (this would be somewhere around 250-300F from what I remember---check the vapor pressure and boiling points of the fuel you are using, and extrapolate for the pressures you run...) BUT at that no-pressure inlet? Where you are drawing a partial vacuum at the inlet of the pump? Remember high school chemistry where you boiled water at room temperature? Well....how well does a fuel pump push a bubble of gasseous liquid fuel? It doesn't. And then you drop pressure. And THEN you my get into flashing in the fuel rail. But the origin is at the INLET side of the pump, not the engine end! The act of quick pressure dropping will cause it. And that is sourced at pickup side of the pump. If you think about the 'surge tank' design, what do you do? Run a couple PSI on the pump inlet? And run a continuous flow of fuel at low pressure thorough it with a low-pressure pump? It never works hard on the boost side, and keeps the inlet of the HP Pump flooded at far more pressure than you get from the original Carbon Cannister Check-Valve. As to the "hot fuel/cold fuel" remember the days when they had above ground tanks and all the old people in town would be up before the sun to go get a fueling in their Oldsmobiles before the 'hot gas' happened. It's so bad some distribution outlets have sued refineries. The expansion physically can be measurable, but the density change (and resultant BTU Content) can vary GREATLY! Temperature-Compensated pumps are the standard in CNG Dispensing. It's the only way you get a consistent 'GGE'--gallon gas equivalent--the gallons you see may be 13CuFt, it may be 11 CuFt, depending on temperature. (Given the BTU of the NG is consistent at say 980BTU/CuFt) There has been a call in California recently to mandate temperature-compensated pumps as consumer, and business protection device. It's known refineries dispatch "Hot Gas" and dip the tankers when they leave. Last guy on the route ALWAYS gets a 'Short Fill'---anybody who has dipped tanks at a gas station knows the numbers always are off, and in hot weather, by more than when cold. And they absorb the costs as there is no compensation from their distribution network. If they pump temperature-compensated fuel, the consumer gets a consistent BTU content in their mass flow, and then the dispensers can back-charge the refinery for 'lost gas' due to them not dispatching tankers with temperature-compensated meters to fill their bulk tanks... I digress... Quote Link to comment Share on other sites More sharing options...
randy 77zt Posted August 25, 2011 Share Posted August 25, 2011 Tony-i have suspected fuel vaporization between the tank outlet and the fuel pump to be the problem after reading the faq sticky on walbro pumps.Changing to the bosch 044 pump is my usual get-a-bigger-hammer solution to a problem that goes clear back to the 1960's when cars with engine mounted fuel pumps would vapor lock at high altitudes.if the bosch pump isnt fed nice bubble-free fuel it too will probably fail.I think my unused spare tire well will be home to a surge tank with with a low pressure/high volume pump feeding it.Raising my base fuel pressure to 4 bar will be enough to get the 440cc injectors to hit my 350-400rwhp target for sure.Currently the bosch pump is below the fuel outlet with a 85 micrron earl's pre-filter in front of it Quote Link to comment Share on other sites More sharing options...
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