silicone boy Posted February 4, 2004 Share Posted February 4, 2004 I was looking around the internet for a boost referenced fuel pressure regulator I'm going to use for a turbo Chevy. Most, of course, boost fuel pressure in a linear fashion with increasing boost pressure. I came across a couple that have rising rate regulators for turbos. Do any of you guys use one of these? What are the advantages and when would you consider one to be mandatory (or even recommended) Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted February 4, 2004 Share Posted February 4, 2004 I wish the search function were up and running, but I understand it costs bandwidth. I have my opinions on the RRFPR, as many know, but here it is in a nutshell. The RRFPR works well in an EFI that infers air mass using a 1 Bar MAP sensor (manifold absolute pressure) and the TPS. That's because at boost the MAP sensor reads no higher than 0 vacuum, and there is no knowledge of pressure above atmospheric. So rising the fuel rate non-linearly is effective in getting a good air/fuel mix out of the range of the EFI's ability to fuel. This is what Honda uses. Nissan, on the other hand, uses an AFM or MAF to directly measure air mass. Remember, vacuum is not air mass. If the air mass is known, it doesn't matter whether it is above atmospheric pressure or below - the EFI simply adds fuel to match the air to get a good air/fuel mixture. And the ECU is programmed to add fuel at a constant fuel pressure, maintained by the FPR that is manifold referenced. Unless you want to run richer than the factory ECU is programmed at boost - and factory a/f ratios at WOT are about 11.5 to 12:1, there is no reason to richen it any more. If you are adding fuel to limit detonation, get an intercooler instead, and make more power. A RRFPR is often just a bandaid, or a "shotgun" fix for a problem more directly solved by a good EFI system. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted February 4, 2004 Share Posted February 4, 2004 Sleeper... I keep asking you this one... what about the type of RRFPR that is designed to not affect fuel pressure until a user-defined boost level is reached? Cartech sells one kind of RRFPR like this. You could set the fuel rate to increase, say, 2psi for every 1psi of boost, but set it not to start affecting fuel pressure until after you hit 7psi of boost, therefore you wouldn't be affecting the stock fuel pressure up to stock boost levels. Cartech sells this model as the FMU used on N/A cars that have been converted to turbo, but to me it seems this would work PERFECTLY for turbo'ed 240's. Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted February 4, 2004 Share Posted February 4, 2004 Sleeper... I keep asking you this one... what about the type of RRFPR that is designed to not affect fuel pressure until a user-defined boost level is reached? Cartech sells one kind of RRFPR like this. You could set the fuel rate to increase' date=' say, 2psi for every 1psi of boost, but set it not to start affecting fuel pressure until after you hit 7psi of boost, therefore you wouldn't be affecting the stock fuel pressure up to stock boost levels. Cartech sells this model as the FMU used on N/A cars that have been converted to turbo, but to me it seems this would work PERFECTLY for turbo'ed 240's.[/quote'] I don't know enough about them to say if you can get one with two adjustments - one determines the onset, one determines the rate. It sounds like a big PITA. It's most certainly NOT perfect for a Z, even one with an AFM. The reason? Because it fuels based on boost alone, without factoring in your RPM. With a Z you can hit full boost by 3000 rpm, and your fuel pressure will not vary from there to redline. If you are correcting for a lean condition at higher rpm, you will be fat rich at mid rpms if you want to tune for a safe a/f at redline. You tell me, given two possible adjustments, how you can tune that for a nice a/f ratio anywhere? Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted February 5, 2004 Share Posted February 5, 2004 You tell me' date=' given two possible adjustments, how you can tune that for a nice a/f ratio anywhere?[/quote'] LOL noooooo you tell ME! that's the problem I'm facing right now... again looking at my own dyno results and the A/F curve... waaaay too rich in the mid range, and way too lean above 5k rpm... I have thus far agreed with your points on the RRFPR... that's why I haven't ended up buying one! But I'm still left with a lot of questions... how can I make my setup run better... how can I tame this rediculous curve... and w/o spending a fortune on SDS or Tec or some such. Is there ANY way, say for less than $400, that I can tune out the odd fuel curve in my setup? Quote Link to comment Share on other sites More sharing options...
Brad-ManQ45 Posted February 5, 2004 Share Posted February 5, 2004 Megasquirt... Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted February 5, 2004 Share Posted February 5, 2004 megasquirt... after all is said and done I think it would be more than $400. Or at least it would be close. And I have considered that option again and again, but it seems like it is too technical of a swap for me... not that it's not a great system I just see too much room for things to go wrong or not to work and with my luck with this car so far I'm not taking any chances! Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted February 5, 2004 Share Posted February 5, 2004 You tell me' date=' given two possible adjustments, how you can tune that for a nice a/f ratio anywhere?[/quote'] LOL noooooo you tell ME! that's the problem I'm facing right now... again looking at my own dyno results and the A/F curve... waaaay too rich in the mid range, and way too lean above 5k rpm... I have thus far agreed with your points on the RRFPR... that's why I haven't ended up buying one! But I'm still left with a lot of questions... how can I make my setup run better... how can I tame this rediculous curve... and w/o spending a fortune on SDS or Tec or some such. Is there ANY way, say for less than $400, that I can tune out the odd fuel curve in my setup? If I could tell you I would. For me, it's all theoretical , I jumped ship on the AFM and went with the Z31. I am much happier as a result, I'm sure! FWIW, you could probably get a safe rough tuining on your fuel curve with either regulator. Considering a cheaper, simple adjustable FPR could get you there too, that may be the best solution before you get a better fuel management. Quote Link to comment Share on other sites More sharing options...
SportZ2 Posted February 5, 2004 Share Posted February 5, 2004 I don't know if this will help but I used the Vortech FMU on my t4 turbo setup on my 280Z and it made a big difference. The factory setting was 8 to 1 and it didn't effect my fuel pressure out of boost. My lean problem was solved. You can also buy a kit that allows you to make adjustments to the FMU. 4 to 1, 6 to 1, etc. Quote Link to comment Share on other sites More sharing options...
yo2001 Posted February 5, 2004 Share Posted February 5, 2004 two adjustment RRFPR will let you adjust the max fuel pressure under boost. But can't adjust when the fuel pressure start to raise, if that makes sense. Basically, it'll start raising FP as soon as the boost comes in but it'll stop and start bleeding at set PSI. you can find a way to controll the signal line with bleeder like boost controller and may be make one yo do what you want. that's my guess. Z31 setup $250 8) Quote Link to comment Share on other sites More sharing options...
jeffp Posted February 6, 2004 Share Posted February 6, 2004 I have some input on this issue. First of all I have a reply to this answer::::A RRFPR is often just a bandaid, or a "shotgun" fix for a problem more directly solved by a good EFI system. I disagree, I am sure you can program dutycycle to compensate for the fuel pressure, but WHY? You need to keep in mind the pressure drop/increase in the intake manifold. You just cant make calculations easily for flow bsaed on duty cycle. The injector flow is a closed loop system, meanint that idf you have negative pressure in the intake, the injector will flow more fuel when you have pressure in the intake you will flow less fuel from the injector because of the pressure differential at the outlet of the injector. So using a 1:1 pressure regulator, takes the flow rart differential out of the equation for fuel flow. 1 pound of boost will get one more pound of pressure in the system, no matter if you are at vacuum in the intake or at 20psi of pressure in the manifold. The variables required, and fuel flow tables required to meter those changes are way more then the current systems are able to handle in my opinion. The tuning would be a nightmare. EVERY CAR you see out there has a pressure regulator on it, and every car will have some sort of regulator on it based on manifold pressure. RISING RATE REGULATORS are ment for POSITIVE manifold pressure above 14.7 psi or at the manifold 0psi manifold pressure. You are more then welcome to try a program tune without a vacuum activated pressure regulator, but you wil have to change your program every time you increase, or decrease altitude, because as you know, the pressure @ 5000 feet is nuch less dense then at sea level.anyway Quote Link to comment Share on other sites More sharing options...
Bernardd Posted February 6, 2004 Share Posted February 6, 2004 Is there ANY way, say for less than $400, that I can tune out the odd fuel curve in my setup? The z31 coupled with the setup as Nathan has is hands down the cheapest and is proven. All you need is the maf, ecu and cas wheel. You can now purchase a Romulator WITH MAPTRACE, for $179. That makes the ecu pretty much the same as standalone to at least 420cc injectors. There should be Nissan ecu specific software available soon, but isn't really needed as the critical tuning maps are known in the z31 ecu. The cost would be whatever the conversion parts cost + 179 for the romulator + laptop if you can't borrow one. And you'll have to get a socket installed. Once the maps are to your liking there are any # of guys on the internet that will burn whatever you want as long as you provide an eprom. I would think that you could do that for less than $400 dollars and tune to your liking. Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted February 6, 2004 Share Posted February 6, 2004 Sleeper... I keep asking you this one... what about the type of RRFPR that is designed to not affect fuel pressure until a user-defined boost level is reached? Cartech sells one kind of RRFPR like this. You could set the fuel rate to increase' date=' say, 2psi for every 1psi of boost, but set it not to start affecting fuel pressure until after you hit 7psi of boost, therefore you wouldn't be affecting the stock fuel pressure up to stock boost levels. Cartech sells this model as the FMU used on N/A cars that have been converted to turbo, but to me it seems this would work PERFECTLY for turbo'ed 240's.[/quote'] That is a fallacy, the bottom line is it adds pressure as soon as boost is introduced. Now they do some tinkering by adding restrictors and one way valves, but I can promise you, get a good spooling turbo, run about 15 psi and hit it in 5th at 3k rpms and see what happens. You will get nasty black smoke, and a stuttering car, if your pump is up to task. The bottom line is that regulator is a patch, and you are never going to have nice drivability with it. I hated mine. I would get an additional injector controller before one of those. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.