viperlp01 said:

But another thing to think about.. The fuel pressure rises as boost rises.. The fuel pump can only pump a constant amount of fuel and a constant amount of pressure persay.. If you raise the pressure too high the pump needs to keep up with that fuel pressure to keep the tune accurate.. Especially when you get into the higher rpms and at a high fuel pressure the pump wouldn't nessesarily max out of the volume of fuel but on the pressure part.. If you were running a high amount of boost lets say 20 psi that mean the fuel pressure at wot/full boost is going to be 20 psi higher than your base..

What im saying is be careful when you mess with stuff like this.. Fuel injectors are tested at a constant fuel pressure to give you the flow number that they portray.. You don't want to push that too much..

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+1

For those who are recommending keeping the 560 evo 8 injectors...I would recommend against it. I saw ~95% duty cycle on pump gas on my bolt on Evo3 16g setup, running 93 octane making 326whp on the dyno with my Evo 8 injectors. I would recommend a larger fuel pump (Supra TT if possible, I don't like the whinebro quality as I've seen many fail in just a few years), an AFPR, a Keydiver chip specific to your setup, and some larger injectors. At that point I would use a wideband O2 and your existing SAFC to fine tune your setup. Once you have that done, you'll be just fine to run about 20psi on your setup and make some 12 second passes.

dsm-onster said:

Actually that is wrong. The pump is wide open all the time, hense the fuel return line that puts the fuel back into the gas tank. The FPR meters out the pressure by constricting the flow back to the tank.

And as the charts and real world results have proven (research walbro 255 flow and pressure), the wally at 65psi base pressure and 25+ psi boost (90+ total psi), it still flows enough to out flow 4 X 750s (180LPH). Four 550s at this total pressure only flow 156lph.

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The pump being constant displacment (wide open) will still see more stress at higher pressures correct? By limiting the return as you said you build pressure all the way down to the pump unless there is a check valve I dont know about.


the higher the pressure in your feed line the shorter you life span on the pump will be because it is a constant displacment pump.
the more you up the pressure in it the harder it gets to flow (bernoulli's principle)

by saying working harder
I am not saying the pump is spinning any faster that is an amperage thing

by saying its working harder Im saying your putting more of a load on the pump. which in turn makes it work harder, which would shorten its life span and possibley make it run warmer.

The wally 255 intank pump has a check valve that prevents excessive heat. More heat than the fuel can displace from the pump. The wally fuel pump relief valve opens up at about 85psi and relieves pressure. The flow goes down, but not all at once. It's a bleeder, so the flow is still there but dimishes at a steeper ramp. Still plenty at 65 + 25 boost to net more than 180LPH. If you need more boost than 25-27psi even from a 16g, then you need more than 650cc of fuel flow per injector anyway .

I've had no issues for years now after running wally/AFPR setup with 65psi base pressure feeding 450s (making them 550s). It works. And though your dead time does change with higher base pressure, 450s still have better response at 65psi base than 550s at 43psi base. That saves headaches dialing in the low trim. . . The wally 255 and 255hp is an amazing little piece of equipment.

But that IS a good point about the bernoulli concept. Makes me wonder about the wally inline pump. It has no relief valve. Perhaps it armeture and compressor are more durable?

dsm-onster said:

The wally 255 intank pump has a check valve that prevents excessive heat. More heat than the fuel can displace from the pump. The wally fuel pump relief valve opens up at about 85psi and relieves pressure. The flow goes down, but not all at once. It's a bleeder, so the flow is still there but dimishes at a steeper ramp. Still plenty at 65 + 25 boost to net more than 180LPH. If you need more boost than 25-27psi even from a 16g, then you need more than 650cc of fuel flow per injector anyway .

I've had no issues for years now after running wally/AFPR setup with 65psi base pressure feeding 450s (making them 550s). It works. And though your dead time does change with higher base pressure, 450s still have better response at 65psi base than 550s at 43psi base. That saves headaches dialing in the low trim. . . The wally 255 and 255hp is an amazing little piece of equipment.

But that IS a good point about the bernoulli concept. Makes me wonder about the wally inline pump. It has no relief valve. Perhaps it armeture and compressor are more durable?

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damn touche...you win haha

Not sure about the inline... It must you would think

Just trying to help with other options. Guys wanting to get the most out of the parts they have can use this. You're not really wrong in the principles, but the wally has a safety for itself (which could take out your motor BTW if you don't know where you are on the flow vs. pressure curve). . . Regardless, the way I see it:

1) For guys with stock fuel, you have to buy a fuel pump because the stocker is good for only 300whp or so worth of flow. You can buy the 190 in hopes to avoid FPR over run. And still have bearly enough fuel for 400whp. And buy $300 550s. Or buy a 255hp for the same price and an AFPR to keep the overrun in check and bump up the pressure to make the 450s flow like 550s.

2) If you already have 550s and want 650s you do the exact same thing as above. This is especially affordable if you already have the wally 255 and AFPR upgrade as many have already gone this route.

3) Get stock 550s from various cars. And still get the wally 255hp and AFPR. Now you have 550s or 650s. 650s being the most an safc/maft guy would want to run. From my knowledge there's no production vehicle with 650cc injectors, that would fit our rail/head. But you could get evo injectors for cheap and a wally255/AFPR and have 650s for much less than hunting down 650s.

Im pushing 27 psi spike and hold 25 psi on pump. My idcs with a wally 190 rewired and pte 680s(which flow 650) are at 78-80% via dsmlink.. So he can defidently up the boost on the 560s which actually flow 590... I just dont like the idea of messing with fuel pressure to fix something that he will have to do in the future..

dsm-onster- there are limits to turn the fuel pressure up i would assume.. The fuel pump max psi is 85 when the pressure valve opens.. There are multiple threads stating that turning the pressure up decreases flow. I would imagine that would be because how fast the fuel is flowing into the fuel rail... It just seems like a biatch to make a consistent tune.. With the fuel pressure being so high it seems like the fuel would atomise better making it possible to run a leaner a/f... I actually just did some research and it actually decreases the amotizing process of the fuel. I would imagine it has to do with how the injectors are designed..

It just seems like your putting alot of stress on components that are tested at a certain fuel pressure. Whats funny is your taking 450cc injectors which are only 450cc injectors at 43.5 BFP. According to this site Fuel Injectors i took a rough estimate by finding the increase of injector size between 370 and 550 to 55psi and then averaged them.. The 450cc injector at 55 psi is only 506.5cc.. So you increased the cc of the injector by 4.7cc every fuel pressure you increase.. so you are at 530cc injectors at 60 base fuel pressure and lets say you push 20 psi of boost then the 450s would now be 623cc injectors.. that seems kinda funny.. The thing to realize here is the actual size of the injectors is directly connected to how much more fuel it sends into the combustion chamber per psi of fuel pressure. My 680s would flow much more fuel per psi increase then the 450s..

Alot of math and estimates but i really does make sense and if you could tune for the different amounts of fuel then you would be good.. Your fuel curve with 450s with a higher fuel pressure would be alot different that 550s with normal fuel pressure.. That could lead to tuning issues..

So the real point is your still skimping out.. Evo injectors are cheap, fuel pumps are cheap.. A rewired 190 flows almost as much as a none modified 255.. http://www.dsmtuners.com/forums/tuning-engine-management/244522-injectors-fuel-pumps.html.. 3 lbs/min

viperlp01 said:

It just seems like your putting alot of stress on components that are tested at a certain fuel pressure. Whats funny is your taking 450cc injectors which are only 450cc injectors at 43.5 BFP. According to this site Fuel Injectors i took a rough estimate by finding the increase of injector size between 370 and 550 to 55psi and then averaged them.. The 450cc injector at 55 psi is only 506.5cc.. So you increased the cc of the injector by 4.7cc every fuel pressure you increase.. so you are at 530cc injectors at 60 base fuel pressure and lets say you push 20 psi of boost then the 450s would now be 623cc injectors.. that seems kinda funny.. The thing to realize here is the actual size of the injectors is directly connected to how much more fuel it sends into the combustion chamber per psi of fuel pressure. My 680s would flow much more fuel per psi increase then the 450s..

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That's just not ture. The point of the fuel pressure regulator is to maintain the pressure differential across the injector. Yes the base fuel pressure goes up from 43psi to 63psi when you apply 20psi boost. But that's done by the FPR to have the injector nozzles still see 43 psi fuel pressure across them, The NET fuel pressure at the injector nozzle is the same as base. 63psi - 20psi boost that is pushing the fuel back into the fuel rail = 43psi. Otherwise, the fuel flow would go down. Because flow through a nozzle depends on nozzle size (450/550/650/etc) AND fuel pressure. Decrease either variable and the actual injector flow goes down.

Yes, the 650s flow more than 450s. Yes 550s flow more than 450s. But if you put the base fuel pressure at 65psi then 450s flow 550cc at zero boost. If you are in boost then the AFPR adds fuel pressure equal to the boost in the manifold to maintain that 65psi across the injector. Yes in your case you would see 90psi at 25psi with 450s set at 65psi base pressure (so that they flow 550cc).

viperlp01 said:

Alot of math and estimates but i really does make sense and if you could tune for the different amounts of fuel then you would be good.. Your fuel curve with 450s with a higher fuel pressure would be alot different that 550s with normal fuel pressure.. That could lead to tuning issues..

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No. It doesn't. The AFPR keeps the NET fuel pressure at the same pressure. This is what prevents tuning issues with the stock setup. This still applies. As long as the fuel pump you're using can keep up with the flow demand at the total pressure (not net). Total pressure being boost + base pressure.

Referencing the AMS chart below. The wally255hp flows 175LPH at 90psi total pressure (65psi base pressure + 25psi boost). This is AFTER the releif valve opens. Pressure doesn't go down flow does. 175LPH is 2917cc/min. Dividing 2917cc/min by 4 injectors equals 730cc injectors. With a base fuel pressure of 65psi, your 680s would flow about 790cc/min. If yyou had a wall 255hp, you could turn your base fuel pressure up to 65psi and run those 650s (which are now 790s because of the higher pressure across their nozzles) to over 90% IDC (730/790) and still have enough pump.

A guy that wants 20% more fuel flow and about 20psi of boost out of a 16g has MORE than enough fuelpump flow for their goal with a wally 255hp at 65psi base pressure. Remember it will flow enough for 4 730cc injectors. The best thing about this approach is that you can buy those evo 560s for real cheap and use 65psi base pressure with the wally 255 pump and your 560s will now be 690s. Enough fuel to push an evo3 16g to the limit of the map. And enough fuel pump flow to surpass the flow of the injectors. Much less cost than getting 650s. And your'se still using quality parts.

For accurately using this mething, to calculate the exact change in fuel flow based on base fuel pressure changes (instead of guessing with linear graphing ), you simply do this:

viperlp01 said:

So the real point is your still skimping out.. Evo injectors are cheap, fuel pumps are cheap.. A rewired 190 flows almost as much as a none modified 255.. http://www.dsmtuners.com/forums/tuning-engine-management/244522-injectors-fuel-pumps.html.. 3 lbs/min

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Well, it's not skimping out to use the oem quality stock injectors and an aeromotive adjustable fuel pressure regulator and a fuel pump that flows plenty well at high total pressures to supply more fuel than your injectors at that high pressure can inject. Better dead times (closer to stock). Atomization won't be an issue. It hasn't been for many others.

You are making your point valid but my information is based on estimated calculations using someone elses formula and you are doing the same.. I don't understand how the flow of the injector doesn't increase as boost rises/fuel pressure rises.. You are the one saying that it does.. My thought process is 450 is just a number at 43.5 fuel pressure. As boost rises that number increases.. Thats simple


My calculations are right btw.. 65-43.5= 21.5*4.7= 101.05+450= 551.05cc... I compared to the orignal number you supplied of 60 my calculation were also right...


DSM-onster- The wally255hp flows 175LPH at 90psi total pressure (65psi base pressure + 25psi boost). This is AFTER the releif valve opens. Pressure doesn't go down flow does. 175LPH is 2917cc/min. Dividing 2917cc/min by 4 injectors equals 730cc injectors. With a base fuel pressure of 65psi, your 680s would flow about 790cc/min. If yyou had a wall 255hp, you could turn your base fuel pressure up to 65psi and run those 650s (which are now 790s because of the higher pressure across their nozzles) to over 90% IDC (730/790) and still have enough pump.

Isn't there a relief valve in the fuel pumps that open at 85 psi??? I thought thats what you said.. Im not downing anything you do. It seems like you have great luck by modifying lesser systems to work at a better level..


DSM-onster- That's just not ture. The point of the fuel pressure regulator is to maintain the pressure differential across the injector. Yes the base fuel pressure goes up from 43psi to 63psi when you apply 20psi boost.

I guess i worded that wrong.. At 20psi of boost with a 60 base fp the 450cc injector can flow a maximum of 623cc of fuel per injector at 20 psi boost/80psi fp... That makes more sense...

Still this is a bunch of math that is not needed ... He has two options.. mess with a apfr or get bigger injectors ..

Hey, I know what you're saying. I'm not really disagreeing with you technically. He does have really two options. But he already has the 550s and he just needs an AFPR and a wall 255 which he'll need regardless.

The fuel pressure raises the flow of the injector because we're talking base pressure here not total pressure. If you bump up base pressure you bump up total flow. Peroid. The rest were talking about is WHY. None of that really matters to the general tuner. All he needs to know is tha if he unplugs the vacuum line and measures the pressure and turns the pressure up to 65psi, he can turn 450s to 550s, or 550s to 650s. The SAFC or maft will have to be adjusted as if you were running the larger injectors when you bump the fuel pressure to that point.

. . . Yes the relief valve opens at 85psi, but not fully. It's a bleeder type valve. The flow decreases at a more pronounced rate. But still at 90 psi total pressure the bleeder valve does not dimish the flow so much that you can't run 650cc of flow (nozzle + fuel pressure) to their full potential. . . An evo3 16g or any td05h turbo with a 7cm^2 housing really needs 650s. Since you MUST have a wally 255 and conequently MUST have the AFPR to make the most of 650s since a 190 fuel pump flows a little less than what 650s can do maxed out, then it's so easy to get 650s with out having to pay so much for them. Just snag up some evo injectors and up the base fuel pressure to 65psi with the required AFPR. The wally can handle it at your dead time will be about the same as stock injectors. Easy tuning with an SAFC or MAFT. Which by the way, you shouldn't go over 650cc flow anyway, right?

So instead of upgrading my injectors i can upgrade my fuel pump and use a afpr to push more fuel through?

That's the point. Yes. Your stock 450s will be 550s if you use a walbro 255hp fuel pump and the AFPR required to run it that can raise the base fuel pressure to 65psi. . . Then when you want more than what 550cc/min can flow. You can get CHEAP evo injectors and use the same 65psi base fuel pressure and run 650s. The fuel pump will certainly keep up to 100% IDC. And last for a long time.