Among other things, you've ignored the concept of injector duty cycle.

Brake specific fuel consumption (BSFC) for a turbocharged engine is 0.6 lbs of fuel per hour per horsepower (or higher). So, for a 400HP motor you'd need 400 x 0.6 lbs, or 240 lbs of fuel. If you're using higher octane, it weighs approximately 6 lbs/gallon, so figure 40 gallons of fuel. Forty gallons of fuel = 152 liters. 152 liters/60 equals 2.53 liters per minute, or 2530 ccs/minute. Divide by 4 injectors, and you get 633 ccs/minute injectors at 100% duty cycle. You don't want to do that, so you make sure you calculate no more than a 80% duty cycle. 633 / .8 = 791cc/minute injectors.

If you figure the BSFC is higher (richer mixture for safety), figure .65. The same calculations (for 400 HP) then yield 400 x .65, or 260 lbs fuel/hour, or 43.3 gallons/hr which equals 164 liters per hour. 164 liters/hr = 2.73 liters/minute, 2730 ccs/min /4= 683cc/min x .8 = 854cc/minute injectors needed.

If you assume 500HP, scale the above up by 25%, making the fuel demands 325 lbs per hour; 54.2 gallons per hour; 205 liters/hour; 3.42 liters/minute; 3420 ccs/minute; 854ccs/injector at 100%; 1067cc/minute injectors at 80% duty cycle.

If you need a certain volume of fuel to make the HP target you're assuming, that volume has to be available at the boost pressure you need to make the HP. If you are increasing the manifold pressure by 30PSI, then you have to increase the fuel pressure by the same amount in order for the injectors to have the same flow characteristics. So, for example, if you need 30 PSI boost to make the HP, you need to find out whether the fuel pump and delivery system will produce the flow volume at 75PSI (base pressure + 30 lbs. boost).

NOTE: Most fuel supply calculations suggest a 20% surplus built into the supply system to make sure you don't run lean at the margins.

The Denso 245 pump I had tested flows 167 liters/hour at 75 PSI. As shown above, a 400HP motor needs 164 liters per hour (with no safety surplus built into the equation). If you design in the 20% safety margin, the fuel supply is 20% low at 400 HP with this pump. If you're looking to make 500HP, a single pump setup using this pump won't satisfy your motor's requirements, and you risk running lean and grenading your motor.

The same methodology can be applied to the Walbro 255HP, which RRE measured as flowing 220 liters/hour at 75 PSI. That would be sufficient for a 400HP car with a safety margin, but is very close to total pumping volume with no safety margin at 500HP, which requires 205 liters/hour.

This explains why Dave Buschur reported that his 575HP motor was running out of fuel, even on his upgraded single Walbro 255HO pump, and why he picked up 50 HP when he figured it out and went to a dual pump system.

 

I didn't ignore anything, but thanks for your input.

The question was never about what fuel injectors or margins of safety...all I simply showed was how much mass airflow 167lph of fuel flow would support at a couple of different air:fuel ratios.


Eric

 

This Denso pump, or anything similar, won't support a 500HP motor, much less a 560HP motor.

 

uhm... so how about for mere mortals? apparently it won't even do 400hp probably on 91 octane gas... i give up the whinebro apparently is the best option with the most annoying noise.

 

trinydex,

The pump can flow enough for more than 400 HP, meaning flywheel HP of course. Use drivetrain losses for your AWD car to find what that would mean in terms of whp.

Even though CO_VR4 doesn't realize it, my crude calculation took BSFC into account. That is where the ~10 HP per 1 lb/min of airflow came from. BSFC is just in units of lb/min fuel per HP. I was using the general rule of thumb using a BSFC of .55 and and AFR of 11.1. If you do the simple math (.55/60*11), that give just about .1lb/min of airflow for 1 HP, or multiply by 10 to get ~10 HP for every 1lb/min of airflow.

If you want to take a conservative approach, you can assume and a .6 BSFC, you can assume ~9 HP per lb/min of airflow. So, the calculations above still come out to ~500 HP and ~460 HP, respectively for the limits of the pump. Again, this is in engine HP.

CO-VR4 added in a general rule of thumb to leave about 20% of room for your injectors, but that is your call. Many people run their injectors at 100%, some like them better at 80%. Since they will be there for a very short timeframe, more people are concerend with idle characteristics and don't choose overly large injectors. But, to each their own. Anyway, you asked a question about the capabilities of the pump, not injectors.

There are more variables to take into effect whether the pump should be ran in your car or not, like knowing the exact boost you will run and knowing the exact flow rates of the pump at different voltages, etc, but from the posted flow rates in this thread, my calculations should still hold true. And of course, it would be a bad idea to run a fuel pump to it's limits, especially time and time again. But, again, I was simply showing what mass of airflow that mass of fuel flow could support and equating that to a HP number.


Eric

 

Eric has his opinions, and is entitled to them. But facts are facts, and usually trump opinions. That's why you need to understand the assumptions people make to come up with their conclusions. Eric has now explained that he used a BSFC of .55. I used a BSFC of .60 and .65, which is the standard range for turbocharged engines. The difference is .10/.65 or 15% in fuel use assumptions just in that part of the calculation. Eric's is 15% lower. If his assumption is too low, you run lean. If mine is too high, the excess fuel is bypassed and returned to the tank.

When considering what a reasonable fuel system is for a stock or mildly modified Evo, you can use a Walbro 255 with no problems, because it will supply the fuel volume at lower boost pressures that your engine demands. If you think you modifications will result in the potential for going upwards of 500HP, that is no longer true. This is where I pointed out why I disagree with Eric's comments.

Testing conclusively shows that one Walbro 255 will not support a 500HP motor safely -- that is, without starting to lose the capability to provide sufficient volume at the needed pressure, and running lean. For that matter, one Buschur modified Walbro High Output pump, which flows much better than the stock Walbro, won't do the job upwards of 525HP, as Buschur's testing showed some months ago, when he finally identified the problem and picked up 50HP just by correcting his fuel system limitations with no other changes. The Denso 245 fuel pump which I had flow tested flows less at 75PSI than the stock Walbro, and much less than the Buschur modified Walbro. I love Denso pumps, which is why I obtained it and had it tested. I'm not dissing the Denso pump, just pointing out that it is not an alternative for a higher HP Evo fuel system. It would be a reasonable substitute for the stock system pump, or a mildly modded Evo.

Look at Buschur's long explanation of his testing results found here -- https://www.evolutionm.net/forums/sh...d.php?t=245064 You'll see that whatever theory shows, when the rubber meets the road cars that don't have a fuel system that provides a safety margin in volume at the pressure needed go lean. His testing shows that the standard Walbro 255 won't support higher HP Evos and that the HO Walbro has its limitations around 500HP. When you go lean on the street, not on a dyno, and there's nobody watching the A/F ratios on a wideband like a hawk, you go "BOOM".

Why would you scrimp on a fuel system when it's critical for the longevity of your motor, as well as for making optimum use of the other expensive parts you bought to improve performance? Do it right, and oversize it so it cannot be a worry or a unidentified limitation.

 

CO-VR4,

I think you're missing the whole point of my explanations and calculations. I simply showed what mass of fuel is needing for what mass of airflow. Plain and simple.

Now, if you wanted my opinion on whether this pump should be used in a car, that totally changes. There are a lot of factors to take into consideration, as well as safety margins, etc. I think we are actually agreeing on a lot of this, but you are misunderstanding what I am saying. I think part of the confusion is that too many people talk in terms of HP, instead of mass airflow or mass fuel flow. HP from one person to the next, from one dyno to the next, from wheel HP to flywheel HP, varies dramatically. One person may be talking about wheel HP on a mustang dyno like Buschur's and one may be talking about flywheel HP, or engine HP. That's why I don't really like to talk in terms of HP...it adds way too much confusion for a lot of people. That's why I showed what mass of airflow the pump would support. The last step I tried to equate that to a HP 'number' using general rules of thumb. Again, even here, if I am talking about flywheel HP and you are talking about whp on a mustang dyno, the numbers could be 30% apart from each other.

Actually, since you mentioned Buschur's testing, that would be a good case in point. I read that thread as well, and if you look into the data, the 'HP' numbers that he is using don't add up either. But, then again, what exact HP is he talking about? Let me explain:


This is a quote from that thread:
This is another quote from that thread:
So, he states that his HO pump at 80 psi fuel pressure (about 36.5 psi boost assuming base FP) flows 310 lb/hr fuel. At a 12.5:1 AFR, that means that it can match 310*12.5=3875lb/hr of air. Or to change this into more usable units (lb/min), we get 3875/60=64.6 lb/min of air. Dave states that this 310 lb/hr of fuel is good for '412 flywheel HP'. Notice he didn't say whp on his dyno. 412 flywheel HP on his dyno is more around like 310 whp, right, assuming about a 25% correction factor?

Well, that doesn't add up at all, does it?. 65 lb/min of airflow should be roughly (again using my rule of thumb of 10 HP per lb/min) equal to about 650 HP (flywheel HP). And Dave said that he ran out of fuel at 542 wheel HP on his dyno. Reversing the 25% correction factor, that is about 720 flywheel HP. So, if I were to guess Dave was either running more than base fuel pressrue or more than about 35 psi on base fuel pressure on that run. He was probably flowing more around 70 lb/min of mass airflow. But there are too many factors to simply guess. AFR, fuel used, fuel pressure, boost, etc, etc.

The numbers are right there, though. He roughly had 720 flywheel HP on his car when he maxed out his single HO pump. Yet, he states that this pump is only good to 412 flywheel HP at 80 psi fuel pressure. He may have even been higher than that on his run...I don't know. But, that would mean the pump would support even less HP. So, something doesn't add up, not even close. I actually sent him a PM to explain this, so I wouldn't 'mess up' his thread.


Eric

 

Dave B. did not support the 525HP in his car without major work arounds. If you'll review his prior posts, I asked him about that. He responded that he had done major changes in the standalone fuel tables enriching the duty cycles in order to keep his A/Fs where he wanted them. When he made the pump change, his A/F went way rich, because the earlier system had not been providing sufficient volume at the pressure he was running. When he had the volume that the standalone was assuming, his A/F went to 9:1, and he had to revise his fuel table and injector duty cycles back to put his A/Fs where they should have been.

The pump simply did not keep up with the motor, and when he went to the dual pump setup, he solved the lack of fuel problem.

 

Whatever 'workarounds' he did with the fuel tables or inecjtor duty has nothing to do with the max capabilities of the pump. I'm going off of his own quotes here. It doesn't matter if you hold the injectors open 100% duty cycle....if the pump can't keep up, it can't keep up.

What I'm saying is that the numbers aren't even close to adding up right. He said that at 80 psi fuel pressure, the HO pump will flow 310lb/hr fuel, and according to him that is 412 FLYWHEEL HP. That's about 41-42 lb/min of airflow. Yet, he dynoed his car at 542 WHEEL HP on his own low reading mustange dyno.

That equates to probably in the neighborhood of 70 lb/min of airflow. Do you see what I am getting at? If one HO pump could only support what he claims, he wouldn't have gotten anywhere close to dynoing 542 whp on his dyno.


Eric

 

I understand your question about Dave's HP vs. pump capacity figures, and would like to hear his response.

I'm simply stating that Buschur's own testing showed that his HO version of the Walbro was marginal at 525HP, and then only by programming longer injector duty cycles to get the fuel into the cylinders and still was having trouble controlling his A/F going lean, which is not possible if you don't run a standalone, and even if you do, is not "best practice". Obviously at that level that pump had no excess capacity whatsoever.

I simply submit that oversizing a pump or fuel system has no downside risk (except for cost, which is not excessive), and that undersizing a fuel system has major risks and associated potential costs, which I'd prefer to avoid.

 

What are you saying is not possible without a standalone? I can increase my injector pulsewidths without a standalone. Your open loop fuel maps in the ECU control your injector pulsewidths, and thus the duty cycles of the injectors. All you need is ECUFlash and some general tuning knowledge.

But, I think that we agree here. Even running that inejctors at 100% duty cycle won't matter if the pump can't provide enough fuel.

I totally agree.

 

Just to clarify something for myself, why no walbros? I have a walbro and have no problems.

 

Because Walbros have a reputation for losing just enough pumping capacity to make an engine run lean.

 

+1, I just plain dont trust Walbro. With a turbo motor, a fuel pump isn't something to go cheap on IMO.

So, has anyone accually used the Denso pump in a car?

If so can you give your impressions? Is it loud? Would it work well using two of them with Buschur's twin pump setup?

 

I have run the pump, although not in the car. Like most OEM Densos, it's very quiet. I expect it has the traditional Denso reliability as well. The down side is simply that, in the stock 38mm diameter configuration, it does not flow as well as the Walbro, and it costs $250 each, the same price as the Buschur modified HO Walbro.

On the other hand, if you are using a dual IN TANK configuration like Buschurs apparently is, and cutting the stock fuel pump assembly to accommodate two pumps, you might be able to use the 50mm Denso Supra Twin Turbo pump (-1020) which flows more than the stock Walbro 255 up to 75PSI (and close to it to at least 85PSI, which would be 42 pounds of boost). That should be enough for almost anyone, and that pump costs in the neighborhood of $175, is very quiet, and dead reliable, as you would expect from a Toyota OEM quality pump.

AFAIK, nobody has actually published actual flow test data for a twin pump system. Buschur plans to, and AMS states that their dual pump system will support 1000HP, but I've not seen any flow testing to show the volume capacity of the twin pump setups. Some other twin pump setups on DSMs showed that two pumps DID NOT pump twice as much as a single pump system, at the same pressure, so it will be interesting to see the flow data when someone tests it in the "on the car" configuration.