Fuel Discussion from Readers Rides

[DQ Driver]

seems you've spared no expense....
any reason why you have a denso 190 versus the powerful pumps that one would typically see accompanying such mods like a cosmo, supra, or walbro?

[greentrbo95gst]

because once you rewire 190 it's enough for up to 600 hp and many people dont know that and go big, which creates fuel pressure problems. Never needed an fpr until i got the venom fuel rail.

[DQ Driver]

ok.. let me bring out my calculator and i'll get back to you

[Mike C]

A 255 pump only creates a fuel pressure problem if you're not using an adjustable FPR. Running a 190 pump with a 50 trim, highflowing head, big cams, and alot of boost is not very smart, rewired or not. Better safe than sorry when it comes to a $100 fuel pump.

[talon guy]

well it looks like he is having no troulbe w/ it so far....

[Iwishiwascool]

its quite possible to create large numbers using even a stock fuel pump.

A pump Rating takes into consideration the resistance, aka the size of the line its pumping through. If you increase the size of that line, decreasing resistance, the pump is going to be moving much more than 195 lph.

This is why a 20g can run easily on the 195 as long as you eliminate the banjo bolt on the filter which is the bigest restriction in the fuel system...

or so Ive heard.

[greentrbo95gst]

the car gets plenty of fuel. It's monitored by haltech with a wideband. If we werent sure about the fuel pump we wouldnt use it. I would not wanna sacrifice a $20k setup by usin somethin we are not sure about.

[DQ Driver]

ok i found my calculator... your empirical data reigns, but let me crunch some numbers for the sake of cleaning the dust off my ti-86

Constants
14V supply to the pump (hardwired)
43.5psi base fuel pressure via afpr

4 x 850cc injectors = 204 lph
denso 190lph @ 43.5 psi @14V = 210 lph (RRE test)

ideally this pump will supply all the fuel those injectors could pump out with all things optimal. But you have to question how well the engineers designed the algorithm for the alternators charging pattern to keep the battery at that consistent 14V. It's not out of the ordinary to see 1.5-2V swings on newer cars under load. I've heard about many instances in which the denso pump suffered around 120 mph traps and results in knocks counts due to poor fuel delivery. This problem was easily solved by dropping in a walbro or supra pump in the tank. Do you have an in car fuel pressure gauge?

Empirical data has also has shown that 550's can net 10 second time slips and trap 120+, so why choose 850's. A little extra insurance never hurt anybody, that's all i'm trying to say.

2 pennys

[Iwishiwascool]

This is why mikey is the mathmagician

But...

How are your fluid dynamic skills. Is a 195 lph pump still flowing 195 lph when you decrease the resistence within the system?

[Iwishiwascool]

SteveTek has said that the stock pump is good for something like 400HP or so with the restrictions removed.

Fuel pumps are rated to flow X liters per hour at X psi. Less pressure will let the pump spin faster and flow more. Sure, you say that the base fuel pressure at the fuel rail is still 43 psi (stock example), so how does making the fuel line larger change the pressure at the pump? The important fluid mechanics concept called head loss. Smaller line will have a greater head loss. So if the pressure at the rail is 43 psi, the pressure right after the pump may be closer to 50 psi. Bigger line would drop is closer to 43 psi, and busted... more fuel flow to the engine.

[greentrbo95gst]

i wont argue with that. fuel pressure in the car stays at constant 43.4 psi and chargin at wot is 13.9

[DQ Driver]

The lines are going to help the fuel pump flow more due to the elimination of 'head loss'. RRE's test procedure was not documented well..however

My assumpltion is that they measured the Denso pump to flow
210lph @43.5psi @14 volts on a test bench and the 43.5 psi was directly at the pump not on car with complete fuel lines. Hence the 210 lph still holds true compensating for this 'head loss'.

My question is, do you want only 6lph of difference between your maximum injector flow and your maximum ideal fuel pump flow? Not even putting into consideration acceptable deviations of flow that a company accept when mass producing parts, plus or minus tolerance percentages

6lph/ 4 injectors = 25cc of compensation at each injector


i'm done... so sleepy

[Mike C]

Mike's mathematical data proves my point. Does it work under ideal, yes. Is it a tad risky, yes. My point was: you've got $20000 in mods on a car and your skimping on a $100 fuel pump. Just my .02. Good luck.

[Gunner]

Tech tip: Use the smallest injector that you can get away with and run more fuel pressure. Injectors work better, and offer a better and more repeatable spray pattern with high fuel pressure and closer to 100% duty cycle.

Also, lets say you have a stock pump in tank, and a 255 inline pump. With that helper pump, the stocker will be flowing a lot more than it would be under stock conditions. The same goes for Kens theory of removing some restriction in the fuel system, but not nearly to the same extent. I presume there would be some gains there, but when you can get Walbro 255's brand spankin new for $82 bucks it doesn't seem worth it.

[Iwishiwascool]

this same concept is being more thoroughly discussed on columbus racing right this second.

I asked the dude who sorted the BS there who happens to be a former moderator here... to come sort it here.

Since im not fully even confident that my assumptions are correct.

[Iwishiwascool]

It will help, but alas, you'll still need a pump.

Ken, what you're saying IS correct, but I don't think it will make as big of a difference as you may assume. The old, and I think still best philosophy after much research is that BIG pump, BIG pressure, and SMALL injector is the best combo. Someone in the area will be employing this tried and true method in the near future.

I definitely agree with said philosophy. The only disadvantage would be doing this on a daily and frequently running at 100+ injector duity cycle. The increased pressure being forced into the injectors over time would cause it to fail.... so ive heard.

[Iwishiwascool]

http://www.modulardepot.com/?show=articlesdet&aid=24