Need some help with fuel pump selection...

[N20LT4Bird]

I bumped the nitrous to a 150 shot and the fuel pressure safety switch was cutting the nitrous a second after it was engaged. (Thank you fuel pressure switch! ) I have a walbro 255 in my tank now, which is supposed to be rated for 600 HP. I think I may be walking this line with the 100 shot and crossing it with the 150 shot.

I am looking at this pump to add in-line when the juice is activated.

http://www.msdignition.com/fuel_7.htm

MSD says its rated for a little over 500 HP alone. My question is, when adding another pump in series, am I addding any more fuel? Or am I only getting as much fuel as the largest pump will support? I know that many nitrous and s/c kits supply in-line pumps to boost fuel, but they are a larger pump than the one in the tank....usually. This MSD is smaller than the one in the tank.....so does anyone have any advice or experience they would lend?

[raroZ28]

What size fuel line are you running? FPR?

[N20LT4Bird]

stock lines, stock regulator, SVO 30lb/hr injectors.

[raroZ28]

You need more volume. You can only force so much fuel stock lines, it doesn't matter which pump you have. I would say to upgrade that line to some bigger stuff. It's all about volume. Bigger line=more fuel. I would think that with the bigger line the walbro would be fine. Could be wrong though.

[Kevin - Blown 95 TA]

I have the same issues except that I already have an in-line pump which seems to take the load off the in-tank pump so that all the in-tank pump has to do is keep the in-line pump fed with fuel - I run stock FP. At least that's my theory. I am presently installing a TPS switch to tell the in-line pump when to turn on because right now it is on a toggle switch and I leave it off except when I need it so it doesn't die a premature death from being on when it's not needed (99% of the time). That's OK at the track, but bad for the street. I need to see if there is any delay activating it this way. I am going back to the track this fall after the too hot weather is over, then I am going to log with a wideband and see if I can also log my FP somehow. I have Lucas 42# injectors and can't decide if they are right on the edge, but that's Ok momentarily at the track. I think my setup works with the extra T-Rex pump, but i was dissapointed the Racetronix 255 (made special by Walbro)isn't enough after all the trouble I went through to put it in there. I also think my fuel lines are sufficient for now, but I am going to upgrade them anyway once I figure out what to do back at the tank.

[Injuneer]

The stock lines are not the limiting factor. While I run braided S/S lines, they are roughly the same size as the stock. My supply line is -6AN which is about the same as the stock 3/8" plastic line. My return is also -6AN, and thats just a little larger than the stock 5/16" plastic line. I'm running 800HP through the injectors (dry nitrous system), and my fuel rail pressure is 58psi. So I don't think you have a problem with the line size.

The thing you have to remember is that the amount of fuel per HP goes up with nitrous.... maybe 10% more per HP overall. So if you are running a pump that's good for 600HP NA, it might only be good for 550HP if a part of that HP is made with nitrous.

Adding an inline pump, as long as it is similar in size to the intank pump, will net you either a higher volume at the same rail pressure, or the same volume at a higher rail pressure. Think of the pump flow as a graph of pressure on the X-axis and flow on the Y-axis. The pump "curve" can be approximated by a straight line that show fuel volume drops as pressure increases. But if you run two pumps in series, you only need to make part of the total pressure with each pump, so the pump will operate at a point on its curve where both pumps push the same volume, and each contributes a portion of the required pressure. And that flow volume will be greater than you would have gotten out of either pump individually.

But, you generally run an inline "booster" pump when you want a higher pressure. If you want more volume at the same pressure, its often better to add another pump in [EDIT] parallel. That means it either needs to have a sump off the stock tank (whatI have done) or it needs its own tank.... a separate fuel system for the nitrous system.

I have two Bosch pumps rated at 205LPH. One of them is good for 500HP, so I only run one of them normally. When I flip the arming switch for the nitrous system, the second pump turns on. That way you aren't circulating an excessive volume of fuel through the system when you don't need it. Circulating fuel can increase the fuel temperature. First it picks up heat when you pump it (efficiency of the pump, heat loss to fuel) and it picks up heat as it passes the exhaust system and through the engine compartment. I've seen setups that push so much fuel through the system that they need a fuel cooler to handle the heat buildup under low engine load conditions.

For your setup, consider a separate fuel cell for the nitrous - maybe with a little bit of "racing fuel" in it, a pump that pulls off the fuel cell, a supply loop to the nitrous solenoids, and a pressure regulator and return line.

[N20LT4Bird]

Thanks, Fred, Kevin and Raro for the input. The fuel lines will stay as is, I think they are sufficient too.....and my car isnt fancy like Fred's, requiring braided line

Fred, the seperate fuel cell is an idea that I have kicked around, but would like to avoid if possible. Yes, it would be the "ideal" set-up, but I am not sure its worth the extra expense, weight, and inconvenience for the additional 50 HP. (Let me know if you disagree, please.) I am not planning on adding any more nitrous (above the 150 shot) until I build a better lower end, so if I can get by with just a booster pump, I would like too, for now.

My fuel pressure switch is cutting out because the volume is not there, causing a sudden drop in pressure. So, if each pump supplies part of the total pressure, the volume should be able to be maintained.

If this is true, what is the advantage of running a seperate fuel cell for the nitrous?......(if im not going to be running a 250 or 300 shot).

Oh, and has anyone ever used one of these MSD pumps?

[Kevin - Blown 95 TA]

Fred, you said your pumps were in series - did you mean to say that they were in parallel?

But if you run two pumps in series, you only need to make part of the total pressure

If you want more volume at the same pressure, its often better to add another pump in series.

Matt SLONOMO had the setup you described. He put in a separate fuel cell & pump in the spare tire well for the nitrous and he put leaded race gas in there. But I think his second pump might have gone thru a regulator straight to the fuel solenoid on the nitrous system.

[N20LT4Bird]

Fred, you said your pumps were in series - did you mean to say that they were in parallel?

I assumed thats what he meant......

[Joe 1320]

A seperate fuel cell for the nitrous is a great setup..... on demand power and difference in octane rating too. You could run high octane leaded in the stand alone fuel system for the nitrous and high octane unleaded in the traditional tank. Reduced lead fouling of the 02 sensors, no tank draining, etc.... of course you could also use unleaded.

[Injuneer]

I think you will be fine with the inline booster pump, if you are just looking at the HP levels you are at now. You will gain in flow. Alternatively, get a larger intank pump. There are "twin" pump setups available.

I ran the NOS inline booster for many years on my car. But the NOS dry kit required 85-90psi when the juice sprayed. But there was no problem with the fact that the inline pump ran continuously, any time the key was "on".

I agree a separate fuel cell/system is a complete PITA, but so is putting another sump in the stock tank. It just happened to be easy in my case, since the tank was out of the car already. And the sump and dual pumps wasn't my idea.... the guys that built my engine did it. They just liked the Bosch pump I had for my NOS kit, and put an identical pump in the tank, the kept my old pump outboard, off the sump. They like the Bosch pumps better than anything else, and when they had a choice, they used them. I saw one twin-turbo Porsche that they did that had a bank of 4 of the 205LPH Bosch pumps.... and that's good for 2,000HP

Unfortunately, an awful lot of the work on my car was done by "others" while I was working in Italy for 6 months, and only getting back to the US for a weekend every 4-6 weeks. So I had to put a lot of faith into the guys working on the car, plus having a good friend who already had one of the fastest 4th Gens around, and built by the same shop, watching over the shop and my car.

[Kevin - Blown 95 TA]

I think you will be fine with the inline booster pump, if you are just looking at the HP levels you are at now. You will gain in flow. Alternatively, get a larger intank pump. There are "twin" pump setups available...

How do they keep fuel to the pumps during cornering, etc? The stock pump has that white plastic bucket with a check valve on the bottom that the pump sits in (which I still have) and I'm wondering what you do to maintain that integrity with a dual pump setup or is it just disregarded? I know there is some baffling in the tank, but not sure what happens if you don't use the bucket.

[raroZ28]

it still doesn't make total sense to me how more pumps will really help.

You are looking for more volume, not more pressure right?

Say you're blowing through a straw, and you're measuring how much air comes out the other end. You're blowing as hard as you can, but because the of the size of the straw you can only blow so much. Take a bigger straw, and blow as hard as you can, and you're going to get more air out. Correct? I am not second guessing, I wouldn't second guess Fred when it comes to this, trust me, I'm just trying to understand how more pressure is going to create more fuel volume... I'm not saying bigger is better, because too big would cause a pressure drop, but when talking about fuel line... I would think going up from 3/8" to 1/2" would be more sufficient and not create a drop in pressure, but increase volume.

Where am I getting confused?

[raroZ28]

How do they keep fuel to the pumps during cornering, etc? The stock pump has that white plastic bucket with a check valve on the bottom that the pump sits in (which I still have) and I'm wondering what you do to maintain that integrity with a dual pump setup or is it just disregarded? I know there is some baffling in the tank, but not sure what happens if you don't use the bucket.

I didn't use the bucket when I did my tank, I found an online tutorial that showed just using clamps to clamp it down without usign the bucket. I read later how it can have adverse effects, but I've yet to see any. Car has been on low fuel many times and I have taken corners and it hasn't done anything.

I think the line holds more fuel than people realize so something simple like a corner wouldn't throw it off. Now if you drove on a slant and all your fuel went one way for a while then you'd be screwed. But I don't think the canister would help much in a situation like that anyway.

[Kevin - Blown 95 TA]

I didn't use the bucket when I did my tank, I found an online tutorial that showed just using clamps to clamp it down without usign the bucket. I read later how it can have adverse effects, but I've yet to see any. Car has been on low fuel many times and I have taken corners and it hasn't done anything.

I think the line holds more fuel than people realize so something simple like a corner wouldn't throw it off. Now if you drove on a slant and all your fuel went one way for a while then you'd be screwed. But I don't think the canister would help much in a situation like that anyway.

Your points are valid, but my car probably uses twice as much fuel at times, so I have to be cautious about it. On the other hand there is also fuel in the filter and my in-line pump, so maybe it's enough to make a difference and not run lean unless you are on a long carousel turn at a roadcourse as you mentioned. And since I have the in-line pump anyway, I may not have to go that route, it's just that I thought the 255 Racetronix upgrade would be enough and it wasn't.