How much ??? (stock fuel system)

[HAMMER]

Sled:

2006 Mountain Apex with MPI supercharger (Stage-I)
Nitrous System (built myself from several manufactures parts)
Stock - Engine, Compression, Exhaust, Fuel Pump, Injectors
Cold Air Intake - Bypass Valves
VDO boost gauge to intercooler (cross-checked with two others and its correct)

Conditions:

5000ft elevation
Sustained wide-open-throttle runs

Boost is RPM based with the Rotrex supercharger

Off the bottle - RPM 10,200 - Boost gauge shows 9 lbs
On the bottle (45-shot) - RPM 11,000 - Boost gauge shows 10 lbs
Compressor maxed out at 150,519rpm (11,000 engine RPM)

Off the bottle - Air fuel ratio flashing 12.1 and 12.2
On the bottle - Air fuel ratio flashing 11.8 and 11.9

Horsepower:

Maximum sea-level horsepower for the Stage-I at 150,000rpm is 240
Atmospheric Pressure = 14.7psi, +Boost 10psi, Total = 24.7
Atmospheric Pressure 5000ft = 12.2psi, +Boost 10psi, Total = 22.2
Total Pressure Loss, 24.7-22.2 = 2.5psi
Percentage of loss 2.5/24.7 = 10.1%
Subtract -- 240 x .101 = 24.24 = 215.76hp
Add -- 45hp for nitrous = 260hp

Conundrum:

I've read on TY that the stock Apex fuel system would not support over 235-240hp.

I've read on DynoTech: "Fuel flow was about 160 lb/hr at 42 PSI ... plenty of fuel flow available for booosted engines well over 250 observed HP".

I've read an MCX quote of 270hp on the stock fuel system.

How much horsepower will the STOCK fuel system support ???

 

[TBird]

The info i have from several sources is that the Stock fuel system supports approx. 270hp, thats why MCX set their std kit around 260hp, they want to have a little margin.

 

[TWIN TURBO]

I've made a real 340HP with stock injectors on gasoline no meth injection or any super tricks but???

 

[woodsrider]

If memory serves me right I think you are good for 17-18#s boost at 6000ft elev

 

[dynotechjim]

Hammer I poked around in the data on DTR and didn't see a listing of gross fuel flow from pump to rail (that's the FUEL A reading and the bypass FUEL B gets subtracted to give us net fuel used). When I get to the dyno today Ill look on database to see if I can find that on Art Andre's SC Apex before he upgraded his pump. My question is if your rail bypass valve is boost referenced to raise pressure (to give stock injectors more flow) how much does that higher working pressure drop gross flow in lb/hr? Does your system raise rail pressure on boost? Maybe Art's data on my dyno computer will show that, if rail pressure rises with boost rise, I can tell how much gross fuel flow drops.

One other issue that's been more of a problem with EFI machZs if you watch dootalk is fuel pumps losing their capacity over time, and losing top end pressure (= leanout) with awful results. Just last week I had a troublesome Apex FP turbo that had been flawless for a year, now acting surgy,the dyno found pump was fine at idle/ cruise but losing pressure/ volume as revs climb, causing leanout. A new pump/ sock filter took care of that. I dont know how common pump issues are on Yamahas but it seems too common on Skidoos.

I think it would be good to have a $20 hobbs switch in the fuel system set to turn on a red warning light on the dash if pressure drops a few psi below stock.

 

[dynotechjim]

heres one of Art Andre's dyno runs, note how fuel flow A begins dandy, but then mysteriously drops as revs climb!? I would think if pump was bad, it would be bad at low RPM but can't figure out why it drops as revs climb. Maybe some voltage drop at pump as revs climb? Now I need to go back and look at that Apex turbo that was losing fuel pressure.

 

[dynotechjim]

sorry forgot to include boost pressure rise inches of hg (2 inches of hg = 1 psig). left out hp to give fuel flow better resolution

 

[HAMMER]

Jim -- I'm going to poke it with a 60-shot this weekend ... If I'm able to keep my air fuel ratio below 12:1 ... I guess I won't worry about what the max is for the stock fuel system ... because I will have both my super and my nitrous system at their limits ... I do have an MSD pump and all the plumbing on-hand if I choose to go that route ... but I'm thinking it wouldn't be worth the hassle for 15 more hp ... it goes pretty good the way its set up now.

 

[rxrider]

HAMMER - Tbird is right on. According to Erik at MCXpress the stock fuel system can support 14 lbs of boost in their Apex MCX260 kit. The MCX260 kit puts out 260+ HP at 12.5 lbs, at 14 lbs the MCX260 kit puts out about 275 HP.

 

[Srxspec]

HAMMER, let us know when it blows up, that way we will all know where the limit is!

 

[HAMMER]

Thanks for the input guys !!!

I've been doing plug checks (apex is pain in my arse) to verify my O2 readings and everything looks good ... just wanted to triple check with "the collective" (little star trek humor) and see what the other wrench benders have on the subject ... It's running so good now I think I'll just leave it right where it is ... If I need more horsepower ... I'll buy a turbo ... ;-)

 

[HAMMER]

Did some more digging around and found this:

Glen Hall’s GT25 Turbo Apex

Found the stock fuel system good enough for 13lbs.
Ran it at 14lbs ... Air Fuel Ratios at upper limits.
Attempts at 15lbs found the stock fuel system inadequate.

Soooo ... stock fuel system is adequate for around 400-CFM