one thing to keep in mind guys is that fuel injector sizing has nothing to do with this. if your duty cycle is wide open and fuel pressure is falling off, that means the supply is maxed out. if the fuel pressure was holding strong, injectors wide open, air fuel getting lean - that is when you have maxed out injectors.

going to a larger injector when your fuel pressure is falling isnt going to change a whole lot. some of you may be discussing slightly OT... but for those with fuel pressure dropping, a larger injector will not be the fix.

 

Just for comparion... I have seen a APS TT car max out a single walbro as low as 510rwhp (dynojet) with our stage 1 kit. On the other end, I have seen a car max out a single walbro at 673rwhp (dynojet) with our stage 2 kit. So how much from there do you think that supercharger is eating up in parasitic drag?

It is to my belief that all Walbro 255 pumps, perhaps, may not be created equal.

There is still other food for thought...

What if your engine combo isnt the most efficient? A reduced Volumetric Efficiency (****ty intake manifold, or cams / headwork that are not proper for your setup) will make less HP out of the same mass of air/fuel mixture compared to a more efficient setup. This also goes for the state of tune (aggressive versus not aggressive).

I am not a supercharger guru, but I would wonder if you could use your logged gauge pressure to get an idea of your how well your setup is running efficient or not in comparison to a car with comparable setup. For example.... Wouldn't a more VE engine running the exact same combination of parts (supercharger and pulley sizes and intercooler and pipes) actually make LESS boost PRESSURE but MORE HP at X RPM and equal compressor speeds due to the engine ingesting the air more efficiently? I would assume this would also reduce belt slipping because there is less pressure differential for the compressor to fight and also have a side effect of compounding HP gains by requiring less compression of the air (which reduces density by adding heat) to match the mass airflow.

It seems that with a supercharger setup, the details matter a lot more. A turbocharger's wastegate controlled compressor speed will make up most of the differences on a turbocharged car.

 

yeah I dunno. I've thought about maybe the SSV on my car possibly creating turbulence, but no one knows for sure. Howevever we hooked the FRP's boost reading directly to the blower so the manifold has no influence or delay on the readout. I have a cosworth intake manifold preordered, but that'll be 2 months at the earliest before I get one.

Charles, how soon do you think the twin pump setup will be ready to ship?

maybe I should just have the stage 2 line put in right now instead of waiting for the twin pump assembly to do it

 

Also keep in mind, at a lower fuel pressure setting the pump has less work - and its flow will go up. The pump will actually flow greater ammounts of fuel at a lower fuel pressure. However, lower pressure can reduce atomization quality of the fuel spray pattern thus reducing how efficiently you can actually use the fuel. Its quite the conundrum, the balance is where its at. This is why there are industry standards for comparison environments, such as fuel pressure ratings for injectors.

The quality of a fuel injector can come into play here as well. A higher quality injector will have improved atomization which will allow more efficient use and burning of the fuel that is injected. You do not need to inject quite as much fuel when you are burning more of what you are actually injecting. Higher quality injectors are very expensive! my HKS/Denso 1000cc injectors were like 250 EACH... but I hear the price has since dropped.

So many factors to consider!

 

Check your fuel pressure regulator. Blip your throttle at idle...the pressure should go up. If it goes down, you have an issue in your fuel pump assembly, or an FPR that is too loose. Try tighenting up the FPR.

Keep us posted.

 

yeah I think at least in my case the issue is in my fuel pump assembly because the FRP was the first thing that was messed with and even replaced the unit with a known good one

I'm using RC750 injectors. I know they're not the highest quality ones on the market or anything though

 

Quaman and I were talking about just about the same thing . When I went the larger IC and pipe . I gained whp with out gaining any boost . I was able to free up air flow [ TO ] the motor . So in turn freeing up air flow [ AT ] the motor it self will have the same results . As far as belt slipping , I was able to move where the belt slipped at from 6300rpm down to 5900 rpm , but it still started to slip at 13psi . To get it to not slip , you would have to have better grip on the pulley itself . There have been several ways found to increase belt grip . How much of a psi increase due to thoughs grip fixes is yet to be seen . I think Sentry is the closest to finding out . Im installing the all cog system soon to take care of it .

 

off topic - Booger, are you using the stock radiator? If I remember right you had to increase your pipe diameter to match up with the intercooler you got. I'm using the slip koyo radiator and there doesn't appear to be much room for me to go that route to increase the piping diameter. So instead I'm hoping water injection will serve as an intercooler substitute along with all the other benefits.

I figure I'm going to be close to the edge if not past what the stock intercooler is able to work with. There's always that NX N-tercooler kit too, but I'd rather not run a million cooling systems

 

yah, it rises and responds as normal...

I personally installed this kit on Jason's car.and just haven't had the time to try to trouble shoot it any further..

it runs perfect up to 6000rpm, then the fuel pressure dramatically falls off

when we discovered the problem on the dyno, i pulled the pump assembly..it appeared that the stock fuel pressure regulator delete plug was not sealing- causing a leak internally..i fixed this, then did another pull on the dyno, the fuel pressure did the same thing...

When Jason told me another forum member was having the same issue, I figured a fuel pump issue- not faulty, just issue with a supercharged setup and the walbro...

Jason: we'll spend some more time digging deeper soon, lets pull the assembly again, possibly swap pumps even (not likely cause but if we cant find anything else-worth a try)...

-TODD

 

keep us posted


my tuner thought I was running out of injector so we stepped up to 750cc just to be absolutely sure since it was doing it with 440cc and 550cc injectors. In hind sight now that obviously wasn't the problem, but I was (and still am) new to fuel systems

 

Still have stock rad. The first part of the IC pipe is stock Vortech , to the BOV . After that its all 3inch . Im going to have to go to slim fans to get the cog system in . Even a slim radiator...dont know quite yet . Looks like it will work with just the fans. I added the W/M injection for a safety margian

 

yeah I'm adding the W/M injection for safety too with raising the detonation threshold

I hope it might also help combat the fuel pressure issue since it does add methanol to the engine. I'm hoping it might counter the fuel pressure drop issue I have some and back off my booster pump a slight tad

 

It will reduce your A/F . Mine was almost 3/4 of a point .

 

wow that's probably a pretty effective power gain then

i'm assuming my exhaust and additional boost I wasn't tuned for will lean me out too. I was just thinking the methanol would basically take care of the colder air from the W/M injection, but I guess it won't

 

It can very greatly I think . All depends on when you start to spray , how soon you go to full spray , and how big of injector you use . Until I get a EMS and get the belts squared away . Its used for safety....then for power

 

Buy a new Walbro.

I had a similar problem and had no idea what it was. It was first diagnosed by a shop as a my stock fuel system being maxed out.....so I bought a return system from CJM.....and the problem was still there.

Then, I bought a more accurate fuel pressure gauge to make sure I knew what was going on....gauge was fine.

fianlly, I decided to try a new walbro even though mine was only a couple of months old.

BINGO!!!! I had a bad walbro, and the new fixed all my probs!

 

Hello all. This is Jason's buddy Alex, and I thought i'd see if I could help with any suggestions.

Sentry: Did you guys check the actual voltage to the pump before and after the MSD booster pump? Is it actually adding volatage? Or is it losing voltage through the stock wiring which the MSD is really just bringing back to normal?

If you guys think it is the pump maybe he can swap my stock TT Supra fuel pump into the car? They are good to a little higher power goals than the 255 Walboro, but they also pull a LOT more amps. I'm just trying to eliminate everything without pointlessly buying new parts.

I know we (Supra guys) always run new wiring and relays when putting dual pumps in, whether that is adding a single Walboro to the stocker or adding another Denso pump. This would be a cheap easy thing to do just to rule out that variable. It almost seems not the case as only a couple people so far have experienced this, can't rule it out though. Putting my pump in would definitely neccessitate new wiring I would imagine.

There are no external leaks, and I'm confident that Todd patched up inside the tank pretty well also. I can't imagine it being a leak then. It falls off steadily as RPMs climb though. Almost to 20psi. I dunno it seems like a voltage drop problem to me, but I could be wrong.

Alex

 

I don't remember if we checked the voltage or not. Charles from CJM mentioned that early on and I told my installer about trying that, but I don't remember what came of that. I know one guy a long time ago with a TT setup was having similar issues, and his voltage was just fine. His issue was something not sealing all the way in the pump assembly


ok what year and build date are the cars with this issue?

mine was made in aug 02 model

 

Well Jason's (Barzten1) build date is August 02 as well.

Alex

 

well that's an interesting coincidence...hmm