Walbro and CTSC

[spdntckt]

Perhaps a dumb question, but the 'standard' CTSC Setup comes with a fuel pressure relay which - to my understanding - bumps up the voltage to the stock fuel pump to ~20 volts in order to help it keep up with the higher pressure demands under boost...

if you replace the stock fuel pump with a walbro fuel pump, should you remove that relay? (eg: does the walbro function properly at 20volts?)

 

[Racerxjling]

Sorry I don't know the answer to your ?

I have the CTSC "hi boost/9lb kit" but I scrapped their fuel management for the following:

RC550 injectors
Walbro 255? HP fuel pump
AEM FPR
AEM ECU

and LOTS of tuning from Shane @ Autowave in Huntington Beach, CA. It was well worth it as my a/f is very linear.

Good luck.

Jeff

 

[spdntckt]

Jeff -

Thanks for the note - only problem is the car is ODBII, which greatly limits optoins for a true EMS

 

[drew]

I don't have a field tested answer for you either, but...

I am installing a standard CTSC with only a Walbro HP255. That pump should have the capacity to easily supply the fuel needs.

The Walbro has supplied other FI applictions with 400HP without problem.

I think that you will find that if you install a Walbro AND the "boost a pump" it will override the ability of the pressure regulator to return fuel and cause your engine to run rich (or "burble away" as Doug Hayashi states) and effectively voiding any HP gains.

I was going to do some testing with a Haltech wide band O2 sensor and some test pipes. Have no time for it this year...too many projects.

Drew

 

[maynard]

Do a search for TBW EMS. Looks like soon there will be one avaible. I sure hope so!!

 

[Briank]

Perhaps a dumb question, but the 'standard' CTSC Setup comes with a fuel pressure relay which - to my understanding - bumps up the voltage to the stock fuel pump to ~20 volts in order to help it keep up with the higher pressure demands under boost...

if you replace the stock fuel pump with a walbro fuel pump, should you remove that relay? (eg: does the walbro function properly at 20volts?)

It is likely you will not need the voltage boost with the better pump, the main problem you need to watch out for is overloading the fuel pressure regulator.
If the FPR can't return enough fuel to the tank the pressure will not be controlled. Keeping the relative pressure constant is very important to controlling how fuel the injector delivers.

 

[Onsoku]

Perhaps a dumb question, but the 'standard' CTSC Setup comes with a fuel pressure relay which - to my understanding - bumps up the voltage to the stock fuel pump to ~20 volts in order to help it keep up with the higher pressure demands under boost...

if you replace the stock fuel pump with a walbro fuel pump, should you remove that relay? (eg: does the walbro function properly at 20volts?)

I have the same question. Mine is a 91, with I/H/E/ standard CTSC with the Walbro 255. What is the rec. AFR using using this setup? Searching the forum, it seems that a range of 10-12.5 would be best for longevity?

dynomike, how is your schedule looking? maybe we can setup a visit!

 

[makena88]

Jeff -

Thanks for the note - only problem is the car is ODBII, which greatly limits optoins for a true EMS

Not really talk to Mike at Autowave they have a solution for that with the AEM EMS now.

 

[ScienceofSpeed]

Here are some new offerings:

stand-alone engine management for OBD2 1995-2005 NSX:
http://www.scienceofspeed.com/products/engine_performance_products/NSX/MSL/EMS/

high boost / fuel system for Comptech Supercharger & stand alone engine management:
http://www.scienceofspeed.com/produ...ts/NSX/ScienceofSpeed/High-Boost-Comptech_SC/

The Walbro should see a straight 12 V. You can bypass the factory resistor and remove the Comptech "boost a pump" voltage bumper.

The kit above includes everything that you'd need to convert the Comptech fuel system to use stand alone engine management like the AEM EMS.

Cheers,
-- Chris

 

[Larry Bastanza]

The Walbro should see a straight 12 V. You can bypass the factory resistor and remove the Comptech "boost a pump" voltage bumper.

Chris,

The above statement is based on using the above mentioned kits with stand alone fuel management correct??

Thanks,
LarryB

 

[dynomike]

Do a search for TBW EMS. Looks like soon there will be one avaible. I sure hope so!!

Engine management for obd2 is now available. I have made a system that will adapt an AEM ems to a 1995-2005 nsx. Everything in the system is plug and play, no wiring modifaications are needed .Here is a link to a car I did with the system with dyno sheets. This is 1998 nsx with CTSC.
Systems are in stock and ready to ship. The systems are available through myself. Please PM me if you are interested.Msl engine managemnet link

 

[Onsoku]

The Walbro should see a straight 12 V. You can bypass the factory resistor and remove the Comptech "boost a pump" voltage bumper.

Cheers,
-- Chris

Chris, I'm trying to be absolutely clear about this one...so you're saying the above applies with the CTSC setup, yes? I want to make sure, because I really don't want to buy any more stuff than I need...like the VFAC they've been recommending to me to cure my 3rd gear ping issue.

Many Thanks,
Rob

 

[ScienceofSpeed]

Hi Larry --

Yes, that statement is correct when using the kit we provide. Fuel pressure remains constant across the board w/o boost-a-pump.

Regarding the FPR getting overwhelmed - we replace the factory FPR as it is not compatible with the Comptech fuel rail. The provided FPR can handle fuel volume for 1000 hp applications, so this is not a problem.

Onsoku -- regarding "all the parts you need", yes, this would be a complete system. Nothing else is needed. The VAFC recommened wuld not be needed with stand alone engine management, as ignition and fuel calibrations are under complete control with stand alone engine management such as the AEM EMS.

If you are not able to purchase the complete upgrade at this time, we have had good success with replacing just the fuel pump and recalibrating the FMU. We recently had a customer's CTSC in our shop which was running lean on the top end. Replacing the fuel pump and recalibrating the FMU gave a more consistent AFR and allowed the car to pick up around 20-30 hp through the range. It was possible that his stock fuel pump was on the way out.

The stand alone engine management and fuel system properly tuned however remains the best and only way to offer 100% control of longterm reliability.

take care,
-- Chris

 

[thouchin]

This thread got confusing fast and Im not sure which CTSC this thread refers to but I will ask for the new autorotor kit...
If I use a walbro 255lph fuel pump, should I not install the boost-a-pump?

T.J.

 

[The Kid]

This thread got confusing fast and Im not sure which CTSC this thread refers to but I will ask for the new autorotor kit...

The original whipple style blower, the autorotor kit wasnt out yet when the thread was started:wink:

 

[LJSB]

Perhaps a dumb question, but the 'standard' CTSC Setup comes with a fuel pressure relay which - to my understanding - bumps up the voltage to the stock fuel pump to ~20 volts in order to help it keep up with the higher pressure demands under boost...

if you replace the stock fuel pump with a walbro fuel pump, should you remove that relay? (eg: does the walbro function properly at 20volts?)

Why not call Comptech and ask?
Talk to the front of the horse.

 

[john85259]

I called Comptech about this a couple months ago and the person I spoke to (whose name escapes me at the moment) wasn't sure what the fuel pump pressure should be as a function of boost. He said he'd try to send me some data from a dyno test but it has yet to arrive. He also said that they have had no problems with people using the stock fuel pump with the voltage boosting module. The implication behind this statement is that if a good, stock fuel pump works fine with the standard Comptech package why bother changing the fuel pump to an unknown quantity? I have to admit that there is a certain logic to this argument.

Since logic is sometimes not one of my strong points I bought a Walbro high pressure/high volume fuel pump anyway. I installed boost and fuel pump pressure gauges in the ashtray and have been monitoring the boost and fuel pump pressure relationship. (Got a great deal on Cyberdyne boost and fuel pump gauges with memory, the pair with senders for $156 from Don South at www.speedsolutions.net.) Here is the data I have so far. It was collected over a month or two as I was driving the car around so there is some variation in the data but the trend is pretty stable.

Boost Pressure Fuel Pump Pressure
_____<0 ______________42
_____0.6______________60
_____0.8______________65
_____2.1______________67
_____2.3______________70
_____2.7______________67
_____3.5______________72
_____3.7______________74
_____3.8______________74
_____4.0______________76
_____4.3______________79
_____4.4______________78
_____4.5______________77
_____4.7______________79
_____5.0______________80
_____5.5______________82
_____5.6______________82
_____5.7______________79

When plotted in Excel it is roughly bilinear with one straight line from 0 PSI boost to 0.8 PSI, and a second from 0.8 PSI to 5.7 PSI.

I looked at the documentation for the fuel pressure regulator on Comptech's site and it shows fuel pressure vs boost pressure curves that are linear. I'm not sure why the data for my car is bilinear. I need to get some more data at low boost pressures (0.8 to 2.0 PSI).

My car is a 91 with 115,000 miles and as far as I know the fuel pump is original to the car. The fuel filter was changed about 25,000 miles ago. My concern is that the stock fuel pump might not be in good enough shape to deliver sufficient fuel pressure. I have a pretty good idea of what the pressure curve is for my car but I don't know precisely what the fuel pressure would be if the fuel pump is healthy.

For lack of anything better to do, I'll drive the car around a bit more and collect additional data and then I'll replace the stock fuel pump with the high pressure/high volume Walbro without the voltage booster and see how the fuel pressure vs boost pressure data looks. If it's equal to or a bit more than the old fuel pump with the voltage booster I'll leave it alone. If it's less, I'll start goofing around with fuel pump voltage and see what it takes to get the desired pressure. Once I get it in the ball park I'll put the car on a dyno and set the fuel pressure to the optimal value by checking the air/fuel ratio under load. I'll also check if fuel pressure stays steady under high boost conditions or if it drifts down over time.

I'm wondering if other cars have a similar bilinear relationship between boost and fuel pump pressure. If anyone has any measured test data on how fuel pump pressure varies with boost on a Comptech supercharger please feel free to share it with the rest of us.

Thanks.

John Crawford

 

[DDozier]

For lack of anything better to do, I'll drive the car around a bit more and collect additional data and then I'll replace the stock fuel pump with the high pressure/high volume Walbro without the voltage booster and see how the fuel pressure vs boost pressure data looks. If it's equal to or a bit more than the old fuel pump with the voltage booster I'll leave it alone. If it's less, I'll start goofing around with fuel pump voltage and see what it takes to get the desired pressure. Once I get it in the ball park I'll put the car on a dyno and set the fuel pressure to the optimal value by checking the air/fuel ratio under load. I'll also check if fuel pressure stays steady under high boost conditions or if it drifts down over time.

I'm wondering if other cars have a similar bilinear relationship between boost and fuel pump pressure. If anyone has any measured test data on how fuel pump pressure varies with boost on a Comptech supercharger please feel free to share it with the rest of us.

Thanks.

John Crawford

This bilinear relationship is probably due to the OEM fuel system using a large resistor to reduce voltage being sent to the fuel pump while at low RPMs and idle, and then when demand is higher the resistor is bypassed and a full 13.8 volts is sent to the fuel pump. Then in the case of the CTSC as the engine transitions to boost the voltage is increased again to something like 20 volts. So the fuel pump actually runs at three different speeds when the CT fuel management is used.

I think you will find that the car will run very lean at high RPM's without the bust-a-pump in the picture, the fuel pressures will not likely increase to the 70-80-90 psi area without it, resulting in a lean condition as the pulse width on the injectors will not change and the pressure will be lower.

If you attempt this, you should be monitoring AFR while you do this if a lean condition exists, stop.

I do not see any real issue with running the CT boost-a-pump with the Walbro, you may have to reduce your base fuel pressure at the fuel pressure regulator to bring everything back to relative even at idle, again you have no way of knowing this without AFR monitoring, or you may need to replace the ramp rate spring in the fuel pressure regulator to match the new fuel pump better. You may also run in to a need change the return line orifice as it is adjustable to.

I am sure the folks at Comptech played with all the combinations of the ramp rate springs and return line orifice until they got the desired effect. You will probably have to do the same.

If you go ahead just be careful, I am not sure I would move forward without the wideband O2's in place.

Dave

 

[drew]

I now have +year of a CTSC, Walbro 255LP with a boost-a-pump and it works fine. I monitored the system with my autoinnovate wide-band data recorder. In fact, I would not run the car without the booster.

You MUST change out the fuel pump on a 115K mile car even if you are not running FI. The pump degrades over time and I got a pretty good HP gain just by changing the pump to a Walbro (prior to the CTSC).

It has been a while, but I think you should be hitting 90PSI on the high end of your boost pattern. My system now is pinging a bit on 3rd gear on WOT up a steep hill...I'm not sure what is up with that though.

Drew

 

[john85259]

DDozier and drew,

The bilinear data makes more sense when the increase in fuel pump voltage is considered. I didn't know about the return line orifice. Thank you for mentioning both of these.

Hearing that someone has used the Walbro with the voltage booster is a valuable piece of information. I think I'll do the same. If the pressure looks good I'll leave it alone and check the air/fuel ratio on the dyno or get some instrumentation that will allow me to check it on the car. I'll have to shop around and see what is available. I wish I had thought of this when I was at the PRI show last week. Duhhh.....

Additional Pressure Data Points: I drove the NSX to work today and managed to hit 5.9 PSI on the freeway on-ramp. Fuel pressure was 85 PSI. On the way home I hit 6.0 PSI with a fuel pressure of 82 PSI. The variance in fuel pressure could be due to how long the engine stays at that boost level, or maybe other conditions like temperature. It was quite a bit colder in the morning that it was in the late afternoon. If it's supposed to hit 90 PSI at max boost it looks like the fuel pump is lagging behind a little or the regulator needs to be adjusted. No matter what, it's wise to replace a fuel pump that is 15 years old and has 115,000 miles on it and then move forward from there.

Thanks for the information and suggestions.

John

 

[DrivingAmbition]

The Comptech system does not use the factory stepped voltage system. It only uses the factory wiring to power the voltage booster relay. It picks up its main power from the engine fuse box. The Comptech system uses running voltage most of the time and when about .5 psi of boost is seen in the intake manifold is switch's to about 20 volts. When installing the Walbro pump you should remove the complete Comptech voltage boost kit and put the car back to the stock wiring. But you will definitely have to change the settings on the FMU. It should be possible to get the FMU to work with the Walbro fuel pump (I have never tried it) but it will take someone with the right equipment to do it (dyno, A/F gauge, FMU optional parts). I would not recommend changing to the Walbro fuel pump unless you are installing the AEM EMS, larger injectors, and a 1:1 FPR. Hope this helps. Shad:smile:

 

[john85259]

Shad,

So, is it reasonable to conclude that when using the Comptech supercharger system it's best to replace an older stock fuel pump with an identical new one and leave it at that? (Seems likely since that it what they told me when I called.)

It's nice to get a definitive statement from someone who knows.

Also, do you have any idea what the pressure vs boost curve is supposed to look like? On my car it can be described by two lines defined by three data points: 42 PSI fuel pressure at 0 PSI boost, 60 PSI at 0.6 PSI, and 85 PSI at 6.0 PSI. (Approximately.)

Thanks.

John

 

[drew]

I'll defer to Shad as the expert.

I would also like to provide a datapoint for a C30A: CTSC whipple (standard pulley), Comptech provided fuel regulator + voltage unit and a Walbro 255HP.

I spent over a hundred hours data-logging (AFR, intake pressure, fuel pressure, TB butterfly valve) this set up and I am happy with the results. It is my daily driver and I have driven for over 14 months now with this configuration.

My data show good results with a walbro and the "boost a pump". I've even passed smog with excellent results...I am not running rich/lean at all.

Your results may vary, my success is no guarantee of yours.

Drew

 

[Arshad]

Yet another data point... I'm running C30A, Whipple 6lb with the Walbro 255 with the voltage boost REMOVED. Emissions test also passed without any issues here, and the car has been running fine. I was told by more than one person to remove the voltage bump and use the stock wiring when putting in the Walbro since it doesn't require it.

 

[john85259]

With all this information it's kind of tough to figure out what to do. Comptech says to run the stock fuel pump, others have had good experiences using the Walbro high pressure/high volume fuel pump with stock voltage as well as with the Comptech voltage booster.

I snooped around on the internet and found a graph at http://www.stealth316.com/images/flowtest-walbro.gif that shows how flow varies with pressure and voltage for several fuel pumps, including the Walbro GSS 341. If you take a look at the graph you'll see that there are two lines for the Walbro GSS 341, one is red and another is brown. The brown line was generated by RC Engineering and was published in a magazine. The data for the red line appears to have come from http://www.vfaq.com/pump-Walbros.html. This introduces uncertainty because we don't know which one is right. To be conservative we should use the red line because it is lower than the brown line.

I decided to calculate how much fuel flow is needed to generate 355 rear wheel horsepower and then see what kind of fuel pump voltage is needed to obtain this flow from the Walbro GSS 341. Assuming that the brake specific fuel consumption for a supercharged engine is a conservative .6 lb/hr/HP, I calculated that we will need a fuel flow of 160 liters/hr to support 426 flywheel HP (1.2*355 RWHP). Going to the chart and looking at the brown line (RC Engineering data) we can see that with 13.5 volts the Walbro GSS 341 puts out just over 160 liters per hour at 90 PSI. This implies that using the standard fuel pump voltage with the Walbro GSS 341 high pressure/high volume fuel pump will generate sufficient fuel flow at the expected maximum operating pressure of 90 PSI. If we think the red line data is correct then we'll only get 140 liters per hour and we'd need to increase the voltage an unknown amount to get the desired fuel flow. However, if we use a more reasonable BSFC of .55 lb/hr and assume frictional loses of 17% rather than 20% the fuel flow requirement needed to generate 355 RWPH decreases to 144 lt/hr.

This appears to justify removing the voltage booster if we are getting 355 RWHP or less and are running a Walbro GSS 341 high pressure/high volume fuel pump. If we are expecting higher horsepower than this we'll need to increase the fuel pump voltage to get the needed flow.

Does any of this make sense? Did I make an error in my calculations or methodology?

Suppose we decide to run the voltage booster with the Walbro GSS 341 fuel pump just to be safe. Will the excess volume flow past the fuel pressure regulator and back to the fuel tank without any problem? Will the Walbro GSS 341 run forever at 20 volts or will there be durability problems? Would it be reasonable to reduce the voltage booster from 20 volts to maybe 15 or 16 volts? If so, how might we best accomplish this?


John Crawford