Outer Limits 4x4 Board

PJ.zook wrote:I would have thought MAP sensors would be much more suited to positive pressures than MAP

errr...did you mean something else.

i only say this as Mud4b had to use a td surf map sensor as he said the MAP sensor on the jimny cant read positive pressures.
The modified one i can make puts extra voltage into the map sensor(thats already at 5v) to trick the injectors into staying open longer. Its got an adjustable dial, and with an exhaust o2 analyser you can dial in the correct voltage. But the only problem is, if you want to then turn off the supercharger(the sc12 and sc14 models with clutch) then you have the problem of tuning that back to standard.

Many high performance modified jap cars, GTR's and the like, are modified the air flow metres removed and tuned with 2 and 3 bar MAP sensors. They remove the AFM as it is a potential restriction in the intake path.

Layto....

Gwagensteve wrote:I wasn't casting aspersions about what you were planning wasabi.

Yere, I know Steve, it's all good. I'm just trying to find a cheap way to get a bit of extra torque down low and hopefully some more power at highway speeds. If all goes well then I'll let everyone know what i used, but I dont want people trying it while I'm still working things out, destroying thier engines and blaming me

In regards to SU's, I dont think a standard SU would be THAT great in a north/south OffRoad engine. Where the fuel bowl is positioned would cause the same kind of problems met with the Weber 32/36 starving on inclines I would think. I run twin 1.5" SU's on my Mini race motor and they can sometimes starve under heavy conering by pushing the fuel out of the bowl. I can only think if you flipped them to north/south you would then have the same problem on inclines/declines rather than corners.

Now the HIF34 or 44 carbs would be nice. These are basically an SU but with the fuel bowl mounted directly underneathe the carb rather than to the side (the main cause of starvation). I know on my street Mini when I changed from SU's to HIF's my starving issues were solved. Infact, I have two 1-3/4" HIF's in my shed at the moment, might have to look at making a new manifold and giving them a run... Have to see exactly what runs off the current manifold first though

if you make a manifold keep us posted as i want to run a sidraught carby to stop weber woo's . boner

lol yeh sorry i meant MAF not MAP, so MAP better than MAF.

Spike_Sierra wrote:

PJ.zook wrote:I would have thought MAP sensors would be much more suited to positive pressures than MAP

errr...did you mean something else.

i only say this as Mud4b had to use a td surf map sensor as he said the MAP sensor on the jimny cant read positive pressures.
The modified one i can make puts extra voltage into the map sensor(thats already at 5v) to trick the injectors into staying open longer. Its got an adjustable dial, and with an exhaust o2 analyser you can dial in the correct voltage. But the only problem is, if you want to then turn off the supercharger(the sc12 and sc14 models with clutch) then you have the problem of tuning that back to standard.

Hey Spike how do u put extra voltage in the MAP sensor when it is already at 5v. The N/A MAP sensor outputs a voltage of between 0 - 5 volts and is cross referenced to an array of injector pulse widths. A standard MAP sensor will read roughly 4.8-5ish volts at atmospheric pressure(1 bar), to zero volts on deceleration, a vacuum of about 27in/Hg. Increasing the voltage above 5 volts will possible damage the computer, as the inputs are usually rated to 5v. Sound like you are talking about a injector duty cycle interceptor.
Cheers Dan

cj wrote:Another carb to consider for offroad work is the Stromberg CD. IMHO they or the SU would be a better choice than the Weber. They won't quite deliver the same potential top end but their all around performance would be better.

x2 zenith stromberg CD's have the fuel bowl under the carb. Most easy place to find these is under the hood of a rangie.

Using a positive pressure (2 bar/3bar) MAP will require a aftermarket ECU, as the factory zook ones will only read a slight bit of positive pressure before deciding to not play anymore.
Basically they will read 5V at 2BAR or so, but you need to re-program/replace the computer so that it will understand that 5V siganl to be 2BAR maifold pressure.


Layto....

unsure on the technical side of things, can take no credit(or diss) for that.
got all info from http://www.go.jeep-xj.info/HowtoMAPsensor.htm

Spike_Sierra wrote:unsure on the technical side of things, can take no credit(or diss) for that.
got all info from http://www.go.jeep-xj.info/HowtoMAPsensor.htm

Interesting, if you follow that link back to the link he got it from, the guy has got bigger injectors and uses this mod to lean out the mix a bit. The g13bb computer most likely has a 16*16 table to calculate injector duty cycles based in the MAP input and rpm. So as said b4 the maximum duty cycle set to this table will be when the MAP sensor is maxed out @ 5V and at max rpm.
A easier way to manipulate these would be to adjust the fuel supply by getting an adjustable fuel regulator, and up the pressure to your injectors.

Cheers Dan

I had an old Pajero a few years ago, it was a 2.6L astron 4 cyd. I had a garrett T4 bolted to it with a dirty big SU carb (2 1/4" i think), it was a draw through set up. I ran 15psi through this set up and it never gave me any greif offroad. Angles in all directions and also rough ground, it ran without any glitches.
So i'm definatly a huge fan of SU carbs running on a turbo motor for offroad applications.
Driving around normally,'Did' give me better fuel ecconemy, but obviously like most of us, I recon turbos sound cool spooling up so it didn't get driven normally all that much. I only ran 31-10.5/15 desert Duelers but they would light up at the drop of a hat when you hit the throttle. Pitty it had not much ground clearance, it was a great car.

Tim

Oh yeah, also some of the series3 landrovers and early range rovers ran SU carbs on them. Might not be the right thing for a rock buggie but still handle some pretty serious offroad stuff.

JrZook wrote:

Spike_Sierra wrote:unsure on the technical side of things, can take no credit(or diss) for that.
got all info from http://www.go.jeep-xj.info/HowtoMAPsensor.htm

Interesting, if you follow that link back to the link he got it from, the guy has got bigger injectors and uses this mod to lean out the mix a bit. The g13bb computer most likely has a 16*16 table to calculate injector duty cycles based in the MAP input and rpm. So as said b4 the maximum duty cycle set to this table will be when the MAP sensor is maxed out @ 5V and at max rpm.
A easier way to manipulate these would be to adjust the fuel supply by getting an adjustable fuel regulator, and up the pressure to your injectors.

Cheers Dan

can you explain a bit further on what a fuel reg does, where it goes, where i can get it from etc, either on here or pm

Fuel regulators are used to push a bit more fuel into the engine.

They normally have a boost line to them and are also adjustable for base pressure.

By increasing fuel pressure with boost, more fuel enters the engine for any given injector duty cycle compared to stock boost pressure, so the engine can make more power.

They are a very crude way of adjusting fuelling and can only be setup by the use of a wideband A/F meter, best on a dyno where all conditions can be monitored. They definitely cannot be set up by the seat of the pants, by ear, or any other non technical way.

They might be part of a tuning solution, and are definitely cheaper than replacing the injectors with something with more flow if you anly need a little bit more fuel, but they aren't a fix all. You'll only know you need one if your injector duty cycle is being monitored on a dyno so you know you're out of flow.

Steve.

Steve has pretty much summed it up in regards to a fuel regulator. It basically increases the fuel flow for the whole rev/load range. Again with any mod it will need means of testing somehow, dyno, wideband a/f etc. With only low boost the adjustable fuel reg should cut it for ya. But have a look at some jaycar kits such as the 'digital fuel adjuster' and 'digital pulse adjuster'. With these kits the duty cycle of the injectors can be adjusted to accommodate some sort of boost.

Dan

One thing I haven't been able to find much info on is the need for a fuel regulator on a carby supercharger setup. Would you still need one or when you tune the carb for boost, does that do the same thing?

The generalised answer is Yes...

If you are making more power then you need to pass more fuel through the carb - usually requiring a large needle and seat.

High fuel pressue will cause the needle to lift, flooding the carb and producing poor idle etc. with a boost adjustable reg you might have 3/4 PSI fuel pressure at idle and increasing pressure as the engine gets on boost to supply the extra fuel required.

Make sure you have a solenoid on the system however otherwise engine vacuum will shut the regulator off completly.

On a blow through system - you must have a boost controlled reg - otherwise the boost pressure will lower the fuel pressure possibly to the point of pushing fuel back into the tank.

( usual disclaimers )