Why does everyone say a Zener diode is better for tricking the MAP?

[turbovanman]

Hey guys, I am running a Dawes cut-out raiser and have no problems with how it works. I see posts all the time on using a Zener diode. You all say it works better? Why? They both trick the MAP so why is the diode better? Thanks!

I'm not sure what the dawes thing is, but the only other things I've seen for tricking the map involve a grainger valve or a bleed. Both of which need to be adjusted until they're in just the right spot. That's alot of work and grainger valves tend to be very temperature sensitive so they don't stay exactly where you set them so it could drift a PSi or two. And bleeds are going to screw up the entire range, even under vacuum the bleed will be letting out some of the vacuum so the map won't see full vacuum.
As for the diode it is simply a set voltage, it won't let the map go above 4.7v, so the computer never sees a boost level high enough to shut down the engine. It doesn't matter if it's cold out, hot out, and it doesn't mess with the map sensors readings, it still sees the correct vacuum and boost right up until you pass 13.5psi or so..

[turbovanman]

The Dawes is a bleed but doesn't leak until you hit the specified pressure.
Thanks for the info!!!

[GLHNSLHT2]

The dawes device is just a grainger with a T instead of being setup like a boost controller. I tried the zener and unless you can get an adjustable one I'd say stick with the grainger. If you run a stock puter and get the right zener you're not letting the puter see over about 11psi. Run an MP puter with the right zener you're probably closer to the cutout that the puter sees but it's still just close. I like the grainger setup much better. You can get right up to where the computer cuts out. I'm able to run more boost with it. I've never had to play with it after it's set unless I turn the boost up more by quite a bit.

[lametec]

Quote:

Originally posted by UnaClocker As for the diode..... It doesn't matter if it's cold out, hot out

Actually, Zeners are affected by temperature (like any other non-compensated electronic device). In addition to that, there's prouction tolerances and the fact that there is no standard zener that's exactly the voltage we need.

[turbovanman]

So we have a tie so far!!!! :big grin:

[87Shadow]

Zeners don't need to be dailed in, as the computer still controlls this aspect. Yes they are affected by temperature, however a simple coating of hotwax or hot glue solves that problem. There are tolerances when you buy them, it'll be like 5-10%. It will depend on the manufacturer, and electrical component you are purchasing. Usually it is stated by the manufacturers on the products data sheet.

[turbovanman]

So far, it looks like it doesn't matter which way you do it?

[Mopar_Nutz]

I've always thought that a bleed style was superior to a zener because you can adjust it to get the max possible fuel before hitting cutout, where with a zener you can't. It seems that zeners will always cheat you out of a little fuel unless you get an adjustable one.
bleed style;
+ you can adjust to get max fuel before cutout.
+ And if something DOES go wrong, you'll still hit cutout instead of infinite boost
- they cost more

zeners;
+ cheap
+ when it's in, it's in. No worries about cutout
- cheat you out of a little fuel
- no safety of cutout

adjustable zener
+ no cutout ever
+ you can adjust to get max fuel before cutout
- no safety of cutout
the price is somewhere beteen the zener and bleed.

Seems to me that it's all a matter of preference. Also I may have missed some points, but this is all to the best of my limited knowledge

[Casper]

Quote:

Originally posted by GLHNSLHT2 I like the grainger setup much better. You can get right up to where the computer cuts out. I'm able to run more boost with it. I've never had to play with it after it's set unless I turn the boost up more by quite a bit.

First let me state, that I used a Dawes cutout raiser/g-valve to let me run up to 22psi in my Spirit. I have never used a zener.

With that being said, I believe a properly tested zener is superior. Going WAY back in time to before we lost Gus, there was a lengthy discussion on the FMML about how a bleed or g-valve on the MAP line actually causes the computer to see less pressure, and thus provide less fuel.

IIRC Gus, who devised the g-valve method, admitted that this was the case and said that a RRG FPR was needed to mask this phenomenon.

Think about what a g-valve is....a spring loaded pressure device. In order to run 22psi I had to open the valve more than I did to run 16psi. That means the valve was opening and bleeding off pressure MUCH earlier in the boost curve. The less pressure the MAP sees, the less fuel the computer provides. I, like Gus, used a RRG FPR to mask this phenomenon.

With a zener, the MAP signal will always be accurate up to the zener's voltage. Beyond that, the computer will be providing enough fuel for whatever amount of boost corresponds to the zener's voltage. Sure, higher boost levels will also require a RRG FPR, but it will only be working to provide fuel above cut-out, or the zener's voltage level. Whereas, with the g-valve the RRG FPR has to provide fuel to make up for what's being lost due to the bleed in the MAP line AND provide fueling above the cut-out point.

Long story short....it is a less efficient method.

A more efficient method is having the cut-out removed from your calibration.

The most efficient method is to run a calibration with a 3bar MAP.

[87Shadow]

It doesn't really matter which way you do it, its upto you.
You can even just recal your computer...same results, different paths.

[spoolboy]

This is what I do:

http://www.fwdmopar.com/sites/dennis/howto.html

Adjustable AND more repeatable than the G-valve style.

I have had better luck with a check valved map bleed than with the G-valve type.

[Casper]

Quote:

Originally posted by spoolboy This is what I do: http://www.fwdmopar.com/sites/dennis/howto.html Adjustable AND more repeatable than the G-valve style. I have had better luck with a check valved map bleed than with the G-valve type.

Dennis, that page is now quoted/linked by the PT (aftermarket) turbo king, Bob Stockum. He likes that method alot!

[russ jerome]

Quote:

Originally posted by turbovanman I see posts all the time on using a Zener diode. You all say it works better?

People who say they work "better" have never run both under daily high boost drives. You could fill a page on the downsides of a zener diode. Wont bore you with all the details, keep your bleed/grainger on map line with smallest restrictor that will not set CEL.

[glhsken]

Quote:

Originally posted by russ jerome People who say they work "better" have never run both under daily high boost drives. You could fill a page on the downsides of a zener diode. Wont bore you with all the details, keep your bleed/grainger on map line with smallest restrictor that will not set CEL.

Ummm not all of them. I've used both, I preferred the zener..