Ever had your wastegate line blow off? Wastegate fail? Ever just set something up wrong and blew an engine? Me either. But that sure as heck doesn't mean I am gonna sit around and wait for it to happen!

I have designed an overboost protector around a Hobbs pressure switch. What this system does is turns off the power to your coil when desired "overboost" setting is reached. What you do is set the Hobbs switch slightly higher than your boost setting on your wastegate, EBC, MBC whatever. Once that pressure is reached due to a boost control failure, bam, coil is turned off. And as we all know, an engine needs Air, Fuel, Spark and Compression to run. IF you take away spark, the engine CANNOT create boost or run any longer. The beauty is, once you go back below that set "overboost" setting on the Hobbs swich, bam, power is back on. Now your car drives like normal again so you can drive it home and find out what went wrong. It is so simple, I can't believe I haven't seen it before. So anyways, on to how I went about doing this.

Items needed:-One Hobbs pressure switch. Sold at most forced induction related sites, as they are very popular with many many setups/kits.-About 5 ft of 16g wire depending on how exactly you route this setup-About 1ft of vacuum hose-Zip ties of course-A couple crimp-on connectors for the Hobbs tabs and relay if you choose-A SPDT relay(5 pin automotive relay. Should have pins 85, 86, 87, 87a, and 30)-*S14 owners only*-you will prolly need more 16 gauge wire to run due to the location of your positive coil wire.Items recommended:-A soldering iron and rosin core solder( I recommend soldering connections as I always do.)-A multimeter. I used this so I could set my Hobbs switch up with my air compressor. Use the Ohm setting and alligator clip the probes onto each connector of the Hobbs switch. Then just adjust the screw so you get resistance only past desired boost level.-An accurate boost gauge(I used my AVC-R)

Now for install instructions: (DISCONNECT BATTERY BEFORE YOU DO ANYTHING!)

Number one: Clip your stock positive coil wire(black with red stripe on both S13 and S14. S14 guys, you will have to look near the distributor cap to find it/and prolly have to run a little more wire to wherever you choose to mount the relay) and strip both ends. Run the ECU side of the coil wire to pin 30. Run the coil side of the positive ignition wire to pin 87a. Solder on that 16 gauge piece of wire to pin 85 or 86(doesn't matter as the relay coil is not polarity sensitive. Make a small "jumper" out of a piece of 16 gauge wire and run it from pin 30 to pin 86 or 87(doesn't matter as the relay coil is not polarity sensitive).




Number two: Run the 16 gauge wire from pin 85 or 86(whichever you chose) to wherever you plan on mounting the Hobbs pressure switch. I recommend putting it near the intake manifold to get an accurate pressure reading on what is entering your engine. You'll need to set the Hobbs switch approx 2psi higher if you use a hotpipe boost source. But I wouldn't recommend that as the Hobbs switch box clearly says to avoid high heat. I mounted mine here:



Number three: Find a good ground point. Run some 16 gauge wire to that point and ground it using a crimp-on connector. I used whatever that ground is on front of the passenger side wheel well. Sand the contact point well.



Number four: Tap into a good boost source. FPR line is probably your best bet.



Number five: Crimp the connectors onto your ignition tap wire and the grounded wire and connect them to your Hobbs switch.

Number six: Remove that rubber plug on top of the Hobbs switch and tune it. I removed the vacuum line from the intake manifold and used an air compressor. But in order to do this, you must have a multimeter and use the method I described above. If not, you will more than likely need to do trial and error.

I tested this with the limit at about 7.5psi and it definatly works. Feels just like your engine had no spark. Go figure!haha But as soon as boost drops below that, the engine comes right back on and runs normal. So, unlike common "pop off valves", you will NOT have an abnormally rich condition on the way home to replace your wastegate line. And this is ADJUSTABLE!!!

Before you boost away, try jumping the Hobbs switch terminals to see if the car shuts off and that you did everything properly. Just touch each end of a small piece of wire to each terminal on the Hobbs switch while the car is running to make sure it shuts off. If not, then this is useless to you still and you made a mistake somewhere.

I set mine at about 15psi and I run 12psi most of the time. So, if a wastegate line ever blows, I'm ready!

Thanks Lance!

Modified by nissanfanatic at 10:50 PM 12/9/2005

Modified by nissanfanatic at 5:11 PM 12/10/2005
Modified by nissanfanatic at 5:20 PM 12/10/2005

Very good idea! Thanks for sharing.

thats an awesome idea. but however i have a audio and visual warning feature on my ebc with boost cut function so its not needed for me. however if didn't, i would've set it up. sounds very effective. but up north here the temp varies up to 100 degrees between summer and winter. i know its adjustablel but i don't always have access to a air compressor nor do i have a multimeter. but anyways you set yours at 15 psi and runs 12 psi. well i've set mine at 14.5 psi and runs 13.8-14.2 psi depening on temperature and gear. so it might not be the best bet for me since i'm running soo close to the limit anyways and it doesn't seem as precise to tune as it would be with a ebc.

Not many people have reflexes fast enough to be able to see/hear a warning signal and get off the gas in time to stop a .63ar or any common turbocharger for the KA from going in excess of 20psi...

Using a safe 2psi over max boost allows for change in temperature.

AVC-Rs have features that can allow you to have steady boost across all gears. Things such as F/B speed and start duty. I do a steady .85-.87kg/cm2 across all gears.

Hobbs switches go well past 15psi in settings. That is just what I set it to.

Read the poor guy's thread from a few days ago where he overboosted from 10psi to 17psi. I designed this system for guys like him so they don't have to worry about overboosting.

Nice work Cory.

This gets made into an article as soon as I get the new software in.

so its kinda like a "spark cut" instead of "fuel cut" with say the governor but instead based on boost..........ingeneous.

Edited my first post.
Modified by nissanfanatic at 10:51 PM 12/9/2005

nissanfanatic wrote:
Read the poor guy's thread from a few days ago where he overboosted from 10psi to 17psi. I designed this system for guys like him so they don't have to worry about overboosting.

hey, are you talking about me? if so, thanks for all this info! im gonna try to make one of these to save my next motor!

Yes I did have you in mind. But there have been plenty of others.

No offense intended. I actually wish I had came up with it sooner to save more engines.

thanks to this, u prolly will save my 4th engine

nice idea.

how could this be integrated into the diy coil power mod where power comes directly from the battery through a relay. i believe that was posted some time ago.

Great write up! I plan on doing this when I replace my turbo.

eddiec wrote:nice idea.

how could this be integrated into the diy coil power mod where power comes directly from the battery through a relay. i believe that was posted some time ago.

You'd interrupt the signal from the ECU that triggers the relay feeding the coil. Relay gets no trigger = no coil spark.

Yes, as stated above. This write up was acutally written up for the DIY better spark that I posted back in the day. But it can be easily adapted to any stock setup as well.

it would probably also be alot easier to do this mod if u did his ignition mod as u already had to add some extra wire to do the ignition mod........maybe u should also link the ignition mod writeup somewhere on the original post just so that people have more pics to go off? it might help some.

It is in the sticky at the top of the page as well as on http://www.ka-t.org/tech

VERY nice work Cory!! Excellent idea, and a very nice writeup to boot. We're all always looking for cheap solutions to common problems, and this is one of those things that I could see a lot of people doing just so they sleep better at night. Might I suggest though that you put a quick blurb up top of the article, explaining exactly what it is that the setup DOES (besides just "protects overboosting."). It'd make the article easier to understand instead of having to read the whole thing to see what's going on. Something like "this system will cut ignition in the event that..." etc etc.

Nice work man, I'll add it to the stickey list

EDIT: btw Cory, do you want the link in the stickied thread to read "Cory's DIY..." or "nissanfanatic's DIY..."?

Alright I'll put that part in!

You can just use nissanfanatic as most people would be like "who the heck is Cory???" lol

Excellent write up man.

Fiz, this is important, We need this sticky!

Chezedik wrote:Fiz, this is important, We need this sticky!

Yup, added to the stickey list yesterday

It is the ignition mod, the only difference is that the signal for the relay's coil isn't just run to transistor, but to the switch first. So the switch can kill the signal to the coil to stop fire. All that is required is that 87 be wired directly to the battery, 30 goes to ground. 86 runs across the switch from the ECU, and 87a goes to coil. Then it functions as both mods at the same time. You will also have to ground the switch.

I wanted to add that it is so simple it is genius, good work fanatic!
Modified by Chezedik at 12:16 PM 12/12/2005

No... 30 always goes to "common" or constant 12v.

and in order for this to work, the positive coil wire must run to 87a. As the secondary route of electricity(where electricity goes when the relay coil is activated) is through 87.

The pressure switch completes the circuit which activates the internal coil of the relay.

Yeah, I'm bringing it back from the dead. I recently cracked my ring-lands in pistons 1-3 do to overboosting (failed W\G). Once my motor is rebuilt and back in my car i want to install this DIY over-boost protector. But there are a few things i don't understand about his write up1.What type of hobb's switch do i need NO or NC?2. what size amp range should i use for my relay(20,30 or 40)?3.how he states to hook it up doesn't make sense to me (don't you need a 12v power source to the relay)

nissanfanatic wrote:Now for install instructions: (DISCONNECT BATTERY BEFORE YOU DO ANYTHING!)

Number one: Clip your stock positive coil wire(black with red stripe on both S13 and S14. S14 guys, you will have to look near the distributor cap to find it/and prolly have to run a little more wire to wherever you choose to mount the relay) and strip both ends. Run the ECU side of the coil wire to pin 30. Run the coil side of the positive ignition wire to pin 87a. Solder on that 16 gauge piece of wire to pin 85 or 86(doesn't matter as the relay coil is not polarity sensitive. Make a small "jumper" out of a piece of 16 gauge wire and run it from pin 30 to pin 86 or 87(doesn't matter as the relay coil is not polarity sensitive).

Number two: Run the 16 gauge wire from pin 85 or 86(whichever you chose) to wherever you plan on mounting the Hobbs pressure switch.

Here is a diagram of the relay. He says to jump out pin 30 to pin 86 or 87. that don't make any sense to me or am i reading it wrong



any help on wiring the relay up would be appreciated, thanx

Hey guys, sorry to bring back this post. I know it's a stickie already, and I just needed clarification on something.

I want to build one of these, but have only found pressure switches for NOS, but they also look just like the one Nissanfanatic used on his install. Will those work or is there one specific for just air?

Jegs has some and there are some on ebay, and they all say for NOS. Also, I'm boosting only 7psi because I'm only using FMU plus walbro255 (which is exactly why I need overboost protection), so I need one that will have the ability kick in around 8 or 9 psi.

If anyone knows the where to get the one Cory used I'd appreciate it. Thanks

nice idea cory!!!!!!!!

No reason to bump a thread that started 3 years ago

this thing really is back from the dead, but if it wasnt i wouldnt have ever seen it. im glad i did cause im going to do it as soon as i turbo!!

If anyone needs a pressure switch, ggogle Hobbs Switch

If found it at http://www.alliedelec.com

It comes preset from factory at 10PSI, perfect for those boosting 7 or 8 PSI, but either way it has an adjusting screw at the top to change the PSI level at which you want it to activate. Pretty cool.

NOTE: it has to be a "Normally Closed" switch, so that it normally transmits the current, and when the boost gets too high it "opens" like a breaker.

With his I'll feel a little more comfortable revving my 2
Modified by oz240red at 5:59 PM 12/11/2008