rx-7fc

i am going to be buying a rpm switch from summit racing and wanted to know how to hook it up and i am going to be using it for the vdi

NZConvertible

There’s a little bullet connector hanging off the trailing coil wiring. It’s to hook up a diagnostic tach. You can use that.

rx-7fc

what about geting it to work for the vdi

fastrotaries

what a bullet connector? You mean the ones that are strictly male, and look like a *****.

kleach18

I also would like more info on this. Anybody know of any write-ups or any links or anything????????

kleach

scathcart

What he is doing is using an MSD rpm switch to open the solenoid which allows air to flow into the VDI and open it. The MSD unit uses RPM pills, bought separately, and are available in 100 rpm increments. When the pill that is attached rpm is seen at the box, 12V is supllied to whatever you want turned on, such as the VDI solenoid.
He might have order the MSD unit with the dashpots instead of the pills, but it is unlikely.

My main issure with this is the snapping open of the VDI, instead of the stock way it slowly opens. Could cause some funky **** in the upper rpms. Could work great. I don't know, cause I drive a TII. Good diea though.

This is just a guess at his system idea, but I'll bet it is correct.

kleach18

One of my buddies set up the MSD rpm activated switch and it kicks ***! He set it to open the aux ports at 5k by taking a vacuum sorce(can't remember exactly which one) and somehow making the ACV open up the ports. At 5k it pushes you back into your seat. Not sure if I explained this right but thats what I'm pretty sure he said. Hey Sean let me know if you think that sounds right!! Or if you could help me understand what he did that would be great too!

kleach

scathcart

Close!

The aux ports open under pressure, be it from exhaust back pressure (s4), or air pump pressure (s5). Free flowing exhaust on an s4 kills the aux. port operation, and it is possible to plumb into the air pump like a S5.

Why he used the acv, I dunno. I would use a stock solenoid, and plumb the air pump line into the soleoind, and the aux port tubing onto the other nipple of the solenoid. Then wire the solenoid up to the MSD switch, with one solenoid terminal grounding, and one taking 12V from the MSD unit when it turns on.

Basically, the solenoid would be closed until 12V was applied to it, (via the MSD unit at whatever rpm) and then the open solenoid would allow the air pressure to flow to the auxilary ports, opening them.
This is not too hard.

Another idea is to use an electric corvette air pump. Plumbed staright to the aux ports, the msd switch would turn on the air pump at whatever set rpm. This is great, b/c it allows you to add free flowing exhaust, and lose the parasitic drag of the air pump. It is also a tad harder as finding wrecked corvettes at the wreckers to swipe a pump from may prove difficult.

Hope this helps.

christi

Can I ask a stupid question?

What is a(an) RPM switch?

kleach18

Thanks, that helps alot. Well his car is a S4 so when he put a free flowing exhaust on it he wired in the MSD activated switch. But he also took out his air pump as well. So what would he of used for the vacuum pressure to open up the ports?? He also has a switch inside his car so he can turn the MSD rpm switch off. Is there a benifit to this?? Sorry for so many question! But this really helps me understand how to do this so I know what I'm doing when I do it! Still don't quite understand it all that great. If you want you can email me or IM me =kleach18

kleach

kleach18

It a switch that activates something when the engine hits a certain RPM.


*EDIT* For example: I want my car's aux ports (5th and 6th ports) to open up when my car's tach says 5000 rpm's.

kleach

christi

Ok, I think I got that much figured out.. but what is it's main purpose?

scathcart

It is an aftermarket electrical unit made by autotronic (MSD), primarily used in racing. It takes a tach signal to measure rpm, and when the user pre-programmed RPM is met, the switch sends 12V to whatever accessory it is wired into.
An example of a very common use is in nitrous oxide injection systems. Since nitrous backfire(fuel/nitrous mixture explodes back through the intake manifold system, commonly blowing apart the intake runners) can occur with system activation below 3000 rpm, a switch is put into the system so that the system can not be activated below 3000 rpm. The MSD switch only provides 12V to the nitrous and fuel solenoids when the set RPM is met.
You could also use it to activate a light or buzzer, telling you when to shift, or a "you are near redline" buzzer. It simply allows you to send anything voltage when your set rpm is reached. There are ENDLESS possibilities.


In RX-7's, the VDI and auxilary ports are not open all the time. They open when a certain pressure is made, which occurs around 3950 for the auxilary ports and Lord-if-I-only-knew-since-I-don't-drive-an-NA for the VDI system. These systems increase power to the engine, and open at a higher rpm so bottom end torque can be preserved.
Some modifcations to RX-7's stop the functioning of pressure to these systems, and since they add horsepower, it is common to want to get them refunctioning. Using a pump and an msd switch to turn on when the pressure is allowed to be sent allows the system to stay working, and allows the user adjustability as to when thye power increase comes on.

Hope this helps.

scathcart

I dunno how he got it to work using vacuum. Again, I am not an NA owner anymore, and I would need to study some the FSM to figure that out.
Vacuum could be taken off of anyone of the vacuum fittings on the engine.
There is almost no point for the switch inside. That would simply allow him to turn off the auxilary port activation, making his car slower. Maybe he wanted to be able to activate it at higher rpm when driving (for more of a hp shock), but it would only make his car slower.
Really, a 4000 rpm pill into an MSD unit will make the most power and keep the stock-style powerband. There is no real point to the switch other than the "coolness" of showing someone the shock at a high rpm.

rx-7fc

the one i am thinking of buying is the summit one not a msd

rx-7fc

and i have a s4 86-88 and i put a 89+ intake manifold so i need the vdi to work

scathcart

Link? AFAIK, summit only sells the MSD rpm switches. Msd is a product brand, not a store.

Seeing as how you are swapping intakes, what are you gonna do for plumbing? Just use the sir pump? You need to get pressure from somewhere. The RPM switch is merely a way of controlling when that pressure reaches the solenoid, not providing the pressure itself.

christi

Yes, thank you. Understanding it more. Don't know too much about these things - hey, atleast I'm asking questions, gets me there!

jspecracer7

What a combination...rx-7 with girl...that WANTS to learn, not just drive

rx-7fc

i know msd a product brand not a store

rx-7fc

here is the summit one

christi

Yeah, and sometimes sucks cause I don't know what I'm doing or what I'm looking for... but I eventually (sometimes) find it.....

Halfbaked420

Ok guys, I just bought my first fc. 86 GXL. It has an open exhaust, and the kid that I bought it from removed the air pump. How exactly would I go about getting the 6 ports to operate correctly again? I've been reading about the MSD, but still need some info. Where can I find an MSD to buy and how exactly would I go about hooking up another air pump to the engine?

rx-7fc

bump

rx-7fc

bump