Cheap Rev limiter?

subarooster · Post by **subarooster** » Thu Feb 18, 2010 6:34 pm

Okayy, had a thought today. I've been looking around at rev limiters lately (ignition cut ones) and most units have come up at around $400 - $500. So it got me thinking. i wonder can i manufacture one for under $50? I had a look at the old "monsta" tacho i had that i never use and got an idea.

If I hook up the tacho and use the shift light as a trigger for a changeover relay, it might just work. I was thinking of running the negative side of the coil through the (always on) pins on the relay (30 and 87A) and then when triggered it will change over to the other pin (87). This will hav to be earthed so the spike has somewhere to go, otherwise it will feedback and cause pre ignition. So set the shift light to come on at say 6000rpm and as soon as it hits that the relay will changeover, then it will change back, then changeover ect... cutting the ignition briefly.

The way i see it, i think i can get it to cut at around 5 times a second to giv that lovely brap! brap! brap! sound. And because its cutting the ignition instead of the convention fuel cut, it mayy shoot small flames from the exhaust. The idea sounds a little riceyy and boy racer but i'm keen to giv it ago. Tomorrow arv i shall have a go and report back. Cheers, Tom

Post by **TOONGA** » Thu Feb 18, 2010 7:01 pm

because its cutting the ignition instead of the convention fuel cut, it may shoot small flames from the exhaust.

please video your motor imploding

otherwise it sounds like it might work

TOONGA

BaronVonChickenPants · Post by **BaronVonChickenPants** » Thu Feb 18, 2010 7:16 pm

The old GTHO phase III Falcon's had a "magical silver box" that worked in a similar way, I imagine they would have been dumping a lot more raw fuel than your tiny little suby engine, but then it's only until the revs drop below the ignition cut, which shouldn't take too long.

I think the concern should be the result of dumping unburnt fuel into your cat converter, they really don't appreciate that sort of thing.

Jordan.

subarooster · Post by **subarooster** » Thu Feb 18, 2010 7:31 pm

haha the test subject is a shagged ea82 so i'm not overly concerned on it imploding.. just curious, thats all.

and the cat converter is buggered as well so all good.

Gannon · Post by **Gannon** » Thu Feb 18, 2010 9:45 pm

You hoon.

I might have to come over to see this

D3V1L · Post by **D3V1L** » Thu Feb 18, 2010 10:09 pm

bee r rev limiter does this. ignition cut....and almighty backfire and flames occur,,,

davo

Outback bloke · Post by **Outback bloke** » Fri Feb 19, 2010 5:41 am

The EA82 has an inbuilt rev limiter. It is called engine design.

subarooster · Post by **subarooster** » Sat Feb 20, 2010 7:17 am

haha yeah, but i wanted to make it adjustable. Tried and tested yesterday and had pleasing results. but way to over the top for my liking... Sounded like a WRC car at full revs before take off but ripped it all out due to it being very gay. lol

Gannon · Post by **Gannon** » Sat Feb 20, 2010 7:49 am

Did you video it?

I wanted to see it

discopotato03 · Post by **discopotato03** » Sat Feb 20, 2010 8:50 am

Yeah , I also reckon EA82 heads were common with some diesel design and "revved" accordingly ...

I can almost hear "Fuju" thinking - "Hmm , breathing and revs . What a novel idea . Lets make a four valves per cylinder engine and try this 50 yr old breakthrough idea out .... "

.

Gannon · Post by **Gannon** » Sat Feb 20, 2010 9:00 am

So how high will an EA82 rev till it runs out of puff?

Surely if it can rev past 5k under load, it would have enough flow to rev much past that without any load.

Maybe ignition timing and valve bounce play their part in limiting its revving capability

thatsgoodsquishy · Post by **thatsgoodsquishy** » Sat Feb 20, 2010 7:22 pm

I spent a couple years regularly winding mine out to redline (6 or 6.5?, cant really remember) and i thought it pulled fairly well at high revs, hence why i kept doing it:D
Mine was a red blooded super version from 85 though, dont know if the unleaded version had any changes that reduced top end power? I guess they wound the timing back a bit at least:(

I have very fond memories of my L

Morcs · Post by **Morcs** » Sun Feb 21, 2010 9:15 am

Auto Meter MonsterTachs with a shift light has a built in type of rev limiter not so much limiter but makes it miss a little so it reminds you change/ back off.
Have one on a Holden HX V8 ute.
Think it grounds the coil.