hit the dyno today made good number but with bad results. 391.8hp with 295ft/pds @ 15 psi on 91 pump gas. I had inigtion break up @ 7500 and made the rear iron break. Tunning was spot on low 11 afr need to stop reving so high till I figure out was it happening.

 

I was just going to ask if you knew what caused the ignition breakup.

I wouldn't think just ignition breakup would cause an iron to break... I'd think you'd have to spark with REALLY bad timing for that to happen.

Breakup would just be misses, which might cause some extra unburnt fuel...

Did you have a revlimiter set up?

Ken

 

ouch, I would suspect timing, but you are on the sketchy edge for pump already imo ...

 

the same thing happen to BDC on the other forum the miss causes extreme rich and that can also cause pre ignition. Under that stress so little can cause it. I had not tune to that level yet. timing was around 16 deg but you could see it on the dyno sheet were the it started to break up. I think the plug were firing but they were not able to light the combustion chamber. I might need to upgrade some stuff. I was running complete stock ignition. Very old plug wires and trailing plug in all holes. Fix it and try again!!! This time I will not rev so high the first pull I will stop a 7000rpm

 

what rear iron are you using? I know the later ones from the REW and even the S5 IIRC had more reinforcement around some of the bolts to make it more robust. That is some pretty nice power tho!

 

yea i would def upgrade to a s5 rear iron, more cast around dowel land.

 

I was using S4 iron. I use whatever I can get my hands on. I am on a very tight budget so I have no money to spend on good parts.

 

Did you figure out what caused the missing?

 

not sure I don't know if the miss cause the break or the break caused the miss. It is hard to tell. I have video and dyno sheet.


http://www.markfreeze.com/video/geoff/rx7.wmv

 

I have found using stock plugs suffering from pre-ignition @ 1.1-13bar in the higher gears after a good power run. Sounded like strong popping noise and big lose in power. I tried many things like adding more fuel and pulling timing back but there was no overcoming the problem.
Once i changed the plugs to NGK competition with prong tip the problem was gone. I was then able to push the boost up to 1.6bar with no issue of pre ignition, Some times i now can get spark miss with the new plugs but this was a lot different to pre-ignition that was happening before with the stock plugs.
With spark miss/blow out, the engine just dies for a split second like someone has turned of ignition

I do all tuning on the road and i am very quick to back of the throttle if it doesn’t feel rite. Running the stock plugs at 1.3bar just didn’t feel rite.

I suspect stock plugs get to hot and can not relieve the heat fast enough which causes the pre-ignition, The NGK competition seem to not suffer from this and allows you to run even more boost.

Sorry im not sure what part number they are, im away from the garage at the moment so i can’t check. I was advised to use these plugs from a local tuner that has had lots of experience with tuning high boost street 13b’s. but I do know they are very cheap. They only cost me $11nz each which is aprox $7us.

 

I also run s4 motor and have not crack an engine yet on 98 pump gas with 1.6bar.

 

pretty intersesting thanx for the heads up

 

that sound like right thing to do. I would like to find those plug part number

 

bobybeach maybe talking about ngk part number R6725_(_ means, what ever heat range)(105,11,115 cold plugs,, stock is a 7 heat range on leading and a 9 on trailing).They have a platinum tip and small platinum ground like a normal none rotary plugs ground but smaller !I think the miss is more of a plug gap ordeal i used to have missing problem when installing procharger's on lt-1 transam's/mustangs extra if i went much over 10 pounds with out closing the gap to .035, they would miss right around around 4500 to 5500,, close the gap and the miss was gone.only problem is because of the design u cant close the gap on bur9eq and bur7eq plugs, witch has a gap of around .050!Here is a place that has some more info and pics,, hum rx8 plugs in a 7 may have to use to leading plugs on the trailing side (see link). http://www.silverbulletrx7.com/plugs/

 

While we're on the subject, are s5 irons compatible with a stock s4 motor?

 

I’ve just checked the plugs, the ones i use are B10EGV, Twister7 is rite you can close the gap up also. I taped the gap smaller while tuning to help eliminate any miss spark, but i was told that closing the gap can lead to premature erosion of the electrodes so its a bid of a trade of.

The one thing that i want to stress is that an ignition miss is totally different to the dangerous pre-ignition that stock plugs seemed to suffer from at much lower boost levels to what im now running with the B10EGV plugs.

 

Also the B10EGV needs a thin wall or narrow sparkplug socket or modified socket to work with the 13b rotor housings. This is because it sits flush with the surface of the rotor housing. I had to bevel the tip of my sparkplug socket to make it work.

 

B9EGV are a very popular plug in Australia for all Rotaries.

I think the big HP turbo guys use B10EGV, there is also an ever colder plug available. Its like B105EGV or something.

I'm pretty sure these plugs are a racing 2 stroke motorbike plug, but they work well in our application

 

great info thank guy. I am pretty sure that was my problem my plug look very cooked. I will post pictures when I get a chance.