No AI.

And yes the humid air is what allows it, If the weather changes and it gets cold and dry, I can't run the timming like that.

 

Out of curiosity what seals and plugs are you running? I've tried running similar aggressive timing at 18-19 psi with no AI on a motor I built before with RA super seals and 9/10 spark plugs. It ran fine and registered zero knock (not that its an accurate measure but in past experience knock is usually registered to some degree with working sensors) but when I tried a long sprint test that went up to 5th gear, after pulling over, the idle wasn't as smooth as it was before. After pulling the motor out, realized nothing was damaged but the seals had warped barely towards the triangle side, it was almost not noticeable. Then again this was colder weather and probably no humidity at the time. Since it was a motor I built for a friend, he didn't mind if I broke it since I could just rebuild it again so I used it as a test.

thewird

 

More than likely preignition since it can't be heard (although can be seen on a cylinder pressure trace).. =(

 

What fuel is used for this 18/19 psi?

 

Ra super seals. 9's all the way around. I built the engine.

93 octane gas I premix a 1/2 ounce per gallon. Nothing else

This engine is on its last leg, compression is weak, one of the reasons I started playing with the negitive split, tryin to get the car to hold Idle. I have done a tons of 5th gear pulls( i tuned this car in 4th and 5th gear). This engine has seen 297kph. Its has been beat'n on hard. The high load pulls never seemed to bother this engine.

Getting back to NEG split... I think what I did was wayyyy to aggressive on the trailing side, this is where I am mainly concerned, i want to be able to drive around smoothly in vacum at high rpm and not torch the motor. It seems every time I start driving in vacum maintaing 6,000 to 8,000 rpm, holding constant speed, it kills compression and cooks spark plugs. Thewired, this is what seem to kill my motors. Not boost, but high rpm vacum in 1st and 2nd gear, I try to tune these sections of the map and I cook engines.

So, can we step outa boost and talk about the vacum aspects of it.

 

I think Barry was mentioned this one day when I was talking on the phone with him about his cylinder pressure logging. He was playing with extreme advanced timing and this is what he thought( the advancement causes slight preignition but the engine will still run.

 

Just use the stock map for vacuum and you won't cook your motor in vacuum. I would only ever use negative split in the idle area or very little in the high vacuum cruise. Think about it, by adding 10 degrees of negative split or more, you are adding 10 degrees or more of timing. This is going to make your EGT's too hot and warp your seals or flatten your springs. The same way people **** up their motors when they're CAS isn't locked correctly even if they aren't beating on it at all. You could decrease your leading timing to have the high trailing split but then you'd be losing torque so that is pointless.

If you want to do correct testing for negative split, you NEED accurate EGT probes pre-turbo and be sitting on a dyno making your changes to achieve maximum bhp without going overboard on the exhaust temps. EGT's are everything when it comes to timing, without them you are just guessing. Which fyi is fine if your using conventional method of tuning as there is enough information out there to make a safe timing map.

*Insert arghx provided Mazda testing graphs on apex seal temperature to prove point* LOL

FYI, the motor I was talking about continued to pull hard even after the it started idling funny. We actually kept testing/racing it against my car since it was faster with the more aggressive tune AND warped seals. Probably put about 800 km on it since the "incident" and it kept running the same but we knew it needed to be rebuilt. Maybe this is the same exact issue your having with reduced compression as you have the same seals that will warp and not break when the timing is too hot.

thewird

 

I hear you about the stock map, But the sock map is not smooth fuel wise, I wanted to try this out, i cooked the engine one other time in vacum with stockish map, stock seals, the fuel was way off but in doing that it didnt cook again... until I overly advanced trailing timing a month ago

one way to learn is to try

I also drove the car for more than a week with the rear rotors plugs firing backwards, under boost with load. Audible det, like a hammer hitting the motor, was heard 15-20 times that was done at 10,000miles, a bout a year ago, when I ran the motor under boost with the plug backwards and the engine didn't let go, I got aggressive as hell with the tuning and boost, I wanted to see how far I could push the 5501300 35r setup. I want it to run head to head with a stockish 1000cc bike from a roll. From 60-170 I am like 3 cars back, Whats really fun is when they give me a 3 car lead, by 170-180 they are right at my door, fun fun stuff o and I crush stocks 600's, I love the looks you get from those guys...

I have daul egts 2 inches off the exhaust ports. Gauges go to 1600 so any thing above that i can't see. The neg split was causing higer egts, cooking seals and warping stuff. I don't dis agree with any of that. I just wanted to try it, you even said "We actually kept testing/racing it against my car since it was faster with the more aggressive tune AND warped seals." If I can get 25,000 miles out of the engine with the abuse the engine took, I am happy as hell, not only that. I can hear the engine in a way I never could before. When the engine is straining from overly advanced timing, I can hear it strain, so I now know when to back off...

At low rpm where the egts stay low i am going to use neg split cause the car drives smoother, but above 2-3k its going to go back to how it was and have had it for the last two years.

Saturday night, on my way to work, my vacum gauge developed a slight tick to it with a little little miss. I haven't been boosting hard, just high rpm vacum, maitaing high engine speeds for a min or more. I now have 60psi rear 45-50psi front, They were in the 80's 3 months ago. my front rotor always runs hotter. The extreme advance on the trailing, sped the death of the engine, starting to yank it out this morning.

YAY now I get to build another engine, ordering a core and a rebuild kit today. I will pull this one out of the car and apart.

 

O and it was a side seal wear that finally killed the engine. Both front and rear side plates had extreme side seal wear, and 2/3 of one side seal was missing

here are some pic of the engine torn apart- https://www.rx7club.com/general-rota...miles-1007216/

 

just to point out, advanced timing decreases egt, as long as you do not massively overdo it so it starts to misfire