lzamboni

iTrader: (8)

Hi all, my car had the engine blown "again". So I asked some people here in the forum to find if there was something strange with the timing or any of the specs of the tuning.
Some people said there were some areas that needed to be fixed but some others said that they could be ok as far as they were corrected in some other place in the tuning.
So basically I got nothing.
But after showing the tuning setup to a respectable RX7 tuner, he pointed out that there were some cells were the leading timing was after the trailing timing and that he never used that setup so he didnt know if it could cause any major problem.
So the question is, could that cause an engine to break the apex seals?
Here are the pictures of the timing used in the engine:




Basics of my setup is half bridge port, GT35R, Twin power, 850cc and 1600cc injectors, and all the supporting mods.
Thanks...
Leo

gusfd3s

if you check "display split" it will be much easier for us to see the actual split.

thewird

iTrader: (8)

Timing looks fine at first glance but we don't know the scaling used on that map and/or the afr being used.

thewird

WaachBack

iTrader: (21)

Im at work and cant see the pictures, but yes, negative split in boost can lead to a blown engine. The only time that it is acceptable to run negative split is at idle.

Nick_d_TII

iTrader: (6)

Neg. split seems like a bad idea to me, but if you know how to do it safely I guess it can be done. Not sure what kind of gains can be had and if its better to just stay with positive split, and safer.

Good reads. https://www.rx7club.com/single-turbo-faq-122/how-many-run-no-split-timing-325400/

https://www.rx7club.com/single-turbo-faq-122/advancing-timing-high-rpm-101226/

There is another good one, can't seem to find it 'Timing: a definitive thread'

thewird

iTrader: (8)

In case you guys haven't noticed, there is no negative split on that map.

thewird

arghx

iTrader: (3)

Split = Leading timing advance (degrees BTDC) - trailing timing advance (degrees BTDC), even if there are negative numbers in the map.

Negative split only exists in cells where the trailing timing number is quantitatively bigger than the leading, meaning that the trailing plugs are firing more degrees of crankshaft rotation before the trailing. A higher number means you are firing the plugs sooner. It's kind of annoying to do this calculation though, so that's why people have their EMS or a spreadsheet calculate it.

Now let's do a sample calculation.

So start with your P18 row. Assuming this is a stock MAP sensor and calibration, plus default scaling, that's probably a little over 15psi or so. By default P18 is 20000 PIM:



20000 PIM = atmospheric pressure + 1.0 kg/cm^2 boost = 14.22 psi boost. Plus let's add about 1 to 1.5psi because the stock map sensor scaling is off some. So we're at anywhere from 14 to 15.5 psi maybe.

Now let's jump to P18 (a little less than 16psi), N15 (6000rpm). First take our leading value:




The leading plug is firing 10 degrees before top dead center.



But the trailing plug is firing -1 degrees before top dead center. Any negative value actually indicates that the plug is firing after top dead center. 10 - (-1) = 11 degrees split at 6000rpm near full boost.

Correct. Whoever looked at that map may have assumed he was reading a split map. That's an honest mistake. I presume that whoever tuned this originally emailed you these maps?

So the question is, is that timing map safe? Well that all depends. We don't even know the scaling of the map, I just assumed it was default. We also don't know the AFR or the fuel quality (91? 93? methanol injection or mixing a little race gas in there?). Would I run that on my own personal vehicle with 91 octane, half bridge, and the 9:1 compression FD rotors? No, and that's mostly because I think there isn't enough safety built into it for aggressive porting. On straight pump fuel at 14+ psi I prefer 15 degrees of split for motors with heavier porting, if only for peace of mind.

The Rx-8's run negative split at idle. Their ignition system allows the leading plugs to fire independently, instead of the 2nd and 3rd gen Rx-7's wastesparked configuration. You should never see negative split under heavy load though.

WaachBack

iTrader: (21)

I didnt notice, pictures are blocked on my work computer. I was just saying.

lzamboni

iTrader: (8)

I am sorry I didnt have more information. And thank you very much for everybody's input.
Some more specs of the engine to see if it helps.
If I am not mistaken, the map here is for a run at a maximum of 18 PSI.
The car was running Water/meth at 50/50.
But it was setup in a way that when used on the low setting of the boost controller, it will run up to 12 PSI max without the Water/meth.
If run at the High setting, it will run up to 18 PSI and with the water/meth.
The apex seals went when I was doing only 11 PSI on the low setting so no water/meth was being injected. Of course always with 93 octane gas.
And yes it is better with the Split checked I am sorry I am new at using the FC-Edit.
Here is the picture:


The negative cells seem to be early on the timing? If I am seeing it correctly?
Also I am posting here the other parts of the tuning to help:








Hope this helps.
Thanks again.
Leo

thewird

iTrader: (8)

Split is very aggressive and in some cases not smooth transitions.

thewird

lzamboni

iTrader: (8)

Yes thats what I mostly heard. The problem is that I would like to know if the agressiveness of it could cause the apex seals to go like they did.
I know it is almost impossible to know for sure but if some other people have had bad experiences with slplits like this ones (or maybe good experiences), I would like to know
Thanks anyway for all the comments so far.
Leo

lzamboni

iTrader: (8)

So then here is the simplified question: Does ANYONE ever run negative split succesfully? Or it is always bad?

arghx

iTrader: (3)

The negative split is not causing a problem in those areas. Remember that Rx-8's run negative split from the factory under some low load conditions.

the split under boost... well it's not conservative. But could it have blown your motor? That's hard to say as just an internet diagnosis. There are so many other factors. The leading map doesn't look dangerous though. It seems like whoever tuned it put a leading map in there and either didn't know enough or didn't care enough to adjust the trailing ignition properly.

thewird

iTrader: (8)

There is no negative split on your map. Negative split can be used in vacuum for certain situations to improve smoothness. Cruising or idle is where its been played with. Negative split should never be used under boost.

Your asking if the map could have blown your engine. I don't think anyone could tell you this with certainty. I can say that there wasn't much time put into that timing map. The leading timing is pretty safe at high boost but at lower boost its aggressive I believe. I think the aggressive lower boost leading timing and the aggressive split might make for an unsafe timing map but there are other factors like fuel ratio that could make the overall map safe. In my opinion that is a bad timing map, if I were you I would get someone else to tune your car like Steve Kan.

thewird

lzamboni

iTrader: (8)

Thanks so much for your input guys. I have a lot of experience with piston engines but I am still learning about tuning the RX7 and sometimes it is pretty stressing to have to give it to somebody else to tune and hope is done right.
Well I guess I will have to tell they guys to tune it very safe and some other day I will get it to Steve Kan or some other known Rotary tuner.
Thanks again everyone for your help.
Hopefully I will have a happier story to tell soon with the new rebuilt engine.
Leo

enzo250

this engine is a bridgeport correct? and your running pump fuel?

If both are true your tuneup is way to aggressive for me. split is too aggressive and all over the place, lead timing is wrong for your type of engine and fuel, im going to guess that's it's too lean too...
Can this cause your broken apex seals. Absolutely. Stock mazda apex seals will always break when you rattle/detonate a motor. There's no second chances..

Seems like your tuner just used a basemap from the internet and made small changes to it..

I would highly recommend bringing your car to an experienced tuner.

arghx

iTrader: (3)

I really don't see any glaring problem with the leading map. It's running at most 11 or 12 degrees up to maybe 6000rpm, at any level of boost much over 10psi or so.

What really stuck out to me were the default injector transition settings in settings 5. Didn't the car stumble or have a lean spot getting into boost? How do we know the staging wasn't so bad that it detonated during transition? Those default settings are for 850cc secondaries!

enzo250

depending on fuel it can be...
It's pretty obvious there's a problem since he's breaking apex seals...
Not every engine runs the same timing values. It's not plug and play.
What you think works in one engine doesn't mean it's going to work in all engines..

lzamboni

iTrader: (8)

Ok now there is more interesting info. Thanks guys.
But you are taking into account the fact that the car runs Water/meth anytime it goes over 12 PSI right?
Even though I only did it 2 times for a very short burst and the rest of the time I only used the low setting for no more that 12 PSI and no Meth. And that is when the seals went at 11 PSI.
Also the only thing they could find that was kinda wrong was the spark plug wires that had too much resistance. Even though they were working fine before and not giving any signs of problems?

Thanks again.
Leo

arghx

iTrader: (3)

11 psi? that puts you probably at the P16 row with that scaling. and your split is 7-8 degrees there. 7-8 split is pretty aggressive for a half bridge even on 93... but that doesn't guarantee a blown motor.

Do you have a wideband in the car? Did you notice it having a lean spot or hesitation that could be due to injector staging?

BNA_ELLIS

You'll probably find your motor blew because of you injector seetings under settings 3 tab.
Looks like you would of run lean. Has the map been played with since it was tuned? if not it was only chance why it didn't pop when being tuned.


rgds
Brian

lzamboni

iTrader: (8)

Ok, to arghx, yes I have a wideband and even the Dual EGT gauges. I didnt see any strange readings or hesitation but I didnt drive the car much either. Also on the EGT, on normal cruising speed when the AFR was between 13.5 and 15, the EGT was around 1500 to 1600 F. And when accelerating some, the AFR went to around 11 and the EGT's could go down to 1300 or 1250. The only thing was that there was most of the time a difference of as much as 150 degrees between the 2 rotors. I know that some difference is normal due to the geometry of the manifolds but I dont know if that was too much?
Now for BNA ELLIS, the car has not been tuned after I picked it up. I drove it for less than 2 weeks and I was babying it just to make sure it was ok before I did anything crazy.
So yes, it was only chance that it didnt pop during the tuning session.
Now, the first time it DID pop during the tuning, but the installers said there was nothing wrong in the car and the builder said that it looked like a foreign object hit the apex seal because of the marks that it left inside.
Now I dont know anymore, it could have been just the tuning again
Well thanks for the help so far.
Leo

lzamboni

iTrader: (8)

Ok, to arghx, yes I have a wideband and even the Dual EGT gauges. I didnt see any strange readings or hesitation but I didnt drive the car much either. Also on the EGT, on normal cruising speed when the AFR was between 13.5 and 15, the EGT was around 1500 to 1600 F. And when accelerating some, the AFR went to around 11 and the EGT's could go down to 1300 or 1250. The only thing was that there was most of the time a difference of as much as 150 degrees between the 2 rotors. I know that some difference is normal due to the geometry of the manifolds but I dont know if that was too much?
Now for BNA ELLIS, the car has not been tuned after I picked it up. I drove it for less than 2 weeks and I was babying it just to make sure it was ok before I did anything crazy.
So yes, it was only chance that it didnt pop during the tuning session.
Now, the first time it DID pop during the tuning, but the installers said there was nothing wrong in the car and the builder said that it looked like a foreign object hit the apex seal because of the marks that it left inside.
Now I dont know anymore, it could have been just the tuning again
Well thanks for the help so far.
Leo

lzamboni

iTrader: (8)

crazy internet It keeps dropping and doing some strange stuff. Sorry for the double post.

thewird

iTrader: (8)

The settings are fine. From my understanding, the car was tuned. There is nothing wrong with those settings.

Honestly, I really do think tuning is the cause of your engine problem but that is only my opinion.

thewird