Pete's RX-8 Time Attack project

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Re: Pete's RX-8 Time Attack project

Post by PeteH »

ECU? I'm likely to go with Adaptronic modular. It's the best at running everything else on the 8, and I've confirmed it can run a triple.

Nice idea about the moveable lambda, although it makes the job three times as long!
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Re: Pete's RX-8 Time Attack project

Post by 13Black »

Three times as long? The 2019 season start is way past my life expectancy anyway so at least make it as crazy a build thread as possible for my enjoyment :D

This is one of my favourite threads though, I hope you have plenty of things going on to keep us updated, whatever it is.
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Re: Pete's RX-8 Time Attack project

Post by ChrisHolmes »

Does the fact that the combustion chamber is moving in the rotary change the maths regarding the flame speed as the front edge of the chamber, and the mixture it's holding, is moving away from the spark origin. Hmm! Of course the rear is moving toward the spark origin so do they cancel out?
Could moving the spark plug or plugs improve things?
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Re: Pete's RX-8 Time Attack project

Post by 13Black »

I would imagine with my tiny mind that because the rotor is shifting the fuel/air mixture around as one 'unit' as such, that it wouldn't make much difference as the space that the flame is expanding into is created by the leading edge of the rotor, and the tail end is pushing the mixture toward it, again as a whole unit, so the flame I expect would still move at the same speed relative to the rotor, but in absolute terms a little quicker.

Like a sound wave within a moving train or something, is what I'm picturing. I like trains and pictures and crayons.
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ChrisHolmes (Thu Jan 04, 2018 8:59 pm)
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Re: Pete's RX-8 Time Attack project

Post by PeteH »

I've often wondered myself, and am not 100% sure. I am sure that the turbulence in the rotary chamber must be far greater than that in a piston engine, because of the relative shear between the rotor and the housing, and because of the very peculiar shape change. Turbulence is good for flame speed, so that helps counteract the very long and wide and shallow combustion chamber. I think, since a flame is actually a visual indication of a chemical oxidation process, that the flame front is governed by molecule-to-molecule interaction, and if all the molecules are moving in unison (i.e. ignoring turbulence for the moment) then the mixture has no clue that it is moving, and the flame front progresses at the same speed regardless of the rotor rotation. (Or, just use Nick's train analogy).

There are some other effects that I wonder about. The mixture is being flung at high speed in an arc of roughly 180degrees. This sounds like a pretty good centrifuge to me. So I wonder if there is sufficient time for the petrol vapour in the mixture to migrate towards the housing walls. It's possible that the burn at the spark plugs / housing is more rich than the burn at the rotor surface. I don't know if this actually happens, or even if it matters.... :-k I suspect it's one reason why rotaries flood so much more easily than piston engines (in piston engines the rich mixture presumable gathers near the piston, and away from the spark plug).

Another one is the spark plug firing duration. The spark plug probably fires for a duration of between 2ms and 3ms, which isn't very long. But at 10,00rpm there is only about 6ms between each pass of the apex seal. In a piston engine it doesn't really matter because the spark plug is always acting on the same part of the mixture, and you (in theory) have the whole of the compression and firing stroke available. But in a rotary, if you fire at the start of the compression stroke then you actually fire in the preceding chamber! And because we have two spark plugs, which are closer to the apex seals at TDC, the time available to fire is even more constrained. Suddenly the spark plug firing duration becomes more critical.... If the firing of the trailing plug is too retarded, and continues for too long, then we will definitely attempt to fire the next chamber :shock: We tend to think of ignition timing as happening at a point in time, but it is actually a duration, and the critical timing of the rotary makes this a very interesting problem.
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Re: Pete's RX-8 Time Attack project

Post by 13Black »

Do you think there would be enough compression at the trailing plug's overlap with the trailing apex seal to actually cause a combustion event?

Also remember that the ignition dwell at 10,000rpm is just over 3ms, and if I remember correctly, reintroducing charge to the coil should stop the spark at that point shouldn't it? Or did I dream that.

Maybe should stick to trains and crayons.
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Re: Pete's RX-8 Time Attack project

Post by Lemon »

might this be of use?

Thanks, Stu

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Re: Pete's RX-8 Time Attack project

Post by PeteH »

Thanks Stu. Nice to see a You Tube video from a proper expert!

Nick. No I don't think it would actually be possible to properly fire the partially compressed mixture, but it sounds like a bad idea, and you may create a small area of partial combustion that rapidly develops as the mixture is further compressed. If that happened then it will definitely detonate at some point.

Yes, the coil charge during dwell stops the spark, but only after the spark has been going for it's 2 to 3ms duration. The spark duration is built into the coil, and not adjustable (as far as I'm aware). Interrupting the spark by initiating a new charge cycle will overload the coil, heating it, and killing it, so you can't really use that to manage any "spark overlap". Your only option is to adjust your timing to safe limits, or fit faster coils. I'm happy to be corrected here. It sounds like a subject for Phil....

I did find some US drag coils that charge in about 0.3ms! But they weigh about 1kg each, so I don't fancy fitting six of those.....
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13Black (Thu Jan 04, 2018 11:15 pm)
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Re: Pete's RX-8 Time Attack project

Post by Phil Bate »

Sorry I'm a little confused as to why there is any, er, confusion :-k I've probably missed something, but it should all be the same for a triple-ganger.

Yes you should ensure that the coil is depleting before the next charge event occurs for maximum efficiency - if it's still discharging, as soon as you apply current to the primary again the spark is interrupted as charging resumes. However this is all generally covered when you adhere to the maximum duty cycle supplied by the manufacturer and you'd have to be going some to be riding it. With about 4.2msec of charging even Rotary Revs' monster 585R coils will discharge in 2.6msec. At the upper RPM limits when the dwell is getting down to the 3msec mark the discharge will be even shorter, keeping the whole cycle well within the pass of the rotor. Discharge time depends on a few things but relatively speaking generally conforms to the old adage "You only get out of it what you put into it". And remember - the heating of the coil is related solely to current flow in the primary, which occurs only under charging.

Just strap six D585Rs to the block and give the ECU the dwell and timing tables, it will handle the rest! :D
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Re: Pete's RX-8 Time Attack project

Post by 350matt »

Pete

there's been a request on the shed post to share the details of your build?

shall I pop a link on there to this post?
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Re: Pete's RX-8 Time Attack project

Post by PeteH »

Oh, famous at last! :lol:

Yes, please do, thanks. Nice plug for the RX8OC as well....
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Re: Pete's RX-8 Time Attack project

Post by mrspiller »

Nice write up pete , I’m sure the haters will have enough to say but stands good ground


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Re: Pete's RX-8 Time Attack project

Post by 13Black »

Big group-wave to all the armchair car reviewers over at Pistonheads bumping up the forum's view count today then yeah? :snog: Heeeey sweeties, the club's advertisers just want to say thanks.
:inlove: :inlove: :inlove:
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casey (Mon Jan 08, 2018 6:41 pm)
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Re: Pete's RX-8 Time Attack project

Post by PeteH »

Ha Ha. Don't get excited Nick, it turns out it was benedwards64, just helpfully suggesting PH could also be a good forum for a bit of a TA thread :thumleft:

Small world, this little rotary community ;)

I don't think too many PHers are coming this way; if they logged onto an RX-8 forum they would probably worry their computer would need a rebuild :lol:
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Dazza44 (Mon Jan 08, 2018 6:32 pm)
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Re: Pete's RX-8 Time Attack project

Post by 350matt »

unfortunately or fortunately PH has long since left its TVR owners origins behind

the membership is now huuuge so its now the largest motoring forum on the UK net

sadly it seems to attract some of the worst kind of keyboard warriors and self anointed genius's ( genii?) but its still worth dropping in there
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Re: Pete's RX-8 Time Attack project

Post by benedwards64 »


PeteH wrote:Ha Ha. Don't get excited Nick, it turns out it was benedwards64, just helpfully suggesting PH could also be a good forum for a bit of a TA thread :thumleft:

Small world, this little rotary community ;)
*waves*

Yep, there are some murky parts of PH generally not worth frequenting, but there's some genuinely fascinating stuff going on in the readers rides forum. My own car made readers car of the week a while ago - the FB comments etc were laughable but the thread's had some really good feedback, and even convinced one or two people to buy Image


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Re: Pete's RX-8 Time Attack project

Post by 13Black »

PeteH wrote:
Mon Jan 08, 2018 6:24 pm
Don't get excited Nick
It's not that simple
:bounce: :bounce: :bounce:
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Re: Pete's RX-8 Time Attack project

Post by PeteH »

All been quiet on the build front recently. But I have fitted these:
Seibon Carbon Doors.jpg
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The bare carbon doors weigh 7.7kg The bare steel Mazda doors weigh 16.3kg. So the weight saving just due to the door change is 17.2kg. On top of that I have removed all the wiring, the door cards (to be replaced with a thin skin), the electric windows, the door lock mechanism, the restraining strap, and replaced the glass with polycarbonate. I'm not sure of the total weight saving, but it must be well over 25kg just in the doors. The change from heavy clunky thunky doors, to "blow away in the breeze" doors, is quite astonishing. 8)
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Re: Pete's RX-8 Time Attack project

Post by mrspiller »

Wow , that s a huge weight reduction


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Re: Pete's RX-8 Time Attack project

Post by Phil Bate »

I know it's a racecar but it looks like the fit is good too :thumleft: any snags?
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Re: Pete's RX-8 Time Attack project

Post by PeteH »

Phil Bate wrote:
Sat Feb 17, 2018 11:46 am
I know it's a racecar but it looks like the fit is good too :thumleft: any snags?
I was amazed by the fit. They just bolted on, everything fitted, and the shutlines are the same as stock! There are just two snags:

1. The window channels are narrower than standard, so the window rubbers don't fit properly, so the window is fully wedged into the rubbers at the moment. This doesn't bother me at all because when I fit the polycarbonate windows I probably won't use the rubbers anyway. If you wanted to keep windey windows then it may be possible to grind out the channels a bit. It wouldn't take much.

2. The door catches are bolted in with counter sunk screws. In the carbon doors there is no metal reinforcement in this area, so the catch isn't very firmly bolted in. In an accident the catch would definitely pull out of the door. I will be making an aluminium reinforcement plate.

Oh, and they don't put drain holes in, so I got about a gallon of water in them. Needless to say, they now have drain holes.

And a BIG shout out for PLASTICS4PERFORMAMCE. They are going to be doing some special windows for me. I'll keep you posted on this one.....
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Re: Pete's RX-8 Time Attack project

Post by Lemon »

PeteH wrote:
Sat Feb 17, 2018 10:49 am
"blow away in the breeze" doors, is quite astonishing. 8)
one would assume you have seen the video of that M3 at "the ring" then...
Thanks, Stu

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Re: Pete's RX-8 Time Attack project

Post by Liam22 »

Impressive weight saving Pete. Doors are next on my list. I have the standard Plastics4Performance windows ready to go on.

Will be interesting to compare what can be done on the standard doors but I'm not sure I can bring myself to remove the internal door bars.

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Re: Pete's RX-8 Time Attack project

Post by macgtech »

Nice!

How much were the doors...or shouldn't I ask?!
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Re: Pete's RX-8 Time Attack project

Post by PeteH »

I got a tip off from a member on here that they were on eBay. They were about a quarter of their true cost :shock: , so they didn't stay on eBay for long.... :lol:
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