rotary engine question

[beast]

what dictates where the maximum power is in the rev range on a rotary?on a normal piston engine its down to the cam(usually) but obviously there are no cams on a rotary!!!
also,what mods need to be done to a rotary to allow it to rev higher?lightened rotors?
most of the cars i have seen featured in mags tend to only run 1 bar boost!!dont rotary engines hold up well to big boost?have read about the race cars running upto 2 bar but there doesnt seem to be anyone running in the middle ground.


regards  rich

[Martiny]

Well, there is no cam, thats true. But think about what the cam controls - it controls the open and closing times of the ports.

In a Rotary, the Rotor itself opens and closes the ports. The LOCATION of the ports is what determines the tuning characteristics of the engine.

So, to move Power up or down the rev range, you need to machine the ports or even move them somehow.

The boost limitation is down to how much detonation (Self ignition at the wrong time) that the seals can stand up to. The standard ones are designed for standard boost. You cannot turn up the boost without doing a whole lot more mosifications.

Yes, 2 Bar is possible (with lots of money!), in fact ANYTHING is possible if you spend enough money to acheive it!

Hope this helps :-)

[beast]

thanx for the reply.your explanation of the port sizes ect does eplain it to me.by seals do you mean the apex seals?if so what benefit do you get from 3mm ape seals over 2mm ones?do they just last longer?


rich

[Martiny]

Well, its mostly the Apex seals that are vulnerable, yes. I suppose the 3mm ones might be stronger, hopefully some of the Engine builders on here will answer that.

You get seals made from different materials, though. Ceramic seals apparently are very resilient to detonation. Carbon seals stand up to higher RPM better, but make the engine harder to start.

Steel, which is what is standard in the 3rd Gen is a good all round compromise.

[zevans]

You won\'t see many street cars running over a bar because you will always run into lag problems... this doesn\'t matter when you\'re hooning round Castlecombe and never going under 5000 revs, but pootling round the town at 30mph, it\'s gonna be a pain in the arse.

Same applies to tuning for big power at big revs by diddling the timing / cams / porting - anything you gain at the top you pretty much lose at the bottom.

This is why clueless 350Z owners think the RX8 is "slow".

[20B_boy]

Originally posted by zevans
You won\'t see many street cars running over a bar because you will always run into lag problems...

You wont see people running over a bar on the street cause pump fuel doesnt allow it that safely.

Not sure what how much boost you run has to do with the amount of lag on a turbo??

[zevans]

Turbos big enough to flow a lot of air - ie high boost - are always going to have to be physically bigger than a turbo which can\'t flow as much air - so more lag, as a rule.
 
(And the bigger your IC the more lag as well...)

[20B_boy]

Originally posted by zevans
You won\'t see many street cars running over a bar because you will always run into lag problems...

So you are actually relating running over a bar to having a big turbo... They dont have to go hand in hand tho, eh? Thats where my oringinal comment lied. E.g. a GT35R isnt a big turbo but is going to be lots of fun over 1 bar for sure - with very minimal lag

Theres a difference between a turbo that can make high boost and a turbo than can flow a lot of air. You could put 2 bar thru a GT35R or a T88-34 both to great effect - but they shift rather different volumes of air...

[Icesurf3r]

Originally posted by 20B_boy
You could put 2 bar thru a GT35R or a T88-34 both to great effect - but they shift rather different volumes of air...

I have a T88-34, in what way does it differ from the GT35R?? As i understand it from reading the posts, the GT35 is a slightly smaller turbo, so will spool up faster, but the T88 will shift a higher air volume?? Is this correct, or am i just completely mad lol :confused:

[Rene7FD]

The question is, what amount of air does the engine (want to) inhale at the desired boost, at wot + max rpm. If the smaller turbo can supply this amount of air at say 80% of it\'s max capacity, then the smaller turbo is the better choice : same result at full chat, but with less lag and earlier boost.

(the 80% is to keep the turbo from ever reaching it\'s limits)

René

[zevans]

Originally posted by Rene7FD
The question is, what amount of air does the engine (want to) inhale at the desired boost, at wot + max rpm. If the smaller turbo can supply this amount of air at say 80% of it\'s max capacity, then the smaller turbo is the better choice : same result at full chat, but with less lag and earlier boost.

(the 80% is to keep the turbo from ever reaching it\'s limits)

René

Nicely put - that\'s what I was getting at. You want a turbo that\'s JUST big enough - and a turbo that\'s just big enough for 1 bar boost at 7000 revs is always going to be bigger than a turbo that\'s big enough for a mere 7psi (1/2 bar).

Plus, some of the lag is just the physical matter of moving the air around and sucking it in quick enough, and dealing with pressure changes, so the more air the more lag too!

Running 1 bar on a turbo not up to the job will put heat into the charge (= less power) and will not be efficient (=more lag), and conversely running 1 bar on a setup that could handle 2 bar will not work efficiently (=unnecessary lag.)

So 20B_boy, you\'re right, it\'s not always directly related, but generally speaking there\'s a correlation.

In terms of flow - most ported rotaries aim for power, ie torque high up the revs - so you\'re always going to need high-flow tubbies. If you had a car tuned for torque low down (like an Evo 400, or even come to think of it a TDi type engine) then you might not need such a high-flow turbo because you\'ll be changing up at <6000 revs anyway.

Now someone will mention hybrids...

[petemillis]

Zevans, I drive a Skyline GTSt as well as the RX7. The GTSt has 0.6bar of boost as standard. I am running the same turbo at 0.85bar. If I change the exhaust vanes to steel instead of the standard ceramic, then I am still running the same turbo yet can safely up the boost to well over 1bar. No difference in lag.
In fact I have seen 1.3bar on the ceramic internals on mine for short times without breaking it.

With regards to increasing the boost on the rotary, provided the fueling can be matched properly and the intake temps kept down then there is no reason why there should be a problem with detonation. What is more likely to cause problems is the higher combustion temperatures associated with the high boost and more fuel.

[zevans]

Originally posted by petemillis
The GTSt has 0.6bar of boost as standard. I am running the same turbo at 0.85bar. If I change the exhaust vanes to steel instead of the standard ceramic, then I am still running the same turbo yet can safely up the boost to well over 1bar. No difference in lag.

Fair \'nuff! Have to wonder why Nissan picked that particular tubby then, but there you go. (At one point me 300ZX ended up with a Stage II turbo on stock exhaust - now that -was- amusing.)

Of course the other problem is anything over 300 horses is hard to drive on the public roads at full chat... turbo or NA!

[petemillis]

0.85bar in the wet is fun.....
Provided the boost and fuelling are well matched, a bigger turbo doesn\'t need to suffer from lag either. You just need something to kick it into life.
I\'ve just added a nitrous wet kit (only fitted with 25hp jets at the mo till testing complete) to the Skyline. Tested for first time yesterday, again in the wet. Now, the turbo spools up instantly and I get far stronger pull at 0.7bar with nitrous on than I did at 0.85bar nitrous off.
One advantage of nitrous is that it significantly (like massively) cools the intake charge as well as allowing more fuel to burn. So a small shot, say 25hp, could help an RX7 running higher boost than standard by reducing the risks of det and cooling the intake.
Good thing about nitrous is that it doesn\'t affect the day to day driving or economy of the car. A bottle may only last for 10 minutes before refilling, but that\'s 10 minutes of WOT. Also, unlike other tuning mods, you\'re not putting any additional stresses on the engine on a day to day basis. And how often does anybody use WOT on a regular basis on the road? Another god thing is that with traditional mods, they increase peak horsepower but often don\'t do much for hp and torque from as low as 3000rpm. Another thing (yawn) is that you get used to the feel of traditional mods as they are there all the time. With nitrous you keep it switched off except when absolutely necessary (like a Merc CL500 up your bumper, or when you\'re on the strip). That way, you really feel the difference when you want it, and don\'t end up taking it for granted!
I know there is much debate on whether nitrous is suitable for the rotary, but provided things are kept to a sensible level, then I can only think of benefits.

[bnaellis]

Originally posted by zevans
You won\'t see many street cars running over a bar because you will always run into lag problems... this doesn\'t matter when you\'re hooning round Castlecombe and never going under 5000 revs, but pootling round the town at 30mph, it\'s gonna be a pain in the arse.

Same applies to tuning for big power at big revs by diddling the timing / cams / porting - anything you gain at the top you pretty much lose at the bottom.

This is why clueless 350Z owners think the RX8 is "slow".

I think you will find that lower boost will increase lag not vice versa. Also there quite alot of people running over  1bar.
The thing you will find they have in common is water injection and or higher octane fuel.
People run 1 bar or less because they want the car to be reliable while not having the above.

rgds