Lowering a rotaries compression ratio?

[BlitzBoy]

And it begins

Private joke between me,"Special Needs" and the "Smiler" lol :rollin

Col just remind Smiler who does the better launches and 60fts lol

[m1tch]

My mate Phil who has a semi pro drift FC3S has got a bridgeported engine with a fairly large turbo but its running wastegate spring pressure, so about 0.5bar or so, due to the porting and free flowing air there is oooodles of torque for drifting

[Prof]

Mines got modified inlet and exhaust manifolds, not like I think they have much of an effect on torque. Power yes..
 
But regardless, nothing, barring nitrous (or increasing compression hugely), you do to an engine comes remotely close to boost pressure for giving torque, its not how engines work. Prof, have you got any info on other high hp RXs barring Blitzboy thats not running 1.5bar+ thats got anywhere near as much torque as power?
Most I see seem to have torque in the low 300s even when power is 500+?
 
His at just under 400 with 550bhp isnt bad. But when 2litre turbos running more boost and pump fuel can have the same power but still 100lbft more, you see where im coming from.
 
But you cant have it all, just wondered if you can, not the end of the world!

I think the only useful info I can give you are these 2 facts:
 
1) The design of the combustion chamber (long chamber) means that the engine has less torque than an equivalent piston displacement - but can make much higher horsepower for the displacement. Much like the sports bike engines - higher revving engine will make more top end power. It\'s hard to get large amounts of torque from a rotary unless you are prepared to port the engine. Engines are effectively an air pump - the more air you can push through it the more torque it will make - you can either do that by pushing the air in (supercharger or turbocharger), or you can port the engine and allow it to suck much more air in on it\'s own. The highest torque engines are invariably those that are both ported and running boost. In ascending order of torque and power the porting:
 
Stock < Street < Bridge < J port < Peripheral Port
 
(there are degrees of street porting and also bridge porting (like half / full))
 
Another way to make a load more torque is to add another rotor - triples make sack loads of torque.
 
2) The relationship between power and torque:
 
torque * RPM * constant = hp
 
This means that with higher RPM engines, they can make more power - but not necessarily have high torque.
 
Why does torque drop after a certain RPM?
 
Torque starts to decrease because the engine cannot breathe as well. Due to the speed, the chamber does not fill with air as well. A designer can get around this problem with "tuned intake" which sets up a resonance to pack the chamber with air, but it only happens at a certain RPM. The next evolution of design is to make a variable system which packs the chambers with air at all RPM; this is usually called "variable tuned intake runners" or something like that and involves valves which open and close to create a different size for the airbox and manifold. Take a look at the 4 rotor LeMans engines that made use of this idea.
 
Why does power continue to increase after torque decreases?
 
Remember that the power is essentially the product of the RPM and the torque. At first, decrease in torque is small and is not enough to offset the increasing RPM, so the overall product still increases. Eventually the decrease in torque becomes large enough that it outweighs the increase in RPM and we see the power start to drop. Because of this, the power peak will always be after the torque peak.
 
So to come back to the porting - which you so readily dismissed in favour of the turbo - it\'s the way on a rotary to make big torque and power - it always has been, turbo\'s can help but work way better on a rotary that\'s ported properly.

[matt p]

^^^^^^^^^^^^

Lovely write up there Prof, just learnt a lot there

Matt

[StavFC]

All correct info Prof, but simple fact is more boost gives far more torque than any other single thing you can do.
A stock port engine pushing 2bar and 400bhp has massively more torque than a big port engine running 1bar and 400bhp.
 
But if big boost just isnt happening on pump fuelled rotaries, so be it, knew the situation from the start, not a big deal, was simply a question why.
 

My mate Phil who has a semi pro drift FC3S has got a bridgeported engine with a fairly large turbo but its running wastegate spring pressure, so about 0.5bar or so, due to the porting and free flowing air there is oooodles of torque for drifting

But thats not what we are talking about.
The car still has next no torque for the power level compared to if it was running proper boost.
Even im only running 0.8bar on a ported engine and happily wrecks the tyres in the dry in 3rd if provoked, but they still drive like a fairly powerful high revving small capacity n/a car rather than the usual big boost turbo car, thats why they rarely look like smoke machines.

[Prof]

A stock port engine pushing 2bar and 400bhp has massively more torque than a big port engine running 1bar and 400bhp.

Mathematically improbable... :confused:

[m1tch]

The more air you get into the engine the more torque you will have, are you saying that 1bar flowing in this size pipe:



Has the same amount of air going into the engine as this pipe:



Im pretty sure that a larger pipe with a lower boost is going to flow as much as the smaller pipe at stupidly high boost - bit like porting in a rotary really, my engine is on stock ports and so needs to be streetported to let more AIR in and therefore increase POWER and TORQUE. I can bolt on a huge turbo and run big big boost, but as the air can\'t get into the engine, the engine will be restricted still as the airflow into the engine isn\'t good enough else everyone wouldn\'t bother with porting at all

[m1tch]

This Rotor in the Curtiss-Wright engine - used for industrial purposes and low RPM has buckets of torque due to the large amount of air getting into the engine:

[StavFC]

I dont know how many big boost turbo engines you have actually played with themselves over the years, but you two have some odd ideas of what does what :confused:
 

Mathematically improbable... :confused:

Why?
 
Boost makes torque like nothing else even close, ANY engine. Drive any forced induction car with huge torque for its capacity, its running big boost regardless of anything else done, end of story.
 
Easiest example for people to think of is a restricted engine for class rules, WRC a fine example.
300bhp from a 2litre turbo as the restrictor totally ruins top end airflow, but it has nigh on double that in torque because it runs about 3.5bar peak boost.
 
300bhp from a 2litre turbo could be done at less than half a bar with "good airflow" and "big ports" and no restrictions at all. But you think it will have over 550lbft?
 
No.
 
And exactly same case with a rotary or any type of combustion engine.
 
I can only presume the Curtis Wright thing was a joke, as its pretty obvious why that makes torque... :confused:

[Rzla]

Why do you keep going on about lbft of torque like it is the most important thing in a car?
Rotaries make less torque than a piston, now get over it.
At the same power bands rotaries are still quicker!
Look at Blitzboys for an example.
Is that why when Rotary powered cars that are running 400bhp race scoobys and evos (why do all the AWD owners quote their torque figures?) that have 400bhp and 400lbft torque (the rotary has a lot less torque) still beat the higher torqued piston powered car?
And the rotary was running 0.8bar of boost and the piston 1.2bar+
Yes I was there because it was my brothers rx7 that raced my mates cars and it was not just once it was a number of times and a number of AWD cars.

[StavFC]

Im not talking about racing or what can beat what, and regardless, a race is a crapload more variables in a race than power or torque, esp transmission losses a 4wd has a big power disadvantage if all else is equal anyhow.
All of the above has nothing to do with what im saying, so lets not go off topic
 
Rotaries make ....ing good for their "size". Nothing to "get over" so stop being so defensive.
 
But torque, and more to the point boost matters, simple as. Another, even simpler analogy if it helps...
 
You drive your rotary, blitzboys rotary, any car, just imagine it was running perfectly, no det, all lovely...
You drive it at 1bar. THEN you drive it again so it ran 1.5bar then drops back to 1bar at peak power, making exactly the same peak power figure. You think it will drive the same all the way thru the revs just because its got the same peak power?
 
Anyhow, I had my answer about low compression rotors ages ago, believe what you like about the rest, lol

[Prof]

Maybe the point we were trying to make was that without the porting the high boost just won\'t do anything much other than really heat up the intake air pushing your potential for knock right up there.
 
But if you want to ignore all the advice people give and keep quoting high boost = major torque increase then fine - it\'s not my engine :rolleyes:
 
Ever wonder why when you look at what a load of people are doing and think - why are they doing it that way - that maybe - just maybe - these people have arrived at this formula because it works - that\'s not to say that other things shouldn\'t be tried - but perhaps it\'s better to ask why is that not done ?
 
It seems that most of the high power rotaries overseas that run turbo boosted engines only seem to go over 18/19 psi when they use c16 - pump gas on a rotary with boost just seems to have a limit around that point.
 
No matter what you do - upping the boost beyond that point will just bring trouble - very careful attention to combustion, timing, affects of premix on effective octane of your fuel will all have to be considered.
 
No matter what - for bigger torque figures with a turbo - you need to port - simple inescapable fact. Perhaps you should up your boost and see how far you get, as an empirical test - at least then you can get your lump ported out nice after you\'ve blown it
 
 
Just thought this might help:
 
Torque is proportional to the air passing through the engine (it\'s an air pump after all)
More air = More Torque.
 
A Turbo allows more air to be pushed into the engine
Higher boost = more air = more torque.
 
Porting allows more air to enter the engine
 
So these two things go hand in hand - which is what we\'ve been trying to say.

[m1tch]

Can you post up the photos of the blown water seals when the engine gives up at high boost? Are you going to port it when the engine is apart?

[BenLewisMav]

So just to clarify, does porting move peak torque up the rev range, or, because more air is able to enter the engine full stop, does it increase torque at all revs?

I\'m going to forget about things like resonance/pulse tuning, overlap etc for a sec, but I\'ve always thought that large ports = crap low end drivability, but if it\'s letting in more air then it should produce more torque?

[Andy_k]

Your answers are on Rx7club.com mate have a search.