Lowering a rotaries compression ratio?

BlitzBoy · August 07, 2009, 08:49:27 AM

Quote from: Prof;632599One thing I did notice in the graph that Stav put up - that his AFR\'s were going higher than 12 near the peak power (after peak torque) which doesn\'t give much safety margin - that\'s a good candidate for pulling some timing and WI if ever there was.

That Dyno chart is not his car Prof, its from a car in the US

mx1311 · August 07, 2009, 10:59:34 AM

jeez, this got out of hand

i am on mrc not driftworks?

BlitzBoy · August 07, 2009, 11:06:50 AM

Im waiting till I see pictures of ex girlfriends next hahahahaha

BlitzBoy · August 07, 2009, 11:07:20 AM

Not wet Not wet hahahahahahhahahaha

Bulla · August 07, 2009, 11:11:13 AM

Quote from: BlitzBoy;632660Im waiting till I see pictures of ex girlfriends next hahahahaha

:rollin I wondered how long it\'d take.

Prof · August 07, 2009, 11:36:21 AM

I aint getting my \'old boy\' out !:D :rollin

DRAGON · August 07, 2009, 11:38:14 AM

Good thread, its healthy to have different opinions.
Reminds me of when MRC used to be an interesting forum.

matt p · August 07, 2009, 11:56:16 AM

So whats your thoughts on it Ross?

Will be could to get a tuners opinion to

HaywardRotary · August 07, 2009, 12:11:42 PM

Hi Stav,
Back to your original question about compression ratio I will try to help.
If you run more boost then you effectively getting a higher compression ratio anyway, in fact you are getting a variable compression ratio using a turbo due to alot more than 9 to 1 ratio and volumetric efficiency max being acheived,so really it makes little difference to det except that to acheive and equivalent ratio with lower compression rotors you need to run more boost.
Hope this helps.
Regards
Carl

najiru · August 07, 2009, 03:21:18 PM

Very interesting and reading it I don\'t think you guys have a vastly differing opinion, essentially approaching the same problem from different angles as I see it.

The original question from stav on lowering compression is a fair one and was answered early on. Seems to me prof is describing how in the rotary world torque is achieved and has always said that combining these changes with high boost will of course give better results.

The statement that higher boost gives better torque returns than anything else is probably true but only over a specific boost range that is very much dependant on the design of the engine in question. Where the upper limit of that band is on a rotary without porting etc etc may be considerably lower than for the average (or not so average) piston engine.

DRAGON · August 07, 2009, 03:30:59 PM

We had a stock mazda engined FD, ran 1.6 bar 357lbs 432.6hp on pump fuel, lasted for a year and half, then boost spiked and died.
Dont agree that lowering compression ratio is pointless, as boost will make up for it.
I agree that lowering compresion ratio is good for more boost, thats why we did it in the drag car.

mx1311 · August 07, 2009, 03:33:38 PM

what was the porting/turbo intercooler setup on that motor ross?

BlitzBoy · August 07, 2009, 04:00:52 PM

Quote from: DRAGON;632749We had a stock mazda engined FD, ran 1.6 bar 357lbs 432.6hp on pump fuel, lasted for a year and half, then boost spiked and died.
Dont agree that lowering compression ratio is pointless, as boost will make up for it.
I agree that lowering compresion ratio is good for more boost, thats why we did it in the drag car.

Did you use the S4 rotors 8.5 CR or did you manage to machine them yourself Ross?

Rub87 · August 08, 2009, 10:05:21 PM

lower CR and more boost is the way to go, this will give lower PCP\'s (peak cilinder pressure in pistonlanuage) this pcp\'s going over xxxbar will lift you head, bent rods and induce detonation

I\'ll give an example, as I\'m a dieselman, I run lets say 17:1 CR and 2.4 bar of boost, this will give a pressure before combution of approx 180 bar, now lets say I run stock CR of 19.5:1 and run 1.8 bar of boost I get also a pressure before combustion of 180bar the difference whne going from 19.5 to 17:1 CR is relative small, but the amount of more toque I can make running .6 bar more boost (assuming rest of engine etc is all capable) is huge

in rotarylanguage this pressure means risk on detonation and risk to blow a waterseal

also the arguments being made that bigger ports : more torque are vague, especially for NA engines, as huge port NA engine will have less troque down low, and probaly only at high revs a little more, but this little more at higer rpm give the typical plenty of increase in HP, this is because bigger ports: lower gas speed, less %VE at low rpm\'s and worse scanvenging, same with a piston engine, big cams and ports : less torque at lowe rpm\'s

just my 2c

StavFC · August 23, 2009, 11:49:22 PM

Nice to see a couple of people on here understand the point of lowering compression, and amusing but totally unsurprising that most dont but argue and mock people who dissagree with them. Good old internet heros eh!

As a side note, my boost controller failed the other day and the car ended up running 1.7bar boost, and though thankfully it didnt pop (maybe the water inj saved me), the midrange torque was now HUGE, felt a totally different car, like all cars do when running big boost, something that no porting or bigger turbos can EVER do to the same extent.
If the comp was lower thatd have been safe to do on pump gas.

You "experts" can discuss that all you like.

But as lowering comp isnt an easy thing to do, its a moot point it seems.