resjsu

I know I started another thread witht he same title but no one responded to it because I think everyone thought it was done.....

This migth be considered an elementary question but oh well.....

Alright so the rotor basically sucks the air in to the chamber right? If my engine is a 1.1 liter engine then each rotor is designed to suck in .55 Liters right? Regardless of the actual amount...... If they are designed to pull in that much air/fuel mixture.... how does porting help if the engine is only able to suck in the same amount of fuel? Unless You have a forced air induction system, i just can't get how street porting alone (even with an exhaust will work)

Does this make sense? It almost seems like commen sense that street porting alone will not do anything... is there something im missing?
(cool icon, irrelevant)


..... Thanks for answering my previous questions and this one also.

REVHED

You're assuming that any given engine operates at 100% efficiency all the time. This is far from the truth.

The actual air an engine can ingest is called volumetric efficiency or VE. Torque is directly rated to VE. All the things we do to an engine such as porting, intake and exhaust mods are attempts to improve the VE thereby increasing the torque and power output.

It is actually possible to have a naturally aspirated engine with a VE of over 100%.

Hope that helps.

LokiRx7.1

iTrader: (1)

Nope, .55 liters is one rotor. .55 divided by three is, 0.183 (3 repeating) So each face of the rotor at the compression stroke compresses a space equivilant to 0.183 Liters Now on your Intake stroke your carburator or FI depending on throttle input, is shoving fuel into your engine, yes your rotors do help by pulling in air. by porting your motor, you allow more fuel and air to enter that space in a given time. So if you cram more air into the same sized space, you RAISE compression. Because of the Venturi effect of carbs and throttle bodies, it doesnt allow air to escape. So in essence you have created a sort of forced induction.

Basically larger ports fow more air into a given space, the space does not change however the pressure does. A larger amount of fuel and air and a more pressurized intake charge has more stored energy, thereby when ignited burns more aggressively.

Street porting alone, will not do much. Any kind of porting alone with no supporting mods wont do much. But thats not the point, it allows a better engine effieciency with those mods. What Im saying is if we have the same supporting mods on the same engine, I will out-perform you because I am ported, which allows my engine and mods to operate more effciently, Basically, if I have a hole for around 300 CFM and I stick a 600 CFM carb on to it, it will only flow 300 CFM through the hole, although it will flow it faster than a stock carb. If I port the hole to 600 CFM then all the carbs potential will be used.

Now The Final Final answer,
On a stock setup, you may see a 3-5 HP increase IF that, with an aftermarket intake AND exhaust, it could allow for gains in upward of 20 HP or more. So yes street porting does make a difference

(I know I bastardized this to hell but I want it to be simple straight-forward and understandable. )

Chris

DriftFB

Well, the 1.1 Liters comes from how much fluid the engine can displace. Every time the rotor goes around air and fuel are drawn in by the vacuum. But either the vacuum isn't strong enough or the rotor passes the opening (port) too fast for a full 1.1 liters to be brought in. Or 1/6th of 1.1 liters to be exact. So, by increasing the size of the ports more air and fuel can be drawn in during the same amount of time.

Hopefully that answered your question.

MattG

iTrader: (2)

Yea if you look at the ports then look at streetports. They are huge! Think plain and simple.

If you drink out of a 1/4 straw your going to get some water, but if you drink out of a 1/2 inch straw your gonna get a ton more water!

Water=power! lol

I have a Streetport Engine and I was running stock everything. I noticed some power increase over just a normal port. But nothing to write home about.

So if your gonna go Streetport, you gotta upgrade your shyt or otherwise its pointless.

I dont know if that anwsers your question, but I think its helpful in a way

trochoid

iTrader: (6)

Look at it this way. If your mouth can hold the above mentioned 0.183 l. and you are sucking from a narrow straw, when you use a bigger straw, you can suck the same volume faster/easier. You now have a ported big mouth. If you make a proportional increase in the little brown ring in the back, you have better flow in and out, thus better VE.

Don't take this personally, I've been up nearly 24 hours and feel like being silly, but the point is the same.

Matt, your a putz, you took my line while I was typing this out.

MattG

iTrader: (2)

Hey the straw theory was mine!!

trochoid

iTrader: (6)

Guess I'll have to settle for the string theory then. You got the inny right, you just forgot about the outty.

MattG

iTrader: (2)

HAHA oh well, THey say great minds think alike!

REVHED

I've got a suggestion for you. If you don't know what the hell you're talking about then don't pretend you do. Each rotor face displaces .55. Not a third of that. If you don't know that then I don't think you should be giving advice to newbies.

rotariesrule

porting is all about timing. when the port size is increased, the time that the port is open is increased. when the time the port is open is increased, more fuel and air can get in and out of the engine thus increasing its VE. when more fuel and air can get in and out of the engine more horsepower and torque are produced. when more horsepower and torque are produced more smiles are produced.

REVHED

It's not *just* about the timing but also the physical area. Though obviously the two are related.

rotariesrule

i concur.

resjsu

I dunno. The straw analogy..... I get what you are saying but if all that can fit is a certain amount, then drinking out of a hose wouldnt make more difference.

**(Analogy)**If you suck air in and fill up ur lungs they have a maximum amount of air they can hold right? Doesn't matter how wide or narrow the opening is...... you can only fit so much ai rinto your lungs. Bare with me....So what im thinking is lets say stock engines have their lips narrow and a street port is like widening their lips.....the chamber (lungs) can still only hold so much air, no matter how fast it takes for the air to get it....Unless you force air in right?
So basically a ported stock engine doesn't really do much........ and cmon 3-4 horsepower? how can you say that... cuz im sure you didn't get it dyno'd for a 3-4 hp increase. On a good day my car can feel like it has 3-4 HP gain. Not poking fun at anyone but I am trying to understand. I appreciate the all the responses.

trochoid

iTrader: (6)

What you are missing is time and motion. While the air and fuel is being drawn in, the assembly is rotating, it does not wait until it is full to move on to the next step, compression. Just because the volume is there does not mean it is filled to capacity by the time the compression starts. Porting allows the mix to enter at a faster rate resulting in a 'fuller' fill, thus improved VE.

While an earlier poster said this result in a higher compression ratio, it does not. Compression ratio is simply a measure/ratio of the largest volume in the cycle compared to the smallest volume,(TDC).

resjsu

There it is! that makes sense man thnx.

blwfly

iTrader: (4)

wow cool this is boostin up my knowledge
thanks guys for good explanations
i love these things

rxtasy3

iTrader: (2)

enlarging ports in a rotary does the same as increasing lift and duration with a cam in a pist-on. that to me is the most simplest way to explain it. and as in a previous post, street or bridge porting is useless unless u can get more air in and out of the engine with bigger carb/throttle body and better flowing exhaust.

LokiRx7.1

iTrader: (1)

1.1 Liters is the total displacement of the engine, If I had a V8 of 5.7 liters and I wanted to find one bank of cylinders, I would divide it in half. If I wanted to find displacement of one cylinder, I would FIND AN EIGTH OF THAT. Each rotor has three combustion faces, so in order to find complete displacement you must assume that to find one side of the rotor so you know what it makes on the compression stroke, you must find a sixth of 1.1, And if Im wrong and you care to educate me YOU DONT HAVE TO BE AN ***.... Total engine displacement is a total of all combustion faces in an engine. thats how they find it on piston engines, so why should a rotary be any different.

Everything I said makes sense, If take a 350 Chevy with a 365 CFM factory carb. And an Intake designed to flow 365 CFM give or take, and I plop a 750 CFM Holley double pumper on there, it just wont flow the same as if I got an intake and port matched the head. Besides the fact on a piston engine you'll need a larger cam, larger ports, and you might consider overboring it.

I honestly think that is how a rotaries displacment should be properly found. If I am wrong because it ends up being more than 1.1 Liters, than I dont think its a 1.1L Why should we claim amazing power efficiency compared to a piston engine, when we cant use the same method. Now I know I am talking about something I dont know about, because I have no info telling me what a rotors face equates to in displacement...

Thanks for being a DICK and provideing me with all that helpful useful information!

You could be cool about it and explain where I am off base. I think I explained the concept very well, you dont need to blow up on me just because I was wrong on one point. Or the fact I was trying to help someone out.

Oh and if all I do to a 350 is intake and exhaust, compression IS raised. How it doesnt on a rotary is beyond me....

And last time I check compression, from a compression gauge that you thread into the spark plug hole, is the overall chamber PRESSURE, being that if it is low the rings, or apex side seals, or head gasket (depending on what kind of engine) are bad. My gauge stores that pressure until I release it, I dont know about the ratio, but in pounds the chamber pressure will see an increase if you jam more air into it. If you are using the same space and cramming more air into it, it really is beyond me how that pressure does not change.

Sorry I am being an *** now, I wasnt in a good mood BEFORE i read this thread...

LokiRx7.1

iTrader: (1)

Again I realize I am being an *** hole, someone educate me since apparently I have no Idea how displacement is "properly" found on a rotary..... Other than the displacement deal I dont think I was all that wrong. But please try to understand what I am saying...

gsl-se addict

iTrader: (3)

With the rotaries, the rotors turn at 1/3 the shaft speed, so only one face of each rotor is used in one revolution. Each face displaces ~0.55 liters. One rotation of the engine pumps 1.1 liters of air (assuming 100% VE). Some people say the rotary should be considered 3.4-3.9 liters if you are going to include all the combustion chambers. Others say it is a 2.4-2.6 liter because each rotor fires on every engine revolution (360°) instead of every other revolution (720°) like on a piston. I don't mean to start a debate on the rating of the rotary. Just pointing out that there are different ways to look at it.

T_Racer

iTrader: (1)

Join the club on the rotary displacement debate. I have seen both sides argue, seemingly all with different arguments. Dave Coleman, of Sport Compact Car, who I normally admire for his wisdom and advice, kinda had a lame brain argument. It started off comparing rotaries to four cycles with the argument that the accessories and such are all from a four stroke engine, blah blah blah. That one just kinda got me, but the rest of the article was pretty good, arguing that the Renesis should properly be labled as a 2.6, not 1.3. I forget the points of it, but there are lots more out there debating both sides of the issue. Though for my .02, the measurement should be easy to find, as 2"=2" will always be true, no matter how some people want to measure things. And I do agree, the Volume of EACH rotor face X 3 for each face, X 2 for each rotor, = total displacement.

Also Loki, I think that some peope are talking about compression RATIO, not compression pressure. You are right that the compression pressure would increase with mods, but they are right that compression RATIO will not increase, naturally.

Cheers,

SparkienSuggah

now we're getting different measures of displacement

A 4 cycle piston engine DISPLACES volume through the movement of its piston heads, these piston heads make one complete cycle every rotation of the engine, therefore the automakers will claim that (say ford...) their engine (say 80's rustwang) displaces 5.0L
HOWEVER the ford engine only opens the intake valve once every two rotations, meaning that only 2.5L of air is sucked into the engine per rotation.

with a rotary engine, the rotor face and trochoid surface form a chamber that swells to a specific volume (.55L on a 12a) before closing the intake port and beginning to compress the intake charge. this swelling happens once per revolution, per rotor, meaning that a 12a sucks in 1.1 liters of air per revolution. This leads people to conclude that it is a 2.2 litre (or the 13b is a 2.6L) engine if one was to think in piston terminology. the rotary engine is simply able to make more effective use of its volume displacement than a piston engine PER ROTATION. (i dont make any other claims than that)

multiplying the volume per rotor face (550cc) by the number of faces (3) would yield an incorrect number as to the displacement because the engine would require three rotations to utilise that volume. ford would then rate their mustang motor as a 7.5L V8 (the volume consumed every three revolutions)

i tried to stuff a 500cc water bottle into the intake potion of the throchoid in my bench engine, but the shapes were wrong.. im looking for a liter of silly putty if anyone wants to donate...

REVHED

Ok, what I said was uncalled for.

Snapshot

All the scientific explanations aside: I’ve had 2 street ported engines custom built & coupled w/ big *** Holley carbs & a RB header to duel exhaust system. There is absolutely no comparison between a stock & street ported engine. Bridge ported can also be streetable & will blow your mind.