how about some serious overbore? would it be possible to get a few hundred cc more out of the I4? might be nice in combo with that 2.6 stroker kit (if it ever turns out that it tests out okay)
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how about some serious overbore? would it be possible to get a few hundred cc more out of the I4? might be nice in combo with that 2.6 stroker kit (if it ever turns out that it tests out okay)
Few hundred CC - as in 0.1+ L? No way. You only have 4 cylinders to work with.
care to elaborate? what's the maximum you could hone each cylinder to? the porche 944 had a 3.0 L i4 motor . I don't know the other specifications of the block though. I'm just curious because i haven't heard of anyone doing this.
Let's see... assume a 2mm overbore.
Stock bore = 86.5 mm. Stroke = 100 mm
Displacement = ~ 588 cc per cylinder ==> 2350 cc = 2.35 L total
Over bore = 88.5 mm. Stroke = 100 mm
Displacement = ~ 615 cc per cylinder ==> 2460 cc = 2.46 L total
An increase of 110 cc. Not bad, but 2mm overbore is significant.
i take it back im at 88mm there is noway your going to get more then that out of the 4g64 without sacrificing the integrity of the block i have pictures somewhere i'll have to host them and get them on here
what warm jsut saud we dont got a 2.4L block we got a 2.35L block lol, i think they make differnt cc blocks theres lei ak 2380cc block or somthing also
from what I understand that's pretty common. most of the time an auto manufacturer will just round up to the nearest nice round number. the 4g63 weighs in at 1,997 cubic centimeters but it's badged as a 2.0; I would assume that this is because A.) no one but gearheads like us give a shit about what works out to three thousandths of a liter and b.) those 3 thousandths are probably within the statistical error of the manufacturing process.
the 64 is probably badged as 2.4 cause again, no one cares about five hundreths of a liter and also because 2.35L SOHC would look awful silly cast into a valve cover :lol:
lmao this thread is funny.
can sombody tell me why you would lose torque if you have a huge diameter exhaust?
cause its just not making sense to me..
On an N/A engine you need a certain amount of back pressure in order to get the most volumetric efficiency out of the engine. Once you increase the diameter of the exhaust you start to lower the pressure. It gets pretty complicated but on a properly tuned naturally aspirated engine, exhaust gas scavenging actually helps pull in fresh air for the next combustion cycle and with piping that is too wide it doesn't fully evacuate the cylinder of the combusted gases.Quote:
Originally Posted by dknight3
For a turbo engine, you want large diameter piping because you want as little back pressure on the turbine wheel as possible since it's restrictive and won't allow the turbo to spool as efficiently.
^^ pretty much it :D
Another thing to note is that you're going to gain top end with a larger exhaust because the engine is much more volumetrically efficient at higher RPM. You may lose low end torque as a trade off because the engine has less VE down low.
edit: this is an extremely simplified view of cause-effect, but what you need to know is that the engine needs the tuned exhaust that maintains a scavenging effect and proper exhaust gas velocity for low-end power.
I've always heard that backpressure is the enemy, regardless. But as everything is a trade off, backpressure is a result of a smaller diameter piping required to make velocity that makes torque. Velocity is what you want, but it comes at the cost of backpressure.
You're right, backpressure is bad but it goes hand in hand with longer and smaller diameter piping.
thanks.
yeah i heard backpressure was bad too, but ive heard that no back pressure is bad, i know, both are true, bigger pipe is like taking off your headers kinda.. the less backpressure the more its like leaking before your muffler kinda..,
turbos still create some backpressure, do the the fact it only has like around 8 inchs of tiping to shove a turbine and spin it so it kinda pushes aginst the valves a bit, and if you got less backpressure on the turbo it can spool faster :), but you want some pressure you spin the turbo itself,
warm correct me on my mistakes lol
I have a headache now. :smt021
Read that again duh. backpressure = bad. exhaust velocity = good. If i understand this correctly it's because the higher exhaust velocity generates some kind of suction or 'scavenging' effect which pulls the burnt air/fuel mixture out of the cylinder and aids in drawing in fresh air/fuel charge. I've also heard that excessive valve overlap in combination with high exhaust velocity can actually pull some of the mixture out of the cylinder, hurting performance. correct me if i'm wrong please.Quote:
Originally Posted by 6G72gearhead
but its still never good to run no backpressure just a little bit is the best , for a little 1 cylinder take the muffler off the thing it will burn it up, like flowmasters, theres always gonan be some kind of pressure in that tube no matter how you look at it
Ive posted this same thing time and time again. Backpressure is not what you get rid of when you upgrade piping. Bigger piping means bigger exhaust pulses which become farther arpart. When you have the right diameter pipe for your setup, one exhaust pulse will help pull the next one through the pipe, which means for a faster exit for the exhaust gas.
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http://www.hondacivicforum.com/m_39893/tm.htm
The more you kow.
i dare not click on that, yeah that sounds right seth, if you ever watch a split cat back exhaust at idle, it pulses out one side usually the shorter end, sometimes out the other, ive seen like 3 pulses out the right and 1 out the left, somewhat like umm air pockets form in the tube fore about like 8 revs a puff pops out, with a split like umm matts dads car with the split catback i bet youll see that if it was pointed at the ground you would see the sand usually pulseate out at idle, if its perfect it will pulseate out one side and then the other,
i got an image in my head, like it creates a pressure bubble and after it has enoth pressure to get out the other end it shoots for it, kind of, after the pressured ball floats threw the tube it creates a slightly negitive pressure, and drags the next one along, thats what im thinking seth means, thast what im thinknig why some exhusts have a 2 tone them pressure differnaces like a "bu" and a "bo" at the same time lol
im probably completely wrong about this whole post lol, but i agree with seth! :) :mrgreen:
What Seth posted is right, but back pressure is a product of exhaust diameter and length like I said before.
Just make a hole with your hand and blow through it. It gets easier to blow through when you loosen your grip and increase the diameter, doesn't it? Same if you place both of your hands together and then shorten the path the air has to travel by removing one hand. More flow capacity = less back pressure. And back pressure creates flow restriction as you can feel with this simple demonstration.
stock pipnig is fine for a reg n/a accualy i think for any n/a unless your reving to like the moon, for boring it out it should be slightly bigger, wit ha turbo you wnt it way wideer the an 1/8 an inch, do to the fact it shoves a ton of air into the engine, a ton of air has to come out, make more pressure in the same tubing, and too pressure much is always bad and you lose lots of performance and bog down, like and this goes for alot of things it just bepends on how you look at it
"you cant shove 10 pounds of crap in a 5 pound bag"
so you have to get a second bag, or big a 10 pound bag, in this case you can find a way to make 2 small pipings or just make it larger, same goes for intake you cant suck 100 cfm threw a 5 cfm hole, thats why you buy a turbo, but still cant shove it in there fast enoth under higher conditions
Stock piping isn't good because it has tons of restrictions. Just look at it. However, mandrel bent 2.25" piping with a free-flowing cat and muffler would be ideal for a 2.4L N/A setup.
well i mean a stock n/a lol its made for the car, porbably change the muffler and chhange ot uthe cat, and it would be set for a stock engine
Yes, it's made for the car, but Mitsubishi has to cut corners to keep costs down. IE: the pipe bends SUCK and you'd benefit from a mandrel-bent system even on a stock 4G64.
true but i mean do the same size piping is stock a little bit wider for a blown out n/a, plus if your gonan widen it you gotta widen everything on the exahust including headers and shit, everything smaller then what you widened will create some kind of pressure change at that spot, for instance gonig 3 inch from headers to the stock muffler it will do no good
higher pressure form the engine then to a lower pressure tubing(aka widened) if widening it widin the whole thing from the edges of the header that touch the engine to the tip on the muffler
The fewer bends you have the less restriction with smaller pipeing. A well thought out exhaust system would ideally use the fewest bends to get the gasses out from under the car, while using a pipeing tuned to the powerband of the engine.
yeah to big is bad is what im trying to say