Either u have aftermarket cams, or ported polished heads, valve angle job and corresponding headers etc the stock TB may possibly be good enough.
hey bother dont with this if you have stock engine unless you only want a more sensitive throttle response..
seen some mods with air filter and enlarged TB only while everthing else stock...normal cams, no polishing, valve job,no headers or forced induction.
this doesn't give you that much power it just makes your throttle more sensitive,
heres the argument - I have seen ppl say "dude I bolted on a big TB so it pulls in more air so the ECU puts in more fuel so = more power"
sure you felt the surge when you drive dude thats only becoz at that throttle plate angle the air you are drawing in is more becoz of the larger dia.
if the 10% throttle input revved upto Xrpm now it will be (X+n) rpm
it will make more power if the original TB was so restricted that the power was being held back due to the bottleneck.
so if the existing TB is a bottleneck (and also if the OEM manufacturer was a retard) then it would make sense to upsize.
think of VE.. (im trying to simplify it in layman terminology, ther eis much much more to this ...)
what the hell is this ? ideally theoratically if an an engine is 100% efficient, so theoratically it pulls in air fuel mix
= to the displacement of the engine at WOT.Since the 4stroke engine has has one intake stroke for every 2 revolutions of the crankshaft we can suck in x units of air= displacement of the engine in 2 revolutions.
so to find the qty of air sucked in we multiply the displacement by 1/2(the engine speed) assuming it is 100% efficient for simplicity sake. so our Volumentric efficiency is 100% but in real world the engine may acheive say 50% efficiency..
for now if we want to increase the air flowing through our system we will use porting polishing, crazy cams etc etc etc and later on use a turbo/supercharger and run the engine at very high revs and increase airflow than what the stock TB was designed to handle.
A stock engine may have a TB size perfectly port matched for this mass and velocity of air flow, so unless we use crazy cams etc etc or forced induction we are in no way increasing the airflow. If the OEM TB was obstructing the airflow to such an extent that the VE was reduced to
(50-x)% then it makes sense to upsize the TB to remove this bottleneck.. Im sure car manufacturers have taken care of this already... if u have a stock engine with no other mods why upsize your TB ?
bolting on TB on stock cars and saying the ECU pumped more fuel got you more power doesnt make sense to me...
e.g the speed density fuel map has x= MAP reading , y= RPM ,z = duration of Injector pulse , so if the ECU sees more air it simply looks up x2y2z2 instead x1y1z1 so u just getting the stock power (over simplified ) of a higher rpm at a lower throttle position.
what the the MAP will indicate depends on how much air you pull in, its only that the MAP will now indicate higer value for a lower TP angle becoz for this TP angle more air is sucked in becoz of the larger TB size.
(guys plz dont confuse alpha/TP angle with speed density reading this last sentence,speed density= MAP,alpha/Tp angle=TP angle)
none of the cars in iNdia work on alpha-n so dont worry abt this...
Ideally OEM guys design the engine for driveability and mileage ,you could say they distributed the entire range of the power in the throttle pedal so its not so sensitive to slight inputs during normal driving.
so a slight throttle input will pull in a certain qty of air which will make the car accelarate gently in a civilised manner, what a larger Tb would do is increase the amt of air for the same Throttle position, as a result more air= MAP sensor indicates greater value = ECU uses a value from the fuel MAP corresponding to that MAP value and more aggrressive pickup (not more power)
but hey the TB maynot be that bad,Im guessing that at WOT maybe you will see the gains becoz there the ECU goes in open loop , its here the extra air may help a bit will it be noticeable is the question ?
the slight obstruction due to the butterfly type of throttle plate caused in the OEM TB will be minmised slightly due to the larger bore TB so it may help at these WOT conditions..
if I can put it like this .. what u are doing is fooling yourself, you could wear 10kg wt on ur shoe and drive the car, sure you will floor the throttle more as compared to without the weight, so you get the throttle response without the cost of new TB...
upsize this if this is a bottleneck after upgrading the airflow otherwise its good for just a sensitive twitchy throttle feel, bolting on a TB without supporting modifications will not make large power gains(Im assuming who ever bolts on a large TB is also port matching it to their engine correctly)
(also if we think of velocity of airflow, its much higher when passing thru a narrower pipe as compared to extreme super large dia TB port, this may not be felt so much in case of fuel injected systems in some cases but we can keep this thought in the back of our minds..)
if you have plans for crazy mods exceeding what the OEM TB was designed go for it but till then it wont make big bhp gains on its own as just a bolton only...
