Car modifications - the dummies guide! Part #3

Izso

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Before I start - I'd like to highlight that what I'm going to discuss here today is considered basic NA engine modifications. I'm not going to go into the little hardcore mods, just only the most obvious and the most basic. If you start asking about the Power Linz or the Singh Groove, that means you're knowledgeable and shouldn't be reading this.

I'll talk about forced induction later since that is very much in the *really expensive* price range. I don't believe in plug and play BOT setups because if you're going to BOT, do it in a bigway and boost in style! Not a paltry 0.2bar boost...

And there's a reason I keep showing the engine bay picture above. It may not look the part but it has been modified with almost everything I'm about to discuss today.

Right. On with the show!



Oversized pistons and stroker kit

"There's no replacement for displacement". Remember these golden words! No matter how much you trick out your 1.3L car it's still a 1.3L car. And a 1.8L will eat it for breakfast. So consider a "stroker kit" and "oversized pistons". What are these?

Stroker kit's are exactly that.. they stroke.. and caress.. and pump up and down.. the pistons. The longer the stroke, the more displacement. Usually this is done by changing the crank shaft. You can opt for a aftermarket crank shaft or if you know how, transplant one from another car model into your own. Just be sure it won't over stroke and result in the pistons shaking hands with the valves. There's some theory that the shorter the stroke the better the lower end torque, the longer the stroke the more power there is in the mid to high. I've never been able to confirm this so if someone could care to share that would be good.

Oversized pistons are exactly that too. Bigger, wider pistons. Depending on your application, you can opt for high compression pistons, flat top pistons or low compression pistons. For NA you usually opt for high compression pistons since the higher the compression, the more bang for buck. Forced induction applications usually opt for low compression pistons since turbos / superchargers require the lower compression. I have heard of psychotic high compression forced induction cars and apparently it's do-able without killing yourself, so it all depends on your tuner. Pistons generally have two common types, forged and cast iron. Forged pistons are lighter, stronger than cast iron types but are considerably more expensive. Stock OEM pistons are usually cast iron. Again if you know how, you can transplant pistons from other car models into your engine. You'll need to change piston rings and it's usually recommended to change the crankshaft bearings. Why? Better oil flow and changing out the worn bearings is always a good idea.

To fit oversized pistons you'll need to bore the cylinders in your engine block to fit the pistons. This is the tricky bit, overbore and you might get too close (or hit) the water jackets (this is where the coolant flows), this'll mean major cooling issues and possibly a warped block. Big time nasty! So do your research, find out how much is "safe" to bore and then only buy a suitable piston to plonk in.

Lastly, the conrod - or connecting rod. The thing that connects the piston to the crankshaft. Why is this important? Because you can affect the stroke as well with custom length conrods. It's the only thing holding the piston to the crankshaft so it better be able to take all the punishment you're gonna dish it! So it's generally a good idea to get forged or reinforced conrods when you modify your car for big power. Again - if you know how, you can always transplant from another car model.


Race crankshaft bearings


How does all of this affect the displacement of the engine? The bearings don't have any direct relation to the displacement but the stroke and piston size do. Looking at the diagram below (thank you Wikipedia) it explains in a picture what I've been trying to say in words. The stroke distance determines how high/low the pistons go therefore increasing the orange section. The width of the piston also affects the orange section. The orange section put together is the total displacement of your engine.


One complete cycle of a four cylinder, four stroke engine. The volume displaced is
marked in orange.


FUELING



Next up I'd recommend upgrading your fueling system. Why? Like the equation says, more fuel + more air = more power. You've upgraded the displacement (the area where the fuel and air burns) so feed the engine properly. Assuming you're going for high compression, the engine will suck in a lot of air so it's only appropriate you fuel it just as much otherwise you'll get a catastrophically lean engine and probably burn a piston or two. This is true even for forced induction engines since their ECUs are designed to make the air/fuel mixture rich to protect the engine.

Fuel pump upgrades is a no brainer. If your tuner says your stock fuel pump isn't pumping the fuel fast enough change it! If your existing pump is sufficiently pumping enough fuel, then throw in a fuel regulator so you can control the fuel pressure. It's like a water hose, you turn the tap on and the water just flows, but squeeze your thumb over the outlet of the hose and you get a fine spray. Control your thumb and you get a different spray pattern. Same concept. How does this affect power? It basically helps with combustion, the more complete the combustion the better it is for you. The finer the fuel spray is the easier it is to burn. So depending on how you want it to burn, adjust your regulator accordingly.

Note - Some modern cars have a 'returnless' fuel system. Meaning the fuel only flows one way and there basically isn't any room to install a fuel regulator. You can either opt to just upgrade the pump to squeeze in more petrol (like opening the water tap more to allow more water) or you modify the whole fueling system to be non-returnless.




The fuel injector is essentially the equivalent of your thumb on the water hose outlet. The bigger the injector, the more fuel it will allow to flow through. Having said that however, bigger is not always better. Injectors have a 'optimum' flow point and installing a 1000cc injector on a 1.3L car is pointless and you're underutilizing the injector. This might spoil the injector in the long run. That's a laymans way of explaining how injectors run best at 80-85% duty cycle and using the wrong size might underutilize or over exert the injector.

To be continued Part #3 - More engine mods

Sorry.. this is taking more parts than I expected. I talk too much!
 

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D7zul

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already digging inside the engine ey..

nicely done :top:

:biggrin:
 

Yong_5290

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Short stroke big bore = high rev
Long stroke = better low end

Most bikes also have very short stroke with fairly big piston so a twist on its accelerator easily make up to 9k rpm and goes beyond that
 

Dino@Casper

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Like Yong Mention

Short Stroke Engines will be able to sustain higher RPM, where else Long stroke Engine would have better low end torque.

An example would be if you tie a string to a rock, if you use a long string you will it harder to spin it faster as compare to a shorter string.

If I remember my physics correctly Torque = Radius * Force
So the force in this sense is the combustion from the spark plug pressing down onto the pistons. So given the same bore size and setup the longer the stroke the more torque.

Hope this helps you guys understand slightly more. :P
 

Izso

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Yong and Dino : muchos gracias senor!

I was actually going to throw in camshafts and pulleys but that really made the article super long
 

amirmambo

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Dude keep it up man !! Great write up and following you step by step even though im broke !! Hehehe still got the balls to learn stuff up and later on apply it when i get the chance :biggrin:..Again bro,great info for everyone which is still new in the car mod world :dancing:
 

alantjw

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i had reached this stage.. but i was stuck... cos my cylinder walls curenly cant be bore anymore.. so need change an engine.. owh well.. wort the try..
 

mines998

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Izso said:
Yong and Dino : muchos gracias senor!

I was actually going to throw in camshafts and pulleys but that really made the article super long
And don't forget about head gasket. ^^ I'm your fans now....haha
 

Izso

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i had reached this stage.. but i was stuck... cos my cylinder walls curenly cant be bore anymore.. so need change an engine.. owh well.. wort the try..
Ah? If it can't be bored then get extra strong liners. You won't be able to go larger (pistons) anymore but the liners will save you from catastrophic failure.

And don't forget about head gasket. ^^ I'm your fans now....haha
Head gasket... erm.. why la? As long as your head bolts are good and the gasket is properly installed, it won't leak. Remember - I'm talking about basic mods. Stuff like modified thinner / thicker gaskets, metal head gaskets, these are for the more adventurous.
 

series5401

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bro, nice write up on na modes.. but, if u have time, waiting for u to write up on the other half of na modes, which use carbs.. eheheeeeee.. not using efi bro.. :(
 

mines998

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Izso said:
Ah? If it can't be bored then get extra strong liners. You won't be able to go larger (pistons) anymore but the liners will save you from catastrophic failure.

Head gasket... erm.. why la? As long as your head bolts are good and the gasket is properly installed, it won't leak. Remember - I'm talking about basic mods. Stuff like modified thinner / thicker gaskets, metal head gaskets, these are for the more adventurous.
Erm..so need to yr part#4 I guess.
 

Yong_5290

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Like khguan mention, most stock oem piston are made out of cast aluminum due to its
strength and light weight characteristic
 

Random Post Every 5 Minutes

Hi all,

Hope u guys can help me on this matter, my current engine is going to die.... :sad_smile:

i't hard to find aura hf , especially Gtti nowdays....

rgds.
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