I already know all the basics. That site is like my bible too. I know a good amount about the engine. I have trouble remembering all the different things
Last edited by kinkyllama on Wed Dec 15, 2004 4:27 am, edited 1 time in total.
1) Oversized pistons are simply pistons that are slightly larger to make up for any machining of the cylinder bore (usually done when rebuilding an engine)
This can mean more power but not really from the overbore which is typically pretty small..... when a decent shop rebuilds your engine with some high performance pistons they decrease the clearance on the sides to make for better sealing and allow for more ring support.... which also makes more compression due to the fact that there is less air/fuel/exhaust escaping past the rings
2) Head porting can make a huge difference on a badly designed cylinder head.... most of the time this is an "art" as many shops that do porting keep their technique a secret.
Just making the ports larger can actually make your car loose power.... most porting guys try to make a very smooth transition into the cylinder from the intake as well as enlarging certain areas of the cylinder head.
Some guys will actually add material inside the head as they grind out other areas....they want to keep the port velocity high (small holes) while minimizing restriction due to poor flow lines.
Our stock cylinder heads are not too bad but I would suggest you get porting done by a profesional.... as an amature you might accidentally dig into the oil passages or coolant passages which basicly destroys your head.
3) Porting is removing the aluminum in the ports inside the cylinder head and polishing is where they make the ports super smooth. Stock heads are cast so they will have all kinds of irregularities such as bumps. This makes turbulence and decreases the amount of air that can rush into the cylinder.
Porting and polishing can make 5hp to 25 hp depending on the design of the stock head..... I'd have to guess it's probably going to be good for roughly 12hp???? Not too sure.... perhaps someone else might have a better guess
4) stronger valve springs help you run higher RPM levels.... there is something called "valve float" where the spring is unable to make the valve fully close (because it's not strong enough).... which can cause the piston to slap the valve and break or bend parts of the valve train.
Upgrading the springs is generally a good upgrade but it's not the only thing you have to look at when trying to make more RPM. You also have to remember that the force on the piston increases with the square of the velocity..... so more RPM makes way more force on the piston and connecting rod. So connecting rod bolts which hold the connecting rod and piston onto the crankshaft will stretch then break causing severe damage to the engine.
If I wanted to raise my RPM by a significant level I would look at upgrading a number of things....
Lighter pistons
Lighter connecting rods
ARP high strength connecting rod bolts
High performance bearings
Stronger piston pins
Stronger springs (possibly dual springs)
Lighter valvetrain
Lighter flywheel
Higher RPM doesn't necissarily mean more power..... look at my power curve with the new intake.... as the engine passes 6000RPM the power drops off very quickly.
Odds are at 7000RPM I would make less power than I do at 3000RPM.
Sure if I did a whole pile of upgrades I might make more power at higher RPM but more often than not it means that I will be loosing power at lower RPM.
It's a tough one..... high RPM cars are nice but they don't necissarily make their maximum power at that point.
One of these days I will explain how to take a power curve from a Dyno and calculate the ideal shift points based upon your gear ratios.
Don't worry about asking questions..... that's what some of us are here for....to help other people out.
Everyone is at a different level on this forum..... so feel free to ask away.
Tom (360 Dynamics ) would have a good idea about pricing..... I haven't had mine done yet so I don't know what the cost is going to be.
$50 an hour sounds like a decent price.... and ya.... I'd imagine there would be a couple days of labor involved when you include testing it on a flow bench.
Just a rough guess.... perhaps $600 ???
I guess it depends on where you go and how good the guy is.
I personally would spend the money elsewhere..... on simpler modifications.... the less modifications you have the less power a porting/polish will make.
If you have your car totally modified with a better intake, performance header, more agressive cams, mandrel bent exhaust, larger throttle body, larger injectors, adjustable fuel regulator, aftermarket ignition and a re-tuned ECU chip (or some sort of fuel management system) then I would look at porting the head.
Polishing is cheaper and doesn't require special equipment or "talent" to do it so I would suggest this way before porting.
So to me.... porting should be done by a pro with experience and a flow test bench.
If you were to read a bunch of books on the subject it's possible you might be able to do it yourself.... but I highly recommend that you don't do it unless your absolutely sure you know what your doing.
Ideally you would want to take it to a shop and get it tested before and after your porting job to ensure that you made positive steps in increasing flow at all RPM levels.
Making the ports huge helps at higher RPM but at low RPM the port velocity is too low and it won't make for an efficent burn (so your car could run very lumpy and have very little power at lower RPM and mid band RPM levels)
