8psi+ engine build path

Some people are satisfied with running 8psi while others crave more power. Unfortunately for all 420a owners out there the stock bottom end will not last under higher boost. Some people claim that they can run 10 psi on stock internals but be warned that elevation effects overall pressure. To give an example the air pressure at sea level is about 14.7 while the pressure at Denver is only 12.1. So the actual pressure at sea level at 8psi is 22.7psi while Denver is at only 20.1psi. If you run too much boost best case scenario you will ruin your pistons, while worse case you will ruin your block and head. Its best to error on the side of caution, however, if you want to run higher boost or just want a stronger engine for low boost then it's time to re-build your engine. If you follow these suggestions you will have built a tough motor so do yourself a favor and build it right the first time. BE WARNED THOUGH, anytime you make modifications to a car you are running a risk of damaging numerous components. When in doubt seek the help of a professional and never do something that makes you feel uncomfortable.

Before we talk about the parts you will need to acquire lets talk about what you will need to do with the block and head. You will be required to pull the whole motor. Some will argue this point, however, I will not support the idea that you don't NEED to have the bottom end looked at. Over time many things happen and if you want to have a reliable car after you add boost do not take shortcuts. Take your block into a machine shop that you trust and have them look at a few things. First have them check the seals, rubber wears out over time and it’s a good idea to just have these changed. Second have them inspect the crank. The stock crank will handle most anything you will throw at it, however, you want to make sure your crank is perfectly straight as the smallest amount out of true will effect hp, torque, volumetric efficiency and reliability just to name a few. Next you will want them to check the concentricity of the cylinders. Over time they have the tendency to become oblong. To fix this they will bore the cylinder, usually in .020" increments, and you need to know this before you buy pistons. Please note that this boring of the cylinders does not give any noticeable hp gains so get the smallest bore that will make the cylinders concentric. If you get the largest all you will have done is weaken your cylinder walls. Next you will want the block decked (a term that means to machine the mating surface that the head sits on so it's perfectly flat) and "hot tanked" after all the machining is done.

All right lets talk about parts!

Step 1: Pistons
After you talk to the machine shop and find out if you NEED an overbore you are ready to buy pistons. Forged is your only option. If you think Hypereutectic pistons are a good choice please read this...
http://eatsleepdsm.proboards.com/index.cgi?board=420aspecific&action=display&thread=113
Also you will need to choose a compression ratio for your pistons. Stock for the non-turbo is 9.6:1. Now for a turbo car that is a higher compression ratio you might want to lower that. It would be easier to tune with a lower ratio and a popular one for this car is an 8.8:1.

Step 2: Piston Rods.
Stock piston rods are your next weak link. Upgrade to forge rods for peace oof mind.

Step 3: Fuel
If you have upgraded your fuel system already by using a fmu well... it's not going to be enough. Here is the problem with the 420a, it's controlled by a MAP system. This makes it hard to tune from our ecu as the sensors can not determine how much fuel the car needs when possitive pressure is added from the turbo. There are really only two options that work well with this car. First option is a simple, yet more expensive option. Hahn makes something called a portfueler. This is a flange that is sandwitched between the head and the intake runners. This flange has 4 high flow injectors on it and includes a way to program these off of rpms. You still use the stock ecu with this option, however, one of the biggest draw backs is that you cannot control spark. Second option is Mega Squirt which is a stand alone system. You can run it with or without the stock ecu. Options are pretty much unlimited with this, however, it is very difficult to install. There is a section on both dsmtuners.com and 2gnt.com that cover the install of this and I would suggest posting your questions there until there are a few more people on this site with the technical knowledge.

Other suggested parts:
MLS head gasket, APR head studs, new water pump, mechanical timing belt tensioner, new timing belt, performace cams and higher hp/torque rated clutch.

So those are the BASIC upgrades you will be looking at to run a higher psi then 8. There are many other upgrades that you will need to do as the pressure increases though. Because of that this thread will remain open for comment. Please feel free to add your own comments here if you have found that you needed to replace certain parts in order to take you to that next level. Things such as getting a better clutch at a certain HP or adjusting the timing at a certain psi.