Forced Induction 101
Forced Induction 101
This is an engine modification article. It describes how to modify your engine to really perform its best. For a low boost engine, less than 10 PSI, not alot needs to be done. You can run that low level of boost with HUGE gains on a stock engine, although if you follow the recipe below, you will gain more, and have something more durable. Most of the tips, other than compression ratios apply every bit as well with NOS. The stuff below are needed for more than 10PSI, on up as high as 35PSI(!), and I have seen higher levels in some cars, but not with stock passenger car blocks.
Now, as for blocks, make sure you have a good "Square" block. In other words, the bores not only have to be honed out with a torque plate, but the block should also be decked, align bored, etc., to make certain aver machined surface is perfect. If it is not a 4 bolt block (with SB Chevys I prefer to start out with a 2 bolt block) machine it to accept 4 bolt caps, slayed outer mains if possible, crossbolted as wekk, if possible.
The Ford Modular blocks are perfect in that respect. Use the Windsor or forthcoming SVO iron block for this. The Aluminum blocks have main bearing walking problems, so with mega boost levels, stay with iron. Also, make sure you use a steel crank. Lunati Jet Forgings are awesome pieces, the price is not super evil on them, and they work well. For the SB Ford guys(5.0), you can get a nice storker crank while at it...no much more than stock stroke, and since the rods and pistons are also going to be new, may as well go for it..no replacement for displacement.
The 331 inch "302s" fit most stock blocks without any clearance issues. For the mod motors, Lunati one of the places that will custom forge a crank, although one is more than likely in the works from them. But, the truck motors, the Windsor blocks, have good steel cranks stock. And they come knife edged. Either way, make sure the cranks are cross drilled for better oiling, and chamfer the oiling holes. Cheap insurance.
Now, you need to spin something onto that crank.
For high boost levels you NEED strong rods. Stockers will not live long, and we do want this engine to stay together, right? Whether you are building a 3.8, 4.6 or 5.0, or whatever, get good rods. They are available for all of the above. You will need H or I beam style steel forged rods, and go the extra mile and order them bushed for full floating piston pins. Another neat trick is on the big end (crank end) drill a tiny hole pointing up the rod, toward the piston...and I mean tiny...like 1/64th inch. This will spray oil at the bottom of the piston, as well as the pin, cooling the piston head.
Speaking of the piston, this is very important. The piston and ring package can make or break you. They absolutely, positively have to be good, high quality forged pistons. No way around this. Arias is one of the better brands for pistons for many years. To get more info on pistons and brands check the Forged Pistons Tech Tips.
For a forced induction engine, go conservative on the Compression. Keep it around 8.5:1. That means dished pistons in almost every case. If you can afford it, have the skirts coated with an antifristion coating, and the head with a heat coating. Polish the piston head. You do not want any sharp edges on it, as that can #1 - be a stress riser point, #2 - a hot point for detonation to start. Both are dealy. As for the pin, go full floating as I said earlier. I use double Spirolocks every time. Overkill? Maybe, its always better to overkill than not far enough. Wrap them up with plasma-moly rings, or at the least, chrome-molys. It is prefered to use the Child's & Alberts Zero Gap setup on the top ring, and a standard C&A Plasma second compressoin ring. Also run low or medium tension oil control rings. Low tension is worth a good 35-50HP depending on the engine. Make sure your maching shop has the pistons and rings available when he machines the block so he can match them. The C&A zero gap rings are neat though, they actually use a pair of offset rings in the land, effectively sealing the gap. FAR superior to the ZGS rings.
Now, we have the basics for the short block, except for cams. This is all up to you, depends on what the engine is, depends on the car, gears, ect., but keep in mind that a blower will make a big cam seem milder. For any street motor use a hydraulic roller regardless. For a race motor, go as far as a solid roller.
Now, on to the heads. Aluminum is VASTLY prefered. They dissipate heat better, preventing detonation. As for porting work, they don't need to be ported any more than any other engine. Do what you prefer, remember it has to be a driver. Just clean up the ports, get rid of any flashing, and smooth the bowls. Get a good 3 angle valve job. Run stainless valves, swirl polished every time. Stainless valves live long, and although the ones with the cut down stems are going to gain you some HP, the chances to bend them are better.
Now, we need to do something to bolt it all together. Its preffered to use ARP hardware, or Milodon. Heads always get studs, as do the mains. To seal it up, you 5.0 guys have it easy. FelPro makes the lock wire head gaskets. The rest of us, you have cut your own head gaskets out of soft copper with great luck, and I will usually cut the heads for stainless wire-rings. Just make sure you spray it with Gaskacinch.
To keep things lubed, especially on a turbo or Vortec set-up where the engine oil lubes the blower bearings, run Synthetic oil, and use braided stainless lines to the turbo(s) or blower. Also, run a hi-volume oil pump, and I usually do some porting work on the bearing caop the bolt to to allow the oil to flow smoother. Run at least a 1 quart oil filter, even if it mean remotely locating it. You will need to run stainless, minimum dash 8 size to the cooler you will need, anyway.
As for the cooler, go with as large as you can, and regulate it with a thermostat to keep the oil around 190 degrees. If you can fit a larger capacity oil pan, go for it. If you have the money to go all out, run a dry sump system. Either way, wet or dry sump, you should have at leat 10PSI of oil pressure for every thousand RPMs you turn, with at least 40PSI at idle.
More pressure is OK; less, your never want to run with, especially with turbos. And, don't just turn off an engine with a turbo, let the engine idle for about 30 seconds to a minute after you stop. This allows the turbos to spool down with oil pressure. Also allows them to cool off a bit, reducing coking on the bearings.
Remember turbos spin about 40,000rpms, and are in the exhaust stream. Vortecs can't be hurt by this practice either, as they are lubed by engine oil too.