I just bought a '91 ranger with the 2.3l crossfire, I know it has 2 sparkplugs per cylinder, I think they fire one after the other. Any info on these engines? Do they respond well to performance mods?

 

This is not a "crossfire" engine. Both plugs fire at the same time, 2 at the top of the compression stroke igniting the fuel mixture, and two on the exhaust stroke which is termed "waste spark." Several mfgrs use this configuration, and have for several years. The main objective of this system is lower emissions.jd

 

The only performance mods these engines respond to is a turbo and thats with forged internials. You can build a radical n/a 2.3 from help from racer Walsh and others, but FI leaves it pretty streetable and fast.

 

The 8 plug head is a nice, solid piece of cast iron, but the flow isn't real "free". A port and polish will help some, as will a mild cam (your engine uses roller followers), but from there, prepare to spend a little money. You won't find a more solid engine, parts just aren't cheap, at least not performance parts. The turbo is a sure way to amp it up, but as stated, you'll need forged pistons before you think about really pushing the power, the stock cast aluminum pistons are only adequate as it is. It's one of those engines that is better either left alone, or fully built, it's a great motor either way.

 

Port and Polish is a waste of time and money. Polished ports do not flow better than unpolished ports, I don't know who came up with that idea. Sure it makes sense, but its one of those things that looks good on paper, but in real life it causes stratification of the flow. A rough surface does the same things the dimples on a golf ball do, it breaks the air as it hits the surface, prevents it from stratifying, and reduces drag within the intake/exhaust. I'm not saying you want a really rough surface either, I'm just saying a rough surface is better than one that is polished smooth.

Porting an engine without doing the cam is pointless. Large ports reduce bottom end performance, so additional mods need to be done to support the larger ports. You need to either improve the engines ability to run at high rpm, or you need to stay with near stock sized ports. Or if you run forced induction of some kind, either a turbo or a supercharger, that would definitely support larger ports. Even so, the engine will not perform as well when you are not running boost.

 

Good flow isn't the strong points of these heads, however, ford and racer Walsh make performance heads for these engines and maybe a few others.

 

Bear river, you're absolutely right about polishing, at least on the intake side. The way I understand it (and feel free to set me strait if I'm wrong), a somewhat "rough" intake port produces turbulence as the air is drawn through, which keeps fuel droplets airborn longer, increasing fuel vaporization. By over-polishing the intake ports, the flow is too laminer, and the atomized fuel falls out of suspension as it is drawn into the engine and compressed. I know this was a particular problem on older, carbureted and TBI engines where the mix had to travel long distances, and might not be well atomized to boot. I also thought multiport injection systems were less fussy about this. And AFAIK there is no problem with port-matching and highly polishing the exhaust side of the head. Espessially on this engine, which has exhaust ports that are only about 2/3 the size of the intake ports. Like I said, straiten me out where I'm wrong.

 

Fuel injection is less prone to this problem, but the reason a laminar flow forms is because the smooth surface allows the air to stratify by both creating drag, and then not disrupting the air layers that form. As far as the exhaust, is it worth your time to polish it? Polishing will not improve flow on the exhaust any more than it will on the intake.

The original ports are properly sized and flow matched to the engine in its original configuration. The engine is tuned to use any given quantity of fuel as efficiently as possible. The reason the exhaust ports are made so small is because they are trying to squeeze more torque out of the engine.

If you look closely, you will find the exhaust valve open before the end of the power stroke, and the exhaust immediately begins to escape. If your port is too large, the gases will escape too quickly, which means the pressure that drives the piston is released too soon. That is that much less power that the engine produces. This effect is more noticeable at lower rpms, since at high rpm, the gases have less time to escape. Also, the smaller port means the gases move faster. This higher speed means the gases will still be moving, even when the piston is not, leaving a vacuum in the cylinder and purging as much exhaust from the cylinder as possible. If the port is too large, the the gases will stop or even reverse direction when the piston stops, and that leaves more exhaust behind.

Don't get me wrong, the original design can be improved upon, you just have to be careful how you go about it, and have to understand where the power comes from, and how the engines really work.

Even with forced induction, there is little need to change the port sizes, unless very high levels of boost are to be used.