Jeep Engines - Oljeep

, .170 MOPAR PERFORMANCE PARTSPORTED CYLINDER HEADUsing ported cylinder heads is a very popular way ofincreasing an engine’s performance. However, ported headsaren’t cheap. At this point, think how much you’d pay forported heads for your race engine. Write it down nowbefore reading the rest of this section.Ported heads could be worth 20 to 50 hp more than standardheads. But, unlike camshafts and valves, you can’t put aspecification on a ported head to tell how good it is. Acamshaft has lift and a valve has diameter, both of whichyou can use as guides. Ported heads are more related to“who did them.” Visual inspections don’t seem to help.“Pretty ones” may not make any power at all, or they maybe great. Even cost isn’t a good guide. You can take yourheads to a porting service and be charged $500 to $5,000,or even more depending upon how much work is done. Justspending a lot of money on heads doesn’t mean that theywill go fast. You can say that if you want better headsthey’ll cost you more, but the total dollars spent in relationto value isn’t totally reliable.There are some pretty straightforward reasons for this.First, ported heads are all hand labor. The fancier you get,the longer it takes. Extra time costs extra money. You alsohave to factor in flow bench time and the knowledge of“where-the-thin-spots-are.” If you port your own heads(cast iron), it’s a good bet that you’ll ruin at least one headby breaking through into the waterjacket. A porting servicewill usually take one head and cut it up to find where thethin spots are before porting the actual set. All of this has tobe factored into the price.The performance that ported heads offer varies a lot. If youdo your own you might be looking at 5-15 hp. An econoporting service could give 15 to 25 hp. New ported headscould yield between 35 and 55 hp. The performance gainslook good, but let’s look at price.Ported head assemblies can cost as much as $900 to $1,200each. On the surface this sounds like a lot. Looking at thepower numbers, getting a higher output, higher quality piecemay be worth the extra money. In truth, it’s a much betterdeai than that. With a porting service, you provide the headcasting (probably used), valves, etc. With a new ported headassembly, you receive it fully assembled - valves, springs,retainers, and new castings. A new casting costs as much as$350. This again sounds high, but there are a couple tricks.First, this is a new head casting-not used or rebuilt! Second,you can get a used casting for half this price, but you’ll haveto install bronzewall guides and regrind the seats before youget a good head. The problem is that horsepower potential isdirectly proportional to the number of valve jobs done on thehead. In other words, the more valve jobs done, the lesspower the engine makes. A new casting has the absoluteminimum number of valve jobs-one.Now, if you add $300 (on the average) for new valves, springs,retainers, seals and locks, add the cost of the new casting(about $350) and the porting costs (on average, $1 50 - $200 forone head), you could wind up spending $1,000 - $1,250 for arace prepared head. However, a new ported head assemblytypically costs between $900 - $1,200, and comes fullyassembled with hrund new parts. Often times, a new portedhead assembly is the best deal. Cost vs. perjhnance is the key.Do your homework first and then decide where best to spendyour money.Swirl PortsThe term “swirl port” was introduced in 1986-87 and waspopularized by the press and racers. We use it in our MopurPerformance Parts Catalog relative to many of ourcylinder head castings. Many standard production cylinderheads have swirl ports and they have a swirl port intakeshape. Their ports were designed using swirl porttechmology. All these statements are true. The confusionseems to come in relative to the combustion chamber shape.There are many wedge-shaped combustion chambers andit’s (difficult to put them into specific categories. One of thelatest is the heart-shaped chamber. The term was first usedby us in reference to our small block 3 I8 V-8 ‘A’ engineswirl-port head (approximately 1986-87 production). Thisseerns to be where the tie-in comes. Since the 3 18 had bothswirl ports and a heart-shaped chamber, some peopleassumed that the chamber was the “swirl.” It wasn’t!The press (primarily performance magazines) hasn’t helpedthe situation. They tend to misuse the term “swirl” inarticles on horsepower development, cylinder heads andairflow. This isn’t totally the fault of the press. Racers alsotendl to misuse the term. Since it (swirl) is the latest “trick,”every racer has swirl heads. This all leads to confusion. Totry and clarify this situation, we’ll need to back up and givean explanation based on technology rather than “hype.”..T - -Tri