One might find a naturally aspirated engine build-up story in a magazine labeled Turbo & High-Tech Performance odd, but in an industry dominated by the Honda market it's our duty to illustrate the high-tech side of naturally aspirated Honda performance.
In a recent Honda build-up story, we explored the advantages of adding deck space to increase the rod length in a B-Series engine. While this seems to be the latest craze in all-motor performance, a question came up in a conversation--is a deck-plate necessary? What does it take to make power? Horsepower vs. torque, high rpm vs. low-end power, long rod vs. short rod and so on and so fourth.
These interesting questions spawned even more and the outline of a story materialized. This all comes down to engine theory and an engine builder's beliefs. Before you start flooding our e-mail systems with your thoughts, remember that this is an evaluation of the differences between the two modes of thinking and where minds clash, controversy soon follows. It is not an exercise to prove or disprove any theory, just understand each in a common context on an OHC engine. It is also not a strictly Honda-only issue, as all theories discussed here are transferable to any OHC powerplant.
For some time, we have wanted to do an engine build comparison but could not figure out a way to strike the perfect chord with our readers--until now. After months of preparation, we have gone to some of the best in the import and domestic business. Managing the engine building and machining is Dan Benson of Benson Machine. Cylinder head manipulation will be handled by Bill Craddock from BCE Racing Heads, while Tony Ramos of JE Pistons and Brian Crower of Crower Cams and Equipment Inc. are handling parts development. Here is a quick background on the men behind the motors and their opinions concerning these displacement increasing methods.
Dan Benson is the man who revolutionized the strength of the Honda block by replacing the inferior Honda cylinder sleeves with ductile iron replacements capable of taking on boost pressures in the 30-plus psi range. His work can be seen in some of the fastest racers that include Stephan Papadakis and Lisa Kubo.
Bill Craddock is known for his extensive knowledge of Mitsubishi and Honda cylinder head technology. Bill's list of racers is widely known and he has been involved in many high-horsepower street cars. Lanny Higa ran deep into the 10-second zone in street trim, while others were in full race trim to equal his e.t.s. We're talking full interior, with no weight reduction. John Shepherd's Eclipse turbo is another one of Bill's creations. This vehicle dominates the East Coast, laying down 9-second times on street tires. A few more big-name racers supporting BCE product are Stephan Papadakis, Shaun Carlson, Mike Simon and Len Monserrat.
Crower Cams and Equipment is another industry leader in the import market. You can guarantee that all the top racers have started with or are currently running Crower rods. Now the company is on a roll helping to develop even more import cylinder head parts.
JE Pistons has been in the trenches since the beginning of the import revolution and has been able to develop different designs to better the combustion efficiency of a Honda engine, whether the application is boosted or all natural. Just like Crower's list of racers, all the top racers are or have at one time ran JE pistons in their race engines.
The Theories
One of the biggest controversies in engine building is deciding to go with a long-rod or short-rod engine. Extending the rod will benefit those who believe in bigger stroke with more torque and low-end power.
The short-rod approach creates high-rpm engines with fast piston speeds that mainly rely on peak horsepower with the engine revved in its sweet spot most of the time. We plan to build both styles on these pages documenting the differences as we go along. In their final form, each engine will be dyno tested to illustrate the difference in how--or more, precisely, where--in the powerband each makes its impact felt.
In a stroked deck-plate application, an engine is not only stroked via crankshaft, its rod ratio is also changed by lengthening the rod's center-to-center measurement, extending the deck height as well as installing taller sleeves. On our B18A engine, we not only have an advantage of a taller deck height to begin with over the B16A, we will also add an additional 25mm to the deck. This in conjunction with a billet 95mm Crower crank gives us a rod ratio of 1.63 and a center-to-center rod length of 154.94mm. This approach theoretically results in an engine that will produce more bottom- to mid-range torque while also slowing the piston speed. The advantages of this route are more bottom-end power and more displacement with some loss on the top end and a coinciding reduction of heat caused by friction. This helps maintain durability.
With the short-rod engine, we not only start with a short-deck engine block, we modify it for a GS-R stroke, which changes the rod length to 132mm for a resulting 1.32 rod ratio. The theory behind this engine is that all the horsepower will be realized in the top-end of the powerband. This means the engine will have to always be turning high rpms to effectively propel the car down the quarter mile.
Theoretically, the advantage of this engine is that it should produce more top-end power, but will not make as much in the mid range as the long-rod engine. The disadvantage centers around torque and whether the short-rod engine will generate enough to pull the weight of the vehicle from a standstill. Considering most sanctioning bodies have a 1,600-lb minimum weight requirement, the engine should technically build enough to launch a race car. Street cars may or may not be a different story.
The Engines
When comparing the engines, there are many different variables that can have an effect on their powerbands. Keep in mind our main objective is to figure out the difference between a short-rod and a long-rod engine. This is not to determine which is better; that is decided by the type of car and the expectations of the car that the said engine is installed in.
Figuring out a cylinder head was the most difficult part of this story. Since there are also many variables involved in determining the cylinder head and valvetrain characteristics, we have decided to keep things neutral by sticking with the same specs for each engine. A GSR ported head for both will be used but eventually we will play with the cam profiles to maximize potential. The accompanying spec boxes outline the hard parts of each engine and the accompanying Round Table sheds light on the concepts and preferences of each engine. The Round Table is hosted by Turbo's Gary Castillo and features enthusiastic input from Brian Crower, Bill Craddock and Dan Benson.
Turbo: What do you feel is going to be the major output difference between the two engines?
Dan: One is going to run a higher rpm. The shorter rod, in my opinion, is going to increase the piston speed. The long rod is going to slow the piston speed and dwell longer, which is said to allow more air and fuel into the cylinder. Theoretically, the short-rod set up should pick up a lot more power on the top-end, due to the piston speed.
Turbo: So with the short-rod motor, are you expecting the torque to equal the long rod version or fall off?
Bill: That is one of the many things we are trying to find out. Technically, we have results of what happens when this is done to a domestic push-rod engine, but with overhead cam heads being more sophisticated and efficient, it's a whole new can of worms.
Turbo: So as far as cylinder head comparisons go; between the two, would you say porting and cam profiles will be different?
Bill: If we were to get more in-depth into the issue, technically we would have to port the head to provide the best horsepower output to cater to each block. What I have done in this situation is use a full race-spec head, built around a neutral application where it could be run on both engines. Now, if I were to do a head for each, the major difference would be porting the intake ports to cater to a short-rod or long-rod engine.
Dan: (pointing at Brian Crower) Your engine will be the lower-rpm motor, but should produce good torque.
Brian: Well, my engine is running a longer rod, so mine should be able to turn some high rpm. Theoretically, it should be able to do 9,500 rpm forever with no problems.
Dan: Then mine will do 10,500 rpm with no problem! (laughs) Theoretically, the longer stroke will start running out of horsepower at a certain rpm, while torque runs out at 5,250 and then horsepower takes over until it runs out. My engine will be based on the same theory, but when horsepower takes over, mine will continue to produce more power in the high range until it starts to run off.
Brian: Because of the short stroke.
Bill: Then the physics of the horsepower take over in high-rpm compared to the loss of torque.
Dan: With my engine, I look at beating you at the top end of the race. Because your engine will produce more torque, you should beat me out of the hole, but I should be able to catch you in the end.
Bill: (laughs) Brian will be at the track with his Honda-powered tractor and Dan will be there in a Honda-powered dragster.
Dan: (laughs) Brian's just trying to sell cranks to everybody.
Brian: (Sarcastically) Ha, ha, ha!
Dan: OK, this is how my wanting to prove a short-deck, short-stroke engine came about. When I raced Comp, I could have easily went the long-rod-stroke route but I stuck with the high-rpm route. I think this is new to most because this isn't a Chevy Comp Class engine, it's more like an F1 engine minus the turbo.
Turbo: OK, so with the all-motor class set at a 1,600-lb limit, what would you consider is too much or too little amount of torque?
Dan: That's judged by tire spin. So with Brian's motor, if he could hook up the power he is planning to make in the low to mid range then he should be able to holeshot me pretty good--If he could hook up. If you're spinning the tires too much, you're not going forward; if you don't spin the tires, then you are moving forward.
Turbo: To clarify: When you mean spinning the tires, you mean spinning the tire in excess, right?
Dan: Correct.
Bill: This is where tire size and gear ratios come in handy. Due to the different powerbands that engines will produce, gear ratio will also have an effect on how well the car as a whole will perform on the track.
With the short-deck, fast-piston engine, this would be considered a velocity engine so it has to leave at a higher rpm. Judging how much the car weighs, the engine has to make a certain amount of torque in order to not have the rpm fall off. If the weight of the vehicle doesn't shock the engine, the end result will be usable top- end horsepower. With the long-rod motor, feathering the pedal may be your only option because of the torque we think it will produce.
Brian: Think of it this way, we are giving the reader two options and two different routes to take. One should make power at a certain rpm and the other should do it at a different rpm. Each will also make torque at different points in the powerband. This test is a way to give the reader two different choices for their application.
Turbo: Now about camshafts. Of course, there is a big difference between the long-rod and short-rod camshaft profiles; what are your plans for each engine?
Bill: That's the thing that Brian, Dan and I are going to have to work to make it neutral for both motors. Realistically, we would have to put the biggest cams possible in his big-bore, short-rod engine.
With Brian's motor, we would like to build his cams around his power range and where it curves off. What's unique about this project is that we are starting from a neural point--the head--because we are primarily testing the differences between the blocks. In a normal situation when somebody builds an engine they rely on me to set up a cylinder head built specifically for that engine. The head is what plays a key role in extracting every pony out of the engine. This time, we are comparing the long-rod short-rod theory, so the head has to be neutral to start; later, we will start playing with head theories.
We are going to try a different cam, say, with bigger lift or longer duration, but the same cams for both engines to show the difference of how each handles the profiles. Eventually, we will do the roller rocker stuff but for now, we would like to show the reader how the engines will be affected by profile.
Brian: We will also start playing with cam profiles to cater to the long-rod and short-rod engines. I think we will see a major difference when playing with ramp speeds, durations, lifts and lobe centers since one has a slow piston speed and the other sports a much faster piston speed.
The long-rod engine will have much more time on the intake stroke to get the needed air/fuel mixture, so we would see a longer duration cam. With the short-rod engine, we would have to work much quicker with ramming air and fuel in during the intake stroke; I expect to see high lifts and quicker ramp speeds for this application. We are waiting for the completion of the engines to see what the differences will be.
Bill: Man, this is going to be a great tech story--I want to read it already.
Dan: I think this will probably be the biggest tech story Turbo magazine has ever done.
Turbo: It's not done yet. You guys better make sure you have these engines ready for the engine dyno! Don't burn me on this story!
Dan: (laughs) As long as Bill stops playing Grand Turismo and gets us our cylinder heads, I'll hold up my side of the bargain.
Brian: Oh man, I love that game! I make my son play it to win some money so when I get home from work I can spend it on my Skyline. It's pushing 1,000 hp.
Bill: My son does too. I like playing the rally stuff, though.
Brian: I haven't got my license for that yet. I'll have my son get me the license so I can start playing.
Dan: You guys need to grow up!
The Round Table
Dan BensonStock Deck, Short Rod
Brian CrowerDeck Plate, Long Rod
Bill CraddockNeutral