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Motorhead Memo: Size is everything

By Kip Woodring

Unlike many, I don’t pay much attention to all the new bling-bits in H-D’s ever expanding P&A catalogs. For me, it’s mostly about the stuff shown in the much thinner, much more serious volume known as Screamin’ Eagle Pro Race Parts. The ’09 edition was a bit slow in coming, so I had hoped that meant lots of new, really good bits and pieces would be contained therein, once I got my grubbers on one. To my great disappointment, upon finally perusing The Motor Company’s latest, there’s damn little to rejoice about for performance fans. Wait! Let me rephrase that…

The ol’ cliché reads: “There’s no replacement for displacement.” For fans of the axiom, life is good in SE-land circa 2009. Which is as it should be I guess, because if the trend continues, that line will soon be amended to read, “There’s no alternative to displacement”! It’s something of an indictment, I realize, but like the government, when it comes to engines, we get what we deserve. By demanding cleaner air, allowing more regulation of emissions, and insisting on sticking with archaic air-cooled V-twins in our all-American motorcycles, we are painting ourselves into a performance corner. Truth be told, I doubt the factory has any choice anymore—the older hot rod tricks are simply unfashionable and borderline illegal these days. That’s not Harley’s fault, really. They do what they (still) can, which is pretty much to treat the efficiency of a Twin Cam engine as a constant and add power by adding size. In case you missed the memo: It wasn’t always so. There were other ways.

Most of us recall that Evolution big twins were nearly the opposite case. You got 80 inches to play with—pretty much end of story. (Yeah, I know the aftermarket developed larger engines and bits, but the factory never did, and that’s who we’re talking about.) What happened instead were incremental, inexorable and eventually significant improvements in volumetric efficiency, courtesy of the parts offered in the old Screamin’ Eagle catalogs. (You know, the “off-road use only” stuff!) This has since transmogrified more and more into “street legal” kits—which when installed by your friendly local, can be “warranted” for the full OEM two years. Hmmm… smacks of marketing when you look at it that way, so maybe some of this is Harley’s fault after all.

Anyway, to my mind this boils down to some obvious gaps in the SE product line these days. For instance, commensurate with tighter regulations and the not coincidental increase in displacement, occurring in 2006, we have 96-inch engines for which there are virtually no specific factory hop-up parts! Don’t get me wrong, there are pieces in the Pro Parts book that one can employ to good effect on 96-inchers, but almost everything is intended for 88/95 motors—well, that or making a 96-inch engine into a 103-inch, 110-inch or even more. But doing the same things one once did to 80-inch Evos simply isn’t happening for those who want to stick to 96 inches. It was not all that cool when Harley used to offer only those things that improved volumetric efficiency for Evos. Is it really that much cooler now, to offer mostly extra inches for the current big twin? It’s as though the pendulum has swung back and forth to two extremes and left not much middle ground. Seems the balance has been lost here.

Is it simply a sign of the times that enhancing efficiency has been sacrificed in favor of augmented effectiveness? Is there a tenable reason the factory won’t or can’t come up with basic hop-up parts for the Nine-Six Twinkie? Maybe we should examine the relative pros and cons of the two approaches to power and see.

A substitute for inches?
OK, treating displacement as a given, we can look at what was possible when taking an Evo from bone-stock to two Stage III levels (not to mention Stage IV). The worst-case Evos were the California models, which often made less than 44 hp at the tire. Even the 49-state machines at their best typically only managed about 50 rwhp and 62–64 lb/ft of torque. Extracting right from the source (the 2009 SEPRP book, page 11), a so-called Stage III setup (high-flow air cleaner and exhaust, re-jet, 10.2 pistons, bolt-in SE4 cam) generates 80 rwhp and 82–83 lbs/ft of torque. This is the “torque” configuration, amounting to tidy increases of 60 percent in the horsepower department and nearly 30 percent more… well, torque for (not counting labor) about $1,600. That’s about $18 per pony if you keep score.

Here’s Stage III “full race” numbers: 85–87 lbs/ft torque, 90 rwhp, which costs almost $1,000 more for increases of almost 10 hp and a half a dozen lbs/ft of torque. Suddenly, 80 percent more power and 40 percent more torque comes at closer to $28 for each and every horse in the corral.

Bearing in mind these are improve­ments in efficiency from a given engine size, let’s look at the relative benefits of using increased inches on a Twin Cam to achieve similar ends.

Does bigger equal better, or cheaper?
Twinkies started life as a shining example of the bigger is better philosophy, born at 88 inches and amenable from day one to increases up to 120 inches. That original 10 percent displacement “advantage” over the Evo, translated almost directly into (you guessed it) almost a 10 percent bump in “as delivered” horsepower (at 62–64 rwhp) and torque (about 72 lbs/ft) an increase of slightly better than 10 percent! So far, so good, right? Well, hold on, because there is no Stage III setup for 88-inch engines! Rather, we get a stage III “torque” option, involving (no surprise) a step up to 95 inches, including cams, high-compression pistons, bigger barrels (natch!), and a carburetor, yet no heads and only cursory discussion of exhaust! All that kit “stuff” and the additional seven cubic inches come at a cost (on the surface) of about the same $1,600. Some issues: Doing essentially the same thing to an EFI bike requires calibration to the “tune” (pardon the pun) of somewhere between $300 and $900, which can be more “spendy” than any carb (not counting any dyno-time expenses). That means true costs are often in the region of $2,000 to $2,600 (again, not counting labor). The power-per-dollar quotient comes out, realistically, at nearly the same as the Stage III “race only” Evo, though way more than the “torque” Stage III setup. And this doesn’t even take into account the distinct possibility that most TC88s will need expensive gear drive upgrades for long-term reliability. Hopefully this illustrates that whatever its virtues, the “no replacement for displacement” approach ain’t cheap! Moreover, the percentage of improvement over stock for a Stage III 95-inch Twin Cam “conversion” isn’t anything to write home about—like a mere 20 percent more horsepower, though torque at the tire increases the same 30 percent as (and raw numbers considerably more than) the Stage III Evo.

The Harley way, or the highway?
Performance “stages” we’ve compared have another problem in common: They aren’t exactly legal and can void warranties. Yet, that’s a moot point for a couple reasons. For example, if you’re gonna play with more displacement and get some real power for your trouble, the other Stage II 95-inch kit for TC88s is within $100 or so of the same cost as the street-legal Stage II, but the difference in output is, well, priceless! You trade a set of cams that work for a warranty that won’t, with the same increased displacement. But, they aren’t making 88-inch Twin Cam engines anymore (or 80-inch Evos, for that matter) so what’s to stop you if you own one of these machines? Though in a way, this thinking leads to a less obvious, yet more critical point: Namely, that there’s nothing about any of these factory SE stages that puts reliability in real jeopardy. (The emissions warranty is the only one that really gets violated when you go beyond street-legal.) A word to the wise contemplating similar approaches for 96-inch Twinkies, and who can see a bit beyond two years into the future!

Speaking of similar approaches for 96-inch TC engines, as mentioned, there are virtually no offerings of factory hop-up parts targeted to that current production displacement. Since adding inches is, in some fashion or another, practically the only game one can play with these engines, the logical question is, “Which fashion”? After all, there are factory kits to make your 1584cc into 1690cc or 1800cc, or even slightly more than 1850cc. But, for a change, let’s look at it in terms of kits that will make your 62 hp into 85 hp, 100 hp, or more—ignoring displacement, warranties and emissions—in favor of sheer…

…Bang for the buck!

Let’s see: What do you suppose would happen if we just did the usual air cleaner and pipe swap, then merely added a set of “off road” SE Pro Kompressor heads with a SE257 cam set and some pushrods? That $1,200 (excepting labor) should get you notably better results from your 96 inches than you’d get with the Street Legal Stage II kit at 103 inches! Of course, those seven extra inches in the 103-inch kit (if installed by a dealer within the first 60 days you own a new machine) also comes with a warranty, because you are really buying peace of mind. On the other hand, the hopped-up 96-inch is only guaranteed to put a huge grin on your face for years to come. In the end, those who want to spend money on power increases will find various paths (based on different motivations) that generally involve increasing volumetric efficiency, regardless (or inclusive) of displacement or the strings that might be attached.

Should you choose to cut those strings altogether, you could have it all and go—really go—with “race” kits in either 110-inch or 113-inch configurations. They’re certainly not cheap, but these kits attack power in­creases on both fronts (size and VE) very successfully. Either of those two choices gets you approximately 50 percent more torque and nearly 90 percent more horsepower—out of a mere 20 percent more displacement! (Proving to some degree, I hope, that increasing efficiency should be priority one and adding inches to that accomplishment, an augmentation to get you the last of the best your engine can offer.) That’s also the top of the food chain for genuine Harley bits as well. (You see where this is going?) I mean, sure there’s 120-inch and even 131-inch options in the self-same SEPRP catalog, catering to the precious few for whom too much is barely enough, but they are not Harley engines any more than an S&S engine is. JIMS motors are simply the “horses” the factory chose to back, since I doubt they could buy S&S, and there’s nothing wrong with that. But let’s be clear about the fact… and one other.

There comes a point when you need to determine whether the best value in your pursuit of extra ponies is to “massage” the power plant that came with your scooter (in one or the other of the ways we’ve just discussed) or simply pull it, put it on eBay and opt for a so-called crate motor. There’s a law of diminishing returns at work when modifying any mass-produced street motor. They are not a totally blank canvas upon which you can paint any power fantasy you desire. There are limitations and com­promises to any design intended to please all the people most of the time, or even most of the people all the time. Worse, if you don’t plan ahead, before you know it you’ve spent more than a crate swap would cost on an engine that won’t ever offer the same bang for the buck. Pleasing your individuality might just take a real race motor, engineered as such from the ground up. By then, you’re no longer doing it by the book… let alone the SEPRP catalog. That “stage” in the proceedings is where JIMS, S&S, TP Engineering and others come in and, sadly, Harley gets left out.

One comment

  1. Well I will have to be honest about my 98 fatboy I have ridden a harley since i was 16 i am 62 , i bought this thing from a woman whos husband died she said he just bouight it took it to the shop spent about 2000.00 on it and it is supposed to haul ass i have a 89 rp evo when i first rode it didnt impress me , i live in the high country near tahoe so the straights and air are not good till you go to the valley. after i figured out how high geard the fat boy was then i was imporessed i let a good friend get on my rp and he can ride to. and we raced im on the fat boy and out of the whole i think he was at least 30 yds and in 3rd gear before i hit second then i started catching hiem at the top end i was ahead past a hundred about the same distance30 yards but the thing really came on and if it was geard different it would really be quick i raced a brand new 103 inch same thing he smoked me for a smaller second and i was gone the thing has the sand s cam and heads and it has 105 thousand miles on it and i love it


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