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V-twin Tech: 95 Conversion

Rider Magazine
January 25, 2006
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Current stock Harley-Davidson Twin Cams have enough power for most uses, but not “more than enough.” More than enough is what most riders want, and that’s what we’re offering here. We’ll show you how to get a very real and very useful 33 percent or more gain in performance at low cost, without exotic modifications, with no loss of reliability and without the use of Harley-Davidson parts or services.

There are about 650 Harley dealers in the United States, and about 5,000 non-franchised shops that work on Harleys. A majority of Harley owners get their service and modification work done by these non-franchised shops. Some of the very best performance work is done in such places.

These shops find it difficult and relatively unprofitable to buy their parts from Harley dealers. Besides, some of the best engine parts aren’t necessarily offered by The Motor Company. The most important element of a successful engine build is the mechanic. If you have one whose skill you trust, then you have the person you need to build your 95-inch Twin Cam Torquer. Never mind where they hang their hat.

Even though many riders who want a 95 conversion turn to a professional for the build, many will choose to do this work themselves. And why not? All it takes is a little mechanical know-how, some patience and the instructions detailed in this story (and a service manual, of course). With this in mind, we present enough information to do this job in your garage. Besides, while someone else may do the conversion, it’s always good to know what’s involved in making a 95-inch torque motor.

This is an unusual hop-up article because it emphasizes midrange performance and ignores the peaks (torque and horsepower). We’re not after maximum peak horsepower. Our intention, instead, is to show you how to build a practical engine, an engine that does its best work under the conditions almost all of us consider normal riding.

If you choose to build it, you will have one of the finest street or touring engines it’s possible to own. I am confident that you’ll agree with this bold statement after you ride your Twin Cam motorcycle with the modifications we suggest. Many hundreds of other Harley owners have built such an engine, both Evo and Twin Cam, with great success.

Reality Check

You, I and most of the folks we ride with do not race their Harleys. We spend the great majority of our time cruising in top gear with our engines turning between 2,500 rpm (60 mph) and 3,500 rpm (85 mph). Even when accelerating onto an interstate or freeway, most riders seldom rev their engines past 4,500 or 5,000 rpm. The occasional friendly roll-on generally starts in top gear at 60 mph or so and ends by the time we reach 100 (4,100 rpm in top gear). Think about it-how often, if ever, have you hit the engine’s rev limiter?

How much power a typical Twin Cam engine produces at 6,000 rpm is unimportant. What do you care what the power output of your engine is at six grand if you never turn it past five? I like to think that there are two sorts of Harley power: barstool and useful. Yes, I have a prejudice.

It’s fun to own a bike that has an extraordinary excess of power (say, more than 100 horsepower). Smoking the tire, black streaks on the road, blowing by your friends-these are fun. Talking about such things is even more fun. This, to me, is barstool power. It is more for discussion than actual use. Such infrequently used power is bought at the expense of everyday performance.

Barstool engines generally don’t do well at the rpm we normally ride. They’re off the cam at normal rpm, and respond poorly to throttle input. They may need to be downshifted once or even twice to accelerate briskly from 50 mph in top gear. They’re generally built and tuned to begin doing their best work at rpm we never use-unless racing. They’re less reliable due to the highly stressed valve train and the rpm they must turn to perform well.

Useful Harley engines, on the other hand, are those that have been modified to genuinely increase performance in the rpm range we normally use. If done properly, in fact, such engines have wider powerbands than stock engines. They’re more responsive, they’re smoother running, they retain stock reliability and-this shouldn’t surprise you-they’ll win a top-gear roll-on with a barstool engine every time.

So our 95-inch conversion is a useful engine, at least one-third more powerful throughout the normal rpm range than a stock Twin Cam 88. It’s more responsive to throttle input and its power delivery is smooth and predictable. It’ll make your friends downshift to stay with you in a roll-on.

As explained above, we chose to show you how to build our useful engine without genuine Harley parts. The only thing you need to buy from your Harley dealer is the shop manual. I believe that the quality and design features of the parts recommended in this article are excellent, and they’re what I would use for my own engine build. Best of all, it is simple and cheap to build.

The Parts
Pistons: I strongly recommend that you consider the excellent forged pistons from Wiseco, along with the company’s boring service. Wiseco’s Harley pistons are among the most, if not the most, sophisticated pistons made today. They incorporate the most advanced design features and the most accurate production quality available. The flat-topped 95-inch pistons we used are the result of many hundreds of hours of engineering and on-the-road development.

Wiseco has a boring department that does nothing but fit Wiseco pistons to cylinders. This is what they do for a living, and you aren’t going to find better quality anywhere. The turnaround time is less than a week, not counting shipping time. You may have a very good boring service near you that you can use. However, if you don’t, use Wiseco’s service. Wiseco can furnish and fit the piston kit to the highest standards.

Gaskets: We chose to use the fine coated and/or multi-layer steel gaskets from Cometic. These are the latest in gasket design and have proven themselves to neither leak nor lose torque. The original Evo head gaskets were composite and would crush. This crush, in turn, reduced head-bolt torque and allowed combustion-gas leakage when the engines were not fully warm.

Cometic’s three-layer dimpled head gaskets don’t leak and don’t lose torque. Harley’s Screamin’ Eagle head gaskets are made by Cometic. We chose the 0.030-inch-thick head gaskets for two reasons: to establish a useful squish height at running temperature to reduce the likelihood of detonation, and to raise the cranking pressure of the engine to a reasonable maximum of 190-plus psi for maximum torque and efficiency.

Cams: If there is a single element that contributes the most to the fine performance of this engine, it’s the design of the cams. Exhaust-system design and a free-flowing air cleaner are also critical. But it’s the cam that determines at what rpm useful power begins. Simply put, the earlier the intake valve closes, the lower the rpm at which the engine begins to do its best work. We used the Andrews TW21 cam set, which has an intake-closing angle of 30 degrees. This cam is similar to my original JM20 design also made by Andrews-but no longer available.

Air cleaner: Rick had already fitted a Doherty air cleaner to his bike and I saw no reason to change it. The Doherty-like the Arlen Ness Big Sucker, the Rivera Engineering Smoothie and the new K&N-flows more than enough air to meet our engine’s requirements.

Exhaust system: Exhaust design is an area that’s difficult in several respects. Harley owners demand style in their systems. They also want small mufflers. These two factors alone make it difficult to produce a system that folks want to look at or buy, let alone build one that actually performs well. And, unfortunately, very few owners or even manufacturers understand how exhaust systems work in any detail.

The SuperTrapp 2-into-1 system we used to get our best results is probably the best all-around exhaust available for Harleys today. It combines large volume flow with good wave dynamics. Its closed end cap sends a strong pressure wave back up the pipes to help stop intake-charge loss when the rpm is too low for the closing angle of the exhaust valves. This accounts for the pipe’s strong showing below 3,000 rpm. At the same time, its multiple-plate outlet provides high-volume flow for operation at high rpm. There are well-proven alternate exhaust systems.

The Bassani pipe we tried proved admirable, dropping off only ever so slightly at 2,500 rpm (60 mph). It was a very loud pipe.

The BUB Jug Huggers surprised us all with their midrange performance, nearly mirroring the ‘Trapp and Bassani, although their drop in performance at 60 mph in top gear was fairly substantial. Still, if you prefer the look of twin pipes as Rick does, they’re a good choice.
For touring bikes, a set of Kerker Touring Mufflers with the high-performance (short) baffles works very well in the normal rpm range. In previous testing, I discovered that these mufflers, on stock header pipes, performed almost as well as the SuperTrapp 2-into-1 system. Except for the baffles, these mufflers are the same as sold by Harley. The short baffles, to replace the stuffy Harley version, are available from SuperTrapp, which owns the Kerker name. While these systems have proven themselves to be very versatile, other systems are not so lucky for their designers.

The Hard Krome Side Burners (from Drag Specialties) that Rick had fitted to his bike when we started on the original 88-inch engine with stock cams provided a nice, predictable powerband. However, on the 95-inch engine with the Andrews TW21 cam set, the same pipe had a noticeable drop in power between 2,200 and 3,000 rpm. The difference was the cam. Neither the pipe nor the cam design is at fault-they simply don’t work well together. So if you choose another exhaust, you may not get what you hope for.

You may wish to substitute some of the parts. I urge you not to, as you’ll almost certainly get less performance if you do. This is a good performance package, and the parts are matched. If you change the air cleaner, please make sure it is a high-flow replacement or you’ll lose top-end power. If you must use another cam, please select one that closes the intake valves as near to 30-degrees ABDC (after bottom dead center) as possible.

EFI Tuning
Our modified engine doesn’t require radical tuning changes. Rick’s EFI had the Harley-Davidson Stage II download, and it ran rich in the 20-40 percent throttle range, both as an 88 and as a 95. I suspect it would have been fine with the stock settings. In fact, Rick reported that his original TC88 with the Doherty air cleaner and Hard Krome Sideburner ran perfectly well with the stock OE setting, and that he only installed the Stage II download on the advice of others.
We intend to refine the tuning of his bike with a Power Commander from Dynojet. The Power Commander can be tuned on the side of the road and is a proven product with a good performance history. There are a fair number of tuners who have experience with it.

Carburetor Tuning If your Harley is equipped with the stock carburetor, it only needs the following modifications. First, remove the aluminum plug covering the idle mixture screw and open the screw between one and 1.5 turns. Adjust the screw for best (clean and responsive to the throttle) idle when the engine is warm. Second, fit an early (1988-89) 1200 Sportster needle. Don’t change the main jet, as the stock jet is already two sizes too rich. Don’t fit one of the modification kits-they’re disastrously rich.

As good as the stock carburetor is, a well-tuned Mikuni HSR 45 adds power at all rpm. When slightly modified, Mikuni’s HSR 45 delivers the best throttle response I know. It’s an excellent instrument, and I recommend it highly. However, as delivered, they’re too rich for best results with our 95-inch motor. Purchase the Mileage Kit from Fox Distributing in the Chicago area (630-513-9700) and install it. The kit consists of a smaller idle jet, a leaner needle and a smaller accelerator-pump jet. Instructions are included and installation is easy. Be sure you get the tuning manual with the carb. You can also download the manual from www.mikuni.com. This engine with the tuned 45 delivers about 48 mpg at highway speeds with near-instant throttle response.

Ignition (Carburetor Version) Except for a heavy-touring rig, the stock advance curve set works well, and there’s normally no need to change any of the ignition parts. The Screamin’ Eagle racing module, with its slower advance, might be required for lugging a loaded bagger up the steep side of the Rockies. If you detect any detonation (pinging) under load on a hot day, downshift to reduce the required throttle setting. If the detonation is a common event for your riding conditions, consider the retarded Screamin’ Eagle racing module.

THE PROCESS
Preparation for the Work
Immediately before you start work or deliver your bike to your mechanic, thoroughly wash it. Get all the dirt off any area that’s going to be exposed when you disassemble the engine. Take a look at our first picture and notice that we didn’t really clean our bike and that sand is lying next to the open crankcase. Make sure the work area is clean. By clean, I mean like a paint booth. It’s amazing how many engines lie open in the same room as someone using a grinding wheel, or with the doors open on a windy, dusty day. Remember that Harley engines are very fragile when it comes to dirt and dust because they use roller bearings. Roller, ball and needle bearings are very, very sensitive to dirt. Keep it clean!

Tools and Cautions
You must have a torque wrench, and you need some special tools. In particular, the cam installation depends on several tools that the job would be difficult to do without. The expense of the required tools may equal the labor of having the work done by someone who already has them and is familiar with the work.

If you’re doing the work, clean your tools before you tear down the engine. Get all of the grit out of the corners of the sockets and box-end wrenches. Wash them with soap and water. If someone else is doing the work, gently suggest they wash their tools. Offer to pay extra for this. I’m not joking; dirt is the most common and greatest enemy of long engine life.

Cam installation is touchy in a Twin Cam engine. You need the special tools, and you must follow the procedure in the shop manual. It’s possible to do damage to the bearings if you’re not careful. Even Harley had some difficulties getting it right at first.
Keep all the parts you remove covered. You’re going to have your engine apart for a week or so. Protect them from dust and dirt. I use resealable plastic bags from the grocery store for this purpose. I also write the contents on the bags with a Sharpie marker for convenience. If you’re doing the work yourself, preview the disassembly procedure by looking at your bike with your shop manual in hand. Check and double-check every part and every step. You don’t want any parts left over, and you want them all in the right place.

Disassembly of the Top End
If you have a digital camera, you might consider taking photos as you work. Should there be some confusion about routing cables and wires, etc., during reassembly, you can refer to these photos.

Block up the rear of the bike until the rear wheel is off the floor. Shift the transmission into top gear. You will use the rear wheel to rotate the engine during teardown and reassembly. After removing the seat and disconnecting the battery, remove the fuel tank and any side panels.

You have now successfully disassembled the top-end of your Harley. Clean up the area and prepare to replace the camshafts. It would be a good idea to return all your tools to their proper places, make sure all the parts are covered to keep them dust-free and review the manual’s procedures for removing the cams. Although special tools are required, it’s no more challenging than what you’ve just accomplished.

If you choose not to install the cams yourself, you can assemble your new 95-inch top-end, ride the bike to a shop and have the cams installed. The top end’s assembly will be covered in our next issue, which goes on sale August 22. — Joe Minton ****** Camshaft Installation

A note from Joe about cam installation. The Twin Cam engine has a much more complicated and assembly-critical cam chest than earlier Harley Big Twins. More specialized tools are required, and they’re expensive. Beyond the couple of hundred dollars in special tools, you need a hydraulic press for cam disassembly and reassembly.

Although we’re laying out the entire cam installation here in a simple-to-follow outline, I recommend that you consider having an experienced mechanic install the cams. It would be cheaper than buying the special tools and, well, the job can be touchy, and prior experience is helpful. If you’re determined to do all the conversion work yourself then you should, by all means, buy the tools and learn the job. There’s nothing terribly exotic about installing cams in a Twin Cam engine; the shop manual clearly shows the procedure and you should have no trouble following and learning it.

For a one-time cam change, however, the easier and less expensive method is to have it done by someone with the tools and experience. If you wish to remove and install your own camshafts (and take the cams to a dealer for exchange), here is an overview of the process which, with your service manual in hand, should pose little difficulty. — Joe Minton

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