Harley-Davidson Twin Cam performance upgrades

Twin Cam overview

All of our upgrades are offered as well developed parts combinations that are known to interact correctly. This is based on continuous R&D, both on our dyno and on over 100,000 miles of real world riding with the 6 Twin Cams that we have owned since their release in 1999.

This includes two Dynas, a Softail, and three Glides, all of which were modified in some way, so we have a good cross section of experience across the model range. We also listen carefully to feedback from our customers, and work closely with our parts suppliers, particularly Head Quarters who we have dealt with for 20 years.

Head Quarters parts used in a Twin Cam 95 inch conversion with cams and stock cylinder heads

Head Quarters parts used in a Twin Cam 95" conversion with cams and stock cylinder heads

click here for a dyno graph

The reason that we don't offer more parts combinations from other suppliers, is because our experience has proven what works. What is the point (for example) of having an engine that produces very little torque at lower RPM, has to be revved hard to make a high horsepower number, and then sticking it in an Electraglide that is used for loaded up touring?

In fact, the best way to choose a particular performance upgrade is to be realistic with how you personally ride and what you want to achieve. We are happy to discuss this, and then recommend one of our packages that will suit. Everything that we offer is based around, not just performance, but driveability and long term reliability.

Head Quarters forged pistons are the best available, at any price.

Head Quarters forged pistons are the best available, at any price. Using components of this quality has a major influence on long term reliability

Cost is also a consideration, and this may be the deciding factor. We won't try and oversell the bigger builds to those who don't need them. In fact our 107" Sport Touring conversion with HQ heads, which was designed for the Twin Cam 96, is a classic example of a lot of "bang for the buck". This upgrade produces 120 ft/lb of torque, 110 hp, works with the stock throttle body and injectors, utilises the original cylinders bored out, and doesn't require the engine to be removed from the frame. Neither does it require an aftermarket battery or starter motor.

This excellent value conversion works with all of the Dyna, Softail, and FLH range of bikes, including the Drive By Wire versions.

Since we are a workshop based business, as well as a parts supplier, we can obviously do all of the required installation work, as well as any machining that is required. Correctly tuning the bike is also of paramount importance, and this presents many difficulties for the inexperienced, particularly now that everything from Harley is now fuel injected. We are an Authorised Direct Link Flash Tuner Tuning Centre and experience with accurately dyno tuning the EFI models allows us to offer any of our Harley performance upgrades as a "turn key" package. Drop the bike off, and then pick it up completely done, including "break in" on the dyno under controlled conditions, and fully tuned.

Twin Cam stage 1. Exhaust, air cleaner, and fuelling modification

The stock exhaust and air cleaner are relatively restrictive from a performance point of view, and are also often changed for noise and cosmetic reasons. Prior to Harley switching to Electronic Fuel Injection, these upgrades could be done relatively cheaply with just the addition of slip on mufflers, an air cleaner , and a jet kit for the standard CV carb. Now that everything is EFI, this basic Harley performance upgrade has become a bit more involved, as we now also have (depending on model and year) oxygen sensors, catalytic converters, an active intake valve and an active exhaust valve to deal with. Our Direct Link Flash Tuner tuning software allows us to remove any of these, if required, and reprogram the ECM so that the bike both runs correctly, and doesn't register a fault code. When we use slip on mufflers we can also program the active exhaust valve to remain open at all times.

Whilst the stock air cleaner element is restrictive, this is also true of the air cleaner box, as it also has to reduce intake noise. We change the whole assembly to achieve the best result, and often these air cleaner upgrades can reuse the stock cover, which helps keep the price down.

Exhaust systems have a massive influence on the way air flows into the engine at different RPM levels and throttle openings. The way we need to tune a "brand X" pipe is not the same as the requirements of a "brand Y", so an EFI download for one system is often completely wrong for another. Even identical combinations invariably require "tweaking" the maps to achieve acceptable driveability.

Many exhaust choices are based on looks and noise, which is very subjective. However, the fact is that many systems do not work well, either they don't make the power expected or they cause large holes in the torque curve and driveability issues. Noise does not always equal power!

For the carburettor models we use the Head Quarters jet kits and the standard CV carb. This is exceptionally cost effective and works very well. Rather than splash out on a bigger carb (which isn't really needed), the extra money would be far better spent installing better camshafts.

It would be easy for us to claim that a simple "Stage 1" can be done without the need to spend more money on correctly tuning the bike (we'd certainly sell more parts that way)! However, we would prefer to maintain our high level of customer satisfaction.

2010 FLHT Stage 1 using Supertrapp chrome Supermeg, Ness Big Sucker, and dyno tuned

2010 FLHT Stage 1 using Supertrapp chrome Supermeg, Ness Big Sucker, and dyno tuned here with Direct Link Flash Tuner. The 2010 FLs use a new software level in the ECM and require a different tuning method. We are right up to speed with this

It is our experience, as well as that of other top engine builders and tuners in Europe and North America, that the Supertrapp 2 into 1 Supermeg is, in many cases, the best all round exhaust system for street use. This system yields consistently good results, both in terms of overall power and driveability. We can tune with the pipe, not have to try and tune around it. These systems also work well at the higher performance levels, so it is not necessary to change the exhaust if you subsequently make further performance upgrades. They are not excessively noisy, which is an asset for those who do a lot of touring, and when it comes to MOT time.

We accept that not everyone likes the looks of a 2 into 1, so we are also continuously experimenting with other styles of pipes. Please call or contact us for further information regarding alternatives, as this will always remain fluid. We won't sell you something that doesn't work.

One of the new 2010 Dyna Wideglides One of the new 2010 Dyna Wideglides One of the new 2010 Dyna Wideglides

Three of the new 2010 Dyna Wideglides, each done a different way. As well as the excellent Supertrapp Supermeg, we have been experimenting successfully with the Freedom performance pipes. Although loud, they work very well, unlike most other pipes of a similar style, which cause a dip in the torque curve. Each of these fuel injected Harleys required individual dyno tunes with Direct Link Flash Tuner, because of the influence of the different exhaust and air cleaner combinations

Twin Cam "Bolt in" Camshafts

In terms of overall power increase, changing to the right cams yields a better result than a big bore conversion done without cams. Camshaft design is both an art and a science, and the correct choice, for the type of Harley and it's intended use, is paramount. At this level "bolt in" cams are used. This term is used to define camshafts which will install without the need to change the valve springs, or perform any valve to valve, or valve to piston clearancing.

2010 Fatboy

This 2010 Fatboy came straight here for modification before it was even registered! Still 96", it now has Teflon coated Supertrapp Fat Shots, Doherty air cleaner and Head Quarters 500 bolt in cams. We then carried out the break in, and Direct Link Flash Tuner EFI tuning, on the dyno. This cost effective, and rideable upgrade produces 90hp and 97ft/lb of torque

For the Twin Cam 88, 99-06 (except 06 Dyna) we use the Head Quarters 0034 grind. For the Twin Cam 96, 07-current (and 06 Dyna) we use the Head Quarters 500 or 525. These give no loss of torque at low RPM and a very strong mid range pull, as well as good top end power. All of the Head Quarters cams, including the high lift grinds used with ported heads, are gentle on the other valve train components. It's important to remember though, that some exhausts can interact badly in some areas with any camshaft upgrade, so exhaust choice is also a factor. An exhaust that puts a hole in the torque curve at the stage 1 level will likely cause more noticeable issues here. Once again the Supertrapp Supermeg remains the prime choice.

Head Quarters Twin Cam bolt in cams and upgraded cam bearings

Head Quarters Twin Cam bolt in cams and upgraded cam bearings

As far as installation is concerned, we always change the inner cam bearings for the more durable Torrington bearings, and unless the engine is very low mileage, we will also install new lifters. We don't want comebacks, and this way we don't get any. Please take account of these extra parts and labour costs when comparing our package prices with those who choose to ignore this essential step.

These cams have stock diameter base circles, so adjustable pushrods are not a requirement. However, installation does require rocker arm removal. As an alternative we can use Head Quarters Easy Install pushrods. These have a wider adjustment range than regular adjustable pushrods, and can be installed by cutting out the old rods and installing these without having to remove the rocker arms. They also require some of the pushrod tube parts to be changed in order to get access to the adjusters. Whilst this adds to the parts bill, it subtracts from the labour cost. The key advantage, however, is that the adjustment facility can be used to fine tune the preload on the lifters.

Head Quarters upgraded bearings etc

As well as upgraded bearings, correct camshaft installation also benefits from adjustable pushrods, different tubes, and the best lifters available, the HQ Black Ops

Twin Cam big bore conversions

The next stage is a capacity increase, and unlike it's Big Twin predecessors, this can be done to a useful degree without removing and stripping the engine to bore the crankcases for larger cylinders, or the installation of a longer stroke crankshaft. Both the Twin Cam 88 and 96 utilise the same cylinders and Harley sell bored out versions of these which give 95 and 103 cubic inch respectively. Many shops choose to install new cylinders, but since we have a machine shop, we bore and hone the existing Twin Cam cylinders to the new size. This has the dual advantage of costing less and also being more accurate. A rather rare, "win win" situation which also represents better value. We also bore these cylinders even larger to give 98 and 107 inch conversions using Head Quarters pistons. It is now well proven that these cylinders are strong enough and stable enough to accommodate this extra bore increase.

Primarily these conversions give us more torque, and because the top end of the engine has to come apart we can also tailor the compression ratio to the camshaft choice and ensure that the quench (sometimes called squish) is at it's most efficient, which is far from the case with a stock engine. With stock cylinder heads, these conversions work well with the Head Quarters bolt in cams which also give a big improvement in horsepower.

One of our Harley Twin Cam big bore conversions using Head Quarters parts

One of our Harley Twin Cam big bore conversions using Head Quarters parts and stock Harley cylinders bored and honed here

Twin Cam Head Quarters cylinder heads

It is our view that these are the best heads available for street ridden Harleys. Using OEM castings as a base, the workmanship, design and build quality of these heads gives a service life in excess of anything else available. Whilst many alternative offerings use substantially oversize valves and ports to try and give high peak horsepower numbers at high RPMs (often at the expense of part throttle driveability and mid range torque), these heads feature intelligently shaped ports and moderate valve sizes.

This approach achieves the flow gains by virtue of high port velocity. The up side of this is a very high and fat torque curve that starts low in the rev range. What this equates to in the real world, is a Harley that is very tractable at low speeds in heavy traffic, yet blisteringly quick and responsive at all throttle openings. Used in conjunction with Head Quarters cams, which are designed to take advantage of this high velocity porting, we can build a number of engine combinations designed to suit any street use from a heavily laden Glide to a hot rod Dyna. These very tuneable combinations are suitable for both carburettor and fuel injection applications. At this level, we can use the higher lift Head Quarters cams, with the cam choice made to suit bike weight, gearing, compression ratio, and it's intended use.

These Head Quarters ported cylinder heads for the Harley-Davidson Twin Cam engine are used in our higher performance upgrades

These Head Quarters ported cylinder heads for the Harley-Davidson Twin Cam engine are used in our higher performance upgrades. They are designed to produce high torque at part throttle as well as good peak torque and horsepower numbers. The use of manganese bronze valve guides, one piece stainless steel valves with hard chrome stems and stellite tips, and spring kits with titanium top collars, coupled with accurate machining and stock valve stem protrusions, give a longevity far superior to the standard heads.

Component parts of one of our 107

Component parts of one of our 107" builds for the Harley-Davidson Twin Cam 96. The cylinders are stock Twin Cam, bored and honed here to suit the Head Quarters pistons. This is the largest we can go without removing the engine from the frame and generates an exceptional torque curve. The stock throttle body and injectors can be reused. As this only requires the top end to be removed and the cams changed, the labour content is no different to any other Twin Cam conversion such as the 88-95 and 96-103. Competent tuning, at this level, is mandatory. Click here to view the dyno graph.

Twin Cam bigger bore and stroker conversions

The next stage is to increase the capacity beyond what can be achieved by simply boring the existing cylinders. These larger Harley performance engine builds require the engine to be removed from the frame and completely disassembled, which obviously has an impact on the labour charge. For larger cylinders (we primarily use modified Screaming Eagle 4.060 bore cylinders), the crankcases must be accurately bored to accommodate the larger spigots. 2003 and later cases also require converting back to the, stronger, drive side Timken bearing, which better supports the crankshaft. Both of these essential operations are done here in our machine shop. For the Twin Cam 96 we build 113" engines with the stock 4 3/8 stroke crank, and 120" engines using aftermarket 4 5/8 stroke cranks. The Twin Cam 88 requires a new aftermarket crank for both of these builds.

We can also use these cylinders and custom made pistons to convert the Twin Cam 88 to 104" with the stock 4" stroke crank. These larger builds also require our Head Quarters ported heads.

The workmanship and thought that has gone into these kits, together with a precise tune, ensures excellent driveability, exceptional performance, and long engine life. Our 113" is arguably the nicest motor for the heavy Glides yet developed.

2007 Streetglide

2007 Streetglide with one of our 113" (1850cc) conversions, being broken in and tuned on our Superflow cycledyn dyno

Harley-Davidson Screamin Eagle 120R

We are already involved with this new "race" engine from Harley-Davidson. We can build these a number of ways into existing crankcases, including an uprated version with Timken bearing conversion and a plugged and welded crank. Or we can supply, install, and, most importantly, correctly tune the crate motor. Please be aware that a number of other components must also be upgraded, including the throttle body, injectors, clutch and compensator. Also, at this level, the correct air cleaner and exhaust choice is essential. Please be guided by our experience. Tuning is the key to getting acceptable driveability from these engines.

SE 120R motor installed here in a 2010 Fatboy

click here for a dyno graph


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