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Don't let the Harley heat monster ruin your riding.
Reduce  Engine Surging
Improve Throttle Response
Reduce Engine Ping


HD 2007/2008 Engines

High Heat on 2007/08 HD engines

HD 2007/08 Performance Recommendations

Cool your exhaust temperature with the Wide Band O2 upgrade for 2007/08 HD

Harley Camshaft Specification Tables

HD Twin Cam Engine Builds
TC 128 HP 95 CID
TC 100HP Street Engine

The basics of Fuel Injection explained

Rammer Performance Air Cleaners
TC Performance Heads 100+HP

Pro Tuning on a Shade Tree Budget


How to build a High Performance Shovelhead Engine

The following information for building a high performance Shovelhead engine was discovered in the archives of a Harley-Davidson dealership.  The list of modifications has been attributed to the HD Engineering Group responsible for XR-750 development in the late 70's or early 80's. While it is probably not possible to validate this claim, some of the ideas presented in the modification list are very interesting. Many of the recommend modifications are closely aligned with performance work being done in the 90's, not 1970's technology as practiced by many Shovelhead mechanics.

This does lead us to the conclusion that the originator of this document was familiar with advances in air flow technology as practiced by engine developers like Colin Chapman (Lotus Formula 1 racing, Cosworth Engineering) in the 60's. It is an interesting footnote that the concept of high velocity port design did not make it to mainstream Harley-Davidson performance engine modifications until the mid to late 90's. This Shovelhead modification document distinctly shows "D" shaped ports, optimized for high velocity over the more popular "bigger is better" philosophy that was used then, and unfortunately is still used today.

At least one Shovel engine has been built using many of the ideas present here, with excellent results. As a favor to the Shovelhead fans that frequent the Nightrider Performance Site, the original text and drawings are being presented. Changes used in the current Shovelhead engine build are also noted.

 With modification like this, it is quite possible for a Shovelhead engine to run with the EVO and Twin Cam engines.  We hope you find the information helpful.


Area to be Modified Original Modification Description Current parts
Compression Ratio 9.5:1 9.5:1
Pistons by JE, Wiseco or Keith Black
Cylinder Stock bore to be shortened. See figure 2.
3 5/8" bore standard length
Squish Band Clearance .040" to .050". See figure 1
Piston To be machined per figure 1 and figure 4.
Piston to cylinder clearance to be set at .002"
Keith Black Pistons
Clearance .002" to .003"
Camshaft Sig Erson #274 HLH

Valve lift .525" @ .053"
Intake Open 8 degrees BTDC
Intake Close 36 degrees ABDC
Exhaust Open 41 degrees BBDC
Exhaust Close 7 degrees ATDC

This cam is not available.

V-Thunder SHV-4020
Ignition Timing 36 to 38 degrees BTDC With Crane HI-4 ignition module.
Valve Springs Spring load at full lift to be 335 lbs. STD Heads
Valves Manley thin stem FL valves
Valve Head Diameters
1 15/16" intake
1 3/4" exhaust
Valve Stem Diameters
5/16" intake
11/32" exhaust
STD Heads
Valve Guides Use XR-750 intake valve guide with seal
Use Branch or Manley exhaust valve guide. No seal.
STD Heads
Valve Spring Collar Use Branch upper and lower. Lower collar must be modified for valve stem seal clearance. See figure 8
STD Heads
Cylinder Head Machine squish band per figure 3.
Intake port to be welded in per figure 6.
To compensate for reduced port height, intake port must be widened around the valve guide area per figure 5.
STD Heads
Air Filter Modify existing air cleaner filter back per figure 9.
Exhaust System Use 1977 collector muffler. Header pipes to be interconnected 15" from muffler with a 3/4" I.D. tube. 2-1 Exhaust system like SuperTrapp
Carburetor Modify the standard Keihin carburetor by boring to 40mm (1.575"). Use 185 main jet and a 100 idle jet. Use main fuel nozzle per figure 0.

If the float bowl has been for accelerator pump bypass, the bypass must be closed off.

Keihin 40mm CV
S&S Super E
Other modifications Exhaust pipes and intake manifold will have to be modified as a result of the lower cylinder heads. The cylinder head bolts may have to be shortened by 1/8" to prevent them from bottoming.  


Table of Contents
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Modification, Installation, Maintenance and Tuning Index  will help you find most of the information you want on one page.

How to get Professional Tuning Results at home
Testing the Innovate Motorsport LM-1 portable air fuel meter

Profession Tuning on a Shade Tree Budget

Veypor VR2 Data Logger and Instrument Panel
Video Installation and Demo
Purchase VR2

Engine Performance
How to Build a
TC96 2007 Engines
TC88 70HP Stage1  
TC95 128HP Stage 3
TC95 100HP Street
TC96 2007 Stage 1/2
EVO 64 HP Stage 1
EVO 74 HP Stage 2
EVO 82 HP Stage 3
EVO 95 HP Stage 3
883 to 1200 Upgrade
Shovelhead Modifications

New EFI for EVO and TC

Performance Gallery
Horsepower Gallery
Evolution 80
Twin Cam 88/95
Evolution Unlimited
Sportster Unlimited
Drag Strip Gallery
Land Speed Racing Gallery
CV Carburetor
Modifying the CV carb
Tuning a CV carb
Selecting a cam
Install a TC 88/95 cam
Install a Big Twin cam
Install Sportster cams

Camshaft Specifications
Twin Cam

Exhaust Systems
EVO Exhaust Testing
TC Exhaust Testing
Khrome Werks AR100 test
Making Drag Pipes Work

Shop Manual
Carburetor Troubleshooting
Finding Manifold Leaks
Cylinder Heads
Pistons and Cylinders
Belt Drive
Shop Manual Appendix
$20 Bike Lift
Plug Wires
Spark Plugs
Engine Tuning
Nitrous Oxide
Motor Oil
Stutter Box
General Information
WEB Links
Buy Books and Manuals
Performance Calculations
Estimate Horsepower
Estimate 1/4 Mile Time
Estimate Top Speed

Engine Displacement
Exhaust Length
Gear Ratios
Air Density

The Nightrider Diaries
The ramblings of a genius a, a madman and something in between.

Where is Sifton Cams?

Autocom Active-7 tested

Harley-Davidson EFI
-EFI basics explained
-EFI modifications explained

183 HP, 2 carbs, 2680cc

Copyright 1997-2006  Stephen Mullen, Oldsmar, FL -+-