Depends on the year and displacement — a carburetted 88" puts about 57 HP to the rear wheel, a 96" about 65, and a 103" right around 70. Cycle World strapped a bone-stock 103" Softail Deluxe to a Dynojet and got 70.9 HP / 87.2 lb-ft. Harley leaves a lot on the table for emissions and noise: that same 103" with a free-flowing air cleaner, a 2-into-1 and a tune makes about 79. That's why Stage 1 is the universal first step.
Free-flowing air cleaner, exhaust that actually breathes, and a fuel tune to match. Done right it's worth 10–15% — a true 2-into-1 with a proper dyno tune can push toward 20 — on a 103" that's roughly 8–11 HP, putting a good Stage 1 near 80 at the rear wheel. On a carbed bike the "tune" is a re-jet — which this calculator gives you for the CV40, HSR series, and S&S carbs.
The cam that matches your displacement, heads, compression, and how you actually ride. A big cam in a stock-head 88" is a waste of money. This tool carries 31 grinds calibrated against published dyno data — build your combo and compare curves. Torque at 2,500–4,000 RPM is what you feel on the street, not the peak number.
Once you're past bolt-ons and a mild cam, stock heads become the cork. Ported heads or good aftermarket castings let a bigger cam actually breathe. The calculator's 14 head options show you when the heads become the limit — watch the curve flatten up top with stock heads and a big grind.
If your Twin Cam has spring tensioners — any year, any model — switch them to hydraulic. The spring tensioners suck; that's the whole story. Gear drive sounds tempting, but it depends on crank runout: gear drive needs runout under 0.003", and most stock cranks with miles on them exceed that, unfortunately. Measure before you buy gears. And don't build a 100+ HP motor on worn tensioner shoes.
The stock CV40 supports more power than most people think — jetted right, it'll generally carry a build to about 90 HP before it becomes a noticeable airflow restriction. A well-tuned, heavily modified CV40 can push to a hard cap of around 100–105 HP on a maximum-effort build, but venturi velocity drops off badly at that point, which is where a larger flatslide like the Mikuni HSR42 (or 45/48, or S&S Super E/G) earns its keep — more top-end power and crisper throttle response. The calculator jets all of them — main, pilot/intermediate, needle position — for your combination, elevation, and temperature.
Big bore kits are one of the best dollars-per-HP moves on a Twin Cam, but compression, cam, and tune have to come along for the ride. The calculator covers the TC88, 95" SE big bore, TC96, TC103, 107" and 117" big bores, the CVO 110, and the 124" stroker — punch your kit in with your cam and heads and see the whole picture before you buy.
No — and that's on purpose. Twin Cam (1999–2017), Milwaukee-Eight, and Evo are different platforms with different heads, cams, and parts that do not interchange. This site is Twin Cam only; m8dyno.com covers the M8 Gen 1. Mixing platform parts data is how people buy the wrong cam.
Calibrated against two independent published dyno runs on a 103" — Cycle World's bone-stock Softail Deluxe and Fuel Moto's 20-cam shootout — and good to about ±4.8 HP on known combinations. But it says it right on the chart: estimates only — actual results vary. It's built to compare combinations honestly, not to flatter parts.
McGonster Monster Motors LLC (“MMM,” “we,” “us”) operates twincamdyno.com as part of the MMM tool network (with mcgonster.com and related domains). This policy explains what information we collect, how we use it, and the choices you have.
The calculator on this site runs entirely in your browser. The engine, part, and jetting selections you make are not tied to your identity and are not stored on our servers.
If you contact us directly (for example, by email), we collect whatever information you choose to include, such as your name, email address, and message.
We use privacy-focused web analytics (such as Cloudflare Web Analytics) to understand aggregate traffic — pages visited, general location, device type. Our analytics does not use tracking cookies or build a profile of individual visitors. Cookies used for advertising are described in the Advertising section below.
We use Google AdSense to display advertising on sites in the MMM network. Third-party vendors, including Google, use cookies to serve ads based on your prior visits to this website or other websites. Google's use of advertising cookies enables it and its partners to serve ads to you based on your visits to this site and/or other sites on the Internet.
You may opt out of personalized advertising by visiting Google Ads Settings, or opt out of some third-party vendors' use of cookies for personalized advertising at www.aboutads.info/choices. For more information about how Google uses data when you use our partners' sites, see How Google uses information from sites or apps that use our services.
Visitors in the European Economic Area, the United Kingdom, and Switzerland are shown a consent message and can choose whether to allow cookies for personalized advertising.
Some links on this site are or may become affiliate links through retailer affiliate programs (such as those operated by eBay, Amazon, Summit Racing, JEGS, and J&P Cycles). When you click one of these links and make a purchase, we may earn a commission at no additional cost to you. Clicking an affiliate link may set a cookie or tracking parameter on the retailer's site so the purchase can be attributed to us — this is handled by the retailer, not by MMM directly.
If you choose to enter your email address in the optional newsletter signup (for example on the printable dyno sheet), we use it only to send you McGonster Monster Motors updates — new tools, build guides, and site news. Signups are delivered to our inbox by FormSubmit (formsubmit.co), which processes the form submission on our behalf. We do not sell or share your email address with anyone, and you can unsubscribe at any time by replying to any newsletter email or writing to mcgonster@gmail.com. Printing a dyno sheet never requires an email address — the signup is entirely optional.
We use information to operate, maintain, and improve the tools on this site; to respond to messages sent to us directly; and to understand aggregate site traffic. We do not sell personal information, and we do not share it with third parties except as required to operate the site (such as our hosting, analytics, and advertising providers described above) or as required by law.
This site is not directed at children under 13, and we do not knowingly collect personal information from children.
We may update this policy from time to time. Changes will be posted on this page with an updated “last updated” date.
Questions about this policy? Email us at mcgonster@gmail.com or use the contact form on mcgonster.com.
These Terms of Service (“Terms”) govern your use of twincamdyno.com, operated by McGonster Monster Motors LLC (“MMM,” “we,” “us”) as part of the MMM tool network. By using this site, you agree to these Terms.
The calculators and tools on this site are free to use. There are no paywalls and no account required.
All horsepower, torque, jetting, and other outputs from our tools are estimates based on physics models and published dyno data. Actual results vary based on your specific engine, components, tuning, environment, and build quality. These tools are for informational purposes only and do not constitute professional mechanical advice. MMM is not responsible for mechanical damage, injury, or other loss resulting from the use of information provided by this site. Always follow manufacturer specifications and consult a qualified mechanic for your build.
This site links to third-party retailers such as eBay, Amazon, Summit Racing, JEGS, and others, in some cases through retailer affiliate programs. We may earn a commission on qualifying purchases made through these links, at no additional cost to you. We do not control, and are not responsible for, the content, pricing, availability, or policies of any third-party site you visit through a link on this site.
Sites in the MMM network display advertising served by Google AdSense. Advertisers are third parties; an ad appearing on this site is not an endorsement by MMM of the advertised product or service.
MMM is not affiliated with or endorsed by Harley-Davidson, Harbor Freight, Honda, Holley, Edelbrock, or any other manufacturer or brand mentioned on this site. All brand names and trademarks are the property of their respective owners and are used for identification purposes only.
This site and its tools are provided “as is,” without warranties of any kind, express or implied, including but not limited to accuracy, reliability, or fitness for a particular purpose.
To the fullest extent permitted by law, MMM is not liable for any direct, indirect, incidental, or consequential damages arising from your use of this site or reliance on any information it provides.
We may update these Terms from time to time. Continued use of the site after changes are posted constitutes acceptance of the updated Terms.
Questions about these Terms? Email us at mcgonster@gmail.com or use the contact form on mcgonster.com.
