750 horsepower question - Honda Shadow Forums : Shadow Motorcycle Forum

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Old 06-30-2011, 07:25 PM   #1 (permalink)
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Default 750 horsepower question

I admit to being ignorant when it comes to mechanical issues so I thought I would ask the experts. I was reading that the 750cc Harley XR750 engine produced about 90 HP. I also read that the 750cc engine in my Shadow produces about 40 HP. I know the Harley was a racing bike but how can two engines of the same size produce such drastically different amounts of HP? Also are their techniques to increase HP in the lower HP engines?
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Old 06-30-2011, 08:53 PM   #2 (permalink)
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Riddle me this, my 1985 VT1100 reportedly makes around 74 HP. From 1987 forward, Honda detuned them to produce around 55 HP. How? Don't know the mechanics of it but I am willing to bet as to the why.
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Old 06-30-2011, 08:57 PM   #3 (permalink)
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I think back in the day they used different criteria to measure horsepower. My 1100 is more powerful than the 700 I had, maybe not by 15hp or so, but it's a solid 10hp more. According to specs, it's only 4hp more. Also, most dyno graphs for Harleys seem to be off modded bikes. A factory 1200 Harley is only putting out about 75hp. Ironically, that's the same amount as a Shadow. Granted, Harley has more performance parts it seems, but still, any of those items can be mounted onto a jap bike.
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Old 06-30-2011, 09:02 PM   #4 (permalink)
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Intake design and flow, valve size, exhaust flow, compression...lots of variables. Also, does it make the horsepower only at a certain RPM range? An engine can have a lot of HP and very little torque. I think if we could see the detailed engine specs side by side we could figure it out. There are ways to increase HP, the most common way is to get the engine to more more air through it from the intake through to the exhaust.
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Old 06-30-2011, 09:08 PM   #5 (permalink)
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my 2000 XR650R has 68 HP in stock trim from a Sgl Cyl liquid Cooled 4 stroke and the full race versions get bumped up to 80 hp.The Compression Ratio is 10.6 to 1 stock and will throw you over the bars if you arent careful trying to start it.
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Old 06-30-2011, 10:16 PM   #6 (permalink)
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I saw on the internet where the newer VTwin 750 engine peaks at 37 HP.

This was a dyno run on a complete stock Aero.

The older 4 cyl 750's had much more power.
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Old 06-30-2011, 10:46 PM   #7 (permalink)
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Highly stressed engines are not as reliable.
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Old 06-30-2011, 11:30 PM   #8 (permalink)
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Quote:
Originally Posted by dismaltrader View Post
I was reading that the 750cc Harley XR750 engine produced about 90 HP. I also read that the 750cc engine in my Shadow produces about 40 HP.
...... how can two engines of the same size produce such drastically different amounts of HP? Also are their techniques to increase HP in the lower HP engines?
In 1996 (and many other years), the Honda Magna made 87 hp from a V-4 750 cc engine. It also had a compression ratio of 10.8 : 1 The cams are much more radical. It has 4 carbs to feed the beasts thirst. Timing actually has some advance to it.
These are conditions that your 40 hp Shadow vt750 doesn't have. Instead your compression is 8:1. The cams are mild and conservative with very little overlap. The timing has very little advance. You have a single carb that is jetted lean for emissions. If you would like to make hp, install 10:1 pistons, radical cams, ignition computers set up to advance the spark, carbs with rich jetting and large capacity to deliver the mix. (Or better yet, FI.) Etc.
My 83 VT750C made 66 hp off the show room floor. If you duplicated it's specs, you could easily have 70 hp to play with. Look up Honda VT750 custom
AFT customs will be happy to fix you up with some HP. AFT Customs Metric custom bikes choppers and motorcycles. Metric choppers

Highly stressed engines aren't as reliable. Agreed.
BUT.... they are a He11 of a lot more fun!!

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Old 07-01-2011, 07:27 AM   #9 (permalink)
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The trend in HP went down as the trend for better "sound" went up.

My 1986 Shadow 700 has more power than the modern 1100s. This is because in 1986, Honda was designing bikes for performance. It turned out that the American market better preferred bikes that sounded better, so Honda de-tuned the engine, change the intake and exhausts, changed the compression ratios and engine timing so that you have a bike that sounds more powerful, yet makes less power.

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Old 07-01-2011, 08:41 AM   #10 (permalink)
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The 1996 Harley Wide Glide only had 57 hp out of its 1338cc motor in 1997 the VT750 C2 Shadow had 88 hp then in 1998 the VT750 C2 had 43hp
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