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Old 11-30-2008, 05:31 PM   #1
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Default MOTOR QUESTION

What is the difference between a 13mm and 14mm crack in a buggy motor. I see some RB and Nova motors have 13mm cranks but most of the new motors have 14mm cranks. I ran a 5 port RB for a while and it had a 13mm crank all my new motors have 14mm cranks. What exactly does the extra mm on the crank do, I would think a 13mm crank would be lighter and the RB ran good with it. Thanks
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Old 11-30-2008, 05:34 PM   #2
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my understanding is that the smaller cranks have a little more abrupt bottom end,but not as much top end,in theory.i could be wrong,but thats my story...
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Old 12-01-2008, 10:02 AM   #3
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What's up all the motor mod people out there dont have a answer!!!!
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Old 12-01-2008, 10:36 AM   #4
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Marcus,

The 14mm obviously has a slightly longer stroke. As the stroke lengthens you could (might) see a bit more torque at the low end... but that will also depend on the port timing, deck height, bubble volume and compression ratio the mfg'r chose. In reality a longer stroke engine is a bit more forgiving to tuning, & I bet that was the mfg'rs ultimate goal for the mill your referring to.

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Old 12-01-2008, 11:58 AM   #5
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Marcus Falconie, Engine collector! How do you not know all about engines? From our conversations I would think you have owned just about every one ever made, lol
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Old 12-01-2008, 04:17 PM   #6
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Originally Posted by Jaz240 View Post
Marcus Falconie, Engine collector! How do you not know all about engines? From our conversations I would think you have owned just about every one ever made, lol
I know it's crazy, I have a bunch of motors by every manufacture out there they all have different bore and stroke the # of ports go from 3,4,5,6, & 7 turbo and std. plugs 13 & 14 mm. cranks and in the end the exhaust still smells the same lol, and out of all the motors I have only 2 stand out the V-spec and the OPS SFV21B and you cant get that in the USA any more but the Radical 621T is close. I know you hate your V-Spec because of the service you got from OS but once you get it running you will love it. They are just so consistant from the start of the race to the end.
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Old 12-01-2008, 04:43 PM   #7
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Originally Posted by chunk t View Post
Marcus,

The 14mm obviously has a slightly longer stroke. As the stroke lengthens you could (might) see a bit more torque at the low end... but that will also depend on the port timing, deck height, bubble volume and compression ratio the mfg'r chose. In reality a longer stroke engine is a bit more forgiving to tuning, & I bet that was the mfg'rs ultimate goal for the mill your referring to.

chunk
14mm refers to the diameter of the cranks barrel, not its stroke. The reason some motors have gone to a 14mm crank is strength. When a good mod'er starts grinding on a crank inlet it can get pretty thin and some were breaking. The added mass can take a little bottom end punch away, though with really aggressive onroad clutch set-ups it can actually give more snap on the bottom.
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Old 12-01-2008, 04:50 PM   #8
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Here's the answer most people are waiting to hear. There are several reasons as to why companies offer the two sizes.

1.) Cost- It costs less to make a smaller crank, not much less but a little less but the main reason for the cost cutting are the bearings. A smaller bearing with smaller balls and races cost about half of what a bigger 14mm ID bearing costs. Thats why most of your economy engines still utilize the smaller crank and bearings. It keeps cost down while still getting a decent performing engine.

2.) Crank Intake Timing and Bore- A larger diameter crank is able to support a bigger center bore combined with increased crank timing which results in increased case and cylinder pack. By making the crank diameter thicker, companies can remove more material without sacraficing the strength and integrity of the material used while still increasing performance demanded by racers abroad.

3.) Larger Bearings- The increased ID of the crank allows the use of bigger balls and bearing races to support the demand of todays engines. As time and technology accelerate, so does engines performance and it is very difficult to increase the engines performance potential without increasing the overall strength and reliability of the powerplant so the larger bearing are utilized to meet those demands.

4.) Stroke- Yes, by increasing the ID, you are able to increase the OD which allows the crank pin to be moved outward increasing stroke resulting in increased torque throughout the entire powerband especially on the bigger block engines that need to push around the heavier trucks, again without sacraficing strength of material.

I'm sure there are more reasons, but after having designed cranks in the past and talking with some of the engine manufacturers, these are the main reasons for the different sizes. Where does it end??? Bigger strokes? Billet Steel or Titanium? Who knows???
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Old 12-01-2008, 06:52 PM   #9
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MY BAD! don't know where my head was Wingracer is correct about the crank sizes.

Guess my A.D.D. got ahead of my fingers agian!

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Old 12-01-2008, 07:32 PM   #10
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Originally Posted by Marcus Falconie View Post
I know it's crazy, I have a bunch of motors by every manufacture out there they all have different bore and stroke the # of ports go from 3,4,5,6, & 7 turbo and std. plugs 13 & 14 mm. cranks and in the end the exhaust still smells the same lol, and out of all the motors I have only 2 stand out the V-spec and the OPS SFV21B and you cant get that in the USA any more but the Radical 621T is close. I know you hate your V-Spec because of the service you got from OS but once you get it running you will love it. They are just so consistant from the start of the race to the end.
That's the point I've been trying to make to you for months. You have found your perfect engine in the O.S V-spec! Why not just stick with the engine you know and love, why do you keep trying all these new engines only to be disappointed? I have found my perfect engine in the jammin JPX .21 so I have stopped looking for bigger and better and more. I searched, I found, I'm done. You should try the same. Stick with what works for you. Stop collecting and start racing!!
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Old 12-02-2008, 07:53 AM   #11
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That's the point I've been trying to make to you for months. You have found your perfect engine in the O.S V-spec! Why not just stick with the engine you know and love, why do you keep trying all these new engines only to be disappointed? I have found my perfect engine in the jammin JPX .21 so I have stopped looking for bigger and better and more. I searched, I found, I'm done. You should try the same. Stick with what works for you. Stop collecting and start racing!!
It's just a hobby of mine to collect and I race 2 times a week the motors are what I love about 1/8 scale. I just like motors no one runs in the US like CMB, OPS, Boss, and VEGA etc. trust me the V-Spec is what I race with most of the time but I think I will run the VEGA at the Pit on the 6th for the ACS it's fast to.
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Old 12-02-2008, 11:17 AM   #12
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Quote:
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It's just a hobby of mine to collect and I race 2 times a week the motors are what I love about 1/8 scale. I just like motors no one runs in the US like CMB, OPS, Boss, and VEGA etc. trust me the V-Spec is what I race with most of the time but I think I will run the VEGA at the Pit on the 6th for the ACS it's fast to.
I hear ya bud. We all have our obsessions. I think I own about 300 tires and rims, and every color rim, and wing ever released. Come say hey Saturday at the Pit. I run the XRAY pictured in the avatar, and I pit with Tony Veno, and Don Toleffson. My name is James. I'm the guy who is an expert qualifier, and a terrible racer
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