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Rotax 670 build

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WindHorseRookie

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Aug 24, 2020
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Is it ok to start a newer 670 discussion?
If not refer me to the latest and deletes this one please.

I am loooing at building a 670 to replace my 582.
Looking for a list of parts needed to get it right without buying things I won’t really need.
I know there have been several built and hope to find some really good first hand information on parts I need to gather.
as always, and and all help is appreciated
 

Airporthound

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Apr 18, 2014
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Louisiana
Biggest issue with the 670 is the exhaust system. Theirs at least on guy out there claiming 80 - 90 HP and still only turning 6500 RPM. The snowmobile racing crowd is a good power source. Trust but verify. The stock 670 internals are fine.....you'll need a 4 to 1 gearbox.
 

Andy Hughes

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Oct 26, 2019
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Why a 4 to 1 box? I plan on using a clutch C box with 3 to 1. There is a guy who built a 670 used in a Rans Chaos. He used a 3 to 1 but said for even more climb and quicker take off he would use a 2.62:1 Thoughts?
 

MadProfessor8138

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Biggest issue with the 670 is the exhaust system. Theirs at least on guy out there claiming 80 - 90 HP and still only turning 6500 RPM.
Mike Hair can build a system that will give you 105 hp.....for about $650.
PROVEN.....not claimed.

20200824_220124.jpg

That is the system Mike built for me and it's going on my new 670 built by Rick.

IMG_4811.JPG

Kevin
 

MadProfessor8138

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Rick built the 670 for me and Mike built the exhaust for the engine.
I was very clear with both of them that I wanted an honest 100hp from the engine from the beginning.

Rick did some rotary valve work,rave valve work and carb work on the 670.
Mike designed and built the exhaust to match Rick's engine.

Contact each one of them to get the specifics of the build.....

Kevin
 

MadProfessor8138

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Kevin what engine are you building, aircraft and gear box with ratio. I am building a Rans Chaos, C-box, 3-1 gear and have yet to choose a prop.
I'm building a RW19 Ragwing Stork.
Rotax 670 with Mike Hair pipe.
E-box 3:1 ratio.
Warp Drive prop 3 or 4 blade.

My aircraft is made specifically for STOL performance so my setup will be a bit different than others.......
I will be tearing the guts out of the engine for 60 seconds at a time and then babying it the rest of the time.

Kevin
 

Airporthound

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Apr 18, 2014
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Louisiana
I was very clear with both of them that I wanted an honest 100hp from the engine from the beginning.
Can you please tell me at what RPM is your 670 supposed to produce 100 HP. I have read a lot of what 670 owners think they have, but have yet to discuss the actual real time numbers with an operator. I have extensive experience w/ 582, 532 and 670's in the E-A/B and snowmobile racing world. Also very much versed in the gearbox reduction systems and the application of the Warp Drive prop. I am pondering using the 670 in a project and just wanting to discuss this topic with actual operators.
 

MadProfessor8138

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Realistically,it will be 2 years before the engine is put into service so I can't comment on how it performs at this time.

Can you please tell me at what RPM is your 670 supposed to produce 100 HP.
I'm not sure why that question keeps coming up.....it's pretty much a moot point in my opinion.
Each engine is designed to run within a specified rpm range and should not self-destruct if kept within those limits.
Are you asking the question to gain knowledge to apply towards prop & gearbox selection or is the question being asked because you don't want to spend the money on fuel for a high revving engine ?

With your extensive experience with the 670/gearbox/prop,etc........you should be fully aware that what ran absolutely perfect at 7am this morning and pulled like a freight train is needing a bit of adjustment at noon due to temp change,etc....possibly a degree or two in/out of the prop....possibly a minute carb adjustment,possibly change plugs,etc.
Now at noon....the pipe is becoming just a tad bit peaky...and so on,and so on.

There are so many variables to take into account that there is no real answer to the question.
Yes,you can build and design componants to produce particular behaviors at particular rpm's...but nothing is set in stone until the entire combination is run together and tuned by someone that knows what they are doing.
And also take into account......2 identical engines will not run the same.....ever.

Your best bet would be to contact Rick & Mike to give them an idea of your mission goal and take notes when they start throwing the numbers out to you.
They are both a wealth of info and can get you where you want to be.....

Kevin
 

Armilite

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Sep 5, 2011
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Location
AMES, IA USA
A Stock Skidoo/Rotax 670 is (78mm x 70mm) 669.2cc and is 115.7hp@7750rpm with Skidoo's Single Tuned Pipe!

Rotax Ricks 670 Conversion was Dynoed 92hp@6350rpm!

A Stock 670 with R&D Aero's 618 Tuned Pipe, it made 90.1hp@6400rpm, 97hp@6600rpm, 103.8hp@6800rpm, 106.1hp@7000rpm!

The 670 has been Big Bore to (82.5mm x 70mm) 748.6cc!

There was also a 670HO made only in 1998-99 that was about 12hp more!
 

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MadProfessor8138

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93 & 94 cases are provision 8......
However,the crank needs to be machined to match the taper of the gearbox and the case holes need to be worked a little to accept the gearbox bolts.

Kevin
 
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