convert fr 582 to 670

17 posts in this topic

Posted

I had a rotax 670 built for me for use in and exp aircraft. I am lower on power than I thought and low on compression-120- w/ a good known gauge. I checked the squish and it measured .120 w/ a piece of twisted solder parallel w/ the pin up against the cyl wall. After removing the head I saw the squish area is beveled up yet the piston top is flat. the squish is .063 deep into the head and the deck height is .010. So .073 squish but only at the outermost point and gets bigger really fast toward center. My question is, should I have domed pistons in this eng? What is a good squish and cranking compression for a safe stock set up? Thanks.

rotax 670 012.jpg

rotax 670 006.jpg

rotax 670 009.jpg

rotax 670 010.jpg

rotax 670 011.jpg

rotax 670 012.jpg

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Posted

I cc'd the chamber at 38 and the angle of the squish at 15.2 deg. I agree w/ the poster above(Myself) if I had domed pistons I would be in that range 6-12. now I feel my squish velocity is so low I am getting a week charge in the dome and the outer area starts to burn on the way down not producing much but giving high egt(which I will be installing when I go back together) This is a 670 w/ a 582 head built by Rotax Rick for experimental aircraft, . I will contact him to ask why he picked this piston/head combo. I am just not that familiar w/ the guts of this eng if this is normal. I will call some other aircraft builders and get their opinion.

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Posted

 I'm no expert on this by any means but he might have used the 582 head just to get the dual plugs. 

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Posted

The 670 combustion chamber is quite different to the 582 but for simplicity reasons and dual plugs the 582 head is used,although not ideal there are plenty flying in this configuration. I believe if the 670 is bored more than 20 eversize the 582 head needs machining. Rotax Rick was experimenting with a dual plug modified 670 head,best give him a call. I never got to finish my 670 for my fox 3 but the chap who purchased her is committed to finishing what I started, so any feedback from others will be appreciated and passed on.

cheers 

Dusty

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Posted

Yes I agree hard to find a 670 head w/ dual plugs and Rick did say a big overbore would require the head to be opened up. I looked at y pistons more closely and the tops have a slight rocker to them, not quite domed to help match the head squish band. Does anyone know, if it is important for the entire squish to be close to the same clearance maybe getting slightly larger as it goes toward center.

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Posted

Anyone remember the name of the company that was developing those dual plugs built into a single plug body? I seen him at Oshkosh a couple of decades or so ago. They had two electrodes and the top was split so you could attach two separate plug wires. The idea was to give you dual ignition capability with a single plug hole for all the snowmobile engine conversions being done back then. It was about the same time Rotax and others came out with their dual plug hole heads.  I don't know if he ever got his idea off the ground or not.

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Posted

Never heard of anything like that but good Idea.

 

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Posted

What did the guy who sold you the engine say was the Horsepower of the new engine?  Rotax Rick's 670 puts out 91 horse power, and mine shows that for sure.

I think 120 psi is a good compression number, I will check mine and post it when I get home.

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Posted

Honestly after installing the 670 if you told me I still had my 582 I would have believed you. He said 90 hp at 6500 rpm. That is a big jump from 65. Please post your comp I am very curious.Thanks

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Posted

Honestly after installing the 670 if you told me I still had my 582 I would have believed you. He said 90 hp at 6500 rpm. That is a big jump from 65. Please post your comp I am very curious.Thanks

If you didn't change the prop out it would act exactly the same.

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Posted

Could you explain why. I just changed ratios frm 3 to a 2.62 to spin the prop faster, my tip speed is too low.

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Posted

More horsepower needs either a bigger prop, or a prop with more 'bite' to convert the horsepower to thrust.  The same prop, spinning at the same RPM is going to produce the same amount of thrust regardless how much horsepower is spinning it.

Mark

 

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Posted

OK I get that but w/ everything being the same, wouldn't more hp give me more rpm's and allow me to increase my pitch. I did not get that, I got about 200 more rpm's I did adjust my prop but mainly b/c the builder told me the 670 had a lower max rpm than the 582. I gained a little, barely noticeable, not 1/3 more hp.

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Posted

My neighbor is the guy who builds the dual plug 670 heads as well as the exhaust systems. The exhaust system controls the rpm of the engine after the hp peaks with increased rpm the hp drops dramaticly. My 670 hp dyno'd at 92.

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Posted

FoxDB, could you PM me about your 670. Mind is great on my IV.

 

 

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Posted

Hello, I'm new to this forum and reading some old posts. I've been involved with maintaining a couple club 582s for 15 yr. Looking for an R&D exhaust.  FoxDB, can you tell me more about your neighbor who builds the exhaust systems?

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Posted

For my 670 in an Avid Mk IV, Mike Hair made a very nice exhaust by modifying my 582 pipes, at a reasonable cost. 

image2.jpeg

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