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Mill RX8 rotors for 3MM RX7 apex seals?

Old 01-17-08, 06:46 PM
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Mill RX8 rotors for 3MM RX7 apex seals?

Racing beat won't do it. Pineapple's phone is busy. Too late to call Pettit. Anyhow since the 8 rotors are (lighter &) higher compression the 3mm NRS seals should offset that a lil bit (but not sure by how much) and also low boost (10lbs). If it needs to be milled for taller seals then it won't make a cost difference to mill them for 3mm.

There is only one person I know of that has used RX8 rotors in a RX7 but he is no longer with us and I do not know if he used RX8 seals or not.

Any help on this from the engine building experts?
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Old 01-17-08, 08:44 PM
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I've read that someone got lower compression test numbers on RX-8 rotors compared to S5 NA rotors.
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Old 01-17-08, 09:20 PM
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I would prefer if the compression went down with the 3mm, that's the point. Since it's a 13b-REW turbo, if it goes down to 9:1 then it's still an extremely healthy engine but with stronger seals.

Pineapple actually has a set but never finished the project that i'm asking about. I couldn't get any more details other then trading one problem for another, so to speak.

Last edited by GoRacer; 01-17-08 at 09:27 PM.
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Old 01-17-08, 10:44 PM
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You're confusing compression ratio with engine compression, they are two totally different things.
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Old 01-17-08, 10:52 PM
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^ yes, I allways do that but did I get my poit across?
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Old 01-17-08, 11:03 PM
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your post is incredibly confusing. what the hell are you talking about?
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Old 01-17-08, 11:07 PM
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1. Mill RX-8 rotors to accept 3mm RX7 apex seals
2. Balance and clearance rotors and ecentric shaft
3. Install in to '94 RX-7 13B-Rew turbo FD3S
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Old 01-17-08, 11:12 PM
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They're not that much lighter really. If you want lighter, then get some 9.0:1 rotors lightened.
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Old 01-17-08, 11:13 PM
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We are offering this, very shortly.

I have a set of RX-8 rotors that are getting cut to accept the older 2mm seals to use in a 4port T2 block. We use EDM wire cutting which is much more accurate then milling them.
The jig is being built right now and I should have pictures of the final cut up soon.
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Old 01-17-08, 11:24 PM
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after (or before) you cut them have the rotors xray to find out how much casting is there before you cut to far

next ?, if you do this successfully, then what are you going to do about side/corner seals, they are different
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Old 01-17-08, 11:38 PM
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Not really sure what you mean? I actually put an older style corner seal in the rotor and it fit fine, but if for some reason they wont work, whats wrong with putting the RX-8 corner seals in their holes and EDM cutting them to the same depth as well?
And the side seals have nothing to do with any of this?
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Old 01-18-08, 12:03 AM
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I was under the impression that the older style coner seals wouldn't fit/work with the newer side seals.

Didn't think of cutting the newer style side seal...
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Old 01-18-08, 12:16 AM
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The RX-8 side seal is different that the older ones, RX-8's use longer side seals and also only fit in the rotor one way, they are tapered meaning the wearing edge that is in contact with the iron is wider then where the side seal spring is.

But the round corner seal fits fine in the rotor itself, mind you I just put one in....never really took any measurments.
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Old 01-18-08, 12:34 AM
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JHB also does wire cutting but I haven't heard back from them yet. The reason for the RX8 rotors is price not wieght. The lighter weight is just a benefit. I was hoping the 3mm seals would bring down the compression but from what i've been told nothing significant enough to what I thought.
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Old 01-18-08, 12:43 AM
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Bad reason, you can get some good used 9.0's for less


Originally Posted by GoRacer View Post
JHB also does wire cutting but I haven't heard back from them yet. The reason for the RX8 rotors is price not wieght. The lighter weight is just a benefit. I was hoping the 3mm seals would bring down the compression but from what i've been told nothing significant enough to what I thought.
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Old 01-18-08, 08:24 AM
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Personally, I'd rather install the 'correct' parts in the motor rather than save a hundred bucks. not saying the rx8 rotors dont have a use, but for your reasons seems kinda silly.

3mm seals (esp 1 piece) don't seal as well as thinner multi-piece seals, thus your cranking compression (measured in psi or bar) will be lower, relatively speaking.

Here's some info on compression ratio:

http://en.wikipedia.org/wiki/Compression_ratio

It can be altered by changing the shape of the combustion chamber (in this case the sides of the rotors) but the actual apex seals have no bearing on it.
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Old 01-18-08, 08:25 AM
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3mm seals will not lower your compression.

I talked to Marc at JHB about doing the same, I believe it was $450 for a pair of rotors. Get in contact with him though, my memory for pricing is shitty at best.

After talking with Marc, I left a pair of rotors with and EDM wire cutting place in my area and he said we could build a jig and do them ourselves.
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Old 01-18-08, 09:45 AM
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For comparison here's an rx-8 rotors milled with 2mm iannetti seals. The side seals where spec'ed to RX-7 clearance; the cut-off ring was not used; RX-7 conner seals were used.

Unfortunately, boosting at 14 psi, it did not yeild good results compared to the FD rotors. Now, I'm back to the FD rotors, beveled like the RX-8 and I'm happy with it. Good luck and keep us posted if you got good results.
Attached Thumbnails Mill RX8 rotors for 3MM RX7 apex seals?-rx8rotors-.jpg   Mill RX8 rotors for 3MM RX7 apex seals?-rx8rotors-b.jpg  

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Old 01-18-08, 09:55 AM
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there is not enough meat on the rx8 rotors to mill to 3mm, and sometimes not enough even for standard 2mm, the casting is real thin, ive seen too many new rotors go into the trash can for this reason.. also there are some mods you have to do to the side seals to get good power using rx8 rotors, not to mention throwing away the 3rd oil scraper ring...
for your application stick to the fd rotors if you want good results without a headache
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Old 01-18-08, 10:44 AM
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Robert, why throw away the 3rd oil scraper? Just curious.
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Old 01-18-08, 10:58 AM
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yeah, from what i've read, people are starting to get better compression numbers with that oil scraper in place on the pre-Renesis engines. i think the issue with using them was accelerated wear on the housings though. i wanna say it was Crispeed that i read mentioning this, but don't quote me because my memory may not be perfect on who it was that said it. i just remember seeing it.
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Old 01-18-08, 11:02 AM
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by the way, does anyone have a nice shot of a Renesis rotor? i still have not seen one up close yet and it would certainly have a place in this thread.
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Old 01-18-08, 11:04 AM
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Originally Posted by diabolical1 View Post
yeah, from what i've read, people are starting to get better compression numbers with that oil scraper in place on the pre-Renesis engines. i think the issue with using them was accelerated wear on the housings though. i wanna say it was Crispeed that i read mentioning this, but don't quote me because my memory may not be perfect on who it was that said it. i just remember seeing it.
How do you get better compression with the oil scraper?
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Old 01-18-08, 11:10 AM
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Originally Posted by 680RWHP12A View Post
there is not enough meat on the rx8 rotors to mill to 3mm, and sometimes not enough even for standard 2mm, the casting is real thin, ive seen too many new rotors go into the trash can for this reason
I guess I was pretty lucky with the first six rotors I milled for 3mm!
Now I know I was not that lucky trying to lighten them though.

Originally Posted by 680RWHP12A View Post
there are some mods you have to do to the side seals to get good power using rx8 rotors
There is a difference between good power and most power!

Last edited by crispeed; 01-18-08 at 11:17 AM.
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Old 01-18-08, 12:04 PM
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Originally Posted by crispeed View Post
I guess I was pretty lucky with the first six rotors I milled for 3mm!
Now I know I was not that lucky trying to lighten them though.



There is a difference between good power and most power!


dam!! im impressed with the luck you had milling the rotors! i fubard one set and stopped there..

and i stand corrected, to get the most power you need to modify the side seals

you could also flip the rotors on a s.p or b.p application
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