BuckyFD3

Since I am going to be rebuilding my engine in the next few months, I want to run some big boost/power when its run in.

I can machine the rotors myself, which I presume you machine the combustion pockets a little deeper or wider. I havn't done any sums or working out yet as its just an idea but I reckon just .5mm deeper pockets will lower the compression just that little bit to make it safer.

What do people reckon and I'm sure it has been done before.

RacerXtreme7

iTrader: (2)

I'd suggest you just get the s4 turbo (aka: 87-88 Turbo II) rotors instead (8.5:1 vrs s5,s6 which are 9.0:1). There slightly heavier, but are heavier duty and have lower compression. I'd rather have heavier casting in the tub/compression face of the rotors and lighten them on the sides then using the already weaker s6 rotors and weaken them further by machining out what little material exist on the face. Do a search if you wish to lighten those s4 rotors to s5, s6 weight.

~Mike............

BuckyFD3

The problem is getting a hold of S4 rotors, looking at around $1200 for a pair

pistonsuk

?^? how about less than $200shipped.

https://www.rx7club.com/showthread.p...2&page=1&pp=15



Justin

BuckyFD3

Nice one cheers. First I'm going to have a look at my old rotors and see how thick the material is in the combustion area and go from there, do some sums and work out how much needs to be removed to get it down to 8.5 ish.

ronbros3

may be Im dreamin but, did someone make up some aluminum rotors,( boy would that be lite) with a steel insert in the tub area, and steel gears, and no bearing it run on the aluminum as a bearing , and most newer Hi tech race bearings are aluminum, infact the famous chevy fuelie engines of the 50s run a bearing called Moraine 400s and it was aluminum steel backed. not dreamin about that tho.

yodaddy

but if you don't have a "bearing" what are you gonna do when you destroy the bearing surface? you will have to replace the entire rotor rather than just a cheap little bearing

RacerXtreme7

iTrader: (2)

I still think thats a bad idea. Do a search on all the rotary forums and you'll find that the FD rotors are weaker and people are denting the combustion surface on them from either high boost/combustion pressures and temp or detonation. Making it thinner is asking for trouble unless you really intend to run low boost/low power, but then going through the trouble of machining them out to lower the CR doesn't make sence. A lot of the high powered Japanese tuner engines run the older TII rotors for these reasons. Get the older rotors and if you still have a need tomachine something, go ahead and machine material off the sides to lighten them and get the whole rotating assembly dynamically balanced. But hey, its your engine and project, do what you want and have fun with it.

~Mike..............

BuckyFD3

I know what your saying dont get me wrong, but has anyone holed a rotor through det or pinking??? I have done a few pistons before seeing how far I could take the engine (R&D) and I never actually holed one but the ring lands were well screwed.

And since I am JUST machining the combustion pocket I dont really see a problem. Suppose someone has to try it.

How would I go about working out the CR if I machined the pockets?? I know how to do a piston engione but I'm new rotor's Is the pocket the combustion chamber and the rest of the rotor has nothing to do with it??

So say I machined .5mm off the bottom of the pocket, this would increase the volume by X.... blah blah

RacerXtreme7

iTrader: (2)

Some of the rotors pulled out of engines that have dents in them (the dents are usually above the combustion pockets, and NOT in the tub itself) were really high output engines that didn't have detonation or ping. Its most likely from extreme combustion pressures (from lots of boost) and high temps (also from loads of boost) "overboost". Granted, most likely the majority of those rotors pulled that have dents in them had a ping or two. And most likely the apex seals and or the rotor housings cracked too.

Pictures of a dented rotor. http://mazdatrix.com/faq/boost.htm

And yes, machining the pockets out to lower the compression ratio has been done many times. Your not trying anything new.

The enitre face of the rotor sees combustion, not just the pocket/tub.

Not trying to be a *****, but if you have to ask how to figure out how much and were to remove material and how do you figure out the new comp ratio, you probly shouldn't be trying it unless you have loads of extra parts laying around and lots of free time building engines (which may be the case). Its simple to figure out how much material there is to take out, but the really complicated part is figuring out the new shape for your pocket because its a convex compound curved structure and the material amount removed isn't just a quick flat pass of an end mill. You'll need a CNC machine and a good program to do it properly. Do a search on all the rotary forums and google. I know theres a few shops that offer this, maybe you could get in touch with them and they can help you out, although I highly doubt they'd give you a CNC program for it.

For whats its worth, theres many apoun MANY guys running the stock 9.0:1 comp rotors making stupid amounts of power (excess of 600 at the WHEELS). Lowering the comp ratio will yield less power but only give you a little more safety margin in your tuning. It will also slow turbo spool up a bit. I, like most likely the majority don't see a need to lower the comp ratio at all and if I did or wanted too, I'd use 87-88 turbo rotors (CHEAP) and a hella lot easier to just install then machining out higher comp rotors.

Good luck on your quest, theres tons of info on this and other forums. You just have to search for it. I'm sure eventually you get some company names (I know Mazda Trix at one time offered this, as well as Hayes rotary, maybe Racing Beat) and you could talk with those with direct experiance doing this.

~Mike..........

SureShot

Beveled rotors are a good option here.
You get earlier intake opening (a mild bridge port effect) and later intake closing (a J-port effect) AND lower compression.
All this by cutting into only the strongest part of the rotor face.

TT_Rex_7

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/lightweight-rotors%3Dless-torque-379771/

Diffrent thread topic, but it still covers machining the rotors to a lower compression.

-Alex

RacerXtreme7

iTrader: (2)

The scalloped/chamfered/port phased rotors was going to be my next suggestion seeing as though hes itching to machine his rotors.

~Mike............

jacobcartmill

iTrader: (6)

what kind of sick puppy got ripped into paying 1200 bucks for a used set of s4 TII rotors?

crispeed

Most of the dented rotors I've seen came out of stock/slightly modded FD Rx-7s. It's true that all the 89 plus rotors do suffer from this problem but it is the result of abnormal pressure and high temps from poor tuning or operating conditions. High boost and horsepower does not cause this problem. Don't believe it can not happen to earlier rotors also because I've seen it.
Your best bet for a low compression/light weight rotor setup would be to get some 87-88 TII rotors and have them lightened and balanced. CLR motorsports have a set that are lightened to 89-94 balance so you can use your original counterweights.

BuckyFD3

Dont worry I'm not taking things the wrong way, I am looking to run 98RON fuel in my FD and trying to stop the onset of det, so one of the options was to lower the compression, yea I can buy the 8.5CR rotors but in the UK they want stupid money as I hav already said. By the time i get some from the US then get them lightened and balanced its going to be better for myself to maching my rotors. I have access to a cnc miller at work so thats no problem, thats why I am asking.

But if I can run 9.0CR and 98 RON fuel to get 450rwhp then I'll use the 9.0CR rotors and not machine them. Is this possible???

pay 785

rx7tt95

Don't bother trying to mill the FD rotors. I've seen one cut in half longitudinally and it's too thin. You'll end up with swiss cheese!