TwinCharged RX7

iTrader: (14)

Hi. I'm trying to figure out how to set up counter weights on a 4 rotor. The firing order is based on clocking the front eshaft 90 degrees from the rear so each rotor fires by itself.

Is it as simple as leaving the stock (13B REW) rear counter weight where it is and then rotating the front counter weight to a different orientation? Sorry, having trouble visualizing it for some reason.

scathcart

On a 2 rotor, the counterweights are offset 180 degrees from the first rotor, and the rear 180 degrees offset from the front counterweight.
On a 4 rotor, the counterweights are offset by 135 degrees with respect to eshaft rotation, and the rear 180 degrees offset from the front counterweight.

This assumes R26B style firing order of 1-3-2-4.

Stock counterweights will need a significant rebalance. Neither stock counterweight will be clocked in the right position from the factory.

Are you planning on making your own eccentric shaft?

TwinCharged RX7

iTrader: (14)

Kind of. Details will be kept close until I know it works. It's two modified REW eshafts though.

I guess I'll have to change the key slot on the counterweights. I just need to figure out how to clock them.

The entire assembly will be balanced before I assemble and try it. So I just need the stock counter weights in the right position, then I can modify their weight as needed.

TwinCharged RX7

iTrader: (14)

Also, this will have the 26b firing order

scathcart

Ok. Rotate both counterweights counter clockwise 45 degrees.

mono4lamar

iTrader: (32)

I know what you're thinking of doing. It's going to be more trouble than it's worth. "Splicing" the two shafts together is possible but IMO the jointed area would not have enough depth on each end to enable enough CL strength. The only way to mate them would be a third union shaft keyed and c-cliped. You could use pins in addition to the clips but in the end a balanced 4 rotor shaft is $3,000 with counter weights.

You're not the only one looking to make a 4 rotor...

TwinCharged RX7

iTrader: (14)

Haha. I know I'm not the only one. But I like experimenting . Plus I have extra eshafts, so might as well see what I can come up with.

Plus, I wired my twincharged FD for a 4 rotor, so that means I have to try in order to test out the wiring.

Once the machine work is done you should come down and check it out.

mono4lamar

iTrader: (32)

I'll be more than happy to give you my opinion before you spin anything. Text or call me if you still have my number...

MrGoodnight

iTrader: (1)

This is a good excuse to build a 4 rotor, I like it.

John Huijben

iTrader: (1)

I did the research and found that combining 2 shafts won't be reliable.
Counterweights need to be rotated 45 degrees, You can use any OEM front one and just add a keyway, I did this too. For the rear I would recommend machining a new one, if you add a keyway the existing counterweight it will have 2 keyways, the unused one will weaken the counterweight, it might start moving / wobbling.
After rotating balancing is necessary, 4-rotor counterweights are a lot lighter than 2-rotor ones if you go with the 90 degree firing interval, so you need to remove a lot of material.

TwinCharged RX7

iTrader: (14)

Thanks John, appreciate the detail. Do you have any thoughts on how much lighter it will need to be? Seems like the front will be easy to modify, but for the rear, if I stick with the stock flywheel (built in counterweight), will I be able to lighten that enough without making it weak?

I know everyone is saying that 2 shafts wont be reliable. That may be so, but I don't have the skills to make my own 4 rotor shaft, and this is really more for experimental purposes. If it breaks, it breaks, I'll still have fun making it either way.

I'll post results once its done so everyone can see if it works or if it doesn't.

TwinCharged RX7

iTrader: (14)

Also, if adding an extra key way and not using the old one can make it weak or wobble, how do you feel about just adding a second keyway to the shaft as well, this way both key ways would be used.

John Huijben

iTrader: (1)

I believe the weight removed was about 12-15%, intertia removed about 35- 40%
I'm not really sure about what method is best if you want to rotate the flywheel. My rear keyway is in the stock location because it was the easiest to machine. I trialfitted a stock rear counterweight at 45 degrees and thought about adding a keyway, but it looked iffy so I machined a new rear counterweight.
It was a evenings work, but worth the effort.
If you use the flywheel with the integrated counterweight it might be possible to remove the weight, and add weight at the correct location. I would recommend using a seperate rear counterweight though. More flywheel / clutch options.

Think good about what you want out of the engine when it's done. If your any serious about actually building it your going to spend money and a lot of time to build it. You might think 'ah well, if it breaks it breaks' now. But after spending a lot of money, and quite possibly a few years of spare time into it your going to want it to work and function well. Yeah you can save a lot of the money part when your doing everything yourself, but some things just have to be bought such as engine seals, fuel system components, ecu stuff and materials to only name a few.

TwinCharged RX7

iTrader: (14)

Thanks for the info, i'll put some more thought into the counterweights.

From a wasted time and money perspective, most of the car is already way overbuilt (fuel, cooling, ecu, wiring, etc...) So this is really about the engine itself. This part of the build will basically require an engine, a subframe (already have an extra to modify), and a dry sump system (which I'd like to add to my 13b anyways). And eventually a T56 tranny when I run out of stockers haha. Sure I could just buy a 20b for the amount of incremental dollars i'll spend on this, but I'd rather have 4 rotors

RotaryEvolution

iTrader: (30)

the biggest trial will be your through bolt mounting.

i figured on a titanium 3/4" stud to sandwich those bitches together firmly(shaft bores will have to be reamed out slightly to still allow oil flow through the front half). i would also like to put the theory of the torque on the mid section to a test.

building the shaft is only half the problem, balancing it is the other and finding a shop that can put together the proper bob-weights. then the question remains, what is the proper method of balancing: dry rotor weight or saturated rotor weight? i assume most shops just balance them to match your rotor weights, because the oil is slinging out fairly continuously. a 4 rotor engine would require the rotors to be much closer in weight than a 2 rotor would since the center will flex if the discrepancy is large enough.

mono4lamar

iTrader: (32)

Collin, John's words here are worth more than gold. I've followed everyone's 4 rotor engines here on the forums and his is by far the most well thought out, engineered, and innovative.

To get two eshafts together again would be a lot of work for something again that will be more trouble than it's worth. John pointed out the counterweight keying that completely slipped my mind somehow. You'll either need to coin up here or build a 20b if you want more rotors. Yet a 13b can make more power than 95% of people on this forum need/can handle/can afford.

TwinCharged RX7

iTrader: (14)

My project is still in the works. It works pretty good but hasn't been fully tested yet. My biggest problem is that I have trouble staying focused on one project. So I will be finishing my twincharged set up before really rolling on a 4 rotor. All the fab is done. Just finishing touches now.

The 4 rotor (if ever completed) will be n/a at the outset. I'm not going to waste time fabbing an exhaust and intake and mounting it rearward a few inches until I know it works. So it will look like that one on YouTube that has two REW manifolds until I finish testing it. If it works and seems steady, ill move it backwards 5 inches, turbo, and custom intake. And a T56 when I run out of stock trannies.

I intend to coin up as much as I need to. If it doesn't work I can still use most of the parts (except the eshafts and adapters). On rebuilds. And I can sell my dry sump pump and extra injectors/coils on eBay.

So if it doesn't work I won't be out too much money by the time I sell everything off.

I don't expect to have a build thread for a while. I'll be enjoying my twincharged 13b all summer, and won't be taking it apart until next winter unless it breaks. I'm just going to have the eshafts and irons machined and then collect parts over the summer when I see good deals (injectors, could, dry sump pump, etc).

I do appreciate the input though, so keeps any tips coming my way please.