I am planning on porting my 12A and I have discussed having the rotors scalloped and balanced. For the people that have done this or have experience with this, do you think this process is worth it. The car will be a street driven car with little or no track time. If this helps, the other mods would be a weber side draft (currently 40mm but may run it at 45mm) on a lake cities rotary manifold, full racing beat street port exhaust (may have the engine builder build a header an exhaust) and I will have the engine street ported. Any feedback would be appreciated.

 

argument: the costs involved are probably not going to be worth it based on the type of use you have outlined.

counter-argument: that said, i'm guessing half the things we do to these cars would be considered not worth it from a monetary standpoint.

if you find yourself with the money, time and right attitude, then i'd say why not? for your street car, just don't go all-out crazy with them (where they basically cut them down to the recesses), get something a little more aggressive than the Renesis rotors and call it good.

 

Larry, I would use a 45mm DCOE minimum on a 12A. The drivability of a decently tuned 45 is almost indistinguishable from stock. Thr first time I drove one, I didn't realize that it was modified until I opened the hood and was greeted with a bare engine with a Weber stuck off to the side. At the time, my daily driver was a very well sorted stockport '80 GS. So, there would be no gain from going smaller.

Regarding the bevels, you know how I feel about additional port timing If it were my engine, I would add bevel to increase opening time but not closing time. The closing time should come from port shape alteration and not rotor beveling, in my opinion. To make the port shape REALLY nice will alreayd make the closing timing really far out there, so there should be no need for a bevel on closing. But, I've never played with bevels before. I was considering doing bevels or half-bridge and I elected to go half-bridge and that was four engines ago and all but one have been bridge ported since.

 

can the scallop be used to open the intake earlier without having overlap? if yes its a win win.

 

Yes. Don't scallop them... :/ I don't see how, is my point.

The point to scalloping in a "street car" would be to gain power without losing low/mid range torque. The duration of intake opening grows without having to pay for it with lost velocity. But regardless, the scalloping opens to the rotor face, so no matter how you slice it ( pun intended!), you're gaining overlap. Unless of course you de-port the exhaust closing

-J

 

Added overlap is a good thing for low- and mid-range torque.

 

just for clarity, Peejay, is it the overlap itself that's a good thing, or is it the earlier open? i figure for us (with the peripheral exhaust), it's inherently a two-sided coin - earlier open/overlap since we can't really separate them on a practical level. isn't that what Gorilla RE and J9fd3s are alluding to?

my understanding of it is/was that the early open side of the coin is good for low-to-mid-range torque, and on the older rotaries, of course that came with overlap. it would seem that that thought seems to hold true since with the MSP they went early open with both the ports themselves AND bevels, but no accompanying overlap.

 

Right, it's not the overlap itself but the additional port timing without having to close the port extremely late.

 

yeah i want to keep minimum overlap, while opening the intakes earlier. i would like to minimize the amount of exhaust gasses getting carried over into the intake stroke.

on the practical side it just happens to be that the power gained from the increased intake duration is more than the power lost with the overlap, we are talking about street cars here. part throttle and low RPM are where it is going to be most of the time.

i would cite the 13B-MSP as an example, they lowered overlap and gained just about everywhere.

so if i could open the intakes earlier, and not add overlap, i think its an easy choice. if you have to add overlap though, its not the end of the world, the PP engines have a TON of overlap and can be
pretty tame

 

without overlap it will be tricky to exceed VE over 100% as there is no way to flush the rotor pocket with fresh mixture. but as you pointed out the overlap will def not help idle or other conditions with high vacuum in the intake. also it will not help with a street freindly exhaust setup.

maybe semi PP with late opening port and it at closing at the same time as the side ports might be a good idea. if you do not go wild on the exh closing the overlap will be not massive.

 

I looked at the papers on the rotary engine and a side port (six port) opens at 32 ATDC. All peripherals open way before. Like 70 and more BTDC. I don't see how any amount of earlier opening, without a bridge of course, in a side port could even get near the early open of a PP.

 

Who said that it could? What is the point you are trying to make?

-J

 

For what it is worth, all stockport engines that aren't RX-8 engines have some degree of overlap...