Jeebus, I'm so scared to post this. Noob to rotaries here, and noob to road racing also. Here's my idiot question.

We're on a short timeline to build a motor for our next race, which is for budget endurance racing. We've got a center iron with a big street port done, but only stock 6-port end irons. Rotor housings have been exhaust ported.

So, what happens if we just Devcon the 6-ports to eliminate the cave, but otherwise run them with the ported center iron?

Stupidest thing ever, or just less power than if the end irons were also ported? And we expect to be pulling and rebuilding engines given what we're doing to them, so it's not like this is gonna be a 75K motor.

Thanks for going easy on me.

 

Stock ECU I'm assuming? Instead of Devcon why not just disable the 5/6 port activation? Youre going to lose top end as i'm sure you know.

But with the big port on a stock tune the car may run lean and like crap.

 

Yes, stock ECU. We ran several races with the 5/6 disabled on the intake, and the engine had a stock center iron and mildly street-ported end irons. It was running great till we threw a water pump belt and didn't catch it in time. Not a ton of power, but that's not our goal at this point. It came alive around 4,000, and pulled consistently to 8,000. Don't want to rebuild the old engine due to extreme overheating. So, looking through our stock, found we had these ported irons from someone else. Feeling good about the center, less about the ends.

So, I guess we'd been running the reverse before, which is ported ends, stock center. What if we reverse that, but with a bigger center iron port?

Also, if we disabled the 5/6 port actuators (by removing them, so full open like it is) my experience was that we had no torque down low, but the top end was great. Am I misunderstanding this one? Or were you saying disabled as in full closed all the time?

Thanks again for the help.

 

I think he meant disabled as in fixed to be open all the time or removed sleeves like in your previous engine. Also from what I understand the 5th and 6th ports close so late there's not much benefit in porting them anyway. On mine I didn't even touch them. I just opened the secondaries a little sooner and ported the primaries all using Pineapple Racing templates and it runs fine so I think it'll be ok.

 

What kind of an intake setup are you running on this car? I assume a stock manifold since youre using the stock ECU, but which version the 86-88 or 89-91?

 

It will work. Like others mentioned, I would skip the devcon, just because it eliminates the chance of a failure, instead, I would port the 6 port irons. Not by choice, but I ran a ported 6 port with a disable (wired open) 6 ports, on a stock ecu. The car ran fine, sure the AFRs weren't ideal, and I wasn't making the most HP, but it was 99% streetable (except for the loss of torque in the low mid, and the 200-400rpm higher idle)

 

i know you mentioned a time factor, but if you have the time, then you should probably do this ...
and then this ...
though, i would say do the sleeves, not the port itself. keeping them functional might be more beneficial for what you have in mind.

that said, with regards to the original question, if you only run ported primaries, the engine will be fine. obviously it's not the best situation, but it will work.

 

Thanks for the input, everyone. Very helpful. In the end, it looks like our lead mechanic wants to port his own irons, so we're going to start with some fresh S5's and go from there. I'll pass along the info about the actuators.

Since this is a road racing car, low end isn't important, nor is streetability.

Cheers,

Dave

 

When you say the AFRs weren't ideal what are we talking here?

We have an issue with AFRs skyrocketing under heavy load, low RPM scenario with 5/6th ports removed (3rd gear, WOT at <3000rpm). Wondering if that is the cause and how to go about remedying it. Its on a racecar so unsure of how much of an issue this will be as wouldnt likely be that low RPM scenario very often but would be good to sort out.

Jesse