-xlr8planet-

cause thats what Im building.



I know ITO likes to build n/a engines with 0,002 clearance, and turbo engines with 0,003



but ...



until you hit the nitrous, the engine is n/a, and once you hit it ... its force fed.... soooooooo now what?



this engine build is killing me...



any input is welcomed.



thanks in advice guys!



ps: I think I´ve read on this forum about someone using 0,015 clearance? Can that be? Its twice the factory tolerance.

mazdaspeed7

Nitrous is pretty rough on engines, so you definately want to set your clearances more towards the boosted clearances. You are building the engine to make power on nitrous, you may lose a few hp n/a, but that shouldnt matter.



Did you do anything with the porting for the sake of the nitrous? Usually you want to go a little larger than normal on the exhaust port, because the exhaust volume will be greater when youre spraying.



But that being said, a 100 shot isnt that much on these motors, so you would be fine with the typical n/a clearances and build practices.

-xlr8planet-

thanks for your reply



I intent to drive this thing around. Not much, but I want it to be able to drive to the track, so I went with a racing beat street port on the exhaust side and racing beat bridgeport template on the intake.



I have a set of honda cbr 600 rr ITBs, but I havent decided on the lenght of the runners.



CAS and megasquirt



The nitrous system is a nitrous express with 2 foggers, one on each secondary port runner. (shark nozzles)



aiming for 170whp n/a, revving to 7800



with a 100 shot of juice should be a pretty fast little car.

Lynn E. Hanover

Well,

The idea is that the seal would get longer when heated, and there must be some room for that to happen without binding the seal or the corner seals.



So, place two corner seals in the holes, a spring and a side seal. Press in a pair of .0015" gages along the outside of the groove, or .001" if those won't fit. Now there should be just room left between the side seal ends and the corner seal, so that the corner seal can still bob up and down when pressed. So that is the worst case where the combustion gasses would clamp the seal against the inside of the groove and leave the least amount of clearance.



Now with the gages removed, measure just one end of the side seal clearance to the corner seal. Whatever that clearance is will be just fine. Note here that when the gage is wedged into the gap at the end of the seal, that the seal is now pressing against the outer wall of the groove, and the corner seals are pushing against the top of their holes, that will add a bit of clearance



When in use, the rotor gets bigger at the same rate that the (also cast iron) side seals get bigger. So the clearances remain about the same.



But, how about standing on it long enough for the second turbo to come in. Then the high load on the seals stresses the oil flim, makes more heat, and the seal gets longer, before the rotor can absorb enough heat to keep up, size wise.



Each corner seal will get a bit more of a wear mark one side. Each corner seal pushes one side seal around the engine. So, you would expect, that there would be a wear mark on only one side of each corner seal. But in most casses there are marks on both sides. So there are times when the seal is touching both corner seals at the same time. (zero clearance)



Like new side seals in an engine that starts up and drives away with no oil temp (rotor temp). Like just about every one ever built. Just so you know..........



NA engines develop very little cylinder pressure. Boosted or nitrus engines develop lots of cylinder pressure. So, on my NA engines I use zero end clearance on the side seals. Just enough so that the side seals and each corner seal will pop up after being depressed together. The ends of the side seal and that wear groove on each corner seal appear quickly, and provide some clearance. So we do warm up the engine oil temps before we race. We do break in each engine for 2 hours before going to the track. We do mix a bit of extra Redline synthetic 2 cycle oil the first weekend. Best power will be the 4th weekend after a rebuild.



If you can stand to wait a few weeks before you stand on it. Use a synthetic premix, and warm it up first, use zero end clearance. Otherwise, go by the book.........



The .015" thing won't even start. No compression. However if it is a typo......and it was to have been .0015" that would be fine for any NA engine.



Lynn E. Hanover

Lynn E. Hanover

I forgot to mention a few things, because I'm old.........



If you use Renesis rotors in a non Renesis engine you can use early engine clearances. The Renesis exposes the side seals to the exhaust flow, and the side seal clearances must account for that, so go by the book on Renesis tuning.



Nitrus does not add much fuel by itself. It adds oxygen. So, you must add more fuel to make more power. A lot more fuel for power, plus to help keep combustion temps from melting the apex seals. And, since the much more dense mixture with all of that Oxygen will burn much faster, you need to pull out ignition advance along with the added fuel.



So, you might think about a bigger flow injector. Or, a third injector. A controller that can do all of this stuff.



And another thought. One of the airplane guys uses nitrus for takeoff, and shuts off the trailing plugs during nitrus, to eliminate detonation. Pretty clever, those old people........



Lynn E. Hanover

-xlr8planet-

Thanks for your reply Lynn.



Not sure if I mentioned, the engine is a 12a.





The nitrous system I have is a wet system, so it injects nitrous and fuel.



Fuel mangement and ignition timing using a megasquirt standalone. (using a CAS and 8 injectors firing staged). It lets me pull timing whenever the nitrous solenoid gets 12 volts.



I did the rear and front pressure regulators mod, and I will run premix, to be able to use synthetic.



New bearings https://www.nopistons.com/forums/rx-7-tech-...-pr-t74244.html



I think I will go back and re-check my side seal to corner seal clearance.