during the last two weeks i disassembled two FD motors. both motors were in pretty good shape however:

both owners are faced w buying two new rotor housings...





the "WHY" is simple... they were running the OE spec spark plugs. 9 and 7 heat range spark plugs should not be in your engine. this is the inevitable result:




i realize this is not news to many, but it was news to these owners so let's put it out there one more time.

run 10, or colder, heat range plugs in all four holes.

i happened to be talking to Dr Iannetti a few days ago and asked him what was the primary result of cracked spark plug bosses and he said that they eventually connect the compression with the coolant. both motors had coolant problems and neither had significant tells on their coolant rings. all four rotors spec'd out perfectly as to parallel and general surface wear but all four will not be going back into the motors.

in addition to leading to eventual coolant loss, notice the flanking lateral carbon on the housings. the spring loaded apex seal is being lifted off the rotor housing by spark plug mountain(SPM). all the relatively cool compressed intake charge is in communication with the rotor face that has previously ignited and is driving out the exhaust port and powering the turbine wheel. way more compression in the forward rotor face than the following intake face. intake pollution and moving the needle towards detonation.

SPM pushes the apex in and starts a repeating oscillation that results in CHATTER marks on the housing. take a good look at any used housing around 11 o'clock and you will see lateral chatter lines.

lower SPM and reducer chatter.

what's in your wallet? what's in your motor plugwise?

another quickie while i have your ear... if you smell gas on your dipstick, probably, you have leaking fuel injectors. you'd better fix it or:

gas just isn't as good a lubricant as oil. the fix isn't changing your oil more often. the fix is fix the fuel leak. and, yes, the other bearing looked similar.

 

what is the actual difference between the "front" and "rear" rotor housing?

 

My engine builder told me the front and rear housing differences are for the stock twins, if you're running single then you can just get 2 fronts and save some money (hopefully he was right because that's what he had me do, lol)

 

I don't even think it's necessarily a 'stock twin' difference as much as a 'stock' difference.

There's an orientation difference on the EGR ports between the housings. But if you're running full emissions delete, it won't matter.

When Chris rebuilt my engine and I wanted new housings he asked if I intended to delete EGR. I suspect this is why. If I did (and I did), he got to buy 2 front housings and saved money on the rebuild.

As for Howard's original point, I can't say that I've heard of it being common to run 10+ plugs unless you're pushing, like, 450+hp. I'm not opposed to the idea though and will give it a shot once the engine is back in.

 

Hmmm, interesting.
Ive ran my engine with the stock spec plugs forever. Never had an issue. Mind you, I’m not making over 450HP nor do I run emission hardware. She’s been running like this for over 2 decades now.
I guess it’s how you use it and how you put it away??

I’ve always heard if you’re going to run the car track wise, then yeah, gotta run 10’s. Since you’ll be running it to redline most of the time. However, for a street use vehicle, I doubt the OEM spec plugs would do any harm.