Why Is The Rear Rotor More Likely To Die?
12-21-2004, 11:56 PM
#1
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Thread Starter
Join Date: Sep 2002
Posts: 525
Ok, there is a lot of discussion going on right now with the groundzero LIM for the FDs. Groundzero claims that the difference in the length of the front and rear secondary runners acounts for leaner mixtures and higher EGTs (by 250 degrees if I remember correctly). They claim that their manifold equalizes the EGTs between the front and rear rotors. I'm not doubting the quality or merit of their manifold, just the claims. My reason is because the rear rotor breaking apex seals isn't just an FD thing. Every turbo rotary I know of seems to break the rear apex seals more often than the front. I don't think the TII LIMs have the same length difference as the FDs, so what is causing this? I always assumed it was that the coolant flowed from the front to the back, and that the rear chamber was a little hotter, but I'm no engineer either.
12-22-2004, 01:30 AM
#2
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Location: redondo beach
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I dont remember exactley what they said when i was talking with them at ss7, but they said they had EGT gauges coming from each rotor. And if i remember right they also mentioned the path of the runners, that the front was a more direct path (cant remember exactley, was a long time ago)
12-22-2004, 07:48 AM
#5
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Location: Central Ohio (Hebron) Zephyrhills Fla.
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P'cola FD,Dec 21 2004, 09:56 PM
Ok, there is a lot of discussion going on right now with the groundzero LIM for the FDs. Groundzero claims that the difference in the length of the front and rear secondary runners acounts for leaner mixtures and higher EGTs (by 250 degrees if I remember correctly). They claim that their manifold equalizes the EGTs between the front and rear rotors. I'm not doubting the quality or merit of their manifold, just the claims. My reason is because the rear rotor breaking apex seals isn't just an FD thing. Every turbo rotary I know of seems to break the rear apex seals more often than the front. I don't think the TII LIMs have the same length difference as the FDs, so what is causing this? I always assumed it was that the coolant flowed from the front to the back, and that the rear chamber was a little hotter, but I'm no engineer either.
The first thing that comes to mind is the hotter coolant affecting charge temperature and always detonating the rear housing before the front.
Second would be the rear housing deforming more than the front as torque tries to warp the rear housing and iron, and break out the dowels. So all of the causes add up to a bad deal for the rear housing.
Coolant on the Lemans engine goes in the cool side and out the hot side on each housing. So I suspect the NA engine suffers more from the coolant temps than the torque problem.
If you had two injectors that flow a bit more than the others, I would put them in the rear runners. Just a thought.
Lynn E. Hanover
Ok, there is a lot of discussion going on right now with the groundzero LIM for the FDs. Groundzero claims that the difference in the length of the front and rear secondary runners acounts for leaner mixtures and higher EGTs (by 250 degrees if I remember correctly). They claim that their manifold equalizes the EGTs between the front and rear rotors. I'm not doubting the quality or merit of their manifold, just the claims. My reason is because the rear rotor breaking apex seals isn't just an FD thing. Every turbo rotary I know of seems to break the rear apex seals more often than the front. I don't think the TII LIMs have the same length difference as the FDs, so what is causing this? I always assumed it was that the coolant flowed from the front to the back, and that the rear chamber was a little hotter, but I'm no engineer either.
The first thing that comes to mind is the hotter coolant affecting charge temperature and always detonating the rear housing before the front.
Second would be the rear housing deforming more than the front as torque tries to warp the rear housing and iron, and break out the dowels. So all of the causes add up to a bad deal for the rear housing.
Coolant on the Lemans engine goes in the cool side and out the hot side on each housing. So I suspect the NA engine suffers more from the coolant temps than the torque problem.
If you had two injectors that flow a bit more than the others, I would put them in the rear runners. Just a thought.
Lynn E. Hanover
12-22-2004, 08:31 AM
#6
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Join Date: Jul 2002
Location: Fayetteville, Georgia
Posts: 2,483
Wow, Lynn E. Hanover knows a lot about engines, but he can't quote for ****! 
Just giving you a hard time Mr. Hanover.
Speaking of EGTs, what temperature would let you know that the rotor is gonna die? Hah. I'm using my EGT to monitor the rear rotor (as suggested by a few people) and I was just wondering how I would know of a dangerous condition...
Speaking of EGTs, what temperature would let you know that the rotor is gonna die? Hah. I'm using my EGT to monitor the rear rotor (as suggested by a few people) and I was just wondering how I would know of a dangerous condition...
12-22-2004, 10:48 AM
#7
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Join Date: Oct 2003
Posts: 352
In my exeprience with two-stroke twin and triple racing engines there was a somewhat common problem of crankshaft flex. If you're going to hole a piston in one of those motors is almost always the rear cylinder. When the crank flexes the rear piston ends up coming slightly out of time with the front leading to more spark advance and ultimately detonation.
Now I'm not saying this is THE reason for any rotary failure but we have all heard of e-shaft flexing and that would lead to the same condition.
Now I'm not saying this is THE reason for any rotary failure but we have all heard of e-shaft flexing and that would lead to the same condition.
12-22-2004, 11:30 AM
#8
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Join Date: Sep 2003
Posts: 276
what is everyone opinion on intake runner length in a turbo app? in a na set-up the shorter runner will breath (make torque at a higher rpm) than the longer one which will make similar power but at a lower rpm. yes these are simplified ideas.
12-22-2004, 01:38 PM
#9
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Location: Europe, Belgium
Posts: 147
Yeah,
My 20B also had a dead rear and front rotor, only the middel one had 8 bar compression..
The cause was that the intake gaskket between the engine and the LIM was broken at the side of the secondary inlet so that rotor had been running lean... the middle rotor didn't had this, when I opened up the egine, the sideseals and corner tips popped out like it was just rebuilded... In comparision with the rear rotor: I couldn't get one sideseal out in one piece and with the front one broke after trying half an hour per seal...
This was with stock turbo's and ecu so I think it was running only 0.5-0.6 bar boost... So how the hell is a stuped paper intake gasket going to hold the boost pressure when using a big single?
My 20B also had a dead rear and front rotor, only the middel one had 8 bar compression..
The cause was that the intake gaskket between the engine and the LIM was broken at the side of the secondary inlet so that rotor had been running lean... the middle rotor didn't had this, when I opened up the egine, the sideseals and corner tips popped out like it was just rebuilded... In comparision with the rear rotor: I couldn't get one sideseal out in one piece and with the front one broke after trying half an hour per seal...
This was with stock turbo's and ecu so I think it was running only 0.5-0.6 bar boost... So how the hell is a stuped paper intake gasket going to hold the boost pressure when using a big single?
