Single Turbo Discussion Area for discussing single turbo RX-7's.

Losing Compression On Dyno, Any Ideas?

Old 03-28-2004, 11:39 AM
  #11  
Senior Member
Thread Starter
 
Join Date: Feb 2003
Location: NewHampshire
Posts: 100
Default

Originally Posted by 1Revvin7' date='Mar 28 2004, 09:30 AM
So is the edge that seats against the rotor housing rounded?
YES and discolored like from lean/heat but widebands show rich, 3 different widebands have verified this at different sessions.
93FDGT3540 is offline  
Old 03-28-2004, 11:40 AM
  #12  
Senior Member
Thread Starter
 
Join Date: Feb 2003
Location: NewHampshire
Posts: 100
Default

Originally Posted by 1Revvin7' date='Mar 28 2004, 09:28 AM
How long had those cleaned injectors sat around for before they put into the car?
maybe a day or two
93FDGT3540 is offline  
Old 03-28-2004, 11:43 AM
  #13  
Senior Member
 
Join Date: Jan 2003
Location: union, new jersey
Posts: 8,079
Default

did you bevel the exhaust ports?
FikseRxSeven is offline  
Old 03-28-2004, 11:50 AM
  #14  
Senior Member
 
Join Date: Oct 2001
Location: Peoria, AZ
Posts: 10,906
Default

If the porting was done wrong it would cause that edge to be rounded. But if

JRs is Ito's shop then thats not even a possibility.

Well its has to be either bad housings or bad porting. What else woulc cause that rounding?
1Revvin7 is offline  
Old 03-28-2004, 12:01 PM
  #15  
Senior Member
 
Join Date: Dec 2001
Location: Jensen Beach, FL / Sylva, NC
Posts: 2,934
Default

Originally Posted by 93FDGT3540' date='Mar 28 2004, 12:35 PM
tuners dont know, basically grasping at straws, engine builder is one of the better builders and hasnt ever seen this either. The only other things may be internal due to the same problem arising from same reused housings. I need to consult the engine builder for specifics of the build. The tuner thought the rotor housing exhaust port could cause a seals to fail but i would know for sure if that was the issue unless i replaced the housings with new ones. Can an oil metering failure cause this type of damage/heat to plugs and seals? car does not break up. no detonation. its run rich into low 10's and as high as mid 11's on different rebuilds and all with same result. no more then 15-16 degrees of advance
You ask about the the OMP failing. I am hoping your premixing. I doubt this is your main problem but it could be contributing to it.



you should run 8 oz. of premix per tankful.
Jims5543 is offline  
Old 03-28-2004, 12:06 PM
  #16  
Senior Member
 
Join Date: Aug 2002
Posts: 502
Default

Originally Posted by FikseRxSeven' date='Mar 28 2004, 09:43 AM
did you bevel the exhaust ports?
We're not sure if mike's exhaust ports were bevelled, we'll have to talk to the builder about it.



This is something the tuners asked about also. Please elaborate on the effect that not beveling would have. The leading edge of mike's seals have a slight convex curve to them on the sections that are outside the exhaust ports. The part of the seal that passes over the exhaust port does not have the same convex shape. Instead the curve seems to have been worn down so that top of the seal comes to a point with two straight sides rather than an overall arc.



Non exhaust port area shape:

<span style='font-size:14pt;line-height:100%'>)</span>



Exhaust port area shape:

<span style='font-size:14pt;line-height:100%'>></span>



In the last photo I attacked you can make out where the two planes ( / and \ ) come to a point. The each face (symbolized by a "/" in the previous sentence) of the point is black in color. By contrast the area where the two planes meet is silver in color and at the same height as the center of the convex curve for the edge of the seal that does not pass over the exhaust port.



Bear in mind that the difference is extremely subtle, but then again all these motors had less than 2,000 miles on them.
ccarlisi is offline  
Old 03-28-2004, 12:06 PM
  #17  
Senior Member
 
Join Date: Oct 2001
Location: Peoria, AZ
Posts: 10,906
Default

Well it does appear the oil injection is working as you can see where it is clean in the center of the burned apex seal. And yes you should be premixing.
1Revvin7 is offline  
Old 03-28-2004, 12:09 PM
  #18  
Senior Member
 
Join Date: Oct 2001
Location: Peoria, AZ
Posts: 10,906
Default

Originally Posted by ccarlisi' date='Mar 28 2004, 01:06 PM
We're not sure if mike's exhaust ports were bevelled, we'll have to talk to the builder about it.



This is something the tuners asked about also. Please elaborate on the effect that not beveling would have. The leading edge of mike's seals have a slight convex curve to them on the sections that are outside the exhaust ports. The part of the seal that passes over the exhaust port does not have the same convex shape. Instead the curve seems to have been worn down so that top of the seal comes to a point with two straight sides rather than an overall arc.



Non exhaust port area shape:

<span style='font-size:14pt;line-height:100%'>)</span>



Exhaust port area shape:

<span style='font-size:14pt;line-height:100%'>></span>



In the last photo I attacked you can make out where the two planes ( / and \ ) come to a point. The each face (symbolized by a "/" in the previous sentence) of the point is black in color. By contrast the area where the two planes meet is silver in color and at the same height as the center of the convex curve for the edge of the seal that does not pass over the exhaust port.



Bear in mind that the difference is extremely subtle, but then again all these motors had less than 2,000 miles on them.
Does it look like this? or does the apex seal hit a sharp flat edge?



1Revvin7 is offline  
Old 03-28-2004, 12:19 PM
  #19  
Senior Member
 
Join Date: Aug 2002
Posts: 502
Default

We're not sure. We're thinking of using a medical scope to see if we can catch a glimpse of the seals through the exhaust port. If we are able get access to the equipment we'll check out the port edge too.
ccarlisi is offline  
Old 03-28-2004, 12:29 PM
  #20  
Member
 
Join Date: Dec 2001
Posts: 98
Default

Just got back from NYC/LI.....



Hey Mike,

Sorry that the motor isn't working again. I'm clueless as to why the engine keeps eating up apex seals. For those that are curious about this, here're some findings I notice on his car.



First, I don't think there was any fuel issues with the car since we verified the spark plugs almost every 3-4 pulls (reclean them before putting back in). On the first couple of pulls where I dial the a/f in so that I could barely see it register on the wideband. After we pulled the spark plugs out, we notice a very minor color difference with front and rear plugs (not even very noticable unless you looked at it very closely). Knowing mike's engine has suffer melting front apex seals, I decided to richen up the primary injector by 8% (2.7% overall in total fuel). We made 2-3 more pulls (a/f ratio was below 10 where we couldn't even register). Pulle the plugs back out and saw that the front was richer than the rear, I then lean out the front offset to 5% over the rear (1.8% overall in total fuel), make a few pull and then recheck the plugs. It was still running rich, so the final offset adjustment ended to be 2% (.7% more than the rear). Which is negligible (if you think about it). Now that we know both front and rear offset is dial in, we then slowly lean out the a/f to try to tune it out. I tried to tune his car to around 10.5:1 because of mike's past engine history. There was a few times where it the a/f hit 10.7-10.8 but not many time has it get close to 11:1 a/f ratio. As we started to make more pull, the engine vacuum started to drop. It wasn't much noticable at 11psi but when we slowly turning the boost up, the vacuum drop was definately noticable and was evident that the issue still exist. We pulled the plugs out again to check, everything seems fine and shows signs off running rich. The only thing I could really think off is the exhaust port or the shape of the port causing it to run higher EGT than normal. I couldn't verify that w/o knowing what the port looks like but after looking at the worn out apex seals (after the tuning), it seems like that it couldn't have been caused by lean a/f ratio but rather very high EGT at the manifold or the exit of the port. I wish we could have made another pull on the dyno to see how hot the exhaust manifold. Also the turbine wheel and see if there are any abnormal wear caused by extreme thermal conditions.
pluto is offline  

Thread Tools
Search this Thread
Quick Reply: Losing Compression On Dyno, Any Ideas?


Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.