I rebuilt my motor about a year ago and followed the usual break-in procedure for about 500 miles. The motor now has about 1700miles on it. The car is not driven much, but when driven, it gets a workout at about 25psi(BWS366). I tuned it myself, and find every now and again it gets leaner in the 5000 - 6000rpm range and I have to richen up that area of the map.
Could it be because the apex seals are now seating and the compression is now rising and requiring more fuel?

I log fuel pressure and see no drop over the time.

Has any one had any experience with this?

 

depends on how bad the compression was and gains as it breaks in, but even in drastic cases it is usually the idle range where you notice needing fuel, anything beyond that is generally tied to the boost that the engine can generate.

 

Come to think of it, I've had to add fuel to the idle cells. I usually tune idle at the very leanest possible afr , just before where the motor will begin to attempt to stall. Did'nt think anything of it since it would only stall after everything was heat soaked after along drive and I thought it was associated with the fuel compensation map.

 

"it gets leaner in the 5000 - 6000rpm range and I have to richen up that area of the map"

it is interesting that you mention 5-6 K as it is around peak torque depending on the ports.

peak torque is peak airflow and therefore is peak fuel

if this specific area requires more attention than higher or lower i wouldn't be surprised that it could be at least partially related to the important marrying process between the apex seal and housing.

my personal motor gained 16% compression over 4 years so the seal of our motors is a dynamic process.

i bet your S366 at 25 PSI is a hold-on ride

Howard

 

That what came to mind , peak torque. I have cleaned up that area so I'll see if it happens again.

'Hold on ride' Oh yea It was scary at first. I used to be very nervous when taking it out, but over time I got used to the power and now it doesn't seem so scary fast anymore.

 

Did you clearance the apex seals before installing?

I have never once seen compression get better. Every rebuild I have done had its best compression when first run.

 

Clearance? Are you referring to the apex seal to rotor gap clearance? If so yes, they were all within factory spec.

 

"Did you clearance the apex seals before installing?

I have never once seen compression get better. Every rebuild I have done had its best compression when first run."

my experience has been different. perhaps it is due to most of my motors have honed contact surfaces. yes to clearanced.

jetlude, what was the nature of your build rotor housings (new, used, re-honed) and what apex seal and premix?

H

 

Are you sure this isn't just a result of the weather changing?

 

Rotor housings were used and in reasonably good condition. Premix 1.5oz/gallon. Atkins non-cryo seals.

 

I've taken this into consideration. My air temp compensation map has been working well for me so far(I think). Still monitoring this.

 

I mean the apex seal length clearancing... I have the exact spec written down somewhere, but I'd like to say that I use .004" as the difference between apex seal length and rotor housing width with Atkins seals. I've never had Atkins seals that didn't need significant shortening to get in spec.

I, too, hone my rotor housings. Manually. I have enough stuff kicking around that I can probably make a rig to do it automatically, along with a lapping rig.

 

No, I've never clearance the length. How does the length clearance play into all of this?

 

Do you monitor fuel fuel pressure? Filter could be getting clogged or pump getting weak.

Jack

 

Yes, fuel pressure is logged, and in good supply.

 

JetBlue,
On aspect to consider is weak ignition... You are at high load on that system and if it is going to misfire this is usually where it starts.
When it misfires the AFR increases from unburned fuel... And unused oxygen.
Barry