GAMI spread and RAM AIR...Running LOP

[GeorgePerry]

I've been doing alot of LOP flying lately and I've made some interesting discoveries...I'm wondering if others who fly LOP have seen greater GAMI spreads with the ram air door open? 

Here's what I've seen:

At higher altitudes with WOT and RAM-AIR door open, 60% power, my gami spread was terrible (0.8-0.9 GPH).  I talked with John at GAMI and he suggested tyring lean tests both at low altitude/low power setting (60%) with the ram air door closed and high altitude/same 60% power and also leave the ram air door closed.  He said the peak EGT and GAMI spread should be almost identical. 

After we spoke I tried LOP tests at both low altitude (4K) and a higher altitude (9K)  I discovered that leaning with the ram air door closed, the spread is quite good. (0.1 - 0.3 GPH) regardless of altitude. 

However, at altitude (>9K) with the ram air door open the GAMI spread jumps  back up to (0.8 - 0.9 GPH).  The unfiltered ram air effect must cause some uneven induction swirl because the spread gets so bad with it open.

Bottom line for me is with the ram air door closed, flying LOP, the GAMI's work as advertised.  I'll just make a point of only using the ram air when flying ROP at higher power settings.

[N9660M]

George, had the same experience.  Installed GAMIs when I had my engine overhauled.  Just finished my engine break in and started working with LOP.  On a flight back from Georgia a couple of weeks ago was able to get her running very nicely 30 degrees LOP at 9000 feet with ram air shut, but ran very rough when I tried to set LOP with ram air door open.  Don't have fuel flow (that's next year's upgrade) so not sure about the differences between cylinders, but it must have been significant.

[Cruiser]

Well, it makes sense. If you got GAMIs based on the mixture when the ram air was closed, changing the amount and induction of intake air by use of the ram air is going to change the fuel mixture.

On my '84J opening the ram air makes the FF increase by about .2 gph. That's about it. The GPS readout is in kts. and it doesn't change so for the increase in fuel I get less than measureable amount of speed increase.

[Immelman]

I have stock injectors, but I have have had a heck of a time getting to run LOP at WOT... and from what I recall it is worse with ram air. On the other hand, I have no problems running LOP up to about 60% power at low altitudes. Because of these I use LOP when I'm flying around the local area for fun or practicing maneuvers; that is about it.

It is as if the last bit of opening the throttle and/or ram air mess with the induction system just a bit.

[Ned Gravel]

OK.  This is good. 

I normally cruise between 6000' and 9000' depending on the direction of flight and any other factors such as ice etc.  But I have been trying to run LOP since I got the plane to 50 hours beyond MOH.  No luck.  Runs too rough (well at least too rough for me).

Now I see that ramair may have been playing havoc with my attempt to do this.  Next time I try, it will be with the ram air door closed.  

Thanks for the info folks.

 

[M016576]

My experience is similar to cruiser's... if I see any sort of appriciable difference in MP, then I know that it's time to swap out the filter element.  I have yet to see a knot difference with the ram air open... and my GAMI spread is still at .4gph (same when it's closed... stock injectors, too).