RV-8 O-360 Temps and Fuel Flow issues

Hello all,

Just wanted to push out to all of you to see what you guys think about some of the engine issues I have. O-360, fixed pitch, dual P-Mags, Dynon D10 EMS. CYL #3 runs VERY hot even on cold days, even in cruise with CYL 2, 4 not too far behind. CYL 1 runs much cooler than the others. You can see some temps I see on climb and cruise taken on a winter day at altitude. Anything slower than a 100 KT climb will have my #3 CHT shoot to above 430 rapidly.

Also on climb out and WOT I will see my fuel pressure typically drop quickly from a nominal 3-4 PSI to .5 and 0 PSI which sets off the alarm. I've noticed this is often accompanied by an increase in fuel flow. Turning on the electric pump will push these up to 4. Securing the electric pump, the PSI will gradually decrease again to .5-0. Once throttling back to cruise settings the fuel pressure will climb back to nominal.

I am wondering if any of you have any ideas on the fuel flow and the over heating. What's a good way to check the baffles? Are there any good plenums out there for my configuration that has shown good success in cooling so I can do away with worrying about baffles? Searching through the threads it seems adding a washer helps with cooling but I'm not quite sure where that washer is being added....any photos to show this?

Otherwise the motor runs nicely and no noticeable performance issues associated with the drop in fuel PSI.

Any input is greatly appreciated!

Charles,
I have a similar setup with the exception of the prop (Hartzell). Here are my observations.

On a cold day, if I climb with a high angle of attack, my fuel pressure (not fuel flow) will occasionally drop to zero. My fuel flow remains healthy and all other engine parameters are in the green. Turning on the electric boost pumps remediates this. I think the problem may be with the sensor or could be air in the line.

I tend to climb out at 120kts. Anything slower and CHTs will rapidly rise. Due the angle of your climb you have a significant reduction in airflow over the cylinders. High power + reduced flow = high chts.

Your CHT spreads indicate that you most likely have some improvements to make in the baffling. There are plenty of suggestions in the forums on checking your baffles. Here is an example: http://www.vansairforce.com/community/showthread.php?t=113134 Look for others. There is no one magic bullet. Collectively they can significantly reduce CHTs. You should do whatever it takes to keep your CHTs below 400.

After you have implemented all the baffle fixes you can always add a cowl flap on the bottom of the cowl. This will allow you climb at a higher angle of attack or join the 90 Kt conga line to KOSH without overheating.

Two suggestions (if not done already & assuming you have checked for mixture issues)

1. Progressively block the front of #1 to warm it up and deflect air back to #3.

2. Open up the back side of #3 where the fins are too shallow. Search for the "washer trick" but better to make a proper chute for it. Many example here. Email me if you want a template for the chute, and a picture of the install. (also here on VAF)

Mike and Bill,

Thanks for the info and suggestions. Bill, you mention mixture issues: what do you mean in particular? Running it too lean? Even at full mixture it'll drop the CHT's a little but not by much. I would love a template for the chute if you don't mind sending it my way! [email protected]

Cheers!

Wingnut

Full Power FF

If the problem still persists after messing with baffle seals and other airflow solutions, check your FF at full power.
It seems some RV engine installs run lean. My O-320 160 was showing 11.8 gph at 98% power. The Lycoming manual says it should be about 13.9. Some say FF should be .9gph for each 10 hp at full power.
I recently had my carb jet reamed going from 42 to 40 and FF went to about 12.8. Further testing is needed to look for CHT improvements.

Good luck with the hunt.

Can you post some pictures of your baffles and cowl inlets? I chased this with every suggestion and when i finally switched to McFarlane cowl saver baffle seals and made sure that they were fully tucked behind the sides of the inlets I saw a drastic improvement in temps, like 30-50 degrees. Now my #3 actually runs coolest, even without the washer...

Fuel pressure drop with fuel flow rise

I've seen my fuel pressure drop and fuel flow climb (signifantly). I see this when I'm running a tank to empty. In my airplane it indicates I'm getting air in my fuel.

The zero fin depth issue on #3/5 and #2 is a well understood cause of most of these temp issues. The bypass duct solution is a proven fix for the deficient baffle design.

As often as this question comes up, perhaps its time to collect the various "bypass duct" threads and make a sticky? If Vans is not going to fix their baffles, at least this site can provide an easy resource for builders/operators to do so on their own.

You mentioned dual P-Mags. Make sure you have the jumper installed between 2 and 3 on the connector or, better yet, connect your computer and drop the Adv Shift to 0 or -1.4 and your Max Adv to 36.x.

If set via computer, you don't need the jumper installed.

I have the same issues w/ CHT & FF, but.........

One P-mag on a 0-230-D2B w/ Vetterman exhaust RV6 TD. Installed a JPI EDM 830 w/ FF and P-mag at the same time with the jumper . Tons of power, and high CHTs. #3 would reach 425 in climb and full power cruse no matter the altitude. Powering back to 2200 RPM reduced CHT temps.

But.... was able to have low CHTs, after building the harness for the Eicad and setting -1.4 for the shift and 36.4 for the max.Though it feels like some power was lost.

My FF is also low, 11.6 on take off and 12. 8 on climb out. Cruse is high 11's.
Not sure whats up with this. The FF gauge that the JPI replaced was showing 13 something on climb out. The carb was sent to the manufacture 4 years ago for a overhaul. They said the carb was bench flowed at 14 gph.

Both gauges are pretty accurate with fuel used / fuel remaining in reference to how much fuel I put in when at the pump.

I would think more fuel would equal for power / heat?

Any insight is welcomed

2-4 (390* average) seem to be in a pretty typical distribution, albeit high and probably addressed with baffling improvement. However, number 1 is about 70* cooler than the average of 2-4 in cruise. This seems like a pretty big difference for baffling/air flow imbalance. I would not rule out an issue with #1 producing less power than the other 3 and therefore less heat. A lot of things possible, but overly lean relative to the others is a good first start. Have you analyzed your EGTs to determine how far LOP or ROP each cylinder is at the power/mixture levels you are using?

You can try putting aluminum tape on the front of the #1 cylinders fins at varying heights to help increase the temps and push more air to the #3 cylinder. This will help confirm if it is an imbalance issue.

Larry

Rooster -

Yeah I noticed a big improvement on power with the Pmags and the CHT's getting a lot hotter. I also think the holes I cut for blast tubes actually contributed to the higher temps. I'm going to try and plug them for a test flight and see what kind difference that makes. Initially I had the P-MAGs, jumper in, timed at TDC. I knocked that down to 6 degrees past and that helped drop the temps a little. I just built the harness and going to try to move it back to TDC with a -1.4 though I don't want too much power reduction.

Your FF's sound normal to me for an O-360 and I would imagine actually high (vice low) for the 230. My cruise FF's are lower than 11gph though unless you're talking WOT. If they are marrying up with how much you refill, I would think that it is pretty accurate. It should be normal when putting in an EMAG to see increase in CHTs and decrease in fuel burn.

Larry,

Yeah, I'll have to look at some flight data for the EGT's in those respects and see what I find. In the mean time it's to war with the baffling!

Thanks