What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

The mystery of #4...

bjdecker

Well Known Member
Ambassador
Greetings,

I have a bit of a mystery and would like to appeal to the brain-trust for assistance.

The configuration: RV-7, Lycoming YIO-360-A1B6, Hartzell F7497 CS Prop, Dual Lightspeed Plasma III - timed to 20?, Denso IK27 plugs, Avstar AVX-5VA1 fuel injection servo, Standard pistons (8.7:1 CR), Custom Plenum, SW 8406R oil cooler mounted on firewall fed by 3" SCEET duct from above #4 cylinder, Temperature risers are installed in front of #1 and #2 cylinders - #1 is 1/4" lower than "stock", #2 is 3/4" lower than "stock", #2 cylinder is the hottest - followed by #3, #1 and ultimately #4.

The symptom: during climb out, and in all subsequent phases of operation at or above 80 Kias, the #4 cylinder will run ~30? colder than the other 3 cylinders (#4 max is 336?F, others max ~365?F).

Additional data: all 4 cylinders "peak" within .1GPH (e.g. 9.3GPH at 6500msl), and all EGTs are within 75?F of each other for all phases of flight. Probes have been swapped, tested, and appear correct.

My objective is to get #4 up to the same temps as the rest. Any ideas would be greatly appreciated.

B
 
Check this -- not that...


Hey John -- thanks for the reply; unfortunately - nothing in the attached thread was applicable; K-type probes and K-type configs, #2 and #3 gaps are ok, problem is with #4 getting too cold, not the others running too hot...

I wonder if the temp riser in front of #1 is too high and there is a cross-flow behavior that's pushing more air to #4 as a result? #1 sits in front of #2 laterally, and #1 catches the air spilling off the trailing edge of the prop moving DOWN -vs- #2 which catches the air spilling off the trailing edge of the prop moving UP...

B
 
Greetings,

I have a bit of a mystery and would like to appeal to the brain-trust for assistance.

The configuration: RV-7, Lycoming YIO-360-A1B6, Hartzell F7497 CS Prop, Dual Lightspeed Plasma III - timed to 20?, Denso IK27 plugs, Avstar AVX-5VA1 fuel injection servo, Standard pistons (8.7:1 CR), Custom Plenum, SW 8406R oil cooler mounted on firewall fed by 3" SCEET duct from above #4 cylinder, Temperature risers are installed in front of #1 and #2 cylinders - #1 is 1/4" lower than "stock", #2 is 3/4" lower than "stock", #2 cylinder is the hottest - followed by #3, #1 and ultimately #4.

The symptom: during climb out, and in all subsequent phases of operation at or above 80 Kias, the #4 cylinder will run ~30? colder than the other 3 cylinders (#4 max is 336?F, others max ~365?F).

Additional data: all 4 cylinders "peak" within .1GPH (e.g. 9.3GPH at 6500msl), and all EGTs are within 75?F of each other for all phases of flight. Probes have been swapped, tested, and appear correct.

My objective is to get #4 up to the same temps as the rest. Any ideas would be greatly appreciated.

B


Sounds like you have the same numbers I?ve had on my IO-360A1A powered RV-8 for the last 12 years and 1700 hours. Those numbers are identical to my friends? RV-8?s with the same engine. Many years ago, I trimmed the dam in front of #2 with no appreciable change. That cylinder just runs cooler than the rest. Think of the cooler temp on #4 as a bonus and enjoy.
 
UP?

Bring CHT up? Why? Temps are looking good. Think of CHT and cylinder peak pressure instead. You never want to increase it.
 
Sounds like you have the same numbers I?ve had on my IO-360A1A powered RV-8 for the last 12 years and 1700 hours. Those numbers are identical to my friends? RV-8?s with the same engine. Many years ago, I trimmed the dam in front of #2 with no appreciable change. That cylinder just runs cooler than the rest. Think of the cooler temp on #4 as a bonus and enjoy.

Me too. #4 runs coolest by 30F. For me, it is more like 265F when the others are in the 290--300 range.
 
Me too. #4 runs coolest by 30F. For me, it is more like 265F when the others are in the 290--300 range.

Thanks for the data Steve(s), Rob, Jerry. I was beginning to wonder if it was something that I had done.

I guess I'll just enjoy the temps :)
 
Last edited:
Back
Top