Baffle Question, #4 hotter, Question . . pict

BillL · #1 06-02-2018, 04:45 AM

In 20 hours of flight #4 CHT has always been hotter. It does not seem that the GAMI test points to it being out of line A/F wise.

The #2 head was blocked and un blocked with zero difference to #4.

The oil shutter was operated full open and full closed, no change in #4 CHT.

The fin flashing under the plug was reduced and dropped the diff from ~35F to ~15-20F. All other heads are within a 2F bracket.

edit: Swapped the probes from 2 & 4 and the high temp became #2 high as it was now in #4 head.

Has anyone determined that the baffle flap wrapped over the fins in the picture below has any effect? I am thinking it is the only thing left and a bit tentative to just cut it off without and external stiffener. The trouble would be worth it if anyone has data it will have an effect, though.

Any experience with this in VAF land?

[ok I admit, 15-20F is not bad, it just has me stumped. I gots to know . . ]

krw5927 · #2 06-04-2018, 07:00 AM

Watching with interest as my #4 CHT is always about 15F hotter as well. I always thought it must be due to a lot of air exiting through the oil cooler, but at the same time when the upper plenum pressure is stable in flight that shouldn't really matter.

BillL · #3 06-04-2018, 09:22 AM

Quote:

Originally Posted by krw5927

Watching with interest as my #4 CHT is always about 15F hotter as well. I always thought it must be due to a lot of air exiting through the oil cooler, but at the same time when the upper plenum pressure is stable in flight that shouldn't really matter.

Yeah . . . me too, wonderful to have data, I did the test several times to be sure (5 minutes at a time), and looked and plotted the G3X data - nothing.

DanH · #4 06-04-2018, 09:55 AM

Quote:

Originally Posted by BillL

Yeah . . . me too, wonderful to have data, I did the test several times to be sure (5 minutes at a time), and looked and plotted the G3X data - nothing.

I took oil cooler air from behind #3, then ducted it from the cowl inlets, then changed the cooler size and went back to taking it behind #3. It was easy to see the effect on oil temps, but there was no significant change to #3's CHT.

Bill, be bold, bend that tab down 90 degrees and report!

sstocker31 · #5 06-06-2018, 02:43 PM

That tab is definitely going to restrict airflow through those fins, probably cuts flow almost in half. As Dan said, if you gently straighten it and allow the airflow to increase, those fins that are right next to the exhaust will really transfer some heat away from the head.

My .02

crabandy · #6 06-06-2018, 02:55 PM

Bill,
Nothing to do with the lower tab and it was also in conjunction with remote mounting my oil cooler but I attribute a 20+ degree drop in #4 CHT's with the curvy baffling additions.

Unrelated but oil temps increased slightly with my remote mount because I lost some plenum pressure to the cooler face, more mods for another time.....

BillL · #7 06-17-2018, 11:44 AM

Thanks Andy!

Quote:

Originally Posted by DanH

I took oil cooler air from behind #3, then ducted it from the cowl inlets, then changed the cooler size and went back to taking it behind #3. It was easy to see the effect on oil temps, but there was no significant change to #3's CHT.

Bill, be bold, bend that tab down 90 degrees and report!

Quote:

Originally Posted by sstocker31

That tab is definitely going to restrict airflow through those fins, probably cuts flow almost in half. As Dan said, if you gently straighten it and allow the airflow to increase, those fins that are right next to the exhaust will really transfer some heat away from the head.

My .02

I bent the tab out of the way and there was no change in #4 temp relative to the others, still 15-20F.

If, one day something changes, I will post.

Mike S · #8 06-17-2018, 12:01 PM

Have you swapped the probe around to see if it is reading high?

BillL · #9 06-17-2018, 02:03 PM

Quote:

Originally Posted by Mike S

Have you swapped the probe around to see if it is reading high?

Yes, thanks, Mike. I should have included that in the OP. Added.

db1yg · #10 06-18-2018, 09:03 AM

Hi Bill,

I had the same problem (#4 ran 20 degrees F hotter than next hottest) and alway attributed it to the pick up point behind #4 for my firewall mounted oil cooler. My GAMI spread was also good at less than .5 gph--which lead me to believe it to be cooling air flow and not air/fuel flow. After ten years of tweaking the cooling airflow with minimal success I concluded that it MUST be associated with fuel/air flow--so I called Don at AirFlow Performance and explained the situation. He suggested some simple tests which I did then recommended a 1/2 step down in FI restrictor for #4--went down from a .024 to a .0235 restrictor. BINGO--now #4 runs in the middle of the pack for cht with a total cht spread averaging 8 degrees. My GAMI spread is now .2 gph.

Hope this helps.

Cheers,

db