C-90 Performance Mods

"Most engines benefit from breathing easier"

I would agree with that, and the 90's 24° cam would also benefit from that as well. As would the 35° cam of the O-200. Continental did not dyno these engines with the J3 or PA11 exhausts installed. My personal preference is for the sharper lobed O-200 cam, but that's because I never have to launch at density altitudes above 10,000 feet. The 90 cams will outperform the O-200 cam when the manifold pressure drops below 21 inches.

I typically prop the O-200 to give a 55 mph climbout between 2500 and 2800 rpm and an 79-81 mph cruise at 2250-2350 rpm. In a J3, I'm leary of a 55 mph climb at more than 2800 rpm with much less than 3 gallons in the nose tank for fear of unporting the tank outlet during the climb. At 2800 rpm and 55 mph, the J3 deck angle is very steep.

I've designed an offset J3 'muffler' that fits within the stock heat shrouds (so looks externally stock with shrouds mounted) but doesn't muffle and flows somewhat better than stock while also clearing the -12 oil screen housing. I haven't built or flown it yet, but am looking forward to doing so. I haven't given any attention yet to the 11 exhaust.

Better suck and blow help performance. Here's my choice for air filters...as close to an open system as I've tested for static rpm on a C-90 with their P10-7150 FFA/PMA element:

http://donaldsonaerospace-defense.com/library/files/documents/pdfs/007217.pdf

Gap

So, with a volumetric efficiency of about 0.8, at 2800 rpm the 90 and O-200 will pump about 130 cfm. That gives an improvement of 0.4 inch of H2O over the Brackett, for about a tenth of a percent increase in power output. About 0.1 to 0.15 hp. That's about a 2 fpm increase in the J3's rate of climb. Every bit helps.

I haven't had an air filter on my J4 for the last 900hrs

Glenn

JimC said:

So, with a volumetric efficiency of about 0.8, at 2800 rpm the 90 and O-200 will pump about 130 cfm. That gives an improvement of 0.4 inch of H2O over the Brackett, for about a tenth of a percent increase in power output. About 0.1 to 0.15 hp. That's about a 2 fpm increase in the J3's rate of climb. Every bit helps.

Click to expand...

On pretty much a standard August day at 425' MSL, 72F, 29.85" Hg from set to 0' on altimeter...MP gauge read 30.10" Hg. Nosed into the bank on floats...fresh C-90 in a PA-11. Prop Sen 76AK-2-40. Used digital remote sensing Proptach sitting on panel. Here's the WFO static data I recorded with a new Brackett filter element and new Donaldson P10-7150:

Brackett 28.5" 2300 rpm
No air filter 29" 2325 rpm
Donaldson filter 28.9" 2320 rpm

Every little bit helps.

GAP

cubdriver2 said:

I haven't had an air filter on my J4 for the last 900hrs

Glenn

Click to expand...

Probably not many volcanoes or blowing dust where you live?

GAP

I agree wholeheartedly about the every bit part.
So, the chart and text in the link was wrong?
(it doesn't jive with your numbers - it gives a half inch of water difference for 130 cfm, and you are seeing a half inch of mercury - big difference)

JimC said:

I agree wholeheartedly about the every bit part.
So, the chart and text in the link was wrong?
(it doesn't jive with your numbers - it gives a half inch of water difference, and you are seeing a half inch of mercury - big difference)

Click to expand...

Well that's what went down for me, not sure what Donaldson did but I suspect they used a flow bench and not a real engine. I repeated the test forwards and then backwards the same day...same results. The Brackett has two potential flow issues...the foam element (mine was unused) and the backing/anti-backfire louvered metal plate. Both are restrictions versus an open air box. I didn't try just the Brackett filter without the foam element. The Donaldson and K&N/Challenger filters don't use the metal backing. Later I compared the Donaldson vs Challenger in that PA-11 and saw no detectable difference.

I also compared the Brackett versus the Donaldson on my current C-85 Stroked Taylorcraft w/C-150 exhaust, newly rebuilt tight airbox, and saw similar static results with the same prop...Brackett about 2415 and Donaldson about 2440. The rpm bounces around some but the Donaldson again offered about 0.4-5 "Hg manifold pressure and increased static rpm. Yes the static is above TCDS specs and a hundred or so over my previous PA-11 with C-90. Not all engine installations are created equal.

Edit: I install MP gauges to quickly detect carb ice and monitor MP at idle and WFO. Lower is better at idle (10-11"); higher better WFO (I like to see no more than 1" Hg system loss) and as close to ambient air pressure as possible. It's just a way to note a tight engine and infer volumetric efficiency.

GAP

On my other cub I still use the original folded media wash and oil type, last forever

Glenn

I don't like the brackett either (except in very, very dusty conditions).

I typically see about a 25-30 rpm static difference between the Brackett and no filter.

I'm thinking about a C150 exhaust for my O-200 11. How is it working out for you?

JimC said:

I don't like the brackett either (except in very, very dusty conditions).

I typically see about a 25-30 rpm static difference between the Brackett and no filter.

I'm thinking about a C150 exhaust for my O-200 11. How is it working out for you?

Click to expand...

The only comparison (and a loose one at best) is between my former PA-11 C-90-8F with the Piper exhaust and my current C-85-12F Stroker with the Cessna C-150 system...static rpm was higher on the latter with the same intake and internals (I have a C-90 cam in the Stroker). I assume Cessna and Continental did their best to get power out of the O-200 while providing heat for the cockpit. So yes I'm happy with the system. The headers can be curved inwards some (Atlee did mine for the builder) to fit a tight cowl.

Another option that may fit better would be the Luscombe exhaust: http://www.acornwelding.com/pdf/Luscombe/Luscombe Model 8E_F.pdf or similar. Good reports on these as well.

More on this: http://luscombe.org/technicaldocs/baffling facts about your exhaust system.pdf and http://dc65stc.blogspot.com/2010/09/taylorcraft-exhaust-conversion.html

GAP

Main advantage to the C150 exhaust is that I have one lying around.
Are you running the 788 cam in the Stroker?
Or the 24° cam?

JimC said:

Main advanage to the C150 exhaust is that I have one lying around.
Are you running the 788 cam in the Stroker?
Or the 24° cam?

Click to expand...

Well if the C150 exhaust is sitting there then have a go at it...might take some fitting and as I mentioned the headers can be bent closer to the engine. I'm running a C-90 forged cam and required lifter bodies in a C-85 case machined for them...I assume it's a 531076 with 24* overlap (others did the work). The SBM47-16 (Rev. 1960 Supp. No.1) and M49-17 discuss this. Magneto timing to the upper range of acceptable tolerance is important.

Edit: I'd also experiment with exhaust stack length at some point. See if exhaust reversion timing can affect power in that installation.

GAP

"Magneto timing to the upper range of acceptable tolerance is important".

True. In one O-200, I run 28° BTDC with the 9.5 pistons and the 35° overlap O-200 cam. Am thinking about advancing a bit more. Other O-200 is stock.

JimC said:

"Magneto timing to the upper range of acceptable tolerance is important".

True. In one O-200, I run 28° BTDC with the 9.5 pistons and the 35° overlap O-200 cam. Am thinking about advancing a bit more. Other O-200 is stock.

Click to expand...

Seeing as how mine's still wearing a C-85 data plate under TCDS E-233, 28R/30L* is the legal upper tolerance range (+-1*) listed for a STC SE00979AT Stroker. Not sure what an O-200 would tolerate. I'm not an A&P so I just throw $ at the builders.

GAP

I pull a cylinder and look at the pistons ever hundred hours or so. I suspect the 9.5 O-200 would tolerate 28/30, but haven't actually tried it. Wanted to build up a few hundred hours at 28° first. It's also bored 0.015" oversize. So far, so good. Tried Total Seal rings, but couldn't get the valve guides to quit leaking oil due to the increased suction. With them, got a puff of blue smoke every time I cobbed the throttle.

Pre-detonation might manifest itself on the piston tops...pocking and irregular carbon coverage...so if it looks good then fly more. I guess I'd rather have a little more oil on the guides as long as they aren't coking and as a result show offset of the valves. How do the inner valve covers look? Any sign of excessive exhaust blowback through the guides and seals and uniform between cylinders? Are the exhaust valve faces uniform in discoloration and seating/cooling well?

I wrestled with installing higher compression pistons than 7:1 with this latest engine but decided against it as I wanted durability and not to expose the builder to undue scrutiny. Cooling then becomes more critical too. So it works well enough.

They did something to the center main cross-bolting to help it hold hands better, but I expect it wasn't a complete through bolt like the larger engines. The carb is a MS but without jetting mods one has to be careful with A/F ratios feeding power produced.

If I did it again I'd probably try the Luscombe exhaust (maybe with a crossover tube between stacks for a 2-1-2 setup) unless someone has dynoed one and found a loss of performance over a C-150 system.

GAP

No noticable blowback through the guides. Valves and seats look and seal good (I run 93 octane mogas with ethanol). Carb is an MA3-SPA 10-4115 with brass float. 9.5 cooling is not an issue on a J3 (no intercylinder baffles), but I don't think I'd be comfortable running more than 10.0:1 pistons on mogas at advanced timing.

Ok Jim I missed the J-3 part...so an exhaust external to the cowl is not an issue of fit I assume. Well I'd surely experiment with exhaust to see if there's any benefit to be gained.

How's your mixture distribution between cylinders? Do you see any visible color differences on the internals or EGT spread? If so, how have you dealt with it? I was thinking of having Atlee X the outlet of the airbox to maybe straighten the flow into the carb but forgot when it was time to have it done. I don't have an EGT.

Prop...I've read here and elsewhere about which pulls the best...what's your current preference in a Sen or Mac? Lots of Cattos have migrated north to Alaska but I'm reluctant to try just yet.

Gary

The C150 exhaust would have been for my 11, not the 3.

Mixture distribution seems OK - no signs of temperature distress, runs very smooth. J3 is non-electric, so don't have good figures on CHT/EGT. Were they bad, I think it would have shown up during recurrent internal inspections.

Mac 7440 seems to outpull everything else up to 2700 rpm. Above that Mac 7535 comes into its own.
I'm curious about Catto, but no experience.