Not quite the speeds expected

I have just completed the test phase of my RV7. Throughout the testing, I expected higher speeds than what I was getting. I am currently attaining 110-120 knots with 2200 RPM /22 MAP. The aircraft is configured with all but leg fairings and wheel pants. I'd expect the lack of fairings and pants would contribute to a loss of 10-20 knots. That doesn't make up for the 170-180 knots that I am hearing from other RV7 owners.
I have an EFii ignition/injection system with CHTs/EGTs in the 185/1300 range. The ignition timing, however, is rather generic in settings and I am suspecting that it may be contributing to the lack of power. The EFii documentation to tune the timing is rather weak. Anyone have insights or suggestions to 1) identify the lack of speed (fairings, wheel pants) and/or 2) how to insure the timing is set correctly?

2200 rpm? Try pushing the throttle in a bit...

Yes, fairings and wheel pants will be significant.

A few things/questions.
1. Are you reading indicated airspeed and expecting to see 180-200kts? or are you looking at true airspeed?
2. Fairings/wheelpants will not give you 20 kts.
3. Those chts sound way to low. Should at least be around 300 deg F.
4. Did you calibrate your airspeed indicator? Have you flown next to another plane and compared speeds?

What is your fuel flow? Why do you limit RPM to 2200? FP or CS?

185 degrees CHT? That is below typical CHT at idle. Perhaps you timed it for ATDC instead of BTDC?

I’d start with whatever install instruction you got with your EFII system. Perhaps setting timing fixed at 25 degrees BTDC and see what you have before “tuning” is is a place to start.

Carl

My bad! I meant 330-350 CHT. The 185 was my Oil Temp. While I gave 2200 as an example. I've tried the full range of the throttle.

The speed I indicated is IAS. I've compared that to the TAS and GS via GPS. They all are in the same range.

Glen,

As Axel, Rob and Carl said, a bit more info would be good to have, so that feedback is appropriate and beneficial. Here's some Q's:

Engine?
Compression Ratio?
---the above two might guide recommendations on where to set timing. I'd start with a call to Robert at EFII. I see the install guide on his site, but the link to the user's manual is not live. Changing timing can be perilous too, so talk to him on how best to read what you have, and change it as he guides. Rob's idea of fixed timing is a good idea for initial test. Whether that be 20, 22, 25 or whatever depends on your engine. Advancing timing changes CHT faster than it changes horsepower, so it can be risky. However, at 330-350, you have room to play...but it depends on where your power is set during the tests you have flown thus far, and what your test conditions are.

Prop? FP or CS?
MP and RPM?
--- together those give us an idea of where power setting actually is. "full range of throttle" is a bit too general.

Test Altitude? OAT? DA? Altimeter Setting?
--- this will help narrow your TAS results. IAS vs TAS is conditions dependent, not revealed by GPS. They are close together at Sea Level, but less so as you climb...so depending on where you're testing, you may be going a bit faster than you think. GPS is used to verify the accuracy of your IAS/TAS, but that's another aspect of this mission.

Knowing all the components, all the conditions, all the settings, and all the indications will help narrow the results and recommendations. Hope that doesn't sound snarky or over-simplified. A lot of us have done a lot of testing, and it would be fun to help you get to the bottom of it.

Cheers,
Bob

GKnut said:

My bad! I meant 330-350 CHT. The 185 was my Oil Temp. While I gave 2200 as an example. I've tried the full range of the throttle.

The speed I indicated is IAS. I've compared that to the TAS and GS via GPS. They all are in the same range.

Click to expand...

I understand your efforts. Below is an outline of the aircraft and of conditions during a recent flight. Robert (EFii) indicates that 2200 RPM is ~60 of full throttle (2750) so 110-120 kts didn't sound unreasonable to him. I will do a test run at full throttle (2750 RPM) as various prop pitch settings. I'll provide an update of what I see. Perhaps this may all be part of my paranoia of my new aircraft!

Aircraft: RV-7
Engine: IO-375
Propeller: MT CS
Ignition/Injection: EFii

Flight
Altitude: 5500
Engine RPM: 2020
MAP: 20.2
CHT (Avg): 320 deg
EGT (Avg): 1145 deg
IAS: 108 kts
TAS: 118 kts
GPS GS: 125 kts
Heading: 126 deg Mag
Wind Speed: 9 kts
Wind Dir: 334 deg Mag
OAT: 4 dec C

Glen,

Full throttle and max RPM are not the same with a CS prop.

I suggest getting to ~6K’, set the prop at 2500 RPM and apply full throttle. Do some data runs. For these test fuel flow is a key data point.

Keep in mind you keeping the engine at such low power promotes cylinder glazing. Keep the engine above 70% power for the first 10-15 hours.

Carl

What others have said plus

What the others have said, plus...

Read this Kit Planes article and perform the speed tests:

https://www.kitplanes.com/flight-testing-finding-tas-from-gps-data/

GKnut said:

I understand your efforts. Below is an outline of the aircraft and of conditions during a recent flight. Robert (EFii) indicates that 2200 RPM is ~60 of full throttle (2750) so 110-120 kts didn't sound unreasonable to him. I will do a test run at full throttle (2750 RPM) as various prop pitch settings. I'll provide an update of what I see. Perhaps this may all be part of my paranoia of my new aircraft!

Aircraft: RV-7
Engine: IO-375
Propeller: MT CS
Ignition/Injection: EFii

Flight
Altitude: 5500
Engine RPM: 2020
MAP: 20.2
CHT (Avg): 320 deg
EGT (Avg): 1145 deg
IAS: 108 kts
TAS: 118 kts
GPS GS: 125 kts
Heading: 126 deg Mag
Wind Speed: 9 kts
Wind Dir: 334 deg Mag
OAT: 4 dec C

Click to expand...

I wouldn't expect much speed at 20/2000. You don't list fuel flow. EGTs seem really low, so suspect very rich or very lean. DOes the EFII have a baseline fuel map for a 375? I am guessing not. I would not continue running till that is sorted out. I can't help but wonder if you are drowning it with excess fuel or very lean. I hope you didn't use a default fuel map for a 360.

FYI, paranoia during break in is not good. Need to run it like you stole it. At least AFTER you sort out fuel flow and timing.

GKnut said:

and/or 2) how to insure the timing is set correctly?

Click to expand...

I would never tweak settings on an EFI without using a timing light to confirm things. The pickups can be variable and would hope they have you confirm EFI timing matches actual with a timing light or some other means of matching the EFI's thoughts on where TDC is compared to where it actually is. Timing way off normal could be causing the low EGTs and power.

lr172 said:

I wouldn't expect much speed at 20/2000. You don't list fuel flow. EGTs seem really low, so suspect very rich or very lean. DOes the EFII have a baseline fuel map for a 375? I am guessing not. I would not continue running till that is sorted out. I can't help but wonder if you are drowning it with excess fuel or very lean. I hope you didn't use a default fuel map for a 360.

FYI, paranoia during break in is not good. Need to run it like you stole it. At least AFTER you sort out fuel flow and timing.

Click to expand...

The base 360 fuel map works pretty well for the 375, at least on the SDS system. There's some fine tuning to do for sure, but overall it runs well out of the box. The volumetric efficiency is close enough between the two that you easily get within range of where you should be with a little adjustment on the mixture knob.

You can't calculate percent power without fuel flow. I normally cruise around 22/2400 (full throttle, 8500-10500 ft) and can vary my power setting between 45% and 75% with the mixture knob. Airspeed changes over 30 knots are available by only changing the mixture. Do any of your instruments calculate power setting for you? If not, full throttle, 7500-8500 ft, 2400 RPM and 100 degrees rich of peak is a fairly common spot for people to do cruise performance testing. I spent the first 20 hours of engine breakin right around that point (maybe a little richer because of engine temp issues), but it'll give you a good idea of what its capable of.

Glen,

Same thoughts as some of the others...fairly low power for a speed performance evaluation. CHT looks reasonable for 20-squared, and EGT looks perhaps a little low. Are you full rich at 5500'?

You said you were out of test phase, right...so your engine is broken in, right? So, if you want to evaluate cruise performance, replicate what you think typical cruise conditions will be. For me that's 8500' to 11500' MSL, WOT/2300, 20-30° LOP. For max speed testing it's 8500' WOT/2750, 100° ROP (or wherever I can lean to and not go over 400° CHT). 8500' or above is selected for testing to stay away from detonation when leaning. If you're still breaking in the engine, then higher power and staying ROP is a good idea. Sounds like Robert is advising you on timing, so that is good. Tell him I said hi.

I use the NTPS spreadsheet for comparison testing of mods, though initially you may just want to see what IAS/TAS you are getting, and focus on flying, engine management and data recording. That way you get a ball-park figure, and once you have the fairings on, you can refine it with the 4-way tests. Just a thought.

Have fun!

Cheers,
Bob

GKnut said:

I understand your efforts. Below is an outline of the aircraft and of conditions during a recent flight. Robert (EFii) indicates that 2200 RPM is ~60 of full throttle (2750) so 110-120 kts didn't sound unreasonable to him. I will do a test run at full throttle (2750 RPM) as various prop pitch settings. I'll provide an update of what I see. Perhaps this may all be part of my paranoia of my new aircraft!

Aircraft: RV-7
Engine: IO-375
Propeller: MT CS
Ignition/Injection: EFii

Flight
Altitude: 5500
Engine RPM: 2020
MAP: 20.2
CHT (Avg): 320 deg
EGT (Avg): 1145 deg
IAS: 108 kts
TAS: 118 kts
GPS GS: 125 kts
Heading: 126 deg Mag
Wind Speed: 9 kts
Wind Dir: 334 deg Mag
OAT: 4 dec C

Click to expand...

GKnut said:

I have just completed the test phase of my RV7. Throughout the testing, I expected higher speeds than what I was getting. The aircraft is configured with all but leg fairings and wheel pants. I'd expect the lack of fairings and pants would contribute to a loss of 10-20 knots.

Click to expand...

Wait a minute... you COMPLETED the test phase, but never had fairings and pants installed?

Pitot Static System?

Have you checked your pitot static system for leaks? Before chasing suspected engine issues have a competent avionics shop do a pitot static system check. A leaking system can cause low indicated airspeed/true airspeed readings and incorrect altitude readings. Having a chase aircraft fly formation on you giving readouts may be helpful but won’t guarantee your system is airtight and indicating correctly.

A friend had to have his recently purchased RV9A replumbed because of excessive pitot static leaks. When the panel was upgraded the technician used quick connects instead of compression fittings and non-aircraft grade tubing which all quickly started leaking. Nothing like seeing 40knots on final and knowing the airplane is flying fast but wondering “how fast?” We purposely used known power settings for the approach and gladly used the entire runway length for landing.

Given the numbers in post #7, rough calculations give 95 hp and 47% power if the mixture is set for maximum power. That's about the same hp as 75% cruise power on a Lycoming O-235.
Please correct me if my math is not in the ballpark.

Glen, i have the same aircraft, same engine (low compression version) and was chasing the same problem. figured out later that there wasn't one with the aircraft, problem was between the headphones. As others have suggested...

1. get your airspreed calibrated. there are good descriptions how to do that available online. the numbers you are looking for are true airspeed, not indicated.

2. put on gear leg and wheel fairings and adjust them so that they don't interfere with steering of the aircraft. fairings have significant impact on speed, so it's a mute point to worry about a non-performing airplane as long these are not installed.

3. apply full throttle at DA of around 8000 ft, set RPM to 2600 - 2700 (not 2750). mixture has huge impact on power output, select 50 - 100° ROP or so. your engine should make around 75% power at this setting. if you have a 3-blade prop you should expect a slightly lower speed than for a 2-blade. 3 blades have more drag than 2, take that into account.

4. see how fast she flies and report back.

have much fun, it's a fun project.

Kay

Kay,
That tentatively sounds like what I am experiencing. I have run several tests in order to calibrate the airspeed. Short of sending it to a shop, it seems to be in accurate. There is a slow moving front in the area so now would be as good a time as any to cover the mistress's legs. Can't let her get ogled at too much. I'll keep you updated. Thanks for the input.

agent4573 said:

The base 360 fuel map works pretty well for the 375, at least on the SDS system. There's some fine tuning to do for sure, but overall it runs well out of the box. The volumetric efficiency is close enough between the two that you easily get within range of where you should be with a little adjustment on the mixture knob.

You can't calculate percent power without fuel flow. I normally cruise around 22/2400 (full throttle, 8500-10500 ft) and can vary my power setting between 45% and 75% with the mixture knob. Airspeed changes over 30 knots are available by only changing the mixture. Do any of your instruments calculate power setting for you? If not, full throttle, 7500-8500 ft, 2400 RPM and 100 degrees rich of peak is a fairly common spot for people to do cruise performance testing. I spent the first 20 hours of engine breakin right around that point (maybe a little richer because of engine temp issues), but it'll give you a good idea of what its capable of.

Click to expand...

I would expect a similar VE. However, VE is a multiplier AFTER you have estimated the amount of air that will be drawn into the cylinder and that is volume (bore X stroke). Very generally, fuel required is estimated by using volume times VE and adjusted for desired mixture ratio. I would expect a 360 baseline map to be lean if used on a 375. That said it is only 5% greater volume, so probably not an issue.

I am not suggesting that this is the issue, only that it was worth investigating. The EGTs reported are suspiciously low and certainly hope it is not from running on the lean side.

Larry

Recommended EGT

I’m pretty sure EFII recommends a tuning parameter of 1375 F for 20 in mp. The higher mp should be tuned lower. I don’t believe you will ever see much performance at 20 squared. My 14 is in the middle 140’ TAS and 24 square in the mid 170’s knots. PM if you have any questions.