Carburetor STC

[C.J.]

Does anybody know the STC number for the modification that increases the takeoff fuel flow for a Marvel Schebler MA-4-5 carb?  Given I have a Power Flow exhaust I thought it would be a good idea to have the STC mod done. Thoughts??

[ShuRugal]

Why? The power flow exhaust doesn't increase the air charge coming into the engine, it only reduces exhaust restriction and improves scavenging. The power increase it provides isn't the cylinders making more bang, it just reduces the power wasted forcing exhaust through the inefficient factory pipes, leaving more of that power to exit via the crankshaft instead.

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[N201MKTurbo]

7 minutes ago, ShuRugal said:

Why? The power flow exhaust doesn't increase the air charge coming into the engine, it only reduces exhaust restriction and improves scavenging. The power increase it provides isn't the cylinders making more bang, it just reduces the power wasted forcing exhaust through the inefficient factory pipes, leaving more of that power to exit via the crankshaft instead.

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Headers do scavenge better, this does reduce the amount of residual pressure in the cylinders after the exhaust valve closes. This does mean more air/fuel gets sucked in on the intake stroke. It is a small effect, but not zero.

[ShuRugal]

Headers do scavenge better, this does reduce the amount of residual pressure in the cylinders after the exhaust valve closes. This does mean more air/fuel gets sucked in on the intake stroke. It is a small effect, but not zero.

Fair enough. Is that small increase enough to change the cylinder temperature enough to warrant a richer charge?

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[N201MKTurbo]

The STC is a main jet change. It only affects the fuel flow at full rich mixture. The headers won’t change the mixture, but they make more power, so you may need more fuel flow at WOT. Is it running hot during climb? 
 

The hardest part of changing the main jet is removing the carb.

[N201MKTurbo]

5 minutes ago, ShuRugal said:

Fair enough. Is that small increase enough to change the cylinder temperature enough to warrant a richer charge?

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IDK.I’ve only got about 10 hours in C models. None of them had a Power Flow exhaust. I don’t remember any having a CHT issue.

[C.J.]

Just now, ShuRugal said:

Fair enough. Is that small increase enough to change the cylinder temperature enough to warrant a richer charge?

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My CHT has always been higher than I'd preferred at takeoff. After sealing every seam, gap & hole on the doghouse with RTV there was a 30*F decrease of CHT (390 versus 420) as well as oil temp (190 versus 200). According to Power-Flow, HP is increased by 15. I already understood what you're saying re: improved exhaust gas extraction however my mechanic states the STC is recommended by Power-Flow and I'd like to run a bit cooler on takeoff if at all possible.

[ShuRugal]

however my mechanic states the STC is recommended by Power-Flow and I'd like to run a bit cooler on takeoff if at all possible.

That sounds like a good enough reason to do it to me.

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[C.J.]

13 minutes ago, N201MKTurbo said:

The STC is a main jet change. It only affects the fuel flow at full rich mixture. The headers won’t change the mixture, but they make more power, so you may need more fuel flow at WOT. Is it running hot during climb? 
 

The hardest part of changing the main jet is removing the carb.

Hotter than I'd prefer (380*F @ 120 mph climb @ 25"/2500 - WOT/2500 @ 2200# GW. Just looking for some improvement if I can get it.

[kortopates]

It’s not an STC but an alteration.
Are you on Savvy by chance?


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[Greg Ellis]

So, Marvel Schleber has two different carbs for the Lycoming O-360-A1D.  I made the change from the 10-3878 to the 10-4164-1.

The 10-3878 was only giving me about 15 GPH on takeoff, close to sea level, full throttle.  The 10-4164-1 gives me 19 GPH on takeoff.  I was told that it required the change of carbs and not just a jet change.  I did this back in 2018.

[C.J.]

31 minutes ago, kortopates said:

It’s not an STC but an alteration.
Are you on Savvy by chance?


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Thanks for that info. I thought it was a STC. I'm not on Savvy.

[C.J.]

32 minutes ago, Greg Ellis said:

So, Marvel Schleber has two different carbs for the Lycoming O-360-A1D.  I made the change from the 10-3878 to the 10-4164-1.

The 10-3878 was only giving me about 15 GPH on takeoff, close to sea level, full throttle.  The 10-4164-1 gives me 19 GPH on takeoff.  I was told that it required the change of carbs and not just a jet change.  I did this back in 2018.

Thanks for that info Greg. I'll check to see which carb is installed. The price of a rebuilt 10-4164-1 with exchange isn't too scary.

MA-4-5® Carburetor - 10-4164-1 | Marvel-Schebler Aircraft Carburetors (msacarbs.com)

[kortopates]

Thanks for that info. I thought it was a STC. I'm not on Savvy.

make sure you have the richest carb first. the alteration is to increase max fuel flow for the richest carb but only for power flow installs that have lean EGT’s and high CHT’s.
380 chts are not hot - not at all!


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[A64Pilot]

Anyone who has ever put headers on a performance motorcycle or even an automobile knows you have to reject the carburetor because it’s lean after installation.

Your increasing airflow, you have to increase fuel to go along with it.

I don’t know about a power flow, but if it increases scavenging it will lean out the mixture

19 GPH at sea level on a 180 HP engine is a little on the rich side, if your getting 19 GPH at takeoff I don’t think I’d increase it, that’s 200 HP fuel flow

Edited August 5, 2023 by A64Pilot

[C.J.]

12 minutes ago, kortopates said:

make sure you have the richest carb first. the alteration is to increase max fuel flow for the richest carb but only for power flow installs that have lean EGT’s and high CHT’s.
380 chts are not hot - not at all!


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I'll check to see if the 10-4164-1 carb is installed on Monday.

[C.J.]

8 minutes ago, A64Pilot said:

Anyone who has ever put headers on a performance motorcycle or even an automobile knows you have to reject the carburetor because it’s lean after installation.

Your increasing airflow, you have to increase fuel to go along with it.

I don’t know about a power flow, but if it increases scavenging it will lean out the mixture

19 GPH at sea level on a 180 HP engine is a little on the rich side, if your getting 19 GPH at takeoff I don’t think I’d increase it, that’s 200 HP fuel flow

Not currently equipped with fuel flow but I'll be checking if the 10-3878 or10-4164-1 carb is installed on Monday. Further consultation with mechanics after that.

[C.J.]

On 8/5/2023 at 6:26 PM, kortopates said:

make sure you have the richest carb first. the alteration is to increase max fuel flow for the richest carb but only for power flow installs that have lean EGT’s and high CHT’s.
380 chts are not hot - not at all!


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Well, the good news is I'm equipped with the richest carb (10-4164-1). Given there's zero logbook evidence the carb has been overhauled in the last 58 years, my mechanic & I are in agreement an overhaul would be a good first step at this point. For all anyone knows the 10-3878 version might have been this plane's OEM carb back in 1965. Most logbook entries are big on brevity. Any additional advice you'd like to share will be greatly appreciated.

[C.J.]

On 8/5/2023 at 5:00 PM, Greg Ellis said:

So, Marvel Schleber has two different carbs for the Lycoming O-360-A1D.  I made the change from the 10-3878 to the 10-4164-1.

The 10-3878 was only giving me about 15 GPH on takeoff, close to sea level, full throttle.  The 10-4164-1 gives me 19 GPH on takeoff.  I was told that it required the change of carbs and not just a jet change.  I did this back in 2018.

I have the 10-4164-1. So are you getting 19 GPH on T/O with just the stock carb OR is that with the jet change mod added?  Also are you equipped with Power Flow?

[Greg Ellis]

@C.J. I am getting 19 GPH on takeoff with the stock richer carburetor. There is no mention in my logs about a jet change. I do not have the power flow.

[C.J.]

@Greg Ellis  Thanks for that info. 

[kortopates]

Well, the good news is I'm equipped with the richest carb (10-4164-1). Given there's zero logbook evidence the carb has been overhauled in the last 58 years, my mechanic & I are in agreement an overhaul would be a good first step at this point. For all anyone knows the 10-3878 version might have been this plane's OEM carb back in 1965. Most logbook entries are big on brevity. Any additional advice you'd like to share will be greatly appreciated.

The carb would have been OH at time of last engine OH. That would give you the age of the carb.


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[DXB]

On 8/5/2023 at 3:18 PM, ShuRugal said:

Fair enough. Is that small increase enough to change the cylinder temperature enough to warrant a richer charge?

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Having flown pre and post Powerflow in my C, oh boy is there a dramatic increase  max takeoff power and also CHTs - I already have the richer carb, and so I’m going to get the jet modified for sure when  I overhaul it with the engine  in the next year or two. I really could use the 19gph that @Greg Ellis is getting.

Edited August 19, 2023 by DXB

[C.J.]

1 hour ago, DXB said:

Having flown pre and post Powerflow in my C, oh boy is there a dramatic increase  max takeoff power and also CHTs - I already have the richer carb, and so I’m going to get the jet modified for sure when  I overhaul it with the engine  in the next year or two. I really could use the 19gph that @Greg Ellis is getting.

My C already had Power Flow installed but I'm curious what were the after PF CHTs versus the before? 

[Pinecone]

On 8/5/2023 at 3:02 PM, ShuRugal said:

Why? The power flow exhaust doesn't increase the air charge coming into the engine, it only reduces exhaust restriction and improves scavenging. The power increase it provides isn't the cylinders making more bang, it just reduces the power wasted forcing exhaust through the inefficient factory pipes, leaving more of that power to exit via the crankshaft instead.

How do you think it makes more power?

More power comes from burning more fuel.  To burn more fuel you need more air and more fuel.