SrTelemaster150

One of the biggest (cheap) HP boosts in automotive performance is ducting cool outside air into the induction system.

Under hood or inside the cowl air temperatures are markedly higher than outside air. After all, aren't we pulling heat from an air cooled engine in our case. That makes the air inside the cowl much hotter than the outside air. Cooler inlet temperatures allow more aggressive spark advance & on glow engines can help prevent detonation.
On a radial or other engine with a rear facing carburetor, the air could even be pulled through the firewall from inside the fuselage.

FNQFLYER

On this airflow thing. I usually make the dummy inlets that come with kits fully functional, first. I also work on the 1 in 2 out volume thing as a minimum for air into and out of the cowl. On air to carbys (on radials), full size has intake duct why not do same for our models. I haven't run a radial but mates have and as a rule followed the idea of functional intakes etc which seem to work. On baffling buggered if I know I just do what looks right in directing air around the engine. Lastly I do not aggressively tune the engine preferring a more mid range tune. This is on "sports models" of course.

Rudolph Hart

Would the colder outside air be denser (like the writer!) and therefore cause a leaner mixture for a given needle setting compared to taking air from inside the cowl as usual?
With or without proper cowl baffling around the engine what temp changes in incoming airflow can be expected in the milliseconds it takes from air entry to it disappearing down the carburetor while the aeroplane is in flight? i've never worried about it on methanol engines but for this big saito gas twin i think i need to know,it gets real hot in summer here.Has anyone here used a data logger with sensors under each plug to measure cylinder temps? i'm going to look at the eagle tree system and any others that are out there.

Sr good point about drawing carby air from inside the fuselage.On the 50cc edge 540v3 there is a huge cannister tunnel under the electronics tray i can draw from.Cheers.

ps do you need to combine a data logger with a gps to get meaningful inflight readings?

SrTelemaster150

Yes cold outside air will be denser & therein lies the power boost. You are correct in your assumption that a slightly richer needle setting will be required. More air + more fuel = more power.

If anything, drawing outside air should lead to more consistency as the inlet temperature should remain more constant compared to drawing air from inside the cowl.

slamn sammy

Thats what l have got into, remove the cowl and tun the engine and even test fly it and baybe tweek it and when l think l kike it, cowl it up and go fly it and the tuning will change!?? So l'll set it on the ritch side and cowl it up and it will be close. You know it's like going to the Doctor (DO YOU FILL LUCKY?) Seems like l don't have that trouble with the gas engines that have the cab, in the rear. My Saito l just started tuning whit the cowl installed, that O.S. is a tuning Bi***! Don't like the O.S.!!! Was think about the cold (RAM AIR) system, may try it.

Hobbsy

My Feedback: (102)

Running the cowl or not running the cowl will not make a noticeable difference. RC carbs run pretty cool due to evaporating fuel, in fact in certain conditions the intake tube can get frost on it and in other conditions almost always has moisture on it from the cooling effect. This is much ado about nothing. When you run the mixture a couple of hundred rpm rich to compensate for the fuel level changing you've already blown away far more than running an intake duct would gain you.

SrTelemaster150

On a single cylinder I would expect little difference.

You are missing the point of running the mixture a few clicks out. You will not really be running a couple of RPM richer, rather you will be increasing the fuel to bring the mixture back from lean due to the denser air. More #s of air + more #s of fuel will = the same ideal A/F ratio but there will be more of it to burn thus more HP. The cooler intake temperature will also help ease detonation (Ever hear of an intercooler?) & will require less richness for a safety margin. Then of course you can run CDI & do away with such " running a couple of hundred RPM rich" nonsense.

On a hot, muggy July afternoon in Columbus, Ohio, I dropped my 1/4 mile ET from 13.1 to 12.55 by merely dropping my ECT from 179°F to 156°F @ the tree. That's an effective increase of 50 HP in a 4200# car.

Even though the alcohol fuel does cool the intake charge, the cooler air will still be denser as it enters the carburetor & will be cooled further by the alcohol. On a radial engine, that could be significant.

blw

My Feedback: (3)

I know.

blw

My Feedback: (3)

I would think the purposes of setting the RPM a few hundred richer would mostly be to compensate for lean conditions that come from the "unloading", flying the up lines, and to compensate for loss of fuel pressure around half a tank of fuel. If you are setting it just rich enough to compensate for denser air, then you will be running too lean due to the other conditions. Right???

acdii

My head hurts reading all this. After my Chipmunk quitting at altitude with the cowl on, I will make sure mine is sloppy rich with the cowl on, just to be safe. Once I have a few good flights I may lean it a wee bit, but better to be on the safe side, I hate dead sticks on a plane I dont have time on. When my LT-40 quits, easy to bring it in and land without power, but the Chipmunk was a handful and would not come into the wind without stalling without power on. Pretty sure the P-51 would be the same.

blw

My Feedback: (3)

acdii, after going back and reading your post about how you have set your engine it looks like you are way too rich already. Running that rich will rob you of substantial power, gulp the fuel, and maybe begin to vibrate hard. Is this a new engine? I may have missed whether you said it is or isn't.

FNQFLYER

Drawing from my past once again, hot and high (my experience here was with B727 and 737 a/c) was more of a problem than cold for power repeat power but we hated cold cause the engine (no matter what type) would stop if it got cold enough. That being said I have noticed on numerous occassions (in Cairns) the moisture forming on the intake tube of both single and twin Saitos. The engines thus tuned (a little rich, but not screaming lean) all performed ok. Methinks people are over thinking this. You are not in the competitive flying mode just sports type flyers. As my mate says when I get like this (over egging the issue) get out to the shed and do some building. That being said I agree with Snr and blw with their statements

FNQFLYER

Old Fart are you coming to the Nats here in QLD next year? If so are you competing and if so what events.

SrTelemaster150

It's all relative. Running a few hundred RPM rich will still be at a higher output when the needle has been maximized for the denser air. It's like having a slightly larger carburetor. Denser air means more fuel can be burned.

Denser air weighs more. A/F ratios are by weight, not volume. Denser air requires more fuel to maintain the same relative A/F ratio. The 200 RPM richer setting is then adjusted from there.

acdii

Its a fairly new engine, the original owner couldn't get it to run, so it will need some break in, which is why I am leaning towards rich for now, can always lean it out a little bit at a time as I get more fuel through it. All I can say at this time is it will idle slower than the starter will spin it. You would think it isn't starting when in fact it is running after one revolution of the starter, soon as you pull the starter off it slows down and purrs. I feel I have the LSN just right with how it runs.

Rudolph Hart

Well this is a lively discussion with lots of different opinions being expressed and that must be a good thing.Makes informative reading for everyone and it's a good way to form your own opinions.Mine is that this is the most interesting reading we've had here for a long time.This is an area that seems to be full of confusion and if that confusion translates to modellers flying saito's and not being happy with the results they are getting then hopefully this lively discussion may clear things up for people a bit.I remember dave experimenting with different intake tubes on saito's way back?

Acdii if i remember right you said you bought the saito fa1.00 second hand and put some bearings in it.Remember you need to peak the engine first before you lean the lsn.Try it that way please,it makes a remarkable difference to your personal happy meter

As far as methanol saito's go i tune fairly aggressively and rarely have a cooling issue cowled or not for some of the reasons given above,methanol is a great coolant to run through your engine.My worry re ducting is for ALL the gas saito singles which are often cowled and pe reivers site is a good example of what can be done to alleviate cooling issues,how important do you think that is on a gas engine ? going from what i have read elsewhere it's a huge and misunderstood problem that's costing people a lot of enjoyment not to mention money.I'm all for a good debate as long as we keep it civil

ps fnq hopefully we get ourselves organized and do an eastern states trip next year will keep you posted.

Hobbsy

My Feedback: (102)

Pete, people don't miss what they don't know is missing and I don't think they're missing anything due to heated air going into the carb. If we were, some of the engine "greats" would have come up with a solution long ago. We could put ice in a bin on the side of the cowl to find out though.

RC_Fanatic

My Feedback: (1)

Ever notice the cold air intakes on race cars?

the pope

Beer is better when cold and women better when there hot ! Must do some more experiments . Cheers from the wise ol pope

blw

My Feedback: (3)

The Honda S-2000 suffers badly from getting heat soaked if you don't keep the rpms up on launch. It gets a big dose of hot air right in to the intake. Cold air intake boxes are a good thing for the car.

Rudolph Hart

Ok but the intakes on a car at the inlet manifold are WAY back under the bonnet (not talking about racing here) and behind all sorts of heat producing things like radiators for coolant and aircon etc,there's a lot of ugly stuff under there which is why cool air intakes became so popular.Nothing like that complicated with our model engines the carby sits in relatively clean air,the temp of that air could be debated,if it's worth it.My main concern is the heat produced by gas saito's in this instance and easy ways to control that problem in a tightly cowled installation.My methanol saito's that are tightly cowled benefit in a tuning consistentcy from ducting the air round the engine properly particularly in summer.Those saito engines are inverted and the carby is up against the firewall in a very cramped spot.For sport flying on 10% they always pull the benchmark prop figures advertised,rightly so because that's all most people want to do with them.

So,cold air intakes or pre heated slightly...

Barry i have a complaint to make here..popey is stealing all the one liners the irresponsible twit..can you do something constructive about that ?

the pope

Barry i have a complaint to make here..popey is stealing all the one liners the irresponsible twit..can you do something constructive about that ?[/QUOTE]
Hey there old fart . Most people just ignore me and hope that I might go away . Not much chance but you never know ! Cheers the pope

SrTelemaster150

While I agree that a CAI would be of little value on a single of perhaps even a twin, when we start talking 3 or more cylinders on a radial W/the carburetor sitting way back smack dab in the middle if all of that heat, it starts to look like a different story. Add to that a hot exhaust collector ring surrounding the carburetor.

Since the carburetor faces the firewall anyway it would be a simple task to induct air from the fuselage rather than the cowl.

SrTelemaster150

On the Gen-III Chrysler Hemis, a high IAT will cause the computer to pull ignition timing killing the 60' times. Once the car is moving, cold air entering the intake will allow the timing to advance. One trick I learned was to unplug the AIT sensor. The computer then reads the ambient air temperature & the battery (mounted in the trunk) voltage to adjust the timing. Even on cool days, I cut about .1 off my ET.

On the LX platform, a lot of the performance gains were tied to fooling the computer, as well as modifying the parameters. We called the ECU "HAL" as it had a mind if its own often negating gains from modifying the parameters. I was the 1st person to change the axle ratio in an LX. I tried to get a performance tuner manufacturer to work W/me on it, but they thought they knew it all & that merely modifying the tire size data would work. WRONG! The Mecedes based TCM reads the wheel RPM through the ABS sensor as well as the tail shaft output RPM. If the data doesn't jibe W/the axle ratio programmed into the TCM, the car goes into "limp mode" staying in 3rd gear W/only partial throttle available.

I went ahead & swapped in a 3.06 AMG diff from an SRT8 (stock 5.7 ratio was 2.82) & sure enough, shortly after the trans shifted to 3rd gear, the TCM went into limp mode. I found that limp mode wouldn't initiate until the trans had run in 3rd gear for several seconds. I drove the car for several days by accelerating fast enough for the transmission to shift into 5th gear before it went into limp mode so that even W/only part throttle, I could cruise along @ 65 MPH. When I had to stop for a stop sign, (infrequent in my rural area) shutting the ignition off & opening the driver's door would re-set the TCM. I started a THREAD on LXforums & soon found someone to hack a TCM for the ratio change.

Rudolph Hart

Can i talk about shootin now ?