Horizontal vs vertical induction in a 7A

I am nearing the point in my 7A project where I need to order my finishing kit and to do that I must decide on the engine configuration. For the last six months I have been leaning strongly toward an IO-360 with horizontal induction. No scoop on the cowl and 5-7 more HP sounds good compared to the IO-360 with vertical induction. But lately I have been reconsidering the tradeoff. Specifically, I think I have identified some other important factors. I need someone to tell me if I have this correct or if I am wrong or missing something important.

With the choice of horizontal induction comes the following:
1. I have to spend about $1000 more for the horizontal intake sump compared to the vertical induction sump
2. I have to spend a lot more time integrating the Vans snorkel and intake filter that does not fit very well and probably requires significant modifications to work
3. The Vetterman exhaust system cost is slightly higher for a horizontal induction
4. I have to figure out numerous custom modifications to the firewall forward installation for things like throttle cable routing

Do I have these facts correct? I would really appreciate feedback from those who have done either the horizontal or vertical setup for an IO-360, especially in a 7A because the nose gear structure may also be a factor I don?t fully understand. I used to care about the scoop on the front of the cowl but that is not really important to me anymore. Do you love your horizontal setup? Is the extra cost and time involved really worth the extra power? Does the extra power come at the expense of increased fuel consumption? What about the vertical camp? Would you do it again and why? I don?t want to start a war. I just need help from those with some first hand experience.

John Harrell
RV7A
Empennage done
Wings done
Fuselage coming along nicely
www.johnsrv7a.wordpress.com

I was in your shoes not too long ago. One thing I discovered is that the horizontal sump configuration has no room in the cowl for mufflers if that's important to you. Who knew?

Bevan

More heat & less noise...

Another point regarding mufflers:

Both of them (assuming you'll install the Wtterman 4 into 2 crossover system), will give you heat into the cockpit.

You'll then have twice the amount of heat available for winterflying, and in cold climates, that is needed.
The Vans std heatmuff provides too little heat when are temps well below freezing, and a warm cockpit is needed to keep the women comfy... and older pilots too....

Maybe the ground temps when you take off are not that cold, but when you climb up to a cruising altitude of 10.000+, the temps are dropping fast... (2* Celcius per 1000')

And ofcourse less noise, both outside and inside the plane is a good thing...

Maybe you don't need it, but if you're selling the plane in a few years, then that could be important for a potential byer.

I wish I knew this when I was ready to order the engine. Then I would've selected vertical induction on both my RV's, no doubt.

My 2 cents....

Similar time

John

If you buy the M1B engine from vans then they have a firewall forward kit that fits. Everything thought out and shows where to drill the firewall etc etc.
I think the snorkels are now better than they were 5 years ago.
Anyway you would have to make the filter box if you go vertical induction so really it's no more work.
The biggest thing for me was fuel injection. I think getting rid of the carb icing potential is a big safety factor (putting flame suit quickly on) as vans don't do a vertical induction fuel injected.
I actually went with the superior sump which required making a couple of brackets which was really quite straight forward.
There is a heat muff on the exhaust I have which in the winter at 10000 ft is only just ok down low it's fine all year round.

Summary- cowl looks cleaner, little more HP, really no more work, costs a little more.

Peter

jpharrell said:

With the choice of horizontal induction comes the following:
1. I have to spend about $1000 more for the horizontal intake sump compared to the vertical induction sump
2. I have to spend a lot more time integrating the Vans snorkel and intake filter that does not fit very well and probably requires significant modifications to work
3. The Vetterman exhaust system cost is slightly higher for a horizontal induction
4. I have to figure out numerous custom modifications to the firewall forward installation for things like throttle cable routing


www.johnsrv7a.wordpress.com

Click to expand...

I went with the horizontal set up, and here's my 2 cents-

1000 bucks more is about right

The snorkel worked out fine for me. I had to cut and glass to provide clearance for the plane power alternator, but that was very easy to do

Don't know about the exhaust cost, but AO is right about the heat. It's only gotten down to 40 F here, and I can tell it's going to be cold this winter.

Custom modifications? If you buy Van's FWF kit , as I did, everything is laid out on the plans and is straight forward.


Is it worth it? I'm only beginning to explore that question. Starting has been the biggest difference, all previous experience has been with easy start carbs. It does lean very nicely, I'm sure it's more efficient

Problem with vertical induction and fuel injection?

kiwipete said:

John

The biggest thing for me was fuel injection. I think getting rid of the carb icing potential is a big safety factor (putting flame suit quickly on) as vans don't do a vertical induction fuel injected.


Peter

Click to expand...

Do you mean that Vans in particular doesn't offer the vertical induction fuel injected 360 engine? I believe other shops such as Aero Sport and Mattituck do. If I go with a V-induction IO-360 engine from one of the other shops does Vans have a firewall forward kit that works well with that combination?

John

I have a vertical induction and am due for engine start this weekend. The only reason i went with the vertical induction is because I bought it from Mattituck largely on the basis of all the fine testimony of the engine and mattituck and that's what Mattituck had. I also kind of like the scoop on the bottom of the cowling.

The downside is, as you surmised, Van's pretty much pretends there's no such thing as vertical updraft.

Most of the instructions/plans for firewall forward are garbage. The callouts for things on the firewall that you start on with the fuselage kit (firewall penetrations) are also mostly incorrect (but they don't tell you then -- at least on my plans -- that's for the engines they sell and you shouldn't make any holes until you get your engine choices figured out).

Almost no stock item that Van's sells for FF - hoses, principally and fat wires (although there's no way I'd ever order a fat wire from Van's once I ran into the incorrectly crimped connectors that they didn't want publicized) - will fit an IO-360 vertical updraft installation.

But it didn't really matter because by that stage of the build, I found, I relied more on the expertise on my field than the charts and instructions.

I think this thread might be helpful to you, as it was for me when I was at your stage of the built.

When I was making this same decision (I was committed to fuel injection) I had a talk with Mahlon at Mattituck and your summary reflects much of what was said. I personally equate the scoop on the cowl with what an RV should look like so I like it. The only other thing is that the scoop/airbox on the vertical is very well designed and there is some manifold pressure ram effect. I don't know if the horizontal induction benefits the same way...? For my taste, 5-7 HP from colder induction air but more $ and a look that I didn't like as well, wasn't worth a better look, less expensive and maybe not much HP loss when you consider the MP ram effect of the scoop and airbox.
Ultimately the tie breaker for me was looks and I prefered the scoop. Others I know prefer the "clean" cowl without the scoop.

Jeremy Constant

Scoop less

I built the 8, but I believe the 7 to be very similar. I installed one of the early snorkels in the Doll, and it did need minor modification, but it really was no big deal. Since then, I've installed three other snorkels, in other aircraft, and the late models fit much better.

I personally like the clean cowling better for less drag, better looks, and the fact that doing a checkerboard paint job on a vertical draft cowling would be a nightmare.

In most cases, fuel injection offers better fuel distribution, which is a big advantage when leaning for lowest fuel flow.

As always, the choice is up to you. Both require about the same amount of time and effort. It would be nice if Van supplied the firewalls without any holes so the builder could plan his own initialization.

I didn't know...

... that Vans doesn't deliver FI with vertical induction!

In that case I sure would have preferred injection over dual mufflers!
So in this case, the points I made in my post above isn't valid...

But if you can get FI with vertical induction from another engine supplier, then that'll be the route to go for you?

I can't really comment about the cost difference as I don't remember how much was the difference, but VANs FFW, as it has been noted, has all of it and no modificiation is required. My snorkle required little modification and the fit is really good. Eitherway, there is work to be done but in a long run a bit more horsepower is better and I would have wondered why I didn't go that route, when I could.

good luck

Just to clarify, when I ordered mine, there were instructions on the Vans order form that if you wanted vertical induction you ordered the carb firewall forward kit. Then you ordered vertical induction fuel injection from your engine manufacturer which in my case was Mattituck which offered a certified or non-certified choice. I went with a precision experimental silver hawk updraft fuel injection, which is made by the same folks that make the certified updraft fuel injeciton which used to be Bendix. It required tweaking the FAB and some people had better success using a 1/2" spacer to make the fit right. Suffice to say that when you progress to the firewall forward stuff and the systems stuff, there are so many variations that factory can't do step-by-step for all of them, so the builder has much more design and fabrication responsibility. All of this info is from a kit ordered around 7 years ago. They may have changed in that time

Jeremy Constant

RSA-style vertical draft injection is basically a drop-in replacement for a carb. It's not a big deal. Get the FWF plans for the carb and you're good to go. The only real difference between vertical draft FI and a carb is the servo-to-flow divider (spider) fuel line.

I went fuel injected with vertical induction for the reasons you mentioned.

One thing to remember is that the often quoted 5-7 hp advantage of the cold air horizontal induction is only on a test stand. Installed in your RV, the vertical induction benefits from ram air, and the horizontal induction benefits from cooler charge temperatures. Taking that into account, the power is about equal and the choice becomes about money and looks.

I definitely have higher manifold pressure WOT than my friend's horizontally injected RV-8 when we are flying side by side. I would be hard pressed to say which engine actually makes more power in flight.

I will add my .02 to the thread although much of what I experienced has been stated by others here. My setup is just a little bit different but is still close enough to what you are contemplating to be of use (I hope).

I have an ECI-IO340 with forward facing cold air induction on a 9A. When ordering my FFW kit from Van's I ordered the RV7A cowling for an IO-360 and the snorkel for forward facing sumps. All fit almost like a glove. The snorkel especially required no modification from me at all. You do have to modify the baffling in front of the #2 cylinder to provide for the air intake and the air filter. That was about the only fabrication I had to do with the Van's provided components.

With the forward facing sump the cross-over exhaust will not work. If you go with the FFW Kit provided by Van's you should delete the standard cross-over exhaust and contact Larry Vetterman directly for a straight 4-pipe exhaust. I was initially disheartened by having to use a straight pipe setup because I was interested in keeping my airplane as quiet as possible which was going to require some form of a muffler. However, I am very pleased with this exhaust setup. It is much more quiet than I ever thought it would be. Vetterman's 4 pipe system works great. It also bolted up great. The fit was just about perfect with the exhaust. There was one alteration I had to make to the bottom of the cowl just under the exhaust pipe coming out of the #2 cylinder though. The pipe was too close to the fiberglass cowl so I had to fabricate a small bubble on that bottom cowl to allow for air to flow between the exhaust pipe and the fiberglass. Other than this mod things fit perfectly.

Overall, I am very pleased with my decisions on the engine, the forward facing sump, and all the necessary components it took to make it all work together. I do not feel I had to add any more to my build. All the FFW systems demand a great deal of attention to detail and time constructing so these changes, in my opinion, did not adversely affect the build time or complexity.

Hope this was helpful information.

We went with vertical induction because

1.) the engine was tovgood to pass up and
2.) more than several people have said youll get about an extra inch of mp with the bottom scoop

Engine is an IO-360-B1F fwiw

Extra hp probably wishful thinking

Guy Prevost said:

I went fuel injected with vertical induction for the reasons you mentioned.

One thing to remember is that the often quoted 5-7 hp advantage of the cold air horizontal induction is only on a test stand. Installed in your RV, the vertical induction benefits from ram air, and the horizontal induction benefits from cooler charge temperatures. Taking that into account, the power is about equal and the choice becomes about money and looks.

I definitely have higher manifold pressure WOT than my friend's horizontally injected RV-8 when we are flying side by side. I would be hard pressed to say which engine actually makes more power in flight.

Click to expand...

A most interesting post Guy and I think you're right on the money. I have always doubted the so called "5-7 hp advantage" of the horizontal induction engine when installed in an RV for exactly the reasons you have stated.

The intake on the horizontal induction engine is at 90 degree to the airflow and the air routing is relatively convoluted. There's no way that flow can match the efficiency of the "ram" air entering the vertical induction engine through the cowl scoop. However the "5-7 hp" advantage has been bandied around in previous threads so many times that it's become an urban legend despite the fact that there's no data that I am aware of to support it.

There may be some good reasons for opting for horizontal induction but I doubt that any hp increase is one of them.

jpharrell said:

Does the extra power come at the expense of increased fuel consumption? John Harrell

Click to expand...

If the horizontal induction engine produced more hp (which is very doubtful) then it would burn more fuel whenever that extra horsepower was called upon. Horsepower out is directly proportional to fuel in. There's no free lunch.