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Sun May 17, 2009 8:28 am

I need some pro/cons from the vets here. Current scenario: 1641 CC, Engle 110 cam, duel Kardons, stock trans....overall very mild engine on a weekend cruiser. Freeway flyer transmissions always sounded like a great improvement over the stock gearing with today's highway speeds, climbing gas prices and stronger engines. In my mind, it was a given that this was the next step to take. Then you guys ruined that :shock: It wasn't until I read on another post here, where the author indicated that the freeway flyer gears where the wrong way to go, as the fan speed lowers when the engine is turning its highest RPMs & generating the most heat. Got to admit, I read that and it sounded logical/making perfect sense. Now I'm rethinking everything. Would the money be better spent on a bigger engine (1835 or 1915), running on stock gears? Making the assumption that higher displacement equates to lower RPMs & less heat? Remember this would be just for cruising.....nothing more (no dragging, tire burning, etc...) What are your thoughts?

Sun May 17, 2009 9:38 am

ddwbeagles wrote: Making the assumption that higher displacement equates to lower RPMs & less heat?

the displacement has nothing to do with the RPM's the engine runs at a set speed, that is all in the gearing of the transaxle... heat is not really that much of a factor in the engine at a set speed... it takes a certain amount of HP to push the car down the road at a certain speed, so it doesn't matter if you have 50hp or 200 hp if it is using 30... if the larger engine is more efficient than the smaller engine it can actually produce less waste heat at the same power output than the smaller engine..

Sun May 17, 2009 10:56 am

A "Freeway Flyer" trans is a bad idea IMHO.

4th gear is already OVERDRIVE at .89.

75mph is 75mph. It doesn't matter what RPM you are turning. You are using the same HP to maintain that speed. Except with higher gearing you are slowing down the cooling fan and will run hotter down the highway than before.

The VW was designed to drive at 75mph long distances. And tuned right, it will get good mileage doing so. My 63 bus got 31.1 MPG doing 65mph @ 4000rpm.

My next mileage motor will maintain stock gear ratios.

Sun May 17, 2009 11:42 am

i personally think--and i'm no rocket scientist--that if your lager displacement engine is doing less work to maintain a set speed, then a little less cooling is ok.

also consider additional cooling such as a T4 and/or external oil cooler or a deep sump.

my 1776 powered bus will definitely be getting an OD 4th when finances permit.

Sun May 17, 2009 11:54 am

I wish I had gone with a 3.88 R&P in hindsight, because it would have loaded the engine more and helped with turbo spooling. But the 4.12 is perfectly liveable, it still does only 3500 at 65-70 miles per hour on the highway.

Sun May 17, 2009 11:59 am

I have 0.82 but 4th gear mated to a 3.875 r/p with a 2180 and can cruise all day with oil temps never exceeding 205F. And I have only a stock Type 1 cooler with factory tin.

For me the problem of the "Freeway Flyer" was the huge gap between 3rd and 4th gear. You were either reving the crap out in 3rd or lugging it in 4th.

I solved what by getting a Berg 5.

And a "Freeway Flyer" is just a stock tranny with a taller 4th gear. It's not high performance or heavy duty. It will break just as fast as a stock gear box.

Sun May 17, 2009 12:09 pm

borninabus wrote: i personally think--and i'm no rocket scientist--that if your lager displacement engine is doing less work to maintain a set speed, then a little less cooling is ok.

But it's not doing "less work". That's the big mis-conception.

To do 75mph in your VW, it takes "X" amount of HP to do so. It doesn't matter what engine is in there, "X" will always be the same.

So unless the engine you build is more efficient at that specific cruising RPM than a stock engine, it will not be producing any less waste heat than a stock engine.

A 50hp stock engine wil use 30 hp to push a car X mph, just like a 200hp modified engine will use 30hp to push the car the same X mph. It doesn't work "less", it just has a lot more avaliable to use at its disposal.

Sun May 17, 2009 12:20 pm

Glenn wrote: I have 0.82 but 4th gear mated to a 3.875 r/p with a 2180 and can cruise all day with oil temps never exceeding 205F. And I have only a stock Type 1 cooler with factory tin.
I think that you should also add that you are running a smaller than stock rear tire. That counters your tall gears, getting you close to a stock effective final drive ratio.

borninabus wrote:
my 1776 powered bus will definitely be getting an OD 4th when finances permit.
It would be a huge mistake to put a taller than stock 4th gear in it. You don't have enough hp to pull a taller gear.

Sun May 17, 2009 12:25 pm

Barely smaller.... like 4mph slower at 3000rpm.

Stock is 165-15 is 25.394", 71.29mph @ 3000rpm

My 195/60-15 is 24.213", 67.97 @ 3000rpm

Sun May 17, 2009 12:36 pm

Bruce wrote: borninabus wrote:
my 1776 powered bus will definitely be getting an OD 4th when finances permit.
It would be a huge mistake to put a taller than stock 4th gear in it. You don't have enough hp to pull a taller gear.

I haven't found that to be true, Bruce. My ex roomate in CA has a Split window Bus with a 1776, no reduction boxes, and a 'freeway flyer' (I think it's just a 3.88 R&P). It never overheated (despite his shoddy maintenance), and had plenty of power. We did have to shift to 3rd for long hills on occasion, but overall I liked the way it ran. It was a dream on the highway, had a killer top speed for a Bus.

Sun May 17, 2009 4:26 pm

OK- good discussion, but my old feeble mind is struggling with some of the concepts. First, the arguement that a 50hp motor and a 200hp motor will both use the same HP or energy to run at a set speed. Again, admitting that I'm no engineer and don't remember much algerbra or physics, but can pose my arguement this way. If I was a farmer in the feild and had a stump to remove. I could go back to the barn and grab a mule - hook him up - work the crap out of him and get the stump pulled (i.e. 1 horsepower). Or option B, I could go back to the barn, grab a fleet of mules, strap them all to the same stump and yank it out easily. In that comparision, the "problem" was a consistent. Meaning it would take the same amount of energy to remove the stump. BUT, the single mule had to work incredibly hard to pull it verses the ease of using a team of mules. Doesn't the same concept apply to a larger horsepower engine achieving a set speed? Or should I get off the Vdubs sites and spend my time more wisely taking a algerbra refresher course...... :lol: Anyway, you get the point and I certain that your advise is wise, now just trying to understand the science behind the discussion. As always, thanks guys....you again prove to be extremely helpful!

Sun May 17, 2009 4:57 pm

The amount of force applied to the chain to get the stump out of the ground was the same whether it was one mule or two. the car uses the same energy to cruz but gets to that speed faster with more ponies.

Sun May 17, 2009 4:57 pm

It doesn't work that way. Your analogy is one for acceleration, not constant speed driving. In other words, you can pull the stump faster with more power, which is certainly true.

Bugninva and Eric are correct: The only way to produce less heat doing the same amount of work, is to become more efficient at that particular area of the operating envelope. Really any analogy one can come up with, is just another way to describe Brake Specific Fuel Consumption (BSFC) in layman's terms.

Take 2 VW engines, having the same displacement. One has a higher BSFC than the other at 65 MPH on the freeway, due to better heads or what have you. The one with the lower BSFC will be the more efficient one, so it follows that it should also generate less heat since it's burning less fuel. Of course the best way to improve economy in a Bug is aerodynamic mods to make it move through the air easier, but how many people do you see doing that?

Sun May 17, 2009 5:13 pm

Isn't the point of a freeway flyer to lower the RPM? Gear ratios mean that for every X revolutions of the engine the wheels make Y revolutions. The amount of work (the physics term meaning force over distance) being done may ultimately be the same, but there is a mechanical advantage in the taller gearing that allow it to be done easier and with fewer revolutions of the engine. If the engine spins fewer revolutions, it is burning that many revolutions less gas.

Sun May 17, 2009 5:22 pm

Yes, but that's the crux of the matter. The VW engine NEEDS to turn a certain RPM for proper cooling. In most cases lowering RPM while driving faster is a bad thing, since the engine is working harder to achieve the faste speed, while receiving less cooling air.

Sun May 17, 2009 5:42 pm

spectre6000 wrote: but there is a mechanical advantage in the taller gearing that allow it to be done easier and with fewer revolutions of the engine.
You got that backwards. Taller gearing means LESS of a mechanical advantage.

Think of it this way. Freeway flyer gearing means less leverage.

Max

Sun May 17, 2009 5:44 pm

What's the actual difference in the gearing (Idon't recall off the top of my head, and I'd rather eat my dinner and type this than go find it)? I don't know for sure, but I'm fairly certain the required RPMs to reach and maintain highway speed are still plenty high for adequate cooling. Case in point: consider the vast number of VW drivers that have been using them trouble free for years.

Sun May 17, 2009 5:51 pm

Quote: You got that backwards. Taller gearing means LESS of a mechanical advantage.

Think of it this way. Freeway flyer gearing means less leverage.

I stand corrected. However, mechanical advantage is defined both as "output force over input force" (which you have referenced above), and "distance over which effort is applied over distance over which load is moved." So in one sense, yes there is a reduced mechanical advantage, but in the other there is more.

Since we're talking about the freeway flyer transaxel as it pertains to fuel economy, the latter applies.

Sun May 17, 2009 5:53 pm

spectre6000 wrote: I'm fairly certain the required RPMs to reach and maintain highway speed are still plenty high for adequate cooling.

You would think so, but VW designed the engine to operate at a certain RPM on the freeway. You can't go altering things like cooling fan speed (via altering the transmission gearing), and expect nothing will happen. Fact is when you lower engine RPM, you lower fan speed, reducing cooling.

Quote: Case in point: consider the vast number of VW drivers that have been using them trouble free for years.

That just proves that when there IS a problem, they don't post about it or are ignoring the problem all together. I'm not sayng it doesn't work just fine, but I'd also put money on the fact that those same people have never compared head temps before and after the swap. :wink:

Sun May 17, 2009 5:59 pm

First of all the term "Freeway Flyer" is just a bullshit trem used in flashy magazine advertising. VW never used the term.

It is a mistake to run taller then stock gearing in anything less then 90-100 HP.

The cheapest solution is to use a stock gearbox. Then get a 2nd set of cheap stock wheels and taller rear tires. When you go visit grandma 500 miles away, put on the taller tires.