David Vizard's Three Worst Ideas

[carockwell]

We have all read David Vizard's big yellow book and seen his 2 hour lecture on tuning the A-Series Engine on you tube. All that research was done over 40 years ago. They say "hindsight is 2020 " and I am pretty sure David Vizard would agree that the following recommendations turned out to be ill advised based on experience:

1. The 1380 engine was a mistake. It turns out you can only overbore and engine so much before cylinder wall and head gasket stability detracts from the overall power output and reliability. You are really better off giving up a few CC's of displacement to achieve the longer life of a standard +20 or +40 overbore than offset boring the cylinders for 1380. The other problem is once you have a 1380 you cannot expect to overbore the cylinders for a new set of pistons (yes it is possible but extremely expensive), so your block is pretty much trash.
2. K & N filters add power. I used to run a chassis dyno tuning business. I personally did more than 100 air filter swaps where we replaced the standard paper air filter with a K & N air filter. Only one car (a VW Corrado) ever gained power as a result of the swap. Most cars lost a little power. On top of that the K & N filters do a very poor job of filtering air. After a few thousand miles of driving there is dust accumulating in the intake manifold. This never happens with standard paper filters.
3. Modifying carburetors for more airflow. There are several reasons why this is a bad idea for a street car. The first is that improving airflow through the carburetor does NOT mean you gain power. If your carburetor is adequately sized, you will lose power improving the airflow. Only people who are forced to use a carburetor which is too small to meet some racing rule requirement should consider modifying their carburetor. Everybody else should just go to a larger sized carb. The second is that modifying the carburetor can mess up the airflow vs fuel flow ratio meaning the carburetor cannot pull fuel through the venturi resulting in poor throttle response. The third reason is that slimming out the throttle butterfly creates a serious risk of breakage, and your engine swallowing butterfly bits will ruin your entire day.

So those are the three worst ideas for the A-Series coming from David Vizard's big yellow book and I am pretty sure if you cornered David Vizard today and showed him this he would agree.

For something to think about, in the early days people thought reducing restrictions in the intake and exhaust system would result in power gains. This is simply not true. The biggest restriction in most engines is the intake valve, and the goal is to gradually accelerate the intake charge to so that there is not a massive acceleration at the valve. You will notice that Vizard is often measuring airflow resistance and assuming that reducing resistance is the same thing as increasing power. It just ain't so.

[MiniDave]

I completely agree on points 1 & 3, and partly on point 2 - I prefer a paper filter in a stock air cleaner housing because it's so much quieter. I thought the point of the K&N wasn't so much power gain as improved filtration, and I thought this had been proven thoroughly? but your post seems to indicate otherwise? Were the K&N's properly oiled?

In the past, there's "no replacement for displacement" was the rule, but with modern EFI and forced induction that's not true, and keeping the cylinder walls intact and the head gasket sealed is much more important! The 1380 is all the rage in the UK, but with Dan's engine (1275 +40) we proved it just wasn't necessary in order to make a good strong engine - getting the head to breathe is where the HP is at. Also, most people seem to think you need a 2 or 3 inch exhaust to get it to breathe, but I've found a 1 3/4 to 1 7/8 seems to work better, especially since I build for torque and drivability, not max RPM.

Dan also had some experience modifying the carbs and it did not work well IIRC.....causing all sorts of tuning difficuties. Again tho, depends on if you're tuning for race conditions or street.

[carockwell]

K & N got their start with air cleaners on single cylinder dirt bikes. The cotton gauze filter media could really get loaded up with dirt and still do a good job filtering air. The pulsations coming through the intake system on a single cylinder bike were largely responsible for preventing the filter from loading up. Moving to filtering four cylinder passenger cars, the filters are simply ineffective. Nobody is really sure why. I have heard Vizard theorize that little fibers in the cotton gauze vibrate with the single cylinder intake pulses and this both prevents dirt from entering and then brushes it away. Whatever the mechanism, it provably does not work at filtering dust when used in a normal car. When you purchase a new K & N filter, it comes oiled. So all my power testing was done with new, or nearly new filters. Once you have cleaned and oiled the filter they really start to lose their filtering effectiveness. Hold a cleaned K & N filter up to a light and you can see the holes going right through it. And no, they don't make more power after they are cleaned and oiled.  Still, a K & N is a lot better than nothing at all and sometimes it is the only thing that fits!

[94touring]

I actually did the "Vizard" mods to my carbs.  My issue was a rich area down low the twins couldn't work away.  Even my hif44 has a rich area there but it's less of an issue.

[jeff10049]

K&N filters cause lots of problems with MAF sensors at my shop with the amount of dirt and oil they let through once they build up some dirt they are better but most people over-service them and make the problem even worse.  We had a few dusted engines still under warranty with K&N filters come in over the years and they would not honor the warranty the Magnuson moss act only works if the failure is not related to the aftermarket part used. The amount of dirt in the intakes of K&N equipped large diesels is amazing 1/4" thick in places.
Bottom Line if you have a dirt related failure and no leaks elsewhere in the system and a non-stock air filter you are screwed on warranty.

I'm not knocking K&N they might have a place but they sure don't filter that well on the big engines. A new cummins isx 15 liter is $30K I recommend fleetguard stock filters.

That said I wouldn't have a problem running one on a classic car with limited mileage per year driven in nice weather but, on my daily drivers I just don't trust k&n especially with the volcanic cinder dust we have around here takes one day in winter to destroy an engine without an air filter.

[MiniDave]

If they don't add HP, and they don't filter that well.......what's the point of using one at all?

[BruceK]

Well, they are easy to obtain. Can't say that about stock air filter housings for a Mini.

[94touring]

You could always use an Uni pre filter wrap over the K&N. Makes me consider that with this new bus engine I have to install.  Foam is better than gauze when it comes to filtering and flows almost as well.

[jeff10049]

 Uni is good. I would do that I almost mentioned Uni filters.

[94touring]

Looked last night and K&N have foam wraps also.  Didn't look at prices but Uni is very affordable.  Once I get these webbers here with the engine and get the filter dimensions I'll order a foam wrap and be done with it.  My mini already runs a foam filter.  Oiled too of course. Also worth noting is Uni makes a VW round filter which having personal experience with the round VW filters they're the exact dimensions as mini round filters.  I bought a pair of the gauze vw filters for the innocenti because they're a fraction of the cost as K&N.  Just require oiling which I have. Uni offers them in 1 inch and 4 inch height in foam.  Perfect for adding a stub stack on the 4 inch ones. 

[jeff10049]

Back in another life when I was big into race carts and jr dragster engine building we ran Uni filters on all our cart and jr dragster engines they flowed great and filtered great as well.
In the cool bore (aluminum bore) Briggs they were about the only filter that filtered well enough to protect the aluminum bore as you never wanted to scratch a nicely glazed aluminum bore getting it seasoned right was a big thing.

[94touring]

I think they started with dirt bikes if I'm not mistaken. Obviously lot's of dirt and dust to be filtering in those environments.