Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 Are The Cam Upgrades Worth It.

Here is the spec for the cams. Some unusual timing on the standard cam I guess to meet emissions.

I made a discovery today about using the Emerald ECU and the Stage 2 Tune.

I have been using the S&S Stealth air cleaner, which is the AR Stage 1 cleaner. When I first installed it I noticed that it made a big positive performance difference in spite of having less filter area. I attributed that to the stinger inside it.

Since changing to the Emerald ECU with its Stage 2 Tune I noticed that besides the added power it seemed to be running more rich, rough idle, especially when cold. Giving more fuel to the engine was expected but the low end running slightly rough i did not expect. So I have been thinking what might be the effect of more air and I purchased the S&S “one inch taller” air filter kit for the Stealth kit.

It works! Runs very smooth and no coughing and pulls strong. Any of you with the Emerald ECU and a Stage 2 Tune I strongly recommend it the one in h taller filter.

This is great to hear! Makes me excited to get the ECU and cams in. Thanks.

This is interesting Stephen! Do you have the part number for the extra tall air filter?

I did not use two bolts provided, top of third page, but used the Stealth safety wired retaining pin system instead.

With the modest demand for air required by an engine at idle, please explain how it can possibly make any difference to idle quality to have a larger air cleaner element?

Both the factory and Stealth air filters have more than sufficient flow for a non racing engine. It's more likely your prior filter had been over oiled, something that can definately have a negative impact on idle quality.

So thinking about this a little more:

Using a common rule of thumb formula for air consumption rate, then Engine CFM=(engine cubic inch displacement x max rpm x volumetric efficiency)/3456. So a 121 cubic inch engine at 5500 rpm and 85% VE (admittedly a SWAG) will flow about 165 cfm. I chose 85% VE as that is a reasonable number for a normally aspirated modest performance two valve engine.

So any air filter assembly that can flow 165 cfm or greater (as installed) should be more than adequate for our M3W for street driven use. And unless the air filter assembly is somehow deficient in design (see note on stock unit, below) using only the total flow capacity of the filter element itself gets us close enough for a street engine.

K&N in a published whitepaper indicate their testing shows oiled gauze type filter medium such as used in their products flow 6 cfm per square inch on average. So to evaluate an air filter for an intended application just calculate the square inches of the filter and apply the cfm per square inch rating for the particular medium.

In the case of the Stealth unit, the air filter has a mean diameter of about 5.25" and an effective filter height of 1.5" (measure only the fully exposed filter medium) so I get 24.7" square inches and about 148 cfm, which is just adequate for 5000 rpm use, so just a bit undersized if you are running to max rpm all the time. Going to a 1" taller filter (about 2.5" height of effective filter area) gives us about 247 cfm which, while overkill, is useful for higher rpm work (good to 8000 rpm!), but no real practical benefit to those running 5000 rpm or less.

As a side note, while the stock air filter has a larger element than the Stealth unit, it is also closely shrouded around most of it's circumference which can have a noticeable impact on 'as installed' cfm. The stock air filter can be significantly improved by reducing the shrouding effect. One way to do this is increasing the bottom 'cutout' area further up the sides of the cover and reducing the aluminum backplate radius on the upper half to match the filter element radius.

In any case, at idle, where the engine is only pumping about 33 cfm, just about any air cleaner would do.

But don't you need to calculate for the additional area due to the pleats on the filter? Should about double the effective area at a guess. Does also rather assume that the air flow is fairly constant which is not very likely on an over sized vee-twin.

No need to take pleats into account. I should have made it more clear that the 6 cfm rate was for the K&N type of construction with wire mesh supported pleated gauze, lightly oiled.

Air flow, practically speaking, or from the filters' point of view if your prefer, looks pretty constant. Even at idle there is a cylinder pulling in air 1000 times a minute or every .06 seconds. At 5000 rpm that's every .012 seconds.

“Over oiled”, it was a new filter from S&S directly with only one tank of fuel used so less than 200 miles on it. The new taller filter mase a difference. Maybe it was because the stinger gets moved an inch further from the throat.