Original comp 427 air cleaners
 

According to all the modern interweb info out there, there is no way that teeny 8.5 inch stelling and helling air cleaner should have worked on a 425 ci side oiler making 500+ HP? Give it 2 inch height thats 53 sq in of filter area. Using Ci x RPM/25500 yields a required area of 425*6500/25500=108 sq in?

Steve H

There's definitely some airflow restriction.

My guess is that the carbs were jetted to compensate for what would be a rich condition at max RPM.

Check out the SecondStrike tech page. Mike has an aircleaner calculator that works well and shows a fair amount of info on different sizes. Seems to track my experience fairly well.

His carb sizing calculator is good too, albeit developed for drivability rather than peak performance. This one too tracks my experience.

Jim

Def a restriction !!! BUT it looked right :LOL:

Dating back to some time in 2000 if memory serves me correctly (might be 2001, prior to 9/11).
427 center oiler, 10:2:1 compression, 650 holley DB (already dyno tuned) fairly mild street cam as a base for the test on a "chassis" (not engine) dyno. This was done as we were baselining a new chassis dyno at a friends shop and thought it would be interesting to be able to show his customers the difference of what something as simple as an air cleaner could make.

My notes are as follows:

no air cleaner: 322hp
then 14X2 "K&N" air cleaner: 314hp
then 14X4 "green" air cleaner with drop base:324hp
then Stelling and Heller air cleaner (stock filters as we did not have K&N or Green filters in stock at the time):302hp

All of the above were done one after the other. No tweaks or changes where done to the carb or engine timing. Strictly a demonstration for about 20 customers who were at the shop that Saturday. All HP above was measured at the rear wheels.

The car was ERA321, dark blue metallic, running a toploader 4spd and 3:31 rear gear ratio.

I can confirm those where actual results, less then a few minutes apart on a brand new Dynojet chassis dyno. Real world, real wheel HP data. Somewhere in my old files I may have the torque numbers to go along with this but have yet to find them.
As a side note, the numbers above where done before we had a K&N or Green Filter-14" filter top. The filter top would add a huge amount of airflow vs the chrome lid that was used at the time of the chassis dyno runs to the tune of an additional 500cfm, just for the filter top.


Bill S.

PS: Formula wise:
Using the simple formula
http://www.knfilters.com/images/affform1.gif
A= effective filter area
CID=engine displacement
RPM=maximum RPM expected

Using the CFM formula of height X diameter x 6 x 3.14

In Feb 2000 I saw a red Cobra with a strange 198 on the side featuring a (I estimate) a 3" tall, but small diameter airfilter. A silly plague on the dash said something along the lines of 198 mph. The late man's name was Joe Smith, or so ;-)

I figure this car had 530 - 550 Hp. Else, by my coast down test results in 1995 when we defined the resistance of a Cobra at 198 mph, that car would never have achieved this speed. Depending on windshield size and rake.

Would have been a 427 SO. Possibly stroked? However, perhaps back in 1968 he used another airfilter than in 2000.

For all I know, I rather have some clean lines on the hood and sacrifice 20 hp for looks.
Check Morris' evaluation of airflow over his hood. Smith's car was far less sophisticated.
Seems he didn't even have racing seats.

Dominik it appears that you saw one of the most significant 427 Cobras of all, the late Dick Smith's competition car CSX 3035. He was in fact clocked at 198 mph at Daytona and was the A Production national champ in 1967. I met him at Lime Rock in 2006 and he was a real gentleman. Had me sit in his car for a picture and even wanted me to put his helmet on.

One of the reasons the dual quad intake made more sense to me. Still restrictive but at least there are 2 S&H air filters to feed it.

I found by trial and error how restrictive those two small S&H filters are. Here's a link to what I did to resolve things:

https://www.hotrodders.com/threads/a.../#post-4625639

I went to 2” K&N filters on my stroked 428. I have a smooth hood and a 427 LR intake and that was as thick as I could go and still have good clearance to the hood. A compromise but I don’t need every last HP for my driving style. The

Me neither, but it was nice to see that the power I got with the pedal 1/3 down was now available at only 1/4 of the way down. Either way, that's the most I feel comfortable with in 2nd gear as I worry about the tires letting go.

Of course, Dick Smith. I was pulling your guys legs a bit. It was at Lynn Park (red shirt) after Shelby does Vegas in 2000. Perhaps it was just jetted accordingly as Bob mentioned. For good reasons!

That engine builder definitely knew what he was doing.

Just an FYI, the temporary air cleaner was not typically used during racing, but is used for display purposes to keep people from dropping something into the carb, either on purpose :eek:, or by accident :rolleyes:

And most of you all know this, but if a noob is reading this thread and decides to change out his stifling air cleaner for a free flowing air cleaner, and he's running with a vac secondary carb, his car will run worse until he changes out his secondary spring to match the new slower flowing air/fuel velocity that is a result of the larger volume being moved (i.e. the carb is no longer sucking hard and fast through a straw but is instead breathing slowly and easily though a large diameter pipe).:cool: