RPM drops 100 with air cleaner on carb - Ford Mustang Forum
Like Tree3Likes
  • 1 Post By Grimbrand
  • 2 Post By Ivy66GT
 
LinkBack Thread Tools
post #1 of 10 (permalink) Old 12-27-2017 Thread Starter
Apprentice
 
guitarman584's Avatar
 
Joined: Oct 2015
Location: So Cal
Posts: 109
 
Garage
RPM drops 100 with air cleaner on carb

Hey all, Merry Christmas and Happy New Year! Got a weird issue here. After doing the Edelbrock 2027 top-end kit, my RPM drops by 100 RPM at idle. Without the air cleaner it idles around 800-850ish, but drops down to about 700 with the air cleaner installed. The filter is still very clean as you can see plenty of light through it. This has me baffled. The cam that came with the kit has 16" vacuum at 1000 RPM. Could it be the cam causing this issue? There are no changes in RPM above 1500 with the air cleaner on. Thoughts? Thanks in advance!


1965 coupe w/ 302 out of a '68, Edelbrock 2027 top-end kit, Autolite 4100, Mustang II front end conversion, AAW wiring harness, rear-disc conversion
guitarman584 is offline  
Sponsored Links
Advertisement
 
post #2 of 10 (permalink) Old 12-27-2017
Rookie
 
SVThuh's Avatar
 
Joined: Dec 2017
Posts: 47
 
Garage
Its likely the cam. More overlap will affect vacuum. I would bump the carb up to 800ish with the cleaner on and call it good.

SVThuh is offline  
post #3 of 10 (permalink) Old 12-28-2017
GT Member
Classic Member
5.0L Member
 
Grimbrand's Avatar
 
Joined: Nov 2016
Location: Sedgwick
Posts: 2,194
 
Garage
Send a message via Skype™ to Grimbrand
What air cleaner are you running? There's a lot of science to the airflow coming through the filter and the angle it takes as it 'collides' in the middle of the air cleaner before it goes down the throat. Some of the aftermarket units don't do as well as stock, believe it or not!

I'm kind of surprised that with it clean though, you're running into a restriction at *idle*. Usually the price of a poorly designed cleaner is paid on the top end at wide-open-throttle where it just can't pull enough air.
Beechkid likes this.
Grimbrand is offline  
 
post #4 of 10 (permalink) Old 12-28-2017 Thread Starter
Apprentice
 
guitarman584's Avatar
 
Joined: Oct 2015
Location: So Cal
Posts: 109
 
Garage
Quote:
Originally Posted by Grimbrand View Post
What air cleaner are you running? There's a lot of science to the airflow coming through the filter and the angle it takes as it 'collides' in the middle of the air cleaner before it goes down the throat. Some of the aftermarket units don't do as well as stock, believe it or not!

I'm kind of surprised that with it clean though, you're running into a restriction at *idle*. Usually the price of a poorly designed cleaner is paid on the top end at wide-open-throttle where it just can't pull enough air.
This is the air cleaner I have that came with the car:
https://www.summitracing.com/parts/c...21-3/overview/

1965 coupe w/ 302 out of a '68, Edelbrock 2027 top-end kit, Autolite 4100, Mustang II front end conversion, AAW wiring harness, rear-disc conversion
guitarman584 is offline  
post #5 of 10 (permalink) Old 12-28-2017
SHELBY GT 350 Member
Classic Member
 
Ivy66GT's Avatar
 
Joined: Dec 2008
Location: Albuquerque
Posts: 7,965
 
I have never had a car whose RPM did not drop with the air cleaner installed. That is why you need to make the final carb adjustment with the air cleaner in place. Not only does it affect idle speed the mixture changes as well.
Beechkid and Grimbrand like this.
Ivy66GT is offline  
post #6 of 10 (permalink) Old 12-28-2017 Thread Starter
Apprentice
 
guitarman584's Avatar
 
Joined: Oct 2015
Location: So Cal
Posts: 109
 
Garage
Thanks, Ivy and SVT. That's definitely the cheaper option rather than trying new air cleaners to see if the shape was the issue.

1965 coupe w/ 302 out of a '68, Edelbrock 2027 top-end kit, Autolite 4100, Mustang II front end conversion, AAW wiring harness, rear-disc conversion
guitarman584 is offline  
post #7 of 10 (permalink) Old 12-28-2017
Rookie
 
SVThuh's Avatar
 
Joined: Dec 2017
Posts: 47
 
Garage
Quote:
Originally Posted by guitarman584 View Post
Thanks, Ivy and SVT. That's definitely the cheaper option rather than trying new air cleaners to see if the shape was the issue.
No prob brother. FWIW, I have a very similar air cleaner with a K&N on my car (see my avatar photo) and it does the same thing. Set your final idle with the cleaner in place and just run with it.
SVThuh is offline  
post #8 of 10 (permalink) Old 12-28-2017
BOSS Member
 
Beechkid's Avatar
 
Joined: Apr 2013
Location: SoCal
Posts: 4,456
           
In short- yes......nothing to really worry about and not unsusal....that particular type of air cleaner comes very close to the carb air horn....and it is well known (to us old folks) & published in the holley tune books from the 70's that they do choke off the air a bit...... if you remove the air horn you can actually gain about 50 cfm back

:hello:
Member: Never trust a person over 40 who drives a Chevy club
Flatheads ain't so bad!
Certified backyard mechanic I & II
Beechkid is offline  
post #9 of 10 (permalink) Old 12-28-2017 Thread Starter
Apprentice
 
guitarman584's Avatar
 
Joined: Oct 2015
Location: So Cal
Posts: 109
 
Garage
I can certainly understand why it would drop, but it just shocked me that it would drop that much.

1965 coupe w/ 302 out of a '68, Edelbrock 2027 top-end kit, Autolite 4100, Mustang II front end conversion, AAW wiring harness, rear-disc conversion
guitarman584 is offline  
PONY Member
 
67moneypit's Avatar
 
Joined: Jan 2011
Location: Olympic Peninsula
Posts: 435
 
It sounds like you already got your answer now, but I figured I would add some reassurance. Every carbed car I have ever owned/worked on has idle drop with the air cleaner on. As already mentioned, final idle should be set with air cleaner and all vac lines installed. Just for giggles, I ran out and fired up a pickup with a 302, and watched RPMs at idle with and without the air cleaner. Seems to be 80-100 RPM fluctuation. If it matters, testing temperature was with the engine at operating temp around 180, and outside temp of 40 degrees.

- Scooter
1968 Mustang. 351w, T-5 Five Speed, 8.8, 3.73 trac lock rear end. Power, four wheel disc brakes, (CSRP up front, 8.8 discs out back) Shelby Drop...
67moneypit is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Ford Mustang Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a VALID email address for yourself, otherwise you will not receive the necessary confirmation email needed to confirm, validate and activate your new AFM member account.

Failure to provide a VALID email address, will result in the cancellation of your new AFM member account registration.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome
 


Search Engine Friendly URLs by vBSEO 3.6.1