View unanswered posts | View active topics It is currently Sat Aug 19, 2017 10:59 am



Reply to topic  [ 39 posts ]  Go to page 1, 2, 3, 4  Next
 Loses 30 hp with air cleaner 
Author Message

Joined: Wed Oct 23, 2013 8:01 am
Posts: 113
Have a 421 sbc on the dyno.
9.75 comp.
profiler heads
hyd. roller
Vic. jr
800 QJet
Made a few pulls to get the AF good ended up with a B hanger & BG rods should be rich I thought especially with this being done.
viewtopic.php?f=26&t=498#p4213
Here's the pulls.Image
Image


Sat Oct 17, 2015 10:26 am
Profile
Site Admin

Joined: Fri Feb 08, 2013 2:37 pm
Posts: 1744
What type of filter? Actual GM open element or ??


Sat Oct 17, 2015 11:16 am
Profile

Joined: Wed Oct 23, 2013 8:01 am
Posts: 113
tuner wrote:
What type of filter? Actual GM open element or ??

Moroso drop base 14 x 4 white paper filter.


Sat Oct 17, 2015 11:30 am
Profile
Site Admin

Joined: Fri Feb 08, 2013 2:37 pm
Posts: 1744
The effect on left and right A/F is odd. How close is the lid to the top of the carb? Have you tried it with and without the additional baffle retained by the screws near the air cleaner stud? Have you tried a different element?


Sat Oct 17, 2015 11:53 am
Profile

Joined: Mon Dec 29, 2014 1:26 am
Posts: 433
Air filter base: +50cfm
Air filter element: -20cfm
net +30cfm, with no corresponding increase in metering area
(Is that a plausible scenario?)

Was the filter base (but no element/lid) in place on the first run?

_________________
Hate drilling setscrews? Click here! Free!


Sat Oct 17, 2015 1:43 pm
Profile

Joined: Wed Oct 23, 2013 8:01 am
Posts: 113
Attachment:
Dyno CV rod.jpg
Dyno CV rod.jpg [ 328.47 KiB | Viewed 672 times ]
This pull with a leaner rod loss less than the richer one
tuner wrote:
The effect on left and right A/F is odd. How close is the lid to the top of the carb? Have you tried it with and without the additional baffle retained by the screws near the air cleaner stud? Have you tried a different element?


I'm thinking 2 inches, didn't try a different element.
I'll be going back next week, the dyno is 3 hours away.


Sat Oct 17, 2015 3:22 pm
Profile

Joined: Wed Oct 23, 2013 8:01 am
Posts: 113
Something was going on with one of the sensors. we swapped them side to side at one point but didn't note it. If any one was giving the best reading I'd say the left because the bung is in the header & the other side is in the adapter that goes to the flex pipe.

BTW Tuner this is the carb that has the secondary mods done linkage & comp jet. If any thing it should be way rich with a B hanger & BG rod.


Sat Oct 17, 2015 3:26 pm
Profile

Joined: Wed Oct 23, 2013 8:01 am
Posts: 113
Attachment:
100_3910.JPG
100_3910.JPG [ 812.31 KiB | Viewed 669 times ]
Attachment:
100_3909.JPG
100_3909.JPG [ 1013.55 KiB | Viewed 669 times ]
Attachment:
100_3908.JPG
100_3908.JPG [ 1001.82 KiB | Viewed 669 times ]
Of these 3 bases which would be the preferred.


Sat Oct 17, 2015 4:07 pm
Profile

Joined: Sat Mar 29, 2014 10:27 am
Posts: 45
I definitely think your'e too rich based on what you found when using the leaner CV rods. I initially tried DB rods at first in mine (461BBC) but they were too lean. DR was almost there and settled on CP with P hanger for the summer. Now that its getting colder, I found I have to go richer with the hanger (M). Bring some leaner rods and hangers. Nice job on the dyno numbers!


Sat Oct 17, 2015 4:21 pm
Profile
Site Admin

Joined: Fri Feb 08, 2013 2:37 pm
Posts: 1744
Quote:
Of these 3 bases which would be the preferred.


the bottom one, the stock GM. The second might be OK, but the top I don't think so. Can you try them all?

I've never seen a loss with a stock filter unless the element was restrictive.

The straight walled vertical air cleaner spacer, like the tall one on '71 &'72 1/2 ton C10 Chevy PU trucks, and the short one on LS-6 Chevelle with cowl hood, cause the flow to be less than with the plain filter base similar to the one in the bottom picture, and in fact, a vertical wall entry flows less than a naked carb with no filter.

I've done this with a flow bench several times for show-and-tell. The common "small" QJet carb with no filter base at all flows about 750 CFM, and with a GM filter base the flow will go over 800. You can measure the carb with nothing on it and if you put your index fingers around the secondary, resting them horizontally on the air cleaner gasket flange, the flow will increase 30 CFM or so, just from the radius entry your fingers provide.

I think the filter used in the dyno test is causing a flow anomaly on the bowl vents and the bowl pressure is being reduced.

I'm not surprised the filter lid made it worse. Because of the pleats and screen on the underside the filter lid is thicker and encroaches even more on the vent tube(s). The vent tube must not be in a region of turbulent boundary layer flow.

Did you try just the base alone?

Are you using the secondary baffle shown in the picture of your carb? The one retained by the two screws near the air cleaner stud?

The secondary throttle butterfly is not opening beyond the bottom edge of the vertical insert in the body.....??

(By the way, that's a pretty spunky engine you have there. Are you going to turn it a little higher to see just what it will do?)


Sat Oct 17, 2015 6:35 pm
Profile
Display posts from previous:  Sort by  
Reply to topic   [ 39 posts ]  Go to page 1, 2, 3, 4  Next

Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group
Designed by ST Software for PTF.