stumped on tuning - Impala Tech
Performance Our High Performance Area

 
LinkBack Thread Tools
post #1 of 7 (permalink) Old 06-03-2009, 09:31 AM Thread Starter
Member
 
Join Date: May 2009
Location: Pacific City, Or
Posts: 33
 
stumped on tuning

hey fellas, i'm looking for some help with tuning my 66' impala with a 77' 350 and powerglide. when i got the car it was running rough and advancing the timing helped along with some new plugs. recently i installed a new vacuum secondary holley 600 which also helped some. i had it running pretty good then, but i could tell the timing was slightly off in certain points of the rpms, specifically low. yesterday i installed a new msd streetfire distributor and a new set of plug wires and it would bog at low rpms and ping at the high end.
i put a larger accelerator pump and larger jets on the carb which helped in the low end, but the mid range is rough and it still pings on the high end. i've screwed with the timing and vacuum advance and still not improved the situation much. there's no vacuum or intake leaks anywhere. compression is 149 to 160. it does have some type of cam and a weiand stealth intake.
so, what do you think? any suggestions? intake sucks? timing out of whack? is it all related to the powerglide's high first gear? thanks for any help--i'm out of ideas!!
Johnny Rotten is offline  
Sponsored Links
Advertisement
 
post #2 of 7 (permalink) Old 06-03-2009, 10:06 AM
Moderator
 
Join Date: Jan 2006
Posts: 12,383
 
Timing is to high retard it. Pinging is detonation which destroys pistons. Your MSD should have an adjustable vacuum advance. Bring on more advance earlier by adjusting the vacuum can spring. You should have your total advance in by 2,800 RPM.

As to bogging you need to go to either a different accelerator pump cam (don't forget you have two positions to try) or a change in your squirter size. The bigger the number the more fuel you deliver in less time, a smaller number spreads the shot out longer to cover a flat spot (bog). Cam controls the volume and squirter controls the time distribution.

Big Dave
Big Dave is offline  
post #3 of 7 (permalink) Old 06-03-2009, 11:11 AM
BA.
Moderator
 
Join Date: Aug 2008
Location: Miamisburg, Oh.
Posts: 3,136
Blog Entries: 15
 
I agree with Dave on this.

Bryan, do you know what your timing settings are right now for Initial setting, advance and Total as measured? (and at what RPM the advance comes in) Sure sounds like too much total timing for the pinging problem.

If you have a vacuum gauge, it'd be good to know what vacuum you're pulling at idle, this will sort of give us an idea of the size of that cam. You can also use it to help set the best initial timing setting for your motor.

HOW A NOVICE REBUILDS A 66 IMPALA CONVERTIBLE:
http://www.impalas.net/forums/blog.php?u=1432
BA. is offline  
 
post #4 of 7 (permalink) Old 06-03-2009, 11:30 AM Thread Starter
Member
 
Join Date: May 2009
Location: Pacific City, Or
Posts: 33
 
vacuum at idle is around 15. the timing is hard to put a number to because the cover plate may not be correct. i don't have a tach to measure rpms right now. at idle the timing is about 20-22 degrees according to the marks on the plate. i have put the vacuum advance to the ported vacuum off the carb and blocked up the manifold vacuum because it seemed to be too much. maybe i should switch that back and retard the timing?
Johnny Rotten is offline  
post #5 of 7 (permalink) Old 06-03-2009, 02:00 PM
Senior Member
 
Join Date: Jun 2008
Location: Near Chicago
Posts: 703
 
While I agree your initial timing might be too advanced, I would look towards the centrifugal advance for the upper RPM detonation issue.

Dave, on the subject of accelerator pump cams and squirters I think you have it backwards; The squirter size dictates the volume of fuel coming out and the cam dictates the timing and duration for the squirt.
1968 Caprice 396 is offline  
post #6 of 7 (permalink) Old 06-03-2009, 02:29 PM
BA.
Moderator
 
Join Date: Aug 2008
Location: Miamisburg, Oh.
Posts: 3,136
Blog Entries: 15
 
Bryan - for what it's worth, I've ran 20-23 initial timing on cam'd SBC's before and it was ideal for me. I also have a friend or two that has used the same with success.
Definitely check that mechanical advance setting or try to get that total number somehow.

I think your bog issue will be worked out with the right match of pump cam and squirter. With a heavy car, PG and cammed motor, it probably takes a bigger volume and longer duration shot.
Page 4 at this link is a good read about them
http://holley.com/data/TechService/Technical/Carburetor%20Tech%20Info.pdf

Here's one of many charts out there for the pump cams and how they compare. Maybe it will help to check where you're at and what you may want to change to.
http://www.innovatemotorsports.com/f...7&d=1165267512

It's nice to have a selection of cams and squirters around. I used to have a nice full set back in the day.

HOW A NOVICE REBUILDS A 66 IMPALA CONVERTIBLE:
http://www.impalas.net/forums/blog.php?u=1432
BA. is offline  
post #7 of 7 (permalink) Old 06-03-2009, 03:32 PM Thread Starter
Member
 
Join Date: May 2009
Location: Pacific City, Or
Posts: 33
 
thanks fellas for the response! BA, i've put a new, larger squirter and yellow cam on yesterday which helped the initial bog and low rpms. currently it is running poorly in the mid rpms 35 to 45 mph. the consensus seems to be to back off the vacuum at the canister then? keep initial advance the same?
Johnny Rotten is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Impala Tech 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.

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 On
Pingbacks are On
Refbacks are On

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