Holley 850 DP Question - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 06-05-2012, 08:27 PM
396chevelle's Avatar
Registered User
 
Last photo:
Join Date: Nov 2010
Location: mobile
Age: 37
Posts: 253
Wiki Edits: 0

Thanks: 0
Thanked 4 Times in 4 Posts
Holley 850 DP Question

In a nut shell my 496 was tuned on the dyno before it was put in the car. Now that it's in the car it has ran great, but the only issue I'm having is that when idling the exaust will burn your freaking eyes out. Any recommendations? I did want to see what size power valves were in it after I checked my vacuum. I have 6" of vacuum in drive at idle and the carb has a #4 power valve in the primary metering block and a plug in the secondary metering block would you guys recommend droping to a #3 or is the #4 close enough? Primary jets 78-78 and secondary jets 86-86. Carb is set to highest vac seems to run great, but the exaust at idle will make you cry!

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 06-06-2012, 01:54 AM
cobalt327's Avatar
WFO
 
Last wiki edit: Intake manifold
Last journal entry: 1980 Malibu Wagon
Last photo:
Join Date: Mar 2009
Location: Atlanta
Age: 59
Posts: 5,037
Wiki Edits: 1616

Thanks: 128
Thanked 597 Times in 546 Posts
Quote:
Originally Posted by 396chevelle
In a nut shell my 496 was tuned on the dyno before it was put in the car. Now that it's in the car it has ran great, but the only issue I'm having is that when idling the exaust will burn your freaking eyes out. Any recommendations? I did want to see what size power valves were in it after I checked my vacuum. I have 6" of vacuum in drive at idle and the carb has a #4 power valve in the primary metering block and a plug in the secondary metering block would you guys recommend droping to a #3 or is the #4 close enough? Primary jets 78-78 and secondary jets 86-86. Carb is set to highest vac seems to run great, but the exaust at idle will make you cry!
The eye watering exhaust is unburned hydrocarbons, caused by the EGR effect of the cam timing. This is common w/a cam that has a lot of overlap/tight LSA/late closing intake.

If you can, add initial timing. Just be sure to balance the total timing by removing timing from the mechanical advance so the total timing doesn't go too high.

In some cases, dialing in some vacuum advance could help. But having the vacuum at idle that low will make that impractical, though. I'd advise you to use vacuum advance, but in your case use ported vacuum for the vacuum advance. Limit the vacuum advance to 10 degrees.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 06-06-2012, 07:55 AM
396chevelle's Avatar
Registered User
 
Last photo:
Join Date: Nov 2010
Location: mobile
Age: 37
Posts: 253
Wiki Edits: 0

Thanks: 0
Thanked 4 Times in 4 Posts
Quote:
Originally Posted by cobalt327
The eye watering exhaust is unburned hydrocarbons, caused by the EGR effect of the cam timing. This is common w/a cam that has a lot of overlap/tight LSA/late closing intake.

If you can, add initial timing. Just be sure to balance the total timing by removing timing from the mechanical advance so the total timing doesn't go too high.

In some cases, dialing in some vacuum advance could help. But having the vacuum at idle that low will make that impractical, though. I'd advise you to use vacuum advance, but in your case use ported vacuum for the vacuum advance. Limit the vacuum advance to 10 degrees.
OK, Thanks for the input! I'll give it a shot.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 06-06-2012, 09:23 AM
How fast is fast enough?
 
Last photo:
Join Date: Jun 2005
Location: St. Louis, MO
Age: 29
Posts: 8,892
Wiki Edits: 0

Thanks: 17
Thanked 308 Times in 288 Posts
Its very possible that your wot performance was tuned on the dyno with the jets rather than the pvcr's. A LOT of people do that and it is the WRONG way to tune WOT. You may need to step down a handful of jet sizes and open up your pvcr to get your cruise tuned right.

For idle you can adjust the idle feed and bleeds to get an acceptable idle and off idle transition.

Tuning a carb for peak power has very little to do with tuning a carb for peak performance. Peak power is easy, peak performance is much much harder.
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
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:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Holley 850 DP running very rich flooding engine Schoust Engine 13 07-28-2011 05:24 PM
Holley 850 DP on auto Jason7504 Engine 5 01-17-2011 05:02 PM
Holley AED/Proform 850 eric866121 Engine 7 06-24-2009 10:31 AM
Holley 850 Carburetor defference JamesRS Engine 2 04-07-2007 12:03 AM
Holley 850 CFM Vacuum Secondaries.. PITA..!! Viet Nam Vette Engine 18 04-12-2006 07:54 PM


All times are GMT -6. The time now is 10:53 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.