*8 mpg a little low - looking for 10* - 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 06-21-2010, 12:58 PM
2000jack's Avatar
1929 Chopped Tudor
 
Last wiki edit: How to title a hot rod
Last journal entry: 1927 roadster
Last photo:
Join Date: Dec 2005
Location: Rhode Island
Age: 66
Posts: 301
Wiki Edits: 3

Thanks: 0
Thanked 1 Time in 1 Post
*8 mpg a little low - looking for 10*

I have a 29 Tudor that gets 8 mpg. It has a SBC 350 with Chevy Vortec heads (the truck type that supposed to be for better mileage). I have, everything less than 2000 miles on it, new gas tank, lines, gas filters (two), gas cap, K&N air filter, properly functioning thermostat. No apparent fuel leaks, I go into the garage after 4 or 5 days and I smell nothing. Fuel pump less than 2500 miles Choke works fine. Idles good. A new out the box Holley in which I dropped the jets from I believe was 65 to 63. The Holley tech did not recommend to go any lower. I have it timed at 8 degrees advanced. The exhaust pipes are black carbon. Some one suggested that I get a new power valve with the lowest amount of Hg, but I see that the go from 10.5 Hg to 1 Hg on Summit. What is a good street number and how do these things work?

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 06-21-2010, 01:06 PM
Member
 
Last photo:
Join Date: Dec 2004
Location: San Antonio, Texas
Age: 50
Posts: 4,021
Wiki Edits: 0

Thanks: 0
Thanked 23 Times in 23 Posts
read this.

http://www.corvette-restoration.com/.../Timing101.pdf
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 06-21-2010, 01:06 PM
Member
 
Last photo:
Join Date: Dec 2004
Location: San Antonio, Texas
Age: 50
Posts: 4,021
Wiki Edits: 0

Thanks: 0
Thanked 23 Times in 23 Posts
and this.

http://www.bob2000.com/carb.htm
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 06-21-2010, 01:12 PM
Member
 
Last photo:
Join Date: Dec 2004
Location: San Antonio, Texas
Age: 50
Posts: 4,021
Wiki Edits: 0

Thanks: 0
Thanked 23 Times in 23 Posts
8mpg in the city or highway?

what is the curb weight?

what gears and transmission type?

the cam determines the right power valve.

bigger cams require smaller numbered power valves.

the higher the the number the sooner it comes on.

a mild cam will run snappy with a 8.5 but will get better city mpg with a 6.5.

a mild small block should get 10 city/16 highway with a 3.08 gear and th350 trans in a 3800 pound ride.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 06-21-2010, 01:22 PM
2000jack's Avatar
1929 Chopped Tudor
 
Last wiki edit: How to title a hot rod
Last journal entry: 1927 roadster
Last photo:
Join Date: Dec 2005
Location: Rhode Island
Age: 66
Posts: 301
Wiki Edits: 3

Thanks: 0
Thanked 1 Time in 1 Post
Quote:
Originally Posted by 454C10
8mpg in the city or highway?
Ans. [I]Not much City where I am so it is backl roads and highway[/I]
what is the curb weight?
Ans. around 3200 pounds

what gears and transmission type?
Ans. 2.92 & TH350
the cam determines the right power valve.

bigger cams require smaller numbered power valves.

the higher the the number the sooner it comes on.

a mild cam will run snappy with a 8.5 but will get better city mpg with a 6.5.

a mild small block should get 10 city/16 highway with a 3.08 gear and th350 trans in a 3800 pound ride.
These are the numbers I would love to have
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 06-21-2010, 01:25 PM
ericnova72's Avatar
More for Less Racer
 
Join Date: Jan 2007
Location: S.W. Lower Michigan
Age: 47
Posts: 8,959
Wiki Edits: 0

Thanks: 20
Thanked 378 Times in 347 Posts
Need to tell us what cam, compression ratio, rear gears, are you using the vacuum advance??

Total mechanical advance you have, to go with your 8 initial??
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 06-21-2010, 01:52 PM
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
X2, need the low-down on your combination.

There's a current THREAD that deals w/power valves (last couple pages) as well as other tuning parameters on a Holley carb. A search here will also get you a lot of info.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 06-21-2010, 01:53 PM
2000jack's Avatar
1929 Chopped Tudor
 
Last wiki edit: How to title a hot rod
Last journal entry: 1927 roadster
Last photo:
Join Date: Dec 2005
Location: Rhode Island
Age: 66
Posts: 301
Wiki Edits: 3

Thanks: 0
Thanked 1 Time in 1 Post
Quote:
Originally Posted by ericnova72
Need to tell us what cam, compression ratio, rear gears, are you using the vacuum advance??

Total mechanical advance you have, to go with your 8 initial??
I believe it is 25 so that it has a total of 33, not a total of 40 with the old style heads. I bought the motor as a new rebuilt from Phoenix Engine. I have the cam specsIntake 442 @288 and the exhaust 465 @298. Also they gave me @.50 lift 214 int. and 224 exhaust. Standard flat top pistons. 8 inch Ford rear with 2.92 gears. Standard HEI distributor.
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 06-21-2010, 01:56 PM
Hippie's Avatar
Analog man in a digital world.
 

Last journal entry: HEI comparison.
Last photo:
Join Date: May 2003
Posts: 2,255
Wiki Edits: 0

Thanks: 3
Thanked 5 Times in 5 Posts
What Holley are you running?

I went from 7 MPG with a 15,000 mile 9 to 1 twenty over 318 with Edelbrock SP2P, 727 auto and 2.94 gears to 13 average in my '86 Dodge D150. The truck had a totally trashed 1850 600 on it when I took possession. I slowy got it up to 9 MPG with a good tune up, replacement of a defective fan clutch, hotter thermostat and repair of too many tiny vacuum leaks in the heater controls to count. I then replaced the 1850 with a fresh 6619 and with some jetting and addition of a two dtage power valve eeked 10.5 out of it. After about 3 months I replaced the Holley with a remanufactured Q-Jet I pulled off a '93 W-150 Cash for Clunkers victim in the boneyard and immediately picked up another 2.5 MPG. Over the course of all this my idle vacuum went from 15 to 23. I set the idle mixture on the Q-Jet and that has been it. I believe there's more to be squeezed out of it but I needed a break from it so for now I'm just enjoying my 85.7% mileage increase.

Just saw the post with your cam specs, that's not exactly a mileage/RV cam. You may not believe this but I think you're going to want a little lower gear. At highway speed you're probably not into the power curve, or "up on the cam" so the engine is lugging slightly. Lower RPM only helps mileage to a point, too low and it actually hurts mileage. Plus something to keep in mind is aero drag, a '29 isn't the most aerodynamic thing on the road. It may be light but it's pushing a lot of air at 60 MPH.

Last edited by Hippie; 06-21-2010 at 02:08 PM.
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 06-21-2010, 02:05 PM
2000jack's Avatar
1929 Chopped Tudor
 
Last wiki edit: How to title a hot rod
Last journal entry: 1927 roadster
Last photo:
Join Date: Dec 2005
Location: Rhode Island
Age: 66
Posts: 301
Wiki Edits: 3

Thanks: 0
Thanked 1 Time in 1 Post
Quote:
Originally Posted by Hippie
What Holley are you running?

I went from 7 MPG with a 15,000 mile 9 to 1 twenty over 318 with Edelbrock SP2P, 727 auto and 2.94 gears to 13 average in my '86 Dodge D150. The truck had a totally trashed 1850 600 on it when I took possession. I slowy got it up to 9 MPG with a good tune up, replacement of a defective fan clutch, hotter thermostat and repair of too many tiny vacuum leaks in the heater controls to count. I then replaced the 1850 with a fresh 6619 and with some jetting and addition of a two dtage power valve eeked 10.5 out of it. After about 3 months I replaced the Holley with a remanufactured Q-Jet I pulled off a '93 W-150 Cash for Clunkers victim in the boneyard and immediately picked up another 2.5 MPG. Over the course of all this my idle vacuum went from 15 to 23. I set the idle mixture on the Q-Jet and that has been it. I believe there's more to be squeezed out of it but I needed a break from it so for now I'm just enjoying my 85.7% mileage increase.
It is a 600CFM non adjustable float 4 barrels. I have to go to storage to get the exact number.
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 06-22-2010, 07:35 AM
Member
 
Last photo:
Join Date: Dec 2004
Location: San Antonio, Texas
Age: 50
Posts: 4,021
Wiki Edits: 0

Thanks: 0
Thanked 23 Times in 23 Posts
yes, not a gas mileage cam. and too much cam for the gear ratio.

need more initial timing with that cam. try putting the vacuum advance on a manifold source. should have 8 mechanical plus another 15 to 20 from the vacuum advance at idle. so that makes 23 to 28 at idle.

I would reduce the total amount of mechanical advance in the distributor so you can run more initial.
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 06-22-2010, 12:39 PM
2000jack's Avatar
1929 Chopped Tudor
 
Last wiki edit: How to title a hot rod
Last journal entry: 1927 roadster
Last photo:
Join Date: Dec 2005
Location: Rhode Island
Age: 66
Posts: 301
Wiki Edits: 3

Thanks: 0
Thanked 1 Time in 1 Post
Quote:
Originally Posted by 454C10
yes, not a gas mileage cam. and too much cam for the gear ratio.

need more initial timing with that cam. try putting the vacuum advance on a manifold source. should have 8 mechanical plus another 15 to 20 from the vacuum advance at idle. so that makes 23 to 28 at idle.

I would reduce the total amount of mechanical advance in the distributor so you can run more initial.
If I understand you correctly, you believe that the valves are staying open too long at low rpm so that the some of the gas is flowing out the exhaust before it has a chance to fire?
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 06-22-2010, 12:49 PM
Member
 
Last photo:
Join Date: Dec 2004
Location: San Antonio, Texas
Age: 50
Posts: 4,021
Wiki Edits: 0

Thanks: 0
Thanked 23 Times in 23 Posts
bigger cams need more timing at idle. more timing allows for a leaner mixture.

furthermore, a cam that big also requires more rpm at idle and more throttle opening. this causes the carb to idle past the transition slots which make it run very rich at idle. more timing will increase idle speed and allow the throttle blades to be closed more and operate in the idle circuit.

did you read the 2 links I posted at the start of this thread? It is all in there.
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 06-22-2010, 01:54 PM
Member
 
Last photo:
Join Date: Dec 2004
Location: San Antonio, Texas
Age: 50
Posts: 4,021
Wiki Edits: 0

Thanks: 0
Thanked 23 Times in 23 Posts
"An engine with a performance camshaft will also respond well to more initial timing because, at lower engine speeds, the air velocities are reduced due to valve overlap and the air/fuel mixture is poor. Therefore, advancing the initial timing provides longer time for this poorer mixture to burn in the cylinder"

quote from a engine tuning web site.
Reply With Quote Quick reply to this message
  #15 (permalink)  
Old 06-22-2010, 02:07 PM
ericnova72's Avatar
More for Less Racer
 
Join Date: Jan 2007
Location: S.W. Lower Michigan
Age: 47
Posts: 8,959
Wiki Edits: 0

Thanks: 20
Thanked 378 Times in 347 Posts
First step, you need to get the initial timing up to around 15-20 initial. You are going to have to modify the distributors advance limit slot under the mechanical advance mechanism due to the fact that you need to keep the total below 40.

Common mod for those of use that do performance on a regular basis, but it sure does seem to throw people a curve ball when you tell them they will have to dissassemble the distributor and modify it, that there isn't some bolt-on solution.

Well, there is one bolt-on solution...a $300 MSD Billet Distributor that is fully adjustable.
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
vaccum too low?? 357 with comp 280H cam 357 Cutlass Engine 19 06-29-2008 10:26 AM
How low is too low? Ripped Suspension - Brakes - Steering 8 06-28-2008 11:52 AM
Holley versus Q-jet MPG results 454C10 Engine 3 06-19-2007 08:39 PM
700r4 won't stay in manual selected low lldsad@centurytel.ne Transmission - Rearend 4 06-12-2007 06:42 PM
increasing low end torque fast68 Engine 3 07-31-2006 04:27 PM


All times are GMT -6. The time now is 07:36 PM.


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.