would this increase mpg's? - 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 11-16-2010, 12:21 AM
Registered User
 
Last photo:
Join Date: Mar 2010
Location: USA
Posts: 218
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
would this increase mpg's?

Hello guys, i was informed that the cam in my 383 is a bit too big for the gearing in my car. I cruise at 1700RPM in 6th gear doing 70-75mph. My rear end is a 3.42 and I have 16" wheels with 245/50/r16 tires (im pretty sure at least). Fbird88 told me that the cam's operating rpm starts at 2500+, he was close. I was looking at my dyno sheet and the tourqe curve starts off pretty much dead on 2000RPM and drops off right at about 5500RPM.

Now that you have that info, my main question is this: If i change the rear ratio so that my cruising rpm will be 2000-2200RPM, would I increase mpg's or lose some due to the extra rpm? Right now If i drive purely highway I can knock down 22-24MPG. Now that isnt bad, but hypothetically would efficeincy increase if the cam is in its operating range? Thanks.

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 11-16-2010, 01:14 AM
ericnova72's Avatar
More for Less Racer
 
Join Date: Jan 2007
Location: S.W. Lower Michigan
Age: 47
Posts: 8,801
Wiki Edits: 0

Thanks: 19
Thanked 349 Times in 319 Posts
I'm betting MPG would get better if you get the rpm into a more efficient area as far as cam range vs rpm goes. My personal experience is that way, and it is more pronounced with a carb, fuel injection will cover a mismatch like this much better, whereas carbs need a certain amount of airflow velocity to meter correctly.

I have noticed you posted elsewhere this is a 6 speed trans, which is a T-56 which is like a 4 speed then with a double overdrive. 4th is 1:1 ratio, 5th is .070:1(?-ish) and 6th is .050:1...correct?? Have you tried a mileage test only using 5th, and not using 6th, to keep the rpm a little higher?? Could be a way to try it out, no rule you have to cruise in 6th exclusively, just don't use it.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 11-16-2010, 01:29 AM
Registered User
 
Last photo:
Join Date: Mar 2010
Location: USA
Posts: 218
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by ericnova72
I'm betting MPG would get better if you get the rpm into a more efficient area as far as cam range vs rpm goes. My personal experience is that way, and it is more pronounced with a carb, fuel injection will cover a mismatch like this much better, whereas carbs need a certain amount of airflow velocity to meter correctly.

I have noticed you posted elsewhere this is a 6 speed trans, which is a T-56 which is like a 4 speed then with a double overdrive. 4th is 1:1 ratio, 5th is .070:1(?-ish) and 6th is .050:1...correct?? Have you tried a mileage test only using 5th, and not using 6th, to keep the rpm a little higher?? Could be a way to try it out, no rule you have to cruise in 6th exclusively, just don't use it.
thats a really good idea! i didnt think of that. im leaving for a 50mile drive this friday so ill give it a shot!
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 11-16-2010, 03:53 AM
Registered User
 
Last photo:
Join Date: Mar 2010
Location: USA
Posts: 218
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I had to go somewhere a bit ago it was over 30 miles. I figured up the mileage and it was 22.5 mpg, that was with me trying to keep the engine over 2000RPM the whole way. The speedlimit was 45-60mph most of the way. So I guess it dosent really matter if I keep the cam in its operating range?
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 11-16-2010, 10:13 AM
ericnova72's Avatar
More for Less Racer
 
Join Date: Jan 2007
Location: S.W. Lower Michigan
Age: 47
Posts: 8,801
Wiki Edits: 0

Thanks: 19
Thanked 349 Times in 319 Posts
Pretty hard to do accurate fuel calcs on only a 30 mile drive, I'd want to do 200 mile or tankful type averages to learn anything significant.

I don't think you are going to find some miracle amount, if you got to 25 or so I'd say super! with a carb that isn't a Quadra-Jet or a ThermoQuad. A Holley won't unless it has annular boosters and a good amount of time spent with a Wide band AFR set-up to tune it.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 11-16-2010, 04:18 PM
bigdog7373's Avatar
Of course it's fast
 
Last photo:
Join Date: May 2010
Location: florida
Posts: 2,673
Wiki Edits: 0

Thanks: 13
Thanked 48 Times in 48 Posts
Man. i'd love mine to only turn 1700 at 75mph. Mine's at 2300 at 65mph.
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 11-17-2010, 06:22 AM
dmx6's Avatar
Registered User
 
Join Date: Nov 2006
Location: North Carloina
Posts: 63
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Mine just a little different maybe 100 or so less but fuel mileage isn't 22-24 for sure. More like 16!
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 11-17-2010, 10:04 PM
Registered User
 
Last photo:
Join Date: Mar 2009
Location: Burton, MI
Posts: 781
Wiki Edits: 0

Thanks: 34
Thanked 15 Times in 14 Posts
you really don't want to be under 2000 rpm @ freeway speeds.

2300 @ 65 is just about ideal.. unless your engine is built to be an off-idle stump puller!

when I first put my 700r4 in my 72 monte carlo, I had 2.73 gears in the back.. overdrive was basically unusable below 65mph, and it lugged pretty bad unless I ran 75-80mph.

when I swapped out my 2.73's for 3.55's the engine was super happy.
I cruise 2250 rpm @ 70mph with the torque converter locked (toggle switch)
and the car has tons of pickup.. my power band starts right around 2100 rpm so I'm cruising right where I've got lots of torque, I can easily accellerate w/o even unlocking the torque converter (this has to be done gentle since the clutch is't designed to handle much torque)

i am having trans problems so I haven't been able to tune the shift points, but I find the trans likes to use o.d at 45mph which is ok. but locking the torque converter isn't.. my engine doesnt like to make torque that low in the rpm band.

and i generally prefer a slightly agressive shift profile, so I want to move my 4th gear upshfit point to 50mph so that it basicly won't use o.d around town, but can still lock up in 3rd gear.

if that doesn't work, I'm putting a full manual reverse pattern valvebody with a linelock in it.. LOL
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
Turbo 350 line pressure increase Dino383 Transmission - Rearend 2 09-07-2010 09:22 PM
Economical ways to increase horsepower Apollo Hotrodding Basics 10 11-08-2006 02:30 AM
Do I Increase HP With Adding Cowl Induction Setup? JimKramer Engine 5 06-10-2005 03:59 PM
HELP.... i'm looking to increase mpg on my 350 vortec bareit Engine 20 03-07-2005 09:18 AM


All times are GMT -6. The time now is 04:41 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.