pump gas - 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
lost password?   |   register now

LinkBack Thread Tools
  #1 (permalink)  
Old 01-22-2013, 06:12 PM
Registered User
Join Date: Jan 2013
Posts: 47
Wiki Edits: 0

Thanks: 21
Thanked 0 Times in 0 Posts
pump gas

1995 TBI 350 5.7 10.4 to 1 comp. ratio . will this run on pump gas 93 octane?

Reply With Quote Quick reply to this message
Sponsored Links
  #2 (permalink)  
Old 01-22-2013, 06:16 PM
vinniekq2's Avatar
Registered User
Join Date: Jun 2012
Location: BC,Canada
Age: 59
Posts: 11,642
Wiki Edits: 0

Thanks: 694
Thanked 1,340 Times in 1,243 Posts
It will run,maybe not all that well
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 01-22-2013, 08:09 PM
Registered User
Join Date: Jun 2010
Location: TX
Posts: 2,500
Wiki Edits: 0

Thanks: 29
Thanked 272 Times in 252 Posts
It depends on where you set the initial timing advance. If you retard the initial timing advance and set it at 10 degrees BTDC it will run without detonation but the engine may run hotter. If you set the initial timing advance to 12 or 13 degrees BTDC or where the engine runs best, the engine will have detonation.

The upper limit for today's 93 octane pump gas is about 10.3:1 static compression ratio or 8.5:1 dynamic compression ratio with the initial timing advance set at 12 degrees BTDC.
Reply With Quote Quick reply to this message
The Following User Says Thank You to MouseFink For This Useful Post:
lowhirod (01-22-2013)
  #4 (permalink)  
Old 01-23-2013, 01:06 PM
Registered User
Join Date: Apr 2007
Posts: 9,618
Wiki Edits: 0

Thanks: 18
Thanked 229 Times in 185 Posts
Originally Posted by lowhirod View Post
1995 TBI 350 5.7 10.4 to 1 comp. ratio . will this run on pump gas 93 octane?
Assuming this has the original Swirl Port cast iron heads and of course is cam timing limited by the vacuum needs of the MAF measured TBI, this will prove to be too much compression for efficient operation. If the OEM TBI is functioning, there is a detonation sensor that will pull timing out if it hears pinging. This will operate the engine with less than optimal timing, but it will most likely run without you hearing any pinging. However, tests have shown that good all around performance that's power and mileage as well as emissions degrade faster and deeper when the timing is less than optimal opposed to operation with less than optimal compression.

This engine has from the OEM an extremely mild cam so it isn't going to be compatible with very high compression. The TBI likes a lot of manifold vacuum which is a characteristic of mild cams. The OEM TBI will only tolerate cams with a .050 inch measured duration of 190-210 degrees, beyond that the manifold vacuum (Manifold Absolute Pressure, MAP is what you'll see this as a reference) becomes to low for the system to function properly. Even with such a cam as I reference, you'll most likely need a custom chip that rebuilds the fuel and ignition maps to the new relationships of thorttle position to RPMs to manifold vacuum the integration of which is used to compute mass air flow through the motor which is used to select the appropiate fuel quantity and ignition timing.


PS, the OEM cam uses .050 lift duration of only around 170 degrees with less than .4 inch lift at the valve, so even the "big" cam of 190-210 compatible with TBI is a considerable leap in duration and lift while still being a pretty mild cam itself. As duration gets longer the intake valve closes later this lets the cylinder bleed mixture till about the torque peak. The use of high compression ratios is intended to recover the lost bottom end torque that comes with bigger cams that cause bottom end mixture density loss. This is the Dynamic Compression Ratio (DCR) calculation, you can find these calculators on the web, you need to know when the intake valve closes in crankshaft degrees to use them. For a cast iron head you're looking to a DCR of 8 to 1 for regular unleaded to about 8.5 for premium 92-93 octane. For an aluminum head add .5 to the ratio. This is where Vortec type combustion chambers are involved. For older heads including the Swirl Port this can be backed down .2 or more, especailly where bores exceed 4 inches and the spark plug is located well distanced from the bore enter and not angled toward the exhaust valve. Full dish pistons and piston to cylinder head deck clearance is greater than at least .040 inch and especially if this clearance exceeeds .060 inch for iron heads.
Reply With Quote Quick reply to this message
The Following User Says Thank You to BogiesAnnex1 For This Useful Post:
techinspector1 (01-23-2013)

Recent Engine posts with photos

Quick Reply

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:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Please select your insurance company (Optional)


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
Pump Gas Versus Race Gas / dyno results ?? fastlaners Engine 8 04-30-2011 10:51 PM
Is it normal to have to pump the gas several times to get accelerator pump squirt ? fumplet Engine 3 11-16-2010 01:14 PM
mixes marine gas and regular pump gas crussell85 Engine 3 08-20-2010 08:19 PM
mixes marine gas and regular pump gas crussell85 Engine 4 08-19-2010 06:30 AM
Fuel Pump Not Sending Gas To Carb Why?? Its Not Electric Fuel Pump???? zeeman19 Engine 7 02-13-2007 03:17 PM

All times are GMT -6. The time now is 09:47 PM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.