GAS Recomendations - Pontiac GTO Forum
User Tag List

LinkBack Thread Tools Display Modes
post #1 of 4 (permalink) Old 07-05-2007, 08:04 PM Thread Starter
Join Date: Apr 2007
Posts: 2
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
GAS Recomendations

I recently purchased a 1967 GTO with a 428 engine - rebuilt 1000 miles ago. Should I add a lead additive to the gas? Any recommendations on octane? I could use some advice.
Back in the saddle is offline  
Sponsored Links
post #2 of 4 (permalink) Old 07-05-2007, 08:16 PM
GM4life's Avatar
Join Date: Mar 2007
Location: RAF Lakenheath, UK
Posts: 4,162
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
If the engine was rebuilt with hardened valve seats no need for a lead additive. But if not you need lead additive.

GM4life is offline  
post #3 of 4 (permalink) Old 07-06-2007, 09:45 AM
lars's Avatar
Join Date: Sep 2004
Posts: 445
Mentioned: 0 Post(s)
Tagged: 1 Thread(s)
Quoted: 1 Post(s)
GM and the SAE did some pretty extensive research on the matter of unleaded fuel in the non-hardened seat engines back in the mid-70s. Here are the basic conclusions:

If valve seat spring pressures are kept under 120 pounds seated (most stock hi perf Pontiac enigines run 90 to 110 pounds spring pressure on the seat), there is no need for any lead additives, and there is no valve seat erosion, when using unleaded fuel. Valve seat erosion on non-hardened seat engines can occur when using unleaded fuel if towing a heavy trailer at high throttle settings for extended periods (extended time with elevated exhaust gas temperatures - EGT), but there is no adverse erosion under normal driving or short periods of Wide Open Throttle (WOT) application (such as when drag racing). The installation of pressed-in hardened seats poses a higher risk of engine damage than the use of unleaded fuel due to the number of shops performing the installations incorrectly. But unleaded fuel poses no risk of seat erosion under normal high performance driving conditions.

For octane, use the octane needed to avoid/suppress any detonation. Use of a higher octane than that needed to suppress detonation has no advantage. But the engine cannot be allowed to have any detonation, as damage will result. If detonation cannot be suppressed with the highest available octane, you must either lower compression, retard timing, or use an additive that is effective for increasing octane (not many of these around). The additive does not need to be lead-based, since lead is not needed for the seats unless you are doing heavy trailer pulling.

For info, all GM heads manufactured 1971-on have induction-hardened seats in them.

lars is offline  
post #4 of 4 (permalink) Old 07-17-2007, 08:37 PM Thread Starter
Join Date: Apr 2007
Posts: 2
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Thank you very much
Back in the saddle is offline  
Sponsored Links

  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO General Discussion

Quick Reply

Register Now

In order to be able to post messages on the Pontiac GTO Forum forums, you must first register.
Please enter your desired user 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:


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode

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