what to do if you have a high compression engine with unleaded gas today - Page 2 - 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> Hotrodding Basics
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #16 (permalink)  
Old 06-25-2012, 03:35 PM
1971BB427's Avatar
Registered User
 

Last journal entry: Latest changes
Last photo:
Join Date: Dec 2010
Location: Portland
Posts: 1,475
Wiki Edits: 0

Thanks: 12
Thanked 222 Times in 193 Posts
Quote:
Originally Posted by timothale
I have seen a few double hump heads with cracks between the center two exhaust valves. be sure to have them checked for cracks. with the 2 exhaust valves that close together , the heat is concentrated there.

Curious what kind of SBC heads have two exhaust valves together close enough to crack? There's one exhaust and one intake per cylinder/chamber, and quite a spacing between even the 3/5 or 2/4 chambers.
I've seen cracked seats between intake and exhaust on old heads, but never between exhaust and exhaust.

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #17 (permalink)  
Old 06-27-2012, 09:12 AM
Thumpin455's Avatar
Ask me about Ethanol
 

Last journal entry: 65 GTO
Last photo:
Join Date: Aug 2009
Location: Michigan's U.P.
Posts: 155
Wiki Edits: 0

Thanks: 0
Thanked 4 Times in 4 Posts
Quote:
Originally Posted by Mojo56
You are one brave man here... taking a stand in favor of the boogie man...E85.

Be ready for the naysayers...
Have already had plenty of run ins with the naysayers, thing is most of them have no first hand experience with ethanol. I have first hand experience and have been running it for years, building carbs, engines, and not using anything exotic, just slightly modified stock stuff. Usually modified with a drill bit.

You hear or read stuff about how horrible it is, but really that is all just BS. The stuff flat works.

What octane an engine needs depends on a bunch of things. Chamber shape, bore size, material the head is made of, quench, piston design, cam specs, altitude, ambient temperature, any oil in the chamber and ignition timing all play a big part.

All aluminum modern engines like the LSx engines can utilize more compression on pump gas, older engines with iron heads need more octane for the same compression. Premium 93 wont work at 10.5:1 with most older engines that are all iron, even when you retard the timing to the point where it has no power anymore. It needs more octane than that, and there isnt any getting around it.
Reply With Quote Quick reply to this message
  #18 (permalink)  
Old 06-27-2012, 09:26 AM
my87Z's Avatar
Veteran/Firefighter-EMT-I CRT
 
Join Date: Mar 2009
Location: maryland
Age: 30
Posts: 1,685
Wiki Edits: 0

Thanks: 6
Thanked 11 Times in 11 Posts
my engine is 11.2:1 and I mix 5 gallons of 110 octane with 10 gallons of 93 octane to keep it happy. I got smart and bought a 55 gallon drum with an electric pump, this is where I keep my 110 octane fuel. I go straight up to our local dragstrip and fill it up, because i'm buying 55 gallons at a time, I end up getting it for about .40 less per gallon.
Reply With Quote Quick reply to this message
  #19 (permalink)  
Old 06-27-2012, 10:00 AM
ericnova72's Avatar
More for Less Racer
 
Join Date: Jan 2007
Location: S.W. Lower Michigan
Age: 47
Posts: 8,966
Wiki Edits: 0

Thanks: 20
Thanked 378 Times in 347 Posts
Cans of octane booster are a waste of time. If it advertises a 3 point gain when used in recommended amount per gallon - that is really only a 0.3 gain ., ....but they don't want you to know that. Your 91 octane would only become 91.3 .

Another vote here for E85 if you can get it in your area or are willing to blend your own using a barrel of E98. I know several racers in my town using it in street or street/strip cars with no problems and noticable benefits in power and easier engine cooling. Getting ready to go E85 myself on a 13.5-1 comp 406 SBC, my chosen carb is at QuickFuel Carberaton right now getting the correct boosters installed to properly match up to E85 (950 Holley).

If you don't want to go E85, the race gas/pump gas blending is an easy alternative as mentioned. 11-1 with old Fuelie heads will be fine on the 20-40% blend as by F-Bird. I'd expect with ignition and carb properly tuned the 20% figure will be fine.

A note on blending--- a 50-50 mix of 87 pump and 110 race actually comes out higher than the math would suggest. Math says 98.5 octane for this mix, but because race gas has so much lead in it, the real mix is actually closer to 100 octane---a little real tetraethyl lead goes a long way, you get "octane creep" in the mix.
Reply With Quote Quick reply to this message

Recent Hotrodding Basics 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
Got Heads! Unleaded gas problems? steveyb4342 Engine 25 05-08-2007 06:15 PM
high compression obdII on pump gas? sc2dave Engine 3 02-21-2006 04:51 PM
Leaded or unleaded Gas for 327 49dream Engine 7 08-23-2004 12:52 AM
Unleaded gas in a 350 engine jimbobneutral Engine 4 03-02-2004 05:04 PM
gas for high compression trujilloette Engine 5 09-14-2002 12:35 PM


All times are GMT -6. The time now is 03:36 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.