[C2] blending fuel
Thread Starter
Intermediate
Joined: Jun 2023
Posts: 27
Likes: 4
From: Frankenmuth
blending fuel
Hi. Thanks again to all the help with tuning this year. 1966 427 390 rebuilt to spec about 20 years ago. Runs really good since all the tuning help. I run 93 octane. Timing is about 10 degrees advanced at idle. Runs rich but starting and running very good. I get s little spark knock if I'm getting on it in 3rd gear. It's real subtle. Most people wouldn't hear it. Its not very long eve t eithet. Could try and tune it out but wondering if blending in 110 would work for rest of summer until I can rebuild car and fine tune after car season. If so any suggested ratio? If retarding timing is best suggestion silly question but can I get wrench on distributor with the chrome housing? Offset wrenches I have are too short. The grommets and housing are original and fragile. Thanks for any thoughts. TravelTodd427
Drifting
Joined: Oct 1999
Posts: 1,677
Likes: 494
From: Corrales NM
You can add Tetraethyl lead to raise the octane. Nasty stuff, wouldn’t recommend it but it does work and is available. Barring that you can buy 5 gallon jugs of high octane fuel at performance shops and mix some in with pump gas. I can even get 118 octane leaded racing fuel where I live. Not cheap but a gallon of this in a full tank of premium pump gas would raise the octane enough to prevent the pinging.
Last edited by NEVERL8; Aug 26, 2024 at 10:36 PM.
Race Director
Joined: Jan 2003
Posts: 17,696
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From: Central Arkansas
I use one of these for timing changes w/o removing the distributor shield.
It’s not so much the initial timing that results in pinging, but the total timing and advance curve. Mixing in some race gas as NeverL8 suggested will probably take care of it for now.
It’s not so much the initial timing that results in pinging, but the total timing and advance curve. Mixing in some race gas as NeverL8 suggested will probably take care of it for now.
Le Mans Master
Joined: Apr 2001
Posts: 5,438
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From: Sarver Pa
2021 C1 of the Year Finalist - Modified
In my 60 for drag racing I would mix 1 gal of 110 to 4 gal of 93. The engine liked it ! Bumped the timing 2 degs, then backed it off for street and 93 or 91.
Race Director
Joined: May 2000
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The Chevrolet Power Manuals from the era recommend 36-40 degrees of total WOT advance for best power. That would be the sum of initial plus total centrifugal. Do you know the OE centrifugal specs for your engine? They are listed in the CSM and AMA specs that you can download from the GM Heritage Web site. It's lazy and can probably be improved, but you have to test your engine with a dial back timing light to see what it actually is as modifying the centrifugal advance was a common thing even back to when these cars were new. The most aggressive detonation-free map is best, but modern gasoline has slightly less detonation resistance than back in the day.
So it's up to you to obtain and post the data, and then you might get some decent advice.
Most "science" is based on data as opposed to some closed form set of equations like Einstein's Special and General Theories of Relativity, and without data you have no "science". Just ask any quack like "Dr. Fauci".
If it's no too much trouble for you, you might want to search for threads started by me and download my "tuning seminar" to get some basics on how to set an optimized detonation-free spark advance map for your engine.
Duke
So it's up to you to obtain and post the data, and then you might get some decent advice.
Most "science" is based on data as opposed to some closed form set of equations like Einstein's Special and General Theories of Relativity, and without data you have no "science". Just ask any quack like "Dr. Fauci".
If it's no too much trouble for you, you might want to search for threads started by me and download my "tuning seminar" to get some basics on how to set an optimized detonation-free spark advance map for your engine.
Duke
Burning Brakes
Joined: Aug 2004
Posts: 840
Likes: 316
From: The Triangle, NC
I am a big fan of the data on the GM Heritage Site. Thanks for that pointer I few years back - but I am unfamiliar with the “Chevy Power Manuals”. Any pointers to those as a resource ???
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Race Director
Joined: May 2000
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At this time in the late afternoon/early evening you should be drinking BEER (like me, and I'm sure Lars would agree), not iced tea, but anyway...
They were published by GM from the mid-seventies to the early eighties. I doubt if you can find "new" anymore, but used copies may be available on ebay and other similar auction/sell sites.
Other great reference books include "How to Hot Rod Small Block Chevy's" and "How to Hot Rod Big Block Chevy's", both published by HP books back in the seventies. Don't let "hot rod" fool you into thinking that they are just recommendations for some high overlap cams that high school Harry with his highjacker Nova can impress his cruise night buddy morons with a rumpety-rump idle. They have lots of recommendations for "invisible" interior mods for improving OE engine performance including pocket porting heads, most of which cost little if you are doing a rebuild.
David Vizard's books are also excellent references for "warming up" OE engines without going overboard and more. I don't know if any are still available from the publishers, but an internet search should show you what is available, new or used.
Duke
They were published by GM from the mid-seventies to the early eighties. I doubt if you can find "new" anymore, but used copies may be available on ebay and other similar auction/sell sites.
Other great reference books include "How to Hot Rod Small Block Chevy's" and "How to Hot Rod Big Block Chevy's", both published by HP books back in the seventies. Don't let "hot rod" fool you into thinking that they are just recommendations for some high overlap cams that high school Harry with his highjacker Nova can impress his cruise night buddy morons with a rumpety-rump idle. They have lots of recommendations for "invisible" interior mods for improving OE engine performance including pocket porting heads, most of which cost little if you are doing a rebuild.
David Vizard's books are also excellent references for "warming up" OE engines without going overboard and more. I don't know if any are still available from the publishers, but an internet search should show you what is available, new or used.
Duke
Last edited by SWCDuke; Aug 27, 2024 at 11:55 PM.
1967 Pedal Car Champion
Joined: Mar 2020
Posts: 9,140
Likes: 4,248
From: US-PNW
They were published by GM from the mid-seventies to the early eighties. I doubt if you can find "new" anymore, but used copies may be available on ebay and other similar auction/sell sites.
Other great reference books include "How to Hot Rod Small Block Chevy's" and "How to Hot Rod Big Block Chevy's", both published by HP books back in the seventies. Don't let "hot rod" fool you into thinking that they are just recommendations for some high overlap cams that high school Harry with his highjacker Nova can impress his cruise night buddy morons with a rumpety-rump idle. They have lots of recommendations for "invisible" interior mods for improving OE engine performance including pocket porting heads, most of which cost little If you are doing a rebuild.
David Vizard's books are also excellent references for "warming up" OE engines without going overboard and more. I don't know if any are still available from the publishers, but an internet search should show you what is available. new or used.
Duke
Other great reference books include "How to Hot Rod Small Block Chevy's" and "How to Hot Rod Big Block Chevy's", both published by HP books back in the seventies. Don't let "hot rod" fool you into thinking that they are just recommendations for some high overlap cams that high school Harry with his highjacker Nova can impress his cruise night buddy morons with a rumpety-rump idle. They have lots of recommendations for "invisible" interior mods for improving OE engine performance including pocket porting heads, most of which cost little If you are doing a rebuild.
David Vizard's books are also excellent references for "warming up" OE engines without going overboard and more. I don't know if any are still available from the publishers, but an internet search should show you what is available. new or used.
Duke
David Vizard is on YouTube with a number of engine videos: https://www.youtube.com/@DavidVizard/videos
Race Director
Joined: May 2000
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Thanks for updating my ancient pre-internet stone age references. I can't tell you how many revelations/problems I have solved sitting on "The Throne" back in the day.
The early "lap top" computers were too heavy and cumbersome to work with while on The Throne. I still prefer soft cover books and magazines in that environment.
Duke
The early "lap top" computers were too heavy and cumbersome to work with while on The Throne. I still prefer soft cover books and magazines in that environment.
Duke
Race Director
Joined: May 2000
Posts: 12,712
Likes: 2,271
I recall the '67 L-36 OE full centrifugal is 32 degrees. Add 14 and you have a max of 46 degrees total WOT advance, which is well beyond the Chevrolet Power Manual recommendation of 36-40 for best power.
You need to report specifically what the current centrifugal specs are if your post is to be of any use to anyone else.
Duke
You need to report specifically what the current centrifugal specs are if your post is to be of any use to anyone else.
Duke
Burning Brakes
Joined: Aug 2004
Posts: 840
Likes: 316
From: The Triangle, NC
Have Vizards’ books and will search out the GM/Chevy books
Instructor
Joined: Jan 2020
Posts: 146
Likes: 63
From: Wisconsin
Instructor
Joined: Jan 2020
Posts: 146
Likes: 63
From: Wisconsin
I recall the '67 L-36 OE full centrifugal is 32 degrees. Add 14 and you have a max of 46 degrees total WOT advance, which is well beyond the Chevrolet Power Manual recommendation of 36-40 for best power.
You need to report specifically what the current centrifugal specs are if your post is to be of any use to anyone else.
Duke
You need to report specifically what the current centrifugal specs are if your post is to be of any use to anyone else.
Duke
34 degrees all in at 2800 rpm.
Thread Starter
Intermediate
Joined: Jun 2023
Posts: 27
Likes: 4
From: Frankenmuth
Thanks again
Thank you again for all the great advice. Will try a fuel mix as short term fix. Bought those wrenches. And planning to do a timing tweak after a big car show next weekend.
Race Director
Joined: May 2000
Posts: 12,712
Likes: 2,271
34 total WOT advance, which is the sum of initial plus full centrifugal makes sense, which means total centrifugal is 20 @ 2800. Is that what you mean to say?
Duke
Tech Contributor
Joined: Aug 1999
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From: At my Bar drinking and wrenching in Lafayette Colorado
Lars
