Looking for Q-Jet tuning advice....
Thread Starter
Instructor
Joined: Jun 2004
Posts: 220
Likes: 0
Looking for Q-Jet tuning advice....
I've got a relatively stock 69 L-36 with an Edelbrock #1901. I'm ready to start carb tuning using Lars' paper. I have some spare metering rods marked 36B and 48B. What is the significance of the "B" after the rod size? I'm ordering the tuning kit from Summit. Will the rods in the kit from Summit be marked "B" also? Do I want them to be marked "B"? I've heard of short taper and long taper rods, does the "B" indicate one or the other? I'm assuming I want the long taper rods. What comes in the Summit kit? Thanks in advance.
Melting Slicks
Joined: Mar 2006
Posts: 3,456
Likes: 102
From: Piedmont Va
St. Jude Donor '11-'12-'13,'19-'20
I am in the process of tuning my 1901. It's a replacement for pre-1975 carb which puts it in the single or short taper category. I'm not sure what comes in the summit kit, I used an Ebrock kit which had all single taper rods. No idea what the significance of the "B" is...never seen it.
Melting Slicks
Joined: Mar 2006
Posts: 3,456
Likes: 102
From: Piedmont Va
St. Jude Donor '11-'12-'13,'19-'20
"B" means double taper,..used on pre 1975 Q-Jets.
hmm...here is the text from Lar's paper on this subject:
"There are two different “series” of primary metering rods. Q-Jets up through 1974 (the “4MV” series carbs) use the early series rods, also known as the “single taper” rods. 1975 and later Q-Jets (the “M4M” series carbs) use the second series rods, available as single taper and as “double taper” rods. Not only do the rods differ in their taper design, but they are different lengths. Pre-’75 (up through ’74) Q-Jets use metering rods that are approximately 2.47” long overall (total length from the metering tip to the extreme top of the rod). 1975 and newer Q-Jets use rods that are about 2.40” long"
I am not an expert by any means. The rods that came with my Ebrock 1901 kit measure 2 13/32" which seem to be the shorter of the two mentioned here, but there is no "B" designator on them.
Thread Starter
Instructor
Joined: Jun 2004
Posts: 220
Likes: 0
OK, I just came back from the Edelbrock website. It looks like I need kit #1991 for my #1901 carb. This kit comes with single taper rods for the #1901. I have some double taper rods on hand from the carb that came on the car. Can I use the double taper rods in the #1901 or should I only use the single taper rods that are in the kit from Edelbrock? Is there a preference when choosing between single and double taper in my application? Are they interchangeable? Can't find my Doug Rowe book.
By the way ,this carb has been tweaked once already and the 36B primary rods were removed and replaced with 42's. I'm not sure if the 42 rods are single or double taper. GUess I'll have to disassemble it to find out.
By the way ,this carb has been tweaked once already and the 36B primary rods were removed and replaced with 42's. I'm not sure if the 42 rods are single or double taper. GUess I'll have to disassemble it to find out.
Last edited by 69monzaredbigblock; Jul 16, 2006 at 08:45 AM.
Melting Slicks
Joined: Mar 2006
Posts: 3,342
Likes: 7
From: Connecticut
I just bought a set of Edelbrock #1974 rods.
They are .43 and are double taper and are for Pre 1975 (thats what the package says anyhow)
They are the exact same lenght as my 44B rods which came from my original 73 QJ
They are .43 and are double taper and are for Pre 1975 (thats what the package says anyhow)
They are the exact same lenght as my 44B rods which came from my original 73 QJ
Thread Starter
Instructor
Joined: Jun 2004
Posts: 220
Likes: 0
The 38B rod that came out of my Edelbrock Q-jet was double tapered. It looks like the replacement rods from Edelbrock in the calibration kit are not double tapered. I'm assuming they are the correct length. I've spent the last hour at BarryK's website reading the published papers from the Masters of this tuning stuff. Right now I don't know whether to get GM parts or Edelbrock parts. Any thoughts?
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
Again, I've never heard of this Lars guy (and again, what book did he write?), but I have read two books from Doug Roe, who back in the day was Chief Engineer at Chevy's performance division and in his book "Rochester" on page 151 it states, "Rods with a double taper have B stamped on the rod after the taper"
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Drifting
Joined: Sep 2004
Posts: 1,959
Likes: 1
From: North Bend Ohio
Originally Posted by 73, Dark Blue 454
Again, I've never heard of this Lars guy (and again, what book did he write?), but I have read two books from Doug Roe, who back in the day was Chief Engineer at Chevy's performance division and in his book "Rochester" on page 151 it states, "Rods with a double taper have B stamped on the rod after the taper"
http://wiki.corvettefaq.com/index.php?title=Engine
BigBlockk
Later....
Safety Car
Joined: Dec 2004
Posts: 4,071
Likes: 0
From: San Diego CA
Wow... so much discussion over the the importance of something that really isn't important. All you need to do is jet based on the rods and jets. The taper isn't going to have a big enough effect for you to need to worry about. Anyone know the stock jetting of a '69 L-36? That's where you start and usually adjust from there.
Team Owner
Joined: Jul 1999
Posts: 26,545
Likes: 46
From: Huntersville NC
Originally Posted by 69monzaredbigblock
I don't know whether to get GM parts or Edelbrock parts. Any thoughts?
I changed the rods/jets a couple of times and Lars changed the rod/jet combo slightly back in September when he was here in NJ. Edelbrock uses their own numbering scheme and it is even possible that the letter "B" on the Edelbrock rods doesn't mean the same thing as a "B" on the GM rods. (edit.......Never mind, if they are stamped with a "B" they aren't Edelbrock rods!) It might, or it might not, I don't know. Unfortunately I have a very poor memory for this stuff and have to look everything up every time a question comes up!!
I don't even remember which rods/jets are in the carb right now.From Lars' carb tuning paper, 69 L-36 4spd had Qjet #7029215 which came with 71 rods 45 jets. As Kalway said, that's a good place to start.
7029215 Chev 69 396/427 MT 71 45 7036019 AX
Last edited by PRNDL; Jul 17, 2006 at 08:46 AM.
Racer
Joined: Apr 2006
Posts: 477
Likes: 43
From: Millbrae California
Originally Posted by Kalway
Wow a big 427 was set to run on a leaner combo than my lil 350 is. Probably works fine, though.
henry @ oles carb
Melting Slicks
Joined: Mar 2006
Posts: 3,342
Likes: 7
From: Connecticut
Originally Posted by olescarb
1968 and 1969 q-jets used smaller/different jet-rod combinations than a carb for 1970 and later (in most cases)
