Jet sizing: - Team Camaro Tech
Engine General Engine Discussion.

 
LinkBack Thread Tools Display Modes
post #1 of 10 (permalink) Old Nov 6th, 14, 06:31 AM Thread Starter
Senior Tech
 
Join Date: Dec 2008
Location: earth
Posts: 584
Jet sizing:

Is there a way to find out which size jets (and metering rods) came with a particular engine and/or engine car combo:

For example 77 monte carlo with 400 small block.

83 c-10 with 305

76 nova with 250 inline six etc. etc. etc.
puff puff is offline  
Sponsored Links
Advertisement
 
post #2 of 10 (permalink) Old Nov 6th, 14, 01:46 PM
Moderator
____
 
DOUG G's Avatar
 
Join Date: Mar 1999
Location: Maryland, USA
Posts: 19,431
Garage
Send a message via MSN to DOUG G
Re: Jet sizing:

If you had carb list numbers...then yes. As it is just the make/model....maybe.

Just have to dig a little

68 Camaro~LSx ~all motor
1.54 60'--6.95 @ 98.45 660'--10.96 @ 121.53
DOUG G is offline  
post #3 of 10 (permalink) Old Nov 6th, 14, 03:09 PM
Senior Tech
alex
 
Join Date: Nov 2010
Location: boston ma.
Posts: 854
Re: Jet sizing:

Exactly what Doug said if how ever you want to make any changes at all you have to drop three full jet sizes to notice any difference on a Holley. For example if the jet size is 74 you need to drop down to a 70 to start to make a difference . Alex
ss27 is offline  
 
post #4 of 10 (permalink) Old Nov 7th, 14, 05:43 AM Thread Starter
Senior Tech
 
Join Date: Dec 2008
Location: earth
Posts: 584
Re: Jet sizing:

Quote:
Originally Posted by ss27 View Post
Exactly what Doug said if how ever you want to make any changes at all you have to drop three full jet sizes to notice any difference on a Holley. For example if the jet size is 74 you need to drop down to a 70 to start to make a difference . Alex
i guess the next natural question is, do you think, for example, a quadrajet for a 350 is jetted pretty much the same as for a 305?

i used a quad originally off of a 305 on a 350 for a while and it seemed just fine, but this was before i knew or cared about jetting. Now, i want to use that same carb on a 4.3 v-6, due to my recent engine "cooking" experience which i may or may not discuss in another thread.....
puff puff is offline  
post #5 of 10 (permalink) Old Nov 7th, 14, 07:20 AM
Senior Tech
alex
 
Join Date: Nov 2010
Location: boston ma.
Posts: 854
Re: Jet sizing:

Well puff I haven't used a quad in a long time but they are a great carb. It is my understanding that the factory had two versions as far as engines go . there was the small block version and the big block version.Thats why your 305carb ran good on the 350 . The thing with Q jets is it will flow only what the engine needs or calls for. I know that the small block version is capable of flowing 750 cfm the big block version is capable of flowing I believe 850cfm in its stock form and I could be off a tad off on that number. Of course they can be highly modified and there are several places that specialize in doing that . For the most part you can do some nice mods yourself but if it works good for what you have leave it alone. Alex
ss27 is offline  
post #6 of 10 (permalink) Old Nov 7th, 14, 11:27 AM
Senior Tech
Dave
 
Join Date: Dec 2005
Location: Tampa, Florida
Posts: 4,679
Re: Jet sizing:

There are actually five different Rochester QuadraJet main body castings; and yes they do basically break down as to big block vs small block. There are three destined to be bolted on top of a big block engine with the Buick 455 having the highest cfm rated carb. They all differed by primary venture size. That coupled with the big blocks that have different parts that form the variable venture that is the secondaries.

You will probably want one of the smallest venture size for your six. Pontiac used one on their 4.3 liter overhead cam in-line six if you can find one.

Big Dave
Larger Dave is offline  
post #7 of 10 (permalink) Old Nov 7th, 14, 12:15 PM
Senior Tech
Steps
 
Join Date: Dec 2005
Location: New Zealand
Posts: 13,316
Re: Jet sizing:

A 2 jet size on a holley will make a significant difference 1 jet size also makes enough difference to be noticed if fine tuning.
A couple degrees of timing change at a given load/ rpm will make a significant difference
If one is ball park or 'bucket' tuning no u will not notice a single jet size change...
But should notice a 2 jet size.
and rem chance mixture change timing also....
A simple example of this is adjust a idle timing and the mixtures need adjusting and visa versa... it is the same right thru the rpm range

And how much one notices depends on experience and the tools used....O2 data and stop watch only way to go... bucket tuning/ dialling in went out last century

My Spelling is not incorrect...it is creative

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Steptoe is offline  
post #8 of 10 (permalink) Old Nov 7th, 14, 01:51 PM
Moderator
____
 
DOUG G's Avatar
 
Join Date: Mar 1999
Location: Maryland, USA
Posts: 19,431
Garage
Send a message via MSN to DOUG G
Re: Jet sizing:

Quote:
Originally Posted by puff puff View Post
i guess the next natural question is, do you think, for example, a quadrajet for a 350 is jetted pretty much the same as for a 305?

i used a quad originally off of a 305 on a 350 for a while and it seemed just fine, but this was before i knew or cared about jetting. Now, i want to use that same carb on a 4.3 v-6, due to my recent engine "cooking" experience which i may or may not discuss in another thread.....
May be a little fat... but being a vacuum secondary carb, you may be fine.
Will it run....Yes
Will it be exact.....No

Try it and see, then go from there.

68 Camaro~LSx ~all motor
1.54 60'--6.95 @ 98.45 660'--10.96 @ 121.53
DOUG G is offline  
post #9 of 10 (permalink) Old Nov 7th, 14, 08:21 PM Thread Starter
Senior Tech
 
Join Date: Dec 2008
Location: earth
Posts: 584
Re: Jet sizing:

Quote:
Originally Posted by DOUG G View Post
May be a little fat... but being a vacuum secondary carb, you may be fine.
Will it run....Yes
Will it be exact.....No

Try it and see, then go from there.

"fat" = rich?
puff puff is offline  
post #10 of 10 (permalink) Old Nov 7th, 14, 10:38 PM
Gold Lifetime Member
John
 
Vintage 68's Avatar
 
Join Date: Mar 2002
Location: Moraga,Ca.,USA
Posts: 13,705
Wink Re: Jet sizing:

Quote:
Originally Posted by puff puff View Post
... i used a quad originally off of a 305 on a 350 for a while and it seemed just fine, but this was before i knew or cared about jetting. Now, i want to use that same carb on a 4.3 v-6, due to my recent engine "cooking" experience which i may or may not discuss in another thread.....
If you're talking Q-Jets ... then the size of the 'jet(s)' is often not as important as the size of the Rod
There were multiple combinations of a given jet (primaries are easily removed, secondary are often a fixed dia. 'washer' type stacked into body)with a selection of rod size to meet the requirements of a given engine combo.
I have listings of over 200 separate combinations depending on make/model/year/trans/application/etc. and personally have over 70+ just rods in my Q-Jet parts box for jets/rods.
The jets are marked with a numeric code for size and the rods are marked and designated by a Two-Alpha (AA, AB, AC ...) or numeric code from Rochester depending on their location.

Next thing to consider is the 'Hanger' pitch-length. A given 'hanger length' will position the rod further up or down in the jet hole and affect fuel flow at different times in the throttle application or Secondary plate opening cycle - leaning or richening mixture as needed at different power bands.

So you may be able to just substitute a larger rod dia. with the present jet to reduce fuel flow and meet your tuning needs.
Investigate what you have now and adjust as needed/wanted to meet your needs.

1968 Convertible
Some trucks
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Other V8 things - some of which float
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Other V6 things - none of which float
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Oh yeah, and 1 "Straight-Six" ...
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


If a man says something in the garage - and his wife can't hear him - is he still wrong !!!
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Vintage 68 is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Team Camaro Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
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.
NOTE we receive a lot of registrations with bad email addresses. IF you do not receive your confirmation email you will not be able to post. contact support and we will try and help.
Be sure you enter a valid email address and check your spam folder as well.



Email Address:
OR

Log-in










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