Current GM Q-jet Rules

[Mark Yacavone]

Originally Posted by Bob Mulry

The statement "stock inlet location" was included in my 2003 NHRA Rulebook......

The statement was no in my 2005 NHRA Rulebook....

I can't find my 2004 rulebook...

So the inlet location requirement was removed in 2004 or 2005.....

Because B-O-P and Cadillac that came from the factory with a front inlet now could run a side inlet carburetor.....

Edelbrock only sold side inlet carburetors...This rule change greatly increased their market......

The oldest rulebook that I can easily put my hands on is 1995 and at that time it was restricted to the size, inlet location and external appearance. Computer carbs could be replaced with non-computer with the same size bores and venturi...

Hope this helps,
Bob

Note..The Caddy was side inlet.The A/C compressor was in the middle front..
Carry on, Bobbo

[Bob Mulry]

Originally Posted by Mark Yacavone

Note..The Caddy was side inlet.The A/C compressor was in the middle front..
Carry on, Bobbo

My bad............................

[Rich Biebel]

Originally Posted by ss3011

Carter made them for GM back in the mid 70's too .

Yes and they were real poor casting quality IIRC and not colored like a Rochester....Same color as an AFB....

I did not like trying to rebuild one of those.

Rebuilding carbs was a real common job in my gas station days.

[oldskool]

Originally Posted by Bob Mulry

The statement "stock inlet location" was included in my 2003 NHRA Rulebook......

The statement was no in my 2005 NHRA Rulebook....

I can't find my 2004 rulebook...

So the inlet location requirement was removed in 2004 or 2005.....

Because B-O-P and Cadillac that came from the factory with a front inlet now could run a side inlet carburetor.....

Edelbrock only sold side inlet carburetors...This rule change greatly increased their market......

The oldest rulebook that I can easily put my hands on is 1995 and at that time it was restricted to the size, inlet location and external appearance. Computer carbs could be replaced with non-computer with the same size bores and venturi...

Hope this helps,
Bob

Yeah, this is some good info ! Thanks !

So, if this info is correct, that means the Edelbrock Q-jets were not legal 'til after production of them had stopped.

"...1995...at that time it was restricted to the size, inlet location and external appearance..."

That "external appearance" deal is very interesting. I wonder how strict they were about enforcing that rule ? EXACTLY WHAT about the "external appearance" would make a carb not legal ?

Being a Pontiac guy, there are some things that come to mind. The biggest difference I can think of is the big "smokestack" vent, which began with the '70 Calif models, and continued thru '79. So, the questions that come to mind are:

(1) Were these big vent models legal on '67-'69 model Pontiacs, and other BOP engines ?

(2) And there is the question of the opposite situation. How about using a small vent model on a '71-'79 Pontiac, which came with the big vent ?

(3) And, the big vent models looked very similar from '70-'74. But, later models had the vent in a slightly different place, and there were tops with 2 slightly different looks, in the '77-'79 years. So, how close would the appearance have to be ?

(4) And then there were the slashed vent models. Some '60's & '70's Pontiac & Buick models had slashed vents, as compared the the flat top vents, on most models. The SD455 even had a large slashed vent. The slashed vent definitely presents a different appearance. Was it enuff of a difference ?

(5) Another thing that comes to mind is the difference in the appearance of the throttle levers. Different year Pontiac levers were quite different. And other brands, such as Buicks, had a very different looking lever, with a spring which mounted toward the front, on the idle solenoid bracket, whereas most Pontiac springs were attached to the rear, on the throttle cable bracket. So, a Buick carb would look quite different than a Pontiac carb, on the driver side.

(6) Then there is the choke mount type, and choke pull-off type, size and location. All these items presented several different looks, on the different models. So, this would present a different "appearance". The question again is: just how picky were the tech guys, on this "external appearance" rule ?

So, for you guys who were racing back in those days, how do you remember the Q-jet tech details ?

I remember going to a div 4 race, in '75. I took 2 cars. We didn't even get to unload 'em. Wesley saw us & came over to take a look. He named off a bunch of little nit pickin items that I'd have to fix, before he'd even take a closer look. That was my introduction to NHRA & Wesley. There was no way I could fix all those items, away from the shop, so we just watched the race, & went home.

We'd ran all season at several small local tracks, winning quite a few races. There was little to almost no tech. And the tech guys were all Chevy guys, so they knew nothing about a Pontiac. One car did get DQ'd at one race. The boys got tired of gettin beat by a Pontiac with a female driver & protested the car. The tech guys didn't find anything wrong with the engine, so they weighed the car. It came up just a very few lbs light. I'd never even weighed it. Since it still had most all the street equipment, I assumed it was a little over weight. Anyhow, I put a spare tire in the trunk, & she continued winning.

Anyhow, I've always found the variations in Q-jets very interesting. Stuff like an OHC inline six Q-jet, a Q-jet equipped 429 CJ Ford, a straight inlet 454 truck Q-jet, and even a Dodge pickup Q-jet.

http://429mustangcougarinfo.50megs.com/new_page_6.htm

[monte385]

Originally Posted by oldskool

While we're on the subject, I've got more questions.

(4) Haven't seen any pics of the Stock & SS cars running an air cleaner. So, aprox how much power is lost by using a good air cleaner set-up ? I assume there have been lots of dyno and track tests for this, thru the years.

FWIW I dynoed a street engine with a Qjet & with an air cleaner it lost 20-30 hp. We tried several a/c bases & filters & never could get the power up to no a/c pulls. This was a mild 421 that made 530 hp.

[Travis Miller]

Time for a history lesson.

A long time ago in teardown the Q-Jets had the top removed to see if all the plastic pieces were still there. Later we were told not to remove the top, only look at appearance and then measure the venturi and throttle bore. Research showed there was a change in shape of the Q-Jet in 1975. It was ruled that 1965 -1974 looked similar except for fuel line inlet and were called early design. Side inlet could not be swapped with straight inlet and visa-versa. 1975 and newer style had to remain that way including fuel inlet location.

Then came the polished secondary controversy. After a famous carb builder started selling Q-Jets with completely polished secondaries, we were instructed to look for any sign of casting flash removal or even the slightest scratch. Because of that ruling, a lot of Q-Jets failed teardown leading up to the famous "carburetor toss" at the Gatornationals. When a well known S/S racer's Q-Jet failed teardown, he walked over to the ditch behind the tech trailer and threw his high dollar carburetor in the creek. It was soon retrieved by another S/S racer's crewman who wadded into the green slime and picked it up.

Eventually the early vs late ruling was lifted and any year Q-Jet was allowed. So was the fuel inlet location lifted. Only correct venturi and throttle bore sizes for engine/year remain in effect. As with all make carburetors, no flash removal or polishing is allowed anywhere. The 2017 NHRA rulebook in Stock spells out what is allowed and what is not allowed.

[Travis Miller]

There is one style Pontiac Q-Jet that has the bullet shaped cluster in the primary venturi with no outer ring. It is only allowed to be used on the SD Pontiac engine which it came on. We have a few racers who still bring us that style Q-Jet to be looked at. Unless they are racing a SD Pontiac, it is not allowed.

[danoone]

Originally Posted by Travis Miller

Time for a history lesson.

A long time ago in teardown the Q-Jets had the top removed to see if all the plastic pieces were still there. Later we were told not to remove the top, only look at appearance and then measure the venturi and throttle bore. Research showed there was a change in shape of the Q-Jet in 1975. It was ruled that 1965 -1974 looked similar except for fuel line inlet and were called early design. Side inlet could not be swapped with straight inlet and visa-versa. 1975 and newer style had to remain that way including fuel inlet location.

Then came the polished secondary controversy. After a famous carb builder started selling Q-Jets with completely polished secondaries, we were instructed to look for any sign of casting flash removal or even the slightest scratch. Because of that ruling, a lot of Q-Jets failed teardown leading up to the famous "carburetor toss" at the Gatornationals. When a well known S/S racer's Q-Jet failed teardown, he walked over to the ditch behind the tech trailer and threw his high dollar carburetor in the creek. It was soon retrieved by another S/S racer's crewman who wadded into the green slime and picked it up.

Eventually the early vs late ruling was lifted and any year Q-Jet was allowed. So was the fuel inlet location lifted. Only correct venturi and throttle bore sizes for engine/year remain in effect. As with all make carburetors, no flash removal or polishing is allowed anywhere. The 2017 NHRA rulebook in Stock spells out what is allowed and what is not allowed.

The man you are referring to told me that story last year. He said there was casting flash the factory removed. He was selling new GM replacement carbs that he did his magic on. Joe is a good guy . Had several fun conversations with him getting the title for one of his old cars. And eventually they allowed those carbs also

[oldskool]

Originally Posted by Travis Miller

There is one style Pontiac Q-Jet that has the bullet shaped cluster in the primary venturi with no outer ring. It is only allowed to be used on the SD Pontiac engine which it came on. We have a few racers who still bring us that style Q-Jet to be looked at. Unless they are racing a SD Pontiac, it is not allowed.

I think you are referring to the 455HO engine carb. Some of them came without the outer ring, in '71, I believe. A few were also used on some other engines, besides the 455HO, including a 400. These were discontinued when it was discovered that they were not very street friendly. This is just info I've read. Have never had, or even seen one of these carbs, up close.

http://www.classracer.com/classforum...22&postcount=1

The '73-'74 SD455 engines came with an 800cfm Q-jet, which had a slashed vent tube, and the larger venturi primaries with double booster rings.

These articles contain info on both carbs.

http://www.cliffshighperformance.com...history_2.html

http://www.hotrod.com/articles/hppp-...et-carburetor/

https://www.facebook.com/pg/PontiacT...11336215645409

https://assets.hemmings.com/story_im...00-0.jpg?rev=2

That slashed vent brings up another question, for me. Are slashed vents allowed, on carbs that did not come with a slashed vent ?

[Travis Miller]

Originally Posted by oldskool

That slashed vent brings up another question, for me. Are slashed vents allowed, on carbs that did not come with a slashed vent ?

Once again, the main concern is with venturi and throttle bore measurements.