Current GM Q-jet Rules
 

Please excuse this Dummy question. But, I just wanna get this straight in my mind.

In the Class Racer Info guide, I see that for many engines there are a couple of numbers listed for legal factory carbs, and either a 1901 or 1903 Edelbrock Q-jet, depending on whether the engine came with what we call a 750 or an 800 Q-jet. It appears that they are separated by their max allowable venturi size. So, for this post I'll just refer to 'em as a "big" or "small" carb.

So here are my questions:

(1) Have these rules been changed, or relaxed, to allow ANY small carb, for any GM engine that came with a small carb, and ANY big carb for any engine that came with a big carb ? Again, I realize that no carb can have a larger venturi size than what is listed as legal, for the engine.

(2) If the answer to #1 is no, then exactly which replacement Q-jets are legal ?

For example: Can you use a different number carb, from your engine brand, but not from another GM brand ?(such as a side inlet Chevy carb instead of a BOP front inlet carb)

And for the big carb engines, can you use any big E-carb, or just the 1903 ?

http://www.carburetion.com/Rochester.asp

Re: Current GM Q-jet Rules
 

Casting number of the carb no longer matters, measurements do. J.R.

Re: Current GM Q-jet Rules
 

OK, thanks !

That brings up more questions. Since this info is not mentioned in the Class Racer Info guide, exactly when did this new rule go into effect ?

Is the rule only mentioned in an official NHRA rule book, or is there another source I can find online, if I know the correct link ?

Re: Current GM Q-jet Rules
 

It's not a new rule, by any stretch. Been this way for 20 years...Probably more

Re: Current GM Q-jet Rules
 

OK, just going by what I read in the Class Racer Info guide. If I'm reading it correctly, there is no mention of the fact that any Q-jet that is within the legal venturi size is OK.

So, another question: Does an Edelbrock Q-jet have any advantage over a GM Q-jet ? Or, can the good Q-jet builders get the same power potential from either, just as easily ?

Re: Current GM Q-jet Rules
 

I think that would be a question for the good quadjet builders. J.R.

Re: Current GM Q-jet Rules
 

The tech sheet info on Class Racer Info is obtained from the NHRA Tech Sheets. Neither do the NHRA Tech Sheets or rule book specifically describe the situation you are questioning. There is a statement under the Carburetor paragraph of the Stock Cars section of the rule book that states "Replacement carburetors permitted provided they are same model, type,throttle bore, and venturi size." The provision for using Qjet carbs apparently falls under that statement.

Re: Current GM Q-jet Rules
 

hello, question? does the inlet have to be the same location? on any carbs? just curious. thanks

Re: Current GM Q-jet Rules
 

No

Re: Current GM Q-jet Rules
 

"Replacement carburetors permitted provided they are same model, type,throttle bore, and venturi size."

OK. I reckin the words "same model, type" just mean they have to be a Q-jet type carb, and not necessarily a Chevy Model, or Buick model, or whatever car brand you race, or one specific Edelbrock number.

I suppose it only matters how the tech guys interpret the rule. It makes sense to me, since I don't see any big advantage to a particular Q-jet. But then there are lots of very similar parts, from different year cars, that would not provide an advantage, but are not legal.

Don't know if more of these similar, but different year parts will become legal, as parts for the older cars become more scarce, or not. ?

Re: Current GM Q-jet Rules
 

OLDSKOOL, you are overthinking this topic. ANY q-jet as long as it
measures correctly. PERIOD. J.R.

Re: Current GM Q-jet Rules
 

When Edelbrock was a Major Sponsor with the Q-Jet replacement carbs, NHRA changed the rule to allow Edelbrock to sell more carbs......

The B-O-P guys could by an Edelbrock carb to replace the front inlet style....

The phrase "stock inlet location required" was removed from rule book…….

Show me the money and I'll show you a rule change.....

In Stock AFTERMARKET disc brakes, aluminum seats, intakes, heads and radiators, transmissions, 6" clutches, 2 year seat belts and on & on & on......

Re: Current GM Q-jet Rules
 

Got it. Thanks !

Re: Current GM Q-jet Rules
 

" When Edelbrock was a Major Sponsor with the Q-Jet replacement carbs, NHRA changed the rule to allow Edelbrock to sell more carbs..."



So far, I've never read exactly what years the Edelbrock Q-jets were made. I did find this article that says they bought a new one in 1997.

http://www.hotrod.com/articles/edelb...or-replacment/

And this site says production was stopped in around 2002.

http://quadrajetparts.com/edelbrock-...tors-t-10.html

So, I assume production began in the early 1990's. Does anybody know, for sure ? And, the exact year they were made NHRA legal ?

I know now that any correct size Q-jet is legal. But, I'm still curious about the E-Q-jets & the rule change. I was out of racing so long that before I learned to use a computer, a few years back, I'd never even heard that Edelbrock sold Q-jets. And, by then, they'd been out of production for several years. So, ya'll please excuse my ignorance on this subject.

Thanks !

Re: Current GM Q-jet Rules
 

Hey Oldschool: I was told by a very reputable QJ carb guy that he did not see any performance difference between an Edelbrock or GM 207 carb and he preferred the Edelbrock because usually they were nicer cores to start with. Good time to check the classsracer parts section. Good deal there on what you need.

Re: Current GM Q-jet Rules
 

Part of the distinction with the Qjet carbs is that all the GM carbs were manufactured by Rochester, which means they are the same make and model. The Edelbrock replacements are listed in the Accepted Products publication under Carburetors along with Edelbrock's AFB replacements and the QuickFuel replacements. They are listed distinctly because they are different manufacturers (make). No need to list all the carbs by the OEM manufacturer.

Re: Current GM Q-jet Rules
 

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

Re: Current GM Q-jet Rules
 

Yeah, they are quite a few years newer than the GM Q-jets. That alone should mean that a larger percentage of 'em are in better shape.

And thanks for the heads-up ! But I already have a couple of E-Q's. And there are always several for sale on Ebay.

Also, have a small stash of GM Q-jets, and access to lots more.


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

Yeah, Carter made LOTS of Q-jets, in the '60's & '70's. Their name is cast into driver side of the main body. " MFG. BY CARTER CARBURETOR FOR GMC ".

Re: Current GM Q-jet Rules
 

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

(1) What is a ballpark figure that one of the good class car Q-jet builders would charge to build a Stocker type unit, using my core ?

(2) Aprox how much quicker is a Q-jet which is built by one of the top class racer guys, as compared to a good average street/strip or bracket race build ? Just wondering if it would be worth the extra $$, if all you wanted to do was just be able to run slightly under your index, rather than building to win all your heads-up races. (Not looking for any good buys on ready to race carbs--just gathering facts.)

(3) In pics I've seen, it shows the choke plate still in, Stock & SS. So, is it a rule that the choke plate must remain ?

(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.

Re: Current GM Q-jet Rules
 

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

Re: Current GM Q-jet Rules
 

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

Re: Current GM Q-jet Rules
 

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

Re: Current GM Q-jet Rules
 

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.

Re: Current GM Q-jet Rules
 

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

Re: Current GM Q-jet Rules
 

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.

Re: Current GM Q-jet Rules
 

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.

Re: Current GM Q-jet Rules
 

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.

Re: Current GM Q-jet Rules
 

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

Re: Current GM Q-jet Rules
 

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 ?

Re: Current GM Q-jet Rules
 

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