Current GM Q-jet Rules

[oldskool]

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

[J.R. Haddad]

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

[oldskool]

Originally Posted by J.R. Haddad

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

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 ?

[Mark Yacavone]

Originally Posted by oldskool

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 ?

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

[oldskool]

Originally Posted by Mark Yacavone

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

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 ?

[J.R. Haddad]

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

[Dwight Southerland]

Originally Posted by oldskool

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.

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.