how many cfm's were the carbs on the carburated C3's? sorry i own a C4 but was kind of curious because my C4 doesnt have the original motor at all, mine is just a 350

 

The Q-Jet can pull in as much as 750 cfm

 

here it goes again........ one thing normally left out in these discussions is that carburetors are rate 2 different ways dry and wet. quadrajets are rated dry while holleys are wet flow rated which is more accurate as carburetors. flow vapor. so a q jet says 750 its in reality bogus.

 

I wouldnt really get too hung up on air flow as it is also a bogus way to rate them. An air flow machine has an adjustable preset for vacum level. which they use water in a tube and measure how many inches it pulls up the tube for base vacum strength. Carbs are generally flowed around 5" of water. Cylinder heads are generally flowed at 28" of vacum which makes a huge difference in flow #'s. Thats why they have a krazy calculation to determine what size carb works for what size motor you have. Do you have any pics of your engine in the car? That would be interesting as we generaly only see C3's with C4,C5,C6 type motors.

 

The 750 cfm (rated) Q-jets have plenty of capacity for nearly every SB Chevy engine plus many of the BB engines [unless they are really built up]. A 650 cfm [rated] Holley covers the SB engines up to moderately built up condition....but it can't fully supply well built SB or many of the BB engine needs. I don't know if that means anything to you, but that's my .02.....

 

with all this being said, before my engine block bit the dust, it ran awesome with edlebrock 600 carb. moderately built 418 HP and 450 FT LBS of torque with 11.75:1 compression never had a problem with the 600 cfm carb

 

Amen! The constant chatter about how great the Qjet is and it's awesome CFM rating-Bogus is right!

 

Can you show us a reference to back that up?

 

The Rochester Quadrajet was as delivered on any C3 Corvette rated at 750 cfm. Period. people can argue that all they want, and quote mythical formulae like "wet vs. dry", "sunny vs. cloudy", "my weenie's bigger than yours" etc., etc., but there is a reason why the lion's share of C3 Vettes had these devices installed from the factory- they are tunable to a very wide range of engine displacements and very compact which makes them easy to fit under the hood of a C3. If you do have an engine which can use a QJet's cfm limit you'll likely suck the tiny float bowl dry before it runs for very long at whatever speed that might be, but you won't likely starve it for air. If you want a carburetor that will work well at prolonged wide throttle openings, heavy loads, and high rpm's then a Holley is really the best way to go. They are infinitely easier to tinker with than a Rochester and the [big] float bowls won't run dry when you leave your foot in it for a prolonged period, but you DO have to choose the one which has a cfm rating most closely suited to your particular application, vacuum vs. mechanical secondaries, single vs. double pump, etc.- they are also a lot easier IMO to troubleshoot and get running right again when they do screw up, so if you're new to this game it's probably better to go the Holley route-my $1.380.

 

And, here I had always thought Barry Grant was the one who came up with wet flow rating. So, I guess I'd like to see a reference otherwise also.

Only one of the C3's I've owned came from the General with a Q-Jet ('78 L82), while the others had one or more Holleys. FWIW, that long since NOM '78 has had various Holleys on it (including 3x2 and a 1050 Dom) since the warranty expired. Fresh 427 will be getting ~1000 cfm Holley based carb, as well. Just pointing out that not all C3 carbs are the same, factory or mod.

 

For what its worth, the higher horsepower small blocks and big blocks got the Holley carburetors. For instance the L79, L76 and LT-1 small blocks, the L78, the LS6 (and LS7 in the Chevelle since none were produced in the Corvette) and L-88 big blocks all had Holleys.

I think Zora had everything to do with that.

cc

 

Most of the performance C3's had Holley's, not Qjets! The quadrajet became standard fair late in the game when emissions became more of a priority in the mid to late 70's. From what I can tell, the qjet was developed as a poor attempt to more precise meter the fuel rather than go the more expensive route of mechanical fuel injection to meet emissions standards, not necessarily performance. Just my 2 cents!

 

Of the four BB's in 68 three had Holleys

 

Q-jet showed up 1966.
Its early to mid 60s you want to design a carb that can handle many engine/transmission car weight combinations. You have cars as heavy as 4000lb impala's with engines as little as 327 with a " two speed " power glide 3.08 rear gearing. You simply build a carb with very small front primaries to handle this mess. But with enough total airflow to handle the new 369 BB you are now offerering in the 1966 SS 396 impala. HYPO
engines with higher rpm range, soild cams, four speeds, 3.55 on up gearing, generally lighter cars. The small front primaries are of no real big help to them.

 

The Holley carbs were on the high performance GM cars for one reason...the public thought Holleys were "performance" carbs. It's not that they were 'better' at that job, but GM...if nothing else...understood the impact of marketing their product. Holleys had an image from drag racing circles, and GM decided to use them on their hi-perf engines for that reason alone. Holleys are good performance carbs. But, if you want an all-around good carb for idle quality, cruise smoothness, economy, and good performance, the Q-jet is hard to beat.

 

okay so the Holley carburetor has won more n.a.s.c.a.r races then the quadrajet oh wait the quadrajet has never won or been in a NASCAR race. and Holley has won more n.h.r.a pro-stock races, probably because you couldn't even start a pro- stock enginewith one. and the list goes on for a carburetor that we " imagine " is a performance carburetor. that is laughable!

 

Here we go again.

Using NHRA or NASCAR as proof of a carbs performance is ridiculous.

In drag racing the carb operates at one throttle position and full load, that's all it does. You could probably get correctly metered fuel by using the right size windshield washer jet.

NASCAR is only slightly more demanding, the carb has to run in a tiny RPM window at high speeds, matched to 1 gear.


Peak horsepower does not equal Performance, particularly on a road car.

 

All the cool kids are using Holley carbs, don't you wanna be cool, too? What's the matter, won't your mommy let you use a Holley carb?

Holley carbs are pretty crude fuel metering devices compared to Q-Jets, but they get the job done with a minimum of hassle. They are designed to be easily disassembled and reassembled for easy tuning and modification, and it's simplicity is it's virtue on the race track, where the the gas pedal may as well be an on-off switch. Not really made for cruising down the road at part throttle, tho. They meter fuel thru a fixed orifice (the main jets) and when manifold vacuum drops to a certain point, a "power valve" opens and starts dumping more fuel through another fixed orifice. So it's really made to run at either idle or WOT. It's simple, effective, and easily understood. The Q-jet, on the other hand, has a metering rod that effectively lets the main jet orifice change in size as more load is put on the engine. Relatively sophisticated compared to the Holley, but if you wanna change the tune, have lunch first, 'cuz you are gonna be there for awhile. If you really look at a Holley and a Q-Jet side by side, and really understand how they each work, you will see that each has it's strong and weak points. The Q-Jet is really a better carb for a car that sees alot of street driving, and the Holley is a better carb for a car that sees most of it's time at the track. That being said, also keep this in mind: It's a free country, so run whatever the hell you want! Peace!


Scott

 

This thread has officially gone off the rails...

 

Certain classes of racing you could not change the carb from original. One very big reason the higher performance cars used holleys.