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Q-JET VS HOLLEY
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cavas2003
New User
| Posts: 1
| Joined: 08/06
Posted: 08/19/06
09:00 AM
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I have an 84 cutlass with a 403cid (stock with pocket ported heads edelbrock rpm intake(edl-7111) and rpm cam(edl-7112) for this engine, cam degreed in 2 degrees retarded from spec card so I advanced it 4 degrees.). This combo in a fully street car with open headers ran an impressive 8.19 in the 1/8th mile with a q-jet with a 1 inch spacer. I began having trouble with the idle. I had a new holley 830 for another car that is not done yet so i put it on. with a new 50 cc rear pump and cams to eliminate flat spot on launch. I lost .3 of a second and cant seem to get it back. I replaced the front p valve with a plug raised the jets the recomended amount from 78 to 85's still no help. I had to put on some collectors with short 3 inch turn downs because it burn't my shifter cable. lost more time now we are at 8.7's. I put on an NX Hitman with 150hp jets to get back to 8.20's. I spent over $1000 to get the same time again. The plugs are black so I'm thinking I should lean out the a/f mix, replace the 1 inch spacer, remove the collectors leaving the shield in, or just burn the whole car and start over since it has singed my hair after I bent the butterflies with a N2O back fire. So as you can see I need serious help every way I go cost more money and eye brows, I am still having a good time, but it would be better to get back to the 8.19's and eye brows without the N2O. then the real fun can begin.
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rebldryvr
Enthusiast
| Posts: 569
| Joined: 05/05
Posted: 08/19/06
04:22 PM
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This is a list to what I did on my 750 Holley on my 383. Maybe it will help. First keep jets on primary side at 78, raise secondaries to 88, put power valve back ( you'll need the extra fuel for nitrous). Use a size 37 pump nozzle on primary side with a red cam should lose tip in hesitation. Use 25 sized nozzle and brown cam on secondary side to get nice long shot of fuel. If your carb has provisions for two power valves use them. 65 in front and 45 in back then back down secondary jets to 83-84. Use your one inch spacer. Lean out is death to an engine with nitrous. This will make the car drivable everyday and give you plenty of fuel under full throttle nitrous runs. Hope this helps.
Edited 8/19/2006 5:34 pm by rebldryvr
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Posted: 08/24/06
10:31 PM
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get rid of the q-jet and get a holley
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GibTG
Guru
| Posts: 918
| Joined: 08/03
Posted: 08/25/06
02:16 PM
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OF COURSE THOSE Q-JETS ARE TOTAL JUNK!!!!! [extreme sarcasm]
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Posted: 08/29/06
03:11 AM
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I'm going to be the devils advocate here... **LOL** I'd rather have the Q-Jet. I had my share of Holley's and my personal experience was not too good. I'm not the kind of guy who has the time to tinker with the small parts to get it perfect... I know some guys have the touch.. I just did'nt. I must say a properly set up Q-Jet did wonders for my 78 Z-28 I used to have. I learned a few tricks to hop them up a bit over the years. If you decide to go Q-Jet, stay away from the "electronic" version.. they really do suck. The older models are pretty cool.. The "straight in" fuel line body carb flows 800 cfm... the 90 degree jobs were good for 750 cfm. Food for thought anyway... good luck with your project.
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Posted: 08/29/06
12:25 PM
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q-jets are good carbs. They offer milage, plus decent power then hammered.
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GMC90
New User
| Posts: 49
| Joined: 07/06
Posted: 09/01/06
04:13 PM
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How tight is the throttle shaft bushings on that Q-jet because I've seen bushing replacment on those carbs cure alot of problems especially on the idle.
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pwybo
New User
| Posts: 16
| Joined: 05/06
Posted: 09/03/06
05:10 AM
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Most tuners that I know prefer to use a Holley or Demon as they are easier to work with. A carb is just a tools to mix air and gasoline and if properly tuned, either Q-Jet or Holley will get the job done. Get your carb rebuilt, install it on the car and pay for a dyno session. 1 hour (usually $80 to $100) will get you perfect tuning of your carb with proper jetting for AFR at idle to WOT as well as an optimum timing curve and advance. The dyno offers real performance data results and does not rely on feel or guessing. It is easier than the track as you can see the results in real time instead of interpretting them back in the pits.
This will save you time and money and you will be surprised at how much you can get from proper tuning. I have seen up to 50 Hp without adding any parts.
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GibTG
Guru
| Posts: 918
| Joined: 08/03
Posted: 09/03/06
09:34 AM
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FINALLY! Someone with some common sense! Thank you very much for your insight.
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Posted: 09/03/06
07:39 PM
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http://www.circletrack.com/techarticles/ctrp_0607_quadrajet_tech/index.html
There is a reason Holley and Demon carburetors are widely considered among the best high-performance carburetors available. They are designed to make optimum power, easy to adjust, and relatively simple to work on. Given their success, it isn’t hard to see why other carburetor designs have been overlooked when it comes to circle track racing.
But among all the others, there is one, known as the Rochester Quadrajet, that some racers should consider as a legitimate racing option. The Quadrajet was ubiquitous on practically every carbureted Chevy engine installed in a car in the ’70s and early ’80s. Because it is so common, many racetracks allow the carburetor in the stock racing classes. Often, racers are given the option of racing a two-barrel Holley or a Quadrajet. Many consider the four-barrel Q-jets barely the equivalent of the two-barrel carbs because they were designed to work on passenger cars and put a premium on sipping gas. However, given the right tuning upgrades, the extra two barrels give the Q-jet a leg up on the competition.
They may look different, but the primary components of the Q-jet function similarly to that of the Holley. |
“The big difference between a four-barrel Holley, which everybody is familiar with, and a Quadrajet is the Holley has a square bore, meaning all the throttle bores and venturis are the same size, while the Quadrajet is a spread-bore carburetor,” says Johnny Valdez of Jet Performance. “That means it has small primaries with larger secondary throttle bores. Another difference is four-barrel Holleys have two float bowls, two needles and seats, and most have dual fuel inlets. The Rochester has only one float bowl and one needle, as well as a single fuel inlet. So it’s a four-barrel, but it has approximately half the fuel capacity since it has only one needle and seat. This can cause fuel starvation in a racing situation with an unmodified carburetor. The good news, though, is that with the right tuning modifications, a Rochester can be a very good carburetor with great throttle response on the racetrack.”
Jet Performance Products specializes in turning ordinary Q-jet cores into race-ready carburetors. The modifications that Jet makes to a Quadrajet to create its full-on race unit (called the “Stage 3”) are significant, but the end result is a carburetor that is more reliable, provides better throttle response, and works better on the racetrack.
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Posted: 09/10/06
07:07 PM
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Is it possible that you ran the 8.19 in cool spring air? and when you went back it was hot humid muggy summer air ? .3 of a sec isnt uncommon in extrem conditions ecspecially with a car which is put together with bolt on parts a recent car craft issue has a grest article on carb tunning ...............................Good Luck Glenn Kotas
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Posted: 09/25/09
07:54 PM
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Holly alway over Quadrajunk!!!!!!!!!!!
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Posted: 09/26/09
08:59 AM
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Holley for sure over any other carburetor.
Holley is number one for sure.
Professional hi-performance engine builder
Horsepower sells Engines and torque wins races.
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81elc
User
| Posts: 166
| Joined: 07/09
Posted: 09/26/09
05:37 PM
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i run q jet on mild street rides. holleys good for performance. q jet well balanced medium carb
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Posted: 09/27/09
09:01 AM
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I have had a couple Q-jets that were pretty good on the street but they eventually got removed and a Holley took there place.
Professional hi-performance engine builder
Horsepower sells Engines and torque wins races.
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