BKbroiler

Regarding the secondary rods, if "biggest" means thickest, that's what you don't want. The thinner the rod is, the more gas flow it allows. I have Lars' paper too and he shows the various rod diameters and the lettering code on the rod to distinguish sizes. You definitely don't want stock 77 size rods with your setup. When Lars rebuilt one of my Qjets, he put CH rods in it (.0570 tip dia.). That was a good warm weather setup for my car and should be in the ballpark for yours.

daanbc

Thank you for explaining that! I will admit I don't know some things. I just had my 46th B-day wednesday. And I still don't fully understand the whole Q-Jet. I realize there are three phase's. I would love to have someone rebuild it with me who knows what there doing on these. This way I could fully understand how and why everything works on these carbs. I did make a big flaw yesturday on my day off. I hooked up the timing light and readjusted the distrib. to 36, BUT FORGOT TO Unhook and block the Vac. Advance. DUHHH! So tomorrow I will find TDC, pull the distrib. out and replace to make sure it's not off a degree/tooth, then time. Thanks again everybody.!

bobbarry

Your secondaries on your carburetor might be opening too-soon, or not opening soon enough, since the intake and cam likely changed the vacuum-signal it sees. This might be an opportunity for you to learn quite a bit about tuning the QJet.

daanbc

I agree, but where do I start? I really don't want to take my carb. apart and have my car just sit there. Where would you start?

Tim H

Well I don't care if anybody likes it or not the quadrajet blah at best.
But 308 gears are not going to win you any 60ft time trials. up your idle to about 750 in gear.
You want to spin tires?
4:11 gears and a 3500 stall will grant you your wish otherwise your wasting time and money nickle and diming yourself to death.
Your other choice is take out the cam and put in the factory cam.

scottyp99

Q-jets are good carbs if you know how to work 'em, but if ya don't, and you already know how to work a Holley, you're probably better off switching over.


Keep the shiny side up!
Scott

scottyp99

Ya know, an upgrade to a 700r4 tranny would increase your final drive in first gear from 7.76:1 to 9.42:1. Something to think about.


Keep the shiny side up!
Scott

Fivepointfive

I'm old school, so look at what I say with that understanding. First, Your distributor is probably installed correctly. Even if it were off a tooth, you could compensate with timing, or even moving your spark plug wires one direction or another---think about it--when #1 is at TDC, the rotor simply needs to be under the #1 spark plug wire (compensating for your advance, of course). Next, almost all high performance cams need some RPM's to create HP and torque. (on solid lifter cams, you gain a little low end HP by setting the lifters a little snug, and you gain RPM's by setting them a little loose). Hydraulic cams are ground to get the best from both worlds. All the guys who are talking about stall speeds are correct--you need the R's to make HP. (although your sluggishness is more a function of torque) Both your cam and your intake are screaming for RPM's. If I am not mistaken, you have a large cavity under the carb in the manifold. Think about this: If this area is filled with your gas/mixture, and #1 intake opens, it has to suck from this big area--as opposed to a direct tube coming from the carb. So, if you could increase this area by rising the carb (as someone suggested) you would get kind of a ram induction effect--common trick in the old days. Look at the manifold you took off and compare the flow to the cylinders. I think you mentioned that you could leave a light a bit quicker. A higher compression would give you a bigger bang in the cylinder. Back in the days when a guy could afford gas, and automatic transmissions were 2 or 3 speed, a 3.08 rear end wouldn't be considered for any sort of performance. I ran a 5.38 for quarter mile racing. I would leave the line at 3500 RPM's, and shift at 8500. Of course this was only a 300 CID, but the car ran in the 12's with a single 4 barrel.
We all want our cars to perform, but be careful not to make it not practical to drive on the street. Lower the rear end ratio (you will loose some gas mileage) or increase the stall speed. Anyway just some thoughts from an old geezer.

jesse10886

Anyway just some thoughts from an old geezer

the best advice and new ideas i ever got for fixing all my different engines, haybailers, tractors,dozers ect came from thoughts from an old geezer they think of the smartest **** you would never think of make the old man who forgets where he put the glasses on his own face can make you feel stupid lol

Tim H

That would help taking off then when hitting 2nd would be a bog fest.
Around here at the track the advice people give is be in high gear (auto 3rd) at the 60ft mark and let it pull you all the way down the track.
With 3:08 gears he would be crossing the finish line in 2nd gear, there is no use in having a 3 geared trans if you ain't going to use all of them.

scottyp99

Everything is a trade off, ain't it the truth? That's the thing about the 700r4, it lets you have a nice low first gear, but you need a nice wide power band because of the widely spaced gears. That overdrive would sure be nice on the highway, though. My 'vette has a th-350 and 3.07 gears, and I hate how high the revs get on the highway, I've gotten used to cars with OD transmissions, I guess.

I've never even been on a drag strip, and haven't been to watch one in a looooong time, so what do I know about it, but shifting into 3rd by 60 feet sure sounds a little extreme to me, I mean, damn, ya still have 1260 feet to go! Although I do remember, back in the day, friends who ran 5.13 and 5.38 gears, and they would be buzzing up against the rev limiter halfway down the track, so maybe you got something there! It's often been said that you usually win or lose the race on the starting line, not the finish line.


Keep the shiny side up!
Scott

daanbc

Thanks for the advice Gentlemen! I do realize my 3:08's are a P.O.S.. But there the only thing helping when I'm on the highway driving to a place right now. O.D. would be nice but not in the picture yet. Realizing that I use to have the car where I liked it, and now having it slumber out of the hole, I'm leaning towards first making sure my carb. is set up correctly, then either having my heads worked on or the stall convert. One step at a time for me. I just finished my first cam change. So I'm starting to head in some kind of good direction. LOL.

glen242

This is your standard opinion on Q-Jets.

Lars has a great writeup, on another forum, where he compares on a dyno, one of his rebuilt Q-Jets with one of his rebuilt Hollys.

Interesting reading, if you have an open mind. If you do not, and/or do not trust Lars, don't bother reading his writeup, and continue to put forth your standard opinion.

If you do read his writeup, I would be interested in your opinion of it.

Tim H

It takes alot of tuning to a quadrajet to make it anywhere close to the perfromance of an "out of the box" Holley.
If you rebuilt a quadrajet with just an off the shelf rebuild kit and the same to a Holley, the Holley would out perform it.
Some people have to run a quad and thats fine, do what you have to, but if you have the option, the best added part number to a quadrajet is list# 3310!

scottyp99

I don't necessarily agree, but I got a kick out of how you said it!

The OP says he is much more familiar with Holley carbs than the Q-jet, so, in this case, he would probably be better off switching over to a Holley. You can find 1850s on the internet pretty cheap, toss a rebuild kit at one and see how it goes. Getting the fuel line hooked up on the single feed carbs is a pain in the butt, though. It's like they were designed to go on a Ford.


Keep the shiny side up!
Scott

Fivepointfive

All the advise so far can be both helpful and perhaps a bit confusing, but sometimes it is best to go back to basics: The job of the carb is to take a bunch of gas, and mix it with some air, and make it available to each cylinder through the intake valve. Then the closed valves, and the piston heading up compresses the mixture and the plug ignites the gas and the explosion pushed the piston downward creating power--eventually to the rear wheels. Everything you can do to enhance each of those functions will increase horsepower: Bigger carb to provide more gas (but not too much), bigger valves and bigger head ports to allow more gas in and exhaust out, bigger lift and duration on the cam to keep valves open longer, higher compression (domed pistons)to compress the gas for a greater explosion, bigger and better flowing exhaust to get the spent gas out, hotter spark to ignite the mixture. And, of course a bigger bore and stroke to increase the cubic inches of the motor. If every internal combustion engine operated at a constant speed, it would be easy to maximize the horsepower and torque. But in order to optimize all around performance, you have to make some choices. Remember, your maximum horsepower is not at the highest obtainable RPM. However, normally, highest horsepower is obtained at a fairly high RPM. Torque generally kind of parallels along the horsepower curve. Torque is defined as "a moment of force"--so to launch or pull, torque is more of a factor, but generally you should think in terms of horsepower. So in its simplest form, for straight line performance, you want the engine to get to maximum RPM as quickly as possible, and stay as close to that RPM through the gears, and cross the finish line at maximum horsepower. So rear end gearing and transmission gearing and tire size are all factors. If you want your tires to break loose (an advantage to getting RPM's and horsepower quicker), you can increase stall speed, gear lower, use more tire pressure, make car lighter--or build the horsepower into the engine with cam, heads, carb, pistons etc. And you can do some things to increase the horsepower and torque at different RPM's. Top fuel cars create 7000 HP, but they only have to last 900 Revolutions in a quarter mile. So, the trade off for high performance is always cost, usually dependability, and often comfort.

glen242

Here is Lars' writeup on the Q-Jet vs Holley 750.

I hope I am allowed to post this.


400 Dyno Data (with Holley & Q-Jet Comparison)

In a reply I did in the Topic Post “Rochester Q-Jet Setup”
(Rochester QJ set up)
tracksnblades1 had some doubts about the Q-Jet’s abilities compared to Holley-based designs:
Quote Originally Posted by tracksnblades1 View Post
There has been a multitude of articles, writings and the sort published about these carbs. Ranging from excellent to BS. In closing I offer no defense on my comment of the Holleys perfromance. There are those still that believe these carbs are superior to FI also. Any carb can be modified to achieve almost ideal fuel curves and atomization that allows vaporization only to occur in the compression cylce. I have not read mister Lars Papers as refered to. I will. I will monitor his dyno tests as available. If convinced I may concur and reject the findings of the greats like Smokey, Barry Grant, NASCAR and the factory big three engineers who chose the Holley on their max efforts. AGE QUOD AGIS Do what you do, Well. Only the Best
I just finished up another dyno test of a mildly-built 400, and the results follow…

The engine was a stock-block 400 with stock factory cast iron heads. I got compression ratio up to 10.08:1 with flat-top pistons and the stock deck height. The bottom-end was kept stock with some good rod bolts, and the heads were given a good 3-angle valve job. The restrictive EGR intake was scrapped and an Edelbrock “Performer” intake was used to keep overall engine height near-stock so that there would be no hood interference problems. The owner wanted a very mild cam to maintain engine vacuum and power brakes, so a mild hydraulic roller was used. No other trick parts – the engine was pretty much a modest compression 400 with a mild roller in it.

The real purpose of the dyno run was to get good numbers for the owner and to get a good tune on the engine, but we also wanted to get a back-to-back comparison of a well-tuned Q-Jet to a properly set up Holley of similar size. Those results came in as expected…

For the first “out-of-the-box” dyno pull, the Q-Jet was used (17056263). This carb is factory jetted at 70/42/DB, which is awfully lean. I re-jetted the carb to 76/42/DB with a 3/8” float level and .640 secondary rod height. Other carb tuning and parameters were set up exactly as outlined in my Q-Jet Tuning Paper under the “Quickie Performance Setup” section.

After getting the timing optimized (the inefficient chambers in the iron heads took 41 degrees total timing for best power and torque without detonation – an increase from my initial setting of 37). We were using 91-octane pump gas with 10% ethanol – right out of the gas station down the street. Total timing was coming in before 2000 rpm – a very quick curve.

The 4 initial pulls we did on the engine showed a “dip” in the torque curve (with resulting “sag” in the power curve) between 3500 and 4000. This is right where the Q-Jet secondary airvalve is starting to open up, and the air/fuel numbers were showing a lean condition right at the tip-in of the secondaries. The stock “DB” secondary rods in the carb have the “short” power tips, which delay fuel enrichment. We installed a pair of Edelbrock “CL” rods which have about the same diameter (just a small tad richer), but they have the “long” power tips. Richening up the secondary tip-in point really flattened out the torque curve and made the power curve a near straight-line shot towards the top.

Once this had been sorted out and the Q-Jet was correctly tuned, I wanted to do the final run just to prove one of my pet-peeve points: Q-Jets are garbage, and any Holley will outperform a Q-Jet… blah, blah, blah… As I state in all my seminars and papers, a properly tuned Q-Jet will perform almost identical to a properly tuned Holley, except that the Q-Jet tends to produce better torque and throttle response in the low and mid range in a street driven vehicle than the Holley. Now that we had our Q-Jet pretty well dialed in, it was time for a switch to the Holley.

The Holley I selected was a 3310-1, which is a 750 vacuum secondary with the secondary metering block (not the cheap plate). The carb was set up and tuned to spec with 72 primary jets, 80 secondary, and the “tall yellow” secondary spring was selected to assure that the secondaries would actually open. Choke system was removed to give it all the airflow advantage it could get. Float levels, shooters, and all tuning parameters were all set up correctly and verified and “blessed” by noted NASCAR engine builder Steve Yacki (who was also our dyno operator this day). The Holley was given 2 pulls on the dyno, and we verified that the air/fuel ratio on the Holley was virtually identical to the Q-Jet: The A/F numbers matched exactly at many data points, and were never different by more than 0.5:1 at any time through the entire rpm range – the 2 carbs were metering air and fuel at exactly the same ratio, so there was no “fudging” any numbers on these pulls.

The Q-Jet bettered the Holley by 15 ft/lbs of torque on the bottom end, and pulled more than 20 ft/lbs at many data points, with a 10 to 20 horsepower gain over the Holley at many points through the range. The Holley produced a couple of peak numbers at limited points, but not enough to give it any advantage over the Q-Jet. The mass airflow numbers through the Holley were also lower than the airflow numbers through the Q-Jet at high rpm, and this can be seen by the drop-off in the Holley performance at the top of the curve. We even did one Holley run with me forcing the secondaries fully open for the top ½ of the rpm range, but this killed all the top-end numbers completely: The carb liked the “tall yellow” spring.

The numbers between the two carbs are fairly close, but if these 2 engines had been installed in 2 identical street cars, the Q-Jet car would have come across the finish line ahead of the Holley car by a significant margin.

This is not to say that either carb is “better.” But the fact is, that if you set these carbs up correctly, and know how to tune them, they can be made to run very well. There is no point in replacing a badly-tuned Q-Jet with a badly-tuned Holley or vice versa. A well-tuned Holley will run better than a badly-tuned Q-Jet, and this is what is usually the case in the “Holley is better than that crap Q-Jet” argument. If you have a good Q-Jet and know how to set it up, run it on your street car. If you don’t have a carb, or don’t know how to tune a Q-Jet, a Holley will run fine, but you better be able to tune it, too. Black lines are Q-Jet, green lines are Holley:

http://i183.photobucket.com/albums/x...HolleyJPEG.jpg

Fivepointfive

...always impressed with guys who really have their stuff together. That is quite an informative report on the carb comparison. Of course in my day a dyno was the logo for Sinclair Gasoline, and now it is short for what I have become (Dinosaurs). We had to throw some carb on and go out on Friday night to see if it worked. The whole sport has come along way. The engine building has become kind of a commodity, and the tune seems to be the difference. Mixed feelings, but progress nevertheless.

iokepakai

Had a similar problem with 3.08 rear gears,until I changed to a Richmond trans with a 3.27 1st gear.Now the Vette's takeoff's are a lot more crisp.The gear spreads of the 6 speed are just about perfect for my small block. I installed a mid range cam advanced 4 deg.
When you changed your cam you moved your powerband into a higher rpm.Advancing the cam will help to move the powerband to a lower rpm.Did you degree your cam when you did the install.Mine was supposed to be 4 deg advanced but turned out to be straight up.
Good luck hope this helps......

daanbc

Just a quick note: I re-adjusted the timing and rich/lean screws. I got alot more umphh from it. Finally. I'm making strides. She will chirp second and just almost break loose in first. Just a little more tweaking. I love the way this cam pulls all thru second into third! And I really like the aggressive sound. One of these days I'll get the nerve to take the carb. apart and do the "quicky performance" that lars suggested. Thanks......