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I purchased a new Q-Jet carb. for 1979 305 elcamino and now I change out the engine for a 350 300 hp out of a 69 Camaro will the Q-JET still work and not take away power
 

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Not in the least. The 300 hp from that 69 Camaro was back when they rated power as gross hp, not SAE net. That 300 hp in 1969 is about 240-250 by today's rating. Qjets came in 750 or 800 cfm, so you have plenty of flow.

Qjets seem daunting and complex, but they are the single most accurately-metering carb you can get.
 

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If you do the calculations, a 350 spinning at 5000 rpms with .85 VE consumes 430.41 cfm. You'll have 750 cfm minimum. Go have fun :)
 

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not important but the calculation Curtis gave you has nothing to do with the size carb you choose. The engine signal to draw the air through the carb/F.I. causes parasitic drag. A 750 cfm carb will have less parasitic draw than a 500 cfm heavily restricted size carb for that application, so the bigger carb will net more use able power to the flywheel. minor tuning may be required,,,
 

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Pre emissions , MOST muscle cars from 327- 396 C.I. were factory equipped with 550- 750 cfm carbs , that VE formula is a suggestion for grocery getters....
 

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If you get the numbers off the carburetor body, and the number of a typical carburetor used on the ‘69 engine, you can compare jet and rods sizes for the two carburetors.

The stock carb on a ‘69 is an older Quadrajet design than the one used in ‘79. In general, the newer ones are a little easier to adjust (external APT, etc) and less prone to leakage, but their stock jetting is usually leaner. However, I doubt you have verified it is an original ‘69 carburetor, since you did not specify the part number. Many Quadrajets have been swapped and/or mangled by tuners who did not understand them.

Bruce
 

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efi. no more cold starts issues. in the spring turn the key and head for the carwash
 

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I purchased a new Q-Jet carb. for 1979 305 elcamino and now I change out the engine for a 350 300 hp out of a 69 Camaro will the Q-JET still work and not take away power
You‘d really have to present either a part number or venturi and throttle bore dimensions. A 1979 Q-Jet even if having adequate air/mixture flow will be jetted lean for a 350 if it is making any kind of power greater than your 305.

The old time simple CFM formula is inadequate it fails to address the energy losses in the porting system that reduce the available flow at and through the valve, this bring long before and apparently larger than factors of volumetric efficiency.

If you do the conventional sizing equation which is really displacement times RPM divided by 2 times some WAG as VE you will find that if you’re seeking bigger than grocery getter peak torque and power your CFM computation will be woefully short. By the typical formula a 350 with a cam of about 220 degrees at oh-fifty with about .45 to .47 lift at the valve turning about 6000 rpm with a .85 VE will be about 517 CFM. We know from countless dyno tests that this isn’t going to support anywhere near the power the engine is capable of. If we take the VE penalty out we get a carb sized about 650 CFM and a super good tuner can get this to feed maybe 385 ft pounds and similar horsepower at their peaks. We know that strapping on a 750 CFM carb will deliver over 400 at the same or fewer RPM and more depending on the head choice. So it becomes apparent that the old time simple equation to carb CFM is inadequate for chasers after best possible power with a 350 so constructed as I outlined. If you have a cam around 200 degrees intake an .40 or less lift then the equation works sort of OK.

A big thing to consider is that carburetors are tested one barrel at a time with only dry air on a flow bench that uses an electric fan as a suction source:

- First off, the total flow is a summation of each barrel. One only needs to look at the air horn to realize that on an operating engine there is not much to keep any one barrel from interfering with the flow of any adjacent barrel, so it is likely that the actual total flow at WOT on an engine is not as great as the rated flow from the flow bench.

- Secondly, the flow bench is dry air, no fuel, the introduction of fuel reduces the amount of air by a significant percentage.

- A third argument is the reversion effects of pumping cylinders and of energies of the mixture lost to surface drag on the walls of the runner and porting system. In both of these cases the effects are considerably less than the flow rating is actually delivered to the intake valve. An example of the power of these manifold forces can be evidenced very simply in that when you blow a piston you find parts of the wreckage in other cylinders. This provides pretty strong evidence that an engine breathing through a common manifold has a lot of interfering dynamics within the intake system that a flow bench fan does not duplicate.

So in the end for a performance but not racing engine you can dispense with the VE calculation completely and add about 115 to 120 percent to the straight CFM answer if you're seeking max output for a street performance engine.

Bogie
 

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It does not sound like this is an all out power swap. Sounds like a replacement for a worn or anemic 305. The Q-jet will be fine. As a street carburetor it is a good selection as GM built millions of them on 350’s. Unless you want to “tune” for gains the direct swap will be fine as is. I doubt that 6 grand RPM’s are a goal.
 

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Again, please provide the part number off the side of the Quadrajet you are trying to tune. Otherwise it will be about as productive as saying “I have an SBC, what should I do to make it run better?” There are many, many variations of the Quadrajet.

Bruce
 
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