Cliff's Quadrajet Parts and Rebuild Kits
Quadrajet Problem Solving => Dialing in your rebuilt Quadrajet carburetor => Topic started by: Tinkerman on August 25, 2021, 06:55:17 PM
-
Hello,
Have been lurking and learning for several months and just joined. I bought Cliff's book several years ago and it has been very handy. Right now, I am struggling to determine which of the recipes in Cliff's book would be best for my carb.
I am in the process of restoring a numbers matching 69 Camaro Pace Car with the 350/300 L48 engine, TH350 auto trans, 3.31 rear axle, and F40-14 tires.
I am rebuilding the engine to the following specifications:
- Bored 0.030 over to 355 cubic inches
- 10.25:1 compression ratio
- Original exhaust manifolds with new OEM exhaust system
- Original heads and cast iron intake
- AC Delco R45 spark plugs (a little hotter than original R43 plugs)
- Will be using 93 octane pure gas
I am installing a retrofit hydraulic roller camshaft with the following specs:
- Stage 3 cam profile
- Duration at 0.050" is 215 Intake/230 Exhaust
- Advertised duration is 284 Intake and 310 Exhaust
- Valve lift is 0.470" Intake and 0.480" Exhaust using 1.6 ratio pushrods
- LSA is 114. Actually states Intake 106 and Exhaust 114
- Power range is 1700-5500 RPM
I have the original Carter built 7029202 carb. The carb is in good shape with no warping between the air horn, main body, or throttle body.
With a 114 LSA, I am trying to figure out what I would have for manifold vacuum at idle. I am thinking 12-15 psi but not sure.
My initial inclination is to use Recipe 1 from Cliff's book. Would that be the right one for my setup?
Thanks!
Dan
-
The 1969 and 1970 Chevy 350/300hp engines was one of the best engines to ever leave Detroit in any of those applications. It had high compression, tight quench, efficient combustion chambers and very well chosen camshaft.
They idle smooth without much timing in them, strong power to at least 5000rpm's and very efficient. I had one in a 1970 Impala as a daily driver and it would knock down 20-24mpg's w/o overdrive and roast the tires right off the car at will.
Moving up to a larger cam without increasing the compression ratio will soften it up some, especially idle and off idle so you'll have to use larger idle tubes to put more fuel to the idle mixture screws.
I would set the carb up closer to the 7029207 unit which had more idle fuel since those engines used much larger camshafts.
Do NOT drill any airbleeds on that unit. When you are ready to do the build call me at the shop and I'll set you up with what is needed to duplicate the 7029207 specs.
It is imperative to make sure that you establish tight quench during the rebuild. The factory kept the quench under .040" by using a .020" steel shim head gasket with the pistons pretty close to the top of the block at TDC.
99 percent of the folks who rebuild those engines buy "builder" pistons that sit much lower in the block at TDC and add a THICK head gasket. This will lower the compression ratio, hurt engine efficiency, run hotter/overheat/ping on pump gas and kill off considerable engine power.
I get calls from folks all the time who have built SBC 350 engines and very unhappy with them simply because they did not pay close attention to detail and keep the quench super-tight in them.......Cliff
-
Cliff,
Roger that and thanks for the info. I will speak with my engine builder to ensure we keep the quench under 0.040". I don't want to deck the block as it still has the Tonawanda build date stamp on the engine pad.
I have torn down my carb to get the current measurements on everything and am ready to begin the rebuild process. I will give you a call so we can build it to the 7029207 specs.
Thanks again,
Dan
-
I am installing a retrofit hydraulic roller camshaft with the following specs:
- Stage 3 cam profile
- Duration at 0.050" is 215 Intake/230 Exhaust
- Advertised duration is 284 Intake and 310 Exhaust
- Valve lift is 0.470" Intake and 0.480" Exhaust using 1.6 ratio pushrods
- LSA is 114. Actually states Intake 106 and Exhaust 114
- Power range is 1700-5500 RPM
May I ask who is the camshaft supplier?
-
The cam is an Engine Pro part# MC22136. I think they are related to Melling somehow as this is a Melling's grind.
Thanks,
Dan
-
You can calculate the LSA using the centerlines of the intake and exhaust lobes.
Intake Centerline + Exhaust Centerline - divide by 2.
106 + 114 divide by 2 = 110 LSA
"Valve lift is 0.470" Intake and 0.480" Exhaust using 1.6 ratio pushrods"
I assume you meant rocker ratio. Stock rocker ratio is 1.5
"I am trying to figure out what I would have for manifold vacuum at idle. I am thinking 12-15 psi but not sure."
110LSA / I would think between 12 and 14 in/vacuum
-
It's difficult to predict vacuum at idle as there are a lot of things that effect those numbers beyond the camshaft choice.
The true static compression ratio is a big player there, as is where the initial timing is set at idle speed.
I'm not a big fan of adding a butt-ton of timing at idle and consider having to do so to offset the negatives of a poor cam choice more of a "crutch" than anything else.
Carburetor tuning will also have an impact on vacuum production, especially with larger camshafts that lower the signal to the carb at idle speed. Simply bringing in adequate fuel to the mixture screws does wonders for idle quality and vacuum production with many of these engine combo's........Cliff
-
Going to need idle bypass air?
-
Going to need idle bypass air?
Idle bypass air is at 0.075". That is probably borderline but should be enough.
-
Yes, with 110 LSA I'd start out with about .090", fine tune, and see if you have good sensitivity from the mixture screws w/o nozzle drip. At that point there are several tests that can be done to decide which way to move forward if it still needs a little help.....
-
I was going back through the entire idle bypass air system and found the passages in the main body were plugged.
Will I have to remove the plugs in the picture to activate the idle bypass air for my carb?
Thanks,
Dan
-
Yes, and most likely the carb was commercially "remanufactured" at some point. Good news is that the screw in N/S assembly is still there instead of one of those POS pressed in deals......
-
I did not think that carb had the baseplate drilled for idle bypass air from the factory
-
I did not think that carb had the baseplate drilled for idle bypass air from the factory
I think it might be setup for Idle Bypass Air. Here are some pics of what I was tracing out to be the Idle Bypass Air System for my carb from Air Horn down to Base Plate. Am I tracing the right pathways for Idle Bypass Air for my carb?
Thanks,
Dan
-
You are correct with the location of the components for the idle bypass air system.
The carb looks clean, baseplate has been apart as noted by the non factory screws holding the throttle plates in place.
I'd check it over carefully. Some companies to some additional "butchering" during the remanufacturing process, like clipping/cutting the post off the bottom of the power piston......
-
I'd check it over carefully. Some companies to some additional "butchering" during the remanufacturing process, like clipping/cutting the post off the bottom of the power piston......
Why do they do that, any reason you know of?
-
The factory used the APT system to fine tune each carb for a specific application.
Companies that "remanufacture" carburetors are building them as a "generic" unit to fit a broad range of applications. That is why they block off the bypass air and alter the factory calibrations. Doing so allows them to fit many more set-ups and their calibrations are often pretty "fat" so they don't get as many "come-backs"......
-
Wanted to say thanks for everyone's time and especially Cliff for taking the time to speak with me and help me get a good start on tuning my carb.
As a quick re-cap, here is how the Pace Car will be setup:
- Bored 0.030 over to 355 cubic inches
- 10.25:1 compression ratio
- Quench will be 0.030" +/- 0.005"
- Original exhaust manifolds with new OEM exhaust system
- Original 041 heads and cast iron intake
- Original rebuilt distributor using Delco Remy points
- AC Delco R45 spark plugs (a little hotter than original R43 plugs)
- Will be using 93 octane pure gas
I am installing a retrofit hydraulic roller camshaft with the following specs:
- Stage 3 cam profile
- Duration at 0.050" is 215 Intake/230 Exhaust
- Advertised duration is 284 Intake and 310 Exhaust
- Valve lift is 0.470" Intake and 0.480" Exhaust using a 1.5 rocker ratio
- LSA is 110.
- Power range is 1700-5500 RPM
I figure around 12-14" Hg at idle. Based on having a lower idle vacuum, I will try the below recipe on the carb:
- Idle Tube: 0.038
- Idle Down Restriction: 0.052
- Lower Idle Air Bleed: 0.070
- Upper Idle Air Bleed (Main Casting): 0.077
- Accelerator Pump Discharge Holes: 0.027
- Main Air Bleed (Main Body): 0.070
- Main Air Bleed (Air Horn): 0.070
- Main Jet: 72
- Primary Metering Rod: 42B
- Fuel Inlet Seat: 0.135
- Float Level: 1/4"
- Secondary POE Well: 0.035
- Secondary Tube: 0.036
- Secondary Hanger: "B"
- Secondary Rods: "AX"
- Idle Bypass Air: 0.075
- Idle Mix Screws: 0.095
Once we get the engine on the dyno, I will see where in the A/F curve I may need to make adjustments.
Thanks again,
Dan
-
a
-
What size were the upper and lower IAB's when you took the carb apart?
What size MAB's?
Did they clip the post off the power piston or is it still there?
-
What size were the upper and lower IAB's when you took the carb apart?
What size MAB's?
Did they clip the post off the power piston or is it still there?
Upper Idle Air Bleed was 0.077". It was that size at the start. Lower Idle Air Bleed was 0.050".
The Main Air Bleed (Main Body) was 0.050" and the Main Air Bleed (Air Horn) was 0.050".
I am not sure what you mean by the power piston post. I think the power piston (accelerator pump?) is fully operation to include the external vent used in 1969.
Thanks,
Dan
-
why run a hotter plug? i thought that as you increase compression you should run a colder plug?
-
The power piston has a metal post sticking out of the bottom of it. That is part of the APT system and adjusted via a screw in the baseplate.
I would have left the LIAB at .050" since the upper is at .077". Opening up the LIAB with a large UIAB kills the signal to the idle tubes requiring larger ones and you may have to open up the DCR's as well.
I would have also left the MAB's at .050" at both locations and used something closer to the original calibration. Pretty sure that carb was .067" for main jets and 42B rods. The rods were raised to the optimum point using the APT.
Another good idea is to remove the APT screw from the baseplate. I make a custom external screw in the lathe. This will provide full control of the part throttle A/F once the carb is placed in service without having to take it apart and changer metering rods......