Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
M4ME 17085580 primary circuit
theraymondguy:
While the 204/214 112 LSA is not a big cam, it's a fair bit more cam than the stock 178/194 109 LSA I removed.
I'm going through the process of altering the carb now. I'm focusing on the details, slowing myself down.
I opened up the idle tubes and down channel restrictions to the recipe (were 0.033" and 0.040"). I also opened up the secondary wells holes as mentioned in the rebuilding section. FWIW not all drywall screws are created equal.
Thankfully it's a hobby car, I can piddle with it all winter long. Unfortunately I can't tune it much till we have a warm day but I should be a fair bit closer than I was. Next winter it'll be cylinder heads (305 Vortec or rebuild and port the 416s) and I'll no doubt be open in up the carb again.
I believe I had timing at 12* @ 800 RPM prior to pulling the carb.
Cliff Ruggles:
Unless the Vortec heads have a working exhaust crossover I'd stick with the 416's. No need to port them for what you are doing. The little 305 with a small cam isn't moving enough air to require larger ports. Nothing wrong with a nice clean-up, remove casting flash and some bowl blending, but resist the urge to hog them out it will do nothing but slow the air down and hurt low end and mid-range power.........
Cliff Ruggles:
"Cliff, by "miss the cam choice some" do you mean too big of a cam was installed?"
Not at all. If you find that you have to run a LOT of timing at idle to make one of these engines happy it certainly doesn't like the cam you chose.
Even with that said the "trend" has always been to install a cam that puts some "lope" in the exhaust note which is associated with making more power. 99 times out of 100 it's not really helping much and the "menacing" idle quality is simply telling us that the cam used has more overlap than the engine is happy with, lower vacuum at idle speed and will require more timing and idle fuel to be happy.
Even with that said customers tend to go that direction and a few years ago I got myself in all sorts of trouble helping one out. He had built his 350 following guidelines on the Forums and in magazine articles and it sounded bad ass but was a complete "turd" in actual use.
He lowered the compression for pump gas (not sure who came up with that deal but you aren't going to make MORE power with LESS compression), then installed a tight LSA cam with advanced intake closing to bring the lost power back. For sure it sounded great standing behind it but with a stock converter and 4000lb vehicle it was a complete turd in actual use. You'd have to drop the car off of a floor jack to do a decent burnout! The engine was lackluster for power as well until you got it spun up some.
I was enlisted to help so we did another 350 with 10.6 to 1 compression, super tight quench and had Lunati grind a custom cam for it based on the 327/350hp cam. The new engine idled really nice, but relatively smooth, STRONG power right off idle and still pulling really hard well past 5500rpms. It would ROAST the tires right off the car and when it did hook up had you planted hard in the seat till you decided to move the shifter. I thought it was a nice improvement and I was very happy with it. The owner was NOT.
Despite nailing down mid 20's for fuel economy and tons of power over a broad RPM range he HATED the smooth idle quality. He bitched that no one paid it any mind when he idled thru the Dairy Queen car cruises.
First time that happened to me but I completely understand now that some customers goals for the project are to have a "menacing" idle so everyone that hears the car thinks it's bad-ass and having an engine that idles smooth isn't going to cut it........
theraymondguy:
--- Quote from: Cliff Ruggles on January 12, 2022, 03:57:44 AM ---"Cliff, by "miss the cam choice some" do you mean too big of a cam was installed?"
Not at all. If you find that you have to run a LOT of timing at idle to make one of these engines happy it certainly doesn't like the cam you chose.
Even with that said the "trend" has always been to install a cam that puts some "lope" in the exhaust note which is associated with making more power. 99 times out of 100 it's not really helping much and the "menacing" idle quality is simply telling us that the cam used has more overlap than the engine is happy with, lower vacuum at idle speed and will require more timing and idle fuel to happy.
I was enlisted to help so we did another 350 with 10.6 to 1 compression, super tight quench and had Lunati grind a custom cam for it based on the 327/350hp cam. The new engine idled really nice, but relatively smooth, STRONG power right off idle and still pulling really hard well past 5500rpms. It would ROAST the tires right off the car and when it did hook up had you planted hard in the seat till you decided to move the shifter. I thought it was a nice improvement and I was very happy with it. The owner was NOT.
Despite nailing down mid 20's for fuel economy and tons of power over a broad RPM range he HATED the smooth idle quality. He bitched that no one paid it any mind when he idled thru the Dairy Queen car cruises.
First time that happened to me but I completely understand now that some customers goals for the project are to have a "menacing" idle so everyone that hears the car thinks it's bad-ass and having an engine that idles smooth isn't going to cut it........
--- End quote ---
I was informed early in my career as a heavy equipment technician, "no good deed goes unpunished".
If I were to ever get a tattoo, this and a few other pearls would be likely choices as I seem to forget them so frequently.
Cliff, would you mind expanding on your thoughts for the exhaust cross over?
I literally made the decision to not block it moments before installing the intake - thinking that
An aluminum intake will shed the heat easily,
I have no heat riser or stove pipe with the headers, a bit of heat on the bottom of the carb would help the carb while the engine was coming up to temp.
Cliff Ruggles:
Since we are talking about a wet-flow system a working crossover is going to be beneficial. It will heat the intake and improve efficiency allowing us to run a leaner mixture and greatly improve engine performance thru warm-up.
Not having one is NEVER a good idea if you plan on using the vehicle in cold weather, so keep them open on your plow truck engine or you will absolutely hate it in the Winter months.
For part time, warm weather and casual use you can get away with a blocked crossover but it does not improve power or performance since the intake eventually heat soaks anyhow.
You also loose your factory choke if it is divorced or "hot air" so plan accordingly.
So basically I'm recommending to keep them open......Cliff
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