General Category > Quadrajet Carb Talk and Tips
wanna help me pic a cam?
Greasy Harley:
Im building a 350 for my '68 C10. Nothing crazy, shootin' for good dependable motor.
Engine specs:
Bore________4.06" (0.060" over)
Stroke_______3.48" (stock)
Quench _____.037" (±.003)
Compression__9.25:1 (±)
Speed Pro flat top pistons with 4 valve reliefs (-6cc)
Heads are 76cc "493" castings with 1.94" valves that have been moderately ported ( I probably made them slower ;) )
transmission will be Th400, not sure which torque converter it will have, but it will be mild.
I will build a Quadra-Jet M4M for it and mount it on a factory high-rise cast iron manifold. I'm keeping the points ignition.
The truck weighs 4100lbs, with me in it.
I want to focus on dependability and drivability, but I defiantly want it to pull as strong as possible.
Any Cam gurus here wanna help me out?
Thanks,
-Russ
_________
Cliff Ruggles:
What will be the use of the vehicle?
You want the tightest possible converter in a heavy truck with a small CID engine in it. A "loose" converter never works well there.
What rear end gears?.....
old cars:
Sounds like a street build.
If the block has not been bored yet you should consider having the cylinder bores Sonic tested first. 350 blocks can vary a lot in both in evenness and overall wall thickness. Unless you anticipate an output less than or about 350hp. Which is where you might be.
The 493 head being considered a smog head should be avoided. Using these open chamber heads can cost up to 30 ft-lbs torque and similar hp on a relatively mild street build. The Vortec head is probably the best iron cylinder head Chevrolet has ever produced for a small block. Better than fuelie heads. 350 hp is easily attainable.
Expect about 10.4:1 comp ratio with the info you provided (64cc head)
Camshafts. this can be controversial but 217@.050 duration is a very liveable flat tappet street cam
Cliff Ruggles:
Going from memory here and I could be wrong (bad cases of CRS these days and even worse cases of DGS) but I remember 493 castings to be identical to 993's except maybe they were used on 400 SBC's?
If so they will have excellent ports and capable of great power, but as mentioned a large more "open" style combustion chamber so don't make much compression on a 350 build with flat top pistons in it. The more open chambers are a double edge sword, they kill compression but unshroud the valves a bit for good air flow.
Assuming the 493's are the same as 993's (441's, 136's, and 487's will also have the larger ports) they are nice heads and at one time highly sought after by some Class racers who were required to run 76cc heads. 441's, for example are sought after by some engine "builders" who specialize in circle track engines requiring the larger combustion chamber castings.
I'm still in favor of 041's or 186's instead. The later Vortec heads are also excellent as mentioned, but they require a special intake manifold and do not have exhaust crossovers so not heat for the intake. Not typically a problem unless you want a working divorced or hot-air choke, or plan on using the vehicle to plow snow when it's 10 degrees outside!........Cliff
Greasy Harley:
--- Quote from: Cliff Ruggles on August 28, 2021, 08:31:34 PM ---What will be the use of the vehicle?
You want the tightest possible converter in a heavy truck with a small CID engine in it. A "loose" converter never works well there.
What rear end gears?.....
--- End quote ---
Usually just driving around town, short jaunts on the freeway 20-30 miles, haul broken down motorcycles or loads to the dump on occasion. I might go play at the autocross track and run it down the strip a couple times , but just screwing around, nothing serious. I am certainly not building it to race, I will do that stuff just cuz it's fun.
I was going to match the converter to the application, just haven't gotten that far yet, open to suggestions on that also.
It has 3.73:1 gears but I might regear to 3.42 with a TrueTrac in the future. Running 235/75R16 tires (29" tall)
--- Quote from: old cars on August 29, 2021, 04:12:41 AM ---Sounds like a street build.
If the block has not been bored yet you should consider having the cylinder bores Sonic tested first. 350 blocks can vary a lot in both in evenness and overall wall thickness. Unless you anticipate an output less than or about 350hp. Which is where you might be.
The 493 head being considered a smog head should be avoided. Using these open chamber heads can cost up to 30 ft-lbs torque and similar hp on a relatively mild street build. The Vortec head is probably the best iron cylinder head Chevrolet has ever produced for a small block. Better than fuelie heads. 350 hp is easily attainable.
Expect about 10.4:1 comp ratio with the info you provided (64cc head)
Camshafts. this can be controversial but 217@.050 duration is a very liveable flat tappet street cam
--- End quote ---
I anticipate an output less than 350hp. 280-300 would be more than adequate. I'm not running vortec heads, consider me more of a "purest". I'll be using old technology on my 53 year old pickup. That being said, you are 100% right, I could definitely make more power with a set of vortec heads and a roller cam, just not into it.
I'm looking for as much power as I can get running mid grade, 10% ethanol, on a hot day and not have to retard the timing. I'm at 2500-3000 ft elevation (if that matters).
Thanks for all the help, I love this forum.
-Russ
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