budget builder

iTrader: (3)

This is not a thirdgen please don't get angry. I'm asking for a friend. He has a 78c10 knotched stock wt. 355 w/ 540/540 profile cam. He has 3.73 gears th400 tranny 295/55r15 3.5k-3.8k stall and a huge carb tat was put on it for racing when he bought the truck but now cruising around town (putting) he loads up and floods. He does not race like the other guy did. What is the best size carb for him to start off with? Vac. Sec or mech? Elect. Choke or man.? Right now it's got like a 850dp dumping all it can all the time. My friend doesn't race. Please help. Thx fellas

BIRD91ZRAG

iTrader: (1)

A 750cfm vacuum secondary carb would be fine on that engine.

budget builder

iTrader: (3)

Thank you for answering.

skinny z

I'd say that's a go to size and function.
I've always used a vacuum secondary carb for anything that isn't strictly a drag racing deal. That said, not that I've experimented, but the VS carb is every bit as fast as a mechanical carb from published results anyway. The former having one less accelerator pump and hence once less carb shot to burn up fuel so to me that's a little more street friendly.
You may want to consider something smaller even. I had great success with Holley's 670 VS Avenger. It doesn't have all the bells and whistles of the higher end versions although at that stage of my tuning experience, the extra tuning capabilities never entered the picture.

https://www.summitracing.com/parts/hly-0-80670

AlkyIROC

Since it's not used for racing any more, it has too much cam, carb and converter stall. You can't expect an engine built for racing to have good street manners. An engine designed to operate over 6500 RPM doesn't do very good when you're trying to drive around under 3000 all day.

A cam grind closer to a 500 lift grind, converter that stalls below 2800 and a 650-700cfm VS carb will have much better street manners and fuel mileage.

budget builder

iTrader: (3)

Really helping out thx fellas

sofakingdom

iTrader: (1)

What they are all saying.

If it has a single-plane intake on it, he'll benefit greatly from changing it to dual, such as Performer RPM. A cam something around a Comp XE268H or the nearest equivalent Lunati Voodoo would be about right. Pay less attention to lift and more to duration. Look for a cam in the low-mid 220s of .050" intake duration, a bit more than that on the exhaust, 108 - 110° of LSA. A 750 vac sec would work fine; yerbasic 3310 for example. Add the electric choke kit. Follow the Holley Tuning sticky on the Carb forum to dial it in. Bring the converter stall down to something below whatever he operates the motor at most of the time so that it's not below stall while he's just driving around; prob 2600 - 2800.

budget builder

iTrader: (3)

Thk u bunches

budget builder

iTrader: (3)

Thx fellas for the responses. He doesn't want to go back I'm the engine. He loves everything about the truck except for the carburetor loading up and if I'm not mistaken he said he just bought and purchased a 670 Avenger vacuum secondary electrical to see whether or not that would at least remedy the problem. Without having to change cams possibly valve train and swap out stalls

sofakingdom

iTrader: (1)

He's probably not going to be happy with it, butt it's his car, he can try it if he likes.

Thing is, the carb's behavior is just a SYMPTOM of an overall PROBLEM, not THE PROBLEM itself. Kinda like, if you're walking down the street and you see a little old lady laying on the ground turning gray, odds are, even if you can find a woman with the right color makeup to "fix" the gray problem, she's still dying of a heart attack. Same kind of a deal here. "Fixing" the symptom doesn't make The Problem go away. More specifically, papering over the "race carb" situation won't de-race-car the whole setup. It'll still be ungovernable as a street driver.

budget builder

iTrader: (3)

10-4 thx sofa

skinny z

That's a decent carburetor. As mentioned, it doesn't have all of the tunability of more expensive options but I had excellent results with mine over a couple of engine platforms.
Whether or not the problems are elsewhere or possibly even everywhere depending on how the parts play together and it's intended use, the single greatest thing any carbed engine owner can do is install a wide band O2 sensor and AFR gauge. Between that and a vacuum gauge, you can observe in real time what the fuel mixture is during those events when the symptoms pop up. However, the vacuum gauge ( and a timing light ) are a must

https://www.summitracing.com/parts/avm-30-0300

Like a lot of test and tune equipment, there's a learning curve involved however a well tuned carb (and proper ignition timing) make for a much more pleasant drive.
The Holley tuning stickie gives a pretty good foundation for dialing in the carb. The AFR gauge lets you observe additional data points as well as cause and effect.