Good morning everyone. Going tbi to carb stock 350. Was just curious. I have a holley 3310-2 vacuum secondary I'm putting on it. Is it too much cfm or would I still be able to adjust it to run right. Please let me know what you think. Thanks
Tbi to carb.
- Thread starter Jbaer
- Start date
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You're gonna get blasted for going "backward", but that said, a 3310, being vacuum secondary(engine demand operated) is a very forgiving carb. It will have 72 jets in the front if stock, you can drop a size at a time and drive it for a few days to see how it runs to try to increase the fuel mileage potential. You can adapt an electric choke to make it more driver friendly when cold. You may need to address the distributor as the ecm advance may not function correctly, which will cost you many mpg. If it is an automatic you will need a 700R4 adapter for the throttle lever, available from Summit.
TylerZ281500
Yukon Ridin High
Im not so opposed to the backward thinking. but lets take this into scope tbi has a 500 cfm carb. the heads flow terrible in stock form, cam is a tiny peanut, you gain nothing going to a carb. 750 is overkill in comparison to a stock 500 so cfm TB. youll have to jet it down a ton.
i could give you the backwards speech, or sit back and laugh when you carb swap it to a 750, think its faster, praise that its faster but in reality its not but rather ill give you this. theres calculators on wallace racing and other sites to estimate how much airflow an engine needs, id say familiarize yourself with it as a starting point.
i could give you the backwards speech, or sit back and laugh when you carb swap it to a 750, think its faster, praise that its faster but in reality its not but rather ill give you this. theres calculators on wallace racing and other sites to estimate how much airflow an engine needs, id say familiarize yourself with it as a starting point.
DerekTheGreat
Forum Regular
Yes, a 750 CFM is akin to putting a toilet on top of the engine and flushing it. Doubt the secondaries would ever open 100%.
My advice is to keep the T.B.I system or troubleshoot it and make it work again. You will not see any performance gains going to a carburetor and I'm pretty confident the factory distributor won't work.
My advice is to keep the T.B.I system or troubleshoot it and make it work again. You will not see any performance gains going to a carburetor and I'm pretty confident the factory distributor won't work.
The factory small-cap HEI doesn't care. I believe you can run it with a single wire. The ECU doesn't control the distributor as much as it merely "influences" it. I swapped to a Holley Sniper with the truck's TPS connector unplugged and the ESC missing and the distributor still ran fine.
1. This forum already has an entire section devoted to LSx swaps, and carb swaps. This thread belongs there. Perhaps a moderator will move it.
2. There's essentially no advance--"vacuum" or "centrifugal" built into a TBI distributor with the automotive ignition module. Over 400 rpm, the computer controls the advance. No computer, no advance. Which is why "carb swaps" also generally include distributor swaps to one with the ancient 4-pin module, a vacuum canister, and weights 'n' springs. But then you've screwed-up the computer that controls the trans shifting, if the truck is new enough to have a 4L60E. But of course there's no mention of model year, or transmission type.
3. The ORIGINAL 3310 780cfm was a reasonable carb. The later 750cfm versions are cost-cut with straight-leg boosters instead of down-leg, rear metering plates instead of a proper rear metering block, etc. Still, they're popular. A 750 Q-jet tuned to the application would be SO much better than a 3310 in any form. But given the rest of the engine...TBI is better still.
4. You'd be lucky if you didn't have to INCREASE the jet size in a 3310. The crappy-breathing heads and low-rpm nature of the cam would have less signal to the overly-large carb venturis, requiring larger jets to get the same amount of fuel flow.
5. As said...fix the TBI so it runs right, leave the carb on the shelf in the garage. Removes lots of headaches ESPECIALLY if the truck has a 4L60E or 4L80E.
2. There's essentially no advance--"vacuum" or "centrifugal" built into a TBI distributor with the automotive ignition module. Over 400 rpm, the computer controls the advance. No computer, no advance. Which is why "carb swaps" also generally include distributor swaps to one with the ancient 4-pin module, a vacuum canister, and weights 'n' springs. But then you've screwed-up the computer that controls the trans shifting, if the truck is new enough to have a 4L60E. But of course there's no mention of model year, or transmission type.
3. The ORIGINAL 3310 780cfm was a reasonable carb. The later 750cfm versions are cost-cut with straight-leg boosters instead of down-leg, rear metering plates instead of a proper rear metering block, etc. Still, they're popular. A 750 Q-jet tuned to the application would be SO much better than a 3310 in any form. But given the rest of the engine...TBI is better still.
4. You'd be lucky if you didn't have to INCREASE the jet size in a 3310. The crappy-breathing heads and low-rpm nature of the cam would have less signal to the overly-large carb venturis, requiring larger jets to get the same amount of fuel flow.
5. As said...fix the TBI so it runs right, leave the carb on the shelf in the garage. Removes lots of headaches ESPECIALLY if the truck has a 4L60E or 4L80E.
If you still have the factory plug for the distributor, just plug it in and go. Your timing will be locked, but it'll run.
