TBI motor tuning

[jollymon02]

Hey all,

I have a TBI motor running a aftermarket EFI and mild cam. I'm working to get the tuning sorted out. I currently have an HEI distributor with vacuum advance, but have the option to change for a billet and let the EFI handle the timing control, which would make it more like an upgrade from the factory air/fuel delivery.

My immediate question is where should I set the base timing, 0 as factory, or more like a typical SBC 8 degrees base?

[biketopia]

What EFI controller? The holley setups have you index the distributor a certain way, lock timing out to a certain number in the tune then verify it stays there at idle and revving it up. Once that's done you do all your timing curve adjustments through programing only. If you set it at 8, the EFI program thinks it's base line is "0" and puts in 8 degrees now your at 16 and having tuning issues.

[jollymon02]

It is Fitech. Same basic principle. I'm asking if there is a known difference in the tbi vs carb motors calling for different timing for an aftermarket efi. Last distributor car I had was a 70s 2L BMW, so the SBC world is not stored in my brain.

[GASoline71]

Originally Posted by jollymon02

It is Fitech. Same basic principle. I'm asking if there is a known difference in the tbi vs carb motors calling for different timing for an aftermarket efi. Last distributor car I had was a 70s 2L BMW, so the SBC world is not stored in my brain.

Depending on the cam it's gonna need some advance. Start out with 12 degrees or so. The adjust from there. After a few test runs (driving it with a load on the engine), see where the sweet spot is. Small Blocks love advance. However, the TBI "swirlport heads" might negate the gains a bit. They were designed with the severely underpowered TBI in mind.

Gary