Quote:
Originally Posted by C5GTO
Going from 302 to 347 cid would purely be for the extra power. The main purpose for the OD TKX transmission would be to lower RPMs while driving on the Interstate.
A question related to the 347 stroker direction, will the current EFI tune be adversely impacted by the extra cid? If so, would the situation be that the dyno tune done for the 302 cid engine just might be non-optimized for the 347 or the extra displacement really requires a different tune to prevent engine failure?
As I'm putting together a budget for the fixes here, it's important to capture all the line items. I'm guessing a dyno tune is probably in the neighborhood of $750 these days thus a significant line item.
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Joel,
Although you have not indicated the brand or fueling model (Alpha-N, Speed Density, MAF), my guess is Speed Density is what you are using. Fueling model notwithstanding changes in engine displacement, minimally need to be programmed into the EFI setup parameters because EFI systems, when everything is said and done, mix fuel with air in proportions you specify for an engine displacement you specify.
Some systems like the MAF-based variety make the process less time-intensive, but all will require some intervention. Speed Density systems will require the most intervention because although you inform the ECU logic of the new displacement, the engine's volumetric efficiency will change. A larger displacement engine fed by the same heads and intake will be more throttled (lower volumetric efficiency) than a smaller displacement engine with the same heads and intake.
The upshot is that the fueling Ve table(s) will necessarily be different and require a retune. The old tune for the 302, while adequate to start the engine, will be unsuitable to operate the vehicle safely (from an engine's perspective). It is time for another visit to your tuner's dyno.
p.s. I seem to remember your engine is carbureted and not injected. If that is the case then you need a retune for sure — carbs and speed density systems perform similarly to changes in displacement and Ve. If you are considering an EFI conversion for a carbureted engine that you are going to increase dispacement on, then only spend the tune dollars once. Pick your EFI system and take the rebuilt engine and car to your preferred tuner for the tune, don't spend the money twice.