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Tuning large overlap turbo engine

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Hello i have an question its on honda platform but mayb that someone can help out with this

Im working on a b18 turboed engine with the vtec is locked so it works like a big cam with alot of overlap the ecu is hondata i have tuned many other vtec locked hondas but they were N/A and i use Alpha-N to tune those but with a turbo fitted to the car i can't use Alpha-N since i dont have refference for boost pressure.

Has anyone here tuned a big cam turboed car with alot of overlap and if u ever did a honda i would gladly hear how u go about setting up the map

I know theres an option for using primary and secondary tables base on some conditions. But i haven't tried them yet.

If anyone has some guidence i hope u can help me out


The VTEC is locked like it's mechanically forced into high lift operation all the time? There are a few things to consider:

1. If it's possible to make VTEC work correctly (not locked) you should definitely do it unless it's a straight up race car

2. In high lift mode, the overlap increases the internal exhaust gas recirculation. Your engine will burn slowly and require a lot of spark to run in a stable way. Look at the stock VTEC spark maps in Hondata/Chrome etc ECU. Notice the additional spark.

3. In high lift mode, the intake valve closing timing is so late that your effective compression ratio is a lot lower, meaning your low end torque will such. Therefore don't expect it to make much boost or in general be fun to drive at all until you get to higher rpm.

Basically if it's Hondata etc copy all the high lift tables to the low lift tables and modify from there. Or even better, don't run locked VTEC. I don't know what ECU you are using or what you are starting with so it's hard to be more specific than that.

Unless there's a really good reason to lock the VTEC mechanism I'd strongly advise against it. There really are only a handful of scenarios this makes sense and as you've highlighted, your idle quality will suffer and the tuning is more difficult. I'm not personally aware of a way you can run Hondata as an Alpa-N system with a MAP overlay table so you're really restricted to using MAP as your load axis. The problem is most likely to be at and very close to idle where there is excessive overlap resulting in very low manifold vacuum. This results in limited resolution in this area of the table. Fortunately as you move past idle, the vacuum generally improves dramatically.

Things that can help would be to increase your idle speed a reasonable way and you may want to try reducing the overlap using vernier cam gears to improve the idle quality - This however may be at the expense of high rpm performance.

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