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2008 G35S with VQ35HR - Uprev

Practical Reflash Tuning

Discussion and questions related to the course Reflashing


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I recently bought an '08 G35S with the VQ35HR motor. It's got a full exhaust, ported intake manifold (stock intakes/MAFs), and bigger VQ37VHR injectors (384cc vs 335cc for the stock ones).

It was tuned previously (reasonably poorly), but due to the way Uprev works, I have to start from a base tune file instead of what's on the car now.

Nissan/Infiniti ECU's use what's referred to as a K-multiplier (stock value of 26806), which is multiplied by the current MAF value to determine a base fuel schedule.

This is my first foray into engine tuning, but I know that the K-multiplier and the VE table and ignition timing have a reasonably complicated interaction in OEM Nissan ecus and that the VE table is definitely going to need some adjustment due to the intake path modifications. I don't know the correct K-multiplier for the new injectors, but do know how I'd find it on a stock car that I know the VE table is correct on, as shown in the tuning guide. Of course, that really assumes the

If I still had the stock injectors I'd just toss those on to get the VE table right but that's not an option I'm afraid.

The I browbeat the people at Uprev into admitting that (335/384)*26806=23385 is a reasonable rough estimate for the K-multiplier.

Planned process (hopefully within a week or two):

- Test/check/replace all ignition components, clean throttle bodies and MAFs

- Dyno as-is

- Refash to stock

- Adjust K-multiplier for injector scaling

- Set AFR table to single target value, tune VE table

- Get AFR targets into the right safe ballpark for approaching MBT

- Tune intake and exhaust cam phasing

- Clean it all up

Am I missing anything major here?

I don't use uprev these days but I did use it through my old shop so have a recollection of the process. You're unfortunately in a difficult situation where you have larger injectors AND a modified intake tract that will affect the MAF scaling. The problem is that you don't know what you're adjusting for - Incorrect MAF scaling or the injectors. In the perfect world you'd really want to go back to the stock MAF/intake and dial in the k multiplier for the larger injectors then refit the MAF, adjust it further to get your fuelling in the ball park then fine tune your MAF table to get everything finalised. In this instance you're probably best to start by using the injector size calc you did above to get the k mult in the ball park and then fine tune it until your as close to your target fuelling as you can get before finishing up with the MAF scaling. It's not going to be perfect but it's at least achievable.

Yeah, I'm worried about the interaction between the K and the MAF scaling. I'm hoping that because all of the intake path mods are quite a bit downstream of the MAF(s) it shouldn't affect the scaling too much.

I'm going to see if I can track down some HR injectors to make my life easier. Then at least I know it's all VE table and MAF scaling.

I wish Link made a plugin for the HR/VHR motors, I'd just get one of those.

Thanks!

EDIT for those of you who come on this thread later, I gave up on trying to get Uprev to play nice at the level I want, considering the level of modification the car came with. I'll keep the cable/licenses and use them on stock or near-stock cars that are getting parts added.

I've decided to install my Emtron KV8 in it instead - I've booked into the factory training session in April. And I'm very seriously considering buying an Audi TVS1320 supercharger from a local junkyard the to see if I can't machine up an adapter and bolt it up somehow. I think it shouldn't be too hard to make happen with some basic CAD work.