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Tuning Sr20 with large cams. Slight throttle increase issue

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I am currently struggling with a sr20 engine fitted with 280 degree Tomei cams. I can be in any cell and at my target. When I give the engine 15% or more throttle it moves along nicely in the VE map using MAP and RPM as load. But if I stay in the same cell and increase throttle from say 2% to 10% slowly and continue to slowly press the throttle it will lean out say from .9 lambda to 1.4 and struggle to run in the same cell as there's no real change in the VE table and is more severe than transient throttle can adjust for no matter how sensitive I make that. The engine only has less than 1 HG of vacuum at idle with the cams. All of my sensors are calibrated and communicating properly. To insure I could actually make the setup work I tuned the engine in Alpha N and it runs smooth on the Dyno but as VE changes on the street under different load conditions of course doesn't give me consistent drivability as the manifold pressure is changing under different boost/traction areas but it isn't referencing any of that for fuel since it's only looking at TPS and RPM. I am using a Haltech PNP. Confirmed no trigger issues. Made 507whp 435 torque in alpha N on the dyno but I don't think I can let it go out the door like this. I could spend more time on the street and dyno dialing in different areas to likely make it run better (typically in between gears is biggest issue) but I'd much prefer to be able to get around this issue and tune it with MAP as my load source instead of TPS. I did give myself a lot more clarity in the map as a test while tuning with manifold pressure as load source but I was unable to correct this issue no matter how much resolution or time I spent tuning fuel off of the map sensor.

Just to double check, this is obliviously turbo?

Is it a single throttle or individual throttle?

My first concern is that it only has 1hg of vacuum, I have tuned many cars with large cams and also using the tomei 280s and never seen the vacuum so low unless the cam timing was incorrect or someone was using a solid lifter cam on a hydraulic lifter, or the base circle had a hollow in it.

So currently you're running on Alpha N only? Can you tune it using a MAP correction/overlay?

Yes gtx3071 Turbo. Single throttle body. Cam timing is correct and was double checked. Solid lifters. I can probably make a general correction table for MAP overlay but not sure how I'd go about it just yet. As of right now it would really be removing fuel from the alpha N map which just seems odd to have to do. Has 1hg at idle. It has plenty of vaccum as it gets into higher rpm just 1 HG at idle

You can tick off "MAP correction" in the setup menu...

Can you run dual fuel maps and switch between them at your own terms?

Im thinking using TPS at low load/idle and switch to MAP when you got more revs and better vacuumsignal.

I would expect that you should be able to run the fuel table on MAP and not have to use TP. Usually the issue you're talking about I see when on an individual throttle body engine.

Maybe upload a map so we can have a look how it is setup?

Will definitely upload a file and some data logs:) thank you guys

I agree with Chris - that MAP signal is suspicious. My old drag engine that utilised cams with around 300 degrees advertised duration produced much more vacuum than you're seeing despite not idling below 1800 rpm and having a powerband from 7000-10,000 rpm. I'd be double checking everything to do with the cams as a first step.

On the odd race engine that produces a very low MAP signal at idle I have tuned them using alpha-n. If you use a linear MAP compensation table then this will adjust the fuel delivery as the MAP signal varies up and down which keeps your AFR consistent as load varies on the road. With a turbocharged engine you'll need a 4D compensation to adjust the AFR targets as the boost increases too. Depending on which ECU you're using, there are a variety of ways to go about this and some are easier than others.

I may have a test I can perform tomorrow to see if I'm seeing inconsistencies in the map sensor due to where it's getting its source. I noticed my mechanics have placed the vacuum line for the map sensor just behind the throttle body on a vacuum port. Maybe if I run the vacuum line to a port closer to the firewall on the intake it'll give me a better reading? Maybe the high overlap on the cams and the vac port being so close to the throttle body (just behind it) is causing an issue as air from all four cylinders is actually pushing its way back out and that's too much for the map sensor to adjust for being so close to the throttle body? Worth a shot?

If you're seeing inconsistencies in the map reading then it is possible to be causing the fault.

The area where you're talking about moving the sensor to is the optimum location for a map sensor so hopefully might help stabilize the signal.

Let us know how you get on.

We changed the vacuum source for the map sensor to as far back in the intake as we could and it resolved the issue with very low vacuum readings. Tuned in speed density excellent after that. Ugh simple fix but hour long chasing tail sessions.

Great result! All apart of the learning process.

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