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Discussion Starter · #1 ·
I was looking at the VVT settings on some turbomaps and noticed a large VVT transition change on some of these maps. (EG. the one listed below). I was noting how between 2000-4500rpm and load 9000-19000 the cells are set between 30-20.

I have two questions regarding this:

1) Why is it done this way in those cells only?
2)Would this cause an increase in backpressure in the exhaust/turbo and possibly cause higher Advanced PIM readings or bogging issues?

 

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That might reflect off boost, but spooling, in which case the VVT settings will be different :shrugs:

If so, it suggests that's for a turbo that doesn't make significant boost before 4.5K, which for a larger turbo may be about right.
 

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Having a lower number increases the overlap...which I'm guessing helps the turbo spool up faster.
on another note....Highest setting on the vvt is 50, even if you put a higher number it will only go to 50.
 

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Is this really how a turbo car vvt map would be like. almost the entire map the cam is fully retarded besides that few thousand rpms in the wot range.
 

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You will see a spike in PIM when the turbo spools and the airflow increases dramatically. Realistically, if the car is working correctly you should be able to run the car at any VVT setting you want. You should try different VVT settings on the dyno.

When you say that you have a GT28RS, which version is it? If you have one with a 0.64 A/R turbine housing, that may explain your problem.
 

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Discussion Starter · #9 ·
I noticed on my logs the car bogs when it hits a cell with VVT at 25-30, hence why I believe the overlap is causing issues as the turbo is spooling.

When you say that you have a GT28RS, which version is it? If you have one with a 0.64 A/R turbine housing, that may explain your problem
I believe it was a 0.86 turbine housing, but I'll have to double check it later this week. I remember monkeywrench ran a 35R with 0.63 housing and had no issues?
 

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Discussion Starter · #11 · (Edited)
OK, so a few things here in case anyone runs into this in the future I will save you some troubleshooting.

Firstly, my turbine housing is 0.86, 3" all the way to the exit pipe..so backpressure wasn't the problem. I found it odd to be backpressure at 3500rpm so I did some more logging and noted the PIM+AFLV kept going up but the AFR kept getting richer in those cells and I maxed out 19000 load on my map.
From this I knew I was making air but where was it going? Apparently a clamp near the intake manifold managed to loosen itself hence the issue.

Problem corrected and car now boosting fine. I have more tuning to do but that at least answers a lot of the issue. Hopefully, this will save someone time if they ever have this problem.

Jesse, you are right about the VVT settings. I also noticed the boost builds more slowly if you increase the number or builds up faster if you lower it. I assume based on overlap of the VVT system that is how it's supposed to work?
 

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http://users.ameritech.net/trdcelica/VVT_Explanation.pdf

You want high overlap (advanced intake cam) at low speed range/high load for maximum volumetric efficiency.

Here's a suggestion, most people extend the VVT settings at idle (50 typically) all the way down the map. This is not necessary and is based on nothing other than people constantly copying off of old maps when creating new ones. The theory should be that you use advanced cam timing to get better performance off-idle. You can't test this on a dyno, but you should play around with a number of different VVT settings in the higher load cells at low rpm to see which gives you the best feel starting from a dead stop.
 
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