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113 | Dual VVT Tuning Strategies

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hey guys, not sure if its been asked before but im finding it hard to find information on cam timing for superchargers. obviously with a turbo you have the back pressure but I just want to know your experiences are with supercharges. Im assuming you can run abit more overlap with them but depending on the exhaust backpressure. Id just like to a bit more about what I can get away with before I just plonk it on a dyno and hope for the best. Mainly I want to know what sort of general advance/retard numbers you have compared to a turbo. I know its engine specific but id just like to know a ballpark sort of setup.

They dyno is the tool for finding out what works best. You are going to end up trying a range anyway, just start somewhere in the middle.

Hi Brandon,

As David mentioned, the dyno is the best and only real way to get the cam timing set 100% correctly.

Are you tuning on the dyno? What is the engine and tuning platform you're using?

Im running a supercharged toyota 86. I just wanted to know sort of the science behind what sort of overlaps you want. I know turbos have back pressure so overlap under boost is not so good but I want to know do supercharged cars experience similar back pressure just not as dramatic? I dont want exact numbers. Just wondering as I cannot find any info on this type of setup. Eventually when I do it ill use a dyno but its not setup yet so I will be doing a bit on the road when this corona stuff settles down.

Please consider doing your dyno work first, since you will tune everything completely on the dyno anyway. If you are changing power adders, after getting the engine to start and idle, your next stop should be the dyno. That is the most efficient way to break in the engine, verify it's operation, make setup/tuning changes to determine what works all in a safe environment where you monitor the health of the engine continuously.

After it comes off the dyno, then you take it to the street/track -- learn if it has any bad habits that need addressing, or issues that can't be found on the dyno (like overrun situations, returning to idle). Those you can tune on the street.

A supercharged engine is just like a normally aspirated engine, that gets really good air pressure. Start with the factory workshop cam timing, stock VVT tables, and see what it wants. It really doesn't take that long to change the cam timing a few degrees and make a comparison run to see where torque is improved -- it's especially easy if your ECU has good closed loop fueling and can keep the mixture on target even as the volumetric efficiency is improved (or even if you end up reducing the VE).

If you want to save dyno time -- my suggestion is engine modeling. Get one of the software packages that lets you adjust the cam timing and see what the effects of various changes are. Here are a couple of packages that I know my engine-building customers use:

https://www.performancetrends.com/Engine-Simulation.htm

http://proracingsim.com/products.htm

Thanks mate I really appreciate the feedback and tips. So its running a motec 150 and its been tuned by various poor tuners who just wanted coin and did a trash job. The car was constantly running crap and having issues idling and such. I've spent the last year tuning the major aspects of it like starting and making it achieve target. Most of that time was idle and starting Anyway.. I've been focusing on drivability now and stock cam maps on the 86 map are very very bad. Its like 2 big peaks and in the middle drops down more then 20degs. My plan is to make the cams have more achievable targets then before and have them in a close enough range so i can setup the fuel map and keep it goodish for a while till I can afford another tune.

Sorry to hear about your disappointing results with prior tuners. Be sure to let them know you are not happy with how the engine is running and give them a chance to fix it (to save their reputation, they should be offering to do it for free or very low cost -- I know I would!)