Looking for the best option for my fuel table – Turbo engine with Vipec

Hi,

I have a dilemma on how to tune my fuel table. Looking to get more out of my tuning.

What is the best way to tune a turbo engine with multiple throttle body? It’s a drag only bike with 400 plus HP. Using a Vipec V44 on this setup.

Fuel equation: Load = Map

Fuel table y-axis load: TPS or MGP or MAP?

Ignition table y-axis load: MAP

What is better for the fuel table load; TPS/MGP or MAP and why?

Thanks.

Dolfo

Tuning a multi throttle turbo engine is a little more complex than a conventional turbo engine with a plenum and single throttle body. In multi throttle applications the manifold pressure alone is not a great indicator of airflow so we need to also incorporate throttle position.

With your application I would use TPS as the main load axis for the fuel table. You also need to use Load=MAP as the fuel equation and enable the open loop AFR table with MAP as the load axis. This will do a background adjustment to your injector pulse width based off manifold pressure and your desired AFR target.

All you really need to do is set the AFR target table to your desired target and then tune the engine as normal. Once you've tuned the engine at WOT and your minimum boost you can start increasing the boost and your AFR should still track your target. If you start working the turbo very hard you may find that at higher boost and high rpm your AFR starts tapering a little rich. This is because the basic model assumes that the VE of the engine remains constant as boost increases and this isn't going to always be the case. In this situation you can use a 4D overlay table to trim the AFR if it deviates from your target.

There is a webinar we did on a GTR engine that explains the process quite thoroughly - https://www.hpacademy.com/previous-webinars/4d-tuning-link-g4-plus/

For your ignition table you would use MAP as the load axis.

Andre, Thanks for your reply.

What do you recommend using for the 4D overlay table? In the webinar you use MAP as load axis. Why not MGP to compensate for barometric pressure changes? What is better for the 4D table?

I've always used MAP for this overlay table, however up until now I've never really lived in an area where I could experience large changes in barometric air pressure.

Unfortunately dealing with baro correction on a turbo engine is not quite as simple as it is on a naturally aspirated engine and neither MGP or MAP will allow you to properly compensate for barometric pressure changes.

When we experience a change in baro pressure, what happens is that it effects the pressure ratio the turbo is working at. This has two consequences - First it will affect where in the compressor's efficiency you're operating and in turn it will affect the exhaust manifold pressure. As the baro drops the turbo needs to work harder to achieve the same manifold pressure and this means the exhaust manifold pressure increases and his in turn will effect the engine's VE.

MGP will put you in a different zone of the 4D comp table with changes in baro, so this may be able to be used to your advantage. You will still need to spend time seeing how the AFR responds to changes in baro though so that you can decide how to deal with this compensation.

For a drag application I wouldn't get too hung up on baro correction to be honest. In my own experience I usually found I was always making small changes to the mapping between runs so I'd be accounting for any baro fluctuations manually. Obviously this might be a different situation if you are regularly racing at tracks with widely varying altitudes though.

Thanks for clearing that up. I will just go with MAP on the comp table.

I’m thinking of doing a small dry shot of nitrous in the up-pipe in front of the plenum to cool down my IAT.

Do you have experience with this and how to approach this type of tuning? Can the nitrous injection be tuned by a 5D table?

Andre,

Can you help me with the above questions? I want to know the best way to tune when using nitrous for cooling on a turbo engine? Is this difficult? Thanks.

There are a couple of different ways of dealing with nitrous. What you will need to do is add fuel (assuming it's a dry shot) and retard timing (I use approximately 2 degrees per 50 hp as a guideline). you can do this with dual fuel and ignition maps that switch when the nitrous is active or alternatively a 5D fuel and 4D ignition overlay table would also work.

Yes it’s a dry shot but I’m thinking like a 30 shot to start with. Which one do you recommend or is more accurate or simple to tune?

With the dual fuel and ignition maps I have to copy both maps and modify them for when the nitrous come in? And then put extra % of fuel and tweak the igniton? For the overlay tables just leave the fuel and ignition table alone and just modify in those tables when the nitrous hits right?

Thanks again.

switch: Yes you copy your existing maps and tweak the values.

5D fuel /4D ignition: you specify only what you want to add/remove in those additional maps.

Generally speaking, the fuel overlay is in % (100 would mean no change, 110 would be 10% more fuel)

and the ignition overlay in addition (0 = no change, -2 = retard 2°)

Personally I would say that the overlay makes more sense since it allows you to directly see what your engine want based on the quantity of nitrous, but in the end it depend of the way you like to approach your tune.

Actually the table behaviour is a little different to how Ludo explained. The behaviour of these tables is quite nicely summarised in the Link G4+/Vipec help file but let me explain:

If you choose to use dual tables for fuel/ignition, you have the option of setting up the tables as 'Dual Table' in which case they are completely separate tables. If you choose this mode then you would copy your initial table values to the second table and modify as required. You can also choose 'Overlay Table' though, in which case the values will be additive to your main table value in the same way as a 4D/5D table works.

Also to clarify the action of these overlay or 4D tables - A value of zero in these tables will have no effect. A positive value will add fuel/ignition while a negative value will reduce fuel ignition. When the overlay table is used for fuel the effect is a percentage change (ie a value of 10 in the 4D table will add 10% fuel to the main fuel table at that point) but when it comes to ignition the value is directly added or subtracted from the main ignition angle (ie a value of -5 in the 4D table will subtract 5 degrees from the main ignition table).

Personally I'd recommend a 4D/5D overlay table. It's nice and easy and it means that your trims are always based off the main tables which is useful incase you change something that requires the main table to be adjusted.

I should have mentioned that I have no experience with Electronz ECUs. I guess the behavior of those overlay tables differ slightly from a brand to another.

From what I understand Andre, you're saying ViPEC use only additive overlay, while other brand let you choose between additive and multiplicative.

Correct Ludo86, it really will depend on the specific ECU as to how the these tables function.

The way the overlay table is dealt with is still a multiplication - ie 10% in the table will add 10% to the current fuel zone which is the same as multiplying the value by 1.1. It's just a different way of dealing with the 'zero change' point. In some ECUs this is 0% while in others this is 100%. I hope that helps.

Thanks everyone for your input.

I’m busy putting my map together with all the info I got on here.

First we talked about the 4D table when pushing the turbo too hard. But now with nitrous should I only use the 4D table for the nitrous setup and tune the 4D table for what the engine wants or I need to use both tables (4D to correct fuel and 5D for dry shot)? Trying to understand this correctly.

The dyno tuning process is the same as in the webinar? Tune with minimum boost (wastgate pressure) and whn it’s done raise the boost pressure and nitrous then tune the 4D table for fuel and ignition. I hope I understand it correctly.

Thanks.

I'd forget about the nitrous initially and perform the tune using 4D correction (if required) as you raise boost to your target. Once the tune is complete without nitrous, you can set up a 5D table for the fuel compensation for this.

It sounds complex but it really isn't if you just deal with one aspect at a time.

Okay perfect I’ll approach the tuning like you explain it.

Till what IAT’s would you go (boost) before start cooling the IAT’s with nitrous? I know Vipec fuel correction table will compensate on fuel for hotter IAT’s but what will be safe (knock/detonate) before I need to start cooling.

Are you using an intercooler?

IAT will effect both the power and the knock susceptibility of the engine. What you can tolerate will depend on your boost level and fuel. When it comes to air temp though, less is always preferable.

If you're non intercooled, you will be likely seeing IAT reach 100-200 degrees C dependent on boost and compressor efficiency. In this case anyhting you can do to reduce that IAT is going to help. I'd suggest spraying for most of the strip.

If you are using an effective intercooler I'd expect to see the IAT reach 30-50 degrees C (again dependent on boost/comp efficiency). Nitrous will help in this situation but those sort of IATs are acceptable.

At the moment I have an intercooler but I want to remove it and use nitrous instead. The reason for removing the intercooler is the extra weight and pressure loss. I’m also losing a lot of HP and I don’t know where/why I’m losing this HP lost.

My question was: I need to tune the engine with 4D correction without nitrous. Doing this I will raise the boost to tune my fuel tables. But raising the boost will raise the IAT value. So till where I can go in the tuning process on the dyno with the IAT? I want to stay on the safe side so I don’t want to see i.e. 200 degrees C before start cooling it with nitrous. At which IAT should I stop raising the boost and start spraying nitrous on the dyno? Yes I will spray most of the strip to keep the IAT numbers down. I’m running VP C16 in the bike.

Any idea at which IAT’s I have to start cooling the intake charge in this tuning process?

What IAT’s will be consider dangerous for the engine?

If you are seeing over about 60-70 degrees C you're going to most likely need to retard the timing quite a lot to prevent detonation. The IAT itself is not dangerous for the engine, but as the IAT rises, the fuels ability to suppress detonation is greatly reduced. This is the real problem, and how much of an issue you have will depend on the fuel, compression ratio and boost pressure.

Even with a reasonably efficient compressor wheel where you are sitting around 75% efficiency, you're still likely to see compressor outlet temperatures of over 150 degrees C with a boost pressure of 30 psi for example. What you would learn by trying to tune the engine here with no intercooling is probably not going to be of much value to you.

Personally I'd tune the engine at the minimum or wastegate boost pressure just to get an idea of the shape of the fuel/ignition maps and then begin tuning with the nitrous active. There isn't probably much to be learnt from tuning the engine in a state that it won't be actually running (ie high boost and no nitrous).

I’m a bit confuse how to approach this tuning. Because first we talked about dealing with one aspect at a time tuning the 4D table (if required) as raise the boost target. After this tune with nitrous the 5D table.

Can you please explain this again how and when to tune the 4D and 5D tables? If I tune minimum boost pressure I won’t use much correction on the 4D table right? Maybe more correction on the 5D or this will be a fix % of fuel for the shot of nitrous.

I’m going to tune it like you said. First minimum boost pressure then turn on the nitrous and raise the boost pressure. I’m a bit confused how when to use the corrections tables.

Thanks!

Ok I'll try and explain a little more thoroughly. First of all it's important to understand that your tuning should reflect the way the engine will be used. Drag racing is quite unique in this respect and we can concentrate almost solely on the WOT tuning as we don't really care what the cruise mixtures are like. It's all about optimising the use of your time.

My point was that it makes little sense to spend a large amount of time tuning the engine in a state that it will never run in (high boost, no nos) and one which could potentially be dangerous and difficult to tune due to the high IAT.

Here's how I would approach the tuning:

1. Tune the engine to wastegate boost pressure with no nitrous.

2. While still on wastegate boost, optimise the tune with nitrous active. This will let you make any required changes to the fuelling and ignition to suit. Remember if the boost remains constant, the changes you are making in the 5D table for fuel are solely as a result of the nitrous spray.

3. Raise your boost to your target. Due to the Load = MAP equation, as you raise the boost the AFR should track your target very accurately. You may find that as you start getting towards the flow limit of the turbo, the AFR moves rich. Correct these errors in the 4D table.

4. Have a beer. Bask in the glory of a job well done.

That explain all my confusions!!! #4. Is the easiest part of the tuning process. LOL

Now the ignition tuning I still have some questions about this.

The MBT will change with the nitrous on right?

How to tune the ignition table on high boost with nitrous? Just tune for MBT in usual way in main ignition table? Start low with ramp runs and repeat the ramp run looking for MBT? Or I need to use a 4D ignition table for when nitrous turns on and tune the 4D ignition table for MBT?

I should have mentioned, it's important not to start with step 4 first. Too many beers will definitely have a negative affect on steps 1-3 ;)

The ignition timing can be approached fairly easily. You're right the timing will be affected by the nitrous. If you start as I suggested by tuning to wastegate boost pressure with no nitrous, you will have the ignition also optimised to MBT with no nitrous. Now when you bring in the nitrous you can make the appropriate changes - I recommend around 2 degrees retard per 50 hp shot of nitrous. You would make this change in the 4D ignition table.

You can now begin raising the boost and make your ignition timing changes in the main ignition map - The relative amount of retard required for nitrous operation will predominantly be base don the size of the nitrous shot and not the amount of boost.

This is probably not the only way to approach the tune but this is how I would personally deal with it.