Turbo engines with multiple throttle bodies

[Chris Wilson]

How much more difficult to map properly are turbo charged petrol engines with multiple throttle bodies, compared to single bodies on a plenum inlet? Specifically I am thinking RB26 Skyline engine with bigger twin turbos, 280 degree cams and head work. There is an option to map multiple throttle body blown engines differently, somehow, dual mapping or something? Maps to different parameters on and off different levels of boost? Is there much of a performance gain running multiple bodies at such a level of tune, for a track type car? I read many opinions, few are the same

Thanks.

[sam@tdi]

Turbo charged engines with individual throttle can be tricky, not at full throttle, that's relatively easy but getting the 0-20% throttle angle right is very tricky. Especially at area's around 80-120kpaA.

On the RB26 I like to use 3d speed density mapping for fuel and ignition tables and then have a Z-table for every 'lets say 20% throttle angle. You'll need a good dyno and a lot of patience, but the results are worth it

[Martin]

This is a second Load table from an Inv TB Turbo engine that has a Manifold pressure Effcy calculation method, (v2 firmware)

With M800 V3 you can have 4D mapping that might work better than a basic second load table.

The table is just to illustrate how big the fuelling differences are for throttle angles on indv TB turbo engines for the same boost.

[Chris Wilson]

Thanks for the excellent explanations and illustration. I assume people capable of this multi dimensional mapping are limited here in the UK? I would like the map to be pretty optimal, and hope to have the engine (RB26 Nissan) mapped on a proper engine dyno. Having spent a lot of time and money on the thing I'd hate to have it compromised by poor part throttle running, although, as a track car, maybe the benefits will be less noticeable?

[Martin]

The above map was done on the track. Original map was done on a hubdyno.

The car is a 1981 porsche 956 that got special persmission to run Motec instead of bosch motronic. As you would know the exhaust are about 500mm primaries, 100mm seconday, turbo,100mm ATMOSPHERE so noise reduction and lambda placement is difficult. The reduction of under body temps rely heavily on airflow so running on a dyno causes major headaches because it damages bodywork that aparently is irreplaceable. We were limited to minimal constant load dyno`ing and the rest was ramp runs to minimise heat exposure. The car made 427Kw measured un hubs with 200Kpa at 1500m Altitude. (Baro reading 85Kpa)

I must say that the track mapping took a lot of time but the results are worth it! The wonders you can do with logging!

[sam@tdi]

Thanks for the excellent explanations and illustration. I assume people capable of this multi dimensional mapping are limited here in the UK? I would like the map to be pretty optimal, and hope to have the engine (RB26 Nissan) mapped on a proper engine dyno. Having spent a lot of time and money on the thing I'd hate to have it compromised by poor part throttle running, although, as a track car, maybe the benefits will be less noticeable?

It'll definitely be far easier to do on an engine dyno with good fixed throttle angle control, I've always had to do it with the engine already in the chassis on our Rototest, tricky part as always is keeping control of all the variables.

In my experience accurately calibrated part throttle and throttle transients are extremely important on the race track, after all if you just using the throttle like a switch there's a good chance your not getting the best out of the car.

[gring]

The challenge with ITB throttles and turbocharging is that there will be a difference in airflow at different throttle positions but the same boost pressure. This means that the air fuel ratio will change if not accounted for. There are several different strategies that can be employed and will depend on the particular engine. You need get a stable MAP signal using a manifold chamber box to be able to use MAP for any type of correction. I like to use a main fuel table based on TPS and RPM and a secondary table based on MAP and RPM or TPS and MAP to account for the VE differences at different throttle position. I still retain the double pressure double fuel MAP compensation table. I map the engine on the lowest boost setting and get the air fuel ratio correct. Then any changes required are done in the seconday fuel table.

YMMV.

[Hanzie M48]

Hello, hopefully you understand my English.

The setup is a BMW S14 engine with induvidual throttlebodies and turbo. I use M48pro.

-Unfortunatly I can't get the mixture stable. The intake is very short so the Mapreading is instable by driving offboost. I thought that could be the problem.

-To make it easier for me(I'm a starter) I have disconnect the turbo yet and set up the Fueltable as RPM/TPS. Now the Lambda is more stable but not perfect. When I drive in town I only use 40% Throttle.
-Now my question is how can I setup the fueltable when i use the turbo again; Main fueltable as TPS 0-100% and the second fueltable from 110Kpa-210kPa?
-I do not understand how the motec goes from the main fuel to second table? Or is the second a compensation table? Please explain me that.
Do I need 2map sensors then? One to the air and the other for boostpressure?
-And what about the ignition table? I can only choose for TPS or Map, there is no second table.

If you need more info to help help, please ask.

Thanks in advance,

Hans

[Alex B]

Hi Hans,

Have a look here:
http://www.motec.com/forum/viewtopic.php?f=11&t=1272&sid=ce251ae58ca99cff6f049579ed8bd4ec

I think that your best solution would be to use map as a main efficiency/load source and make main fuel and ignition maps with it, then use secondary load table with rpm x th to finetune your fuel with TH.

Best regards
Alex

[Rolis]

The challenge with ITB throttles and turbocharging is that there will be a difference in airflow at different throttle positions but the same boost pressure. This means that the air fuel ratio will change if not accounted for. There are several different strategies that can be employed and will depend on the particular engine. You need get a stable MAP signal using a manifold chamber box to be able to use MAP for any type of correction. I like to use a main fuel table based on TPS and RPM and a secondary table based on MAP and RPM or TPS and MAP to account for the VE differences at different throttle position. I still retain the double pressure double fuel MAP compensation table. I map the engine on the lowest boost setting and get the air fuel ratio correct. Then any changes required are done in the seconday fuel table.

YMMV.

I think this is the easy way to do that!
But one question, do you use first this kind of fuel - map compensation - before second load table compensations?