Turbo conversion - Single or ITB's

(originally posted in the wrong section)

Hi, Newbie here, I'm fitting a turbo to my ZZR1200 engine in my Radical hillclimb car, so converting from carbs to EFI.

I planned on using ITB's but understand that the vacuum reference from between throttle butterfly and head is not suitable for using MAP as load when tuning fuel and ignition.

My question is two fold, at this point I can go either way so which would be best, I will be running low boost, initially looking at 5-7psi.

Should I go the ITB route and use TPS as load for fuel and ignition, if so is the vacuum good enough for boost control/FPR etc?

I can remove throttle butterfly's and spindle, seal holes and fit a single throttle body at entrance to the plenum, would this simplify tuning, using MAP as load from vacuum take-off from the plenum and provide better vacuum reference for boost control etc.

Thanks in advance.

I suggest you fit a boost pressure sensor upstream of the throttle bodies, use that for boost control. Then setup the fuel table using Alpha-N tuning at maximum possible boost. If possible build a 3D Alpha-N compensation table around boost pressure. A MoTeC GP firmware package using the "Multi-Throttle Tuning Method" does exactly this.

I would use the MAP sensor for ignition timing and FPR.

I've setup and tuned a turbo engine this way, and it worked out well.

Hi David, thanks for the info.

As said I'm a bit of a newbie doing an EFI conversion.

For info, I'm using a Maxxecu Sport, this uses MAP (built in MAP sensor) readings for the boost table with a MAC valve to actually control the boost.

Am I understanding correctly.

ITB's - Fit a vacuum take off prior to the throttle bodies, between intercooler and plenum or in the plenum itself and use this for MAP and by default boost control, can this then be also be used for ignition timing. TPS will then be required for fuel tuning.

FPR vacuum is not measured by the ECU just a direct feed to an adjustable regulator. I'm using a MAC solenoid for boost control, this also requires a vacuum source, these should be from after the TB butterfly's.

As I am fabricating the plenum the use of a single TB is not an issue, to clarify, if I was to go this route the following is correct.

Single throttle body - Fit a vacuum take off for the MAP sensor prior to TB and all other vacuums can be taken from the plenum after the TB, with this set up both fuelling and ignition timing can be done using MAP as load.

I'll be talking to my tuner in the new year but trying to learn as much as I can about tuning as I go along.

Cheers.

Frank

Using actual Manifold Pressure for boost control has a problem at high-RPM low throttle. See if the MaxxECU Sport can be configured for an additional sensor for boost control.

You can't use the before throttle pressure as the load axis for ignition timing as this would not vary with load, so it would be best to use TPS only as load for ignition (but this isn't really accurate with force induction, and you should really use the proper MAP channel.

Now that you've told us you are limited by the ECU, I would contact MaxxECU for best advice in your application. I'm suspecting that the single throttle body approach will be their choice -- too bad you will lose that ITB throttle response you've probably become used to in your Radical.

Maxx can easily be rigged for wastegate pressure reference on any AIN channel (though 1-3 do have fixed 2.5k pullups) and the boost control table axis can be pointed to it.

If I'm running ITBs i generally run a vacuum plenum for load sourcing of ignition on a boosted engine... I do this pretty regularly using Maxx's - I've been very happy with the results when clients have asked for an affordable alternative to the point where I use them as my mule ECU on the dyno as well as a few street projects - I'm sure it will be capable of getting the best of both worlds RE: ITB and boost.