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3.2 MAF Conversion


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As some of you are aware I’ve been working on my own 3.2 MAF conversion kit. It’s been a “back burner” project for a couple of years now but is finally coming together and should be ready for testing on the car within a couple of weeks. I thought it was about time I shared a few more details:

 

I’ve gone for a modern Bosch HFM5 MAF unit – its one I’ve used on projects before so I know it’s robust and I've also got reliable calibration data for it. The other advantage of the Bosch HFM5 over other units is that it's got an onboard hybrid circuit which corrects for the pulsing flow and only outputs the net mass flow.

 

I’ve sized the MAF and air filter for flows equivalent to over 300hp so there should be minimal pressure drop even on an uprated 3.2/3.4/3.6. In terms of flow area it’s over 80% bigger than the original VFM and without the spring loaded flap to pull open.

 

The signal conversion runs on a microprocessor, mounted on a circuit board with necessary I/O electronics. This unit takes the mass flow signal from the MAF and converts it into a volume flow signal as you’d get from the original VFM - this means it should be plug and play without any changes to the ECU. This signal is also corrected for air temperature and atmospheric pressure using an additional temperature sensor mounted in the inlet and a pressure sensor on the circuit board.

 

We’ve put the final touches to the software over the last couple of weeks – debugging, configuring the error modes etc. The final step to validate the controller will be a bench test of the whole system to check all the signal conditioning is functioning correctly – I’m hoping to get this done within the next couple of weeks so I can test it on my car before its SORN’d at the end of the month.

 

Here are a few pictures of the hardware:

 

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IMG_1331.jpg

 

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I’m going to do a trial fit on my engine this weekend so I can work out required brackets etc. My plan is to mount the control unit remotely one side of the engine bay to keep the engine looking tidy.

 

Once it’s all up and running on the car I’ll run a set of dyno tests to compare with the post rebuild runs I did in the summer – fingers crossed it’ll deliver a few extra hp and improve the response also.

Edited by MaxDiesel
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Thanks for the positive comments.

 

My current plan is to commission the kit on my car and run it for a while so I can be sure it all functions properly. I'll also do some back to back dyno runs against the old VFM. If this all goes well then I'll look into making up some additional kits in the spring - I haven't worked out a price yet, the MAF unit I'm using is significantly more expensive than the one in the Gekkatek kit but overall I'm hoping the kit will work out less.

 

I've done a bit more work on the hardware side today, here's a few more details:

 

Here's the MAF and the tapered aluminium adapter that brings it down to the right diameter to join the existing throttle elbow:

 

DSC00734.jpg

 

DSC00731.jpg

 

Assembled with the K&N air filter:

 

DSC00742.jpg

 

First trial fit in the the car (with a piece of 2"x2" supporting the filter !) - I'm relieved to find it fits as I knew it would be tight with the large K&N filter:

 

DSC00746.jpg

 

Made up a "mk1" support bracket in steel - longer term will fabricate this in aluminium:

 

DSC00763.jpg

 

The bracket uses the fixing posts on the air filter and one of the mounting points for the orginal airbox on the inlet manifold:

 

DSC00770.jpg

 

DSC00771.jpg

 

All fitted in the engine bay - just need to bench test and connect the control unit then should be up and running :steering:

 

DSC00775.jpg

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What are the differences between yours and the Gakatec apart from yours uses a superior MAF ?

 

Apart from the MAF and air filter etc then I guess the main differences will be what's inside the control unit. I'm not aware of the detail spec of the Gekkatek unit so hard to know how they've done the conversion.

 

The processor I'm using is quite a high spec so it can run the mass flow to volume flow calculation at a high resolution. The temperature correction works from -40degC to +120degC and the atmospheric pressure correction from 800mbar to 1200mbar. I doubt it will ever see these extremes but better safe than sorry.

The other key part of the calculation is converting the incoming and outgoing signals from voltages to flow numbers in order to carry out the calculations - this is done by characterising the sensors. Getting the original calibration curves for the VFM & MAF sensors can be hard (but not impossible). The other way is to derive these by testing the sensors on a calibrated flow bench - fortunately I have acces to one of these. Getting all this information together and selecting all the other sensors was the hardest part and took over a year - a colleague of mine has then helped me write the calculations into the software.

 

The first vesion of the software we've written doesn't include an idle mixture adjustment. In theory given the accuracy of the MAF unit it shouldn't need this but knowing it'll be going onto 25year old cars with unknown injector performance, minor leaks etc. we're working on a second SW release with this included.

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Looks great - is there any scope to retain the factory air filter housing for a standard look

Yes - could do but I suspect you'd loose some of the benefit as the original air filter housing exit is the same rectangle size and shape as the VFM flap so it will act as a restriction.

I guess you could get round this by taking a 90mm hole saw to your airbox.... Ideally you'd remanufacture the meter side of the air filter housing with a larger exit as per the Steve Wong kit but this would make the whole thing a lot more expensive.

 

I just refitted the standard airbox and VFM to my car this morning - it took less than 15mins to do so its pretty easy to switch between the stock set-up and the MAF if required.

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Excellent work Matt :ani_clapping:

 

Put me on the list!

 

A couple of questions .....

 

Does the output from the MAF unit need to be converted to an analogue signal, is there a device to do this with the controller or is it part of the MAF unit itself?

 

If the output from the MAF is to be converted to a signal (emf) equivalent to that of the standard AFM unit for a given air flow then presumably the additional air flow at WOT that the MAF will allow will generate a signal larger than the maximum possible from the AFM. (I hope this sort of makes sense!)

Do the existing maps/tables in the ECU extend /or are extendable for the wider signal range and can the standard injectors and fuel pressure provide the additional fuelling load required of the additional air? Is a custom chip part of the plan? Could the existing chip be mapped to accomodate?

 

Theoretically the gains should be much better than seem to have been reported for current aftermarket conversions. What do you think should be achievable on an otherwise standardish car if the fuelling is set properly to match the extra air?

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Excellent work Matt :ani_clapping:

 

Put me on the list!

 

A couple of questions .....

 

Does the output from the MAF unit need to be converted to an analogue signal, is there a device to do this with the controller or is it part of the MAF unit itself?

 

If the output from the MAF is to be converted to a signal (emf) equivalent to that of the standard AFM unit for a given air flow then presumably the additional air flow at WOT that the MAF will allow will generate a signal larger than the maximum possible from the AFM. (I hope this sort of makes sense!)

Do the existing maps/tables in the ECU extend /or are extendable for the wider signal range and can the standard injectors and fuel pressure provide the additional fuelling load required of the additional air? Is a custom chip part of the plan? Could the existing chip be mapped to accomodate?

 

Theoretically the gains should be much better than seem to have been reported for current aftermarket conversions. What do you think should be achievable on an otherwise standardish car if the fuelling is set properly to match the extra air?

 

 

I got lost after "Does the Output........."

 

On a serious note theres been debate that the K&N filter doesn't protect the engine as well as the OEM paper on, is this fiction or fable?

 

I think you mentioned the possibility to retained the OEM filter, this is a plan B?

Edited by Beaky
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