R35 GTR MAF, HPX MAF testing

[Matt]

Thursday afternoon we ran up my R34 using Z32 MAF as a baseline and compared against R35 MAF and HPX MAF inserts in a 3" adapter in suck through configuration

Using a baseline setting of 280rwkw on the R34 the max voltages on the MAFs were:

R35 (5.07V max)
Z32 (4.7V max)
HPX (3.25V max)

It can be seen from the above that the R35 MAF does not 'read' as high as the Z32 in this size tube so for greater HP figures a larger tube and VQ map would be required. HPX allows for much greater measurement in the same size tube

Housing sizes (ID = internal diameter, OD = external diameter)

R35 housing 74mm ID, 80mm OD
Z32 sensor 71 mm ID, 79 OD
VMC supplied HPX sensor housing was 76mm ID, 81 OD

HPX Testing reused the R35 Low Brain housing due to size issues of the large blue hosing fitting in my engine bay. Initial 3" VQ map used with this housing but require some adjustment for idle (mid range also needed some adjusting but ran out of time)

Previous testing on my vehicles with the VMC tube illustrated idle issues (due to lack of air filter and tube length). The shorter adaptor with filter provided a more stable idle after some minor adjustments to the lower end of the VQ map and I will perform driveability testing next week. Several tuners on here also using HPX have needed to tweak the existing VQ maps (from 0.10.14 release onwards) for their particular configurations but with success

Previously I had tried a blow through setup with 2.5" piping as pictured but due to the sensor insert offset (due to having no raising block on the sensor) this require adjusting the VQ maps heavily to compensate for lack of proper offset. I will source a proper 2.5" pipe and retry the test in blow through in later testing

Previous test dyno graphs
58 GREEN = Z32 run (K=489)
63 PURPLE = R35 GTR run (15% K constant decrease from Z32 MAF)
65 YELLOW = HPX MAF run (adjust K up to 1200)

[vip performance]

Nice!! so what are your overall thoughts of the HPX Maf?? I still need to get my car on the dyno but the end of summer is crazy busy at the shop!!

[PL]

We didn't do a full tune using the HPX - just banged some figures into place to get AFR's reasonable so we could do a comparison of maximum voltages at the same HP level for all 3 AFM's. HPX gave 3.25V at the same hp as the Z32 gave 4.7V. So it's definitely king of the horsepower heap!

It wouldn't run very nicely at all down low at the start. Had to increase the lower numbers in the VQ map quite a bit. Seemed to be pretty sweet then, but we didn't edit the higher areas of the VQ map. We just got the K constant in the right place to give safe AFR's and did a run. I'm thinking the higher areas of the VQ map are probably OK.

I think Matt's gonna swap from R35 to HPX and do some more road testing/tuning to see what they're like in the real world. Hopefully come up with a decent VQ map - at least for that size pipe.

PL

[Matt]

Thats the plan. VQ map auto adjustment needs some work still in the software since I would like to use that to calibrate the maps whilst driving

[skylinegtrhr]

Can You please post some dimensions of this plate on which maf is, or is it just need to be in center of 3" tube?

[Matt]

The sensor block is 10mm in height from the middle of the sensor. With the housing outer diameter of 80mm, radius = 40mm

Therefore sensor sits 50mm from the centre of the tube using the block. If we were to use a larger diameter tube one could lower the block height but it may not be enough to keep the sensor in the centre and may require subtle VQ map changes (in addition to changing VQ map for the increased tube size)

[skylinegtrhr]

!

It wouldn't run very nicely at all down low at the start. Had to increase the lower numbers in the VQ map quite a bit. Seemed to be pretty sweet then, but we didn't edit the higher areas of the VQ map. We just got the K constant in the right place to give safe AFR's and did a run. I'm thinking the higher areas of the VQ map are probably OK.

PL

Hi Pete can You please wrote right procedure for VQ editing (I'm talking on car that wasn't tune previous on some other MAF):
I presume is that as usual we first put main fuel map to zero disable O2 sensor and get K to idle about 14,7 and then edit VQ?
Please correct me if I'm wrong as I'm preparing to start one car with new engine which wasn't tuned before and as MAF is after turbo I can't put some else MAF to start from it.

[PL]

Hey Mario,

I must admit it's something I haven't played with myself either.

The idea was to get a tuned car with Z32 AFM (Matt's R34) and then simply swap to the other AFM and adjust the VQ map until we got the same results with the new AFM. We only did the low load portion. High load portion actually didn't seem too bad.

I did an SR20 last night that had the Z32/550 combo installed and reasonably tuned. Changed to R35 AFM and did the full tune. Hardly had to change anything - just dropped the R35 VQ map in and away it went. Pulled a bit of fuel out via K constant but that's about all. Not sure what max AFM voltage went to - but I took a log so I'll check that out tonight. It was only a little T28 (S15 turbo) so it won't have even come close to maxxing it out.

PL

[nissangts]

Hi Pete, would you assume that it is reasonable to say that the HPX MAF on a RB25/26 should be able to fascilitate 600 kilow @ the wheels?

[PL]

With these "drop in" sensors it's really just a matter of putting them in a bigger pipe if you run out of capacity - and tune VQ map to suit. They quote the HPX sensor as good for 700hp in a 3" pipe. So I put that at about 420rwkw. But fit it to a 3.5" or even 4" pipe and the figures go up a lot.

Bottom line though, is the same as turbo sizing, cam selection and injector sizing - you use the SMALLEST one that will give you the power you want. Obviously using one of these in a 4" pipe may cause you some issues at idle/low load cos the airflow at idle is little more than a light waft of air across the sensor!

PL

[dmac_25]

Matt/Pete

What was the final result for the 3" hpx vq map did the idle light throttle areas clean up with tuning the vq map from what we converted years ago.

Is the plan to use your tuned vq map in the list of afm's for a 3" hpx pipe??

I take it Matt the 2.5" test will also get updated in the vq list if that's what the plan is.

Never had to do any vq tuning yet as haven't had a chance to use the hpx in the car I had it planned for.

[Matt]

I can make available my tune (once I drag it off my other laptop) but it needs some road work to get the mid range running better

I would not be doing 2.5" unless I can get a better pipe where the sensor is in the middle of the pipe. In my last setup the sensor was about 3/4" way in the pipe and required significant VQ map changes

[djstatic]

I would not be doing 2.5" unless I can get a better pipe where the sensor is in the middle of the pipe. In my last setup the sensor was about 3/4" way in the pipe and required significant VQ map changes

I might be able to knock something up for you. What length do you need the 2.5" pipe?

[Matt]

Same length as Z32 MAF (replaces my existing MAF)

[dmac_25]

Nice Matt. I know a few people were having trouble with the original vq map that we derived years ago not idling I take it you sorted that out a fair bit then.

Do you think once you have the 3" vq sorted to go to a 3.5" pipe to scale the vq by X% or just tweak the k as the curve in theory should be close