Lorenfb

"because the stock unit had failed"

Do what?

MitchB

I think the assumption here is the stock AFM failed.

I've been watching these threads for some time. Many Dynos have been posted, but only SSI's is a true back to back comparison of only the change to a Vitesse MAF - done by an independent third party. Call me crazy - but that looks like a significant improvement. 25+ HP with a stock CAT...
Warren - I hope those are RWHP numbers - not actual flywheel numbers!
One could assume (!) that if the exhaust also was improved - to get the gases out more efficiently, even greater gains would be seen.

One thing that hasn't been discussed is the improved throttle response with a MAF. It is the "nature" of a AFM to restrict airflow. It has a door to Airflow that uses a spring to keep it closed! The air flow has to push the door open before it can flow, creating a slight (albeit noticeable) hesitation at lower RPMs.

It doesn't take an engineer to look at an AFM and a MAF side by side on a bench to figure out which will flow more air. Combined with improved mapping that matches the 964 3.6 chacteristics to the specific MAF can only be a win-win. I have personnally experienced John's expertise with mapping DMEs (my old 951) and by all accounts he is very very good at this.

Every poster that has switched to a MAF reports an improvement. Be it better idle, smoother acceleration or outright HP increases (generally all three..).
That's good enough for me. John - will be in touch next week.

Cheers.

SSI Performance

Sorry, I'm not entirely sure what you're asking but one of our customers had a malfunction with his stock air meter. He had no intention of modifying the car however the cost and availability of a new stock air meter made Johns kit very appealing.

It's a little misleading but that is RWHP data, I believe the Dynapack units label the window 'flywheel' because you may enter a multiplier which will calculate engine power while you're operating.

-Warren

jneteler

Personally, I prefer the RWHP numbers as that is what is being measured. And if you think about it, it is also the value that is most important. Who cares what the flywheel HP is if you can't get it down to the road.

The factor is based on a number of assumptions which may or may not be true in every case.

Regards,

JNeteler

Lorenfb

"Every poster that has switched to a MAF reports an improvement."

So where are the data to support it? The case has been made for how an objective comparative
evaluation should be done. This has yet to be posted on Rennlist. All that are presented
are data for compounded mods without attributable results to the key mod, i.e. MAF.

By the way, in my 25+ yrs with many Bosch systems utilizing AFMs, few if any AFMs fail.
Most replacements occur because of poor engine diagnostics or the "roll of the dice"
or the dart "said" replace the AFM.

MitchB

Where is YOUR data that says it's not true?

I think it's pretty damn pompous to sit in CA and tell the good folks in Baltimore that they don't know how to diagnose a failed AFM. They do fail. Pretty simple to diagnose when you take one off and put another one on and problems disappear. That's what I did on my previous 951. Guess I should have requested your long distance diagnostic skills...

A scientific (objective comparitive) comparison must have a back-to-back comparison where only ONE variable is changed, afterwhich data is compared. Change anything else but the single item - different car / dyno / ambient temp / tire pressure / exhaust and the comparison is tainted - and the comparison useless. SSI said they didn't even take the car off the dyno when they switched from AFM to MAF on a completely stock RSA (gotta be the only one left with cat still on it..).

If you can't see that SSI's dyno chart is (finally) a back-to-back - same car/same dyno/no other mods - AFM vs. MAF comparison, then you simply are refusing to consider data or calling them liars.

I don't think they are liars - from Warren's post it sounds like he was NOT pushing a MAF, it was just cheaper than the AFM.

But hey I didn't work for Bosch for 25+ years...

N51

RWHP is the most subjective and the least important.

jneteler

Do tell us why. I'm willing to learn something new.

JNeteler

Lorenfb

"A scientific (objective comparitive) comparison must have a back-to-back comparison where only ONE variable is changed"

That's exactly correct, i.e. only one variable changes!
But with the MAF change, two variables are changed, the MAF and the chip.
And from the standpoint of the chip, what was really changed;
1. just the fuel maps
2. or both the fuel and timing maps.

So that's the real unknown which conflicts with the above statement.
I'm quite sure no one is going to allow a chip inspection which results
in the claim that ONLY one variable changed being highly questionable.
This gets repeated over and over again without it "registering" with some!

N51

Given two experienced and competent technicians, one with an engine dyno and the other with a chassis dyno, both are accurate. With this exclusion, the engine dyno is not skewed with a loss factor. Whatever changes are made, are exact.
The chassis dyno numbers, as they move up or down with any changes, are magnified by the loss factor. As we've seen, the loss factor is not a universally
accepted number. Varies from one tuner to another.

Your car was rated, by Porsche, on an engine dyno.

jneteler

Noah,

Point taken on engine versus chassis dyno.

My comment was directed towards chassis dyno figures everyone seems to be throwing around.

Regards,

JNeteler

springer3

I have been hearing the matra about the AFM air flow restriction for years. It is a myth. A MAF needs a venturi (choke) to channel the air flow to the hot wire. The hot wire has a support structure in the air flow. Every MAF I have seen has a wire mesh to protect the heated wire. The AFM is larger because it does not need a venturi. There is objective data: Colin's post showing that the AFM reduces HP by 4% with the paper element. Remove the air filter, and that effect is gone. In other words, use the filter from your MAF upgrade on an AFM, and you get the same air flow improvement as the MAF conversion.

Not true. There are quite a few posts from disillusioned MAF converters. A stock 964 in good tune has excellent idle, smoothness and power.

Is the MAF better technology? No question. Is it cheaper? The mechanical claptrap in the AFM makes it an expensive piece. All modern cars have MAF because it is better and cheaper. Does MAF work better than the stock air flow meter on a 964? Debatable. Is it worth spending $2000 to get one? If you have a large budget and a highly modified engine, no question. For a street car with the usual modest performance upgrades, the objective evidence is that you can get the same benefits keeping the AFM.

SSI Performance

I'm not sure why that was necessary or relevant to the subject at all. I think any experienced technician will agree that making an assumption like that is a poor method for any automotive diagnostic procedure.

I appreciate you sticking up for us but I just recently found out from a very experienced Bosch fuel management specialist that replacing the air meter and having the car operate properly was actually just a mere coincidence.

They both have their applications in regard to tuning. In most cases I prefer the chassis dyno because the wheel output is the scope of the engines labor and you're right, it's often important to be able to factor the other variables of the driveline.

-Warren

deoxford

Guy's
I have one of the first MAF , I believe made by John. And I will say that till this day I am very happy with it . I track the car mostly and can tell you that I can keep up with most new cars on the track asides from the new 997s. 996's can pull away on the back straight but it takes them the whole section to do it .

I think I got about the same 299 or so in the dyno , and need to go back soon and will repost the numbers.And when the system first went in , I was the car that got beating by Paul's. I still don't know why. Maybe it was in limp mode, I am not sure. But I can back up what Paul is saying to be true

This has been a great upgrade and like I said I have been very happy with it on the track. I can't tell you how many times I have heard " what did you do to that car" The engine has held up pretty good to, and John can tell you I am not easy on it. It just got and new reseal and cams "while your in there " and the engine still looked to be in great shape.

So this is my 2 cents

rotorheadcase

I've got to back up what Derek is saying with my own experience. Our track is a fairly short tight circuit and it's only the latest exotic machinery ie. Turbos, GT2's and GT3's or dedicated lightweight track cars that I have trouble holding off. I can stay with, or out run pretty much any of the other cars in the club. Anecdotally, the previous owner of my car was following me at the last track day in his 997 and he remarked that the car was faster than it had any right to be. Obviously the MAF kit can't take all the credit for that as I've done a lot of suspension work and lightning of the car as well but for sheer straight line speed it's done a lot to make me more competitive with the newer crop of cars.

Say what you will, argue what you like, at the end of the day I'm more that satisfied with the performance gains for a relatively modest $1250.00 outlay. I'm not looking to convert anyone into true believers, just give a balanced view from an end users perspective.

Neil