skir2222

Well I found a nice interesting article about bypassing the air flow meter to get more unrestricted air into the motor on our turbo cars.

http://www.autospeed.com/cms/A_2424/article.html
http://www.autospeed.com/cms/A_2449/article.html

By adding a second pipe to the TID duct after the AFM the flow to the turbo/engine is increased. The only problem is that air coming in through the secondary pipe will be unmetered so something like a safc2 that can alter the AFMs signal to compensate for the addition unmetered air will be needed to modify the AFM signal so the car will run in the correct fashion and not get to little or to much fuel.

Since us S4 T2 guys cant upgrade/modify the AFM, do you think this would be a smart upgrade/idea?

I think we all could benefit from a modification like this and would see added gains to the cars performance.

I would like to see opinions on this type of modification...

arghx

iTrader: (3)

why don't you just install a standalone and take the airflow meter out completely? Also, it's not that restrictive on stock turbo and it's not really a factor on n/a engines in terms of how much horsepower is lost from retaining it.

skir2222

A safc is under 200$ where as a standalone is atleast 1k, I am not trying to imply that this mod can replace the afm but it would allow additional airflow.

NI_Racing

iTrader: (4)

Wouldnt an SAFC remove the need to evade the AFM anyways? SInce you can manipulate the air fuel mixture using the SAFC?

Evil Aviator

I think it is a complete waste of time. The stock AFM is good for about 400hp, and you would want a standalone EMS once you got to that point anyway. The main problem with the stock system in our cars is the crummy old 1980's computer, not the AFM. Also, the bypass would also really screw up the idle on a vane type AFM.

Those who don't have a background in aerodynamics tend to think that a little spring-loaded flapper door will suck ten thousand horsepower out of your engine.

rotarygod

iTrader: (1)

That mod isn't going to work on the RX-7. Although they refer to an "airflow meter", what they really mean is a mass airflow sensor which is a completely different animal. What kind of power are you making that you feel you need this? You can get an afm equipped engine well over 300 hp. You'll need to replace your turbo first though. You will also need to be able to properly tune it. I've never been a fan of the S-AFC as all those letters stand for are Stupid Air Fuel Computer which is pretty accurate. It is limited in it's abilities and can't touch timing. An Rtek would be a much better choice as it is basically a stock ecu that you can now completely reprogram, timing, fuel and all. It is also not $1000. For roughly twice the price of an S-AFC, you get full control, not just a few spots of fuel only. Forget you've ever heard of the S-AFC. It's for people who think doing it twice is cheaper and easier than doing it properly in the first place.

jackhild59

iTrader: (7)

I think you should try it and do a full write up. Let us know how it works, what the problems were, how you overcame them etc. The world is full of people who can tell you what you shouldn't do and why.

Start with a dyno, then finish with a dyno.

If it doesn't work out, then sell the SAFC. No loss.

Aaron Cake

iTrader: (1)

Doesn't a fluid like air always take the path of least resistance? This means that in the case of our flapper door AFM, very little air will end up through the AFM and instead will go through the bypass. There might not be enough air through the AFM to allow the piggyback to compensate.

And as others have mentioned, the AFM is not near as much of a restriction as many think.

j9fd3s

iTrader: (3)

i saw/read about someone using a second smaller AFM for the bypass, so at low speeds the stock AFM still works, but as you increase airflow the second one starts to work.

i think the emanage people were talking about that when that thing came out, waste of time now, and where are you going to put TWO AFMs?1

skir2222

This was just a thought and nothing more, I think its a interesting idea for someone who already has a safc.

I never said the factory afm was restrictive...

I only implied that this mod might be useful for someone wanting additional airflow, not to try and act as a standalone ecu... this has nothing to do with timing. This modification would only alter the afm signal to compensate for the additional airflow... THATS IT

this mod would be only for fc's with basic bolt ons and maybe a hybrid turbo, not a fully built fc because then you would need to alter timing if you are going to upgrade to a much bigger turbo then yes you would need a standalone ecu.

If you read the articles after the modification was done the backpressure in the intake went from 20 to 10inches of water... so there would still be some restriction so I am sure the flapper door pathway would still have plenty of airflow to pull the door open.

Once again this is only a idea and I think it would be beneficial to a FC with basic bolt ons and a safc.

I have a 87T2 with a hybrid turbo, 3" intake/exhaust, fmic, 720cc secondarys, emissions removed running on a stock ecu at 5-7psi.

I am interested in upgrading to a type of fuel management system but not standalone...

Why would I want to adjust my timing? I just want to adjust my fuel at idle, cruise, and wot so it will be getting the correct amount of fuel, not run lean or pig rich.

skir2222

As long as the flapper door still functions which I am sure it would then a safc should be able to compensate for the lose of air flow going through that path.

There has to be a massive amount of suction coming through the TID if the turbo is make 5psi or more so I don't see why the flapper door would not open as long as the second pathway is not larger then the pathway to the TID.

Evil states its not restrictive to 400hp so then this would defiantly work.

g14novak

iTrader: (1)

If your willing to spend all that money, why don't you just buy a RTEK 2.1 and remove the AFM all together?

For what you want to spend building a secondary inlet for the TID and SAFC (which is a terrible investment if you plan on future modding), you could get the rtek and it would go much further than that SAFC will. Would you trust a piggyback for a aftermarket turbo?

skir2222

I am not spending any money, just throwing this idea out there to see what others think and to read. With the Rtek you cannot remove the AFM, where did you get the idea that you can remove it?

https://www.rx7club.com/rtek-forum-168/afm-removal-877818/

The Rtek is a great upgrade, and yes it is much better then a SAFC, but the SAFC does what its suppose to do and works.

Why wouldnt I trust a safc2 with a aftermarket turbo? It adjusts fuel, but not timing, it does what its suppose to... but if I were to upgrade the turbo to something other then what I have now I would upgrade to a standalone due to the fact that I can't trust 20+ year old wiring.

I do plan on upgrading to either a Rtek or a SAFCII, this car is my daily driver and I would like to adjust the a/f to get it where it should be at idle, cruise, under boost/wot...

The SAFCII can do this just fine, but so can the Rtek.

How would the Rtek benefit me over the SAFCII since I will not be changing the turbo, so I won't need the ability to adjust timing.

I just want to perfect the setup I have now, I want everything to perform as best as it can, flow as good as humanly possible, and trim the fuel to deliver the appropriate amount under all conditions since its a little on the rich side with these bigger secondary's.

My whole goal is to get my setup to its limit, I know my setup can produce a lot more power then what its pushing now. I just need to make my final decision whether to go SAFCII or Rtek.

skir2222

Here is something for you all to read...

https://www.rx7club.com/showthread.p...hlight=max+afm

The stock afm maxes out between 325-350hp which defiantly is a good amount of power, but read at the bottem of the post about the HKS VPC. Talking about using that to rid of the AFM to make additional power.

The idea I posted up is almost just like that, you can get the additional airflow but you would need something like a SAFCII to change the afm's signal to compensate for the additional airflow.

This would be good for any Rtek user that is at the AFM's limit, this modification can raise the limit of power above 350hp while still having a functional AFM!

1SWEET7

iTrader: (1)

The SAFCII does mess with timing to allow the fuel to be pulled or added. I forget if it pulls or adds timing, but it does it without allowing you to adjust it. There are other threads on it. You should just get the Rtek.

RotaryRocket88

iTrader: (7)

The AFM removal is in the R&D phase right now, but you will eventually be able to remove it.

You already changed the turbo by turning it into a hybrid. At 5-7 psi, you're not pushing them limits at all, but if you choose to bring that up to something like 1 bar, you will want to have timing control. Stock timing is not suitable for anything other than the stock turbo, and above 9 psi, a stock ECU no longer pulls additional timing. Heck, I even pull some timing for safety with the stock turbo. With an SAFC, you'd end up having to throw lots of extra fuel at it to keep from detonating.

Chris Boots

and no-one has mentioned anything about putting the AFM after the turbo Its possible, has been done, yields good results like better throttle response I hear. Then no tid restriction. Do i run my turbo engines that way? No, but I could. The stock AFM is good up to 350hp and I can dig up dyno sheets proving it. A turbo upgrade works wonders. Probably wouldn't notice a difference if I ran management that deleted the AFM on one of my AFM cars that uses the AFM with the engine management in it, which happens to be... Rtek 2.1s haha. I can hit full boost all day long to what ever I set my boost controller to as early as 3500 rpms if not carefull with a turbo setup I have in one of my cars. Its a good idea, but not for our situation I think. We have AFM's, they're talking about mass air flow sensors. The flapper in our cars would probably not even work half as it did without the mod. -That goes double for turbo MAF's as compared to NA MAF's which have a lighter spring. Now S5 cars have mass air flow sensors... but... that would mean S5 cars have even less TID restriction, the result... eh.

Evil Aviator

Sorry if it sounds like everybody is jumping your case because you posted the link. We are ragging on the article, not you.

The spark plugs need to ignite at the correct time in order for the mixture to burn properly as the rotor travels through its cycle. A change in mixture or boost will change the speed at which the mixture ignites, which will cause the engine to run inproperly with the stock ignition timing. When the boost or mixture is changed beyond the stock level, then a corresponding change in timing will help gain power, keep the engine running cool, and reduce the chance of detonation.

The stock AFM actually already has a bypass passage for idle air, and the vane obviously still works. I just wonder if an S-AFC would be able to control the transition from idle with a gaping hole rather than a small calibrated leak.

The restriction is always in place, and it gets worse as the airflow velocity increases. It just doesn't become significant until around the 300hp range. Many RX-7s that were in the 350-450hp range back in the 1980s had the AFM relocated after the turbo so that the airflow velocity through the AFM was lower, which reduced the restriction. Now that you can get a standalone EMS for less than $1,000, there isn't much point in dealing with the stock EMS once the turbo is upgraded.

skir2222

The problem with placing the AFM after the intercooler is if you are cruising along the highway at 50-70mph lift your foot off the gas enough to shut the flapper door on the afm the car will buck...

I have done a lot of searching on moving the AFM to the ic piping, I think your just moving the restriction upstream, the afm can only read so high, so I wouldn't understand the benefit and I would come to think that it would change the way the car runs greatly since there's a intake temp sensor in the AFM and I'm sure the air before the turbo is much cooler then after the turbo.

I don't think ill ever run more then 10-12psi, I did search and did find that the safc will advance timing when you lean out the mixture. That to me is a little scary but many have used a safc with sucess.

I really do think that this would work due to the fact the SAFCII tricks the afm anyway, as long as the flapper door still opens, which I have no doubt that it will, then this will work.

Can't you change the spring tension on the flapper door? I am sure there would still be a good amount of restriction to open the door.

I just think this is very do-able and maybe Rtek owners can achieve a higher hp output since it would extend the limits of the AFM to maybe 400hp or even possibly close to 500hp? The rtek guys are already maxing it out, we know its limit.

Even if your not hunting for power you can free up some restriction with this.

If you think the door wont open then you can make the secondary pipe smaller then the primary so there is more resistance, even a 1" pipe would help assist everything and raise the limit of the AFM, do you agree?

The AFM door opens under vacuum, so I would think that it would still open with a 2-3" pipe with a Y since the turbo is trying to pull in enough air to produce 5-12psi.

skir2222

Chris, us S4 guys can wire up the S5 AFM... I searched it, but there is no gains to do so.