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-   -   F.A.S.T. or TWEECER (http://forums.corral.net/forums/94-95-tech/512105-f-s-t-tweecer.html)

MYTKWIK 06-25-2004 09:29 PM

Quote:

Originally posted by jallen22
aim I wrong, or does the MAF only measure intake air velocity? if so, what compensates for the positive manifold pressure when under boost? it seems that for this situation, the map sensor (F.A.S.T.)would be a better route compared to the n/a setup that the eec (Tweecer) is geared for. but then its just a guess
This is where most people don't think the equation through. The MAF mesures mass of air and the ACT (air charge temp) sensor messure the temp of the air. If you have those two values you can calculate precisely the volume of air entering the combustion chamber. This is way more precise than speed density and map. Research it... That is why Ford left speed density and went to MAF systems!


BOOST OR PRESSURE DOES NOT MATTER!
Give one reason you need to know the pressure of the air. Air/Fuel ratios is about the amoust of air/fuel in the combustion chamber. Where in that formula does pressure come in? If you know the air entering the chamber (ie maf/act). The all the eec needs to do is look up the desired lambda or a/f ratio and calculate the fuel injector open time needed to achieve this.

Do you see a map on the lightnings or cobras?

Nucking Futs 06-25-2004 10:46 PM

Quote:

Originally posted by AJMcCurdy
Stock EEC doesn't have a provision for boost.

Has anyone looked into the AEM setup for 'Stangs? I was introduced to one at EJ's Dyno shop, it's supposed to use stock sensor input and have wideband capability. EJ does ACCEL DFI and Superchips tuning, and he really liked the AEM stuff...

That is what I would like to know. They are REALLY expensive but after reading for days on the AEM website it seems it can do almost anything but buy you lunch.

I plan on keeping my car for many moons, not to drag it but drive every now and then. If I wanted to change motors or go turbo/supercharger it seems that the AEM system can take care of that. It also controls the tranny so I would only have to get that and not a Baumanator.

SVTCobra347 06-26-2004 01:56 PM

I disagree on the boost not mattering. The engine control has to have "knowledge" of a boost level, or you at least have to have provisions for the injectors to open more and back off the timing under high boost, I.E. a boost retard and a rising rate fuel pressure regulator or FMU. You wouldn't need either if the computer reads boost. It could possibly do so off the ACT, but it wouldn't be that reliable. Too many other things affect the air temp.

That's probably one reason why they don't run very high boost on the Cobra and Lightning. Look at aftermarket turbo kits for most vehicles. They run what, 6 PSI? That's a waste of a turbo, but it is easier to manage. Us turbododge guys don't hesitate to run boost in the high teens, up to a couple of guys running 30 lbs+. And that's on a MAP system. Grand National guys are the same way.

I haven't looked into the Lightning or S/C Cobra much, but I guarantee that computer has some kind of provision for controlling timing and fuel under boost. Otherwise putting a smaller blower pulley on would simply scatter the engine every time.

MYTKWIK 06-26-2004 02:11 PM

Quote:

Originally posted by AJMcCurdy
The engine control has to have "knowledge" of a boost level, or you at least have to have provisions for the injectors to open more and back off the timing under high boost, I.E. a boost retard and a rising rate fuel pressure regulator or FMU. You wouldn't need either if the computer reads boost. It could possibly do so off the ACT, but it wouldn't be that reliable. Too many other things affect the air temp.
That doesn't give me a reason. Why would the injectors need to open more due to boost? They open more do to amount of air. An opened up intake track will flow the same air at lower boost level than a closed up intake track at high boost. How would a MAP matter there? FMU's are used where there is a lack of ability in the injector or lack of size only. ACT would be better for spark control than a map because you want spark to vary on density of air not pressure of air which would be measured by the temp. True many things will effect the temp. But you want to take all of them into account.

Side note I don't need either a spark retard of FMU and didn't for years. It ran completely fine at 15lbs of boost. There are many example of this all over.

Scott Gladney 06-26-2004 02:58 PM

The computers that use a speed density setup (ACT and a MAP) infer air flow based on pressure and temperature. This type of setup is less friendly to changes in the engine than the mass air flow setup. With mass air, the computer doesn't have to infer air flow based on some conversion of pressure and temp, it knows it based on the output of the MAF. You can build in a "boost retard" to a MAF based system if you want. You just go in and at higher air flow numbers and start to pull timing back knowing that as you get up to that amount of air flow you are in boost. It will work just the same as the boost retards that are built into many igntion boxes now, but based on true air flow and cylinder charge instead of just a pressure. That is a much more desired setup in my book. Just my two cents.

Scott

dynotronic 06-27-2004 08:18 PM

"aim I wrong, or does the MAF only measure intake air velocity? if so, what compensates for the positive manifold pressure when under boost?"

No, the MAF measures air mass. If you increase boost on a given engine you increase air mass. On '94'+ EECs the fuel and spark are basically computed from the MAF voltage. Thus, if your MAF reads less, such as an oily hot wire caused by a K&N filter, not only do you run more lean but your ignition timing also gets advanced. Also, if you go to larger injectors and replace your MAF with one that is calibrated for them, you will increase your timing because the MAF voltage scale has been reduced to compensate for the injectors, so you also need your spark tables reprogrammed. One thing to watch out for on a MAP system. If you have a given boost, then modify your engine, this will cause more HP but less boost. Because MAP system's spark tables are vacuum/boost referenced, you have just advance your timing but increased your cylinder pressures - bad.

EJ

GT5.0 06-28-2004 12:20 PM

wow, jako and MYTKWIK, im impressed with both of you, you both seem to really know your stuff, and make valid arguments for both sides of the story. ive got two questions

open-loop and closed loop, whats the difference?

and am i personally in danger of running lean with my motor with the stock ECU? its got a long block perfectly capable of taking in enough air to make 400 N/A hp, but ive still got the stock intake/TB/mass air and injectors on it. 355 stroker with 9.5:1 compression, box-stock TW heads and the TFS stage 1 cam. am i getting too much air for the 19lb injectors to handle? it seems to be doing great thus far, but if we get a cold day is it in danger of running safely?

thanks guys

MYTKWIK 06-28-2004 02:38 PM

Quote:

Originally posted by GT5.0

open-loop and closed loop, whats the difference?

Open loop is when the computer targets a fuel ratio based on a number tables based on intake air, temps, etc. In closed loop the computer tries to be the most efficient and maintain good emmissions. So it runs off the feedback of the O2s, they cycle around stoich (14.64) and the eec tries to maintain that ratio via adaptation.

Open loop is usually when a car is first started until it reaches normal operating conditions and stabilizes. Open loop is also used at WOT for better fuel ratios/power. Closed loop is all other conditions.

Quote:

Originally posted by GT5.0

and am i personally in danger of running lean with my motor with the stock ECU? its got a long block perfectly capable of taking in enough air to make 400 N/A hp, but ive still got the stock intake/TB/mass air and injectors on it. 355 stroker with 9.5:1 compression, box-stock TW heads and the TFS stage 1 cam. am i getting too much air for the 19lb injectors to handle? it seems to be doing great thus far, but if we get a cold day is it in danger of running safely?

First I would say you are loosing power with such a small intake track for those heads and motor size. Your injectors are also too small. It's not that you getting to much air for the injectors, it's that you not getting enough fuel for the air LOL. Of course with a change in MAF and injector size you should adjuct the EEC accordingly

GT5.0 06-29-2004 02:09 AM

haha, i know, i know. im holding out for the turboHPmotorsports kit that includes a fuel pump/MAF/injectors with the turbo/intercooler and accessories to save on money. my real concern is detonation. obviously we cant be certain on anything without putting it on the dyno and hooking up a WB O2, but are there any easily recognizable symptoms of running lean? ive had the car up to 6500 rpm+ regularly without a problem and i dont plan on shifting any higher than that. in the opinion of everyone here, hopefully with racing experience, is there any substantial chance that im going to have a freak accident that drops the bomb on my internals?

MYTKWIK 06-29-2004 10:21 AM

Quote:

Originally posted by GT5.0
but are there any easily recognizable symptoms of running lean?
Pull the plugs and see what they read.

Anaconda 06-29-2004 11:20 AM

Quote:

Originally posted by fox racer
i saw a 670 hp camaro convert. with 22mpg and the FAST kit.
How does that relate to ANYTHING in this thread? Different car, different engine, different electronics setup, different gearing....

GT5.0 06-30-2004 05:06 AM

thanks MYTKWIK, if i do get it to the track, i'll let you know what kind of times you can pull with a stock intake and 19 lb injectors ;)


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