3" MAF/MAFT Combo Questions...

[QuickSilverGSX9]

I'm having a hard time interpreting data and tuning via the MAFT from Ramchargers. If I lean things out, I start getting knock, anywhere from 9-18 counts in fact, and if I leave it at where it is right now (all settings zero'd out), I seem to hit some kind of overrun/fuel cut randomly.
When I hit this overrun/fuel cut, I'm getting no knock and good timing all the way up, at, and even after this happens.
My set up is as follows: 3" exhaust from the o2 back (w/ 3" cat), Walboro 255 high pressure fuel pump, 3" '95 Imapala SS maf, MAFT, and hallman MBC (at 16 psi). As for monitoring, I have a Boost and A/F Gauge, and a pocketlogger.
Also, Drziplock mentioned putting the switch on the MAFT to the ON position for the 3.5" size, I did that just to see if it would help, and I hit my overrun/fuel cut problem even earlier, sub 4000 rpm's.
If anyone has any advice, I'd really appreciate it, I have this nagging feeling that something is wrong, I may be just nuts though, who knows.
-Bill

 

[HighPSI TSi Guy]

i think you are just hitting fuel cut man.. lower the boost and see if it happens..

 

[QuickSilverGSX9]

Well, considering I hit this overrun/fuel cut problem on 14 lbs. of boost, I don't think it's fuel cut. I'm not sure though, who knows. I appreciate the reply though Dave, I think you're the only one who thinks I can be helped.
-Bill

 

[t90tsi]

i am having the same problem with my translator setup. i cant even run 15psi as opposed to the 18psi i was able to run on the stock maf. ive had every switch in every possible possition and it still cuts out. i talked to dave at dejon tool and he told me to call this guy mike at ramchargers to see if there is a fix. seems like we are not the only 2 that have had this problem. seems like there is something faulty with the translator, there might be a recall in order soon if they cant fix this problem. if i find anything out though i will let you know. if you find anything out please do the same.

 

[hostile]

What size injectors are you guys running?

 

[Tallen]

richen up the mid ALOT and see what happens...

 

[HighPSI TSi Guy]

Originally posted by Tallen
richen up the mid ALOT and see what happens...

he technically shouldn't have to run it rich.. part of it i'm sure has to du with the fact that this outflows the stock MAF by like 300%.. part of it also probably has to do with the internal workings of the MAFT that we dont know..

 

[t90tsi]

im running stock injectors, im thinking that they are running at 100% duty cycle and ive heard that injectors can lock up when you max them out like that. i have some 550s but wont be able to put them on till next week sometime, since im away at college. but im hoping this solves my problem. if it does ill keep you posted, because im pretty frustrated right now with the all the bucking. seems like people that have bigger setups on bigger injectors arent haveing any fuel cut problems and claim their cars run great. i just have a stock turbo, exhaust and fuel pump. my friend did some datalogging once and maxed his injectors out at 18 psi on his stock turbo and maf. so i think the injectors is where the problem lies.

 

[QuickerDSM]

It would make sense that you are hitting fuel cut. The less restriction on the inlet side of the turbo allows the turbo to spool faster and flow more air earlier than before. Even though you're running the same boost level the total cfm of air is greater than before.

I hit boost cut at various rpms also, but mine is more to do with ambient air temps (as well as too small injectors). Early in the morning when it's still relatively cold outside, I hit fuel cut at 5k or so. Later in the day when it's over 55 deg. I can run it up to 6k to 6.5k.

Mike

 

[Awdboost]

We need more info on your mods. What kind of turbo, injector size? S-AFC. We need more details.

 

[Tallen]

as i said...set all settings normal...
a: drzip prolly told u that b/c he suspected you may have one of the odd 3" MAF's like i do. if it didnt work dont sweat it
b: my car doesnt like the default settings either
c: you really cant tune well when your FP is probably reeeeallly high
d: i basically got rid of low gear knock by richening up the "spoolup shot" of fuel. my MID setting is like 20% richer than my WOT. as i said before...richen up the MID and give it a run. i think you will like the results.
e: something sounds squirrely...may be boost or FP

 

[QuickSilverGSX9]

hey Tallen, on the MAFT, is the mid setting dependant on the RPM's or throttle position? I'll try richening up the mid, see how the works for me. From looking over all my logs, I really get knock when I start to go WOT and the RPM's increase, that may be my mid range and therefore just need some richening up. I'll do that and see how it works, MID's the only setting I haven't played with yet. Also, you actually advise getting an AFPR? If you do, which one do you suggest?
-Bill

 

[nine5raptor]

Originally posted by QuickerDSM
It would make sense that you are hitting fuel cut. The less restriction on the inlet side of the turbo allows the turbo to spool faster and flow more air earlier than before. Even though you're running the same boost level the total cfm of air is greater than before.

unless he improved the VE of his engine or raised the boost, the total cfm is the same as it was before.

 

[nine5raptor]

Originally posted by QuickSilverGSX9
hey Tallen, on the MAFT, is the mid setting dependant on the RPM's or throttle position? I'll try richening up the mid, see how the works for me. From looking over all my logs, I really get knock when I start to go WOT and the RPM's increase, that may be my mid range and therefore just need some richening up. I'll do that and see how it works, MID's the only setting I haven't played with yet. Also, you actually advise getting an AFPR? If you do, which one do you suggest?
-Bill

with the rpm wire unhooked, the maft uses solely airflow to decide which correction to use. mid is around 1-8psi, wot is 8+

with the rpm wire hooked up, the maft uses airflow/rpm to decide which map to be on by figuring the load.

 

[HighPSI TSi Guy]

Originally posted by nine5raptor


with the rpm wire unhooked, the maft uses solely airflow to decide which correction to use. mid is around 1-8psi, wot is 8+

with the rpm wire hooked up, the maft uses airflow/rpm to decide which map to be on by figuring the load.

the MAFT does NOT know "PSI" it know airflow and RPM. i would assume mid to be the mid RPM range, i would check with mike though. you shoulda said you hadn't messed with mid.. i would have told you to richen that up.. i was under the impression you had tried playing with all the settings.. richen up mid some and see what happens.

 

[nine5raptor]

Originally posted by HighPSI TSi Guy


the MAFT does NOT know "PSI" it know airflow and RPM.

that is what I said, go back and reread it. Mike is the one who specifically said to *assume* the airflow ranges are approximately equal to 1-8 psi and 8+

and no, mid is not the mid rpm range. these are load based tuning devices, not rpm based like the afc.

 

[HighPSI TSi Guy]

how can it be load based when it has no way of knowing load? all the MAFT can know is RPM, airflow, and temp.. that is all.. it does not know throttle.. throttle and boost have the biggest effect on load.. if he is using airflow to determine mid/hi then it won't work properly. you can never assume x airflow = y PSI because different turbos flow differently at different ammounts of boost..

EDIT: i just reread what you said it answered half of what i just said.. if what you say is true it is a very innacurate tuning device...

 

[kpt4321]

Throttle position is actually not a good determinant of load, manifold pressure is MUCH better.

The MAFT can make a guess at boost, but it will not be super-accurate. However, there is no reason for it to guess at boost, when boost is just a way to estimate airflow. I would reason that it switches between the mid and high settings with the rpm and airflow calculations.

 

[HighPSI TSi Guy]

you cannot estimate boost with airflow!! different turbos flow different air ammounts at the same PSI!!!

you are right about pressure beign better than throttle though...

 

[nine5raptor]

the amount of air two turbos can flow is unimportant when putting them on the same engine (neglecting the larger exhaust housing effect). What determines the amount of air you actually flow at a given boost level is the ve of the engine, not the size of the turbo (for the most part).

This device switches maps based on airflow. It says that right in the owners manual. If the rpm wire is hooked up, it uses airmass/rpm (which will give you a very good idea of the load on the engine) to decide which map to use.

 

[QuickerDSM]

Originally posted by nine5raptor
the amount of air two turbos can flow is unimportant when putting them on the same engine (neglecting the larger exhaust housing effect). What determines the amount of air you actually flow at a given boost level is the ve of the engine, not the size of the turbo (for the most part).

This makes sense, but if you free up the restriction on intake side of the turbo, it will flow more air earlier in the rpm range. He isn't running more boost because of this, but he is hitting full boost earlier than before.

Here is an example: On superchargers like the Vortech, when freeing up the intake side of the SC, it typically gains 1-2lbs of boost by doing this. Now I know it's different with turbos because they are "load sensitive", but with everything else being equal, it's very comparable. He is increasing the efficiency of the turbo by freeing up the intake side.

Mike

 

[nine5raptor]

a lower boost threshold doesn't matter as it takes rpm into consideration. whether it is 1 slug/min at 2000 or 2 slugs/min at 4000 or 3 slugs/min at 6000 it doesn't matter as the unit still uses .0005 slugs/cylinder/rev. to estimate the load and pick the map to use.

btw--for those that don't know, a slug is a unit of mass in the english system. 1 slug=14.59 kg for those that are used to the SI system and 1 slug=1 lb/32.2 ft/s^2

fyi--1 slug/min = 32.2 lb/min, so very few if any dsms can flow the amount of air I used above, but it made the example easy.

 

[nine5raptor]

Originally posted by QuickerDSM
Here is an example: On superchargers like the Vortech, when freeing up the intake side of the SC, it typically gains 1-2lbs of boost by doing this. Now I know it's different with turbos because they are "load sensitive", but with everything else being equal, it's very comparable. He is increasing the efficiency of the turbo by freeing up the intake side.
Mike

he may lower the pressure differential across the compressor, making it easier for the turbo to spool/compress, but the engine can still only flow the same amount of air at the pressure level, you can't flow more air past the valves at the same pressure level, by lowering intake restictions.

also, since we have a mbc, the boost cannot go up 1-2 psi as in the case of the supercharger where all of the energy given to it is used to compress air. Ours bypass the extra energy through the wastegate.

 

[QuickerDSM]

Originally posted by nine5raptor


he may lower the pressure differential across the compressor, making it easier for the turbo to spool/compress, but the engine can still only flow the same amount of air at the pressure level, you can't flow more air past the valves at the same pressure level, by lowering intake restictions.

I understand that it will flow the same cfm at the same pressure/rpm. What I'm saying is that because the intake is freer flowing, it will build boost earlier in the rpm range. Say before it maxed at 12lbs at 3000rpms, now it will hit 12lbs at 2500rpms. You don't think that will have an effect on overall flow through the valvetrain?

Originally posted by nine5raptor


also, since we have a mbc, the boost cannot go up 1-2 psi as in the case of the supercharger where all of the energy given to it is used to compress air. Ours bypass the extra energy through the wastegate.

I know this, that's why I said they are different, although the same basic principle applies. The compressor is still freer flowing accross the entire rpm range for both the turbo, and SC assuming the load is the same for the turbo. Obviously the turbo's boost will be limited by the MBC/Wastegate, but it will still produce max boost at lower rpms....

Mike

 

[nine5raptor]

Originally posted by QuickerDSM
I understand that it will flow the same cfm at the same pressure/rpm. What I'm saying is that because the intake is freer flowing, it will build boost earlier in the rpm range. Say before it maxed at 12lbs at 3000rpms, now it will hit 12lbs at 2500rpms. You don't think that will have an effect on overall flow through the valvetrain?
Mike

read this (my other post), it explains how it takes into account for the earlier boost:

a lower boost threshold doesn't matter as it takes rpm into consideration. whether it is 1 slug/min at 2000 or 2 slugs/min at 4000 or 3 slugs/min at 6000 it doesn't matter as the unit still uses .0005 slugs/cylinder/rev. to estimate the load and pick the map to use.

btw--for those that don't know, a slug is a unit of mass in the english system. 1 slug=14.59 kg for those that are used to the SI system and 1 slug=1 lb/32.2 ft/s^2

fyi--1 slug/min = 32.2 lb/min, so very few if any dsms can flow the amount of air I used above, but it made the example easy.

chris