Learn me up on MAF tuning!!!
Thread Starter
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
-Greg with 27 lb injectors you could support around 400 to 420 RWHP. This assumes a BSFC of .4 which is actually pretty good and may not happen and a injector duty cycle of 90%.
-The fuel pressure being stable is all related to your pump, if you have the correct pump it will be stable.
-The stock MAF sensor will be out of range at 254 g/s at around 350 engine HP, that means all additional fueling will need to be added by the RPM vs fuel adder table. (The MAF will not be able to detect any additional airflow)
-Sure you can run 400 RWHP with a stock MAF but as explained the fueling will no longer be controlled by the additional airflow seen by the MAF but instead by the RPM vs fuel adder table
-The point of the 3" blowerworks MAF is to allow you to read the actual air entering the engine and have accurate fueling across the entire RPM range
-The only way to know if your 3" MAF (even a blowerworks MAF) is holding you back is to see how much intake vacuum you have at WOT. If the entire air intake system shows an intake reading of 95 KPA or less at WOT I consider that fairly restrictive. (My 3" system on my 434 CID reads 88 KPA at WOT which is terrible, this car makes around 400 RWHP and would benefit greatly from a 4" system) Just have not got around to building it yet.
I do have a 4" blowerworks MAF laying around and may consider selling it. You still need to get the correct definition file on your laptop to tune the car and the correct bin file. You could use my bin as a start point but the definition file for tunerpro I do not have. (I use Tunercat). You may want to talk with the forum member I mentioned earlier he may be able to help you.
-The fuel pressure being stable is all related to your pump, if you have the correct pump it will be stable.
-The stock MAF sensor will be out of range at 254 g/s at around 350 engine HP, that means all additional fueling will need to be added by the RPM vs fuel adder table. (The MAF will not be able to detect any additional airflow)
-Sure you can run 400 RWHP with a stock MAF but as explained the fueling will no longer be controlled by the additional airflow seen by the MAF but instead by the RPM vs fuel adder table
-The point of the 3" blowerworks MAF is to allow you to read the actual air entering the engine and have accurate fueling across the entire RPM range
-The only way to know if your 3" MAF (even a blowerworks MAF) is holding you back is to see how much intake vacuum you have at WOT. If the entire air intake system shows an intake reading of 95 KPA or less at WOT I consider that fairly restrictive. (My 3" system on my 434 CID reads 88 KPA at WOT which is terrible, this car makes around 400 RWHP and would benefit greatly from a 4" system) Just have not got around to building it yet.
I do have a 4" blowerworks MAF laying around and may consider selling it. You still need to get the correct definition file on your laptop to tune the car and the correct bin file. You could use my bin as a start point but the definition file for tunerpro I do not have. (I use Tunercat). You may want to talk with the forum member I mentioned earlier he may be able to help you.
- I'm a little suprised you quote 90% duty cycle. Is that your observed limit? Is it readily acceptable (vs 80%)? Are the odds of not going "static" decent?
- I called Racetronix today and found out I bought a 255lb/hr Walbro in 2014. They said it can support 550rwhp and at least 4 bar pressure (58psi). They also suggested I need to upgrade my stock wiring harness -- even though it's been fine for the past 9 years.
- I'm considering an HSR that I've had for years OR an FFI. The FFI comes with a bigger TB which makes it more likely I'd want > 3" MAF. (Or, if I find a deal on a 52mm TB). I also have a 4" aftermarket air box (passageway) so there may be good reason to seriously consider a larger MAF. If you decide to sell, please let me know.
- The issue of a different BIN (prior post refering to the difference in our editors) escaped me. I would think the BIN is the same regardless of which editor used to read and alter it.
Thread Starter
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
1986-1989 TPI MAF system limitations above 350 hp
Note: much of this is redundant to what has already been discussed above. Solutions are available. BSFC and injector %DC values were selected for convenience/consistency across both examples, but should be reasonable for this discussion.
Factory TPI MAF sensor limitations (1986-1989):
approximately 359 hp (assuming 86% DC and 0.44 BSFC).
Factory ECM software limitations:
(12.8 AFR) * (2.20462 lb/kg) = 158.11 lb/hr mass fuel flow rate. ECM software supports approximately 359 hp @ 0.44 BSFC.
Factory ECM hardware limitations:
Note: much of this is redundant to what has already been discussed above. Solutions are available. BSFC and injector %DC values were selected for convenience/consistency across both examples, but should be reasonable for this discussion.
Factory TPI MAF sensor limitations (1986-1989):
- Failure-prone Bosch sensor
- Potential flow restriction/pressure drop due to screens, heat sinks and housing diameter
- Limited sensing range
- Open element design is susceptible to reversion
- Temperature sensitive (not suitable for high inlet temperature and pressure)
- Calibration variation
- Sketchy replacement quality in the aftermarket
- Fuel injector capacity 23 lb/hr
- Fuel pressure regulator variation
- Fuel pump capacity
approximately 359 hp (assuming 86% DC and 0.44 BSFC).
Factory ECM software limitations:
- 255 gm/sec air flow range
- Calculated PW is mathematically limited at very rich target AFR settings limiting PE effectiveness. Sorry $6E users.
- DTC sensitivity (Codes 33, 34 and 36)
- Limited load range
- Random scanning/connectivity issues
(12.8 AFR) * (2.20462 lb/kg) = 158.11 lb/hr mass fuel flow rate. ECM software supports approximately 359 hp @ 0.44 BSFC.
Factory ECM hardware limitations:
- Eprom/Memcal programming
- 8 bit A/D converter
Factory TPI MAF sensor limitations (1986-1989):
- I used MAF scalar tables to retune my 383/TPI combo. It seemed to work fairly well including the use of a descreened MAF.
- I would like to hear more about Bosch MAF limitation (heat, air force, etc). I have to assume higher HP sends higher forces into that skinny wire!!!!
Factory fuel system limitations:
- I agree there are variances in stock pressure as I've seen a range of values reported over the past 15 yrs. That's one reason I "upgraded" to a new fuel pump. It also seems to have eliminated the tendency to starve fuel in corners at lower levels. That said, I haven't pushed it as hard in the past 10 years (thru corners) as I did for the first 14yrs.
Factory ECM software limitations:
- I'm not familiar with "DTC". Or, I can't remember it? The codes you list I've seen for the MAF....low/high voltage errors. -- Could you elaborate on this point?
- What limitations have you seen in PE enrichment for $6E users? Pretty sure that applies to me for an 89 with a 165 ECM.
- What are the load limitations?
- I can confirm inconsistent ability to connect laptops to my car via ALDL port. Possibly poor quality ALDL cables being manufactured?
- Looking at your example, are you suggesting mixtures richer than 12.8 --ABOVE 359rwhp-- can't be acheived?
Melting Slicks
Joined: Apr 2001
Posts: 2,121
Likes: 223
From: Ca.
This thread sure does bring back old times! I started with tunercat 32 and 6e, converted to speed density now using ebl p4. One other method to deal with the maf limitations back then was to rescale the maf tables. You would increase the upper limit proportionally across the table but you could lose a lot a resolution.
