Tuners / Gurus step inside - help me diagnose air flow numbers

[BuickMike]

Here is the story -
My buddy has a '87 GN with 11k miles.
Mods are:
TT chip - street tune (91 octane)
3" cold air intake
Accufab adj FPR
Adjustable HD Wastegate actuator
42lb injectors
test pipe with WBo2 bung
Walboro 340
Hotwire

We were trying to get it running correctly and finally figured out that it had a wrong part # reman MAF. MAF #'s were really low and it was lean under WOT at the time.

So, I just so happen to have a good OEM one and we swapped it in.

At this point the car runs great. WOT at 15psi has no knock .....but something is still catching my attention.

Even at 15psi MAF #'s will not hit 255. For example on a 3rd gear pull they start out at 225-230 on shift and work up to 245 or so at the top of the gear. Mt WBo2 shows AFR at 11.8 initially and quickly jumps to 11.5 and works its way to 11.1:1 at the top of the gear.

Before we start here.

Yes, fuel pressure is good. We taped a gauge to the windshield and watched it at WOT. 45psi static and 59 at boost.
Yes, the TPS is set correctly.
No there is no vacuum leak.
I believe my MAF is reading correctly.

That all being said, we all know that boost is not going to equal airflow. My GN is going to be pumping WAY more air at 15psi for example.

So what I'm getting at here is...those who say that the MAF should hot 255 at 15psi....what are they basing this on?
--I'm guessing everyone saying this may have a bigger IC, ported TB, bigger DP, catback, etc.

So let's just assume that his "low" MAF #'s are caused by some restriction post turbo, what could we improve to get more out of the car?

My thoughts are that the stock catback is really restrictive and could be an issue. We can test that by running an open DP and see if the numbers change.

My other thought is that the #3 exhaust lobe could be worn down a little due to maybe the last owner running crappy oil. I learned the hard way when I bought mine. We can probably test that theory by pulling the valve cover and measuring the lift against another rocker on the exhaust side, but I really don't want to pull his virgin, non-leaking valve cover for nothing. I doubt this though. When my cam wore out my car spooled miserably and knocked like crazy over 12psi. His spools strong and pulls hard at 15psi. Plus mine had a real specific exhaust note that was obvious a cylinder was not firing right.

So after all this crap I wrote...do you all think the stock exhaust is much of a restriction in street trim?

 

[TurboDave]

My first question would have to be; When referring to your "OEM" MAF. What exactly do you mean by OEM? Means different things to different people.

Back when I was running a MAF on my 86, and before I started running extender chip, my maf would usually hit 255 at about 12-13# of boost, and they should hit that by 15#.
My 87 (still running a stock maf) hits 255 at just over 13# of boost.

It's possible that the stock exhaust could be playing into this. It's been so many years since I've run one! And back when I did have a stock exhaust, scan tools were non existent for the masses.

 

[BuickMike]

When I say OEM, I mean the real deal unmolested original part MAF. Back in the day my GN would hit 255 on the MAF around 13psi or so too, but I had a ported turbo inlet bell and compressor housing, 63mm TB, port matched upper plenum, Melling OEM replacement cam that is slightly more aggressive than stock, ported turbo elbow, and a hooker catback. Those things are all going to make more airflow at the same boost and that should reflect in the MAF readings. I'd be willing to bet that a motor with cam and heads would max the stock MAF out at 10psi.

 

[bison]

Why would it be a concern if the air/fuel numbers are ok? Even a little rich. When you say 15psi are you using a calibrated MAP sensor or pressure transducer? The air meters reading are very easily changed by altering the air inlet even with no air flow change. I wouldn't expect a lot of boost on 91 octane without knock retard. 15 would be pushing it on 91 octane without an anti detonant


BPE2013@hotmail.com

 

[BuickMike]

Only concern is that maybe I can get more power out of it. 15psi is the max on this car with 91. Any more and I would have to dial timing back a couple degrees. Maybe it will make more power, but 15psi is fine. My thought here is that if those with a few more bolt ons like DP and exhaust are saying that the MAF pegs at 13psi where it takes about 16psi for the MAF to peg on this car, my logic is that removing some restrictions, like a ported elbow and good catback would net higher air flow and probably a good 30+hp while keeping it dialed in at 15psi.

The easy way to try this theory is to have my buddy run the DP open and we will go log again. If we get higher MAF #'s at the same boost, then it's exhaust time lol.

 

[bison]

I've never seen 30hp from a DP on a close to stock car. Maybe 5hp. Maybe an open exhaust and cat delete would get 30hp but usually the boost will jump up quite a bit from the open exhaust.


BPE2013@hotmail.com

 

[BuickMike]

Yeah, I'm with you on the DP not making much of any difference. My point may have come across wrong. My thought is that the stock catback is really restrictive and is holding the car back a little. I'll have my buddy pull the test pipe and run the DP open, dial the boost back in at 15psi, and measure MAF #'s. If they come up quite a bit or peg then the car theoretically is sucking in more air.

Getting more in depth on this. Eric emailed me and said that WOT fueling kicks in on his chip when MAF readings hit 23o or 235 if I remember right. He basically made the chip with the idea that MAF #'s are going to hit 255 and stay there. Since it is below there and creeps up, that is why we are seeing the AFR start out a little lean and go rich when the MAF finally gets over 235. If removing a restriction keeps those #'s pegged fueling will be pretty solid and I will be able to dial in the AFR to whatever makes the car happy.

Stay tuned. Not sure when we will have time to perform this experiment.

 

[TurboTdr3.8]

On my stocker when I added the DP it helped and removed the cat it helped more too so both dp and delete cat I could tell a big difference from factory dp and cat . At 91 and 15lbs I believe you are at the end of the rope to be on the safe side of no KR .

 

[BuickMike]

On my stocker when I added the DP it helped and removed the cat it helped more too so both dp and delete cat I could tell a big difference from factory dp and cat . At 91 and 15lbs I believe you are at the end of the rope to be on the safe side of no KR .

I agree and I'm not trying to get more boost out of the car. I'm trying to get more volume through the motor. The less restriction on the way out the better. More volume at the same boost level equals less heat / more power.

 

[TurboTdr3.8]

I agree and I'm not trying to get more boost out of the car. I'm trying to get more volume through the motor. The less restriction on the way out the better. More volume at the same boost level equals less heat / more power.

That cat holds some back so that might be what you are looking for

 

[BuickMike]

That cat holds some back so that might be what you are looking for

The cat has been removed and replaced with a test pipe. I'm really thinking that the stock exhaust sucks so bad that even in street trim on a stock car that it is being held back.

 

[we4Mateo]

The cat has been removed and replaced with a test pipe. I'm really thinking that the stock exhaust sucks so bad that even in street trim on a stock car that it is being held back.

Probably not. The stock exhaust will flow fine at your mass flow. You probably wouldn't notice a difference other than noise if you ran straight out the test pipe.

 

[Jerryl]

MAF reading at 15 psi @ 4000 rpm is way different than 15 psi @ 4800 rpm.
What was the rpm?

 

[bison]

The cat has been removed and replaced with a test pipe. I'm really thinking that the stock exhaust sucks so bad that even in street trim on a stock car that it is being held back.

We've gone 121mph through the stock exhaust with an unopened engine. It's hard to swallow that but no BS.


BPE2013@hotmail.com

 

[BuickMike]

We've gone 121mph through the stock exhaust with an unopened engine. It's hard to swallow that but no BS.


BPE2013@hotmail.com

Wow. I wouldn't expect that. Of course that being said, it is pretty easy to overcome handicaps on turbo engines. I think there will always be really good debate going on when it comes to mods. There is always the argument of "I went this fast", or "made this much HP" with a certain part.

For example, let's pick a part on my car....perhaps my G body SLIC. It is a smaller unit with 2.5" piping. If someone asked me if going FMIC is worth it I would probably respond that my SLIC has gotten me to 120mph down the back end with 20psi on 91 / alky on street tires in a 3750lb car that only has a TE-44 and so on. That being said, if I finished that run and swapped in a FMIC, set the boost back to 20psi and made another run with all other conditions being equal, would I pick up any MPH? My guess is that yes, I may see another 1-2mph. Does that matter to me? Hell no. My car is faster than I ever wanted it to be....especially since now I was able to dial it in at 26psi with AFR and timing being the same.

Since the MAF is not maxed out yet on my friend's car, it will be easy enough to see what happens to the numbers if we run the DP open and set boost back to 15psi. We are using a mechanical boost gauge BTW. I am surprised that his digital gauge seems to hit the first red LED at 15psi. I don't ever think I've ever seen one that was even remotely accurate on another car.

Maybe in a week or 2 we will pull the test pipe for giggles and grins and see if there is any difference at all. Even if there is no change, the fun of going through the "what if's" and trying it on my own is worth the fun.

Bison, I doubt I'll ever make my way to your neck of the woods or Bowling Green for that matter, but if I ever run into you it would be fun to have some beers and talk shop. I always appreciate when you add your thoughts and knowledge to technical threads.

 

[earlbrown]

Need to pull those virgin valve covers and put some new valve springs in there.


(while you're there, a timing set wouldn't be a bad idea either)



Lately I've been reading that it takes 15# to hit 255.... Years ago the general consensus was it took about 17#. Not sure what changed.

 

[BuickMike]

Need to pull those virgin valve covers and put some new valve springs in there.


(while you're there, a timing set wouldn't be a bad idea either)


Lately I've been reading that it takes 15# to hit 255.... Years ago the general consensus was it took about 17#. Not sure what changed.

Yeah timing set and springs would be good at some point. This is 11k miles so I doubt the timing set is an issue yet. I could see the springs being worn from being compressed for so many years, but they feel ok.

The difference in consensus over the years most likely relates to the common upgrades people had on the cars. I can tell you that on his car 17psi would be needed to hit 255, but remove some restrictions and I'm willing to bet that the psi required to hit 255 will go down. Most people now have 63mm TB's, modded or aftermarket upper plenums, at least a dutt neck IC, 3" DP, catback, etc. I mean, who the hell is still driving around with a stock exhaust anymore?

I will test out my theory in a couple weeks and report back to y'all. Until then you all can think I'm completely nuts

 

[earlbrown]

Those springs were weak in 1987 and the timing set is almost 25 years old. Mileage isn't a factor on those two parts. The rocker buttons are over 1/4 century old too.

 

[turbo nasty]

That nylon plasticky cam sprocket let's go and you'll be sorry. Age can cause cracks

 

[TexasT]

Have you checked the boost gauage against another one? Might not be accurate.

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