sideways_Into_3rd

Here is a brief list of my mods...

Ported LT4 heads (302 / 224 @ 600 lift)
CC306
FLPs
52mm TB
home made 4" PVC CAI (with 2 90* bends and a 4" to 3" reducer on the maf)
Descreened MAF (not ported)

the car made 371 RWHP on the dyno and 342 RWTQ (pretty low for the amount of head and cam i got) though the fuel pump was running out of juice at 4500 .. (but thats besides the point)

the car also ran 12.1 @ 116 mph (M6, slicks, 3500 lbs)

but heres what makes me wonder ... the MAX maf reading i ever seen out of this car is 272 AFGS

my question is .. WHY SO LOW ?! i cant figure out why my maf reading is so low ...

a friend of mine locally has a set of nice LT1 heads with the GTP5 cam .. (236/236) and his maf maxes out at 371 AFGS .. another friend with smaller heads and CC305 maxes out at 320 AFGS and made 350 rwhp ... (both thru 48mm TBs and descreened mafs)

is it my MAF thats bad ? is it my porky CAI thats causing turbulance ? is it my heads ? is it my cam ?

am i REALLY flowing 272 AFGS at 6500 rpm and still making 371 rwhp ?!

heres some pictures of my sewer pipe CAI and my dyno chart .. open to any ideas / suggestions

thanx

Picture of my home made CAI
(ps. very old picture, still had stock heads / mac headers back then)

Dyno sheet

AlexA

My car makes 60+ rwtq and 15+ rwhp then yours and tops out at 317 gm/s @5,600 RPM. I have some valvetrain issues at this RPM but the AFGS isn't *that* far off.

BTW, 302cfm on the intake side? How big are the ports?

-Alex

Injuneer

If you just take 116mph on a 3500# car, my calculator shows 436 flywheel, 373 rear wheel with 14% loss on an M6. So your dyno sheet seems to check.

I'm always a little skeptical of LT4 heads that flow more than 300cfm, and I know what my heads flow and I know mine flow a lot less, and I make significantly more HP - yes its a 381, but the heads have to flow. I've also seen comparitive head flows for a huge variety of LT1/LT4 heads, all done on the same bench by the same operator, by a shop that has built the quickest 4th Gen LT1 on the planet, and there aren't many heads in their catalog that flow more than 300cfm.... George Baxter's (1,125fwHP) come to mind.

Next, the issue of "GPS". A stocker, at 275HP uses maybe 250gps. If you look at 437 flyHP, 0.46 BSFC, and 13:1 A/F you see maybe 330gps at peak HP. You would get a similar air flow if you approached it another way and looked at 350ci with a 90% VE at 6,500rpm. So your 272gps at 6500rpm doesn't make any sense at all. Your friends' numbers seem more rational.

The design of your intake isn't causing the problems.... a poor intake would cause excessive pressure drop, air density would drop, mass air flow would drop, and HP would drop. If you were really flowing 272gps, you would only be making maybe 350HP. But you're making the HP, so it isn't the cold air setup that's causing the oddball MAF reading.

Have you had the PCM programming altered in any way.... specifically, have you altered the MAF frequency vs. GPS table at all?

Have you ever had the A/F ratio checked with a wideband? If the MAF meter is reading that low, the PCM would be adding a ridiculously low fuel rate, and it would be running lean. Unless, of course the miscalibration of the MAF sensor is relatively constant across the flow range, and the PCM is building up some healthy BLM numbers in the 150-160 range.

What are you BLM's?

Have you altered the PE tables to change the target A/F ratio at WOT?

Have you checked for a massive air leak after the MAF sensor?

Have you ever tried someone elses MAF sensor, that you know produces the readings you are expecting... 300+GPS?

JSK333

IIRC, my stock engine with 4" CAI and 3" cutout pulled around 270-something GPS around 5400 RPM... so I'd say your sensor is malfunctioning, or as Fred inquired, your PCM may have been altered in the MAFS frequency tables, etc.

sideways_Into_3rd

well, the heads have been ported many times .. GTPII .. then MTI .. then flow tech in WA .. and was last flowed by flow tech in WA... i'll get them flowed again once i rip the motor out (sometime in the near future) ...

well considering i only made 371.. i wouldnt say im actually making any decent power out of my setup . so maybe the CAI design IS actually hurting proper airflow ???
and i still dont understand how i can make even 371 rwhp with that low MAF readings

the PCM has been programmed many times by myself. though im prrrreetty sure i have stock MAF tables in there.. i will double check !!!

the A/F was checked on the dyno ... as the readings appear on my dyno sheet. it was running lean towards the top end because my fuel pressure would drop (either dying pump or bad filter... both are getting changed) i had the 30# injectors at 100% DC towards the top end (PE values in the +30s ) to try to compensate for the fuel pressure issue ... but needless to say im not gonna keep that stock pump in there...

there shouldnt be any air leaks after the maf... and i will try another MAF sensor soon (once i manage to uncease my damn street twin (another pain in the butt ) and post the results.


so to sum it up

i'll check the maf tables
try another maf sensor
possibly try a proper CAI setup

and i was still reading that low from the maf !? toss the heads in the garbage ?

Schurters LT1

Just for fun have you tryed to clean your m/a with carb spray? you would be surprised on how just little dirt ie k@n spray will make the car go lean?

and you said that with your 30lbs inj you hit 100 d/c with them i have stock in tank and just a inline with stock 24 lbs and i only hit 80% d/c but i had my f/p up to 60 psi? and i only made 350 rwhp ?

good luck!!!

AlexA

Fred hit it on the head - what are your BLM numbers like? If the MAF is reading wrong (meaning more air is coming in, but it reads too low), then the car will always be running lean and your BLMS will be 130+. The assumption is you haven't adjusted the MAF tables (why would you?) and you haven't compensated for this lean condition by lowering your injector sizing.

I would look for leaks in the intake track (especially the elbow UNDER the TB), check intake manifold bolts for tightness, check hoses running into manifold for cracks, and consider trying a different MAF.

-Alex

OneFlyn95z28

JEEESUS!

SID I JUST figured out why your HP is so low!
You STOPPED the Dyno at 6,300? Why? My combo(Simular to your but smaller heads) does not PEAK till 6,800!

Take that thing back and spin it up to par!

To make you feel better at 6,300 I am only making 378RWHP. At 6,800 I peak at 394.99

I Would look there for your missing HP. tha combo needs to be shifted at 6,900...only because PCM will fuel cut at 7k.

The heads in question flowed over 300 when they left MTI the last time they were Checked again here in washington. I thought SID had them checked in Canada?

I agree there is some thing fishy with LT4 heads i always wonder about them myself. i have a set but have never ran them. We are getting ready to embark a on a strange journy to get them to flow like AFR 215RRs

Good luck SID!

sideways_Into_3rd

schurters LT1: by m/a .. do u mean MAF ?? no i've never cleaned my maf .. didnt know u could spray it with carb cleaner !!!

fred / AlexA .. my BLMs were ugly on the old 30#er .. they were way split !!! one side way lean one side half decent .. i recently upgraded to 36#ers (awaiting the walbro still) .. and only fired it up and idled the car .. and the BLMS were WAY WAY lean .. upwards of 130+ which was wierd .. now i dont know if its my brand new SVO 36s that are faulty or what ..

but next time i fire up the car i'll take a log..

unfortunately i have a ceased street twin so i cant really drive around and take a log of cruising

either way .. i'll try the MAF and double check my maf tables ..

thanx .. any other ideas welcome


Ellis, i wasnt spinning my car on the dyno .. the dyno guy was being very ignorant and told me that there is no point to spin hyd lifters past 6500 .. if u notice in my dyno sheet . my hp never leveled off or started to drop !!! so i figured if he'd spin it higher i could've hit some more hp

once i get my fuel pumpin properly i'll take it back and tell the guy to spin till he sees the light come on at 7k
considering my fuel pressure was at 15-20 past 6000 it probably wasnt a good idea to spin her much farther anyway !!!

next time i'll also try to remember to open my cutout ...

but i gotta solve the case of the missing AFGS before i hit the dyno again

thanx

ps. ellis wahts the specs on the 847 cam again ?

OneFlyn95z28

"considering my fuel pressure was at 15-20 past 6000 it probably wasnt a good idea to spin her much farther anyway !!! "

This says it all With fuel you should easily out dyno me.

Hopefully you have not toasted the ring's. I would not worry about the AGF if every thing else is falling in line They will probably come up with Fuel.

Jim is telling me you should with a 350 peak at around 6,600.

The way I have mine installed with 1.6 int and 1.52 ext.
GM #847 234/242 .575/.565 112LSA on a billet core Cost is $204 from GM parts direct.

Good luck!

sideways_Into_3rd

CheerZ .. c ya behind the lights

if u dont come up to race at mission this year im gonna have to make a trip down


ps. just checked my tune .. bone stock MAF table !!!

also found out that a friend of mine with a bone stock car has MAF readings higher than mine at 5800 rpm ...

Injuneer

You've got to keep you "problems" seperate from each other, or you are going to get confused.

Problem #1 - MAF Readings

There is no doubt you are actually making the HP, so there is no doubt you are actually flowing more that 275gps. In that case, no matter what the cause of the bad reading, the PCM is having to correct with added fuel, and you should be seeing BLM's way up near the limit.

-try another MAF

-clean your MAF

-look for another air source (wild stab in the dark - do you have the EGR valve removed and a leak on the blocking plate?)

-one thing that might make the CAI an issue would be a configuration that dumps all the air to one side of the MAF, throwing off the calibration. I don't see anything in your setup, except maybe that 4"->3" reducer is forcing the air all into the center or something??? Try putting the screen back in to correct the air distribution on the inlet side of the MAF and see if that changes the readings. I doubt it, but who knows. In designing a hot-wire flow measurement device (= MAF sensor), you should always try and maximize the straight portion of duct leading up to the device, avoiding bends and reductions.

Problem #2 - Engine isn't making the HP it should

Obvious issues like inadequate fuel, not revving high enough, poor air intake system, etc.

But you have to treat these as two different problems. I would also go very carefully through the tables in the programming and insure you haven't accidentaly altered something, or not updated the tables and input correctly.... maybe have them checked by someone else.

Schurters LT1

Yes you can clean your maf with carb spray clean clean clean it at work we have done e testing and you would not beleve the diff cleaning the maf does we are talking pass and fail here so give it a try.

With an intake leaking i don't think so your iac counts would be down very very low to the ponit where your iac is closed?

take baby steps and fix all the things to get the car at par then hunt for problems
good luck