TheMagikMan

Nothing is making sense. My tune is pretty good, and my MAF readings and injector utilization are consistent with making around 270 crank horsepower. With a double hump head, 10:1 compression, SLP shorty headers and matching y-pipe, 3" exhaust all the way back, and 3" intake tubing I should be making like 330hp at a minimum. MAF reads 204.44 g/s at 4725rpm as a maximum and my 24lb injectors are at 70% max PW (Both consistent with 270-280hp after some math). It seems like there's a flow issue somewhere and I can't for the life of me figure out where. This is incredibly frustrating. Any idea where I should look for missing power? The BLMs are pretty stable after a few iterations and I'm getting minimal knock. But this is driving me NUTS. I have a hyd. roller COMP XR269HR grind, mildly ported and 2.02/1.6 valve heads off a 69 Z/28. Everything on this motor should be supportive of 350-400hp and yet, it doesn't feel or appear even close to those numbers. Any place I should start looking? I don't seem to have a vacuum leak or anything either. From the research I've done, this 358 small block should be a little monster. Stock 86 TPI does match the cfm of the cylinder head intake runners after finding online sources for both (202cfm as-cast for the heads, 198-202cfm bone stock on the runners). This is driving me crazy!

Edit: links for similar spec cam dyno sheets (engine specs included) are below. My cam part number is 8-502-8
https://www.compcams.com/xr270hr
https://www.compcams.com/xr264hr

ULTM8Z

Do you have a WB O2 to verify your AFR?

TheMagikMan

I do not, however you can roughly tell by where the NB voltage sits, and I'm at about 880-890mV so it's right around 12.4:1

Komet

Is this stock TPI? Those other parts might be able to hit 330hp, but not at the rpm the TPI wants to flow at.

Fast355

iTrader: (2)

Is this a Camaro or Firebird?

ULTM8Z

Not sure you can make that assumption. From what I understand, NB voltage is not an indicator of a particular AFR.

ULTM8Z

BTW, 10:1 compression with iron heads and a cam with only about 218°@.050? What octane fuel are you running?

Wonder if the ECM is pulling timing out due to knock. That'll definitely kill power.

BadSS

If you're estimating 270 rear wheel by your extrapolations through an automatic, with drive accessories, and exhaust, then that converts to approximately 338 fly wheel HP which is what those other graphs you link were. Sounds like your not far off the mark to me. In fact pretty good with those heads and if the TPI is stock.

TheMagikMan

It's a Firebird. 1986 Trans Am to be exact.

TheMagikMan

I run 93 octane. Viewing my datalogs, the ECM only detects knock on downshift when the RPM spikes, which is likely false knock, but I can't get it to stop applying knock retard no matter what I do to disable it in the BIN.

TheMagikMan

I'm estimating 270 at the crank, although it's unclear if my estimation tools use crank horsepower or wheel horsepower. I need to get it on a chassis dyno at some point to look and see exactly where it's at.

ULTM8Z

how much retard is happening? Real knock or not, if the ECM is pulling timing, you'll lose power.

TheMagikMan

3.5 degrees at most under WOT, and it all recovers before I get into the next gear.

Fast355

iTrader: (2)

I 2nd his comment. I absolutely can determine WOT AFR from a GM Narrowband.

890mv NB also corresponds to ~12.3 on my AEM Wideband.

930mv = 12:1
880mv = 12.5:1
830mv = 13:1
450mv = 14.7:1
100mv = 15.5:1
30mv = 16.5:1

Fast355

iTrader: (2)

If it still has the stock air filter and ducting that could definitely be your choke point. SLP had to redesign the air intake ducting and filter setup on the Firehawks.

TheMagikMan

It does not have the stock air filter, it has one of those ebay 3 inch intakes with a pod filter on it, which is bad for MATs but flows way more than the stock airbox.