Kwik89GTA

iTrader: (12)

OK, here's the problem...

My buddy, Chris89Formula has just rebuilt his engine, here are the specs:

1989 165 ECM MAF
4 bolt block 355 ci
forged crank, 5.7 rods, 8.5:1 forged pistons
LT4 HOT CAM. 1.6rrs
Vortec heads, SDPC Vortec lower, Superram runners and plenum
42lb FMS Injectors, Racetronix 255 high pressure pump, Vortech FMU
Paxton SN93 charger, MSD 6AL BTM box
SLP 1 3//4 headers and full SLP catback NO cats
No EGR or AIR pump.
Centerforce clutch, Gforce rebuilt T5, spohn torque arm
3.73 gears, MT Drag Radials 275/40 17

Here is the problem, this engine makes poor power, I raced him in my g/f's factory SLP equipped 350 formula and we ran dead even until we both let off at around 130mph..... Her car runs between 13.99 and 13.80. His idle is up and down in RPMs but the air fuel ratio is steady under load...

With tunerpro scanning it, the O2 sensor frequently goes to 4.44 volts and the idle suffers badly, but under load the o2 reading is between 850 and 900 mv. Timing is set at 6btdc. I have no idea about total timing under load, This is the third mail order chip that he has had. Two from ed wright and one from PCMforless. No dyno in the Atlanta area that we can find "burns" chips. Everyone has concentrated on the flash LS1s. His car is drivable but suffers from very low power for what he has. The car will not spin the tires unless it is linelocked.
It seems like everything is right as far as air, fuel and spark but I cant put my finger on why the power isnt there.... Could it be the low compression or the vortec heads? A combination of a few things???

Any help or ideas?

Later, Kevin

SpitotRs305

the power loss you discribe isnt from the vortec heads... it is a tuning issue
think it is time for him to learn how to burn his own chips

Kwik89GTA

iTrader: (12)

That was my first thought (tuning) but with the o2 readings steady, I was leaning more towards the low compression of the motor with only 4 pounds of boost. He really doesnt need that low of compression with such a low boost number.

Maybe nitrous would wake it up!

calebzman

iTrader: (3)

I'm running the same compression w/ no problems. It is the tune. If the a/f is good, it's probably a timing issue. Put a light on it and figure out the total timing.

sofakingdom

iTrader: (1)

How do you know this?

Have you verified that the timing mark is accurate?

What happens if you advance the timing until it starts to ping (being gentle and careful about that aspect of course)? How far do you have to advance it to get to that point? If you have to go more than 10°, your timing marks are off. A common cause of this is using a stock crank damper in conjunction with a bolt-on timing tab. This will cause the REAL ignition timing to be about 35° retarded from whatever the light says.... in other words, YOU THINK it's at 6° BTDC, but IN REALITY it's at about 30° ATDC.

SpitotRs305

why only 4psi? that engine could take 10-15psi all day long... as long as you aint scared

Kwik89GTA

iTrader: (12)

I personally havent verified the timing marks on his car but it is a 8" SFI Fluidamper with the ZZ4 plastic timing cover that has the timing mark cast in to it.

I have set the base timing on the car up to 10 degrees before it shows spark retard on the scan and it is very slow when cranking it over....

As far as 4 psi... that is all that the SN93 Paxton supercharger will push. With the pullies on it now, it is at the maximun impeller speed (35k rpm). It has the upgraded impeller with a 6 rib serpentine. The belt really starts to slip at around 5000 rpm. The motor was built with the hopes the the upgraded blower would push a little more air than it does. It has been rebuilt too.

I really think that there is alot more in his motor. I say a bigger blower or nitrous the thing. But really, I will keep everyone informed if I find out anything. Any other suggestions?

Later, Kevin

Sonix

iTrader: (1)

I don't think any of the hard parts have anything to do with that. Being in the high 13's basically.
I see a pretty good combo there, mid 12's without breaking a sweat.

It's gotta be something silly, bad plug wire, bad coil, leak in the exhaust throwing off your AFR, timing completely out of whack, weak spark, etc etc. I'm basically putting my money on it being spark related somehow, or, as a 2nd guess, fuel or air.

Kwik89GTA

iTrader: (12)

FOUND THE PROBLEM!!!!!!! His brand new from summit racing MSD 6AL was firing when it wanted to above 3k rpm.... He hasnt had it back to the track since I took the box off but it pulls GREAT on the street.

THis was a hard one to find, I found it by trial and error. When I had a timing light hooked up, it would fire great, but it wasnt firing under a load.


Later, Kevin