pulls great off the bottom till about 4500-5000. top does not feel as strong as it should. doesnt appear to be running lean or anything. took it to the track today and couldnt get better than 14.0@95. any idea of what could be causing this?

406
11.3 compression
motown 220 heads
LT1 intake
58mm throttle body
stock ignition
xe284 cam
3000 stall converter
stock gears for now

 

Are you knocking? What kind of gas are you using? Are those heads aluminum?

 

Did you just begin to have this problem or is this a new motor?
I was gonna suggest weak valve springs or ignition but you have something major going on. Looking at the components used to build the 406 you should have a trap speed of around 115 mph. I would guess your losing around 150hp. Check things like the gas pedal opens the butterflies fully, the air intake system is free of obstructions, pinched or kinked fuel lines, plugged fuel filter, low fuel pressure, bad fuel etc. Hope this helps.

 

this is a new motor. i checked to make sure that the throttle opens all the way and it does. they are stock springs on that come on the motown 220 heads. this doesnt feel like valve float. ill check the fuel filter tomm. i really hope to figure this out soon.

i am still running the stock 350 tpi chip. could this be causing it?

 

also what about plugged exhaust? i have removed the cat because it was falling apart. but even after its removed chunks of the cat are still blowing out of the muffler under WOT.

 

That's a good place to start. I forgot about exhaust.
Your motor should run alright with a chip from a 350 mass air car. My 350 ran good with a 305 chip. Are you using injectors from a 350?

 

yeah im using the 350 injectors.

 

Your injectors are too small for that motor. You should be running at least a 26-28# injector. If I were still on line at home I would give you the formula for the correct size injector. I would also add ten percent to the size they give you. Fuel injection is still like carbs in a way. A slightly larger injector than required still gives a little better Q-mile time than the "Correct" size. Another thing to think about is the MAF is restricting your airflow. Try the newer style that is less restrictive. It flows about 20% more than stock, better yet, convert to Accel DFI if it's legal in your area. I want to do that with my modified 350. BTW, I'm losing about 60-80 HP myself. I've been told the elimination of the MAF and better calibration through use of the Accel DFI will get that back for me. (From Granatelli Motorsports).....

 

miker61588:

The injectors are too small...also check your fuel pressure at higher RPMS to make sure that your fuel pump is working well...
Also...the most important thing...GET TUNING....sure the thing runs with the stock chip, but not anywhere near your expectations...because the stock 350 chip is a far cry from your combo...

Captain C:

Granatelli is no thirdgen engineering firm...they are primarily 4th gens and their info on switching to DFI is a bit premature...look for Ski_dwn_it (spelling?) and his posts on his MAF Vette running low 11's on a descreened, de-finned Bosch MAF. Eliminating the MAF won't get you the extra HP...tuning will



HTH,

 

I would agree that your injectors are too small, but that is not your problem. My 350 IROC goes 108mph in the 1/4 on 19lb injectors. It is a full weight car I will add. Don't do the injectors until you find out what is really wrong.

 

thanks for the help so far guys. i did notice one thing. i have never heard this engine get preignition or anything like that. even when i didnt add octane booster. at the compression im at it should ping with the additive in there. im going to disable the knock sensor and try it that way.

 

Even better than disconnecting the knock sensor would be trying to figure out what the computer is doing...

www.moates.net and look under Software (free)

Use it with a laptop, cable to connect it and go...you need to figure out what the sensors are saying before disconnecting the knock sensor...if the computer is detecting knock and retarding the timing, then you can figure on a course of action...but you don't know that...

BTW...if you can hear the audible knock...it is pretty bad, the knock sensor is much more attuned to it than your ears...

 

I agree with 88TPI406GTA

Deff. needs TUNING man thats where your loosing it all.

Your Prob running lean up top.

 

well i found one problem. one of the injectors was unplugged. a totally diff car.

 

That will deff. hurt.

but as said befor You have TONS of Power left untouched with tuning in the chip.

Atleast 50more hp I bet more if you could get it dyno tuned with a wb02 setup