jubelands

The truck on the dyno and made 460RWHP & 590TQ @ only 13psi. However right after 4000RPM's the power suddenly drops off.

The truck pulls insanely hard under part throttle on the freeway but as soon as i put my foot all the way in it, it feels like its hesitating and very rough. The truck feels like it has way more power under part throttle than wide open.

I just recently changed the spark plugs and the coil packs so i don't think its an ignition issue even though it feels like it.

Judging by the Dyno graph, i'm wondering if its a valve train issue such as valve springs or a lifted head considering the power drops off so abruptly?



Uncategorized - dyno click on this link and click full size

brainbypass mod

do you have a larger pic of that?

__________________
03 black lightning - VT powered, tuned by dynojoe.com
"And another thing.....when I gun the motor, I want the whole world to think it's coming to an end"
-Homer Simpson

oiN8io

are you able to get it any higher than 13 psi? even at part throttle?

__________________
1040RWHP/991RWTQ 25psi q16
TWIN TURBOS... enough said!!

jubelands

click on the link in he first post for a larger pic.

So the problem does happen at part throttle as well but only in boost and also its right at that point on the dyno where the power drops off, around 4000rpm.

BTW if you cant see it, the A/F is a flat 11.9 the whole way so its not a fuel issue either.

jubelands

I think the boost controller is set at 13psi, i dont think i'm getting 13psi @ part throttle but i'm not sure. Honestly i have no idea how to use the boost controller; the last tuner who attempted to tune it set it, but he said he was having problems past 4k with the tune as well.

I at first thought it was an ignition issue so i changed everything but i guess its still there. The last tuner said he though it was the valve springs but since he wasn't experienced with fords and since i was barely pushing 13psi I just brushed it off. Now i'm thinking he could have been right.

typhoon43

What are the stock springs rated at? Valve float at 13psi seems really low. If it is valve float, you'd definitely lose power up top.

skidmarkracing

need more info, what turbo, exhaust to turbo, from turbo. looks like a back pressure issue.

Agent 00 L

I am leaning towards Skid's theory here. We definately need more info on you combo. I've "heard" valve float becomes an issue around 18 psi, although I fed my combo a bunch more than that and it kept on making power.

__________________
2001 Silver Lightning, Stock Engine Turbo in the works
2000 Black Turbo Lightning RIP.
SCT Pro Racer Tuned, Stock Engine
540 hp/580 tq - 16psi, Pump Gas, Open DP
11.68 @ 120

BigBobsL

Sure what is being discussed here is that exhaust back pressure can be more than twice boost pressure. Ideally it will not be that high, but it will be higher than boost. If you left EGR tube in system, you can hook it a guage to measure back pressure.

jubelands

Motor is not built, stock heads, cams etc. Turbo is a T-76 ball-bearing turbonetics turbo. Piping to turbo is 4" intake tubing.

Crossover pipe from headers is 2.5" i believe. Exhaust from turbo is 3" downpipe for about 2 feet then opens up to 4" pipe and then splits into dual 4" Magnaflow straight through race mufflers

Prior to putting the exhaust on i did have the downpipe open and dumping about 4 feet after the turbo but the truck had the same problem even with open exhaust.

EGR is deleted as well.

1fst54

What's the AR on the exhaust side of the turbo?

mr12volt

You stated that you just changed the plugs and coilpacks. You didn't by any chance use aftermarket coils did you? I've had nothing but trouble with them!

A NEW set of ford cops with the plugs (NGK tr-6) gapped to about .028- .030 should be all the ignition system needs.

Check to make sure your crank sensor is plugged in all the way and not damaged. ( don't ask me how I know)

Data log your ignition timing under load and see what it is doing.


Hope this helps,

Paul

jubelands

The a/r on the turbo is .96.


I actually did go with aftermarket coilpacks, i went with the accel supercops. Nothing changed at all after changing the cops and plugs. I'll put the stock cops back on again just incase.

Where is the crank sensor so that i could check that. The timinng seemed to be fine when we were tuning it on the dyno. Max timing was set to only 14 degrees.

I'll try and datalog the timing under full load while drivng also though to see if theres a difference from the dyno.

Bad as L

Put a set of valve springs in it....good ones.

Also keep an eye on the air cleaner and make sure it is not collapsing on you.

jubelands

What do you guys think about these: LFP Valve Spring Component Kit Ford 5.4L SOHC [4516] - $249.95 : Lightning Force Performance

Air filter is in perfect condition also.