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What am I missing? Less than 300 rwhp atk_403

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Old 09-11-2018, 06:46 PM
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Default What am I missing? Less than 300 rwhp atk_403
I have a 403 ls2 that is dog slow. Makes no power past 5000 rpm, and way down on power under that. It has a fast 102 intake, prc 2.5 5.3 heads, 13.1 to 1 compression, a 624 lift 247-255 duration cam, 80 pound injectors, walbro 450 pump, e85, true duals, SD tuned. Engine is in a 99 camaro ss t56 trans. My tuner thinks it maybe an internal problem, atk thinks it maybe a sensor. I have a ton of time and money into trying to diagnose this. Any help would be greatly appreciated. Free case of beer if you can point me in the right direction.
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Old 09-11-2018, 07:03 PM
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Do a leakdown check first....
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Old 09-11-2018, 07:11 PM
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Damn, that’s sounds like it’s going to be a rowdy motor when you get it squared away. Damn that’s some big injectors for N/A unless I over read something.
What were you getting for fuel readings lean rich? If nothing popped up from the dyno what’s your drivetrain setup? Maybe something is a miss drivetrain wise.
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Old 09-11-2018, 07:42 PM
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Can you post the dyno graph?
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Old 09-11-2018, 07:44 PM
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Map sensor?
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Old 09-11-2018, 08:13 PM
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Originally Posted by neblackshirts
Damn that’s some big injectors for N/A unless I over read something.
Not that big of an injector when he's on E85.
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Old 09-11-2018, 08:14 PM
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As suggested above.... Leak down test and I would verify cam timing. Was the cam degreed on install?
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Old 09-11-2018, 08:32 PM
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These guys pretty much nailed the next step so need to go there again, but I'm curious why those heads on a 403 with a big cam and Fast 102? I'm just curious
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Old 09-11-2018, 08:39 PM
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Originally Posted by LLLosingit
As suggested about.... Leak down test and I would verify cam timing. Was the cam degreed on install?
yes atk degreed the cam. I will try the leak down test.
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Old 09-11-2018, 08:41 PM
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Originally Posted by wannafbody
Map sensor?
it's worth a shot. I will grab one of the leak down test goes well.
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Old 09-11-2018, 09:23 PM
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Are all eight of your headers primaries hot? That is dead cylinder(s) territory. You can have multiple dead cylinders on a rowdy cam and not realize it.
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Old 09-12-2018, 06:23 PM
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Originally Posted by LLLosingit
Not that big of an injector when he's on E85.

True on injector size and E85
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Old 09-18-2018, 01:18 PM
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Originally Posted by LLLosingit
As suggested above.... Leak down test and I would verify cam timing. Was the cam degreed on install?
cam timing was off a few teeth. Taking it down for a new dyno in 2 weeks
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Old 09-18-2018, 01:24 PM
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Good to hear you found something. How does it feel now? Cant wait to see dyno run.
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Old 09-18-2018, 01:46 PM
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Gotta feel WAAAY better with the cam straight up! lol
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Old 09-18-2018, 01:49 PM
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Originally Posted by spikestang
yes. atk degreed the cam I will try the leak down test.
Originally Posted by spikestang
cam timing was off a few teeth. Taking it down for a new dyno in 2 weeks

Yikes!!!
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Old 09-18-2018, 04:19 PM
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Wait -- a FEW teeth??? That's like 40 degrees off. Must have been retarded not advanced? Lucky no bent valves...
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Old 09-18-2018, 06:04 PM
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How in the hell can they say they degreed the cam,, and be off by teeth? If I paid for an assembly with a "degreed cam" factored in,, I'd be pissed if it was 2 degrees off.. Teeth off? wow..
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Old 09-18-2018, 06:05 PM
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Refund time.... or litigation... shop's choice.
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Old 09-18-2018, 07:04 PM
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Originally Posted by Darth_V8r
Wait -- a FEW teeth??? That's like 40 degrees off. Must have been retarded not advanced? Lucky no bent valves...
Even retarded will bend the exhaust valves. I had a Jesel belt fail and inform me of this. Meh.

There are 44 teeth on the cam gear. Each tooth is 8.18 degrees, so around 16 degrees off.

The cam is typically closest around 8-10 degrees BTDC on the intake side and 8-10 degrees ATDC on the exhaust side.

I'd say the OP got pretty lucky not to bend a valve or eight.
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