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Need Help determining a problem... car falls on its face at 6000 rpm

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Old 02-15-2011, 01:33 PM   #1
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Default Need Help determining a problem... car falls on its face at 6000 rpm

basics.
forged 408 11.2:1 compression
PRC 227 Race Heads
Futral custom cam 248/256 .649/.646 112+4
Manley Double Springs good to .700
Spring pressures are 446/170 respectively
7.500 Pushrods
comp Lifters
Lifter preload measures out at 5/8 a turn or roughly .030 preload
Kooks 1-7/8 Longtubes
FAST 90/90
removing the Lid makes no difference in power(so the lid is not causing a restriction)

car makes great power up to 6k, and then just falls on its face
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Old 02-15-2011, 01:37 PM   #2
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In a 408 with that large of a cam shouldn't you be in the 500hp mark even before it dies at 6k?
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Old 02-15-2011, 01:44 PM   #3
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this dyno is stingey as a *****...
450 hp on this dyno is a mid 10 sec car with a good 60' and some traction in an F-body

we think the car will do 460~470 on this dyno if we can figure out why its not pulling to 7K like it should
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Old 02-15-2011, 03:07 PM   #4
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Assume you logged the usual suspects (e.g. fuel pressure, misfires, MAP) with no help?
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Old 02-15-2011, 03:26 PM   #5
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oh yes... 100% sure its not any of the usual suspects...
fuel is fine, spark is fine, all sensors are fine


Just got off the phone with texas speed... they think the cam may be degree'd wrong.
so I may be cracking into the engine next week and breaking out a degree wheel to see if it got installed correct or not.
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Old 02-15-2011, 05:02 PM   #6
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I have to ask. Did you check to make sure the TB is opening all the way at 100 pedal?
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Old 02-15-2011, 06:37 PM   #7
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Quote:
Originally Posted by YellowToy/A View Post
I have to ask. Did you check to make sure the TB is opening all the way at 100 pedal?


yes... covered under making sure all sensors are working correctly...
but thanks for asking...
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Old 02-15-2011, 06:45 PM   #8
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What do you have behind the LT's?
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Old 02-15-2011, 06:55 PM   #9
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3" Y-Pipe with no cats, and 3 " Magnaflow exhaust

even if this was the problem... I dont think it would fall off that hard or that early.
I'm starting to wonder if the cam got put in wrong because the HP/TQ peak is so low for this big of a cam.

but its on the list to check...easy enough to just pull off the pipes on the dyno to see what its going to do.
I know it will help power.. I doubt it will shift the entire curve over 800 rpm
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Old 02-15-2011, 07:01 PM   #10
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the more I stare at it, the more and more I think its off a tooth or something...
torque should peak closer to 5200 ish on this cam...
which would fix the top end as well...
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Old 02-15-2011, 07:50 PM   #11
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I just had a quick look at my 416 runs, smaller cam, torque peaks around 5100 & hp @ 6250.

No strange looking valley between the two peaks either.

Thinking a bit more, this cannot be your car? No way you would not have degreed the cam...right?

Last edited by ctd; 02-15-2011 at 09:21 PM.
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Old 02-15-2011, 07:54 PM   #12
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Which comp lifters?
7.500 sounds like a lot of pushrod for that setup, especially for only .030 preload. I'd say forget the BS rocker bolt turn method to figure preload and get a pushrod length checker to actually measure properly.
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Old 02-15-2011, 08:59 PM   #13
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Dyno Dynamics dynos are usually stingy on their horsepower ratings. You would need to take it to the track to find out for sure.
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Old 02-16-2011, 01:17 AM   #14
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Quote:
Originally Posted by ctd View Post
No strange looking valley between the two peaks either.
The reason for the swing in the torque curve is the dyno figuring out how much it has to fight the car to create its desired ramp rate. It pours on the load for a second then lets it off then the "sweep" settles in and you get your actual power curve. So the first couple hundred rpms of any pulls on our dyno arent the engine's power curve.... its just showing what the engine's putting to the wheels at that moment with varying amounts of load. It just takes it a second for it to get the amount of load right.

Last edited by Carma Performance; 02-16-2011 at 01:22 AM.
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Old 02-16-2011, 01:22 AM   #15
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Quote:
Originally Posted by Kaltech Tuning View Post
Which comp lifters?
7.500 sounds like a lot of pushrod for that setup, especially for only .030 preload. I'd say forget the BS rocker bolt turn method to figure preload and get a pushrod length checker to actually measure properly.
I'm pretty sure pushrod length is not the issue...
Heads have a .100 thicker deck than stock heads.
pushrod length confirmed by texas speed... who builds tons of these motors, with these heads and stock rockers...
7.5 is correct length...
preload is around .030 which confirms the pushrods are the right length.
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Old 02-16-2011, 01:24 AM   #16
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and I also confirmed today that the cam should peak around 5200 on the torque and around 6500 on the horsepower....
its obviously about 700~800 rpm low...

would the cam being off a tooth on the timing chain shift it that far over?

or would it just run like total dog **** if it was a tooth off..
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Old 02-16-2011, 02:37 AM   #17
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Are we talking about the same thing?

Between the peaks I'm referring to peak torque & peak HP not the initial part of the sweep.

I've only visited a DD dyno once with my passed 346 & found the shape of the curves very similar to the Mustang's that I'm more familiar with.

If the torque was peaking at the higher rpm where it should be when the two curves cross the dip would not be there.



Quote:
Originally Posted by Carma Performance View Post
The reason for the swing in the torque curve is the dyno figuring out how much it has to fight the car to create its desired ramp rate. It pours on the load for a second then lets it off then the "sweep" settles in and you get your actual power curve. So the first couple hundred rpms of any pulls on our dyno arent the engine's power curve.... its just showing what the engine's putting to the wheels at that moment with varying amounts of load. It just takes it a second for it to get the amount of load right.
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Old 02-16-2011, 02:47 AM   #18
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Quote:
Originally Posted by ctd View Post
Are we talking about the same thing?

Between the peaks I'm referring to peak torque & peak HP not the initial part of the sweep.

I've only visited a DD dyno once with my passed 346 & found the shape of the curves very similar to the Mustang's that I'm more familiar with.

If the torque was peaking at the higher rpm where it should be when the two curves cross the dip would not be there.
you guys arent talking about the same thing


as far as two humps...yes they are always there.. it would.. you just would not notice them as much if it was shifted higher up
torque still eventually has to go down...
and it wouldnt fall off this hard this early normally...
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Old 02-16-2011, 02:57 AM   #19
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I figured out that a tooth on the big sprocket is 8.1818181818* on the Manley Double timing set. (360*/44 teeth)
in this engine... an addition 8* would not cause Piston to Valve Clearance issues....
engine has -10 cc pistons...so theres still probably close to .200 clearance

I can only guess at this being the cause of the problem right now as that would shift the peaks both considerably lower and it would suddenly drop off like it does up past 6k rpm's...

I'll pull apart the front side of the engine next week when I get back into town...
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Old 02-16-2011, 11:14 AM   #20
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Even if it's not off a tooth, without checking it with a degree wheel, you cannot be sure that the timing set isn't off...we've seen cams installed dot-to-dot properly off by 7 from their intended ICL (little because of the cam and rest because of the timing set)!
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