HELP! massive HP loss above 4000 rpm, D1SC forged 347
02-12-2016, 04:29 PM
#1
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HELP! massive HP loss above 4000 rpm, D1SC forged 347 So ive recently come back from the tune shop and ran into major issues while dyno tuning, the HP just drops like a rock after 4000 or so RPM. makes roughly 12.5 psi of boost by the start of power loss. didnt even make full pulls to 7000 rpm. the dyno charts speak for themselves. Any help would be appreciated!
99 trans am
tick performance level 3 t56
monster stage 4 clutch
strange 60 w/3.54 gear
stock 99 computer
LS1 block bored .007 over
JE -22cc 2618 3.905 pistons
Scat forged H-beam rods w/arp 2000 bolts
polished stock crank
clevite rod bearings/king main bearings
CNC 243 heads flowing 316cfm @.600 lift w/valve job
fresh stainless intake/exhaust valves
Tick Performance Camshaft: Blower Stage 2 V2,
Valve Spring Type: Tick/PAC #TP660DVSK (titanium retainers)
cloyes single billet timing chain
comp short travel link bar lifters
tick hardened 7.300 pushrods
dual in tank racetronix 320 fuel pumps
1:1 boost referenced regulator @ 58PSI
melling oil pump
ATI balancer
TSP 1 7/8 headers to 4 inch y-pipe with dump
ls6 intake
ported ls1 tb
D1SC w/3.55 pulley
big red race valve (open)
ATI dual intercooler setup
msd superconductor wires
tr6 plugs @ .30 gap
#80lb injectors
holley fuel rails with -8AN feed -6AN return
made 8 pulls total, at first we thought spring was broken so we pulled valve covers, all springs were okay. then we checked preload and pushrod length which were all good as well. double checked fuel pressure and it was steady and rose with boost. The car would pull hard to about 4000 then would still sound fine (no misses or bogging) but the power was just gone. didnt sound like spark blowout. AFRs were below 11.5 and went down with each run. Just kept dropping hp at high rpm. best run of the day was 581hp/590tq @ 5400rpm on the third pull.
PLEASE HELP, i am not the most mechanically inclined but i have all info on parts in the car available to me. This was the first round of tuning since the build. the car has 250 miles on it from the base tune.
dyno chart attached of the final three pulls. All runs show same general curve and power loss. Smoothing factor of 5
99 trans am
tick performance level 3 t56
monster stage 4 clutch
strange 60 w/3.54 gear
stock 99 computer
LS1 block bored .007 over
JE -22cc 2618 3.905 pistons
Scat forged H-beam rods w/arp 2000 bolts
polished stock crank
clevite rod bearings/king main bearings
CNC 243 heads flowing 316cfm @.600 lift w/valve job
fresh stainless intake/exhaust valves
Tick Performance Camshaft: Blower Stage 2 V2,
Valve Spring Type: Tick/PAC #TP660DVSK (titanium retainers)
cloyes single billet timing chain
comp short travel link bar lifters
tick hardened 7.300 pushrods
dual in tank racetronix 320 fuel pumps
1:1 boost referenced regulator @ 58PSI
melling oil pump
ATI balancer
TSP 1 7/8 headers to 4 inch y-pipe with dump
ls6 intake
ported ls1 tb
D1SC w/3.55 pulley
big red race valve (open)
ATI dual intercooler setup
msd superconductor wires
tr6 plugs @ .30 gap
#80lb injectors
holley fuel rails with -8AN feed -6AN return
made 8 pulls total, at first we thought spring was broken so we pulled valve covers, all springs were okay. then we checked preload and pushrod length which were all good as well. double checked fuel pressure and it was steady and rose with boost. The car would pull hard to about 4000 then would still sound fine (no misses or bogging) but the power was just gone. didnt sound like spark blowout. AFRs were below 11.5 and went down with each run. Just kept dropping hp at high rpm. best run of the day was 581hp/590tq @ 5400rpm on the third pull.
PLEASE HELP, i am not the most mechanically inclined but i have all info on parts in the car available to me. This was the first round of tuning since the build. the car has 250 miles on it from the base tune.
dyno chart attached of the final three pulls. All runs show same general curve and power loss. Smoothing factor of 5
Last edited by snapdude; 02-12-2016 at 05:25 PM.
02-12-2016, 05:42 PM
#5
Staging Lane
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Boost rises all the way to end of pull. The tuner let out once the drop happens. It was reading about 12.5 psi at the end of these runs. He said it would have kept going up if he could stayed in it longer. Just some rough math shows the 3.55 pulley should max the blower at around 6900 rpm and 14.5 psi with a 347 engine
02-12-2016, 06:07 PM
#6
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Taking into consideration the details you've shown all I can offer are the things in my mind. What I would start checking/ looking into.
was the cam degreed on install- timing
valve springs- are they correct & up for the job
ignition
compression
The build list looks very good & I can only imagine a sweet T/A. Something is definitely not right. Again, hope you get it worked out & where it should be. Good luck man.
was the cam degreed on install- timing
valve springs- are they correct & up for the job
ignition
compression
The build list looks very good & I can only imagine a sweet T/A. Something is definitely not right. Again, hope you get it worked out & where it should be. Good luck man.
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02-12-2016, 09:06 PM
#9
Belt slippage was first thing that comes to mind. But logs from HPT will help.
Post those over at HPT and in the PCM forum here and someone will chime in with some knowledge.
Many year ago I had a foxbody with a procharger that experienced belt slippage, and nosed just like your chart. Went to a fabbed flip type drive and eliminated the issue.
That would also account for rich conditions.
Post those over at HPT and in the PCM forum here and someone will chime in with some knowledge.
Many year ago I had a foxbody with a procharger that experienced belt slippage, and nosed just like your chart. Went to a fabbed flip type drive and eliminated the issue.
That would also account for rich conditions.
02-12-2016, 10:12 PM
#10
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If boost isn't falling or staying flat then I would look at valve train. Logs would help greatly in diagnosis. I've seen where a tired motor with leaky valves and rings drop power fast like that.
02-14-2016, 04:07 PM
#11
Staging Lane
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would valves really be shot if the heads are brand new? ill be the first to admit that i have limited mechanical knowledge, i just financed the project and own it haha. next weekend we are going to pull the heads and insect all of that stuff as well as pull the timing cover and check the cam. does anyone have any suggestions on what we should be looking for that might explain the results of the dyno graph?
02-16-2016, 09:15 PM
#17
Being brand new doesn't mean that the plug gap is correct.
What is the plug gap?
How much preload? Those lifters like very little preload as they only have about .060-.070" internal travel.
In the past I've run those lifters with .010-.020" preload and had great results.
What is the plug gap?
How much preload? Those lifters like very little preload as they only have about .060-.070" internal travel.
In the past I've run those lifters with .010-.020" preload and had great results.
02-16-2016, 09:23 PM
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Being brand new doesn't mean that the plug gap is correct.
What is the plug gap?
How much preload? Those lifters like very little preload as they only have about .060-.070" internal travel.
In the past I've run those lifters with .010-.020" preload and had great results.
What is the plug gap?
How much preload? Those lifters like very little preload as they only have about .060-.070" internal travel.
In the past I've run those lifters with .010-.020" preload and had great results.
The plug gap is 30 the preload witu 7.3 rods (please forgive my lack of technical knowledge here, I just financed it) if I recall they checked it at 1 and 1/4 turns? We tried 7.25 and 7.275 pushrods and couldn't not get any preload at all.
02-16-2016, 09:45 PM
#19
I would tighten the plug gap up a little to .024-.026.
If you have 1 and 1/4 turns with those lifters you have serious issues as that is way too much preload.
Use a push rod length checker instead of counting turns. You need to find zero lash with the cam on the base circle. Those lifters have very little internal travel and need more precise measurements than counting turns. Once you have found zero lash with the push rod length checker, add .015" to your zero lash length. That is the length push rod you need.
Those lifters can be somewhat tricky to measure push rods with. Sometimes you need to bring the engine to max lift on the cylinder you're measuring push rod length on before measuring push rod length when the cam is on the base circle. This allows the spring pressure to bleed the lifter plunger down and allow you to measure correct preload.
The reason why you probably didn't get any pre load with a 7.25 and a 7.275 is due to what I mentioned above. Those lifters don't like to bleed down which is a good thing and that's what you want when the engine is running. It can make it a little bit tricky though to measure for appropriate push rod length though.
If you have 1 and 1/4 turns with those lifters you have serious issues as that is way too much preload.
Use a push rod length checker instead of counting turns. You need to find zero lash with the cam on the base circle. Those lifters have very little internal travel and need more precise measurements than counting turns. Once you have found zero lash with the push rod length checker, add .015" to your zero lash length. That is the length push rod you need.
Those lifters can be somewhat tricky to measure push rods with. Sometimes you need to bring the engine to max lift on the cylinder you're measuring push rod length on before measuring push rod length when the cam is on the base circle. This allows the spring pressure to bleed the lifter plunger down and allow you to measure correct preload.
The reason why you probably didn't get any pre load with a 7.25 and a 7.275 is due to what I mentioned above. Those lifters don't like to bleed down which is a good thing and that's what you want when the engine is running. It can make it a little bit tricky though to measure for appropriate push rod length though.
02-16-2016, 09:53 PM
#20
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I would tighten the plug gap up a little to .024-.026.
If you have 1 and 1/4 turns with those lifters you have serious issues as that is way too much preload.
Use a push rod length checker instead of counting turns. You need to find zero lash with the cam on the base circle. Those lifters have very little internal travel and need more precise measurements than counting turns. Once you have found zero lash with the push rod length checker, add .015" to your zero lash length. That is the length push rod you need.
Those lifters can be somewhat tricky to measure push rods with. Sometimes you need to bring the engine to max lift on the cylinder you're measuring push rod length on before measuring push rod length when the cam is on the base circle. This allows the spring pressure to bleed the lifter plunger down and allow you to measure correct preload.
The reason why you probably didn't get any pre load with a 7.25 and a 7.275 is due to what I mentioned above. Those lifters don't like to bleed down which is a good thing and that's what you want when the engine is running. It can make it a little bit tricky though to measure for appropriate push rod length though.
If you have 1 and 1/4 turns with those lifters you have serious issues as that is way too much preload.
Use a push rod length checker instead of counting turns. You need to find zero lash with the cam on the base circle. Those lifters have very little internal travel and need more precise measurements than counting turns. Once you have found zero lash with the push rod length checker, add .015" to your zero lash length. That is the length push rod you need.
Those lifters can be somewhat tricky to measure push rods with. Sometimes you need to bring the engine to max lift on the cylinder you're measuring push rod length on before measuring push rod length when the cam is on the base circle. This allows the spring pressure to bleed the lifter plunger down and allow you to measure correct preload.
The reason why you probably didn't get any pre load with a 7.25 and a 7.275 is due to what I mentioned above. Those lifters don't like to bleed down which is a good thing and that's what you want when the engine is running. It can make it a little bit tricky though to measure for appropriate push rod length though.