Built ls3 with mods, low torque numbers
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Teching In
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Thread Starter
Teching In
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but ignition is dyno set, tuner advanced spark until it started to lose power
that's why I asked about camshaft timing, maybe valves are closed too late? when I was cranking engine for the first time without spark and fuel, it was throwing something like compressed air or mixture out of the exhaust ports, never seen anything like that on other engines I built
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Teching In
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they where glowing after few circles on the track when we first seen this. it was definitely on load
Last edited by Goga Samsonadze; Jul 26, 2018 at 11:13 AM.
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Staging Lane
Joined: Sep 2017
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Goga, the signs are all there. A typical case of over scavenging, that is low on torque and glowing headers. Your exhaust system might be too unrestrictive and with this long exh duration the fuel mixture will be pulled out before in the exh iso delivering its energy in the cylinder. Longer exh duration usually bleeds off torque and if you have a fairly good intake side you will just not benefit of the intake charge going to combustion. It will burn in the headers instead(glowing headers).
The fix is expensive (new camshaft) but if you can get hold of a set of lower ratio rockers 1,6:1 it will most likely decrease the glowing headers and make more torque. (Install only on intake side).
I have seen this several times on dyno tests.
Good luck
The fix is expensive (new camshaft) but if you can get hold of a set of lower ratio rockers 1,6:1 it will most likely decrease the glowing headers and make more torque. (Install only on intake side).
I have seen this several times on dyno tests.
Good luck
Thread Starter
Teching In
Joined: Jul 2018
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Goga, the signs are all there. A typical case of over scavenging, that is low on torque and glowing headers. Your exhaust system might be too unrestrictive and with this long exh duration the fuel mixture will be pulled out before in the exh iso delivering its energy in the cylinder. Longer exh duration usually bleeds off torque and if you have a fairly good intake side you will just not benefit of the intake charge going to combustion. It will burn in the headers instead(glowing headers).
The fix is expensive (new camshaft) but if you can get hold of a set of lower ratio rockers 1,6:1 it will most likely decrease the glowing headers and make more torque. (Install only on intake side).
I have seen this several times on dyno tests.
Good luck
The fix is expensive (new camshaft) but if you can get hold of a set of lower ratio rockers 1,6:1 it will most likely decrease the glowing headers and make more torque. (Install only on intake side).
I have seen this several times on dyno tests.
Good luck
Staging Lane
Joined: Sep 2017
Posts: 80
Likes: 6
If the crank/reluctor and the ecu have been changed it’s good practise to zero the crank and fabricate a temporary timing pointer to verify TDC.
We have seen as much as +/-5 degrees off.
The ecu will only show the timing read from the crank sensor/reluctor and if it’s off you will never know if you don’t zero.
So your timing might be off.
Goga, the signs are all there. A typical case of over scavenging, that is low on torque and glowing headers. Your exhaust system might be too unrestrictive and with this long exh duration the fuel mixture will be pulled out before in the exh iso delivering its energy in the cylinder. Longer exh duration usually bleeds off torque and if you have a fairly good intake side you will just not benefit of the intake charge going to combustion. It will burn in the headers instead(glowing headers).
The fix is expensive (new camshaft) but if you can get hold of a set of lower ratio rockers 1,6:1 it will most likely decrease the glowing headers and make more torque. (Install only on intake side).
I have seen this several times on dyno tests.
Good luck
The fix is expensive (new camshaft) but if you can get hold of a set of lower ratio rockers 1,6:1 it will most likely decrease the glowing headers and make more torque. (Install only on intake side).
I have seen this several times on dyno tests.
Good luck
You might be thinking of when the exhaust valve opens too soon in the power phase and the fuel and air are still burning as it exits the exhaust. In that case, advancing the cam more will exaggerate the problem.
As already mentioned, its most likely a timing issue causing a situation where the air/fuel mixture is still burning as it exits the exhaust valve. Either the cam is too far advanced as described above, or the ignition timing is so low that it ignites the air/ful mixture way late causing the aame issue.
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Yes, you can try advancing the cam. Also, did you change the crank or have you had the crank reluctor off/on?
If the crank/reluctor and the ecu have been changed it’s good practise to zero the crank and fabricate a temporary timing pointer to verify TDC.
We have seen as much as +/-5 degrees off.
The ecu will only show the timing read from the crank sensor/reluctor and if it’s off you will never know if you don’t zero.
So your timing might be off.
About timing, I'm not sure about top of my head but, previous LS engine I built, started directly and flawlessly on Link G4+ ecu, while I had to correct trigger setting on this engine, it was backfiring from intake manifold, I corrected trigger degrees, set it to 16 from 10, and it worked well after this. I'm not sure why it was so, because only cylinder heads and camshafts where different from previous engine
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Overscavenging wouldn’t cause high EGT’s, it will usually do the opposite. Its a common trick with the big power adder stuff to keep the exhaust valve cool. Overscavenging will pull FRESH air and fuel from the intake side out through the exhaust BEFORE it’s been ignited, so it is at a much cooler temp than the exhaust gases.
You might be thinking of when the exhaust valve opens too soon in the power phase and the fuel and air are still burning as it exits the exhaust. In that case, advancing the cam more will exaggerate the problem.
As already mentioned, its most likely a timing issue causing a situation where the air/fuel mixture is still burning as it exits the exhaust valve. Either the cam is too far advanced as described above, or the ignition timing is so low that it ignites the air/ful mixture way late causing the aame issue.
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From: Central Cal.
A few things.
If you bored it to 4.030 it's not a 6.2 now and never was.
Second it could be ignition timing is too retarded causing the flame front to start too late and still be burning on the way out the exhaust valve.
Third, don't just go changing the timing of the cam without knowing if that's your problem. Find the problem first, then fix it, don't just guess at it.
Did you double check the timing marks on the cam gears were perfect?
How much ignition timing are you running?
You need to double check your cam alignment and go ahead and get a degree wheel and degree the cam to make sure it's installed and manufactured right.
If you bored it to 4.030 it's not a 6.2 now and never was.
Second it could be ignition timing is too retarded causing the flame front to start too late and still be burning on the way out the exhaust valve.
Third, don't just go changing the timing of the cam without knowing if that's your problem. Find the problem first, then fix it, don't just guess at it.
Did you double check the timing marks on the cam gears were perfect?
How much ignition timing are you running?
You need to double check your cam alignment and go ahead and get a degree wheel and degree the cam to make sure it's installed and manufactured right.
Last edited by 00pooterSS; Jul 27, 2018 at 04:41 PM.
Thread Starter
Teching In
Joined: Jul 2018
Posts: 33
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Thread Starter
Teching In
Joined: Jul 2018
Posts: 33
Likes: 0
A few things.
If you bored it to 4.030 it's not a 6.2 now and never was.
Second it could be ignition timing is too retarded causing the flame front to start too late and still be burning on the way out the exhaust valve.
Third, don't just go changing the timing of the cam without knowing if that's your problem. Find the problem first, then fix it, don't just guess at it.
Did you double check the timing marks on the cam gears were perfect?
How much ignition timing are you running?
You need to double check your cam alignment and go ahead and get a degree wheel and degree the cam to make sure it's installed and manufactured right.
If you bored it to 4.030 it's not a 6.2 now and never was.
Second it could be ignition timing is too retarded causing the flame front to start too late and still be burning on the way out the exhaust valve.
Third, don't just go changing the timing of the cam without knowing if that's your problem. Find the problem first, then fix it, don't just guess at it.
Did you double check the timing marks on the cam gears were perfect?
How much ignition timing are you running?
You need to double check your cam alignment and go ahead and get a degree wheel and degree the cam to make sure it's installed and manufactured right.
Last edited by Goga Samsonadze; Jul 27, 2018 at 05:30 PM.