Desperately need help with tuning
Thread Starter
6th Gear
Joined: Sep 2005
Posts: 6
Likes: 0
Desperately need help with tuning
At my wit's end.
73 convertible with new GM performance parts 383, demon carb, MSD e-curve distributor, and TH400. Has ping or knock under acceleration and I cannot make it go away.
Have tried timing all the way from 32 degrees at 3500 RPM (recommended by GM) down to 20 degrees. Have tried with and without vacuum, ported and manifold. Have tried fuel with octane ratings of 87 to 93 with 104 octane boost added. I'm wondering if this is valve rattle rather than ping. How can I tell? I've also been fooled by exhaust leaks in past but can locate none with stethoscope.
I've also heard of wiped cam on breakin, but engine was prelubed before starting and i have less than 2 hours on engine. I have removed valve covers and all valves seem to move properly with engine turning over.
Please help!
73 convertible with new GM performance parts 383, demon carb, MSD e-curve distributor, and TH400. Has ping or knock under acceleration and I cannot make it go away.
Have tried timing all the way from 32 degrees at 3500 RPM (recommended by GM) down to 20 degrees. Have tried with and without vacuum, ported and manifold. Have tried fuel with octane ratings of 87 to 93 with 104 octane boost added. I'm wondering if this is valve rattle rather than ping. How can I tell? I've also been fooled by exhaust leaks in past but can locate none with stethoscope.
I've also heard of wiped cam on breakin, but engine was prelubed before starting and i have less than 2 hours on engine. I have removed valve covers and all valves seem to move properly with engine turning over.
Please help!
Le Mans Master
Joined: Jul 2005
Posts: 5,752
Likes: 4
From: Austin Texas
I believe that engine has hydraulic lifters, they require no break-in. They are prone to be a little noiser than flat tappets, though. I think you are hearing something other than "pinging".
Thread Starter
6th Gear
Joined: Sep 2005
Posts: 6
Likes: 0
Thanks guys, for the feedback. Had a family emergency and was away from the computer and Vette for a few days.
Will try those suggestions.
Engine is too rich right now, will check valve lash and will also check to make sure timing mark is truely TDC. Even though the engine is from GM, mistakes can happen.
Dallas
Will try those suggestions.
Engine is too rich right now, will check valve lash and will also check to make sure timing mark is truely TDC. Even though the engine is from GM, mistakes can happen.
Dallas
Pro
Joined: May 2001
Posts: 596
Likes: 0
From: Yardley PA
If it's related to timing/compression issues, the ping should not be constant, but typically only occur under full load (acceleration).
If you always hear the same sound I would be willing to bet, that the source is something else and not ping. When you disconnect the vac-advance at idle it should definitely go away if it is real ping.
Classic acceleration pinging sounds a little bit like someone making popcorn in your engine.
Cheers!
Stefan
If you always hear the same sound I would be willing to bet, that the source is something else and not ping. When you disconnect the vac-advance at idle it should definitely go away if it is real ping.
Classic acceleration pinging sounds a little bit like someone making popcorn in your engine.
Cheers!
Stefan
Burning Brakes
Joined: Sep 2004
Posts: 1,167
Likes: 2
From: Ft.Worth Texas
The instructions are a bit screwy for the e-curve dist. Was very hard for me to understand at first.
Make sure you remove the vacuum hose and plug it, set the rev limit to around 5600, and the other two switches to give you zero 'mechanical' advance. I forget the settings but I think they may be 1 and 7. Then set your initial timing to 12-16. Reconnect vacuum and re set the switches to get you the curve you want.....I liked the one that maxed out at 2500 and used the maximum vacuum too.
If you wish I can look at their chart tomorrow and let you know the numbers. Good luck.
Make sure you remove the vacuum hose and plug it, set the rev limit to around 5600, and the other two switches to give you zero 'mechanical' advance. I forget the settings but I think they may be 1 and 7. Then set your initial timing to 12-16. Reconnect vacuum and re set the switches to get you the curve you want.....I liked the one that maxed out at 2500 and used the maximum vacuum too.
If you wish I can look at their chart tomorrow and let you know the numbers. Good luck.
Melting Slicks
Joined: Sep 2004
Posts: 2,412
Likes: 3
Flat tappet or roller lifters? If they're roller I wouldn't worry about cam lobe problems. And how much preload did you put on them?
Also, how do you know it's running rich? My Demon ran rich at idle (fouling plugs) but was lean at cruise and WOT. Don't assume anything.
And I don't see how you could confuse a ping with an exhaust leak or a lifter rattle. Any videos or sound clips for us? What's your compression at and how did you determine that?
Also, how do you know it's running rich? My Demon ran rich at idle (fouling plugs) but was lean at cruise and WOT. Don't assume anything.
And I don't see how you could confuse a ping with an exhaust leak or a lifter rattle. Any videos or sound clips for us? What's your compression at and how did you determine that?
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Thread Starter
6th Gear
Joined: Sep 2005
Posts: 6
Likes: 0
Davidey, thanks for the feedback, we have corresponded privately about the e-curve and I think I've got that sorted out.
Torqvette, I think you are on to something. I've assumed that I'm running rich, because of fouled plugs and black smoke, But 80% of this engine's life has been at idle while I'm tinkering. Only when I test drive do I hear ping, so I immediately stop. (only been out of neighborhood once).
I've tried to lean the carb with idle mixture screws but I think I'm making it worse (afterthought). How do I address the other circuit? Larger jets?
Thanks for the input
Dallas73
Torqvette, I think you are on to something. I've assumed that I'm running rich, because of fouled plugs and black smoke, But 80% of this engine's life has been at idle while I'm tinkering. Only when I test drive do I hear ping, so I immediately stop. (only been out of neighborhood once).
I've tried to lean the carb with idle mixture screws but I think I'm making it worse (afterthought). How do I address the other circuit? Larger jets?
Thanks for the input
Dallas73
Thread Starter
6th Gear
Joined: Sep 2005
Posts: 6
Likes: 0
Sorry Torqvette, I did not answer your other questions.
This is a GM performance products crate engine. Flat tappets, preloaded by GM. Compression 9.3:1 from manual supplied by GM.
Stephan, the ping remains even with vacuum disconnected and plugged.
Dallas73
This is a GM performance products crate engine. Flat tappets, preloaded by GM. Compression 9.3:1 from manual supplied by GM.
Stephan, the ping remains even with vacuum disconnected and plugged.
Dallas73
Race Director
Joined: Mar 2001
Posts: 11,322
Likes: 1
From: Living in the Hartland
HT and ZZ383's have roller cams thus roller lifters. I do not think those come with a balancer so you might either have a bad balancer or mistmatched timing tab to balancer giving false timing readings. Might try to determine tdc and see if balancer lines up
Thread Starter
6th Gear
Joined: Sep 2005
Posts: 6
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You are correct, Fevre, checked the manual and have roller hydraulic lifters. My mistake. I have the HT 383. Checked the balancer today (came already installed) and was TDC on compression stroke showing 0 degrees, so everything ok there.
Beginning to believe Torqvette is right and I'm lean with acceleration despite being rich at idle. I've been trying to retard timing to get ping out, thinking I'm rich, while making it worse. Just got to figure out what to do next. Don't know much about carbs. Thought is was all 'magic'.
Dallas
Beginning to believe Torqvette is right and I'm lean with acceleration despite being rich at idle. I've been trying to retard timing to get ping out, thinking I'm rich, while making it worse. Just got to figure out what to do next. Don't know much about carbs. Thought is was all 'magic'.
Dallas
