Terrible pinging at operating temperature
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 855
Likes: 0
From: Location Location
I think there's a misunderstanding here. The injectors currently in the car are the GM stockers. I have, but have not installed, a set of 30#ers. My suspicion is that the stock injectors are being pushed beyond their maximum sustainable duty cycle. Thus, the lean mixture is detonating heavily under load after optimal temperatures are reached. Does that make more sense? Does it sound likely?
-DM
-DM
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
[SNIP=edcmat-l1]PS I have cleaned literally HUNDREDS of hot wire MAFs with q tips and have only 1 time pushed a wire off.[/SNIP]
Congrats on that. The one and only time I tried that I ended up at the MAF store for a replacement. Guess I'm pretty ham-fisted. LOL
Jake
Congrats on that. The one and only time I tried that I ended up at the MAF store for a replacement. Guess I'm pretty ham-fisted. LOL
Jake
Melting Slicks
Joined: Jul 2006
Posts: 3,356
Likes: 1
From: Chesapeake Va
Originally Posted by DarkMatter
I think there's a misunderstanding here. The injectors currently in the car are the GM stockers. I have, but have not installed, a set of 30#ers. My suspicion is that the stock injectors are being pushed beyond their maximum sustainable duty cycle. Thus, the lean mixture is detonating heavily under load after optimal temperatures are reached. Does that make more sense? Does it sound likely?
-DM
-DM
To push them past their max. duty cycle, you would have to be under heavy accell. At cruise speed, part throttle, whatever, the computers gonna try to compensate for the change in VE with fuel trim and it should run half-way decent
Last edited by edcmat-l1; Sep 9, 2006 at 06:58 PM.
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 855
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From: Location Location
Originally Posted by edcmat-l1
Even if its an unprogrammed 383, with stock size injectors, I wouldnt think it would ping its *** off real low. I could see if it pinged if you got in it pretty heavy, but just not going down the road. How low a RPM does it detonate? Is it like just at tip in at cruise? and if you have 30 LBS inj and suspect its a lack of fuel, why dont you just swap em?
To push them past their max. duty cycle, you would have to be under heavy accell. At cruise speed, part throttle, whatever, the computers gonna try to compensate for the change in VE with fuel trim and it should run half-way decent
To push them past their max. duty cycle, you would have to be under heavy accell. At cruise speed, part throttle, whatever, the computers gonna try to compensate for the change in VE with fuel trim and it should run half-way decent
I'm actually going to do that tomorrow. As long as the ECM will attempt to compensate, I'm going to switch them over.
edcmat, do you know the chamber size on the LT-1 heads? I fear my initial math may have been off when picking pistons.
Last edited by DarkMatter; Sep 9, 2006 at 08:19 PM.
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 855
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From: Location Location
Crap. It seems That in my initial parts selection I made a grave error. I've been doing a bunch of reading tonight, especially over at the KB website. KB's maximum recommended quench height for use with their Hyper/dish is .060". With an undecked block height of .025" and a compressed gasket thickness of .039" I get a quench height of .064".
Can .004" actually cause this much havoc? If so I only hope the pistons aren't utterly destroyed. If it turns out that this is my problem, and the pistons are still useable, would changing head gaskets help?
-DM
Originally Posted by Engine Building with KB Pistons
A running quench height in excess of .060" will forfeit most of the benefits of the quench head design and can push the engine into severe detonation.
-DM
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 855
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From: Location Location
Originally Posted by Casethecorvetteman
Jesus mate thats such a small amount i wouldnt think so, its possible though i spose. If thats all it is just whack in a thicker gasket.
I'd need a thinner gasket actually. But I'm going to swap the injectors out this morning, see if that helps. I don't look forward to tearing the heads off if the injectors don't help. I'll call KB pistons tomorrow. It's still Sunday here in the US.
-DM
P.S. This is why it's important to listen to our friends and brothers from down under. You guys are from "the future".
Le Mans Master
Joined: May 2005
Posts: 5,214
Likes: 66
From: Queensland, AUSTRALIA
HAHA!! Yeah mate, that too!! Bit of a rush job on typing that one and didnt read it before i posted it. Sorry mate.
Its still sunday here for about 2.5 hrs, not long to go til monday
Its still sunday here for about 2.5 hrs, not long to go til monday
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Thread Starter
Burning Brakes
Joined: May 2006
Posts: 855
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From: Location Location
Originally Posted by Casethecorvetteman
HAHA!! Yeah mate, that too!! Bit of a rush job on typing that one and didnt read it before i posted it. Sorry mate.
Its still sunday here for about 2.5 hrs, not long to go til monday
Its still sunday here for about 2.5 hrs, not long to go til monday
Not a problem at all Case. Heck, I started the thread out with a GIANT typo. I typed that I had a 10.8 DYNAMIC compression, rather than static. Can you say BOOM!!??I just came back in for another cup of coffee. Was outside relieving fuel pressure, and decided to get a new cup and check the board fast. Gonna swap out those injectors right now, see if that helps. hopefully it does.
Take it easy.
-DM
Melting Slicks
Joined: Jul 2006
Posts: 3,356
Likes: 1
From: Chesapeake Va
Originally Posted by DarkMatter
I'm actually going to do that tomorrow. As long as the ECM will attempt to compensate, I'm going to switch them over.
edcmat, do you know the chamber size on the LT-1 heads? I fear my initial math may have been off when picking pistons.
edcmat, do you know the chamber size on the LT-1 heads? I fear my initial math may have been off when picking pistons.
Melting Slicks
Joined: Jul 2006
Posts: 3,356
Likes: 1
From: Chesapeake Va
Originally Posted by DarkMatter
Crap. It seems That in my initial parts selection I made a grave error. I've been doing a bunch of reading tonight, especially over at the KB website. KB's maximum recommended quench height for use with their Hyper/dish is .060". With an undecked block height of .025" and a compressed gasket thickness of .039" I get a quench height of .064".
Can .004" actually cause this much havoc? If so I only hope the pistons aren't utterly destroyed. If it turns out that this is my problem, and the pistons are still useable, would changing head gaskets help?
-DM
Can .004" actually cause this much havoc? If so I only hope the pistons aren't utterly destroyed. If it turns out that this is my problem, and the pistons are still useable, would changing head gaskets help?
-DM
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 855
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From: Location Location
Originally Posted by edcmat-l1
Did you measure your deck height? Or are you just speculating? Thinner gasket would work. I would deck the block, but that requires complete disassembly. Definately call KB first. Those pistons are finicky bastards. I wont use them any more. Nuthin but forged for us.
Speculation based on Chevy specs. Everything I've read stated that the piston was 25 in the hole. Also, I was under the impression that the LT1 heads were 54cc, while the LT4 heads were 54.4cc. Hmmm. It gets worse by the minute, I think.
Seems my first foray into SBC design is a total disaster.
Looked at the MAF too. Seems pretty clean in there. Going to clean it up in any case. It's off, it can't hurt. I just finished the injector swap. I haven't fired it up yet though. Waiting to clean the MAF. Plus, how do I de-screen it? Should I just knock it out with a rubber mallet and small wood block??
Thanks again.
-DM
Edit: Saw the snap-ring on the screen. It's out. The elements don't look "fuzzy" so nuch, but they're definitely contaminated with mung. The resistor wires look mostly clean though. Gonna give it a cleaning, then reassemble.
Last edited by DarkMatter; Sep 10, 2006 at 10:37 AM.
Le Mans Master
Joined: May 2005
Posts: 5,214
Likes: 66
From: Queensland, AUSTRALIA
Got the screen out? Easiest way is to take it apart, then just push the screen out with your thumbs.
If you suspect the MAF then just unplug it and see what happens. (should work from MAP in speed-density mode then)
Is the EGR still connected? If this issue is still on going, try disconnecting the vacuum connection at the solenoid and block both ends (the vac hose and the solenoid), this will see if the solenoid is leaking and slightly allowing exhaust gas in all the time (it happens, but disregard if you have it all disconnected)
It could be interesting with the 30lb injectors in place, i cant see a huge drama, but will be interesting to see how it runs with the ECM still set on 24.87 (asuming its still on factory setting)
If you suspect the MAF then just unplug it and see what happens. (should work from MAP in speed-density mode then)
Is the EGR still connected? If this issue is still on going, try disconnecting the vacuum connection at the solenoid and block both ends (the vac hose and the solenoid), this will see if the solenoid is leaking and slightly allowing exhaust gas in all the time (it happens, but disregard if you have it all disconnected)
It could be interesting with the 30lb injectors in place, i cant see a huge drama, but will be interesting to see how it runs with the ECM still set on 24.87 (asuming its still on factory setting)
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 855
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From: Location Location
Actually, EGR solenoid has been replaced. Seemed to be operating a little funny, so for $20 I thought it was best to just replace it. EGR itself holds vacuum for well over 30 seconds (spec calls for 20).
Just got done cleaning up the MAF and gonna go for a drive. Want to see if there's any difference at all. Not going far, just a stop light or two.
Will report back when I pull in the driveway.
Thanks again everyone. Let's hope this helped.
-DM
Just got done cleaning up the MAF and gonna go for a drive. Want to see if there's any difference at all. Not going far, just a stop light or two.
Will report back when I pull in the driveway.
Thanks again everyone. Let's hope this helped.
-DM
Race Director
Joined: Jan 2002
Posts: 12,264
Likes: 88
From: O'Fallon Missouri
Originally Posted by DarkMatter
Speculation based on Chevy specs. Everything I've read stated that the piston was 25 in the hole. Also, I was under the impression that the LT1 heads were 54cc, while the LT4 heads were 54.4cc. Hmmm. It gets worse by the minute, I think.
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 855
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From: Location Location
Hmmm. Seems to have lessened it by as much as half, just by ear. Knock retard isn't coming in as quick or as hard as it was.
Who thinks I should pull the heads to check the piston tops and top ring land?? (no one please :P) I'll wait until I speak with KB no matter what though.
Who thinks I should pull the heads to check the piston tops and top ring land?? (no one please :P) I'll wait until I speak with KB no matter what though.
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 855
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From: Location Location
Originally Posted by STL94LT1
I'm pretty sure LT1 heads have 58cc combustion chambers.
Duly noted. Then my SCR is lower. Probably closer to the 10.5:1 that the motor left the factory with.
That also means all my original math was off. Not good.
edit: all my carpentry experience is laughing at me......"measure twice, cut once jackhole..hahaha"
Last edited by DarkMatter; Sep 10, 2006 at 11:41 AM.
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 855
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From: Location Location
Originally Posted by STL94LT1
To me it sounds like a bad tune. Do you have the means to reinstall the stock tune and see how it runs?
-DM