MAG1 Octane Boost worked??
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From: Platteville WI
MAG1 Octane Boost worked??
I poured in a bottle and the pinging is better but not completely cured. I realize, that this snake oil is not a real fix. The question is, did it richen or lean the fuel mixture or what? What can I do to the carb or timing to duplicate the results? It stills pings under WOT. and slightly under medium load conditions. Background: 1976 stock 350 Auto except Comp Cam and headers. Advance set to 14 and 34 using vacuum advance. Running 93 Shell V-power or BP 92 Ultra.
Jay
Jay
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From: Graceland in a Not Correctly Restored Stingray
You may well be leaning out. But, before touching the carb, where does full mech advance come in, and is the ping during WOT at all rpm's? Might just be a touch too early timing, as pointed out.
Also, this could be due, at least in part, to the heat sensitivity of the fuel. I'm not about to risk pointing any fingers, but not all 93 octane ratings created equally. Have you had this same issue with other brands?
A couple of other possibilities... There is the outside chance that your cam closes significantly earlier than the stock one, and/or you could be suffering from carbon build up, either of which would have the effect of raising your effective dynamic compression ratio.
And, what's your running temp, and do you have cold air induction?? High temps can cause this problem, too.
Of course, I may have missed something obvious, but that's my .02.
Also, this could be due, at least in part, to the heat sensitivity of the fuel. I'm not about to risk pointing any fingers, but not all 93 octane ratings created equally. Have you had this same issue with other brands?
A couple of other possibilities... There is the outside chance that your cam closes significantly earlier than the stock one, and/or you could be suffering from carbon build up, either of which would have the effect of raising your effective dynamic compression ratio.
And, what's your running temp, and do you have cold air induction?? High temps can cause this problem, too.
Of course, I may have missed something obvious, but that's my .02.
Last edited by TheSkunkWorks; Oct 5, 2007 at 04:50 PM.
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From: Platteville WI
Thanks for the reply Charlie. Gas choices are limited where I live. It's either Shell, BP, or Kwiktrip. Water temp runs up to 200 but not over. I test drove the car with the vac. adv. plugged and it had no affect on pinging. Hmmmm. The timing was set by the local Chevy Dealer. I presume the mech adv is 20 (34 total -14 base). Not sure what RPM it comes in at. I'll try to check it myself this weekend. I am part way through reading Lar's Carb paper. Great stuff. What I wouldn't give for more free time to play with this.
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From: Graceland in a Not Correctly Restored Stingray
If you haven't already, check Barry K's sticky on timing, which includes links to several reference articles, including more by Lars. Great info! A timing adjustment may be all you need.
Oh, and I don't believe your vac adv is doing much during WOT. If it were a part throttle ping, that's when I'd look that direction, and in that case would suggest hooking it to port (if not already) rather than manifold to see if it made a difference. But, that's another issue...
Leave you with one of my favorite Lars quotes, "90% of all carb problems are ignition problems."
Oh, and I don't believe your vac adv is doing much during WOT. If it were a part throttle ping, that's when I'd look that direction, and in that case would suggest hooking it to port (if not already) rather than manifold to see if it made a difference. But, that's another issue...
Leave you with one of my favorite Lars quotes, "90% of all carb problems are ignition problems."
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From: Platteville WI
On Sunday, I hooked up my timing light. Base timing was 14 at 700 RPM and the timing hit 34 at about 2600 RPM. Then.... I kept increasing the RPMs and timing went all the way to 38. So, it seems I need to do some distributor work? I can't imagine having mech adv of 24 is right. Is it? If not, can I buy a dist rebuild kit that limits mech adv?
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From: Graceland in a Not Correctly Restored Stingray
You did have the vac adv disconnected, right? If so, I'd simply try backing your initial timing off about 2*, yielding a total of 36* (initial + mech adv) to see what happens at WOT before anything else.
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Joined: Jul 2004
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From: Platteville WI
Thanks again Charlie. Yes, the vac adv was disconnected and plugged. At this point, I'm trying to self-educate before I take it anywhere again. If the dealer can't get it right, who do you trust to not make matters worse?
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From: Graceland in a Not Correctly Restored Stingray
The difficulty in finding someone to trust is why so many of us start learning about all this stuff. The dealer may likely eliminate the ping, but not give you a tune that performs best with your mods. Most of them are all about stock. Read thru Lars' papers and other good info, and you'll get a handle on it before long.
Oh, should have asked before now, but is this an L48 or L82, and do you have your cam card?
Oh, should have asked before now, but is this an L48 or L82, and do you have your cam card?
Last edited by TheSkunkWorks; Oct 9, 2007 at 04:28 PM.
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From: Platteville WI
The cam is id'ed on a service record as Comp Cam "242-2" ?. I looked it up on the web to get the spec's. This was a L-48 car. The block stamp # matches the vin. I also checked the carb id per Lar's paper and found it to be original as well. I would bet that Lars has helped more vette owners with engine problems than anyone anywhere. I've read some of his stuff, but am still digesting.
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From: Graceland in a Not Correctly Restored Stingray
Believe you have an Xtreme Energy XE268H. With that cam installed straight up with it's designed 4* advance, your only compression issue is the lack of it, as the resulting 7.07:1 DCR is far, far below anything that could be considered as critical. Thus, as observed earlier, this engine should probably run on regular w/o issues, so something is definitely wrong with this picture.
It's starting to appear that you're likely getting an incorrect read out of timing, so I'd urge you to verify that your balancer/pointer are indexed properly with true TDC. It's not an uncommon issue, and if the outer ring of your balancer has shifted, your timing could be significantly off... You can pick up a TDC locater that screws into the #1 spark plug hole for about $10 at a most speed shops or better auto parts stores to make checking this a snap.
I know I'm staying away from a possible cure (richening up for the cam and headers), but it's important not to waste time chasing carb adjustments before eliminating anything else that could be wrong. You'll get there...
It's starting to appear that you're likely getting an incorrect read out of timing, so I'd urge you to verify that your balancer/pointer are indexed properly with true TDC. It's not an uncommon issue, and if the outer ring of your balancer has shifted, your timing could be significantly off... You can pick up a TDC locater that screws into the #1 spark plug hole for about $10 at a most speed shops or better auto parts stores to make checking this a snap.
I know I'm staying away from a possible cure (richening up for the cam and headers), but it's important not to waste time chasing carb adjustments before eliminating anything else that could be wrong. You'll get there...
