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Author
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Topic: Bigger jets=pinging. Why?
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ukracer
Journeyman Posts: 65
From: South Wales UK
Registered: Apr 2003
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posted 05-28-2003 01:41 PM
   
The other day I tried bigger jets in my 600DP Holley, going from 66/74 to 72/80 simply because they were all I had around, so 6 sizes up front and rear. When I drove the car, it seemed a little better powerwise but was pinging badly. I thought more fuel (too much probably here) would suppress pinging but when I put the old jets back in, the pinging stopped. Any thoughts?
Cheers, Martin.
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steve'66
Gearhead Posts: 6522
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 05-29-2003 12:48 AM
Martin,You got me, and judging by the lack of responses you got others too.  Running rich should not cause preignition/pinging, it should cool the burn.  SteveW
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ukracer
Journeyman Posts: 65
From: South Wales UK
Registered: Apr 2003
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posted 05-29-2003 11:32 AM
Thanks Steve, I guess it's a strange one then. Only thing I could think was that bigger jets made more power hence more cylinder pressure, giving pinging but I also thought 72/80 was a bit big for a 600 D/P. What do you think?
Cheers, Martin.
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Rustang
Gearhead Posts: 471
From: Clarion PA
Registered: Nov 2000
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posted 05-29-2003 12:57 PM
I've heard before that standard holley jets have a certain margin of error. Something like 2-3 jets sizes variance (?) If they are not original holleys who knows what they're actually flowing. Also you could have a jet damaged from the screwdriver tip. All it would take would be screwing up the taper of the hole(some are tapered some not) to affect the flow of the jet. It might only take one screwed up jet to cause a lean cylinder on that corner of the motor. ------------------
'68 mustang 351 clevor- 10.92@124
'67 Stang, 351W -11.18@118
'69 351C Torino-14.90@100
'78 Pickup 351W-15.56@88
'79 Pickup 460 ET=??
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ukracer
Journeyman Posts: 65
From: South Wales UK
Registered: Apr 2003
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posted 05-29-2003 01:23 PM
The jets are all good condition with no damage and as far as I know they are all genuine Holley parts. Curiously, before swopping the jets over, I found a piece of gasket almost blocking one of the secondary mains and this was just after driving home from a day's racing at Silverstone, yet it gave no symptoms (no pinging, power as normal). Maybe it's time to find a rolling road tuner!
Cheers, Martin.
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capri man
Gearhead Posts: 3385
From: doerun, ga.
Registered: Nov 2000
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posted 05-29-2003 04:13 PM
quote:
Originally posted by steve'66:
Martin,You got me, and judging by the lack of responses you got others too. SteveW
yup, got me too!! ------------------
mike r
racing is real
everything else is just a game.
81 capri-7.51 @89mph 1/8
1.54 60 ft.
http://prestage.com/site/site_display.asp?SiteID=141
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Dynoram
Journeyman Posts: 27
From: long island NY
Registered: May 2003
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posted 05-30-2003 09:16 PM
Did ya try reading a spark plug? Got me intrested now...
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ukracer
Journeyman Posts: 65
From: South Wales UK
Registered: Apr 2003
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posted 06-02-2003 11:17 AM
Nope, didn't have chance to as I had a race that weekend so had to revert to original jets to be safe and have left it like that since. We have no safe roads for doing a plug chop here, I have been racking my brains trying to think of somewhere to test but there is nowhere. Why, what were you thinking? Is it to see how close the jetting is?
Cheers, Martin
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67Coupster
Gearhead Posts: 179
From: Fortson, GA, USA
Registered: Oct 2001
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posted 06-02-2003 12:29 PM
Maybe you were border line fuel limited and the bigger jets put it over the edge causing it to lean out. What type fuel supply system do you have? ------------------
James
67 Coupe
393W, 4 Speed,
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ukracer
Journeyman Posts: 65
From: South Wales UK
Registered: Apr 2003
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posted 06-02-2003 12:42 PM
I doubt it. I checked it with a pressure gauge at the carb just after I built the car as I suspected it was not up to snuff. To cure it once and for all, I fitted a Carter electric pump and the pressure is solid at 5-6psi all the way through the revs. I would really like to read the plugs as a guide but the roads here don't allow it safely. I have an 02 sensor in the headers and readings are about right (.840-.860) at full chat with 66/74 jets but I felt it was a bit lean hence the bigger jets. Plug chop is probably the best way when I can do it.
Cheers, Martin
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