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Topic: BB detonation '70

in Forum: C3 Engines


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BB detonation '70 (1/14)
 11/19/09 6:35pm
Fairlane514
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Houston, TX - USA

Vette(s):
1970 454 4 speed A/C power everything else


Joined: 2/7/2008
Posts: 93

My motor (70 454) is stock  except for a mild cam upgrade, Comp 286 extreme energy.  When cold it runs fine with no detonation, but as it warms to operating temperature it will detonate on slight acceleration through the gears (4 speed).  
The initial timing is unknown, as i cant se the timing pointer and balancer unless I lay across the front of the motor. I set the timing by a vacuum gauge at 15 inches. It is the original distributor with pertronix I.

I was thinking it would help if I could get some colder air into the motor..........or of course retard the timing, maybe a colder plug, I have autolite 42's. 


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BB detonation '70 (2/14)
 11/19/09 10:21pm
lukesvetteLifetime Member
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HOWELL, NJ - USA

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Sounds like timing. Without thowing a light on it, you'll never know...
BB detonation '70 (3/14)
 11/19/09 11:53pm
Adams' AppleLifetime Member
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Duncanville, TX - USA

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#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


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or questionable fuel quality...
Back the timing down a hair at a time until the detonation goes away. Does it start easily when hot?


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BB detonation '70 (4/14)
 11/20/09 12:45am
Fairlane514
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Houston, TX - USA

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1970 454 4 speed A/C power everything else


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Yes, it starts fine when hot.......I buy Exxon 93...........I added two bottles of octane boost (Lucas) with no difference.
I really cant see the timing pointer without laying across the fender. It has power steering and a tensioner pulley right in the way.


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BB detonation '70 (5/14)
 11/20/09 8:59am
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Duncanville, TX - USA

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#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


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You may have a vacuum advance can that isn't working properly, or an EGR valve issue. Either could cause a slight ping under a light acceleration load, without effecting the hot start. Mechanical timing that is too far advanced will cause the ping, but it also normally makes them hard to start("kickback") when hot.
You may need to test the vacuum for the EGR and see if it is working right. Do you have a service manual for your car?


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BB detonation '70 (6/14)
 11/20/09 9:44am
Fairlane514
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Houston, TX - USA

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1970 454 4 speed A/C power everything else


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I dont have an EGR.  The distributor has been recurved with a new vacuum can, and i dont have a service manual.  Im going see if I can turn the motor until its on number one and look at the timing mark. 

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BB detonation '70 (7/14)
 11/20/09 2:35pm
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Duncanville, TX - USA

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#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


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[QUOTE=Fairlane514]
The distributor has been recurved with a new vacuum can, [/QUOTE]

Did you have this pinging problem before that was done? Or, was the distributor worked on because of the pinging?
Adams' Apple2009-11-20 11:36:01

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BB detonation '70 (8/14)
 11/20/09 5:48pm
Fairlane514
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Houston, TX - USA

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1970 454 4 speed A/C power everything else


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I had the recurve because I couldn't get it to idle without it eventually stalling out after about a minute of idling. It seemed to lose timing the longer it idled and the vacuum advance didnt compensate. I thought maybe the original vacuum can wasn't responding to 15 inches of vacuum so I had a guy (recommended) recurve and find a can that would respond to 13 inches of vacuum at idle. 
I think now after all the troubleshooting and carburetor issues and pertronix, it was not idling well because of carb loading up.  
As far as I know total timing is in at about 2500 rpm.
I guess what you're thinking is too much timing too soon?


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BB detonation '70 (9/14)
 11/20/09 7:10pm
Fairlane514
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Houston, TX - USA

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1970 454 4 speed A/C power everything else


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OK........I was finally able to check the timing with a light risking a new haircut in the process. With the vacuum advance disconnected at about 900 rpm I was at 25 advanced according to my dial back light. I dropped the timing to 15...............that should help.  I think I will also leave the vacuum advance disconnected.
As far as total timing, I dont know (it will just have to be whatever it is)........I can barely see the zero mark on my pointer


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BB detonation '70 (10/14)
 11/21/09 12:09am
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Duncanville, TX - USA

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#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


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Shocked Wow...25@ idle is waaaaay up there!  15 will be better, for sure, but it may still be too much. It may not run very well with the vac disconnected, tho...might have a little hesitation at cruising speed when you get on it. Let us know how it works with it at 15.

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BB detonation '70 (11/14)
 11/23/09 5:06pm
Fairlane514
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Houston, TX - USA

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1970 454 4 speed A/C power everything else


Joined: 2/7/2008
Posts: 93

Drove it today and it seems to be ping free...............so, thank you for the help.

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BB detonation '70 (12/14)
 11/24/09 12:30am
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


Joined: 11/8/2003
Posts: 20126

Good to hear! How does it run now?

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Joel Adams
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BB detonation '70 (13/14)
 11/24/09 4:23pm
Fairlane514
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Houston, TX - USA

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1970 454 4 speed A/C power everything else


Joined: 2/7/2008
Posts: 93

It pulls good through the gears, seems like it has a little more grunt to it now.  The carb is still giving me problems at idle and cold starting, so I shipped it today to Cliff Ruggles.

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BB detonation '70 (14/14)
 11/25/09 8:53am
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Duncanville, TX - USA

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#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


Joined: 11/8/2003
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Egg-sell-lent! A little more fine-tuning might be all it needs to be perfect! Good to hear.

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