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Timing question on a sbc

 
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rogus
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Joined: 07 Aug 2005
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2232.14 points


1976 Chevrolet Chevelle

PostPosted: Sat May 20, 2006 11:20 am    Post subject: Timing question on a sbc Reply with quote

I am having the following problem: Got plenty of power at around 2000 rpm after that the power just drops tremendously. I have the initial timing set a 6 degrees BTDC and a new distributor with a vacum advance that doesn't kick in till I get 10" vacum (about 2000 rpm).

Am thinking that the the lack of power is a timing issue?

If it is do I want more advance or less advance?
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Bocephus027
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Joined: 27 Mar 2006
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1972 Ford Mustang

PostPosted: Sat May 20, 2006 12:59 pm    Post subject: Reply with quote

Perhaps you can change springs for the rate of advance? Im not sure what your timing should be at though.
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10sec.et
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Joined: 29 Mar 2006
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Location: Houston,Texas
346658.74 points


1969 Oldsmobile Cutlass

PostPosted: Sat May 20, 2006 2:33 pm    Post subject: Reply with quote

what is your "total" timing?
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af2 wrote:
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Aerosmith
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Location: Ohio
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PostPosted: Sat May 20, 2006 5:59 pm    Post subject: Reply with quote

Stock initial is 8 btdc for most all sbc with auto trans. I run 10 deg ititial and about 36 total. One thing to make sure is that you have the correct damper to timing tab combination. Some sbc had the timing tab at about 2 o'clock to the balancer and some had it at about 12 o'clock. Verify tdc on #1 and make sure your damper and timing tab match up. Another thing is if your damper is an older stock or replacement elastomer type the outer ring could move in relation to the hub.
Another problam I ran into awhile back was a frozen advance plate in my distributor. I was losing power because I was not getting the vacuum advance at low rpm. Lastly, check to make sure your secondaries are opening on your carb. I took a small 4" bright yellow zip tie and put it around the rod on the bottom of the vec advance canister. It will slide easy enough for it not to bind the function but will not slip on the rod. Slide it up to the top of the rod until it touches the canister and drive the car. You have to put a load on it so that the secondaries will open(past half throttle and low vacuum). When you check the tie after the test drive it should be down the rod atleast 1/4" if the secondaries opened, if not you are probably running a 375cfm 2 barrel.
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SMOKEmUP
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Joined: 30 May 2002
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1979 Chevrolet Camaro

PostPosted: Sat May 20, 2006 10:29 pm    Post subject: Reply with quote

Aerosmith wrote:
Stock initial is 8 btdc for most all sbc with auto trans. I run 10 deg ititial and about 36 total. One thing to make sure is that you have the correct damper to timing tab combination. Some sbc had the timing tab at about 2 o'clock to the balancer and some had it at about 12 o'clock. Verify tdc on #1 and make sure your damper and timing tab match up. Another thing is if your damper is an older stock or replacement elastomer type the outer ring could move in relation to the hub.
Another problam I ran into awhile back was a frozen advance plate in my distributor. I was losing power because I was not getting the vacuum advance at low rpm. Lastly, check to make sure your secondaries are opening on your carb. I took a small 4" bright yellow zip tie and put it around the rod on the bottom of the vec advance canister. It will slide easy enough for it not to bind the function but will not slip on the rod. Slide it up to the top of the rod until it touches the canister and drive the car. You have to put a load on it so that the secondaries will open(past half throttle and low vacuum). When you check the tie after the test drive it should be down the rod atleast 1/4" if the secondaries opened, if not you are probably running a 375cfm 2 barrel.


All good advice.
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10sec.et
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Joined: 29 Mar 2006
Posts: 3473
Location: Houston,Texas
346658.74 points


1969 Oldsmobile Cutlass

PostPosted: Sat May 20, 2006 10:41 pm    Post subject: Reply with quote

Quote:
Lastly, check to make sure your secondaries are opening on your carb. I took a small 4" bright yellow zip tie and put it around the rod on the bottom of the vec advance canister. It will slide easy enough for it not to bind the function but will not slip on the rod. Slide it up to the top of the rod until it touches the canister and drive the car. You have to put a load on it so that the secondaries will open(past half throttle and low vacuum). When you check the tie after the test drive it should be down the rod atleast 1/4" if the secondaries opened, if not you are probably running a 375cfm 2 barrel.
great tip. never thought of that.
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af2 wrote:
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rogus
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Joined: 07 Aug 2005
Posts: 61

2232.14 points


1976 Chevrolet Chevelle

PostPosted: Sun May 21, 2006 2:23 am    Post subject: Reply with quote

The timing mark is good. I know the advance weights are kicking in cause I can see the timing advance (from 6 to 10 degrees BTDC) as the rpm's increase. My timing light bit the dust so I haven't been able to get a good reading on Total advance when I wrote this.

Most small blocks from this year did have an initail setting of 8 degrees BTDC however according to the GM restoration kit this engine was normally set 6 BTDC (I assume this was due to the compression ratio being different).
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