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Old 05-29-2006, 01:59 PM
72NOVA454
 
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How Far Should I Advance Timing

Hi

What is the rule for setting timing and centrifugal advance on a performance big block chevy for the street? I've got it running real good right now throughout the rpm range running 93 octane fuel, but how do I know if I've got it advanced as possible? Do I just keep advancing it 2 degrees at a time and road testing it? I know the old saying "if it aint broken, don't fix it" but if theres another 10-20 HP in reserve that I'm losing because of insufficient advance I'd like to capture it.

Here's my setup:

72 Nova, TH350 trans, 454 BBC with .060 overbore and slighlty domed pistons, Comp Cams extreme hydraulic magnum cam, roller rockers, MSD ignition and distributor with adjustable bushings and springs for advance, stock iron closed chamber heads which have been rebuilt with valve job, and were ported/polished, dual plane intake, 2" headers, Holley 750, shift kit. Nothing fancy, typical street performance stuff. It's probably an 11 second car right now but I'm looking for more (aren't we all?)

thanks

Lee

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Old 06-19-2006, 08:31 AM
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Try a vacuum gauge. at peak idle vacuum you should be good to go, listen really carefully for that deadly ping.
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Old 06-19-2006, 12:13 PM
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BBC heads have very slow flame travel and the piston is a large diameter, So BBC respond well to a lot of timing.

Unplug the vacuum advance while setting the timing. Set the initial timing to 15 to 20 degrees and the total to 40 or 42 degrees.

Make sure to use the ported vacuum source for the vacuum advance. There should be no vacuum on the ported source during idle.

If there is vacuum on the ported source then the throttle blades are opened too much at idle, indicating the carb is too small for the engine. This can be fixed with a 0.065" to 0.090" hole drilled in each of the front throttle blades. The extra air allowed into the small holes makes it possible to close the front blades.

What size cam and what compression ratio are you using?

What head casting number?
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Old 06-19-2006, 12:51 PM
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Quote:
Originally Posted by 454C10
BBC heads have very slow flame travel and the piston is a large diameter, So BBC respond well to a lot of timing.

Unplug the vacuum advance while setting the timing. Set the initial timing to 15 to 20 degrees and the total to 40 or 42 degrees.

Make sure to use the ported vacuum source for the vacuum advance. There should be no vacuum on the ported source during idle.

If there is vacuum on the ported source then the throttle blades are opened too much at idle, indicating the carb is too small for the engine. This can be fixed with a 0.065" to 0.090" hole drilled in each of the front throttle blades. The extra air allowed into the small holes makes it possible to close the front blades.

What size cam and what compression ratio are you using?

What head casting number?
I don't know the casting number at this moment (I am at work) however I can tell you they are oval port, closed chamber, 96 cc comb chamber volume.
Also, I do not use vacuum advance. I removed it
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Old 06-19-2006, 12:59 PM
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Quote:
Originally Posted by 454C10
BBC heads have very slow flame travel and the piston is a large diameter, So BBC respond well to a lot of timing.

Unplug the vacuum advance while setting the timing. Set the initial timing to 15 to 20 degrees and the total to 40 or 42 degrees.

Make sure to use the ported vacuum source for the vacuum advance. There should be no vacuum on the ported source during idle.

If there is vacuum on the ported source then the throttle blades are opened too much at idle, indicating the carb is too small for the engine. This can be fixed with a 0.065" to 0.090" hole drilled in each of the front throttle blades. The extra air allowed into the small holes makes it possible to close the front blades.

What size cam and what compression ratio are you using?

What head casting number?
about the cam, It's a comp cams hydraulic extreme energy type - dont know the part number at this moment. It has a long duration and high lift. It's the most radical cam for a "steet" car that they offer in hydraulic.
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Old 06-19-2006, 02:06 PM
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Sounds like a pretty mean combo.

Still, there shouldn't be any vacuum on the ported source. If there is, it will be hard to lean out the mixture at idle and the idle speed will be inconsistent.

what gear and stall speed?
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Old 06-19-2006, 02:44 PM
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Quote:
Originally Posted by 454C10
Sounds like a pretty mean combo.

Still, there shouldn't be any vacuum on the ported source. If there is, it will be hard to lean out the mixture at idle and the idle speed will be inconsistent.

what gear and stall speed?
It's totally stock dude!!!!! - no kidding. It's like a 3.08 gear and stock converter - whatever stall speed that might be - 1500 rpm? and I gotta tell ya, I kinda like it. Yes, someday I will run maybe a 3.7 gear and a 2200 stall converter, but I'm not drag racing the thing. It's a street car. For now it's ok. also, it's a stock rear end (except it's a posi differential). It won't be able to hold up to a 4.11 gear and 2500 stall converter right? It will probably twist the car into a pretzel if I ran that setup right now. Also, the trans is a stock TH-350 3-speed (with a shift kit). if I changed the gear and/or the converter I may blow the trans - which is ok because that would force me to buy a high performance TH-400, but for now the stock TH-350 is holding up to that 550 HP under my current "granny" setup. I must say though that when that car runs "right" she halls *** big time. like 0 to 70 MPH in like 6 seconds, getting rubber and spinning the tires when shifting from 1st to 2nd after installing that shift kit. I'm going to pick up a new steel 2" cowl hood for it tonight. that will give me the room I need to run a taller air cleaner and raise the carb.
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Old 06-19-2006, 03:11 PM
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If you like it then it is a good setup. Of course, you know it isn't the ideal set up for the gears and stall. But, if you are happy with the power then it is good. That says something about BBC torque to be able to run a big daddy cam with a 3.08 gears and stock converter. Try running more timing. That should get it moving even better.
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Old 06-19-2006, 03:23 PM
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Quote:
Originally Posted by 454C10
If you like it then it is a good setup. Of course, you know it isn't the ideal set up for the gears and stall. But, if you are happy with the power then it is good. That says something about BBC torque to be able to run a big daddy cam with a 3.08 gears and stock converter. Try running more timing. That should get it moving even better.
you know it's funny you mentioned that. I have the timing very advanced (not exactly sure how much though - been a while since I checked) but it's time to check it again. I already changed the MSD springs and bushing to make it a bit more aggressive.

What are you running?
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Old 06-19-2006, 03:29 PM
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Quote:
Originally Posted by leejoy
...It's probably an 11 second car right now...

Quote:
Originally Posted by leejoy
...I must say though that when that car runs "right" she halls *** big time. like 0 to 70 MPH in like 6 seconds...
An 11-second car will do 0-60 in about 3.5 seconds, 0-90 in about 7 seconds. I think you're going to need a little more converter and gear to run 11's.
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Old 06-19-2006, 04:15 PM
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Not sure about what you mean with your question "what are you running" but this should cover it.

My 454 is in a 1970 1/2 ton truck (4000lbs). And I have it geared and cammed for a truck that is used to sometimes haul my street/strip car to the track. It has a 3.08 LSD diff, 2200 stall, th400 trans, and 206/212 hyd roller cam. Runs 0-60 in a little over 6 seconds measured my g-tech meter. It has AC, power steering, and power disk brakes, and a 4/6 inch drop. But, it is really just my work truck for around the house. I run 15 degrees initial and 42 total timing with 9:1 cr and 93 octane. The small cam makes a lot of cylinder pressure and will detonate in the summer and if I pull a trailer with anything less than 93. Could have something to do with the vacuum advance coming on too fast.

My drag car is a street legal 1970 datsun 240Z with a 350 (362c cid), GMT5 5 spd, 3.90 gear, 200cc dart iron eagles, and compcam 292H. Runs 11.7 at 120mph on the engine and 10.7 at 135mph (6.9 at 110mph 1/8th) with 175hp N20.

Yes, 0 to 70 in 6 seconds is about mid 13 second street car, not too bad and kind of fun. A mild 3.55 gear, LSD, 2500 stall converter should get you nicely into the 12's. A 3.70 and some slicks can get you deep into the 12's. You will most likely need some suspension work to make 11's and a little N20 to make the 10's. But don't get hung up on numbers, if you like the way your car is running, don't change it. But one day you will need lower gears or a smaller cam to balance out your combo.
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Old 06-19-2006, 09:02 PM
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i totally agree. but numbers arent all BS, and they dont lie in person.

i am running a RB bigblock with 3.23 gears, and wouldnt have it any other way. i love torque everywhere, and long leggs.
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