I've got the GM crate 454 HO engine. I've set the initial timing at about 10 degrees. The car runs fine but my question is: every bit of info I've seen from Chevy says the initial timing on this engine should be 4 degrees. No other engine I've seen is this low. I've set the timing at 4 and the car barely runs. Can this possibly be correct?
Timing on crate 454
SS_Chuck
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I've got the GM crate 454 HO engine. I've set the initial timing at about 10 degrees. The car runs fine but my question is: every bit of info I've seen from Chevy says the initial timing on this engine should be 4 degrees. No other engine I've seen is this low. I've set the timing at 4 and the car barely runs. Can this possibly be correct?
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3,604 Posts
This is part of why I always recommend setting timing using total timing rather than the initial. Aim for total of 36* and see where your initial lands.
The other thing to realize here is that effective timing is the result of both mechanical and vacuum advance systems. The 4* number could be perfectly reasonable if it is combined with a fairly typical 20* vacuum advance on manifold vacuum and a mild cam. This combination would give you 24* at idle. Likely enough to make a mild cam run fairly well.
The other thing you can do as an expirement is find what timing the engine wants for idle. With the engine warmed up, disconnect the vacuum advance and adjust the timing for best idle (highest vacuum at a given RPM). Note what timing this ends up being. Don't try and drive it this way, this is just a way to get some useful information!
Then reset timing for 36* total and note where your idle/initial timing ends up. This will tell you how much mechanical advance you have. You can add vacuum advance to the initial for idle by selecting a vacuum advance can that fully advances at 1-2" lower vacuum than you have at idle.
The other thing to realize here is that effective timing is the result of both mechanical and vacuum advance systems. The 4* number could be perfectly reasonable if it is combined with a fairly typical 20* vacuum advance on manifold vacuum and a mild cam. This combination would give you 24* at idle. Likely enough to make a mild cam run fairly well.
The other thing you can do as an expirement is find what timing the engine wants for idle. With the engine warmed up, disconnect the vacuum advance and adjust the timing for best idle (highest vacuum at a given RPM). Note what timing this ends up being. Don't try and drive it this way, this is just a way to get some useful information!
Then reset timing for 36* total and note where your idle/initial timing ends up. This will tell you how much mechanical advance you have. You can add vacuum advance to the initial for idle by selecting a vacuum advance can that fully advances at 1-2" lower vacuum than you have at idle.
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11,876 Posts
I agree completely that 4* won't work. I run 16-18* initial, 38* total. I've been there, done that. You pretty much can't go by anything Gn states - they are incredibly inconsistent. I just learned that you shouldn't use 5w-30 oils even though its labled to do so on the cap. Turns out the cap in a generic cap. Should be running 10w-30 or thicker. There's a great debate on this topic at :
http://www.sallee-chevrolet.com/Discus/messages/3418/6121.html?1140622193
BTW, are you burning oil, and what carb are you running?
http://www.sallee-chevrolet.com/Discus/messages/3418/6121.html?1140622193
BTW, are you burning oil, and what carb are you running?
I drove a BB Ford F250 for years that burned a quart of oil a month so I just dealt with it. I don't put nearly that many miles on this engine so I haven't really noticed a problem. I am really going to read that link you provided. I am running a Holley 750 with 72 jets. Even though I rebuilt almost my entire car by myself I am a total novice with carbs. The engine seams to be starved for fuel above 3500 rpm. I was thinking about going to an 850.
That is one long thread. Bottum line, I set my timing to desired total, then find the find the initial at idle only for future reference. Also, you have to make sure your timing is stable at the desired idle speed. I have ran into fluctuating advance at idle with higher idle speeds and light mechanical advance springs. My current HEI has right around 18* mech advance built in, so I need 18 initial to get to 36 total, no way around it.
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11,876 Posts
It is starved for fuel up top if your using a 750 vac sec. outta da box.
An 850 has more appropriate jetting, or do what I did - put 84's on the rear metering block (if it has a metering block) of your 750. 72's in the front works for me, but I'm going to 74's to see if its stronger. Double pumpers have higher jetting in th eback so you may be OK there.
An 850 has more appropriate jetting, or do what I did - put 84's on the rear metering block (if it has a metering block) of your 750. 72's in the front works for me, but I'm going to 74's to see if its stronger. Double pumpers have higher jetting in th eback so you may be OK there.
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549 Posts
I am also running 18 initial and 38 total. I would play with the timing and jet the carb up about two sizes and go from there.
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7 Posts
I just tried the timing combination for my HO with MSD & vac advance running ported, used blue stop bushing, blue springs, set total @ 36* initial comes in at around 15*, This was recommended dyno combination and it works awsome. Running a holley 750DP, M20, 3:31 rr
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