Have a timing ??
- Thread starter bertscova
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To make an educated guess, we need some more info. This is a healthy cam, 230/236, I would expect it would want anywhere from 18-22 initial. After that it comes down to you tuning the distributor for your build. 'All in' timing is going to come down to your your chamber design and quench distance. Poor chamber design, old school double hump, require alot of lead for the ignition. High quench distance or .050-.090" has a negative effect on ignition advance as well - it creates more heat soak in the cylinder. If you are running Vortec head, then I'd start with the all in at 32-33 and tune from there. With a more conventional chamber I'd start at 34-35.
In the end, you need to dial this in and curve your distributor for your build if you want to get all you can out of motor. There's a lot of HP and fuel economy to be found in a properly curved distributor.
In the end, you need to dial this in and curve your distributor for your build if you want to get all you can out of motor. There's a lot of HP and fuel economy to be found in a properly curved distributor.
Yes im running the chevy performance fast burn aluminium vortec angle plug head, single plain airgap style intake, a billet aluminium msd distributor and a 6al ignition box 45k blaster coil. Holley 680 built for motor specs. A th350 with 2800 stall and 373 rear gears. A 27" tall tire. Car weights about 3100 with me in it. Does that help with your recommendation
Those heads won't need as much all in timing - they are efficient. I would start the tuning at 32 all in. Any idea of compression and quench? Hopefully over 10:1, and 10.5:1 would be even better.
64nailhead hitting all the right answers. I'd start around 12 initial and 32 all in to start, depending on your driving habits that will tell you if you are dialing in the timing too quick but depending on which MSD dist. you have it should be more than capable on easily dialing in the curve. That stall may be too tight for a cam that big depending on the manufacturer also.
I know there are variables on the actual stall of a converter it was listed 2800 to 3200. I fed all the info on the car engine specs, weight, gear, tire size to compcams and this is the one they suggested. Dist is the MSD Pro-Billet Distributors 85551
Quench is the distance from the bottom of the head to the top of the piston. Things work out well in the range of 035-.050". Much closer and you have potential for the piston to touch the head. Wider though and it starts becoming detonation prone. It's not uncommon to see builds in the .080-.100" range and they will just outright suck at lower rpm's and when cruising. It will force you to drop the timing inorder to cruise at anything happy. Makes for higher cylinder temps and more heat soak into the head, block, piston and spark plug - all bad. Tight quench provides better squish of the air fuel mix creating a cleaner and faster burn, thus leading to a more efficient burn.
WOT, top end performance is not hampered by it much at all though. At 6500 rpm's a quench of .100 will have little to no ill affects on HP production.
Also, those heads you have are referred to as 'fast burn' heads. What is burning fast is the air/fuel charge. Hence the reason for the recommendation of starting out at 32 degrees of all in. And there is an excellent chance that you won't ever need 34+ degrees. The higher the number of all in timing implies that you have to ignite the spark sooner inorder for the max power portion of the burn to occur just after TDC. This same concept is seen in boosted builds where the timing is retarded as the boost increases because the gas will ignite quicker at high pressure levels (more boost=faster burn rate). If you dig into modern heads, i.e. LS, Coyote,etc, you'll see that the all in timing is very low, in some cases as low as 20 degrees. this is because of the efficiency of those heads' chamber design. This includes spark plug location as well.
If any of this is viewed as unnecessary info for your question(s), then disregard. I included it because it is a common mistake in builds and generally an unknown, misunderstood piece of info. I've typed up the 'how to' steps to tuning a dizzy for a SBC many times. If you would like, I can, let me know. Trying to tune it incorrectly can lead to a lot of wasted time and/or broken parts if you make any major snafu's. FWIW, I can attach some pics of broken ring lands out of engines that I've built
WOT, top end performance is not hampered by it much at all though. At 6500 rpm's a quench of .100 will have little to no ill affects on HP production.
Also, those heads you have are referred to as 'fast burn' heads. What is burning fast is the air/fuel charge. Hence the reason for the recommendation of starting out at 32 degrees of all in. And there is an excellent chance that you won't ever need 34+ degrees. The higher the number of all in timing implies that you have to ignite the spark sooner inorder for the max power portion of the burn to occur just after TDC. This same concept is seen in boosted builds where the timing is retarded as the boost increases because the gas will ignite quicker at high pressure levels (more boost=faster burn rate). If you dig into modern heads, i.e. LS, Coyote,etc, you'll see that the all in timing is very low, in some cases as low as 20 degrees. this is because of the efficiency of those heads' chamber design. This includes spark plug location as well.
If any of this is viewed as unnecessary info for your question(s), then disregard. I included it because it is a common mistake in builds and generally an unknown, misunderstood piece of info. I've typed up the 'how to' steps to tuning a dizzy for a SBC many times. If you would like, I can, let me know. Trying to tune it incorrectly can lead to a lot of wasted time and/or broken parts if you make any major snafu's. FWIW, I can attach some pics of broken ring lands out of engines that I've built
I have the bushing in the dist that allows 21 degrees of total advance so if i set initial timing at 12 it should give me 33 degrees of total timing. Atleast on paper. Have some stuff to finish up before first startup. Just need to figure out how fast i achieve full advance
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