Setting timing on 383 (plus a few other questions)
I just bought a Model A street rod a few weeks ago and have slowly been tweaking it to get running better on the street. The engine was freshly built with about 500 miles when I brought it home but was all setup for drag strip.
I had some bog/hesitation when pushing the gas initially so I swapped from the pink holley cam to the orange cam (with 31 squirters) and it seems to have some go now.
Also the car would stall when put into gear (th350) but if I disconnected the van advance it would run just fine. I finally got a timing light and have been tweaking the timing but I can't seem to find a number that makes this engine happy. I was curious if someone could give me some pointers, I know the tunnel ram that is on it now isn't perfect for the street and is probably adding to the confusion but I have ran out of money after buying the car to replace that setup right now :-)
Any advice on what the timing I should be aiming for should be? also the idle? I have been able to get about 11 inches of vacuum so far
Chevy 383 stroker long block
64cc aluminum heads
1.60/2.02 screw in studs & guide plates
hardened push rods
true roller rocker arms
flat top hypereutectic pistions (10 to 1 compression)
gear drive timing set (sounds really cool)
plasma moly pistion rings
new steel 383 crankshaft
cam is .488/.510-234/244 Edelbrock Performer
High volume oil pump
7 quart oil pan
HD Tri-metal bearings
Weiand tunnel ram with two chokeless Holly 450 cfm carbs and K&N filters.
Are the carbs vacuum secondaries or mechanical? You are correct, that tunnel is a problem on the low end but as long as it looks good, who cares?!
I have always had great success in timing specialty engines to which the factory manual does not apply by using manifold vacuum. Disconnect the vacuum advance and attach a vacuum gauge to the hose. Then start twisting the distributor and adjusting idle screws until you nave the engine idling at desired rpm and maximum manifold vacuum. This should be pretty much optimal. Reconnect the vacuum pot. Test drive and if then engine pings at any point in it's rpm/load, back out a degree in the advance and try again. Back out only as much as necessary to stop the ping.
Also, it is critical on Holleys on all engines but especially so on a tunnel ram to adjust the squirter cam just tight enough so no matter how little it moves it squirts. If it is adjusted loose, you will always have a bog as the throttle opens but the slack in the squirter arm delays the extra gas. Another possible cause of a bog is mechanical secondaries that open the carb way too much too early. Vacuum secondaries are better for the street virtually all the time 'cause they can be tuned to open big only when needed. I know guys will pipe in with anecdotal stories of 1000cfm double pumpers getting 35mpg and perfect throttle response but in general, on the street with the wide variety of load conditions, vac secondaries will win nearly every time. This is a problem w/ tunnel rams doe to the big plenum which isolates the carbs from the cylinder pressure signals that are used to signal the carb what to do.
willys36: The carbs are mechanical advance 4160 holleys w/ no choke (http://store.summitracing.com/partde...5&autoview=sku)
I am not a huge fan of the carb's but the bank account is getting pretty low right now, I have been looking at the 4160 390cfm vac. secondary and electric choke as a replacement or possibly the edlebrock performers 500cfm (although 1000 cfm total might be to much) as replacements in 6 months or so.
For both of the carb's they have the 31 squirters in them and originally came with the pink pump cam but that seemed to cause heavy bog (even with the vac advance disconnected). I changed them to the orange cam and readjusted the pump spring and now it seems to pick up a little better. This weekend I messed with the timing some and it won't run on any timing below about 8 BTDC, it will just stall even if I crank the idle screws like crazy. If I set the timing around 12 she run's ok and 14-16 seems to run nice but has the "marbles in a tin can" sound at idle.
I have ordered the MSD advance spring/bushing kit so I can change the mechanical advance and I am thinking of getting an 8psi or adjustable vac can for the distributor since I don't have a ton of vacuum with the cam.
Hopefully I can nail the timing this weekend, I am worried that the balancer has moved or something along those lines because I can't get anywhere near the "initial" setting the most people use on this board and keep it running (4-8)
That's why I set based on vacuum/rattle rather than a 'recommendation'. Need to honor the engine not a book.
Thanks Willy :-) I will give it a whirl tomorrow when my summit box(s) show up with the new springs and what not.
I am also thinking to go pickup a vac advance can that is fully activated @ 8psi from napa and see what luck I have.
Ain't hotrodding fun?
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