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Icelander 10-14-2008 05:26 PM

timing and cranking a 383 chevy
 
Hi, i have a chevy 383, 10,5 compression, iron heads with 200cc intake ports, and the cam is comp 280 magnum, 230@0,50 and 480 lift, and HEI ignition. when it idles best the timing is 18 degree and that is at 900-1000 rpm and the total is 38 degree, OK i was told that these are fair and normal figures but it punches the living hell out of the starter when im cranking her up, OK i can buy me self a high torque mini starter but wont he get the same punishment as this one ? And another thing it seems like the engine performs better with the vacuum advance blinded ?! this cam can barely be used with power brakes, OK can be fixed with a canister but will that somehow help the vacuum advance on the distributor ? Hmmm ? HELP please ?
Thanks in advance. Kristofer.

GMC boogie 10-14-2008 05:42 PM

Try backing the timing down 2. Check the condition of your cables and connections. The late style mini starters work great if you are in need of starter.

Icelander 10-14-2008 06:00 PM

Thanks for your reply, When i retard the ignition 2-3 degrees it is surely helping the starter but not enaugh and the idle speed drops about 150-200 rpm and i can feel a diffrence in how she does not accelerate as freely as with timing at 18 deegre.

Mez 10-14-2008 06:14 PM

one thing to check is see if your distributor has up and down play in it if it does what can happen is when the eng is off it drops down and because of the angle of the teeth on the gear it advances the distributor so it goes to 22 deg or whatever more than you set it at. As soon as it starts it lifts up and retards it to your 18 deg and you can never see it happen. Take the cap off and the rotor and without moving the centrifigal advance move the distr shaft clockwise and counter clockwise and see how much play it has. I find gm dist have allot of play and I make a shim to take up the play and helps with this exact problem.

F-BIRD'88 10-14-2008 07:10 PM

Your 383 with a comp 280H 230-230 .480" 110LSA Magnum cam will want 24deg intial static timing at idle.
To achieve that you need to modify the distributor mechanical advance travel limit to limit the mechanical advance to around 10 to 12deg of internal mechanical travel. This will allow 24deg at idle and 34 to 36 deg at max rpm, full mechanical advance.
This modified advance curve will maximize and stablize the idle manifold vacuum, idle quality both in and out of gear and off idle throttle response.

This usually requires disassembly of the distributor and modifying the mechanical advance mechanism stop limit pin slot. (shorten the slot length)
You cannot usualy do this using available "advance curve kit" springs and stop bushings, alone.
Once done, this set up provides a much more stable ignition advance curve than the typical light advance spring+ vacuum advance method. Especially for auto trans cars.
You'll be using a medium/light spring tension on the advance which is much more stable.

So how do you run 24deg static timing at idle and start the motor when hot?
You have two good solutions that you can use together or separate to allow you to start the engine when hot without starter strain.

1. Install a MSD "Starter Saver" auto cranking ignition retard control box to retard the spark while the motor is cranking over and starting. Full timing is restored once the motor achives 500+rpm idle speed.

2. Install a simple dash mounted ignition power interupt toggle switch on the HEI power wire or the MSD box power switching wire, to disable the spark power during hot cranking. Crank it over with the spark power off, count 1-2-buckle my shoe... then throw the spark switch and it will fire easily.
Both methods work.

Once the advance curve is dialed in properly as outlined and the carb throttles are readjusted, you would have plenty of manifold vacuum to operate the power brakes safely and consistantly. Check you power brake booster, check valve and vacuum hoses for leaks.
You'll likely need a 4.5" rated power valve in a holley carb.
You should be using a high stall (2800-35000 rpm) torque converter.
A "stock stall" torque converter puts too much hydraulic torque load on the motor while idleing in gear with the big cam and reduced available manifold vacuum.. which results in excessive throttle opening at idle to over come the idle load torque, further reducing the manifold vacuum and vac adv timing at idle.

While this advance curve setup does not depend on vacuum advance at idle to get idle timing and idle quality, any vacuum advance you happen to get at idle is just a bonus.
I find a adjustable 10-12 deg vac advance canister and ported vacuum to work best overall.
All timing, carb idle mix and speed adjustment is done with vacuum advance disconnected. Then, re-connect the vacuum advance hose to the distributor.

techinspector1 10-15-2008 03:42 AM

Kristofer, what ever happened when you raised the hood on the 'Vette to experiment with a cooling problem. Just curious. Here is the thread....
http://www.hotrodders.com/forum/heat...ml#post1017543

curtis73 10-15-2008 09:52 AM

Quote:

Originally Posted by F-BIRD'88
1. Install a MSD "Starter Saver" auto cranking ignition retard control box to retard the spark while the motor is cranking over and starting. Full timing is restored once the motor achives 500+rpm idle speed.

.

This is what I'd do.

ap72 10-15-2008 10:37 AM

24* is way too much for 10.5:1 with iron heads, and that cam isn't that big. Kepp it at the 18 you have now and get the starter saver or wire a manual cut out switch to the ignition- a lot of people do it that way.

glen242 10-15-2008 12:03 PM

Quote:

Originally Posted by Icelander
Hi, i have a chevy 383, 10,5 compression, iron heads with 200cc intake ports, and the cam is comp 280 magnum, 230@0,50 and 480 lift, and HEI ignition. when it idles best the timing is 18 degree and that is at 900-1000 rpm and the total is 38 degree, OK i was told that these are fair and normal figures but it punches the living hell out of the starter when im cranking her up, OK i can buy me self a high torque mini starter but wont he get the same punishment as this one ? And another thing it seems like the engine performs better with the vacuum advance blinded ?! this cam can barely be used with power brakes, OK can be fixed with a canister but will that somehow help the vacuum advance on the distributor ? Hmmm ? HELP please ?
Thanks in advance. Kristofer.

I have a 383 with a XE274 cam 230* intake, 236* exhaust, 10.36 static CR running on 89 octane pump gas.

I set my timing to 34* all in by 2600 rpm. I have 13" vacuum at idle and am using a vacuum can per Lars' specs.

Absolutly no problems cranking, either with stock starter or smaller high torque.

BTW, I don't know what initial timing is, it does not matter.

ap72 10-15-2008 12:14 PM

Quote:

Originally Posted by glen242
BTW, I don't know what initial timing is, it does not matter.

Well it kind of matters IF and only IF you don't like holes through your pistons, but hey, some people go for that kind of thing.

glen242 10-15-2008 12:29 PM

Quote:

Originally Posted by ap72
Well it kind of matters IF and only IF you don't like holes through your pistons, but hey, some people go for that kind of thing.

How am I going to get holes in my pistons when my total centrifugal advance is limited to 34*????

PLEASE TELL ME!

ap72 10-15-2008 01:44 PM

Oh, its very simple, if you have 34* of timing at idle, and you're idle is set below 2,700 RPM or so, which I expect for that cam is probably around 900 RPM. Then it would be detonating a LOT from take off- that's kind of the whole idea behind having mechanical advance on a dizzy- so you have more timing when you need it, but not too much when you are carrying a high load at low engine speeds.

to simplify it 34* timing + that cam + that compression (at take-off)= BOOM!

glen242 10-15-2008 02:51 PM

Quote:

Originally Posted by ap72
Oh, its very simple, if you have 34* of timing at idle, and you're idle is set below 2,700 RPM or so, which I expect for that cam is probably around 900 RPM. Then it would be detonating a LOT from take off- that's kind of the whole idea behind having mechanical advance on a dizzy- so you have more timing when you need it, but not too much when you are carrying a high load at low engine speeds.

to simplify it 34* timing + that cam + that compression (at take-off)= BOOM!

Sir:

I said the 34* centrifugal timing was in at 2600 rpm, as the post stated, that is where I set it with an adjustable timing light. I will bet you that I do not have 34* at idle.

I have looked at your other posts for the month of October, and I believe you are badly mistaken on a lot of them.

Things that jump out, aside from the bad advice:

10-02-08 quote

"stock 4.3L is 237 CI....." end quote
That = 55cc per L not the +/- 61cc per L that I learned in school.

10-10-08 + other posts: quote
"I am just an engineer, but..."
Your profile shows you as a mechanic, attending SEMo for construction management ...
Ocupation:mechanic, part time laborer

How can you call yourself an engineer, without a degree???

Your above post, concerning my timing, is stupid beyond belief! You either can't read or you have absolutely no idea what you are talking about!

You registered on this site on 6-13-2005. Your birthdate is July 24, 1985. You were almost 20 years old. You made no mention of studying to be an engineer, instead you said you were a mechanic, attending SEMo for construction Management.

So when and where did you receive your Engineering degree and in what discipline? Was it on the Chessie System (railroad line)?

How come there are no MORON Smilies?

curtis73 10-15-2008 03:40 PM

Quote:

Originally Posted by ap72
Oh, its very simple, if you have 34* of timing at idle, and you're idle is set below 2,700 RPM or so, which I expect for that cam is probably around 900 RPM. Then it would be detonating a LOT from take off- that's kind of the whole idea behind having mechanical advance on a dizzy- so you have more timing when you need it, but not too much when you are carrying a high load at low engine speeds.

to simplify it 34* timing + that cam + that compression (at take-off)= BOOM!

Too many factors to say that is an absolute. I ran 9.5:1 with a 218/224 cam with 110 LSA and was able to lock out my mechanical and run 36* all the time PLUS ported vac.

Chamber design, altitude, thermostat temp, intake air temp, quench, piston design, carb tune, exhaust design/scavenging, stall speed, auto or manual, if the cam is installed straight up or advanced/retarded... the list goes on.

To say that its definite that he'll cause damage is pretty premature at this point.

Initial timing is a pointless number provided it doesn't cause problems elsewhere in the RPMS/load. You can get away with a lot more low RPM timing with an automatic since heavy loading (lots of right foot) will always mean elevated RPMs.

Icelander 10-15-2008 04:33 PM

Hi, to answer techinspector1. We did raise the hood and that for sure helped, out. The temp fell well down. Thanks for a good advice.
Kristofer.
P.s. forgive me not telling you before.


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