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Old 10-20-2006, 09:49 PM
FrankV FrankV is offline
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How to Time a 1995 Chevy 350 on a 1970 chevy truck with nothing but an hei Ignition

I have a 1970 Chevy that i just installed a 1995 Chevy 350 in it. I'm sure you guys know that that year engine is controlled by ecm, and you have to bypass a wire to set the timing. What do you disconnect if anything and at what degrees should the motor be tuned down to in my truck? all i have connected to it is the vaccum hose that goes from the carb to dist.

Last edited by FrankV; 10-20-2006 at 09:50 PM.
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Old 10-20-2006, 09:57 PM
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Unplug the single white wire to put it in bypass mode. Sometimes this wire was also black with a tan ish-brown strip, or tan ish-brown with a black strip. Engine should be set too 0 degrees. If set at 5 degrees it may not pass emission nor get good gas mileage.
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Last edited by justen; 10-20-2006 at 10:00 PM.
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Old 10-20-2006, 10:00 PM
danny danny is offline
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you have a vacuum advance distributor on a '95 engine?
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Old 10-20-2006, 10:18 PM
FrankV FrankV is offline
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Vaccum advance on a 1995 350

Yes i eliminated all electrical wiring and set it up like an older 350. I wish i would have known that they sell aftermarket wiring and ecm set ups for it. Now i can't time it right, need help
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Old 10-20-2006, 10:20 PM
FrankV FrankV is offline
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Justen, It seems that you answer a lot of question all the time. I guess you know your stuff. Right now all i have is the standart plugs that go into the distributor and the vaccum advance. Where do i disconnect the white wire from?
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Old 10-20-2006, 10:27 PM
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Thats the wire that would run to the ecm lol. Being you don't have a computer for a 94 or 95, are you using tbi or carb setup?


I believe the ecm for 94-95 was part number 1227747
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Last edited by justen; 10-20-2006 at 10:29 PM.
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Old 10-20-2006, 10:39 PM
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I'm using a carb set up right now. I was thinking of using that stand alone Holley TBI system, what do you think? But anyways, what would be the proper way to time it correctly.
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Old 10-20-2006, 10:41 PM
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Far as I can think of on a 95 engine, without a ecm it's not adjustable. Unless you swapped distributors. That allows you to adjust it.

Carb maybe easiest, you won't see horse power difference between a carb and tbi. They will be very close to the same. I think 1995 350 was rated at 200 horsepower.
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Last edited by justen; 10-20-2006 at 10:48 PM.
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Old 10-21-2006, 03:02 AM
waynec waynec is offline
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Quote:
Originally Posted by FrankV
I'm using a carb set up right now. I was thinking of using that stand alone Holley TBI system, what do you think? But anyways, what would be the proper way to time it correctly.
You need to give a bit more info, because your description is not clear, nor do we know your level of expertise (so for this discussion I'll assume you are not knowledgeable).

Since you mention a vaccum line to the distributor I assume you installed a distributor of some sort, perhaps the original '70 points distributor? An HEI distributor from a mid-70's Chevy would be preferable... if you use an HEI, be sure to remove/eliminate the resistor in the car's 12v ignition wire circuit before connecting the power wire to the HEI distributor. Or did you leave the '95 "optispark" unit in place? (I don't think you want to use a computer-controlled distributor when you have no computer/ecm, so I'm going to assume you installed a non-computerized distributor, either points or HEI).

I'm not all that familiar with a '95 engine, nor am I a trained mechanic, but here are some general hints...

I would think it would be like any other small block Chevy...

Is there a timing pointer and a TDC mark on the crankshaft?

If there's not an existing TDC (top dead center) timing mark on the flywheel, with a pointer or degree mark bracket attached to the block, you'll need to attach a pointer of some sort on the block near the flywheel, but you will first have to set the engine on top dead center for the firing stroke on #1 cylinder (both valves closed... I hope you know how to do this, or can find out how, because it would take a lot of space to describe the process) and then mark the TDC position on the flywheel, aligned with a corresponding timing pointer on the block. All that is unneccessary if the engine already has timing marks/pointers on it.

Do you know the firing order for the engine you bought? Early carbureted small blocks use firing order 1-8-4-3-6-5-7-2, but if the '95 engine has it's original '95 cam, it's possible a '95 engine cam requires a different firing order (I don't happen to know, and a quick Google search didn't reveal it). Find out. Whatever the proper firing order for your '95 engine is, you need to ensure (as part of the distributor install procedure below) that the wires from each of the plugs terminate on the distributor cap in that firing order sequence, clockwise as you look down at the distributor, eg, with the #1 cylinder wire post at the front of the distributor, # 8 wire next to it going (clockwise) around the cap toward the passenger side, then #4, etc).

Install the distributor, cap, and wires:
Slip the distributor in such that the vacuum advance unit points generally towards the front of the passenger side valve cover and the rotor points in roughly the same direction; you may need to turn the oil pump shaft slot at the bottom of the distributor shaft hole with a long screwdriver to get it lined up so that the distributor will drop into that correct position as it rotates down through the cam gear and into the oil pump shaft slot and seats and points at the #1 terminal... it's a trial & error thing until you get it right. Now rotate the distributor body so that the rotor points precisely at #1 wire post, and ensure all the spark plug wires are attached to the cap in proper sequence (1-8-4-3-6-5-7-2 clockwise around the cap). Install the distributor clamp, but leave the clamp bolt just snug enough that it holds the distributor from turning by itself but you can rotate the distributor by hand pressure.

Then clamp an inductive timing light sensor on the #1 cylinder's spark plug wire, start the engine (with the vacuum advance hose disconnected from the distributor and plugged to prevent a vacuum leak), point the timing light at the timing mark on the flywheel, and adjust/turn the distributor to obtain about 4 to 8 degrees advance at idle (first adjust to where the timing pointer points at the timing mark, then rotate the distributor counter-clockwise (as you look down at it) by hand until the pointer points at the 4 degree mark.

If there is only a tdc mark on the flywheel and/or the timing mark pointer/bracket, you either have to figure out where 4 degrees advance is and mark the pointer or the flywheel accordingly... easier yet, use an adjustable "advance" timing light so that you move a pointer on a dial on the timing light to about 4 degrees to 8 degrees advance and then turn the distributor to align the pointer with the tdc mark on the flywheel. Lock the distributor clamp bolt to capture that setting and then check to make sure it stayed where you set it. Anything in the 4 to 12 degree advanced range will likely suffice, but you can play with that adjustment a bit within that range after you've driven the car, to see if you can notice any improvement in engine performance (idle, acceleration, etc). Or you can take the car to a tune-up shop and let them use their equipment to tweak the timing curve and the carburetor for best economy/performance.

Set the points dwell with a dwell meter if you're using a points-type distributor. Recheck the timing, then remove the timing light and reconnect the vacuum advance hose to the distributor; you'll note a jump in the advance reading when you connect that hose, and the engine will speed up a bit. Adjust idle speed via the mechanical carb linkage.

Hope that helps, and that I didn't make a bunch of incorrect assumptions.

Wayne

Last edited by waynec; 10-21-2006 at 03:17 AM.
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  #10  
Old 10-21-2006, 08:25 AM
dougbfresh dougbfresh is offline
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There are MANY options here, When GM went pointless and started using HEI, there still was NO computer involved, a simple trigger, it had a vacuum advance and timing the engine was basically the same as a point system but there was NO dwell to set. This is how people convert from points to pointless setups, they either buy an early HEI distributor, or buy something like a Pertronix unit to replace the points and condensor in their OLD distributor. The ONLY thing that chnged is the point and condensor were removed-NO MORE DWELL TO SET! Timing was identical to the points system.

Then came simple computers that adjusted timing on the fly, you had to disable the signal to the computer to set the base timing-this typically meant disconnecting 1 connector on the back side of the distributor then setting your timing.

Now with DIS (Distributorless Ignition System), timing is COMPLETELY controlled by the computer NO HUMAN timing involved. There are crank and cam triggers that signal the computer where the crank and cam are at any given moment-there is no vaccum advance per se, the is a vaccum signal (MAP-Manifold Absolute Pressure) on some systems that is converted to an electrical signal that the computer uses to determine load demands.

SO, what EXACTLY are you running on your vehicle?
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Old 10-21-2006, 12:23 PM
FrankV FrankV is offline
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Hello, to your question on what system i am using, i have a non computer HEI installed. And a carb set up. That's it. Will this 95 motor timing be set at 8' degrees like i believe are the old 350 motors, or should it be set to a different Mark like 0' degrees. THanks let me know
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Old 10-21-2006, 03:10 PM
danny danny is offline
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you have cleared up a lot with your last post, you should set your timing to 8 degrees and see how it runs. you may have to adjust it some for the fuel and altitude. the 0 degree is for the computer to control the timing.
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Old 10-21-2006, 04:34 PM
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danny is right, without the computer timing would need to be 5 to 8 degrees. Usually the computer will bump it to 5 degrees for starting. 0 degrees is "only" when you have a ECM of some sort.

I'd first set it at 5 degrees see how it runs, if it's poor. Bump up to 8 degrees.
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Last edited by justen; 10-21-2006 at 04:38 PM.
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Old 10-24-2006, 09:28 AM
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KA9MOT KA9MOT is offline
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Wow! That confused allot of people very quickly.

This is the same thing I did too my BroncoII..........Stripped the computer out, installed and earlier, non computer controlled carb, and distributer and a 4 Pin HEI ignition Module. Very simple and WOW! What a difference!

I don't know the timing specs for a Chebby but it looks like these guys have that covered.

Awesome stuff and noce to see someone else who isn't afraid to experiment.

Welcome to the forum FrankV and keep us updated on this........
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