I'm going to check the timing today on my '86E coupe but I have a few questions first. Where should the timing be set? I was told 6 before TDC with the EST wire disconnected. Next, where and or what is the EST wire I have to disconnect? Yes, I know I need a manual but I have twin baby girls due in a month and the wife has cut ALL Corvette funds for now. Please help me ASAP, I'd like to get this done before she comes home and catches me with the new timing light.

 

You can usually find this wire by the vacuum booster. Has a bullet shaped black connectore that pulls apart. 6 degrees is correct. I like to run mine around 8

 

I had a '89 Formula 350 and ran the timing around 8-9 degrees also. Run premium gas if you advance the timing!!

 

Its located at the back of the engine near the brake booster. It looks almost like a black in-line fuse holder (its usually a brown wire).

When I time my Vette, I let the engine get up to normally operating temperature, then with the parking brake engaged, I put the car in Drive, disconnect the EST and set the timing. When its set, reconnect the EST and you're good. I run mine at the stock 6.

 

Hmmmm, I was thinking it was the "tan" wire at the dist cap? All I run is premium gas and what will moving it to 8-9 do for me? The car has minimal mods, the "free" L98 stuff, K+N filter w/open airbox, Hypertech HO cap rotor and coil, precats cut off.

 

my "tan" wire has faded to brown

 

The warmup is important. Drive the car around for a while and then reset the timing.. This is important because the car will go into open loop and you will get the correct timing advance for warm condition.

I don't know if putting it in drive when setting it is necessary though...

 

Ok, just checked it 8 deg BTDC and I run super in it. Good? The car runs great, I was just wanting to check it. What would make me want to make it 6 deg over having 8 deg? IE: what should I "look" for?

 

Any pics on how to change timing from 6-9 degrees? How would you know what position it is in? I'm guessing I need a timing light. I'm really curious on what this should do in my semi-modded 89. I do run premium so hopefully I won't ping once I figure out how to change it...

 

[QUOTE=formul89]The warmup is important. Drive the car around for a while and then reset the timing.. This is important because the car will go into open loop and you will get the correct timing advance for warm condition.


How do u reset timing i would be intersted in doin 8 or 9 deg for my
highly modded 85, right now its set at 6 deg by my mech.

thanks sami.

 

except for on my 86, i usually run 10-12.

 

[QUOTE=sami85L98]The best way is to set it at 8 degrees, take it for a WOT run and keep bumping a degree it until it pings, then pull it back about a degree and you are at optimum timing.

 

[QUOTE=sami85L98]You need a timing light and, it will be easier, a 9/16" distributor wrench, which is shaped like an 'L' .

You should first bump the engine over until the TDC mark on the harmonic damper can be reached. Wipe off any grease and dirt and mark the TDC mark on the damper with something that will make it stand out and be easier to see. I use fingernail polish, but about anything will work, like chalk, yellow grease pencil, etc.

Warm up the engine then shut it down.

Disconnect the EST wire, which is a brown or tan wire with a black stripe located near the power brake booster. It's a single wire with a weather-pak connector; just separate the two at the connector.

Connect the timing light to the battery; red to positive and black to negative. Connect the other timing light connector to the #1 spark plug wire; anywhere along the wire will work. It just clamps over the plug wire.

Using the distributor wrench and, standing on the passenger side of the engine, loosen the bolt that holds the distributor hold-down clamp, which is located at the base of the distributor. Loosen the bolt just enough to allow you to turn the distributor.

Start the engine - it may be a little difficult at first but play with the throttle until the engine will idle on its own.

Point the timing light at the hamonic damper and pull its tiggger. The light will being to flash. On the timing chain cover there is a timing tab. These tabs are slightly different depending on the year of the car, but you should see numbers on the tab. Look at the mark you made on the damper and see which number the mark aligns with. That's your base timing. If the mark is aligned with 6, you have 6 degrees before TDC.

To change the timing, all you need to do is turn the distributor. As you turn the distributor (by turning the distributor cap) you'll see the timing mark move.

Once you have the timing where you want it, tighten the disributor hold down bolt, then recheck the timing to make sure it didn't move as you were tightening the bolt. If it moved, loosen the bolt again and adjust the distributor some more.

Once you have the timing where you want it, and the hold down bolt tight, shut down the engine, reconnect the EST wire and disconnect the battery for about 30 seconds. This will clear the error code that gets set when the ECM detected the engine running with the EST disconnected.

Reconnect the battery, remove the timing light connections and you're done.

Jake

 

It might be also worthwhile to turn your motor to 0 degrees and check your distributor rotor. If it's not pointing directly at number 1 or number 6, then your balancer has spun on the hub. And that'll make setting the timing a handful.

 

Thanx JAKE ur knowledge and explanation as always clear step-by-step
and in details, may be u r good at typing soooo long sure it will help
the person who started thread and infact u made it easy a difficult job.
And not only u gave us confidence but also make it work.

sami.

 

Ok, just checked it 8 deg BTDC and I run super in it. Good? The car runs great, I was just wanting to check it. What would make me want to make it 6 deg over having 8 deg? IE: what should I "look" for performance wise?

 

I think advancing the timing moves the powerband down to the lower rpm range, therefore, making you think you have more power, i.e. if powerband is between 3500-4500 rpms, I'm guessing you will then have your powerband at 3000-4000 rpms if you advance it from 6-8 degrees BTDC.

Advancing it usually results in better gas mileage and more power at lower rpms. You will need to run a higher grade of gasoline.

Retarding it usually make your exhaust run hotter, maybe poorer fuel economy, makes lower rpms suffer, but lets you run lower octane gasoline.

Don't quote me on this. I just keep hearing it from other tuners in my area.

 

It's all about cylinder pressure; the more you advance the spark, the higher your cylinder pressure becomes, which equals more power (since this pressure is what pushes the piston down).

Think of it this way--when the spark fires before TDC, the mix is already starting to burn as the piston is finishing up its travel up the cylinder. At TDC, you've already got a good fire burning and pressure is rising quickly, pushing the piston down harder. If you advance your timing even further, the fuel/air mix has an even longer time to start building up pressure, meaning more pressure at TDC when the piston starts traveling down, and therefore even more power.

Downside of all is this is that if you have too much advance, the pressure and temperature get too high and you get detonation, similar to what happens with a high compression ratio. Also your NOx emissions go up because NOx levels rise with higher combustion temperature and pressure. It was pretty typical for automakers in the 70's to not add as much spark advance (as well as lower compression ratios) to lower NOx emissions, since the catalytic converters of that period didn't remove NOx emissions (NOx reduction is the 3rd part of a "three-way" catalytic converter).

Also, theoretically you could start having misfires from having too much advance, as the fuel/air mixture isn't compressed enough to light off. But, I've never run into that happening--typically you'll get detonation before you hit that point.

Finally, bumping up the advance shouldn't move the powerband around--it should increase power at all RPMs, although the effect isn't as noticable as at high RPMs since at higher RPM you're already running around 35 degrees of spark lead--a couple extra degrees of advance doesn't affect things as much as at low RPM when you've increased the lead from say from 6 to 8 degrees (a 33% increase of spark advance).

Hope this helps!

Ben

 

I nevr thought to wait til its in open loop-Hmmm

 

You will likely notice that with advanced timing you notice crisper throttle response.

If you advance too far you might hear ping at WOT and high RPM or the ECM may detect ping and pull timing before you can hear it.

You can find the optimum point at the strip or with a scan tool. The former will show optimum timing by best trap speed (if you are consistent) and the latter will show knock counts and the ECM pulling timing when advance it a little too high.