Need help with timing

[sir loin]

I have a 1994 3.1L with a few HP add-ons. My manual says 10 degrees TDC. Will the timing need to advanced for mods like Mallory ignition, fatter cam and Holley car.?

I have it set now at 12 degrees and still tuning by "seat of the pants" method.

What do y'all think?

[SappySE107]

94 3.1 with a carb and distributor? Im confused.

[19Cutlass94]

?


my stock 94 3100 runs 24* advanced.

[sir loin]

94 3.1 with a carb and distributor? Im confused.

I'm confused that you are confused....

Yeah, I went with an Edelbrock intake, Holley 390 cfm, Mallory Unilite dist. with CD box.

Need to know if I need to advance more than the manual says at 10 degrees.

EDIT: Sorry, it's in an Isuzu pickup if that helps.

[SappySE107]

ah, ok. I thought that was TBI but I guess you swapped. I can't help you with the timing but most 94 3.1s on here are aluminum head FWD. Thats probably going to confuse a few others till they read this:P

[merlot566jka]

8-10*

i think you should play with it on the dyno and see what you get

[geoffinbc]

A hot cam will benefit from a timing boost. Advance is 2* until you get pinging while under load. Then back off to the last successful setting.

[sir loin]

A hot cam will benefit from a timing boost. Advance is 2* until you get pinging while under load. Then back off to the last successful setting.

Sweet, thanks.

[powerdoctor]

Agian... do he even have access to a dyno?

Timing depends on the bore vrs the stroke and engine speed period.

Advance is "anticipating" when to light off the air fuel mixture based on piston position relative to piston speed and flame front travel.

As a GENERAL rule of thumb on engines with a 4" bore and 3.7" stroke, your max timing would be somewhere between 34 and 40 degrees.

Get an inductive timing light, set it to 34 dergrees, and have your engine running at about 4500/ 5000 rpm and check where your timing is at.

On a carborated engine you should be able to do this without a problem and with no load.

Remeber if you have a vacuum advance on it, unplug it when doing this.

Your vacuum advance may be a problem as well.

Usuall I don't run a vacuum advance, I run lighter springs and modify the distributor so it will swing on the weights alone from 15 degrees to 38 degrees and let engine speed dictate my timing.

You can do this by modding the weights or stops in your distributor to get more advance, and be able to get the timing low enough for idle.

Remember to lock your pickup in the distrobutor.
Take the vac advance off and fab a little peice of metal that holds the pickup in place like the vac advance linkage used to do and make sure it mounts like the vac advance so your pickup does not move.

You should be able to keep a low initial timing and get your maximum advance by doing this.

Then run it and fine tune your max advance under load.

[sir loin]

Agian... do he even have access to a dyno?

Timing depends on the bore vrs the stroke and engine speed period.

Advance is "anticipating" when to light off the air fuel mixture based on piston position relative to piston speed and flame front travel.

As a GENERAL rule of thumb on engines with a 4" bore and 3.7" stroke, your max timing would be somewhere between 34 and 40 degrees.

Get an inductive timing light, set it to 34 dergrees, and have your engine running at about 4500/ 5000 rpm and check where your timing is at.

On a carborated engine you should be able to do this without a problem and with no load.

Remeber if you have a vacuum advance on it, unplug it when doing this.

Your vacuum advance may be a problem as well.

Usuall I don't run a vacuum advance, I run lighter springs and modify the distributor so it will swing on the weights alone from 15 degrees to 38 degrees and let engine speed dictate my timing.

You can do this by modding the weights or stops in your distributor to get more advance, and be able to get the timing low enough for idle.

Remember to lock your pickup in the distrobutor.
Take the vac advance off and fab a little peice of metal that holds the pickup in place like the vac advance linkage used to do and make sure it mounts like the vac advance so your pickup does not move.

You should be able to keep a low initial timing and get your maximum advance by doing this.

Then run it and fine tune your max advance under load.

Great, someone speaking my language....
I'm running a Mallory Unilite distributor. The instructions say, "...has a mechanical advance of 24* at 4400 RPM.

I can buy a kit from Mallory to change the rate of advance within a range of..."14* to 28*." It's called an "Advanced Curve Change Kit". The Unilite I bought uses mechanical advance but Mallory offers a Unilite with a vacuum

Yes, I have access to a Dyno. Just have to get it there when I have the time (first Saturday of each month).

So at this moment without the dyno, should I stay at 12* or should I experiment 2* at a time.

[powerdoctor]

You have 3 kinds of timing on carborated engines.

Your initial advance... engine at idle, no vac hooked to vac advance.

This can be set from 5 degrees to 23 degrees depending on the distributor.

Your vac advance...

Then your mechanical advance, this wieghts and springs.

Since you stated you have a mechanical, non vac advance dist, get an inductive timing light, set your max advance at 4500 rpm.

Hold the engine at 4500 and turn the knob on the bottom of the inductive timing light to 34 dgrees and spin the distributor till the timing mark on your balancer lines up with the zero mark on your timing tab.

Lock it down and return to idle.

If your idle, or initial advance is is 20/ 23.5 degrees you are fine.
If its lower...still fine.

If its at 30, 34 or something like that then you will have to "curve" it to get your idle or initial advance down.

Remeber you max advance is what you need to pay attention to.
Too much and you will get detonation, too little and you will run rich.

On the flip side too much low end timing and you will have off idle spark knock and will run hot, too little and you will run rich and foul plugs, possibly load your exhaust up and blow the mufflers out.

You also stated it has an mechanical advance curve of 24 degrees.

34 - 24 = 10 degrees.

So if you set it at 10 idle, you should see 34 max mechanical.

Your engine can run as high as 40 MAX, so play with it a little to see where it likes to run.

If it runs rich at a max advance of 40, take some fuel out of it, jet it down.

If it spark knocks at 40, turn the timing down till it no longer "knocks"

If you turn the timing down below 34 and it still "knocks" give it more fuel.

Like I stated earlier, its you max mechanical timing you need to worry about for power, between 34 and 40 MAX.

You will want to get it to run right within that margin for max power by playing with the jetting.

[geoffinbc]

Timing depends on the bore vrs the stroke and engine speed period.

No not true. Timing depends on bore, stroke and engine speed to a point. But the optimal setting depends on heads, cam timing and fuel more than anything because the cylinder pressure at the point of ignition, fuel and the efficiency of the combustion chamber (head) will be the 3 end factors that will matter.

If you take our engine for example with everything being the same and only changed heads (intake, and fuel system aside) the aluminum heads will require less timing to make max power. The aluminum head is a fast burn design with quite a large quench area where the iron heads open chamber design will burn slower and require more timing to make max power. But on the other side of things the iron head will ping more readily due to the lack of a descent quench area and irons slow heat transfer, versus the large quench area and aluminum's quick heat transfer. So take all these factors and mash it together and there is no formula for figuring out what timing works best. So just drive the thing or put it on a dyno. All people can tell you for sure is where to start from. So start from 10* and go from there. Yes the Dyno with a 4 gas sniffer is the way to go but sometime we have to work with what we have. Your butt in the seat.

[powerdoctor]

Betterthanyou is right here as well.

Those factors are a consideration as well as the bore and stroke, speed ect...

This is why I said to use it ( the timing I was talking about ) as a start and fine tune it under load, weather on the dyno or the street.

You should find no matter what your head setup ect... your timing will vary only a few degrees anyways, between 32 and 40, but the "fast burn" heads will have a lower timing requirement, but not a huge difference.

Test it under load and see....


Betterthanyou?

What do feel about using a rich mixture to stop "pinging" and provide the "quench" at a small loss of power.

I have always ran engines a little rich to be safe...

Smoke out of the tailpipes = POWER !!! ..... lmao

[SappySE107]

Fueling isn't going to provide you with a quench area. It will increase compression slightly but not quench area.

There is considerable difference between timing on the gen 3 heads and iron heads. A few is not an 8 degree span in my book, but its your post, not mine.

[geoffinbc]

Throwing fuel and too much timing to reduce pinging is not going to solve the problem. Reason being is that as you increase timing you start your power stroke earlier, before TDC which means power is being produced in the wrong direction. So the less timing you can run to make power the better in any situation. That is why you always see guys bragging about LS engines because they require very little timing to make power.

Now obviously you cannon run the timing after TDC to avoid combustion before TDC because you need to start the combustion process early enough to build cylinder pressure in time for the power stroke and also burn all that fuel in time for the exhaust opening. So with every engine it takes some testing to find what works best.