Just thought I'd share some cool info I witnessed today at MTI. One of the local guys that posts on this site was having Jayson dyno-tune his 422ci Camaro (M6) that was getting some pinging occasionally after he got the PCM custom tuned. It was showing 30-31 degrees of timing across the rpm range. All Jayson did was use LS1-EDIT and back the timing down to 28 degrees total across the rpm range and the car picked up power across the board. Even made the graphs smoother. It was a very noticeable gain, about 5-8 rwhp in most places.

From playing with my own car on the dyno many, many, many, many times, I've never seen any gains past 28 degrees total ignition timing. But, I never thought going higher could possibly hurt performance, so this is a first from what I've seen myself.

Anyone else out there do some extensive dyno-tuning? What is the max timing you guys find where performance peaks or levels off? I'm also wondering if this value changes with different sized motors.

Tony

 

Would a 422 somehow need less timing?

 

I remember Steve (Just Me) saying he ran best at 27 degrees. No dyno figures.

Ryan

 

Would a 422ci motor need less timing? Perhaps. That is what I'd like to discuss as well. Jayson has an idea that the larger motors are more efficient at making power than the smaller motors, and might need less timing. Anyone else have something related to this idea?

Tony

 

Geoff @ Thunder Racing tuned a local 387ci all-bore car recently and lowered the total timing in some places and picked up a good 10-13rwhp in the upper rpms. Timing was originally around 28 degrees and it left with ~25. This motor is running over 11.0:1 compression. After messing with the fuel, another 5-7rwhp was picked up. Just goes to show you what a dyno with wide-band capibilities and someone who knows how to use LS1 EDIT effectively can do.

Jason

 

But in theory isn't a larger engine always 'less' efficient then a smaller one, all other things being equal?

Just out of curiousity, why do LT1s have so much timing? Is that because of the reverse flow cooling? They have higher compression then stock LS1s do, right? I wish Mickey Albert would get in here, he has a very strong 370", I wonder what sort of timing he is seeing. I do know his car has had no aftermarket tuning, not Ed Wright, not Steve Cole, not LS1 edit, nothing. Amazingly he still runs ~ 124 MPH N/A. Just curious, do Z06s and LS1 FBodies/Vettes see the exact same timing numbers? How about an LT1 vs an LT4?

 

Tony,
I've learned a lot since I've begun reprogramming PCMs. I'm sure you know all the factors that influence timing.

My experience to date is strokers need less timing. Compression is also a big factor.

I just finished up a 427 CI Z06 and when I finally had it tuned on 91 octane, I was only running 18.5* of timing. Pretty sad. We had about 1/2 point more compression than we wanted so we are going to open the chambers a bit. We should be able to maintain power and reliability.

Small cams and higher compression really become sensitive. Our IIx (11.2:1 compression) w/ our 224v3 cam only like about 24* total timing on 91 octane.

You can see the problem by looking at the dyno curve. If it gets a bit rough, then there is probably too much timing, even if there is no knock retard. Most the time there is about a 2* window where there won't be any change in power, but running less timing may help in the 1/4mile since there is a lot of heat buildup compared to a short duration dyno pull.

I go through this all the time with people trying to get their cars dialed in over the phone. There is this misconception that somehow 30* is the magic timing number. Not true.

 

One other thing. The longer stroke motors have less piston dwell time. So if there is more spark lead, then you may be pushing down on the piston before it needs to be. Motors with better rod/stroke ratios can run more timing.

 

Tony from what I've seen since 98 most 6 spds work the best around 27-28.5 and most are in that area. Mine when it wasn't getting KR was in this area and felt the strongest and on the dyno showed the same. I have about 25 dynos on my car with timing from 20's up to 28-29. Doesn't most of the 422's after the install with no pcm adjustments show about 25 degrees?

 

Look guys, this is no big mystery. Bone stock 10.1 CR 346 LS1 engines with 93 octane and tuned perfectly can use as high as 30 degs. Everything else will need less. If you run higher than stock compression, you will need less timing unless you run mucho overlap on the cam. If you run lower octane, you will need less timing. If you change the chamber shape, volume, or do away with the swirl vane you will need less timing. If you hog out the ports and reduce runner velocity, you will need less timing. If you run a larger bore you will need less timing. That's right folks, larger bores are far more sensitive to detonation than smaller bores. There is NO across the board, one size fits all, magic number on timing. It must be experimented with your car at the track or on a dyno.

As far as LT1s go, they are a totally different chamber layout and design. The LS1 has a far more efficient combustion chamber design than the LT1, so it requires less timing.

 

It's always made sense to me that a larger CI motor will require less total timing, due to a denser combustion mixture.

What is less intuitive is that you can have timing related power issues without having knock (or at least knock retard), and that you can lower timing and not lose any power. Guys who are running lower octane gas (91/92) with heads/cam should really pay more attention to this area. Doesn't hurt to test out an inverse timing tricker. If you don't slow down, leave the timing out.

 

Excellent replies everyone! I've never put faith in that magic "30 degrees" figure that gets tossed around here. My car has never run any better past 28 degrees. I used to have 30 degrees with just heads/cam, but it went down to 28 when I did the 382ci motor. Now you guys have me wondering if I'll pick up more power by going to 26 degrees LOL.

Damn I wish LS1-EDIT for 98 cars was available! I could have some serious fun with that program and the dynojet/track. <img src="images/icons/smile.gif" border="0">

Tony

 

[quote]Originally posted by Terry Burger:
<strong>
What is less intuitive is that you can have timing related power issues without having knock (or at least knock retard), and that you can lower timing and not lose any power. </strong><hr></blockquote>

That's right Terry. Many people don't know that you can actually run too much timing advance and it will lower your power without causing detonation. What happens is the spark starts combustion while the piston still has quite a bit of upward travel on the compression/ignition stroke. All of this rapidly expanding gas and pressure pushes back down against the piston as it is traveling up. This also puts a big strain on the rod bearings and piston pins. So you see that you can quickly reach a point of diminishing returns on timing and start going backwards on power output. I tune my timing and mixture by trap speed at the track or at my local 'test strip' affectionately know as 'Tullahoma Proving Grounds'.

[ November 25, 2001: Message edited by: 2quick4u ]

[ November 25, 2001: Message edited by: 2quick4u ]</p>

 

From what I've always understood that the less timing you can get away with the better. This has alot to do with the quality of the heads. If you can get a fast burning head you can run less timing. What happens is the more timing you run the sooner the plug will fire. This igniting the fuel on the upstroke of your piston. As anyone can figure out this will cause a loss in horsepower because your motor is in effect fighting itself to get the piston to the top of the cylinder. So the less timing you can run the better. Now take into account that as I stated earlier the quality of your head port etc. has alot to do with this. On a lesser quality head more timing will actually pick up hp. I run an lt1 and run a total of 34 deg. becasue of my head. I lost hp by going up and as I lowerd the timing I picked up hp. Its really a per car thing and each one will act alittle different. Happy tuning guys.

Tim

[ November 25, 2001: Message edited by: 95 Formula ]</p>

 

Another observation about ignition timing. If you are at the track and you cannot hook. If you can, lower your timing some or richen your mixture. This will help kill off a little of your low end torque so that you can hook better off the line. Otherwise you can always throw your track jack, tires, and tools in the back. <img src="images/icons/smile.gif" border="0">

 

Good information Tony. How much is MTI charging for some LS1-edit work? Ive only got ~20 degrees of timing <img src="images/icons/frown.gif" border="0">

 

""Would a 422ci motor need less timing? Perhaps. That is what I'd like to discuss as well. Jayson has an idea that the larger motors are more efficient at making power than the smaller motors, and might need less timing. Anyone else have something related to this idea?""

Bigger engine simply have more compression and use less timing in general. What does an MTI 422 have for compression? Also I've never really checked for sure but how does the computer even know what the timing is? Anyway that's what dynos are for. Change it and test until you get somewhere! <img src="graemlins/burnout.gif" border="0" alt="[Burnout]" />

 

I have seen a 39x cid motor run better dyno number's with over 30* on 110 octane unleaded gas than with 28*. But by judging by these post's this is the exception.

No, the Y-car and F-car do not run the same timing tables. Atap shows that my 01 Z runs slightly more timing at certain rpm ranges than a 01 vette. until you get to around 5400-5500 rpm's. Then the f-body start's to fall off.

 

Consider this:
The flame front has to travel further in a bigger displacement motor (all other things being the sme; octane, RPM & CR) than a smaller combustion chamber, so affecting the timing requirement

 

You cant compare the LT1 to the LS1 when it comes to timing. The LT1 was not as efficient at making power so there was a need for more timing.