Good thread. Normally the intake will change the timing more then if it is carbed or not. You want to run the timing as low as possible that produces the best hp. So if it mph at 125 with 26 deg timing and still 125 at 34 stick with 26. I do a lot of dyno/street and track tuning especially L92 headed combos.

From the tests I have seen. A single plane has wanted an extra 10 degrees timing (with a carb) total at 35 degrees. The efi manifold likes 25 degrees, reason being more that the tq peak will be peakier with the efi manifold and will have a longer spread more linear curve but less pk with the carb manifold. Plus it is changing the air speed/flow into the chamber. Fuel mixture has little effect on timing only if it is excessively rich or lean.

Some engines will like 30-31 degrees with 10.4:1 with efi manifold on l92s, even with a very tight LSA for efi (233-238-110). This cam works awesome with L92s but I find it wants 12.0:1 afr(NA) and 31 deg lead right through the dip. It loved being rich and lots of timing. This tells me with all the overlap and long runners there is a sign of overscavenging, So it typically wants to be richer with some overscavenging, plus the overlap has an effect more of cooling the chamber and I would imagine it could cause some more swirling effect of airflow in the chamber so it liked more lead. A 232/234/112 likes being a tad leaner but less timing around 4 degrees less. The IVC is earlier with the tighter LSA camshaft but the other factors are changing the effect in the chamber. So earlier ICL does not necessarily require less timing.

Same goes for the manifold. I am running a carb and GMPP so I am keen to see how mine responds with 40 degrees of overlap! Still I know Im at 11.5:1 compression and a 48 deg IVC with a single plain. This setup with stock comp and efi manifold would be around 32 degrees MBT with 11.4:1 I would be stuck at 26 degrees. I have a strong feeling I will end up at 30 degrees. But start with less and move 2 degrees at a time. Cammed LSX will ALWAYS fall over before they knock. And they will drop enough to lose 3 tenths and as much as 3-4 mph trap. This is all in 1 degree. Generally though they will always gain something till you get there. So I change 2 at a time till it falls over, generally 1 deg later it will start knocking. So once it falls over normally 2 degrees back from there will be best in 99% of cases.

I will start at 22 degrees and move up and really see what happens, see where it makes its large gains with timing then its small gains. Once you get close you can jet richer and see if it picks up and or gets lazier or jet leaner, see if it likes it or falls over hard. I will be shooting for mid 12 afr and most likely end up at 30 degrees. I will post the results. To be honest I dont think to much when I am tuning, I just listen to the engine. It will tell you what it wants.

Another trick, If you start at 12.0:1 afr and 22 deg and i gets leaner with more timing it means it is picking up power, So you may have to add fuel to compensate for consistent results. When it stops getting leaner(or gets richer) with more timing it is a sign that it has to much. Again once you have found the "grey area" which is normally over a period of a few degrees. You can jet up or down and see what it likes best. High overlap LSX engines I have always got the best results with richer air fuel ratios AT THE TRACK. between 12.0-12.5. Sometimes they really fall over at 13.0-13.5. There can be 2-3 mph in this. On the dyno they normally respond to leaner afr and more timing then the track. This is also a trap you have to watch for. Always shoot for the minimum best timing and the richest best afr on the dyno for best track results. With efi and carb I have seen the efi like richer afr then the carb by 0.5:1. Larger carbs on small cube engines dont respond as well to jet ie dominators. You can jet up and down and have small response to afr but large response to hp. So in this case when u are in the ball park turn the wideband off and tune for best mph. Generally 12.5:1 and 26 degrees is a great starting point and most combos end up here.

 

Good info. Thanks for taking the time.

Ron

 

It sounds like you are under the impression that guys running 32+ degrees are a little on the overkill side (typically)...or am I misunderstaning something??

 

Well, so far many dyno tunes proved the Carbs liked 33-36 so there is no real dispute, but these I have seen have been cammed as well as carbed. Have not seen any non cammed dyno setups with Carbs.

 

My carbed 6.0/243's combo e.t.'ed with 28* of total timing, all in at 2000rpm, idle timing was at 24* then ramped up.... 2cents. Played with timing from 36* down on the chassis dyno too.

 

Not necessarily, depends on the combo/compression but most modern chambers like around 26-28 degrees. Just on my exp of tuning hundreds of LS engines. Carbed or not. It makes no difference, its the combination, heads /cam/compression/intake. My engine has a carb and likes 26 degrees if I run 30 it goes rich and loses even after i pull fuel. 36 deg is SBC territory(23 deg heads). The timing mark on the plug tells all!

cheers

 

Well...that is very interesting to me. You basically confirmed what my cam guy told me. That makes me feel really good about going that route as a really good starting point...and quite possibly the "optimum". Since this is considerably less timing than I was expecting to run, can I use 87 octane????? I have 10.2:1 static cr and 8.19:1 dynamic cr.

 

I'm not going to tell anyone what there engine should like. I can see a lot of guys here are using very wide lsa efi cams on single plane manifolds with less then 10:1 static in some cases which would require more timing then a 11:1 engine with a 108 lsa cam. All depends on the engine. I changed exhausts on a customers car and it wanted 3 degrees more lead. I guess there is no exact requirement. Some engines are more timing sensitive and have less "grey area" then others. I normally run the least amount of timing possible that makes the best power and richest jet. Garry Hunt (gaz05) LS7 makes 700 on pump gas and 26 degrees timing it fell over with more. Low comp motors normally wont fall over till knock, higher comp engines do. Not pointing out anyone in the carb section, from what i see they all have done very well with there combos. I have seen a lot over in the efi section though that quite possibly have left power on the table from over advancing ignition timing and say that L92s make best power with 30 deg lead. That is BS. Just give the motor what it wants best. I seen patrick G make 500rwhp out of a 6L with only 21-23 degrees for example!

 

As for fuel I dont know. I am from Australia and we have 98 ron fuel as our premium but that isnt as good as your 93 which is rated as MON. But the answer is with 8.19 dynamic comp 87 should be no problem. Just start low at 23 move 2 degrees at a time and see what happens. You can run 9:1 dynamic on pump fuel with a good chamber.

 

Initial Timing I have mine at 25* is that to high? It’s a lq4 with 243 heads and .580 lift cam.. fastest pass was a 7.47 on the factory curve 6 tune from msd trying to squeeze a little more out of her. What are y’all running??

 

I haven't done any dyno testing with carb LS stuff but I'm having a hard time believing a cathedral port head, let a lone a rectangle head wants just as much timing as a **** designed SBC chamber.

I'm not saying I'm right and everyone else is wrong, I'm just having a difficult time believing it.

From my experience, regardless of the engine, most people start with too much timing to begin with and keep throwing it in.

What I've been taught, read, done personally; the more efficient the chamber the less timing you need. So why does throwing a carb on a LS suddenly require 10 more degrees of timing? If you have to run that much extra timing to make power, the way i look at it is the whole combo is less efficient.

OR

People aren't doing any actually testing on a dyno or at the track.

Yes I am sure that a wet intake manifold has something to to with it. "Typically" a wet manifold likes run richer than a MPFI manifold. Is the added/excess fuel from the wet intake allowing more timing to be added without determental effects?

With all honesty I would like to see a dyno graph comparing "normal" LS timing curve with 25-27 degrees and the same combo ran at 36 degrees.

I'm not trying to come off as a dick, not at all. Please don't take it that way.

 

i would still like some actual factual basis behind this.

With the common theory we should be able to slap MPFI on a 85 C10 and pull out 10 degrees and make more power

 

I know my LY6 @ 10.8:1 comp with a, carb, Vic Jr., 110 LSA cam w/ 106 ICL, started at 32*, went up 2* every pass to 38* where it dropped off and I backed it down to 35* where at 34* was best 60' and 36 was best ET...35* was the answer.
I also had since fattened the mix up to 11-8-12.0 AFR @ WOT resulting in breaking into the 10's NA.

 

.hello can I ask you a question about a carb ls3?