newschool72

iTrader: (12)

Long story short, friends, our computer went boom and the wife and I decided not to fix it for a few months so the kids could explore this strange place called "OUTSIDE", LOL. Anyway , we moved to a new place and since we were starting over, we decided to get the evil black box running again. Had the thing cleaned and had 62 viruses and some horse thing making it wig out, LOL.
When the computer went down , I was in the process of trying to understand why an engine family with exceptional , fast burning combustion chambers would require so much timing when carb and carbed intake were introduced into the mix.
I think Im on to something, but would like to see some input on the carbed setups on this forum.
So here is the simple question.....How many of us use a low compression 6.0 shortblock, then add L92/LS3, or high end cat heads? My thinking is, with the huge dished pistons in the LQ4 (?), the quench area is basically non existent and killing the combustion chambers ability to get good mixture movement. That would explain the high, old schoolish 36* to 38* timing that is required for some of our engines to make power, IMO.
To see if that holds water, how many of us are running LQ9 shortblocks, and where is your best timing set at? With fly cuts on the smooth flat tops, the LQ9 pistons should allow excellent mixture movement and require much lower timing to make the best average numbers.
My simple setup is just an LS3 crate engine with a dual plane GMPP intake and a custom cam with short intake duration and a tight LSA. I had been running the engine at 34*. It ran great, but didn't sound exactly right. It just had a tight, almost bound up feel from 2K all the way to 7K. Ive been experimenting with lower timing and the engine has come to life! At 29*, the 7K limiter comes much quicker and the engine acts like its hunting a higher limiter setting.
I know every engine is different and no blanket statement can be said about what makes a particular engine run its best, but I would like to see if there is a trend of higher timing required for the dish piston vrs the flattop in the 6.0 truck engine. So, what yall got?

TXsilverado

iTrader: (18)

why get yourself so wound up into petty crap? give the motor what it wants and move on. if it wants 10* at WOT, give it 10*. if it wants 50* give it 50*. you'll drive yourself crazy with the why/how/when/where. 1 engine built identical to antoher wants a completely different timing curve. who cars. give it what it wants and move on.

here is an uneducated guess. cooler air in our dense fuel charge allows for more timing compared to the heat vacuumes that EFI have? or a carb just isnt as efficient....

Prorac1

iTrader: (4)

I did mine as such. I started at 32*

As I increased timing the car went faster.

Once I got to 38* the car slowed down

When I went back to 36* the car picked up and went right back to where it was before I went to 38*.

I never tried 29* because the car picked up ET when I went up from 32*.

Eric L

newschool72

iTrader: (12)

Eric, mine did the same. I started at 31 and moved up , 1 at a time till 36. It fell off, so I backed it up to 34* and was happy with the way the car ran. But something kept bothering me about how the engine felt. That , and the great combustion chambers being one of the big improvements the LS family has over the older SBC. Well, the great CC is only useful if it allows you to make more power at a lower timing setting. That allows the engine to run without having to fight with the flame front on the pistons way up to TDC. I decided to back the timing down to 29 and give it a try. The engine "feels and sounds" right for the first time since I dropped it in the car.
Im just trying to learn a little something and maybe at the same time give someone food for thought, before they start there first, or 50th, LS project. It just doesnt make since to not be able to take advantage of one of the biggest improvements the LS has to offer. That is , unless there is something else contributing to the poor mixture quality that would require all that extra work high timing causes. The combustion chamber is only half of the "hole" the combustion process happens in. The piston top is the other half. If the piston doesn't work with the CC to do the job, then the swirl in the chamber wont happen as efficiently .
With the ease of these MSD boxes to change timing, all it costs is a trip down the track to see. Cant get much cheaper than that , to possibly make better average power. I made the choice to start my timing at 31* based on the results of others . How much harder would it be to start at 27*? You just might find the sweet spot before you even get to popular carbed LSX timing.

newschool72

iTrader: (12)

I agree with you 100% on giving the engine what it wants, but how are you going to know what it wants if you start 5* over what is considered ideal timing for the design engines we run?

87caprice318

iTrader: (1)

sure wish you were closer to me Newschool72

Prorac1

iTrader: (4)

Ok. I can dig what your putting down…but without drag strip testing we still have no proof

I would gladly be the Guinee pig, but I have to keep the car consistant, and I do t know when I'll get back to the track after LS Fest

Doug G

Mine was identical to the above....Never tried under 32* either.
My heads are cut .050 for about 10.4-10.5:1 comp. so compression isn't the issue here.

3pedals

iTrader: (3)

Newschool, Your overlooking the fact that your engine is fueled by injectors.
I am convinced that, and compression ratio are the difference.

TXsilverado

iTrader: (18)

it's no different. if i had 31* of timing as my base and bumped it to 33 and lost time, my next move would be to 29* of timing to see what it does. most guys seem to start at the 30-31* mark and move up and gain power from there. no need to go back below 30 if you keep gaining by going up. it sounds like you're caught up in the heads and piston and not looking at our different intake design, different fuel delivery and our typical lower LSA and ICL cam profiles.

Doug G

Welcome back NS

Too big of a cam for the compression will require higher timing. Been there, done that
Higher compression won't need it with a smaller cam. I think due to the cylinder pressure.

dogsballs

doug has hit it on head. if you ran a sbc with the cams we do you'd run more compression. but ls guys don't, run big cam on moderate comp.

i have 11.9:1 and my sweet spot with locked out dizzy is ~26degs, that's a 236/246 cam

VLS1

Really? Care to divulge further on this?

speedtigger

iTrader: (16)

^^^ This.

We can all speculate for the sake of discussion, but if you haven't done the work to see what it wants by actual track testing, then you are likely to come to all the wrong conclusions. Timing is the easiest thing in the world to do A/B testing. Do the work at the track. Once you know what it likes, you can better guestimate why it is true.

newschool72

iTrader: (12)

This coming from the guy with the lowest timing on the whole carbed forum, LOL. Don't want the secret out?
I agree that the only way to get solid evidence is through track testing, or to a lesser degree, dyno time. That's why, in light of the fact that my health is at a point that I cant just run over to the track and lay down multiple passes, I look at the published dyno testing that's out there for all to see. I saw another example the other day in a test on LS3 heads. It was on a 468cid LS, pump gas compression, Mast CARBED (Dominator) intake, big ol fat cam speced for a carbed setup. On factory LS3 heads and 5 or 6 other LS aftermarket setups, the engine made best average power at 28*.
I can also see where you would say, well, it picked up when I bumped the timing up so no reason to go down. There are a lot of dynamics going on inside an engine when its at WOT. I can see where an engine could find sweet spots that it would run the best in a certain range of timing that's not in the optimal range for best timing, if that makes sense?
I also agree that the cam sizing and compression are relevant to the amount of timing an engine needs. I just don't think its only about the compression, because how is it that we get these lower compression LS engines 90% of the time. Its those LQ4 dished pistons, right? Id like to see a real test on two 9 to 1 LS engines with the same camshaft, with one using dished pistons to get the 9 to 1 , and the other getting there with a larger combustion chamber , that's still a fast burn configuration . Id be willing to bet the dished piston engine would require more timing to compensate for poor mixture action. This is what the question at the start of this post was all about anyway. That and trying to get the guys with the flat top pistons to give lower timing a try. If it helps, then my work is done.

dogsballs

quench is another issue.

speedtigger

iTrader: (16)

Secret? LOL. Here is how it went: When my car went together, I looked to see what most LS guys were running for timing. All of those examples were factory style EFI cars. So, I started out with what they were running. About 26 degrees. I went to the track and started experimenting. When I went down, it went slower, when I went up and after 28 degrees it went slower. I split the difference at 27 degrees. That is the big secret LOL.

As the combo evolved, I would try the same process. It still likes about 27.

TXsilverado

iTrader: (18)

once it cools down and i get a new set of tires i'll be playing with my timing on my flat top high(ish) compressin street motor. i'm currently at 31 as a baseline and have never tried anything else.

Doug G

Anyone hitting the track soon ? Would like to see what happens.

TOO HOT here for me and HUMID as hell....plus I'm looking at converters right now

fast89stang

iTrader: (2)

i'll be going saturday, if it doesnt rain. We are expecting lows in the 70s, so it will be better air than we have had in a while. I know 2 weeks ago, air was horrible. My alternator wasnt charging and I bet humidity was about 100%. i still mustered a 6.47. I wont have time this weekend to experiment more with timing tho. I do know mine has been as low as 32 I think, and kept picking up every time it was bumped. Even ran good at 39 over 38, but ran the same so I bumped it back.