kwiksilverz

I am tuning my twin turbo LS2 (APS kit) and was just curious what others are doing for timing. I ran pump gas along with a dual 15GPH nozzle alky kit spraying straight meth. My current setup is 15* around peak torque with 17* up top with 15-19 psi (depending on what I doing, I turn it up or down)- I am getting 0 kr through the entire pull. I felt this was safe from my past tuning experience with other motors, but was told today that the LSx's don't like much more than 13-15* of timing max under boost (at the 15psi+ levels). Is this true?

Also, the car is running the stock cam too, so my cylinder pressures have to be up there a bit. Just curious what the bigger power guys are doing. The car did 795/778 as it was, but was having issues pushing coolant at anything over around 17 psi. Nothing bad, but it would push. I just want to make sure my timing isn't too much for it to handle.

Lastly, what AFR should I shoot for? I was going for 11.2-11.4, but again was told that due to my cylinder pressures and the fact that I am running alky, I want to keep it around 10.8. What are you guys doing? Thanks in advance.
Joe

kwiksilverz

I wanted to add, I am running 9.4:1 compression with untouched 243 heads.
Joe

LTLHOMER

iTrader: (10)

24 deg with c16. 21 lbs of boost 8.75:1 stock cube motor with ported 241's. No coolant issues.

kwiksilverz

Do you mind sharing cam specs? I wonder if it is due to my stock cam that they were concerned with cyl. pressure. I know the pump gas/alky issue was a concern too since we weren't sure of an actual octane #. I still personally feel from past experience that 13-15* seems very soft, but am fairly new to LS1/2 motors, so I am still learning what they like and don't like . Thanks!
Joe

LTLHOMER

iTrader: (10)

252/244 at 0.050. .700 lift on both intake/exhaust on a 114.5 lsa.

kwiksilverz

Ok, so you are bleeding off much more pressure than I am, that's for sure . Do you run 24 straight across the board, or just in the upper range? Not that I am going to even try 24* with my setup right now, I am just trying to get a feel for how you guys are setting up your timing curves.
Joe

MIGHTYMOUSE

iTrader: (59)

i dont go over 17# on pump and meth. my timing numbers are similar to yours and i have much lower compression (8:1) so i would consider your tune more aggressive than mine as-is

i would move the boost or timing down until you stop moving water and let it ride at that.

your a/f is fine.. there is no need to change your target a/f figure because of meth.

there is no harm in dropping the timing down to see if the car likes it, but the further i come away from where i am at now it hurts power after tq peak.

Pro Stock John

iTrader: (34)

7.9:1
348ci
236/236/114
24 psi
a/a
867rwhp thru unlocked t400
~19 degrees of timing with C16 or equivalent

Jim please correct me on the timing if that's wrong.

qqwqeqwrqwqtq

Your cam is 234/234 113lsa

I looked at the data log from your 867rwhp run and it was 26psi boost and 20 deg timing.

Pro Stock John

iTrader: (34)

Since you guys have the car right now, what do you think would happen if we increased the timing to like 24 degrees on C16, think it would blow up?

kwiksilverz

Cool, thanks for all the info guys. Now when you say your timing is xx*- are you talking locked in throughout the boost range, or does it start higher/lower and taper to that? I am running say 26* or so at the onset of boost, then it drops to ~15* at peak torque, then climbs back to 17 in the upper RPM's. I know some people just lock the entire range at a set timing, others prefer a curve.

I was also told to retard it a bit more pre-boost and it will help spool faster, but I had always tuned like I was tuning an NA motor prior to boost thinking it will make it run better on motor before the boost hits. Any advice here?

kwiksilverz

Also, any advice on cam selection? I have known several people who have had very good luck running aggressive NA cams with turbo cars and making good numbers, and other who will only run a "turbo" grind and do well also. The theory I had always heard about running the big NA cams is it will bleed off cylinder pressure, allowing you to run more boost on pump.

What's the consensus here? I was going to go with like a MS3/4, but someone else recommended the Cartek 2X boosted cam- 224/230 560 lift 114 separation. Anyone here using this? Thanks again.
Joe

qqwqeqwrqwqtq

LOL, I doubt it would blow up, but the headgaskets might not be very happy.

30psi and 30deg of timing might blow it up.

Pro Stock John

iTrader: (34)

Are you surprised the head gaskets hold up?

Quick, I've read conflicting posts about non-WOT timing, some folks say hit it hard with timing so it will come up faster into boost.

kwiksilverz

That's what I have always tried to do, but I have since heard that retarding the timing will spool quicker than more advance?? I dunno. Hopefully someone here has firsthand experience .
Joe

MIGHTYMOUSE

iTrader: (59)

there isnt a firm answer on high off boost timing or low off boost timing for spool, so i just put it in a happy middle where i know it won't cause trouble and leave it.

my timing is vs. boost pressure and vs. rpm so it does lots of things depending on the situation. generally it dips at tq peak and rolls a few back in at peak rpm

PurEvl

iTrader: (2)

19* at 14psi on pump 93 830-850+rwhp. Never even so much a head gasket in 18 months. 230ish cam as well. t88/408.

I run 24* at 8psi , 22* at 10psi etc etc.

Zombie

iTrader: (2)

That definately works with an automatic. My 6 speed seemed to like less timing to build boost faster though. With the th400 it LOOOOOOVES the timing to get it spooled.

kwiksilverz

sounds similar to what I am doing. Sucks that timing via HPT is with g/cyl vs. rpm instead of kpa vs. rpm. I am maxing out my timing table early on and I guess it just carries the last number over through the rest of the range . I guess I can set it to what I want on pump gas and alky at 16-17 psi and it should probably be good there at 20-21 psi with C16 in it .
Joe

Pro Stock John

iTrader: (34)

Better to leave some power on the table unless you are willing to involuntarily redo the engine.

We could up the timing on my car for example, and found out the limit of the head gaskets by finding out when they burn up.