help with twin turbo timing.

[edl406]

I have a sbc 406, with twins, Old fast efi with a lt1 harness. 27lb injectors(yeah I know they are lil small),1000 cfm tb, Isky racing cam, 10.1 comp., edelbrock pro flo alum intake and performer heads.
http://www.iskycams.com/timingchart.php?product_number=201281&timing_chart_id=98
Im kind of confused, well i should say kind of lost. Im having troubles figuring out what timing values to place in the fuel map, (map vs rpm) Im running a 2 bar map. When I set the dist I set it at 6 deg, like the fast directions said (hei ext coil)Now are the timing map values totals with the 6 degrees already added of do I have to add them :hammer: ?
And what is the max timing that I can run with pump gas, where would that go in the timing map??

[matty b]

Whenever I tune, I prefer to get the advance in quickly up to 100 kpa depending on what your motor wants that could be 40 degrees down to 30 degrees. Tune it like you would without a turbo on it. As far as when you get into boost My recommendation is to take out a degree of timing for every pound of boost. Depending on how fast the turbos spool up you may need to pull the timing out fairly quickly so the timing map will look like a cliff but normally boost builds slowly for a second and once the turbos are up to speed the boost comes in rather quickly. I havent tuned a blown motor on the FAST setup so Im not for sure if it has a boost timing compensation window like some other units. What it looks like if it does is a single line of windows and a rising scale of map pressure like 100 kpa then 120 kpa, 140 kpa 160 kpa ect. If it does then you can put in how much timiing you want to pull at those setpoints which makes it really easy to do boost based timing. In that case you more or less make a naturally aspirated timing map and it pulls timing based on that window. If not then you need to just do it the manual way and work your way up. Depending on your motor it may or may not be suseptible to detonation and you may need to pull more than a degree per pound but that is a safe starting point. As far as you r distributor being set at 6 deg this is more or less a base point from which to work. Do not subtract 6 deg from the timing map to compensate just put in the timing values you want. Also remember that youre MAP will move in a diagonal direction from low to high rpm so keep that in mind when setting up the map. The faster your turbos spool the steeper the diagonal will be as the boost will come in at a lower rpm. Your pump gas question all depends on your motor and only a dyno will tell you what you can get away with

[edl406]

thanks for the info. Im going to try the 1 degree drop per psi for later in the tuning. (working on non boost right now)The fast system combines the tables, starts at 8 kps up to 205kpa. I kind of figured out that below 100kpa would be regular tuning. Im still working at the non turbo timing and fuel. I have starting issues, cold start wont take throttle and seems to chug till the temp gets up a little. Hot start has to have WOT to get it to start.
Im sure I can get it , just may take me a little time.

got a question, The BOV's have what appears to be adjustments on the backs of them, they are sequential. I havent driven the truck any where yet, just ran it in my garage, when I rev it hard , I feel just a little pressure coming out of them when I let off of the throttle, that is right around 100kpa, or maybe like -3psi. Should it be releasing pressure then or should I adjust them?
And I have a turbonetics manual boost control but dont know exactly where to set it, should it be backed all the way off for now. or screwed all the way in?

[edl406]

there doesnt seem to be too many willing to stick their necks out on this subject. Im still at it. It appears that under n/a Is where I have to start and Im getting pretty close to where i need to be. I called my engine builder and he gave me good starting points. Then Im going to start with a 1 degree drop per lb of boost when I get the non boost table section done. Ill try to post my table and my engien specs when I get it done so others have somewhere to start.

[camcojb]

this is a very conservative timing map on a twin turbo I've tuned. Timing depends on many things; compression, octane, head design, boost level, etc. For a street deal at say 14-15 psi and a good intercooler I'd like to see at least 25-28 degrees at wot and full boost, but your combo may or may not tolerate that. When you pull too much timing it does affect power, but then again running too much is worse.

I do use at least 40 degrees (usually more) in the light-throttle cruise areas; again, this was a conservative map that won't get you in trouble.

Jody

[edl406]

when are you pulling from the cells with 40 in them? It doesnt seem that I ever pull from those cells. I have only putted around town and not on the highway though. I was told to max out my advance around 3500rpm with 34 degrees because of my compression and pump gas, it seems to do alright with the 34.
Im going to try a little closer to your 100kpa 0 rpm's values Im up in 19.5 and has a hard time starting.
Do you remember what the compression was on that engine and was it pump gas?

[camcojb]

when are you pulling from the cells with 40 in them? It doesnt seem that I ever pull from those cells. I have only putted around town and not on the highway though. I was told to max out my advance around 3500rpm with 34 degrees because of my compression and pump gas, it seems to do alright with the 34.
Im going to try a little closer to your 100kpa 0 rpm's values Im up in 19.5 and has a hard time starting.
Do you remember what the compression was on that engine and was it pump gas?

I've run 20+ degrees at idle with every efi engine I've tuned, from 8:1 to 12:1+ compression. There's also cranking timing in some systems.

That engine map will be in the 40 degree timing at 2000 rpms and up, which is where he cruises. Usually that timing number would be at a lower rpm to start. That motor is about 8:1 since it's a twin-turbo specific build.

[hotrodf1]

If you don't get all the info you need here (which I would think you can), you can also try Turbomustangs.com EFI section. LOTS of guys doing what you are doing over there. It's scary how many of those guys are popping up out there. You never know when you are going to pull up to a turbo'd vehicle and get smoked.

Such cool stuff!! And good luck!

[DeltaT]

Remember you won't really build any boost in your garage so you can't really test your blowoffs - the turbos won't boost mcuh with no load in neutral.

Jeff Hartman's excellent book 'Tuning and Mpdifying Engine Management Systems' has a great chapter, 'EFI-101' on tuning an EFI setup (including forced induction tips) from scratch, I used it to tune my 383 myself (with a wideband built in) and save a lot of money. Over 630rwhp now on 72# injectors.

Jim