Boost on Stock Timing

[Edub1]

Who's running boost on stock timing? How much is safe?

Trying to see where to set my start point on my BTM, it goes up to 5lbs before it starts pulling.

[C-Kwik]

My XS Engineering Kit ran 6.5 psi with nothing but a FMU on stock base timing and no timing control. I had a wastegate fail on me and it started overboosting to about 8-9 psi and I'd get some knock. I'm thinking that was a result of a fuel deficiency though. I'd say you're safe at 6-7 psi with an efficient turbo setup. Consider backing the timing on a less efficient turbo though.

[Florida240sx]

Anythign ovewr 8psi have timing retard.... you could reatard a couple degrees oof base and run 10psi, but need to have an accurate knock meter.

[Biggamehit]

just retard it to 15 to 18* you dont wanna boost on stock timing. detonation will thank you later if you do so.

[Edub1]

Sounds like the KA will take quite a bit of boost with stock timing.

I have a new BTM that allows you to set a start point after which it will pull timing 0*-3* per pound of boost. The start point can delay retard untill after up to 5lbs.

If you guys are getting away with 8 I guess I'll just set it to 5lbs and pull 1*/lb after that.

[KATwo40]

Can't you set it to pull smaller increments than 1*? If possible, I'd opt for .5-.75*

FWIW, I ran 8-9psi with the SAFC2 and 15* BTDC on a T3/T04E .50 trim for a long time on my DOHC engine (stock motor, 200k miles). I now run a tuned daughterboard, but I never had knock issues with the old setup.

[Edub1]

15* is -5 on the DOHC right?

I can do .5 or .75 but the whole slope gets pushed to the right when I use the set point so:

-.5*/lb after 5* would put me at -5* at 15lbs

-1*/lb after 5* would put me at -10* at 15lbs

Or I could do .75 or I could do .5 but start at 2lbs.

My intuition tells me it's better to start later and pull heavier at higher boost where it becomes an issue. If the rule of thumb is .75*/lb, I want to be pulling about 11* at 15lbs. So, the hold off till 5 then pull one plan sounds about right.

[KATwo40]

It's my understanding that the BTM pulls x degrees per total psi, regardless of when to start.

For example, if you set it to 1* per psi, then 15psi = -15*, regardless of whether it begins at 1psi or 5psi.

Someone correct me if I'm wrong on this, please.

[Edub1]

You know I asked a guy at MSD and he said the same thing. However, the directions clearly indicate that it's as I described above.

See fig 1:

[Neejay]

But how would you set that with a regular BTM? (not the newest one)

[Edub1]

You can't

[KATwo40]

You can't

Actually, you can. Just use a manual boost controller in the BTM boost line.

[KATwo40]

You know I asked a guy at MSD and he said the same thing. However, the directions clearly indicate that it's as I described above.

See fig 1:

Hmmm, I see what you mean (second slope depicts 11* total retard based on the parameters).

[Neejay]

Why is it better to have the retard come in at a specific/higher boost?

[Edub1]

Why is it better to have the retard come in at a specific/higher boost?

Lower boost levels don't create the conditions that cause detonation so you can run more timing for more power. And the slope is probably a steep one with regard to higher boost and detonation.

[KATwo40]

Yep...the later you begin the slope, the steeper it will be.

[lrb_2000]

My base timing is at 16* for about 12psi... which is still pretty conservative, but it runs fine.