I read a great thread over on the HPtuners forum about tuning the injector timing normal and makeup tables based on your cam specs. I don't have my truck with me until this weekend but I was wondering if anyone has played with those tables after adding a mild to high duration cam.

A couple people in that forum claimed to have picked up 25ftlbs of tq in lower rpm regions. Also it should take care of the rich smelling exhaust since the injector would inject close to or at the end of the overlap cycle. So no raw fuel would be able to leave strait out of the exhaust valve and out of the tailpipe. And thoughts or experience with these tables?

 

Yes with large/larger camshafts you can have what's called "short circuiting" at lower rpms where fuel is getting blown right out the exhaust valve due to the overlap of the larger cam. Delaying injection timing some from what the stock setting is can help with this.

 

How much would you delay? 17-18% delay were the best results for the two guys on the other forum.

Would you delay until you get the richest mixture? That way you know most or all of the injection is being burned?

 

I've just been reading about this too. I wonder if it would matter on a cam like mine with zero overlap. Sounds like it would make the engine more efficient and add power. Anyone know exactly how to do it?

 

No, you would only lose the benefit of having the stock GM setting, which is to have the injector spray hitting the back of the closed intake valve improving atomization.

 

Ther is an actual spread sheet on HP tuners in one of those threads. You input all your cam info and it spits out a "base number" to start at. Then adjust accordingly. Not real sure how accurate it is, haven't messed with it yet but it's worth a shot.

 

Yea that spreadsheet was created with just guesses. It might be a good starting point but you would need a dyno to really dial in the correct number. There were two guys in that thread who used a dyno to tune the timing. One guy found best results with a delay of 17% at operating temp and the other found best results at 18%. So for us who don't have access to a dyno, do you guys think it's safe to just give use those numbers in our tune?

 

When I tune cars/trucks with larger cams I have been delaying the injector by the number of degrees that the exhaust valve closing event deviates from stock. That has worked well for me so far. But I have not put anything on the dyno. But the engines usually feel better and it seems to cure a lot of low rpm surge.

 

Anyone have a link to the thread?

 

Injector Timing? Reference Periods? refereencing what? - HP Tuners Bulletin Board