Helllo! It's good to be back. I bought another M-body and I'm working on building my 350 for it.

I have an L05 shortblock, iron L98 heads, and Comp Cams recommened the XR264HR cam (212/218 @.050 112°LSA).

I'm going to run a 2" TBI with BBC injectors.

Is anyone here running a similar setup? I'm curious how this combo comes off idle, and how well it drives around town.

In my old van I had a 350 with a 210/215 110°LSA cam it was a pain to tune. I don't feel like I ever got it sorted out (before a rocker stud broke and trashed the whole thing).

 

That cam will produce a very nice idle and drivablilty. The trick to tuning TBI in closed loop is having the correct PID tables adjusted. With a larger carb intake, better exhaust, better heads, larger displacement, and larger cam, the mass air flow seems to bug out. I found RBob's PID tuning for the 7747 a huge effect on getting complete control over my engine (small 212/222 .435/.460 112lsa). The thing just was terrible at idle, I also found the AE to be a bear to tune right. Ended up being the AE was overlapping the sync pulse widths and just not being registered... lean every 1 of 4 complete idle stop lights. I resorted to running rather rich at idle to compensate for this.

 

V8 Astro,

I had that same cam in my 350 Xfire up until this spring. Ran with it for about 4 years. Really nice for the street. I was using 80# injectors with it and was running 13.6's @ 101mph with 3.07 gears and street tires. The heads I used were TFS 23d and was very streetable. In fact, the torque was in the range of 430lbft at the crank at 3700rpm. The cam and head combination responded well to using 1.6 rockers and TPIS headers. Good luck

 

I'm running pretty close to that setup. Differences being that I have LG4 heads with 1.94 intake valves, rpm intake, and the next step up comp cam (218 226). I imagine the two engines would tune alot alike. Jprevost is right there is alot to be figured out with the PID loop, AE, and I have been having a ton of problems comprehending and tuning the Async and Synce switch points. All I know is that if I set them to anything other than whats in a 454 bin the ecm goes bonkers and I get a wicked rolling surge. I just ordered a WB so I'm going to figure this stuff out some time soon.

As for drivability, even with some tuning issues it drives wounderfully. I have a 2000 stall converter and the car litterally launches off the line. Very responsive, I did notice a loss of bottom end torque with the stock 1600 stall converter. For a van I would think the cam your thinking of would be perfect.

 

I've pretty much given up on async fueling mode with TBIs. Just doesn't work. Impossible to get the regular fueling to switch from and to sync mode and async mode without major AFR issues. Even then in async mode the actual injection timing is sporadic which causes back firing and popping out the exhaust.

Async AE is also inconsistent. It is not syncronized with plug firing or sync mode injection. So two things happen: first, the async pulses can be shadowed by the sync fuel pulses. When this happens less AE fuel is injected. Second, AE fuel may or may not be injected for a particular cylinder. So the engine is rough and un-even in fueling on a cylinder to cylinder basis.

With the Ultimate TBI code these issues are corrected. The changing of AE fuel to sync mode has made a significant improvment in engine smoothness and the ability to accelerate.

RBob.

 

We're all waiting on the edge of our seats for that

Thanks for all the replies.

 

Howd you implement that? I was thinking maybe something like storing the AE as a %duty cycle and then multiplying by the DRP to get the actual PW for teh AE.

 

Instead of adding the AE PW to the async accumulator it is added to the sync PW each pass through. This should be done after the BLM adjustment is made and before the DFCO/DE adjustments are made. An AE vs. RPM multiplier table is also nice to have.

RBob.

 

Got it. Guess I was thinking too hard. All the sync firings are relative to a single cylinder firing anyway so the PW is teh ammount of AE needed for each cylinder.

 

To add to this, wouldnt adding the AE PW to the sync PW cause more overall AE as the rpm increases because the firings get closer together? Does it matter?

 

Hence the AE mult. vs. RPM table that RBob mentioned. You could use a lower multiplier at higher RPM's to moderate the AE as (and if) necessary.

 

I thought thats what it was for but the 'would be nice' sort of gave it an optional sound. Im thinking of using the same sort of thing but with the DRP and a %DC so I can jsut have it work like teh stock stuff is for now.

 

What code would you use if you're requiring more fuel than there is time to deliver? You might want to put it into a ram location and do a little math where it calculates the DC and decays the AE. Example; AE wants 120% dc which would be no problem with async mode since it doesn't care about drps. What you'd want to do is have the sync pw maxed 100% (one time at 100% isn't going to hurt things) and then the next sync pw have the left over 20% of AE. This way you're sure you get enough fuel at low engine speeds and quick throttle openings . I'd like to eventually write a patch that does this for the $61 code. I can't tell you how often that async AE has messed with my head.