Tuning for Low Compression

[5_Liter_Eater]

Yea but then I'm just stabbing in the dark for numbers to use for idle and startup airflow.

[jakebdb56]

You running pump gas and no meth? Couldn't recall exactly what the setup was. From what I've seen on a few big cube FI GenIV's Mike & I have done they'll take 3-4* more than "normal" until you get into load. Since it's not an auto you probably won't have to worry about it being lethargic down low since it's loaded better. Some of the auto trucks I've done have as much as 26-30* to get it to spool on footbrake. I wouldn't worry much until you see more than 10psi or so. I don't remember what Inspector12 was running, but then again his motor basically runs on meth lol.

[JDS]

This is JDS99 from Corvette Forum with the 402 and custom 62/65's. I haven't posted on this forum in forever. I'm in the middle of street tuning as well. What is your new setup? Cam?

I just mentioned being at 19deg up top over on the other forum and people started jumping on me. I started at 15, and brought it up to 19 and the car really woke up on top. I'm 9:1 static with 243/251 116LSA cam advanced 4deg. If you're still running 10deg like in the tune you posted, I can imagine it feels like a dog if it's similar to my setup at all. Most I've run on mine so far though while engine breaks in is 12psi, and the 305/35-18 ET Street II's already light up in 3rd as soon as the turbos and cam ramp in.

[JDS]

Oh, and Dave that 3bar hybrid sensor you did works great!

[DSteck]

Oh, and Dave that 3bar hybrid sensor you did works great!

Sweet. Hope it made your life a little easier.

[realcanuk]

I am far from an expert but running a 402 with 9.8 compression and also running a lot more timing than you have. Timing also woke up my setup and its running great with 19 degrees up top/

[5_Liter_Eater]

I will take a log tonight that shows where boost starts, I want to say it starts ~.60 g/cyl. So when you guys are talking about "a lot more timing" do you mean out of boost? I think what everyone is seeing (low timinig) is a result of the 50% scaling/shifting of the main spark table. I did see that I forgot to change the IAT spark table back after I copied a bunch of stock stuff back into the tune and it's robbing a bunch of timing. I know I am being very conservative with the boost timing, I'm more concerned with the out of boost and transition timing. I'll take and post that log tonight showing driving around, getting into boost on gates (~11#) and on 16# which is where I'm limiting myself to for the time being on pump (93) and meth.

Sorry, the setup is an iron block 408 @ 9.6:1, All Pro cathedral heads, stock LS2 intake and TB. Cam is a 231/239 614/621 on 118+2. TTIX kit with 62/65 turbos and 2.5" downpipes to a 3" center section and 2.5" Corsa sports.

[5_Liter_Eater]

OK here's a good log with lots of general driving around and a decent amount of pulls on gates and mid boost. I've attached the log and the config and vcm scanner.cfg since I pipe my wide band through the AC. Also the latest tune just for completeness.

You can see (histo 12) that boost comes in at .4 g/cyl. Wastegates make ~11# which is ~.76g/cyl and SP3 makes ~16# which is at .92 g/cyl.

Flame suit on.

[5_Liter_Eater]

OK so I took everyone's advice added a shit ton of timing, mostly out of boost and I know I can ramp it out a lot slower when coming into boost. Car feels a lot snappier! I don't have to give it very much gas at all to get it moving. It used to lug around and I'd really have to give it gas for it to get out of its own way. I'm really shocked at how much timing it liked, hell it could like more. The previous main spark table was based off a stock table and just shifted 50%. The new table adds as much as twenty degrees to a good portion of the non boost area and even carrying on into boost.

I really want to play with it more and see how crisp I can get it. I really wish I could push timing around in real time with VCM controls on a load bearing dyno to find the ideal spark in each cell but it doesn't appear possible with the E40. It won't light up in VCM controls.

[realcanuk]

Huge difference in timing from the first tune you posted. Glad its running better and I am sure that's the issue for the most part. I know the setups are different but just in case it helps you can compare to my spark table. My car runs great in or out of boost.

[5_Liter_Eater]

Thanks! Is your tune scaled 50% as well?

[realcanuk]

Thanks! Is your tune scaled 50% as well?

No, its not scaled. I just used the stoich / ifr trick. Scared to scale with the automatic.

[jakebdb56]

I saw your first reply yesterday and meant to comment, but I see you figured it out. It'll definitely wake it up! Now for some videos, videos or fail... lol

[Pekka_Perkeles]

OK so I took everyone's advice added a shit ton of timing, mostly out of boost and I know I can ramp it out a lot slower when coming into boost. Car feels a lot snappier! I don't have to give it very much gas at all to get it moving. It used to lug around and I'd really have to give it gas for it to get out of its own way. I'm really shocked at how much timing it liked, hell it could like more. The previous main spark table was based off a stock table and just shifted 50%. The new table adds as much as twenty degrees to a good portion of the non boost area and even carrying on into boost.

I've seen similar things with heavily scaled tunes. What you probably don't want to know how high EGT's you have had with your previous tune (with so much lower timing)... I would also suggest EGT probes with both banks, they aren't that expensive and they are useful in cars like yours.

[MikeOD]

I've seen similar things with heavily scaled tunes. What you probably don't want to know how high EGT's you have had with your previous tune (with so much lower timing)... I would also suggest EGT probes with both banks, they aren't that expensive and they are useful in cars like yours.

I was going to make a similar statement...EGT comes up when you don't have enough advance in the engine...and on a build making 900+ HP, I think EGT probes are very worth it.

[5_Liter_Eater]

I just never had cause for concern because the scaling of the main spark table in conjunction with the larger injectors should have yielded a stock-like timing table until into boost. Its just that the new motor doesn't like the stock timing table one bit.

Still I'll look into EGT probes and how to utilize them. But now that the sluggishness is ~solved, I now want to focus on why I need to throttle the crap out of it to get it to start.

[MikeOD]

I now want to focus on why I need to throttle the crap out of it to get it to start.

It probably just wants to pretend it's a 2010 Camaro that's just been flashed...

Have you done anything to the cranking advance and airflow tables?

[5_Liter_Eater]

No I've observed what you're talking about re: a freshly flashed camaro. This is persistent.

I've dicked around with so much lately in not sure what my cranking advance and ve tables look like.

[MikeOD]

It's also worth saying...if you changed timing THAT much, you probably should now revisit your airflow model...a small change to timing won't have much affect on that, but a big change will definitely throw that off some.

Does the car sound like it's struggling to crank or is the starter turning it easily, it just doesn't fire?

[MikeOD]

Based on your idle airflow table...you're commanding ~1.76x the stock idle airflow in order to idle (at 850 RPM). That's seems reasonable to me given the larger engine, larger cam, and less timing at idle...that said, you're commanding completely stock startup airflow and startup spark advance.

I'd try taking the Startup Airflow table (Idle Startup Airflow vs. ERT vs. ECT) table, and multiplying it by ~1.76...you might then find the startup flares way too hard/high, but at least you'll see you're on the right track...you'll probably wind up with less than stock times 1.76, but more than stock by a decent amount. I think you're especially going to notice a startup flare because you've got the startup flare control spark table zero'd out. I've found if you've got too much startup airflow and then the spark is too agressive in the flare control table, the car will oscillate RPM and struggle to idle initially...might even stall...so you need to balance the airflow and the spark control.

If it sounds like it's turning over really really easily, you could also try more cranking advance...but you might not need to after the airflow tables.