396V8

hi all

after a long time of struggling around with little to no success, i finally decided to switch to OL and tune via WbO2..`727ECM

all i can say, i should have done this a long time ago...
the engine is under control now, sure some minor things are still to care for, but overall its running much better!

what really improved is take off from stand still, also part and low throttle driveability improved a lot.

i managed to tame cam surge at around 2000 rpm also a lot, by dropping timing to 35° and richen up the mixture between 1600 and 2400rpm, around 50-60kpa (thanks to Orr for pointing in this direction)

what still give my issues are the following things:

car starts very good when cold, very good when hot, but doesnt like half warm starts...it doesnt catch immediately, when i push slightly on the gas, it starts...it seems like its flooding..this happens, at around 32-68°C, where the crank fuel PW is near the same..or maybe too little fuel? i dont know for sure now (stock tables run also near equal PW here)

next thing, when i step on the gas lightly, i get a short rich spike, then leans out, then settles, but this is also only when warming up...when the engine is at temperature, the lean condition doenst happen any more...
IIRC, short rich is TPS AE, so that seems to be ok, MAP AE is the longer lasting one, so Delta MAP AE vs coolant temp would be the hot ticket, is it?

last thing, just let me know what think about this...

i was long fighting with cam surge around 2000 rpm, i was so eager, that this is the "cruise rpm" and i MUST drive here(the brain can sometimes be a big enemy) and tried nearly everything to get the perfect smooth running engine here..needless to say, it didnt work well (it works good now, but as i said, real rich with less timing)



after thinking and looking at a different way,i come up with this...

i want be able to drive around 2000rpm without surge, but the real cruise rpm for my cam (236/240) is higher, i would say 3000-3500rpm...

that is also, where this cam is in its powerband, so it should be possible to take some fuel out here, and add some spark...just for light load, dont like that fuel is burnt, when its not necessary, the same method, that is used on stock engine with short cams at lower rpm..agree?

i hope someone will chime in (again), all i can say is thank you, im really happy with the progress that i have reached now with your help

antman89iroc

Ok, I'm using a MAF system so I probably cant help you with your specific changes but I have an otherwise simular cam and situation.

First, I have been unsuccessfull with closed loop. I know it is possible but open loop gives soooo much better control over the fuel, at least for me. I got a better understanding of why when I read the Edelbrock Pro-Flow electronic fuel injection manual. Go the their web site and down load it. Up to about page 10 they describe why a cam change alters the fuel requirements and go on to specify the spark timimg and fuel ratios that are required on an engine with a cam almost exactly like ours. There are even charts showing each curve at different loads (or vacuum). It's a must read.

Now since every combo is a little different you gotta make changes from there but it's a good starting point. I have yet been able to program closed loop to run as smooth as open. I had the same problems you describe and have been able to cure them all with spark and fuel. I believe you'll be surprised how much spark advance and fuel are required at low rpm/load. Now I am running ~13-13.5 AFR at cruise and getting better milage than up at ~14-15 AFR! Sounds backwards but it's true. Presumably because the motor is makine good power and the required TP for cruise is lower.

Also one more tip regarding tuning. Since you are tuning SD it may be different but what I do is tune when everything is up to full temp. Especially watch the manifold temp. For my HSR intake it runs best when up to about 140-160F. Other intakes may be different but what I found is that it is always richer when the MAT is below "normal" range even if the coolant temp is normal. I usually run to full coolant temp (10 min or so) then shut down and let the manifold heat sink, then I log and tune from there. As far as warm up go you gotta start fresh each morning and see what's going on and make adjustments from there. Probably startup enrichment or OL vs coolant temp etc.

One last thing which is probably the first thing really, if you have changed injectors you gotta make sure your injector offsets (batt & low PW) match your injectors. Not just the injector constant. I couldn't get anything to make sense until I corrected this.

396V8

Hi Antman!

thanks for your reply!

i will have a look at the edelbrock Manual, every bit of Information can be useful!!

i know that a cam have Major effects on an engine,vacuum down low, fuel, driving rpms, etc..
Also run around 13.5 AFR at cruise, but i only run 35° advance---more adv leads to cam surge...i added a lot fuel in some low rpm Areas to overcome enleanment when taking off from a standstill...works great by the way..
regarding MAT, i relocated it in the airflow, where no manifold heat is present, and adjusted the MAT table accordingly..

i think, you meant, when the intake gets heated up, fuel atomization is better...i also noticed that, with warm intake, it runs a bit nicer, and doenst make lean spikes with throttle movement
Adjusted the inj Offsets, like you stated...i found a great paper and even an excel spreadsheet!
personally i think.that im getting more and more in Tuning, and finally Piece by Piece it becomes a big Picture

my start up enrichment seems to be fine, as start up enrichment Comes in when engine is running..you can also see this in datamster, commanded AFR..i think my Problem is in the crank fuel pw, as i found out, it tends to be linear to a good amount, mine goes down rapidly at 20° and stays nearly the same to full operating temp...

anyways, i will get a look at the edel Manual and Keep posting

thanks

Orr89RocZ

iTrader: (20)

You'll probably want to play with that table. Warmer motor needs less start crank fuel. If having a hot or warm restart issue, try leaning those values out alittle at a time, esp if alittle throttle input helps the start. Means it needs air to overcome rich mix

antman89iroc

When you say "at cruise" what RPM are we talking. At 1600 I run around 39, 20-2200 I'm running closer to 46 at low loads. Of course every combo is different. I presume your 396 is a 4" stroke 350? I'm running a 3 7/8 stroke 400 so there may be differences there. Even if cam duration specs are close things like LSA can make a lot of difference due to late intake closing and the static compression (mines 10.4) comes into play as well. What I found to be the smoothest is mid 13's in the light-medium load range (cruise) but close to 12.5 at very light loads. I also found that rolling the timing back at light loads seems to cure some of the surging. For example, I have about 43 advance at 1800 at light load but it pulls back to 32 on overrun. That seemed to be one of the keys to getting the surge out. I'm running a MAF system so it's hard to compare apples to apples.

The way I understand it- the cam overlap allows some exhaust dilution of the intake charge making it slow to burn and unstable. The advance give it time to get burning and the extra fuel helps it to stabilize. The Edelbrock manual explains it all very well and gives some starting points very different than I am used to. Some of it seemed backwards to me until I tried it and it worked. Then I thought about it some more and it started to make a lot of sense.

Orr89RocZ

iTrader: (20)

That is correct. Its a type of egr action. Self egr basically. When egr is active, the exhaust gas partially or completely burned is mostly inert and changes mixture properties. It slows down burn and alot more advance is needed to get everything lit.

I think forcing more fuel in helps compensate for the extra inert gas and along with more advance, helps overcome cam surge which is reversion or too much egr action. Just something to play with to see the effects but i noticed on my cammed motors they feel better and smoother when more rich then lean.

antman89iroc

I speculate the "extra" fuel is actually for the "inert" gas leaving the rest of the "air and fuel" at the correct mix. If the fuel is left alone the mix is really left lean due the exhaust being present. In reality, what reads as say 12.5 on a wide band may actually be ~14 fuel to "good air" in the cylinder.

An interesting note in APYP/ARAP the "gobs" of timing they put in the lower end was probably for emissions/EGR but it ends up being pretty close when a higher overlap cam is installed due to the reasons sited above. My SA table ended up looking a lot like the stock APYP SA table when it was all said and done. I took out the PE spark so the Hi LV8 has spark at the mid range but the middle load mid-range still has a big dip in it lol.

396V8

Hello!

cruise rpm with my cam i would say, at least 2800rpm...in fact, the 396 is a 415 now, had some issues with he 396..just the sig stayed the same
intake is single plane efi, 236/240 on a 110 cam,AFR 195 comp port heads, comp is 11:1, stroke 3.875 x 4.125 bore

you are running a lot of timing....what heads are you using?

to your AFRs, thats what i found also..rich tend to smooth out a lot..im running also around 13 now at light load, and about 12.5 on very light loads...that cured most of the surge for me.