Big cam 304 Tuning help needed

[Deuce]

What might help with the hopping is to richen the idle up a bit. I think I covered this somewhere before, but a tight LSA likes richer at idle I found. The timing is something than could help depending on the exact conditions, but I know more timing helps them idle better, but also more timing can make an engine at light loads and idle more snatchy when it comes to sudden transient loads which can feed back into bunny hopping and stalling, so it might work better with a little less timing when idling along in gears but more usually helps with idle in N, those two load conditions should use different cells in the tables anyway I'd think.

I'd start with adjusting the idle timing in N and watch for the highest vac, then go from there. On the main table those areas close to it can be adjusted to get the most stable idle driving conditions.


I will have to look up the exact setting, but a long standing issue I found in 12P is there is a timeout setting somewhere that delays a transition from idle to main table and back during mid warm up, this causes the idle AFR to go from whats set in the idle fuel table to the main and back for some given amount of time. So the AFR could go from 12 - 13 to all of the sudden 14.7 and then after a time is resumes back to the idle table around that 12 - 13 AFR. This was never an issue in wide LSA or stock cams, but I found it to be a minor issue on the stock Buick L27 since they run an LSA of 111 deg and you could hear and feel it in the factory tune, but once I went to 109 in my restro mod VP, it almost always stalled warming up abruptly about 50% of the time, as if someone just turned the key off. Because it was intermittent, I never picked up on the fact I had dealt with the same issue many years prior until one day just watching on the dash on TP I saw the AFR jump to 14.7 and it stumbled and nearly stalled, the stall saver caught it, but I was like "ah ha, I know this problem!"

I had this fix for my old vacationer from more than 10 years ago, but forgot about it and what it was called, but after digging on this forum early this year I found the old posts I made, it was actually 202 that helped me find the issue in the first place. I applied this to my hotted VP with the 109 LSA cam, I was also able to tweak the idle and warm up AFR table at the same time better than I did the first time knowing what I know about cam tuning now. Now it warms up much smoother and no more stalls! And it totally repeatable every time. But unfortunately, my chip programmer died exactly on the moment I went to update the EEPROM and I haven't got around to buying a new one given I am always short on money these days.

I have it all saved on this PC and my RT modded 808 as well. I should have a log txt file of the changes I made and call up what the setting for the table switching is called. I know I set it to 0 sec, it was like something around 20 odd sec or something normally.

I was able to get my idle down to only 50 rpm over stock too iirc after fixing that and the other minor tweaks.


One day I want to build that Formula Holden based engine for my VP S and I have converted the FH official tune to 12P and noticed that they ran not only 1600 rpm idle, but also that nearly all the settings other than the main tables were stock, so all the warm up and idle stuff and parameters that are critical to a good low speed, start up, warm up and transients for a large cam where totally stock. So looking at the cam specs, I reckon I could get the idle down to 1K or less once dialed in from that atrocious 1600 rpm band aid they used. Even the idle spark tables were stock too.

Not only that, the injector data was stock, kinj flow and all. But they ran larger injectors for sure. So it was all very poorly executed. But the main tables all look to have been done well and without a doubt on a dyno, so at least it will be a good starting point.

When started with this new engine combo, it was stalling out at idle. Leaning it up (from around 10:1afr) and adding some timing got it to where we are now and drivable.

Idle in D is the issue more than N/P for me.

[vlad01]

Yeah when I mean rich, I meant relatively. So I found 14 -14.5 AFR or there abouts was ideal for the 112-113 LSA. Stock is about 13.4 iirc for the 111 LSA cam, my 109 liked around 13.8. 10 AFR is really rich, it's probably fine when it first fires up and starts the ARF cold enrichment decay count down, but warm or hot that would run like a pig.

I feel that the tight LSA likes close to that stock or sometimes slightly richer but dislikes it too lean, but a wide LSA is the opposite, it tolerates lean very well but hates going too rich around that stock AFR and richer it just dies in the ass.


The acceleration enrichment also reflects this, tight wants a good squirt, when wide likes almost zero AE. And of course LSA angles anywhere in between those two ends are somewhere in between for those requirements.

[Deuce]

Yeah when I mean rich, I meant relatively. So I found 14 -14.5 AFR or there abouts was ideal for the 112-113 LSA. Stock is about 13.4 iirc for the 111 LSA cam, my 109 liked around 13.8. 10 AFR is really rich, it's probably fine when it first fires up and starts the ARF cold enrichment decay count down, but warm or hot that would run like a pig.

I feel that the tight LSA likes close to that stock or sometimes slightly richer but dislikes it too lean, but a wide LSA is the opposite, it tolerates lean very well but hates going too rich around that stock AFR and richer it just dies in the ass.


The acceleration enrichment also reflects this, tight wants a good squirt, when wide likes almost zero AE. And of course LSA angles anywhere in between those two ends are somewhere in between for those requirements.

That's good info, thank you.
I might do some more VE work to get AFR at idle into the 13's.

I don't think I've done very much on AE yet (I might have made a small adjustment) and previous cam was 113° LSA. I think it does need a fraction more fuel shot on accel though.

[brindo]

Just putting this out there as another option.
Do you have a manometer or would invest in one? They can be a pretty good tuning aid and at times can provide a better indication of engine tune over the WB O2. Sometimes you can see things the MAP sensor doesn’t.
Failing that, is it worth temporarily closing the throttle plate a bit to get the IAC position up a bit, then watch it rise or lower with timing and fuelling changes at idle? Then make changes till you get the lowest IAC position then timing wise come back a bit.

Make no mistake I am no expert and have a car that bucks under very light cruise too.

[Deuce]

Just putting this out there as another option.
Do you have a manometer or would invest in one? They can be a pretty good tuning aid and at times can provide a better indication of engine tune over the WB O2. Sometimes you can see things the MAP sensor doesn’t.
Failing that, is it worth temporarily closing the throttle plate a bit to get the IAC position up a bit, then watch it rise or lower with timing and fuelling changes at idle? Then make changes till you get the lowest IAC position then timing wise come back a bit.

Make no mistake I am no expert and have a car that bucks under very light cruise too.

I don't have one. But may one day.

Good thought on IAC. It certainly didn't behave well at 1.35v closed. I backed off to 1.04v and now 1.0v and it's infinitely better. I need to get it down a little more though anyway.

[AngelMarc]

Your ECU allow delaying injection timing. if not, and you get desperate, ought to be able to delay signal from distributor and add that degree to timing advance everywhere to get same result. Just be aware of rotor phasing at some point. Unless i'm not aware this is a crank sensor setup. I don't know aus models worth a damn.

[vlad01]

The issue is the 808 is batch injection, the only adjustments are double or single fire. So even delaying the injection via other means as you mention wouldn't do much as most of the injectors are landing in a random part of the engine cycle. So this is where fueling, AE and such are very important with certain cams.

The later models with MAF brought in sequential and EOI timing but as far as I know, they were only on the V6, not aware of a v8 version. The 808 being older and best supported make it universal for basically almost all engines.

[immortality]

The last of the Holden V8's, VS series 3 and VT 304's were MAF tuned with full sequential injection.

[AngelMarc]

Sounds like ECU swap time.
P01 or P59 and mount a 24x wheel to the crank like myself and other have. Somebody here did that on a Jeep; I did it on a motorcycle engine. I bodged the shit out of that setup.
Verifying crank sensor readings- https://www.youtube.com/watch?v=yv8rvb0K32Q
Actually running it- https://www.youtube.com/watch?v=g_Q6pFgmySY

On the off chance your willing to build a custom PCB, I'll mention my other project.
viewtopic.php?p=132802#p132802
Going to try an engine test again soon; hopefully next couple days I be able to show proof it works pretty good. All the bench testing looks good.

If it can't be full sequential EOIT adjustment, then I'd go with whatever spreads the spray out the most I guess, even throttle body injection, and probably just deal with some "weird" O2 reading and open loop only or something. Was going to say I've never messed with big cams, but many motorcycles do the same stuff.

[vlad01]

ECU change I think is over the top, it's just a matter of dialing in the above mentioned stuff. No one is ever going to get a big cam to idle like OEM, it's an air speed and low speed VE issue that is mechanically fundamental. But with good tuning, you will get it decent enough regardless if it's fancy sequential or old school batch. Most tuners that work on both say that going to EOI sequential is diminishing return territory anyway and all that I've talked to say there is no diff over 1500-2k rpm which agrees with my experience as well.

But I might add to your note on spreading the fuel, TBI etc... I found a narrower jet injector to work far better on these batch injection systems and also on more hot engines. The modern wide angle, 6 hole for eg injectors make starting and idling harder. My observation is the newer injectors atomize too much and the wider angles they tend to have spread the fuel all over the port walls, where the older injectors land the fuel on the back of the valve where it happily sits for the next valve event where it is vaporised as soon as the valve cracks open and the suction forces to vaporise as it's accelerated past the seat, that is also very low pressure there, and high velocity, far higher than the port walls which favors vaporasation over what can be achieved in the port alone. With bigger cams, the velocity falls at the lower speeds, so the walls end up hindering the fuel delivery until enough accumulates and becomes the manifold fuel often seen in EFI parameters where it does eventually pool up on the valve where it can do it's work. With narrow back of valve shot, it cuts a lot of this slower middle process out, hence why it seems to run better when the injector timing isn't timed with valve events or when it simply can't be. The engineers of the time knew what they were doing, it wasn't a technological limitation with injector patterns, rather a deliberate design to get the best out of batch injection which was the technological limitation at the time.

My current daily has the newer wider angle 4 holes, and it all fine everywhere, but at the lower speed and start up there is a slight but noticeable untunable backwards step compared to it's original narrow angle injectors. I also found the same minor issue with my hot engine in the other car, it runs the 6 hole FoMoCo F series injectors, very fine spray and wider, it just doesn't fire instantly just like the stock one with the newer injectors.

My other two cars still have the older design and, one OEM and one aftermarket 1 hole design, both start and idle superb, where the newer injectors idle fine in the other cars, but have that slightly rougher idle and slower start (the stock one) and the hot one is hard to say for sure given it's pretty modified, but it was more fickle with the starting, needing more fuel than just the injector flow differences and what the cam would suggest otherwise.

EOI would work around all of this, but for the older systems, the narrow injectors work best I found.