Big cam 304 Tuning help needed

[Rhysk94]

What timing numbers are you guys ending up around with the cammed 5L's ?

Also what is your timing down low at take off & cruising area's, that will have a lot to do with its manners

[Kevspec]

If the heads are cleaned up especially the chamber it will effect the amount of timing it will take

[vlad01]

Only way to determine timing other than at idle with any accuracy is a dyno.

Generally I found with a bigger cam, timing increases at low rpm cells and idle, but decreases in the mid to high rpm and that seems to be regardless of CR, but of course CR will lift the the lot up or down but not really the shape of the map.

Exhaust headers also have a significant roll in timing too, short and choked primaries like OEM or cheap nasty headers will decrease timing and lower knock threshold, long and correctly tuned headers will lift the knock ceiling and timing to get to MBT will increase as well.

At idle, you simply up or down the spark and watch for max vac. Normally most larger cams want around that 28 deg at idle. Ranging between 25-30. Most stock are like 20 deg.

[Wade]

In the Greg banish tuning book he talks about idle timing and retarding it as much as 10deg from mbt and from the main spark table. If you match both tables it can make it feel flat during the transition from idle to main spark tables. Plus having spark in reserve at idle allows idle control to advance idle timing if needed. If idle timing is already at mbt then it’s got nothing left ect.

[Deuce]

I was actually going to do a big write up and guide on cranking/cold/warm/hot starting and warmup for cams as I found some very counter intuitive results that go against 99% of the advice and hearsay on the net. But my health limits me to smaller stints of being able to do anything really involved at the moment and likely for some time, it's on the list but I can't promise anything for a universal guide write up.

Hey Vlad,

Did you manage to get some of or all of this big write up done?
I'm keen to read it and see what suggestions I can take away?
If not, let me know and I'll start a thread on "big cam tuning tricks and tips."

[vlad01]

Sorry, I hadn't. My ongoing health woes didn't leave me with much capacity in the last 12 months to do much other than home duties when I could and my memory is shot and all, so I forget things almost immediately most days due to short term memory issues and brain fog. I'd have to tune up something to refresh it all in my head and hopefully have enough energy and motivation to write up about it after the fact. What I wrote up in this thread is most of the jist of it anyway. What I wanted to write up specifically about is the systematic procedure to follow so one can interpret whats going on and then dial it in. I vaguely recall a number of the parameters were interdependent so it had to be rapidly iterated in a certain order over multiple days to dial it in, cold days at that iirc.


Maybe I can help you go though the process on here and we can all build a cam tuning thread or perhaps continue the one I stated so it's all in one thread.

[Deuce]

Sorry, I hadn't. My ongoing health woes didn't leave me with much capacity in the last 12 months to do much other than home duties when I could and my memory is shot and all, so I forget things almost immediately most days due to short term memory issues and brain fog. I'd have to tune up something to refresh it all in my head and hopefully have enough energy and motivation to write up about it after the fact. What I wrote up in this thread is most of the jist of it anyway. What I wanted to write up specifically about is the systematic procedure to follow so one can interpret whats going on and then dial it in. I vaguely recall a number of the parameters were interdependent so it had to be rapidly iterated in a certain order over multiple days to dial it in, cold days at that iirc.


Maybe I can help you go though the process on here and we can all build a cam tuning thread or perhaps continue the one I stated so it's all in one thread.

Cheers Vlad, sorry that your health woes are ongoing.
I'm easy either way. We can continue on here, or I'm thinking quote your earlier words into a new thread specific about general tuning.

I've got 11.3:1 355" 248/252 solid on 107° lsa. $11p.
It runs and drives fine (now) but I'm still concerned with low idle in drive. My next move was going to be more timing under the ideal idle rpm.

One piece of advice I would add, is set that 3-4 shift at minimum TPS to not engage until over about 65kph. Therefore it holds 3rd around town and bucks less.

[vlad01]

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.

[VK_3800]

There's a thread around here somewhere about return-to-idle tuning too, a few possible tips there. I found that significantly more timing in the low rpm rows of the main spark table, than the idle spark, was quite helpful.

[Deuce]

There's a thread around here somewhere about return-to-idle tuning too, a few possible tips there. I found that significantly more timing in the low rpm rows of the main spark table, than the idle spark, was quite helpful.

Idle spark adv as a function of MAP:
24.96 across the board.
Approx 80kpa/1000rpm
Main Spark timing map, 26° 80-100kpa, 400-1200rpm.
I might lift that whole area to 30deg and see what happens
Average 12.779 AFR from 110cell hits (samples) on a recent short trip (servo to home) 1000rpm/80kpa as a good estimate for idle AFR it is seeing.