fuel tuning with long duration cam

[sprattzvx]

hi all. just wondering what typically is the angle to take when tuning longer duration cams. from the tuning ive done with the cammed l67 it would appear they will run rich at lower rpms and suddenly lean out over a few hundred rpms as they come into there efficiency range. but that cam was pretty mild. if some one was to install say, a cam with a duration of 242/242 on a 116 lsa, in a fresh unstarted donk for simplicity sake with stock injectors working of stock base ipw/constants table, what would be the first thing you more experienced people would look at in the startup tune? afaik the wideband isnt really too reliable at a rich idle with a large cam.

[yoda69]

Shouldn't be idling a motor with a new cam anyway, normally meant to keep it up around 2000RPM for 20 minutes anyway, although if it is a roller cam this is no longer a problem.
If the RPM is up around 2000RPM the wideband should be fine for monitoring, and asjust realtime as required depending on ECU.

yoda69

[sprattzvx]

yep hydraulic roller cam. so blm off and just pull fuel out to get as close to stoich as possible, then blm on and allow the ecu to trim the fueling as it sees fit. simple enough. so theres no guru tips to be had. bugga

[Holden202T]

probably the most important things i've found are:

1. idle rpm, thats the main thing that bigger cams need, more idle rpm, once thats set you can usually atleast keep the motor running enough to get the fuel and spark dialed in.

2. spark is the next thing, usually bigger cams will want more timing at idle, with a map system you try and increase / decrease the timing to get the most vacuum, in a MAF system i would assume this is the same as a higher mgc reading ?!?!!?

3. dialing in fueling - the bigger the cam the more fuel you waste at idle, (blows out the exhaust half burnt due to overlap of the valves) so on a stocker where it might idle at 14:1 or something like that, you might find a big camed motor will need 13.5:1 etc, really this depends on what your motor likes, i usually just increase fueling at idle till the engine sounds smoothest .... ie. too lean will make it hunt at idle, and too rich will usually make it sound more cranky (and foul plugs more often) .... its alot of trial and error an experience for this one but even without experience you'll soon work out what it likes.

[sprattzvx]

good stuff 202. after seeing the carbon buildup on my last pistons ill be looking to keep the fueling as close to stoich as i can at idle and cruise. think my generous pe settings would have not helped either. over-cautious.

[Holden202T]

yeah theres a fine line between pleasure and pain