tuning for larger cams

[E-Rue]

im trying to remember little snipets of old posts about the timing and fueling requirements of larger cams. if i remember correctly, they need less fuel at idle and low rpm, and more timing at idle and low rpm?
is this right?

i found after i installed my new cam it was hard to start, and stalled as soon as i droped it into gear. i checked the plugs and they were totally black. i tried lowering the fp a lot, and i could get it to back up, but only if i kept a little throttle while i droped it in gear. as soon as i let off the gas, it would die. i also tried advancing the timing by a couple degrees manually to see if it would keep from stalling, but didnt have any luck. i figured before i try much more id ask to make sure im going in the right direction. i know im gonna have to do some chipping to get this thing to run like its susposed to, but i didnt want there to be something wrong with it, and me be blaming it on the program, rather than the real problem.

background: i just swaped cams (mccoys 512 cam) in my performer plus motor, everything else stayed the same.

thanks for the help.

e

 

[leroy]

Watch the integrator when you make the fuel pressure adjustments to make sure which way you need to go.

A new chip is the real solution. Having wideband and an emulator makes quick work of it.

Jim

 

[10secTy]

With the larger cam you pull less vacuum. Which does two things.

#1 it will pull less vaccuum on the fuel pressure regulator which will give more fuel at idle.

#2 It will pull less vaccuum which will put you in a differnt part of the idle VE table. This will also give you more fuel at idle.

So you need to watch your datamaster and see where in the KPA it is idleing.
Then make the changes to bring your integrator back to 128.

Then once Idle is set up start retuning the main VE table as the cam will affect your entire fuel curve.

Nolan

 

[myclone]

With the larger cam you pull less vacuum. Which does two things.

#1 it will pull less vaccuum on the fuel pressure regulator which will give more fuel at idle.

To cure an overly rich condition is the only solution to shorten PW and lower the FP? Im especially curious of what to do with larger injectors (~83lb/hr) as Ive heard that you can only shorten the PW so much before you have to look else where for solutions to an overly rich idle with a big cam

#2 It will pull less vaccuum which will put you in a differnt part of the idle VE table. This will also give you more fuel at idle.

Is this situation cured by rescaling the fueling vs MAP table(s) to give you less fuel at a given (higher in a big cam situation) vacuum?

so you need to watch your datamaster and see where in the KPA it is idleing.
Then make the changes to bring your integrator back to 128.

Any "changes" in particular that would be best to concetrate on here?

Then once Idle is set up start retuning the main VE table as the cam will affect your entire fuel curve.

Nolan

Understood.

TIA for any info.

 

[10secTy]

To cure an overly rich condition is the only solution to shorten PW and lower the FP? Im especially curious of what to do with larger injectors (~83lb/hr) as Ive heard that you can only shorten the PW so much before you have to look else where for solutions to an overly rich idle with a big cam.

I would not lower the fuel pressure as then you might run out of injector at full boost and high RPM. I only shorten PW.
As for how low you can go on PW, I have Peak and Hold injectors Idling at 0.35 PW with no problems at all. Do not try this with saturated injectors they will not like it. The Delphi's seem to be ok.

Is this situation cured by rescaling the fueling vs MAP table(s) to give you less fuel at a given (higher in a big cam situation) vacuum?

Well yes and no. Yes less fuel at a Lower(less) KPA reading in the idle VE table. But it is not just a simple move everything over fix. You must tune the table to match what you need.

Any "changes" in particular that would be best to concetrate on here?

I like to have the long term intergrators zeroed out and just use the short terms to dial it in. Basically fire it up and watch what the short term blm's do and adjust accordingly. Make sure you are at operation temp when you decide to make changes as start up fueling stays on till 56C. Once you are past that point make changes to get to 128. Then once its dialed in put the truck in gear. It will Idle in gear in a different KPA and you will have to adjust that as well.

As for the off idle VE tuning once again use the s-term BLM and take it easy till all the non boost tuning is dialed in. Once you are happy with the numbers you have (128) start at low boost and use your DIY WB to dial in the Boost fueling.

Nolan

 

[myclone]

Thanks for the info Nolan. Much appreciated