CAM LOBE SEP & EFI??

[1project2many]

Some of the cam advice may be left over from the old days. Slower processors and early code didn't play as well with a big cam. Rapid intake pressure spikes would trigger acceleration enrichment and rapid timing changes, rich exhaust would drive short term and long term fuel toward the lean extreme, engine speed would start hunting, and it would create a cycle that was really tough to control. Today's controllers are so advanced that it's a very different game.

A properly tuned ecm does a great job of eliminating all sorts of compromises we had to make with carburetors. Increasing idle speed, advancing timing at idle, running a loose converter so the car didn't surge at a stop light, stinking rich exhaust are much less common these days. Can you make the system behave like a carbureted engine? Sure. If you're comfortable with carbureted engine behavior by all means, install a computer and tune it to do the same job.

You mentioned what all you could do. What can I, an EFI newbie, accomplish??

More than anything, the answer depends on your patience and your expectations for engine behavior. I think you could probably dial in many of the spark and fuel settings rather quickly and make it so you can drive it without blowing up the engine. What usually takes time is driveability around town, start up, and idle. That process usually requires multiple drives, datalogging, change calibration, and drive more.

[Vettepilot]

Ok, thanks.

One thing I hate about IAC is how slow it is to return to low idle. (On all cars with EFI.) I know it's to resist stalling, but I like an engine to crisply rev, then instantly return to idle.

No, I don't want to tune to be just like a carb. I just want to be able to run cams with moderate overall timing, but a tight LSA, with EFI.

Vettepilot

[MO LS Noobie]

On the later OBD 2 cars this is called throttle follower, it mimics the old dash pots on carbureted vehicle. You can adjust it for more or less delay

[steveo]

if your IAC is too slow, throttle follower doesn't fix it or settings not available, and you want your idle to drop quickly, you can play with your timing advance vs idle error settings or whatever it's called in your definition. actually that's a very powerful setting that can increase or decrease cam lope and other things. another way to roll is you can close off the IAC passage by an aribtrary amount and then muck with your throttle plate. that way the IAC only makes fine adjustments and the throttle plate does its thing. finally on race cars i have deleted the IAC and just set a slightly higher idle that runs a bit crappy for the first few seconds but cleans up real quick as startup enrichment tapers off.

[steveo]

Some of the cam advice may be left over from the old days. Slower processors and early code didn't play as well with a big cam. Rapid intake pressure spikes would trigger acceleration enrichment and rapid timing changes, rich exhaust would drive short term and long term fuel toward the lean extreme, engine speed would start hunting, and it would create a cycle

with the old slow ECMS i had usually run open loop, disable AE, lock down timing outside of operating range, and just do my best. results have been really good and 'better than a carb n points' but definitely not economical, but it's the customers fault for not wanting to swap to an ECM that doesn't suck. 'not playing well' i think was just people not doing a good job, sometimes doing a good job is simplifying a crappy system until it behaves

[Vettepilot]

Thanks guys.

Is Megasquirt any good?

But then I'm not sure what I would use for the TBI itself...

Vettepilot

[steveo]

most old 160 baud slow ass old tbi ECMs (which are probably older than the original nintendo entertainment system and have about the same processing power) have a newer 8192 baud cousin that is quite easy to re-pin for and better to tune. that'd be much easier than a megasquirt which is a total do-over.

you can really use most any TBI with most any TBI ECM if you are handy enough

edit: but to answer your original question, yeah, megasquirt is just great. really nice product. tuned 2 of them now, difficulty medium but rewards are great

[Sledhead2]

Do some research on the thumper cams, they are noted for being a POS.

Look online and you will find they are known for being all sound and no go, along with no vacuum at idle, thus no power brakes.

If your looking for the classic rumpity rump rump sound, there are way better cams that will give it and go.

https://www.chevelles.com/threads/thumpr-cam.1164438/

[1project2many]

One thing I hate about IAC is how slow it is to return to low idle. (On all cars with EFI.) I know it's to resist stalling, but I like an engine to crisply rev, then instantly return to idle.

So this is a part of tuning. Three factors affect idle speed. Spark advance, fueling, and air intake. For older ECM's the timing affected idle fastest, fuel next, and IAC last. Many of the OE vehicles are programmed to decelerate more slowly. Both emissions and OE needing "vanilla" tuning play a part in that. Newer ecm systems, and systems with electronic throttle control, can drive IAC and idle speed changes very quickly.

with the old slow ECMS i had usually run open loop, disable AE, lock down timing outside of operating range, and just do my best.

When I built the 302 in my '57 in 93, I was told the 350 hp 327 copy cam I was running was too big. I was using an 83 Camaro ECM back then and my only paid for tune from Turbo City ran like poop in OL. But CL wasn't bad, all things considering. Very wide INT and BL limits combined with mild VE changes were all that was done. I was very disappointed with that tune considering I worked for GM dealer and felt the vendor had promised it would run well. After learning to tune I had to give the tuner props as he worked entirely from paper specs and only got one shot to get it right.

[Vettepilot]

I used to be a hell of an engine builder and tuner. I also used to be pretty hot at learning new tech.

But now, at 70, learning all this EFI tuning stuff is sounding more daunting than I want to take on; maybe more than I CAN take on.

Maybe a newer, self learning EFI setup is how I should go... (And whatever dam cam it will support.)

???

Vettepilot