David Vizard's Basic Cam formulas.

[Deuce]

I'll add that 10+ yrs ago I had the opportunity to ask David vizard 1 question while he signed my copy of his book.
Now at the time I was a Harley parts guy doing all the performance builds at the dealership, so cam selection was important for me, I had noticed screamin' eagle offering some cam's specific for EFI bikes, and they all (as you can probably guess) showed wider LSA on these cam's.

So I asked David 'Your books all refer to carburetor builds, what would you change for an EFI build?'
He replied 'the engine (or he might have said cylinder) doesn't know what's feeding it.'
Or he may have worded it differently, but basically to that effect.

Certainly changed the way I approached cam speccing.
Unfortunately it was after my current motor was in. Although that wide LSA crow is about to be replaced by a higher comp bottom end with camtech 107lsa

[vlad01]

Yeah thats it! I also say to anyone myself, the engine doesn't care what you think, it needs what it needs and your job is to figure that out.


I am pretty sure the wide LSA/EFI thing started with the LS engine and monkey see, monkey do I guess. But GM did it so the engine could meet EPA specs since pushrod can't have separate VVT for the intake and exhaust therefore must at a minimum have that built in design to meet those specs, where as DOHC you bet ya they command a tight LSA where it matters and widen up where that matters too.

[immortality]

The factory 304 cam is on a very wide LSA too. By the time the LS came around EFI had already been around a long time and we were well into the full sequential stuff.

You have to remember OEM's worry about NVH, EPA, drive ability and all that other crap and the relatively low power goals where the small cams were all that was required.

[vlad01]

Prob not the best place to put this, but this thread relating to cams and tuning and idle quality prompted me to revisit an old curly issue where the 12P tune always jumps to 14.7 AFR at warm up. Bigger cams hate this I found and it's so hard to figure out, I had to dig up my own posts from 10 years ago.

It's a transition from idle AFR tables, to main and back to idle table for 18 sec.

Here is a screen shot from the posts that 202 finally figured it out back then.

I had one of my tunes back then set the delays to 0s, but even a couple of sec should help a lot.

Probably should do a dedicated thread and write up/flow chart type of thing as a guide on how to go through the motions of tuning a large cam idle, start, warm up, cold and warm transients, AE/DE etc...

It gets complex fast, far more so the wider the LSA and having that still fresh in my head would be good to write down.

14-7 afr jump at 44c at idle fix.png (171.52 KiB) Viewed 5726 times

[immortality]

The later MAF stuff you can just set it for open loop idle.

[Deuce]

Probably should do a dedicated thread and write up/flow chart type of thing as a guide on how to go through the motions of tuning a large cam idle, start, warm up, cold and warm transients, AE/DE etc...

It gets complex fast, far more so the wider the LSA and having that still fresh in my head would be good to write down.

If you do, I will certainly appreciate this info early next year. Although running 11p, it's certainly a good start for me.

[Gareth]

Probably should do a dedicated thread and write up/flow chart type of thing as a guide on how to go through the motions of tuning a large cam idle, start, warm up, cold and warm transients, AE/DE etc...

It gets complex fast, far more so the wider the LSA and having that still fresh in my head would be good to write down.

Second that, I look at different tunes for the same cam and see very different ways of achieving results...

[vlad01]

I think some of this conversation could use its own thread... It would be very hard to find this info later for future reference...

I've learnt a lot in the last few pages

Well you did ask for this, even back then.

[inj gtr202]

Probably should do a dedicated thread and write up/flow chart type of thing as a guide on how to go through the motions of tuning a large cam idle, start, warm up, cold and warm transients, AE/DE etc...

It gets complex fast, far more so the wider the LSA and having that still fresh in my head would be good to write down.

Any detailed information regarding IAC tuning would be fantastic.
I've got mine "drivable" but still far from ideal.