At what point does a cam become to large to tune? I have a couple of cams in mind and don't want to go to big. The first cam is a comp hyd roll. It is a 242/248@.050 .576/.600 on a 112. The other cams are single pattern with less duration and more lift and the same lobe sep. I will start tuning my own stuff after the 29th of Aug when I get my adapter from Craig Moates. The cam I have now is a 236/242@.050 .555/.576. It isn't that bad but the cam is jacked up because of a lobe sep regrind.

 

No problem,

Traxion, has a cam around that size and he runs 12s. I think the only problem that you may have is idle, but if you widen some bias values you should be just fine (ie: idle rpm error, O2 error).

 

I'd strongly recommend you find a commented hac of the 8D code, and start investigating things.

That is a bunch of cam. Not to be flip, but you'll need to take advantage of everything you can. Chamber size, quench area, CR, and especially overlap.

With alot of overlap comes self EGR'ing, ans with out know the exact exhuast latencies for O2 sampling you might be out on a real limb. If so then Open loop is going to be your only answer.

Another hint at someone needs to build an ecm bench and go thru things to really establish the limits of the stock code.

 

If your looking for performance loose the sh!ty EGR.

 

The EGR crap is gone. I have 11.2:1 cr, 58cc heads, and a flat top piston with an 11cc shave at zero deck. The comp cam has 73 deg overlap according to comp. My computer says it has 21 deg. I need a little cylinder bleed off for the compression ratio.

 

A mini-ram that accomodates EGR?.

If your addressing my post, ANY cam other then a 0 overlap one will have some self EGR'ing to it. Having both the valves open with the exhuast having more presure then the intake, the engine will suck in some exhaust. Also the piston moving down with be drawing in some from that effect.

The reason you have to richen up the idle, and add timing with the bigger cams is because of this.

 

Didn't read his sig, thought he was TPI. Yes I understand the overlap, but I think its the characteristic that often gets ignord by some people when selecting a cam. My self if have 114 lob sep, and I love it, makes great tourque. But just from playing around on Desktop Dyno, It says had I went with everything the same just went with 108 lob sep I would have 30 more top end hp. Everyone nows that the big boys (not me) run huge overlap and there gas milage reflects. But thats not important. You are right Grumpy in your description of self EGR'ing for Idle, any overlap at all will make the engine harder to tune at low rpms. It is hard to accomadate the motors dynamics though tuning, this due to the non-repeatability factor at Idle. Still I think your motor would set up nicely.