ox sensor on sequential efi,high overlap cam....

[Jemison Richard]

Tom,

Hi.  I'm not sure I follow your thoughts here and let me apologize for that
right from the start.  I don't want to argue or nit pick - we may be saying
the same thing.

> -----Original Message-----
> From:	Tom Sharpe [SMTP:twsharpe at mtco.com]
> Sent:	Tuesday, December 01, 1998 8:18 PM
> To:	diy_efi at efi332.eng.ohio-state.edu
> Subject:	Re: ox sensor on sequential efi,high overlap cam....
> 
> Group thoughts,
> 
> Wide centers help Idle. Why??? Exhaust closes sooner??? Intake opens
> later???
> Narrow overlaps have more torque and higher efficiency (BM??) at peak.
> Seem to
> be peakier and "get UP on the Cam" more/sooner.
	[Jemison Richard]  If you imagine a center line right smack between
the lobes with both lobes up - if now the intake move toward the valve it
should be clear that the intake opens sooner (relatively) the wider the lobe
centers are.  By the same token, the exhaust closes later.  As the lobe
centers decrease intake opens later and exhaust closes sooner.  Now this is
assuming symmetric lobes and all that.

	I just want to be clear that OVERLAP and LOBE CENTER are reciprocal
terms.  As the lobe center increases, generally the overlap decreases and
vice versa.  Again, cam grinders can play with these numbers and make all
sorts of timing arrangements.
>  
> Overlap causes EGR as well as intake charge in exhaust system. (intake and
> exhaust dilution).
> 
> EFI is probably worse as most squirt fuel on the intake valve before it
> opens.
> Called "settle time" by Edelbrock. (more time to evaporate). That means
> the
> richest mixture is sucked in (thru) first.
	[Jemison Richard]  Actually, efi should be better than carburetion
with wild cams.  With carbs velocity changes drive carburetors nuts and
excess gas is pulled into the cylinder then gases rushing backwards through
the carb also pull gas even further richening.  EFI on the other hand is
squirting gas irrespective of gas flow.  The problem with efi is that as the
fuel is pulled through the cylinder - extra fuel isn't going to be pulled
into the cylinder so the actual cylinder A/F will be lean under some
conditions.
>  
> Exhaust tuning (pulses) suck the cylinder dry at some RPMs and block the
> exit at
> others. Turbo motors don't care. Cam duration and centers (overlap) can
> really
> hose up a system or make it purr like a kitten.
	[Jemison Richard]  Turbos actually do care I believe.  Most turbo
cams are wide center line, mild duration, moderate to high lift cams.  You
don't want to lose all that pressure out the exhaust pipe!  Also, cylinder
filling is largely taken care of my the pressure developed by the turbo.  So
you don't need cylinder scavenging.  You already have a large pressure
differential across the cylinder to remove combustion gases and recharge the
cylinder.

	If you've ever heard a turbocharged Indy car idle you know they sit
and purr along like a Volvo.  Not a lot of heavy timing.   But then again -
they're only about 160 cubic inches too.  
>  
> Assuming we can measure the AFR with our O2 sensor (or EGOR) and tune to
> 14.7 or
> 12.5 or xxx, it still will not tell us how the motor is running. We still
> need
> to adjust each combination,,,, say to highest vacuum or whatever,,, so the
> it
> runs good (and does not polute). We still need to tune.
>  
> Maybe we just set the idle speed above the problem areas for those of us
> with
> too much cam...( like too short shorts ) a lot is good, more is better and
> too
> much is just right.
	[Jemison Richard]  I agree with you here.  Why worry about it.  If
you're running this much overlap you're not staying up nights worrying about
emissions!  You're racing! 
> starting to ramble    sorry  Tom
	[Jemison Richard]  

	I'm in the process of turbocharging a 4 cylinder inline 4 stroke
motorcycle and have talked with many people who have already worked with
similar setups.  So while my comments are not based on personal experience
with this bike,  they are based on working systems running both efi and
turbo.  I believe if I can find the right sized injectors that I can get my
bike to idle quite smoothly and will be working toward that end.  I'll keep
you posted as to my progress.  In the mean time, check this turbo bike setup
out http://www.ptw.com/~gsxr1100/   

	Also,  grab your favorite cam grinders spec sheets or catalog and
compare hot street and turbo cams and check me out on this.

	Rick