[Supras] SAFT, AFM signal add-ons

[Jim Jobe]

>     Your statements about the 7M TPS providing accelerator pump-like functioning is comforting, as is your contention that the stock richness under boost is not that bad (will follow suit with the Lex and 550 injectors).  I've searched out and saved a couple of charts illustrating A/F ratio vs. relative power, and I agree with you, on the assumption that the A/F is not richer than about 10:1.  Speaking of which, I'm curious about your statement that your engine did not run well at 10:1.  Any leaner, and EGTs would be higher.  Any ideas?  

EGT's wouldn't necessarily be higher.  Ignition timing can change EGT's, too.
How well it runs also depends on RPM.  But, understand I have a standalone EMS
and run much more than stock boost.  :-) I shoot for 12's up to about 5 psi,
11.8 up to about 20psi, then richen it up above that.  Good times.  10:1 =
misfire = bad times.

>     I've looked at the Apexi SAFT information and a writeup intended for Mitsubishi 3000 installation (not that different from the 7M) and now understand it pretty completely.  It still rubs me the wrong way, though, that a near-step change in throttle position at off-idle is not compensated for due to frequency recalculation latency (I did not see any TPS pot input for the SAFC for a stronger "accelerator pump", but if it was there, I could have missed it).  

Apexi SAFC and HKS SAFR do not have accel pump modifiers.  The second gen AFC
does read the TPS which allows you to set seperate low and high throttle maps.
However in my experience neither need to adjust the accel pump.  The VPC
does have the good old response knob which most find needs to be turned
up all the way for the best throttle response, however even that doesn't
respond like stock.  I guess it's possible that Apexi COULD tweak the
afm input to spike the accel pump just like HKS did with the vpc, but
it's not something you can modify.

>     Yeah, a pot in series with the air temperature sensor would work, but a paralleled thermistor with the right curve should be better, since it will track in percentage terms.  Common thermistors exhibit a fixed and predicable percentage change per temperature increment, much like the way compound interest works.  There are many sources, like Fenwal, Yellow Springs, and VECO.  

IMO you want to change only the range.  Adding another in parallel
would change the entire response curve, wouldn't it?  This would
really throw off the intake air temp compensation.

>     I'd like nothing better than a WB O2 sensor, but the prospect of having to set up A/F, then remove it to avoid temperature damage is not appealing.  I do have several thermal conductivy exhaust gas analyzers here including two Sun units from some time ago, and a Marquette unit.  I could use those on the road for WOT tuning also.  There is a section of westbound I-80 here where I can hold WOT for 10-15 seconds in 4th gear, an uphill climb, where cops are scarce.  

I run my FJO 100% of the time and do not have a narrowband at all thanks
to the standalone.  I have the EMS tracking the wbo2 for closed loop
operation.  Have not had a problem with it at all as long as the sensor
is at least 5-8" away from the turbine.  With the stock ct26 the factory
location has worked well for the NTK sensors.

>     IC piping:  I do not understand the point in using PVC pipe, especially since most of it is Schedule 40 (relatively thick wall as compared with steel exhaust tubing or even copper tubing, M grade being thinnest wall).  When I do the upgradies you mention it will be with thin wall steel or M grade DWV copper.  

We've used PVC in a pinch, more as a joke.  It worked surprisingly well
so we left it until the new IC came in and we fabbed up hard pipes from
steel.  2-2.5" OD is good for the ct26.  Regular or thin wall steel is
ok - you're splitting hairs.  :-)