Limits of TPI computer

[SRavet at bangate.compaq.com]

Jussi T Kosonen <jkosone1 at cc.hut.fi> Wrote:
| 
| 
| Hi you all!!!
| I have few questions about stock TPI computer limitations.
| 
| I own a -85 Vette (MAF computer) with quite heavy modifications that
| include....
| 
| 	-400 cid block bored 0.03"
| 	-stroker crank 3.875"
| 	= 420 cid
| 	-Dart II Sportsman cylinder heads
| 	-Compucam 2040 cam duration @ .050"=210/216 gross 
lift=.440"/.454"
| 	-SLP T-Ram manifold
| 	-Accel 58mm throttle body
| 	-Hedman Hedders with 1 5/8" tubes 3" collectors
| 	-Dual 2 1/2" exhaust tubing no catalytic converter
| 	-3" Flowmaster mufflers
| 	-modified MAF and air filter housing
|  
| with STOCK computer,fuel pump, injectors 24lbs/hr, fuel filter.
| 
| And that is what worries me ......
| 
| Is the stock TPI computer able to operate my engine??
| I know that computer with MAF is quite tolerable with engine 
modifications
| but still I fear that I'am not using the full potential of my engine.
|  
| I have the TPIS Insider Hints book that states that stock injectors
| are able to produce +450 HP and they also say that it is better to 
| use small injectors with high fuel pressure than bigger ones with
| lower.
| 
| I don't know how much HP my engine is producing but taking in a account
| that my cam is so mild I estimate    less than 450HP...
| but that book doesn't tell me what pressure should use.....
| currently I have set it to 45PSI....
| 
| The question is......could I damage my engine at high RMP with
|  too lean mixture..?

Yes you could, but you would probably see a "Block Learn" error first.  
Block learn is what allows the ECM to "lean" a new fuel curve for your 
engine.  It is a modifier that is added/subtracted to the base injector 
timing stored in the table.  It can only be adjusted so far, though, and if 
the computer can't increase it any further and it still sees lean operation 
then it will set a "block learn out of range" error.  This won't help WOT 
much, since feedback is not used then.  Your best bet would be to hook a 
high impedance multimeter to the O2 sensor and have someone watch it while 
you drive to see if you are rich/lean.  If you are lean at WOT, you should 
probably create more fuel flow by increasing the pressure or getting bigger 
injectors.  The block lean will take care of adjusting part throttle 
conditions, and the larger injectors will increase fuelling at WOT.  If you 
get a scan tool or Diacom software, you can see the block learn values, O2 
sensor values, etc. all as you drive around.

What's your 1/4 mile time?

--steve

Steve Ravet
sravet at bangate.compaq.com
Baby you're a genius when it comes to cooking up some chili sauce...