EFI stuff for Supercharged v8?

**thechuckster** · 10-07-2006, 06:37 PM

error in my last sentence - shoudl have read don't come back without ...

talk to shawn (MS-75 ?) about andra requirements for 10 second cars

**barned01** · 10-07-2006, 09:03 PM

OK I tried playing with an injector calculator (i am in the same boat as you robbos_toyotas....well not about the 302 but about understanding efi) i tried this web site:
http://www.z31.com/software/injector.pl
number of injectors:8
Brake Specific Fuel Consumption:0.5 (blowed if i know what that means)
duty cycle:0.8 (leaving a little for reserve)
horsepower:725 (550+30% to account for drivetrain loss so 725 is the closest value)

it gave me the value of 594cc/min

so if this is correct and hopefully someone can confirm it then 600cc/min injectors seem right on the money for you...
that would probably mean somewhere between 550 and 600 would suit your application depending on how fudged the figures i used were

**barned01** · 10-07-2006, 09:19 PM

damn my maths sucks
i should have done 800 hp instead of 725
so
1050cc/min

but the more i think about it, the more confused i get as there is no mention in the calculator about engine capacity

**Starfire** · 10-07-2006, 09:21 PM

Have you considered using staged injectors?

You could use 16 injectors (2 per inlet port) and turn them on and off independantly of each other. A little harder to set up but a whole lot cheaper to buy (as you only need smaller capacity ones) and it tends to give a nice factory lilke idle.

**oldcorollas** · 10-07-2006, 09:43 PM

as i said before, use megatune...

then again, megatune is based on VE, and i can't imagine the ol V8 getting close to 100% VE...

it also depends ont he boost you want... not power figure... power is irrelevant

302cid, with 0.5bar boost, assuming 100% VE, and 500cc injectors and 12:1 AFR...
gives a pulsewidth of 15.2 milliseconds.

use that as a baseline and modify based on boost and expected VE..

then compare that to the amount of time you have per engine cycle at 80% duty...

too easy

**Norbie** · 10-07-2006, 10:05 PM

Pulse width just confuses the issue. Injectors can be rated in hp because you can make reasonable assumptions about the amount of fuel required to make 1hp (since AFR's need to be in a fairly narrow range or the engine won't run). Therefore RPM, engine capacity, induction type etc don't really matter - all you really need to know is how much power you're making and how many cylinders you have.

**oldcorollas** · 10-07-2006, 11:17 PM

i know

but those Hp calculators assume engines don't rev over about 6-7000rpm, above which the available time decreases..
so you have to "oversize" the injectors relative to the "proper" size... (is all i was trying to add)

**The Witzl** · 11-07-2006, 11:14 AM

Originally Posted by oldcorollas

i know

but those Hp calculators assume engines don't rev over about 6-7000rpm, above which the available time decreases..
so you have to "oversize" the injectors relative to the "proper" size... (is all i was trying to add)

This is where you have to be careful about the brand of injector you choose. Here is two different ends of the spectrum:

Rochester/Delphi = Big dirty dribbles and spurts of fuel. Typically chosen by the bigblock/blown V8 boys who need p00loads of fuel and dont give a shit about tuning resolution.

Sard = precise, accurate, and underrated flow figures (allowing room for high rpm/short pulsewidth applications without needing to oversize your injector). Has very good tuning resolution at the low end of the scale.

Here's a quick graph for the scientific types to understand

What does the graph mean?

well the graph shows that the Sard has much better tunability down at the low end of the scale. This means that your tuner can get your fueling much more accurate for all the times you arent burying your right foot into the go-pedal - which is 80-90% of your on street driving.
This means that your car will be much more economical to run with much cleaner emissions for your everyday driving.

Yes the Rochester has the flow everywhere else, but for the high tech performance engines we mostly run this isnt a problem - your tuner will just be running the injector at a higher duty cycle than with a Rochester style injector. At the high end of your RPM scale, tuning accuracy isnt important because the time between events is much much smaller, and thus inaccuracies have negligable effect on economy and emissions.

**Robbos_Toyotas** · 11-07-2006, 05:57 PM

Originally Posted by oldcorollas

as i said before, use megatune...

then again, megatune is based on VE, and i can't imagine the ol V8 getting close to 100% VE...

it also depends ont he boost you want... not power figure... power is irrelevant

302cid, with 0.5bar boost, assuming 100% VE, and 500cc injectors and 12:1 AFR...
gives a pulsewidth of 15.2 milliseconds.

use that as a baseline and modify based on boost and expected VE..

then compare that to the amount of time you have per engine cycle at 80% duty...

too easy

I dunno, i suspect id need to run 15-18psi

**thechuckster** · 11-07-2006, 07:32 PM

that amount of boost (1.0 to 1.5bar) in your engine would be crazy - especially that you built it at relatively high compression to generate NA power.

Unless you're going to strip it down and change pistons (to lower CR's) then i'd be aiming at moderate levels of boost (e.g. 5-7psi).

cheers,
Charles.

**Robbos_Toyotas** · 11-07-2006, 08:07 PM

Originally Posted by thechuckster

that amount of boost (1.0 to 1.5bar) in your engine would be crazy - especially that you built it at relatively high compression to generate NA power.

Unless you're going to strip it down and change pistons (to lower CR's) then i'd be aiming at moderate levels of boost (e.g. 5-7psi).

cheers,
Charles.

yeah im putting some lower compression pistons in it, and probly changing the cam as well..