can injectors be too big?

[barryogen]

I'm doing some mods to my car including after market computer, injectors etc, and the thought occured to me that maybe injectors can be too big... can they?

essencially looking at some either 410cc or 680cc, and aiming at a lowly 275-300WHP, the cost difference is bugger all, so it really comes down to which is better suited.

From what I've read the 410cc ones are enough for 325 WHP, so does that mean that the 680cc ones are good for ~50% more?

[Ako]

Yes, you can go too big. Makes for issues with low load tuning - normally best to go for some which will do the job you need, without going overboard. All the injectors I sell at work are the same price (apart from the big 1600cc rotary ones ), if you could just go for the biggest size for any application it would make life a lot easier when I put an order in

For the power you're looking for I'd say 550cc at a minimum, 600cc is closer to what you're after.

A very generalised rule you can work off is 550cc per 100hp (crank), if you base your guesswork off that you'll be near enough. My wee injector calulatory thingy says that for 230kW (flywheel), with 4 injectors, at 85% duty cycle, you're needing 570cc squirters - just find the next size up from that, and you'll be right.

[fivebob]

I'm doing some mods to my car including after market computer, injectors etc, and the thought occured to me that maybe injectors can be too big... can they?

Yes they can be too big, the bigger the injector the poorer the atomisation of the fuel. Ideally you should size you injectors so that they are at 65% duty cycle at peak power, this should allow enough for the duty cycle to be kept below 85% at redline.

Also big injectors can have problems at idle, though that depends on the ECU that's controlling them.

From what I've read the 410cc ones are enough for 325 WHP, so does that mean that the 680cc ones are good for ~50% more?

Don't know what you've been reading but that sort of WHP will require 530cc/min Injectors, 410cc/min should be good for about 250whp before you exceed max duty cycle.

[barryogen]

I'm doing some mods to my car including after market computer, injectors etc, and the thought occured to me that maybe injectors can be too big... can they?

Yes they can be too big, the bigger the injector the poorer the atomisation of the fuel. Ideally you should size you injectors so that they are at 65% duty cycle at peak power, this should allow enough for the duty cycle to be kept below 85% at redline.

Also big injectors can have problems at idle, though that depends on the ECU that's controlling them.

From what I've read the 410cc ones are enough for 325 WHP, so does that mean that the 680cc ones are good for ~50% more?

Don't know what you've been reading but that sort of WHP will require 530cc/min Injectors, 410cc/min should be good for about 250whp before you exceed max duty cycle.

http://www.hassturbo.com/catalog/toyota.html
from the stage one kit...
"Stage-I has produced 200-210whp with 5psi of boost and up to 220-230whp with 7psi."
and from further down the page...
"*At stock 1Z/2Z Toyota fuel pressure these injectors flow 410C"


I haven't been able to find any details on what the OEM ones flow, but others are using them to do ~250WHP.

[suberimakuri]

fivebob.... 65% max !!
then you say 250whp on 410cc maxed....

my experience has been:
idles' not normally too bad, slightly rich is ok......
it's from overrun -> very low throttle/map that becomes a pain....
have it pop a bit or smooth and 10:1.
depends on injector opening time a lot too.

[RomanV]

viewtopic.php?t=33637

[fivebob]

fivebob.... 65% max !!
then you say 250whp on 410cc maxed....

Yes, if it was sized correctly it would be 65% at max HP. However that does not stop you running 85% duty cycle at peak HP and achieving those figures. Which is what a lot of people do, and then run past the 85% duty cycle above peak HP.

my experience has been:
idles' not normally too bad, slightly rich is ok......
it's from overrun -> very low throttle/map that becomes a pain....
have it pop a bit or smooth and 10:1.
depends on injector opening time a lot too.

That is totally dependent on the tune and the way the ECU controls the injectors. Some are far better than others and I wouldn't expect to see those sort of problems surfacing when using a Motec, Autronic, or other high end ECU, and if they did they can easily be tuned out

[barryogen]

thanks for that... essencially you want the best size for what you're doing, so consult as many people as possible that know what they're talking about, and go from there.

so same as everything else then