Injector size query

[lautray]

After logging a little & seeing injector duty cycles up to 104%, I am in need of some new injectors. The next logical step up is to 36lb injectors. Have found some 42lb green top injectors for a very good price (cheaper than 36lb set). So, the question is: are the 42lb injectors too big, or will they do the job as well as 36lb? Is there a case not to go the 42lb? These seem great value, & also "future-proofs" mods down the track too.

Thoughts appreciated.

[DaveHAT]

After logging a little & seeing injector duty cycles up to 104%, I am in need of some new injectors. The next logical step up is to 36lb injectors. Have found some 42lb green top injectors for a very good price (cheaper than 36lb set). So, the question is: are the 42lb injectors too big, or will they do the job as well as 36lb? Is there a case not to go the 42lb? These seem great value, & also "future-proofs" mods down the track too.

Thoughts appreciated.

Mr K,

A relaible source has told me that there are potential hassles with going bigger also. I am in much the same position as you, seeing Injector rates over 100% at certain points. :(

The possible problem that going bigger can induce is that much as the smaller injectors stuggle to keep the fuel flow up, the larger 42lb etc ones can stuggle to reduce the injector flow at lower injector cycle rates. :puke:

Luke should have some good feedback for you. :werd:

[Azza]

Mr K,

A relaible source has told me that there are potential hassles with going bigger also. I am in much the same position as you, seeing Injector rates over 100% at certain points. :(

The possible problem that going bigger can induce is that much as the smaller injectors stuggle to keep the fuel flow up, the larger 42lb etc ones can stuggle to reduce the injector flow at lower injector cycle rates. :puke:

Luke should have some good feedback for you. :werd:

Would that be of Garry's beast? BTW he's got the big motor back in and it's up for sale. (This cars is good for low 11's if not high 10's if you can keep it in a straight line:eek: )

[SSUte01]

Erik,

I have 42lb Deplhi 'Green Top' injectors originally purchased for a FI setup so they are a hangover from that. The work fantastically for me. It took a lot of trial and error to get all the small PW iterations correct but now they are spot on. Your cam is bigger than mine and I dunno about your heads but the 42lb in all honesty are more than big enough. Prior to final round of mods/tuning mine made 350rwhp (261rwkW) @ 55% IDC. That has since risen to 62%, so as you can see plenty of room to move.

36lb would be perfect, somewhere around 85-90% at 6500-7000rpm. But that is as far as you would want to go. Injectors as I understand it do 'funky' things as soon as you push beyond 90 odd %, they simply dont have the time to open, inject, and close again prior to commencing the next cycle and this can cause anomolies.

My advice go the 42lbs because

a. provided they are servicable they will work fine
b. they are chaeper
c. they give you room to move.

[lautray]

Luke, just what I wanted to hear :) . Will be investing in some asap.

[RedVYIISS]

Eric,

My 42 lb'rs ran out of grunt when we were tuning and we've got around this by running very high fuel pressure.

For my F/I application, at idle it's for all intents and purposes a stocker, running 5 bar fuel pressure, ie it runs negative MAP, idles at 700 rpm and although injector duty cycle is naff all it idles beautifully. My application would be much more difficult to tune for than yours so I can't see any problems with you going for 42 lb (green top) injectors.