stock injectors vs bigger injectors on a boosted apex

[Yamaharider74]

hi i have the bigger injectors in my sled its an 06 apex did have a head shim but want to take it out because have motor all apart and leave bigger injectors in and run less boost so i can run pump gas and have the snappier bottom end ,question is without head shim and using the bigger injectors,dropping the boost to 6 pounds will i need to run a fuel additive or can i just run premium fuel on that set up , ireally only ever trail ride and ditch bang

 

[mbarryracing]

I ran stock injectors originally with my Motec at 12 lbs boost decompressed on pump gas. Pretty much maxed out on Injector Duty Cycle around there.
You should be safe to run 6 lbs boost on 91 octane or higher pump gas, which injector size is irrelevant... Injector size is to match fuel flow with airflow / boost level at a given fuel pressure and wont dictate what boost level you will be able to run without your head shim on pump gas... Octane rating of your fuel you run will dictate that, that and altitude.

 

[Yamaharider74]

I ran stock injectors originally with my Motec at 12 lbs boost decompressed on pump gas. Pretty much maxed out on Injector Duty Cycle around there.
You should be safe to run 6 lbs boost on 91 octane or higher pump gas, which injector size is irrelevant... Injector size is to match fuel flow with airflow / boost level at a given fuel pressure and wont dictate what boost level you will be able to run without your head shim on pump gas... Octane rating of your fuel you run will dictate that, that and altitude.

I ran stock injectors originally with my Motec at 12 lbs boost decompressed on pump gas. Pretty much maxed out on Injector Duty Cycle around there.
You should be safe to run 6 lbs boost on 91 octane or higher pump gas, which injector size is irrelevant... Injector size is to match fuel flow with airflow / boost level at a given fuel pressure and wont dictate what boost level you will be able to run without your head shim on pump gas... Octane rating of your fuel you run will dictate that, that and altitude.

okay thanks for the info ,i wonder then if i should just leave head shim out and run 6 pounds of boost then see how things go

 

[mbarryracing]

What was making you think of taking the head shim out?

 

[Yamaharider74]

What was making you think of taking the head shim out?

Well I like the snap it has without the head shim with boost but maybe I should just leave it in as a fail safe , I just thought if I run 6 pounds of boost and good fuel it would be more usable on the trails without a head shim
I was running 13 pounds of boost which is fun but thought maybe could make it more snappier off the bottom end by making it back to stock and adding a little boost

 

[mbarryracing]

Gotchya, I see your angle. I've never been able to really quantify how much more responsive off the bottom end stock compression is over decompressed... I guess it depends on CR and how much decompressed... I am spoiled because I just advanced the timing down low some in my Motec to compensate for being decompressed 1 point.
I also believe the heavier clutch weight for higher boost level HP contributes to delayed response, too.
I do think you will miss the pull at 13 lbs vs 6 lbs though...

 

[Yamaharider74]

Gotchya, I see your angle. I've never been able to really quantify how much more responsive off the bottom end stock compression is over decompressed... I guess it depends on CR and how much decompressed... I am spoiled because I just advanced the timing down low some in my Motec to compensate for being decompressed 1 point.
I also believe the heavier clutch weight for higher boost level HP contributes to delayed response, too.
I do think you will miss the pull at 13 lbs vs 6 lbs though...

Okay well thanks a bunch for the info I appreciate it and now I will decide if to leave the 13 or go with the 6 and reinstall head shim I never thought of playing with the timeing to make up for the head shim being in there

 

[mbarryracing]

What are you running for a fuel controller?

 

[Yamaharider74]

What are you running for a fuel controller?

Power commander 5 ,

 

[TurboTime]

With

Well I like the snap it has without the head shim with boost but maybe I should just leave it in as a fail safe , I just thought if I run 6 pounds of boost and good fuel it would be more usable on the trails without a head shim
I was running 13 pounds of boost which is fun but thought maybe could make it more snappier off the bottom end by making it back to stock and adding a little boost

With 6lbs of boost you are able to run just premium with no problem and no need for Race Mix and/or Octane Boost. I would however not mess with the timing as that, potentially, could change the need for higher octane..

 

[Yamaharider74]

hi and thanks ,for the info i will not touch the timing one thing is with running premium i am thinking about leaving the head shim out or is that ,maybe not advisable

 

[mbarryracing]

If it were mine, I'd leave it at 13 because 6 is just too boring for me now (im at 16 now because 12 got boring... LOL) and besides you should already be clutched for 13...
If your cam chain timing was adjusted to compensate for the longer distance from the head shim, redo that. If not, investigate doing that otherwise you will loose response too.

 

[Yamaharider74]

If it were mine, I'd leave it at 13 because 6 is just too boring for me now (im at 16 now because 12 got boring... LOL) and besides you should already be clutched for 13...
If your cam chain timing was adjusted to compensate for the longer distance from the head shim, redo that. If not, investigate doing that otherwise you will loose response too.

Okay thanks are meaning when the guys notch the cam gears to adjust the timing ?i actually never checked that I will look and see maybe I will leave it at 13 lol it is a lot of fun what weights were you running in your primary and what did you do to your secondary /and why gearing I can't even remember what I have mine at anymore lol

 

[mbarryracing]

Yes, slotting the sprockets to get the cam timing / overlap corrected.
I've been running a few different weights, currently TEAM weights with a Heel Clicker spring but the engagement is almost 5k rpm. Response isn't an issue... LOL.
Also been running an old Team TSS roller secondary which I like alot.

Have an appointment to tune on the track dyno at FPP in a few weeks, trying an new set of FPP quad force weights and a SW spring to lower the engagement. Then will see if the Team TSS roller secondary or the stock secondary with a purple EPI spring puts more power down.

 

[Yamaharider74]

Yes, slotting the sprockets to get the cam timing / overlap corrected.
I've been running a few different weights, currently TEAM weights with a Heel Clicker spring but the engagement is almost 5k rpm. Response isn't an issue... LOL.
Also been running an old Team TSS roller secondary which I like alot.

Have an appointment to tune on the track dyno at FPP in a few weeks, trying an new set of FPP quad force weights and a SW spring to lower the engagement. Then will see if the Team TSS roller secondary or the stock secondary with a purple EPI spring puts more power down.

Okay that machine of yours sounds like it rips pretty good engaging at 5000 ya wouldn't have any hesitation ,want to get mine running spot on one day I hope lol thanks for the info