Do I need bigger injectors?

[CALL911]

The car:


1995 Z28, LT1,fully forged 383, 8.8:1 CR, meth injection, maxed out D1SC, FMIC, 2 Walbro 255 LPH in tank pumps (2nd one kicks on at 4#'s of boost). Super Vic EFI intake, 24X conversion.


The change:


Have had AFR 180 heads, and Mototron 60# injectors with good success. But now am stepping up to a much more appropriate sized AFR 227 for my setup.


Will I need to go with bigger injectors? I can't get ahold of the guy who tuned the car last to see what the duty cycle was on the dyno. I know if I went with a 75# injector size, it would be okay, and I will do that if I need to. But don't want to if its not necessary.


Let me know what you guys think.

[Fastbird]

Personally dude, let's iron everything out, and I say we should have a set of the 72's on standby at the dyno just in case. With your AFPR you might be able to bump the base pressure and extend the capability of the 60's by a fair amount though. Remember the same injectors you have I was running in my Vette @ 761/760 with plenty of overhead. Granted that's a base pressure of 58 PSI vs the 43 psi you're at, hence the bump the base pressure and get more life.

[chile]

I think it wouldn't hurt to keep the duty cycle down. Do you know your max pulse width?

[CALL911]

In an ideal world, it would be best to have the bigger injectors on standby, but they aren't cheap. And I would hate to buy them just to sell them if not needed.

[popo8]

Im only running 60s with my 227s

[Fastbird]

Im only running 60s with my 227s

But his D1 and larger cam are going to have a marked impact on how much air, and subsequently fuel, is needed.

[popo8]

But his D1 and larger cam are going to have a marked impact on how much air, and subsequently fuel, is needed.

Oh, ok. not aware what cam he is running.

[79LT1Monte]

I would put it on the dyno and watch everything closely before you make the call. Like you said those injectors aren't cheap and if your duty cycle is reasonable keep what you have.

[CALL911]

I would put it on the dyno and watch everything closely before you make the call. Like you said those injectors aren't cheap and if your duty cycle is reasonable keep what you have.

Well, that would be another option. Unfortunately, if I pay to have it tuned on the dyno, and learn that my duty cycle is too high and need the larger injectors, after I buy the new larger injectors, then I am out the money for the dyno, as I will have to get it tuned again on the new injectors (this is to say nothing of the PITA of getting time off of work and scheduling another dyno tune). All that would be MORE expensive than just buying the bigger injectors off the bat and having them ready to swap right there (which as stated before, I don't want to do either).

I need an accurate assesment prior to going to the dyno. Past finding someone with a very similar setup, and checking their duty cycle on their injectors, or finding what my duty cycle was on my last dyno tune, I am not sure how to go about this. Past, just checking to see experts advice in this forum.

[CALL911]

Oh, ok. not aware what cam he is running.


A GIANT one!

[79LT1Monte]

Don't you know anyone with data logging software or at least a capable scan tool to check the duty cycle before the dyno? I would definitely agree you want to know if you have a problem or not before you pay for a dyno tune, I thought you were just going to data log your car on the dyno.

[popo8]

A GIANT one!


Lol... Last i saw u were stuck on keeping the same cam. Did that change?


Larry (Popo8) Co-owner
LTXtech.com

[CALL911]

Don't you know anyone with data logging software or at least a capable scan tool to check the duty cycle before the dyno? I would definitely agree you want to know if you have a problem or not before you pay for a dyno tune, I thought you were just going to data log your car on the dyno.


That may be a possibility, and a good idea. If I can't find the info from my last dyno tune regaurding the duty cycle, this may be the means to do this. Thanks.

[CALL911]

Lol... Last i saw u were stuck on keeping the same cam. Did that change?


Larry (Popo8) Co-owner
LTXtech.com

As of right now, it hasn't changed. The large custom cam is not ideal for my setup, but I love the powerband, the feel, and the sound. If I decide I really want to go all out with my setup, this will be the item that would need to be changed. But, with amazingly getting traction at 614 at the wheels with the previous combo, and I can only expect to have a significant loss in traction after the heads have been changed, more power seems irrelevant to me. For those that want to race their dyno numbers, and braging rights around the number it may be good and fine, but thats never been what I am after. I'd rather have power I can use.

[popo8]

As of right now, it hasn't changed. The large custom cam is not ideal for my setup, but I love the powerband, the feel, and the sound. If I decide I really want to go all out with my setup, this will be the item that would need to be changed. But, with amazingly getting traction at 614 at the wheels with the previous combo, and I can only expect to have a significant loss in traction after the heads have been changed, more power seems irrelevant to me. For those that want to race their dyno numbers, and braging rights around the number it may be good and fine, but thats never been what I am after. I'd rather have power I can use.

Ok, so your keeping the same cam...

[CALL911]

Ok, so your keeping the same cam...

lol, sorry if that was a long winded way of saying "yes".

[Ryan Stout]

I know a certain dyno day that'll help you find out! But I'd just bump the base pressure up to 58 if you need. Or buy injectors to have on hand, and return them if you don't need em.

[CALL911]

I know a certain dyno day that'll help you find out! But I'd just bump the base pressure up to 58 if you need. Or buy injectors to have on hand, and return them if you don't need em.


I saw your dyno day. Assuming everything falls in place, I will have the car tuned in the spring. The whole point of finding out before hand is to avoid the cost and hassle of getting injectors I may not need or pay for additional dyno time. The pressure can only go up so much, but it can be experimented with. Right now, I'm going to try and find someone that can take a look at things before I go with a laptop.

[Fastbird]

Problem with looking before the dyno though is that you'll be running around, untuned, getting into some power in order to check the DC at boost. Not the way I'd recommend going about it.

Posted from my Rooted and ICS'd Rezound

[CALL911]

Yeah, not ideal, but past finding from the last tune what they were at, I'm not sure there's another way. I guess I could always buy them, and return them if I don't use them.

[Ryan Stout]

Can you tune it? If nothing else just take a bit, go out and get a conservative street tune and see where you're at.

[CALL911]

Can you tune it? If nothing else just take a bit, go out and get a conservative street tune and see where you're at.

No. IMO theres a right way and a wrong way to go about tuning. The wrong way would be someone like myself not fully knowledgeable in tuning attempt to do it. The right way, and the only way it will be tuned, will be by someone who knows what they are doing and perform a full tune on it as it needs. I'd rather pay once and have it done right.

[Ryan Stout]

Understandable lol. Is there anyone out there with a similar combo?

[NuckinFutz93]

I am on 80lb @80%DC on my D1SC 396 with AI 215cc LT4s, worked AI LT4 intake, and a opti. IDK if that info helps, but thats what I got.

[CALL911]

I am on 80lb @80%DC on my D1SC 396 with AI 215cc LT4s, worked AI LT4 intake, and a opti. IDK if that info helps, but thats what I got.

Actually, it does. What size is your cam? How much boost? What RWHP? I think that's a fairly similar combo.

[CALL911]

So I just heard back from my tuner. He said I was running 90+% duty cycle on the dyno pulls.

It looks like I will definately need to step up to some larger injectors.

Now my question is, can/should I leave the 60# injectors in for now after I get the car together on its current tune? I need to be able to drive it around, check for leaks, change the oil and drive it about 2.5 hours to get it tuned again. I don't mind swapping injectors at the dyno, but want to make sure I will be safe driving it around in the mean time.

[blackbirdws6]

90+ is up there but it will be fine driving it around. I wouldn't beat on it like crazy and I would just keep a good eye on the A/F gauge if you have one. Did the tuner mess with the fuel pressure? Siemens makes a nice 80lb high impedance injector which I use.

[CALL911]

90+ is up there but it will be fine driving it around. I wouldn't beat on it like crazy and I would just keep a good eye on the A/F gauge if you have one. Did the tuner mess with the fuel pressure? Siemens makes a nice 80lb high impedance injector which I use.

Keep in mind that 90+% was on the OLD combo, and this combo will undoubtingly need more fuel. Granted I am just going to fire it up, get the old gas out of it, and baby it down to be re-tuned on the new setup (absolutely NO boost, or getting into the throttle). I do have a wideband 02, and I will be keeping an eye on it.

[blackbirdws6]

Ahh gotcha. Yea, I would hold off going WOT until you get the new injectors for sure.