At what HP or point do we need bigger injectors?

Pokageek · Jun 22, 2005

By next week I will be installing my new 306, some porting, flat top pistons (higher compression), b-303 cam, pullies, CAI. Heads and intake will follow but not right now.

RIO5.0 · Jun 22, 2005

I would say your at that point...I wouldn't even throw the 19s in that set-up...24s should suffice...unless you have future "boost" plans....

HISSIN50 · Jun 22, 2005

I would not want to push much over 300 horsies with stockers.

final5-0 · Jun 22, 2005

At stock fuel pressure, its my opinion that 255 to 265rwhp is getting close to the limit.

Remember...300fwhp is only 255rwhp and its even less if you got an auto trans.

Just thought I throw that out there cause you see lots of peeps say 19's are good for 300hp.

Just too much bad stuff can happen if you go lean at wot so make sure your good to go when it comes to your fuel system.

Later
Grady

HISSIN50 · Jun 22, 2005

whoops, thanks Mr Grady. I meant to put 300 BHP (I figured he was lookin at BHP numbers since it sounds like the motor is out of the car). Good of you to make that notation.

And you are right again - some folks (one in particular I can think of) says he runs 19's with 400 BHP - not something I would even remotely imagine doing. As you poignantly noted, the injector and tune are only as good as the leanest point. I tend to go a little on the overboard side (not with EFI - I cant) but with jetting.

final5-0 · Jun 22, 2005

HISSIN50 said:
whoops, thanks Mr Grady. I meant to put 300 BHP (I figured he was lookin at BHP numbers since it sounds like the motor is out of the car). Good of you to make that notation.

And you are right again - some folks (one in particular I can think of) says he runs 19's with 400 BHP - not something I would even remotely imagine doing. As you poignantly noted, the injector and tune are only as good as the leanest point. I tend to go a little on the overboard side (not with EFI - I cant) but with jetting.

Jetting

That word might confuse some peeps

It tells me ............................ your no young pup

Later
Grady

Pokageek · Jun 22, 2005

Thanks guys. The manufacturer estimates me at 302 FWHP with my setup including aluminum drive-shaft (doesn't add more HP but free's up 5-7hp at the rear wheels. So subtract that and I am at 290-295 or so... I think stock is 19lbs right? I was hoping to avoid the added injectors cause I think to add larger ones, I have to get a custom tune of my chip or tweecer- which I don't feel like fooling with..

SO..basically anything over 300FWHP BAD idea with stock injectors. Got it, ok.

ALSO, while I found some good experts on this site, I will be adding a 155l fuel pump b/c not sure where the stocker leaves off and it's old anyway. I think it said up to 90psi. This should work fine for my set up right? I know it is good for 400hp+- but wanted to make sure I wasn't missing anything.

Thanks much!

HISSIN50 · Jun 22, 2005

final5-0 said:
Jetting

That word might confuse some peeps

It tells me ............................ your no young pup

Later
Grady

LOL. Sorry. Jets were used in carbs, which came just after the horse drawn carraige.

I am 130 years old. Oh wait, I just feel like it. Subtract a hundred years. I am too poor to have nice new toys, so I have always had older stuff, most of it carbed (all the bikes are carbed).

Don't forget that when I get irritated, I often wonder aloud if it would be cheaper to get a new intake and carb instead.

CManT1914 · Jun 22, 2005

This chart gives you a rough estimate of how much HP injectors can support. All numbers are at the flywheel. I'd go with at least some 24's.

I've been posting this pic a lot lately, lol. Good luck

Pokageek · Jun 23, 2005

Hey, thanks cman! But my fuel pump does say 90psi..I think my stocker injectors are 19lb? Wouldn't that put me up to 425 max hp instead?

CManT1914 · Jun 23, 2005

Pokageek said:
Hey, thanks cman! But my fuel pump does say 90psi..I think my stocker injectors are 19lb? Wouldn't that put me up to 425 max hp instead?

If your fuel PUMP says 90 something, then that's lb/hr rating, stock fuel pumps are 90lb's. Your fuel PRESSURE is what is most definitely stock at around 38-40psi. To check fuel pressure, you'll need a fuel pressure gauge that threads into the schrader valve on the fuel rail. But unless you have an adjustable fuel pressure regulator, (which is needed to adjust fuel pressure) then it's most likely stock.

mackey · Jun 23, 2005

CManT1914 said:
If your fuel PUMP says 90 something, then that's lb/hr rating, stock fuel pumps are 90lb's.

It isn't 90lbs. It is 90 liters per hour that it flows. You could never get 90psi out of a stock fuel pump.

CManT1914 · Jun 23, 2005

mackey said:
It isn't 90lbs. It is 90 liters per hour that it flows. You could never get 90psi out of a stock fuel pump.

My bad, I still had injectors on my mind, they flow by punds per hour. I forgot pumps went by liters. Either way, 90 was his fuel pump, not his fuel pressure.

Pokageek · Jun 23, 2005

I bought a 155l fuel pump but I also remember it being advertised at 90psi...not sure what that meant. So your chart also suggests you can get an adjustable FPR and get the psi up? Is this the less expensive route as upossed to buying injectors and a puter/ Any suggestions on which one's to buy with what disks? Thank you again!

urban96 · Jun 23, 2005

Pokageek said:
I bought a 155l fuel pump but I also remember it being advertised at 90psi...not sure what that meant. So your chart also suggests you can get an adjustable FPR and get the psi up? Is this the less expensive route as upossed to buying injectors and a puter/ Any suggestions on which one's to buy with what disks? Thank you again!

the pump is capeable of 90psi but on the fuel rails theres a pressure regulator that limits that to around 38psi (stock) and the excess fuel is returned to the tank

Pokageek · Jun 23, 2005

How about adjustable FPR and get the psi up? Is this the less expensive route as upposed to buying injectors and a puter? Any suggestions on which one's to buy with what disks? Thank you again!

CManT1914 · Jun 23, 2005

Pokageek said:
I bought a 155l fuel pump but I also remember it being advertised at 90psi...not sure what that meant. So your chart also suggests you can get an adjustable FPR and get the psi up? Is this the less expensive route as upossed to buying injectors and a puter/ Any suggestions on which one's to buy with what disks? Thank you again!

You can get an adjustable fuel pressure regulator, PN# 1707 from summit or the like. This allows you to up the fuel pressure, which is a LOT cheaper (but should be temporary) means to get more fuel out of your system. I bought the BBK AFPR because I won't be able to recalibrate my MAF for my new 30lb injectors before I do my heads/cam swap. So I am gonna bump my pressure up to around 60, and I should be set for a little bit. It IS cheaper (around $100 for the afpr, as opposed to $250 for injectors, $250 for a new MAF and inlet pipe) but really it's only a bandaid fix, and should be done properly, that is with bigger injectors and MAF.

Pokageek · Jun 23, 2005

ok thanks much!!!

Pokageek · Jun 23, 2005

CManT1914 said:
You can get an adjustable fuel pressure regulator, PN# 1707 from summit or the like. This allows you to up the fuel pressure, which is a LOT cheaper (but should be temporary) means to get more fuel out of your system. I bought the BBK AFPR because I won't be able to recalibrate my MAF for my new 30lb injectors before I do my heads/cam swap. So I am gonna bump my pressure up to around 60, and I should be set for a little bit. It IS cheaper (around $100 for the afpr, as opposed to $250 for injectors, $250 for a new MAF and inlet pipe) but really it's only a bandaid fix, and should be done properly, that is with bigger injectors and MAF.

I went and bought the FPR. It was on Summit just like you said!

Yes, but to truely do this right we should get a tweecer or custom chip burn too right? Why is the FPR only a band-aid? My guess is because the further the fuel pressure, the richer it will run right? What problems can this cause if true?

Also, how do you all know what MAF to choose for which injector? Is this the key to really getting it to work right or is it the computer tune as well?

CManT1914 · Jun 23, 2005

Pokageek said:
I went and bought the FPR. It was on Summit just like you said!

Yes, but to truely do this right we should get a tweecer or custom chip burn too right? Why is the FPR only a band-aid? My guess is because the further the fuel pressure, the richer it will run right? What problems can this cause if true?

Also, how do you all know what MAF to choose for which injector? Is this the key to really getting it to work right or is it the computer tune as well?

When doing a good H/C/I buildup, you need to consider when you buy injectors and a MAF, whether or not you're gonna mod it further in the future, i.e. blower, turbo, nos etc. If so, you will probably want to step up another injector level. If you were gonna be fine with 24's, go ahead and get the 30s, that way you have room for improvement later on.

As for the AFPR, it's only a bandaid, because you're running your stock injectors harder than they were designed for, not to mention the extra pressure on the lines. This can only last for so long. It's not neccessarily gonna run richer, because you're gonna need that extra fuel. A custom tune is the ultimate answer to get the car running right, but some people can't afford it when doing a buildup. There is nothing wrong with just using an AFPR!! But you would be better off getting bigger injectors, MAF, and a custom tune.

When selecting injectors and a MAF, there is no secret to matching them. If you get 30lb injectors, get a 30lb MAF. That's it really. Hope this helps, feel free to PM me or just post some more if you have questions. I'm going through this exact same fuel dilemma right now with my buildup. Good luck!
-Chris

At what HP or point do we need bigger injectors?

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