402 stroker injector recomendations?

[Bruce Melton]

I have a LS2 402 on order and want to be ready with some "safe" sized injectors. The motor should make ~ 550 FW. I ran SVO 30s on my old (now deceased) head and cam (420RW) motor at ~80%.
I like Bosch Ford injectors, do we think the Ford 42s (or 36s>43#) which make ~50# would be a good safe choice? Or is there a better choice? I will be running MAF, LS6 intake and 236-242 cam..

Appreciate your thoughts,

Bruce

[Tordne]

I was plannign on running FMS 42lb injectors in the Iron block 408 I was going to order (sad story) :bawl:

42's are pretty big for a NA motor.

Side question. Don't you recon the 402 will flow more than 511 grams/second of air, and therefore max out the MAF?

[Bruce Melton]

I think it will be close on MAF but I am running a LS6 with ported TB not a FAST and I have not heard of that being issue. Gives me something more to worry about though, Thanks.

[superls1]

You probably already know this:

BSFC x HP / # of Injectors = Lbs/hr rating of injector @ 100%

BSFC - Brake Specific Fuel Consuption; it is a measure of how 'efficient' the engine is at converting fuel to HP; the lower the number, the more 'efficient' the engine is; I use .45 for the LSx engines
HP - use crank HP (estimate if not exactly known)

So, assume 550HP at the crank (or 468RWHP assuming ~15% drivetrain loss):

.45 x 550 / 8 = 30.93 lbs/hr

Remember, this is 100% duty cycle, and you want some margin of safety. So, shoot for 85% max duty cycle. Therefore, divide by .85

30.93 / .85 = 36 lbs/hr

Let me know if I can help.

FYI, the C6 Z06 has ~40lb/hr injectors. I have used both the Ford 36# (43 @ 58psi) and the Racetronix 42# (48 @ 58psi) in some 402 applications. I have good results with both.

[Bruce Melton]

You probably already know this:

BSFC x HP / # of Injectors = Lbs/hr rating of injector @ 100%

BSFC - Brake Specific Fuel Consuption; it is a measure of how 'efficient' the engine is at converting fuel to HP; the lower the number, the more 'efficient' the engine is; I use .45 for the LSx engines
HP - use crank HP (estimate if not exactly known)

So, assume 550HP at the crank (or 468RWHP assuming ~15% drivetrain loss):

.45 x 550 / 8 = 30.93 lbs/hr

Remember, this is 100% duty cycle, and you want some margin of safety. So, shoot for 85% max duty cycle. Therefore, divide by .85

30.93 / .85 = 36 lbs/hr

Let me know if I can help.

FYI, the C6 Z06 has ~40lb/hr injectors. I have used both the Ford 36# (43 @ 58psi) and the Racetronix 42# (48 @ 58psi) in some 402 applications. I have good results with both.
It seems if you get the LTFTs in the -5 range it runs the injectors beyond the equations, or is that just my experience? My old motor sucked up all the SVO 30s could pump @80-85%. If the LS7 is using 40s it seems 43 would be damn close? The stock LS2 is now 32 or 33# I think.
Better safe at 50 (42s)???
BTW -I almost had a nervous breakdown over cam selection.

[superls1]

BTW -I almost had a nervous breakdown over cam selection.

What's the lift and LSA?

RE the injectors: There have been a few posts lately of people talking about injectors being too big. Obviously, if you are trying to fill a dixie cup you don't want to do it with a fire hose. But, it seems that most people can tune 40-50lb/hr injectors without much issue.

[Bruce Melton]

What's the lift and LSA? 238-242/605-610/113 LS-X

RE the injectors: There have been a few posts lately of people talking about injectors being too big. Obviously, if you are trying to fill a dixie cup you don't want to do it with a fire hose. But, it seems that most people can tune 40-50lb/hr injectors without much issue.

Well I would rather have them be too big than get heavy on the duty cycle. The problem is there is such a huge gap in pulse width between idle and WOT @7K the low end will be hideously out of control. This engine is designed to favor torque over hp but as a road race engine it will see a fair amt of sustained high rpms.
I have a guy holding a set of 36s for me but--

[redhardsupra]

according to my own spreadsheet:
http://redhardsupra.blogspot.com/2006/02/injector-sizing-spreadsheet.html
a 408 running at 13:1AFR and 7000rpm, will do just fine with 42s running at 58psi, leaving you with a nice margin of error.

[Bruce Melton]

according to my own spreadsheet:
http://redhardsupra.blogspot.com/2006/02/injector-sizing-spreadsheet.html
a 408 running at 13:1AFR and 7000rpm, will do just fine with 42s running at 58psi, leaving you with a nice margin of error.

Did I do this right? I assume you meant SVO 42@~50#?
Thank you, nice spreadsheet!

http://home.new.rr.com/meltn/402inj.jpg

[redhardsupra]

yup, about right. this is for ballparking not precision work anyway, especially that injectors only come in certain sizes

[eboggs_jkvl]

Nice spreadsheet! It says I am close on my injector selection as I am running 60s

[Darkness]

My 408 makes 520rwhp and with 38# injectors I'm only seeing 83% DC at WOT.

[Bruce Melton]

[quote=Darkness]My 408 makes 520rwhp and with 38# injectors I'm only seeing 83% DC at WOT.[/quote
Zowie!

[redhardsupra]

well, since we're hijacking this thread anyway... ;)
the reason i created this spreadsheet to figure out something that bugged me for a long time: why do some people get away with tiny injectors and big power, while others (like me) run out of bigger injectors so quickly?
ultimately, power comes from air and fuel, mixed at a certain ratio, consumed at rate dictated by rpms. so why would the outcome numbers differ so far? i know people used to tweak IFR and that would probably throw off the true numbers of logged IPW, which are used for IDC, but if everything's configured correctly, then shouldn't it all be fairly cut and dry?
Darkness, what's your setup for IFR? what fuel pressure? any fuel pressure regulators?

[eboggs_jkvl]

My 408 makes 520rwhp and with 38# injectors I'm only seeing 83% DC at WOT.

Really hard to believe. That's a lot for 38# injectors.


Elmer

[Bruce Melton]

well, since we're hijacking this thread anyway... ;)
the reason i created this spreadsheet to figure out something that bugged me for a long time: why do some people get away with tiny injectors and big power, while others (like me) run out of bigger injectors so quickly?
ultimately, power comes from air and fuel, mixed at a certain ratio, consumed at rate dictated by rpms. so why would the outcome numbers differ so far? i know people used to tweak IFR and that would probably throw off the true numbers of logged IPW, which are used for IDC, but if everything's configured correctly, then shouldn't it all be fairly cut and dry?
Darkness, what's your setup for IFR? what fuel pressure? any fuel pressure regulators?

Hijack away, as that is the greater question.

It does seem that + LTFTs are part of the stock tune which may account for their ability to run these things with smallish stock injectors. It seem that whatever method you use to get - trims eats injector capacity more than PE tweaks which of course are often leaning.