Injector Linearity
by Joe Lubrant (PTE)
First of all I do not wish to argue semantics, terminology, or definitions of linearity. If someone was to flow a Stock injector, 36# Bluetop,868, 42.5# 009,MSD50 & 55 at say 3ms,6ms,12ms, etc to Static opening, what would the results be?
The 36#BT at idle & midrange pulse widths(45 PSI) flowed 15-17% more than a Stock Injector, & 20-22% richer at static opening.
The 868# so called 36# at idle& midrange pulse widths flowed 24-25% richer than a stock injector, & 16-17% richer at static opening.
The 42.5# 009 at idle & midrange pulse widths
flowed 57-58% richer than Stock Injector, and 42-44% richer at static opening.
The 50# Delphi (MSD) at idle & midrange flowed 60-65 % richer than Stock Injector, and 65-70% richer at static opening.
For additional information, the stock injectors we used flowed 29.5 to 30# at
45 psi static flow.
The 36# Blue Tops flowed 36-37# 45psi Static.
The 868 flowed 34.5 to 35.1# 45psi Static.
The 42.5#009 flowed 42.6 to 43.8 Static.
The 50# Delphi (MSD) flowed 49-51# Static.
So if some one were to ask what injectors exhibit a nonlinear flow characteristic compared to a stock injector or a flow plotted curve I would have to say 868's,& 009's. BTW the Red stripe injectors 38/40# exhibited the same (non-linear) flow characteristics as the 009's, although I didn't use them as an example.
If I was asked what upgrade injectors are the most linear and easy for most to program, it would be the 36#BT,& 50# Delphi/MSD. Of course the 38/40# 42.5# etc. are easy to program now that flow characteristics have been established.
The examples I gave above were comparisons with certain type injectors
compared to a typical stock GN injector. This type of comp. is helpful when
putting together a programming scheme.
We have also flowed all types of injectors using our state of the art flow bench
(developed for the ZR-1 project) and have plotted their flow characteristics.
Believe it or not there are LINEAR injectors.
I found it ironic that I took a 50 Delphi injector that happen to flow 50.3#/hr at 45psi at 6000rpm static, and then flowed it at 70% duty cycle at 4000rpm and it flowed 35.1#/hr. Heck I would say that's pretty darn linear??
In closing to address the original subject, yes tip in problems can be in the
program.
But I have found more often then not IAC, TPS settings, or MAF problems have
been the culprit.
If I remember correctly if you set your fuel pressure at 3-bar (43.5) and put the vacuum. back on the regulator it would drop about 4 to 5 PSI...to 38-39 PSI. Of course this depends on the manifold vacuum at idle, which of course can be affected by some things, like a hotter cam. Also higher idle at colder temps would affect the vacuum applied to the regulator.
I would suggest that fuel pressure should always be adjusted with the vacuum. line off, and also important that the engine be fully warmed up.
Remember injectors are rated full delivery at a certain pressure, most are rated at 43to 43.5 PSI (3-bar) i.e. 42.5#/hr at 43 PSI. So if you set your fuel pressure at 35-36# vacuum ON, then with vacuum OFF it could only be 40 PSI. If this was the case you would not get full delivery of the injector at WOT, even if the injector was programmed to go static.