Dodge RamCharger Central banner
1 - 6 of 6 Posts

Registered
Joined
2,187 Posts
Discussion Starter · #1 · (Edited)
My PF4 has two options for fuel pressure, 43 and 58 psi.

Assuming the pulse width can be trimmed enough with the current injector size, I'm wondering if the higher pressure would help with atomization enough to make a noticeable difference on the 360's economy.

At the current 43 psi it has a minor part throttle lean misfire with a commanded 14.5 AFR. I can drop the AFR into the mid 13 range, the misfire clears up and power noticeably improves. It becomes a gas sucking pig however.

I find that somewhat odd. One would think that with MPFI, the Eddy' modern closed chambers and good quench the AFR could run decent in the 14's. A symptom perhaps of the 226/230 duration, 110 LSA cam, single plane intake and low rpm reversion? (2500ish) Sucking some of the fuel out during overlap combined with the short intake runners' poor low RPM pulse wave effect?


** I looked at the cam card. the LSA is 110 not 108 as I previously stated. I corrected it **
 

Registered
'79 Dodge Power Wagon Macho
Joined
4,165 Posts
The cam could be responsible for your issues. What's the LSA of your cam? - not that it really matters because you got what you got unless you change it. You can try the higher fuel pressure setting but your regulator and injectors might not be able to sustain higher pressure. Is your regulator adjustable and are your injectors rated to flow up to 58psi? If not then it becomes moot to up the pressure as the regulator and injectors will only flow a given amount - but higher pressures are always better - better atomization.
 

Registered
Joined
7,435 Posts
My PF4 has two options for fuel pressure, 43 and 58 psi.

Assuming the pulse width can be trimmed enough with the current injector size, I'm wondering if the higher pressure would help with atomization enough to make a noticeable difference on the 360's economy.

At the current 43 psi it has a minor part throttle lean misfire with a commanded 14.5 AFR. I can drop the AFR into the mid 13 range, the misfire clears up and power noticeably improves. It becomes a gas sucking pig however.

I find that somewhat odd. One would think that with MPFI, the Eddy' modern closed chambers and good quench the AFR could run decent in the 14's. A symptom perhaps of the 226/230 duration, 108 LSA cam, single plane intake and low rpm reversion? (2500ish) Sucking some of the fuel out during overlap combined with the short intake runners' poor low RPM pulse wave effect?
Yeah. Could be the single plane intake/ cam choice giving you some issues.
Part throttle lean is a fairly easy fix with a Holley carb. You'd think with a MPFI there should be a way to tune it to deposit a little bit more fuel at that certain point? Or, jog my memory... can you tune your fuel inkection setup?
 

Registered
Joined
2,187 Posts
Discussion Starter · #4 ·
Yeah. Could be the single plane intake/ cam choice giving you some issues.
Part throttle lean is a fairly easy fix with a Holley carb. You'd think with a MPFI there should be a way to tune it to deposit a little bit more fuel at that certain point? Or, jog my memory... can you tune your fuel inkection setup?

Adding fuel is easy, a few keystrokes and done. Don't even have to raise the hood or plug anything in. The issue is need for that extra fuel. Not sure what it is about my setup that has an issue. After some more thought it occurs to me that if Finnegan can get 17 mpg out of the hot cammed, mpfi 700 hp 528 Hemi in Blashpemi, {when it was still NA} that kind of blows the 110 LSA/reversion theory out of the water. Hemi heads are notorious for crossflow during overlap. Mine idles slightly bumpy at 700 but cleans up completely by 1000 rpm. No hint of a lope with the EFI. The same cam ground on a 114 would have a granny smooth idle. Cam card is below. It's pretty mild, 1.5 rockers.

I'm beginning to wonder if I have an injector or two that's not flowing at spec. Simply not delivering the required fuel for one or two cylinders to burn properly at a narrower pulse width. Taking a look at the plugs might answer that question, or having the injectors flow tested. Or perhaps setting it in the 14's and shooting the header tubes with a heat gun, see if any are running noticeably hotter.

When the stroker kit goes in I'll have to do something with the fuel anyway. Either raise the pressure, get bigger injectors or maybe both. I think the current ones are supposed to support 500 hp, but not certain. I'll have to pull out the paperwork and see what's in it. I'm guessing it should make about 450ish at 5500 rpm, maybe a little less. Seems to be about avg for 408's similar to my combo.

I'll do some digging on the net on pressure, atomization and burn rates.

Font Paper Document Magenta Carmine
 

Registered
Joined
2,187 Posts
Discussion Starter · #5 ·
The cam could be responsible for your issues. What's the LSA of your cam? - not that it really matters because you got what you got unless you change it. You can try the higher fuel pressure setting but your regulator and injectors might not be able to sustain higher pressure. Is your regulator adjustable and are your injectors rated to flow up to 58psi? If not then it becomes moot to up the pressure as the regulator and injectors will only flow a given amount - but higher pressures are always better - better atomization.
The regulator will be fine, it's downstream of the fuel rails. Running a return style setup, although it's optional with the PF4 I never liked returnless systems. The regulator is adjustable and vacuum referenced as well. The setup wizard for the EFI asks which fuel pressure you're using, 43 or 58 so I'm guessing the injectors can handle the pressure. Just not sure if the fuel map can be trimmed enough to match the cubic inches and HP [pounds per hour] at the higher pressure.
 

Registered
'79 Dodge Power Wagon Macho
Joined
4,165 Posts
In my Trans Am I was running a hand built MPI and a cam with 114 LSA. I ran my fuel pressure @ 45psi at the regulator and had 28lb injectors (the biggest available back in the day) and made over 500 hp. My 0 to 60 was 2.5 and best 1/4 mile time was 11.9 @ 118 something mph (no NOS) in a 3400lb car. My car also had NOS but not on that run. Boy if I didn't have my motorcycle accident, my T/A would be even more pyscho today with the better EFI systems and components available today. I built my old car for auto X events and not drag racing. It had 3.73:1 gears and a T-56 tranny - not the best for drag racing but a killer on a road course. A return line on both injected or carbureted engines is extremely important. I chose GM back in the day because Mopar never had a front engine V8 rear drive modern muscle car so I had to jump ship for decade and a half. GM was the logical choice as Chrysler and GM engines are fairly similar. My old Trans Am smoked 1000cc bikes and Vipers all day long with no giggle gas. I even raced a Lamborghini Giardo (V10 AWD with a 6 speed manual) and rocked him 3 times in a row and no giggle gas. Boy those were the days!
 
1 - 6 of 6 Posts
Top