APEvoVIII

Fishing for some opinions here. Have had a standard 255 in the tank since god knows when...at least 7 or 8yrs. It's always whined, maybe more so recently...sometimes it screams, sometimes its quiet. I'm wondering if I switch to a 255hp, will I be able to just drop it in and go, or is retune absolutely necessary?


Problem is I'm starting to get high rpm knock. Nothing really significant, 2-3 counts only above 6k. CEL flash is set to <3 counts slow, <6 counts fast. I occasionally get a slow flash, even recently in this nice fall weather. I log religiously, and rarely will have a knock-free 3rd gear run.


Some info...stock motor, hta green, hks 272, BR street core, 750cc inj, standard bolt ons. The injectors are dated as well, but not as old as the pump. They are pretty well pegged at 90-92% in upper rpm. I tuned with Tom about 3 years ago. Results were great. We finished up around this time of year so conditions were favorable. The following summer the car ran well. I lowered the boost a tad just to be safe, but its Tom's hybrid mbc + ecu boost so it more or less lowered itself to accommodate weather conditions.


Wasn't until this past season when I started getting consistent knock as I described. Been trying to rule out causes. I moved since we tuned. Had wonderful shell gas for tuning. Now live in a small town and Sunoco is the best bet, but it likely gets filled with the same tanker as every other station in the area.


I digress....I'm not leaning out up top significantly but afr is floating up from mid 11s in the midrange to high 11s up top. To make this not-so-short story as short as possible...I'm considering replacing the pump with a 255hp. Walbros definitely have a service life which I may have surpassed. I'm wondering if I drop in a 255hp, will the difference in flow completely jack up my fueling? I understand it will richen me up a bit, but that's kind of what I'm going for. Are the differences between the two so drastic that I will need tuning? I'm not one to shortcut anything, but my power level is where I want it, and frankly I don't feel like going though the tuning process again. I have an ls1 project going on at the same time and its got most of my attention. I just want the Evo to be knock free.


I know the most appropriate answer is to get retuned if I change the pump. I'm asking for opinions and/or experience if anyone feels that the pumping capacity of the two pumps differs so much that a retune is necessary, or if it is close enough to a standard 255 to be considered a direct replacement without causing me to go too rich, but at the same time potentially solving my problem, or at least ruling out a failing pump. Looking for anecdotal experiences from anyone who's possibly been in a similar situation...or mathematic analysis lol. Not looking for the famous EvoM "get tuned bro, that's my .02"


Thanks folks

lostsoulsevo

iTrader: (10)

The old pump is prolly going bad, hence high rpm knock. I would drop in a new one and log a few pulls. You shouldn't need a retune

Ted B

iTrader: (6)

And you've had the wrong pump in your car since then. The standard pump is intended for normally aspirated applications, not turbo cars. Pumps in N.A. applications never apply anything greater than base pressure.

I suggest you get the proper pump.

ridenrunwv

I didn't catch this. I originally read this and was thinking the tune should probably be fine after changing pumps.

You will need your tune modified if you switch to a pump that's going to maintain a reasonably higher fuel pressure.

Ted B

iTrader: (6)

To clarify what I wrote above, standard duty pumps aren't designed to keep up with a rising rate regulator. That doesn't mean they won't work, but the HP pumps outflow the standard pumps in a rising rate situation. Always get the HP pump for any turbo application.

APEvoVIII

Honestly, I installed the damn thing so long ago I don't even remember who I got it from. My first round of upgrades was a buschur stage 1 or whatever. It was intake, full exhaust, mbc and forge dv and I think I chose to add in the fuel pump for safety. Here's how long ago it was...I believe the package included a mail in ecu flash from........big Al from dynoflash!!!!! This was in like 2006 so I don't know what the model # of the pump was. I assume I got it from BR since that's where I exclusively shopped in the beginning, and I'll also assume that they would have carried the right pump. I figured I had a regular 255 since I didn't even realize there was the high pressure version until a few years ago, and I notice some evo specific vendors have both the regular and hp models. Well if I'm gonna replace it I'll find out when I pull it out. Shame, I was hoping I could drop in something with a bit more capacity without having to retune. I'll just get a new one for now and have a fairly new 255 when I inevitably go double in the future.

Ted B

iTrader: (6)

I don't think Buschur would have sold you a standard pump.

Anyway, these Walbros are noisy in general, but if the pump becomes noticeably noisier, that should be assumed (in my experience) as a warning that it's about to fail.

APEvoVIII

I suppose I assumed that because I didn't become aware that the two different versions existed until some years after I already installed mine, I thought I had the regular one, and the HP255 was newer. Now I understand that the 255lph we all have is likely the HP model. Mine has always been noisy since day 1, but I think after 8 years its reasonable to say a new pump would be wise.


While I have your attention Ted, if I could ask a question....say I were to do the modified relief valve on the new pump for increased flow. Do you think it would be "drop in" compatible with the current tune? Or would there be changes in fuel pressure so drastic that would necessitate ecu adjustments? Obviously to optimize the change a re-tune would be advantageous I'm sure, but are we talking minor tweaks or major adjustments? I won't solely rely on your opinion, just looking for some insight. I'll clarify with my tuner, but he's a busy guy and it can be difficult to get a response sometimes...


Thanks for your help on the matter

lostsoulsevo

iTrader: (10)

You'll be fine with the modified Wally as a drop in pump. You may run a little richer, to say you don't need a tune would be naive. Like I said install the new one and pull some logs. That's the only way to tell.

Ted B

iTrader: (6)

Modifying the relief valve would theoretically affect the tune if the boost pressure previously caused the valve to open. This would cause a change only in those boost ranges where this occurred.

APEvoVIII

I appreciate the advice gentlemen. I think I have the answers I needed.