Just wondering if after changing my Walbro 255 to the Spec C fuel pump (both are very similar) whether a map tweek will be required? Bearing in mind I was already running a Sard fuel pressure regulator which has been set up properly in the past and mapped.

I would imagine the fuel pressure will remain the same but fuel flow may have changed. But this would only cause a minimal difference on closed loop idle and not have an affect at open loop, where AFR's are set by mapper? (Its just that I seem to be getting better Mpg since changing to the Spec C pump, hence question).

 

I just swapped my Walbro for an RCM pump.
Pressure reads the same on the regulator so no map required.
the only other difference is that, because the RCM pump has better delivery at high demand, the engine may run slightly rich at top end.

 

But Im wondering if the Spec C fuel pump has a slightly lower fuel flow rate than the Walbro 255, if that will cause the opposite and run a tad lean in certain conditions?

 

If you suspect the delivery pressure is lower with the spec C pump then a map tweak might be the safest (and cheapest) bet.

 

Is it really worth 'chancing it' and not getting it checked?

 

Very true.

 

Its not just pressure its also flow it effects.

However you will be making it safer as the walbro should be flowing more fuel, but if its richer than mapped you will lose power.

Simon

 

By the same token, if its richer than mapped then it was mapped with falling fuel pressure and you perhaps need to find a new mapper!

 

This could turn into an epic what if thread if we arent careful lol.

 

Indeed, I am going to carry on wiring up my dyno cameras and cancelling my subscription to this topic right away. LOL

 

Quick question - why put a spec c pump in there rather than the walbro ?

The spec c flows at 245 and the walbro at 255.

Confused as to why the change.

May be running leaner on boost as fuel delivery might not be keeping up but it is unlikely that is the case as the power you are running would be within the flow rates of either pump.

As for Stu - where above does it say it is running richer now ? Please put your wooden spoon away

 

I believe the Walbro was malfunctioning, started making very strange noise when priming. Also lower revs on idle, jerkiness on take off in 1st gear, worsening fuel consumption. Since switching to the Spec c pump all those issues have gone. Plus I had a nearly new Spec C fuel pump lying around!

Thanks all for info so far

 

I miss read and thought you had gone from spec c to walbro..

get it checked then.. no question

 

I was replying to this quote right here...

To which I correctly replied:

Please advise why you think there is some wooden spoon involved in that conversation exchange?

 

Which was my misread that he had gone from spec c to walbro lol