I don’t see how you could do that without replacing the exhaust camshaft. Then you needs to re-shim all the buckets. And that point you may as well have just installed a XDI hpfp. lol.
From a cursory search it appears that some vehicles (not necessarily Fiesta ST), people have been regrinding stock cams to reduce the base circle on the HPFP cam lobe (without touching the rest of the cam lobes). I see mainly references to BMW B58 motors, but it could work in theory on any cam driven pump.
You then increase the shim thickness under the bucket to take up the slack.
This assumes that there’s enough extra travel available in the stock HPFP to make it work, and it won’t completely destroy the pump in the process. From the look of it, the B58 can handle an additional 40% lift (and this additional flow). However this might only be compatible with an aftermarket pump
In the first place. I doubt there’s that much overhead in our stock pump. The way to find out would be to do a full travel measurement on the pump with the cam removed with a dial indicator, and then compare with the min and max lift measurements with the cam installed
if it did, it would be a much cheaper option than a whole new pump. A couple hundred for a reground OEM cam + core plus an extra shim for the bucket.
Note, if you regrind your original cam, you just have to reshim the HPFP bucket which is where this mod shines, but swapping out for a new cam core requires readjusting lash on the whole cam, which is a lot more work.
