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Unfortunately I don’t know the part numbers for the springs as they only come as part of the selector hub for 1st2nd gear.
Your only hope is to find another box and strip
It to plunder it for parts.
Ford cosworth Amal valve was by far the most reliable boost controller I used. Just different sized drillings for the insert into the valve needed. Bit trial and error at first, but never had one fail, and that was running 2bar+ boost lol
Unsure how well the Grp n timing would work on the bp270’s tbh.
Regards what’s best, it all depends what you’re after. Peak bhp then 197, but in my opinion you get better drivability from Grp n on standard cams.
If you click on my link in my avatar, you can see 230bhp with a 197 head and inlet fitted to a 172 block. It may have also had some quite lairy items inside the engine as well 😂
I haven’t used this setup personally, but I just use the Karcher patio cleaner attachment turned upside down. I mix up BH autofoam in the bottle for the patio cleaner (karcher pw), as it has rust inhibitors in BH AF and send it under. I find it works really well tbh.
I have no data on oil flow from the pumps, so difficult to comment tbh. But just closing up the tolerances on the original oil pump works very well, but it’s an ‘in combination with’ kinda thing.
It’s got the potential to be the same story as the diesel boxes having ‘bigger bearings’ in them...
The reason they let go is because the oil pressure on the f4r is absolutely dire.
The cranks flex, centre main spins and goodnight vienna.
There are many reasons for them to fail, which I’ve listed many times before. But as far as being a ticking time bomb, I’m afraid I disagree.