wanted: mathematical genius or rd250/350 owner

[Gil Gallad]

ok, i'll try and explain as best i can. i built a suzuki gt350 engine using new liners etc, so it's basically the same as the rd350. 64mm x 54mm bore and stroke. the problem is oil delivery. i know people who have converted rd250's to 350, but only used the 250 oilpump, leading to seizures. question is: how much more oil delivery would i need for an engine [rounded out] that's 30% bigger? if i knew the flow from an rd250 and 350 i would have the answer. do i need 30% more? or doesn't it work like that in reality? at the minute, my only option seems to be fit a t/gt500 oilpump 
cheers, gil.

[m in sc]

the reality there is that the 250 rd pump doesnt put out less. the gearing inside the pump is different, and therefore puts out the same at the end of the day. you can trust me on this one. however, if somebody put a 350 pump on a 250 bottom end w/out changing the gearing, therein lies the problem. IF you use a 250 pump and shaft on a 350 bottom end, with 350 primary gearing, it actually will over oil.

look for a GT350 pump. (actually they are what, 315cc?)? in my opinion though, the old GT pumps over oil anyway. just adjust it up a bit.  or, maybe look at a gt380 pump if you're still worried about it.

side note, erik k wanted me to do a gt250/rd hybrid quite a few years ago.  (rd jugs on a gt bottom end). he was telling me he wanted to beat rds on the track. i asked him why didnt he just race and rd , he looked mortified. lol. 

[Gil Gallad]

thanks for that  ;D another mate just texted me and explained the rd system is totally different to the gt - something about autolube, so i presume that question of mine is pretty much kaput. getting hold of a t350 oilpump over here is pretty much impossible, so the gt/t500 was my next choice. i wish i could fit a gt380 pump, but they are totally different.
cheers, gil.

[m in sc]

to be honest, i wouldnt worry about it. the crank will still get fed as they have direct lines, correct? , and the bores are only 10mm more or so. with modern oils, there really isn't a concern in my mind. I'd run it.  the 500 will pump way too much. hell, it pumps too much on my t500. ! 

[Gil Gallad]

thanks mate, i'll take your advice on that. watch this space.
incidentally, i built a gt285 and that engine runs on standard gt250 pump and settings. it's absolutely fine  8)
cheers, gil.