125 vs 250 VTwin engines
- This topic has 5 replies, 2 voices, and was last updated 2 weeks ago by .
-
Posts
-
-
-
Oil pump is the same but both engines make peak power at 10500. So anything above 11000 isnt good for the cam tensioners and valves long term but the 250 can tolerate it a little better than 125cc (just larger valves and pistons, crank, clutch basket , flywheel etc)
-
AFAIK the workshop manual on oil presure check gives a higher number for 250 than 125:
250 -> 2.0 ± 0.5 ㎏/㎠
(at 65 ℃∙3,000 rpm)125 -> 0.9 ~1.1 ㎏/㎠
(at 65 ℃∙3,000 rpm)Unless it’s a typo maybe that suggests that oil pumps can be adjusted for increased oil presure?
-
AFAIK the workshop manual on oil presure check gives a higher number for 250 than 125: 250 -> 2.0 ± 0.5 ㎏/㎠ (at 65 ℃∙3,000 rpm) 125 -> 0.9 ~1.1 ㎏/㎠ (at 65 ℃∙3,000 rpm) Unless it’s a typo maybe that suggests that oil pumps can be adjusted for increased oil presure?
Pressure is changed inside the engine because there is bigger holes for oil to flow around the pistons and cylinder head, also the 250cc has a bigger cooler, so need to move oil quicker as the 250 cylinders warms up quicker. But i personally have taken apart both engines, the oil pumps look the same. My suspicion is that the 250 will have a smaller internal sprocket for the 250 to spin the pump a little faster, but alas, i did not measure both oil pump sprockets. The manual is correct that it makes more pressure, so i have been corrected there.
Both GT125R and GT250R have identical redline, it’s strange on GV Aquila as the redline is longer (doesn’t mean it’s good for it) , its the same engine used on both GT and GV. Engine acts funny around 11,000 rpm (it doesn’t like it for too long) but peak power is at 10,000-10500 rpm. Good cruising RPM is 6500-7000 rpm. Higher good revs is 8,000 to 9,000 rpms (you will feel it when you hit a certain RPM the engine has a better rhythm between 6500-8000 rpm, either 250 or 125cc) . Engine will last longer if you don’t redline it.
-
Thank you so much for the insight.
If I ever have the chance, I’ll check that. I usually cruise at aprox. 7k(80kmh) but I’m always curious if there is room for improvement. If it’s just that I might swap the sprocket…someday.
As a side note I upgraded the oil cooler of my 125 to the bigger one from a 250, maybe if the oil pressure is an easy upgrade too I’ll do it also.
-
No need to upgrade the oil pump, changing to 25o cooler is the #1 engine mod for the 125cc , your rear cylinder will thank you!
Front cylinder not a problem as it gets a lot of air anyway.
Sprockets, try a 520 chain conversion kit (52T on a 428 chain rear wheel is too big for long distance riding) , 520 sprockets have 46T rear or 48T (take it from GD250R sprocket will fit)
If you keep 428 chains, try 15T front and 52T rear (Can’t change size on rear on 428 chain sadly) but if you don’t care about acceleration, 15T may help reduce the revs further for more speed
Don’t forget new clutch , new springs , and valve clearances go a long way , use the service manual (GV125 and GV250 are the same clearances as both engine use shims)
-
- You must be logged in to reply to this topic.