My new mill, an OBR 30.5

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I tell ya what...them boys at obr sure can make some killer power! I would like to send in my prostock for a full mod but hell...I have all I need with the 30.5 PS. looking forward to some ripping around vids.
 
here we go...

the 2 bolt race port top end by OBR for 30.5cc stock case. the old head and piston to the right. tidy little set up getting 8hp old of the old bones.



 
8hp??? With a head replacement.also why does the top of the piston look so hammer toned.good luck but I believe 6 hp is gonna be max for that set up.
 
the piston top has a mottled finish, not sure the rating on the swap specifics, hopeful for more. i did polish the chamfers a bit more to make more uniform. the piston was not what i expected, kinda dimpled like golf ball. WAY more than stock and more than 4 bolt prostock

once i get a tow with this unit i'll know more
 
heres the combo.

stock 2 bolt HY case

OBR 2 bolt race port top end kit

990 walbro

RCMK pullstart

basic cup airfilter, for the $ easy, effective and fits

heat cycled ready for action, we'll see





 
1/2 gal. thru it. man the revs holy crap! AND torque! a step beyond 4 bolt PS fo sho ! the pull away rip is awesome, esp. jumping off on the 9500 clutch.

the ring pop is ear popping, head is still ringing! love it!

sucks the gas, looks like i need MT tank on it
 
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next on the bench , WT 990 carb. 600+ hours on this one. high end seems clogged.



going thru some airfilter sets and combos . the dual foam cup first one up, also added outerwears. working on disposable pre-fitlers protos for super dusty as well, and working in TGN rednecks thick /thin



heres a few



the one on the left is actually a filter canister, screen and foam go inside or outside , no screws! like some cans cover combos
 
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Ildy666 said:
8hp??? With a head replacement.also why does the top of the piston look so hammer toned.good luck but I believe 6 hp is gonna be max for that set up.
Click to expand...
the piston head dimpled ? guessing it aids in gas speed across dome and perhaps better heat dispersion as well.

seems like a ceramic glaze , thats what it looked like??

did not quite make 8hp, but much closer to 8hp than stock... but in reality, i had the OBR 8hp reed setup on my mind
 
just made a disposable pre-filter, 36cents and about 10minutes. its going on a 3" filter screen plus a redneck.





elastic came came on the mask material and it came in handy.



for < $12 i can make about 32
 
surgical mask material, its a 3-ply blown non-woven polypropylene, goes down to about 2-4 microns and water resistant. is a bit much for an engine, should last about a weekend. flow will fall pretty quick i suspect we'll see.

i will dropped the inner ply before actual use, and maybe add cool logo/print , the yellow and pink butterfly did not make the traveling team and plan on sticking with the blue. i have not sourced bulk filter media but i sure i'll look about for it. once i test them of flow and heat tolerance i can send u a few
 
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Still on the OBR 2 bolt ported, and WT990. really nice combo for fun power and rip.

>5gal. thru it and noticing a finicky tune cycle , since humidity and temp have been dropping(kinda all over the place) always needs a tweak. at stock 990 settings, which is perfect for break-in BTW, will be WAY rich and if left too long warming it up WILL foul plug (CMR7H )the warm up seems to be the critical for settings and plug life... seems a minute too long at operating temp and too rich and obviously the other way is just as bad. have not jumped to the iridium plug yet which seemingly may tolerate the temp swing without fouling. the prostock with the thick case hardly ever fouled a plug , maybe the ported head and stock case just run higher temp, not sure, but the new plug diet about every 6-10hours seems excessive ?? maybe not for the performance .

i 'm gonna blame it on the humidity...and the fairly NARROW sweet spot on the ideal tune, and squeezing past it is an instant foul!

thats the tweaky race port tune issues i have encountered but definitely worth it

but is it worth an iridium plug?

and "glazed piston top" is totally clean , thats running 25:1 with 927 and premium ethanol-free gas.
 
I was having a finicky tune on my Gizmo FullMod that was an air leak on one of the carb isolator gaskets. I wonder if going to a CMR6H would help with any of the fouling issues.
 
i would say hotter plug like a cmr 5 or 4 SHOULD be less fouling because its holding more heat and keeps carbon burned off. with a cmr7 getting it through the warm up without fouling is the trick, esp. with more power. the cmr 7 can shed alot of heat and if u add a rich setting AND the unit is cold its could foul easily. a hotter plug(4,5,6) concentrates heat in the dome and can be punishing to the engine parts. the cmr 8 iridium is just gonna resist deposits and keep chamber cooler hopefully without needing hi temp burn off.

it gets even more narrow and tedious with heavily modded stuff , add some humid air and it just gets hair pulling.
 
Going to a hotter plug will only damage engine parts if there is detonation. Your plug obviously isn't in the self cleaning temp range so no chance of a hot electrode causing deto. I don't think going to an even colder plug is the solution even if it has a tiny electrode. But w/e It'll probably work fine on these tiny motors lol
 
had good success with cmr 7 , and ran several cmr5 no real difference, but only had 7's in the ported set up, with definite foul rate increase. i think iridium may give improvement with mod demands ...we'll see.

the temp and humidity have had big swings so maybe some consistency there would help .
 
a little update on my experience with the plugs on the 30.5cc OBR 2 bolt race ported top end on HY stock case. cmr 7h is the go to plug. seemingly high humidity will see fouling increase, but definitely better top end ... the iridium has pull time since December around 50hours without foul even through foggy days, BUT mill has lost the top end ...definitely blunts it . changing back to cmr7h to get back top end. hopefully its not compression.

still has pull away torque thru power band just missing top 5% revs maybe... we'll see
 
i know , just the foul rate in humid conditions was crazy.

esp. when squeezing the top to get it all. ideal settings with decent peak will foul 4-6 hours.

if i go with a richer settings it stretches to about 10-12hours which i felt was ok.

the humidity and narrow tune with the porting was quite different than stock.
 
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