Anyone Do Their Own Porting?

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, and others.
Seandonato73 said:
Whichever opens first. But it's used to get the old charge moving out of the cylinder faster. The main transfer event is both of them open.
Click to expand...
thanks Sean!
i got a problem then... because no way i can port a 24 deg blowdown on my g320rc clone and 30mm stroker crank (g340rc). to lower the transfer duration would involve cutting the cylinder base and if i do so, i'll have free-porting issue on the exhaust side... or JB weld the transfers, which is a no-go with g320.
even w/o cutting anything i got very tiny margin left from the piston skirt to seal the exhaust from the crank case.

here are my findings:

1615442104235.png
 
Last edited:
Unfortunately some times your just stuck porting around the cylinder, to try and make the best of it. By chance have you measured a zen piston height vs the rovan? I've found that sometimes they have different heights that may help out achieving the numbers your after.
How small is your exhaust skirt margin? Typically I would say you can get away with + - .020" ish.
 
its pretty hard the measure the skirt margin.. but it is about + - .020" ish. (0,5-0,7mm)
both Rovan and Zenoah pistons are identical in height. both are 29,12mm. wrist pin positions are identical too.

until i had caliper in my hand, i measured the diameters too. ZEN is 37,93mm all around the circumference.
Rovan has 37,84mm / 37,91mm... the later is perpendicularly to the wrist pin.

since i cannot lower the transfer timing, i'll not touch it and will check the ideal time-area... to see where i'm
 
hi gents
some motors only allow you to do so much to them. when I started with the boat motors all was also around transfer duration and blowdown. then I started doing motors not even worrying anymore regards above. and I will tell some of my best strongest Zenoah 30,5cc run by far the best not even close to what the blowdown should be. I am new to cars so this is a new arena for me, but I will get to know them better. a friend of mine bought a 30DEG NORHT 4X4 with a 38cc motor fitted from the factory, this was snail mail on its best. we couldn't get this motor to perform. no bottom end pull and only slight top end, so we decided to pull the motor apart to see if we could put more life in it. this motor for sure has some serious issues.
std squish 1,8mm, never seen this huge in my life, 174 exhaust, and 144 on intake, I don't even speak about the small transfer openings. I removed the base gasket and end up with a squish around 0,85mm with some free porting on the exhaust side, but not to much. I raised exh up to 185* and intake to 157*. this motor was for sure a bigger animal after this was done to it, but I still think his pipe is way too small.
 

Attachments

  • 20210320_195556.jpg
    20210320_195556.jpg
    80.7 KB · Views: 15
  • 20210320_195612.jpg
    20210320_195612.jpg
    65 KB · Views: 14
  • 20210320_195617.jpg
    20210320_195617.jpg
    67.7 KB · Views: 14
  • 20210320_195645.jpg
    20210320_195645.jpg
    86 KB · Views: 15
hi there
in a car with fix gearing, i'd look for wide power range, like in motocross. it means low exhaust port time-area value in combination with a high transfer port time-area... plus a pipe that is giving most of the power at around 11-12k rpm. e.g some with 25-28" long from the ex port till half of the baffle cone. (of course the diffuser and baffle-cone angles DO matter too)
i have no experience in gas boats at all (and limited in the cars either), but would assume they are tuned for high rpm and has their power characteristics more like the road racing bikes. meaning maximum value for exhaust port time-area and a minimum transfer port time-area. (if you exclude the variant of area, it means high blow-down). pipe length should be around 18-20" for 15-17k rpm... calculated with 185* of EX.
have you tested the 38cc after porting? did it work well with the free porting at the ex-side? 38cc is a 40mm bore and 30mm stroke engine. i'm not far either from having free porting on EX side in my 38mm bore 30mm stroke Rovan.. with stock base gasket of 0,5mm.
 
Totally different animals mate, boats go for max rpm and top end power. Tbh I'm not surprised your weren't impressed with the engine out of the box, clone engines don't typically wow and impress. Sloppy tolerances, port numbers all over the map, and crappy castings. Seems with some care they can be made decent. I'm not a fan, nor will ever be a fan of free porting. Your loosing fuel mix out the exhaust and hurting your crank compression. There is another theory on it but that's another subject.
 
we will run this motor on Sunday in a club race. will make a video to share.
the quality of the marine zenoah barrels outshines these cheap versions. even with a brand new dremmel cutter, the chrome flake away as on a rcmk or zenoah, you really have to work the cutter.
 
john addinall said:
we will run this motor on Sunday in a club race. will make a video to share.
the quality of the marine zenoah barrels outshines these cheap versions. even with a brand new dremmel cutter, the chrome flake away as on a rcmk or zenoah, you really have to work the cutter.
Click to expand...
Found on cheap cylinders it best to start off with a diamond burr and "trace" your outline to grind the plating away. Seems to help with chipping. Large chamfers seem to help with plating retention as well.
 
I use a large mix of cutters, rc engines are the smallest of what I mess with. I've also found I like different profiles for different tasks. Wouldnt dream of using suck a large burr doing transfer work, or finger porting. The roof angle is too important to chance getting an odd bevel from a larger profile. Best to stick with an 1/8" burr for that work. Actually I use very few cutters above 1/8" for these little guys.
 
hi all.
we had some really nice racing yesterday. the 38cc was way better than before. here is a short video of it. these are all 4x4
the bakkie in the 3rd spot from start running the motor i did
some of the baja's that also run
 

Attachments

  • 20210328_094506.jpg
    20210328_094506.jpg
    377.7 KB · Views: 8
Last edited:
MonsterAir said:
I was just watching that vid!.... Well isn't a +2mm stroker with machined head considered a big bore?.... I was thinking the same about have a local machine shop do a few for me but now that I'm learning these cases need more room to accommodate the stroker cranks this whole endeavor seems kind of useless. If all the major performance mods need to be done with heavy machinery then I guess I'll be stuck buying OBR or ESP gear.



For some reason I feel like this isn't the proper way. lol


Click to expand...
well for one thing he should be covering the bearings even if you clean after its best not to get metal shavings in them at all at least thats my thought
and shaving the crank takes away balance correct? I wouldn't do that either
john addinall said:
hi all.
we had some really nice racing yesterday. the 38cc was way better than before. here is a short video of it. these are all 4x4
the bakkie in the 3rd spot from start running the motor i did
some of the baja's that also run
Click to expand...
damn that track is sick I wish they had a track around my location even a poopy one the best we got is the end of a street and the dustiest freeway interchange area which I will never go on again unless it rains cause my bearings can't take that kind of a beating
 
Last edited:
Reed266 said:
well for one thing he should be covering the bearings even if you clean after its best not to get metal shavings in them at all at least thats my thought
and shaving the crank takes away balance correct? I wouldn't do that either

damn that track is sick I wish they had a track around my location even a poopy one the best we got is the end of a street and the dustiest freeway interchange area which I will never go on again unless it rains cause my bearings can't take that kind of a beating
Click to expand...
Did you read the entire conversation or just the parts that stuck out? We already covered that you don't shave the crank down, and clearance the case halves.
 
Back
Top
✖
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock    No Thanks