Zen260 Squish & Timing

[happybradboating]

Hey Gas boaters,

I hate to mix in a question about gas boat stuff on IW but with Jim's BD not in service for close to a week I want to finish building my mod Zen260 motor. At this point without gaskets I get a measurement of .0185 in regards to the squish on the dial a gauge. What would be a good setting? One person on Jim's BD suggested .016 when I was in the process of buying tools for gas boat motors.

In addition, if I was to do any exhaust timing porting does anyone have any suggestions on improving performance without going to far and struggling to find the needle?

Thanks

Brad

 

[Daniel's Racing]

Brad,

IW has accepted gas talk for some time. LOL.

Do you have access to someone that can trim the base? If you wanted to get .016 with a blue gasket you would need a .0185 base cut. If you wanted to live with 18.5 thousands you could go without the gasket, cylinder directly on case with the proper sealer. Open Exhaust duration of 185 and intake at 157 with the proper size and shape and just a few area's of the transfers modded and dress all the sharp edges well and you will have a long lasting good strong engine.

 

[Scott Schneider]

Follow this and you will be running along side the top builders engines

http://www.modelgasboats.com/Magazine_Content/Tech_Articles/Engine_Porting/

Or: http://www.modelgasboats.com/Magazine_Content/Tech_Articles/RCMK_Engine_Modification/

 

[Rick Reisinger]

Follow this and you will be running along side the top builders engines

http://www.modelgasboats.com/Magazine_Content/Tech_Articles/Engine_Porting/

Or: http://www.modelgasboats.com/Magazine_Content/Tech_Articles/RCMK_Engine_Modification/

 

Read ob-1 the author is a master builder my mentor

 

thank you scott

 

Rick Reisinger > Trick Rod's >Trick R/C

 

[Tom Foley]

Great info here . In my opinion cut the base and use a gasket if you can . Don't be bashful ..cylinders are cheap !! Have fun testing is the main thing .

 

[happybradboating]

At this point I don't have a lathe to cut the base. I figure on most likely using form-a-gasket to seal things up without a gasket. The smallest copper gasket I have is .002, .005 and .010. It seems like using a copper gasket will take me the wrong direction for now. I had thought about sending out some parts to be worked on, but that will be down the road.

I have modded the motor so far with directions from Scott Schneider.

Regards

Brad

 

[happybradboating]

Another question I have is what squish should I try for with a Zen290 upper end? Same as the Zen260?

Brad

 

[Scott Schneider]

Honestly .015 to .020 range has been just fine.

With Zenoahs if you do a minor clean up lathe turning your stock as cast pistons dome for uniformity within the squish area and then attach some 220 wet/dry to piston squish area and lap into the heads squish area making it uniform as well, you can get away with and find power gains running this way tight as @ .010" or so. ( With these cast in head cylinders raising compression pressure is what we want to do, and in a lot of cases too tight a squish attempting to find compression gains without truing up both piston & cast head can do more in killing top rpm power than running greater clearance )

Zenoahs are tough doing this, RCMK's quite easy being there cylinder casting are more accurate and pistons already lathe trued.