Port Timings

[Nickk]

:?: Hello there.

I will get to the point, i am trying to build and engine of the glowplug type but trying to get some accurate information on port timings is near impossible. i understand the basic principles and i am using rotary valve/crank intake admission but all the information i have managed to get so far has been muddled at the best. my calcs give some very strange answers ( i.e, inlet and exhaust practically on the same line !! )

Engine : 12mm Bore , 12 mm Stroke

Admission timing ?? ( Crank inlet) so far 55 deg BTDC, and 55deg AFDC

Inlet : Height and area ??

Exhaust : height and Area ??

This might be the wrong forum to ask but the general web site was most helpful (nice pics ! ) any information would be good

[jydracing]

Hi nickk first off what are you going to use the engine for? i can give you numbers for an marine engine. But depending on the nitro content and what the use of the engine is for will govern the timming numbers. on my outboards i run the numbers as followes

Exaust........195 deg
inteak or crank....open at 65 deg with 215 dig duration
boost and transfers .......121 deg
compression ratio at 10.5 to 1
head clearance at .003
nitro content of 69 % with 12 percent syn oil

I have been racing these numbers for 20 years now with execlent results

[oldlugs]

Hi nickk first off what are you going to use the engine for? i can give you numbers for an marine engine. But depending on the nitro content and what the use of the engine is for will govern the timming numbers. on my outboards i run the numbers as followes

Exaust........195 deg
inteak or crank....open at 65 deg with 215 dig duration
boost and transfers .......121 deg
compression ratio at 10.5 to 1
head clearance at .003
nitro content of 69 % with 12 percent syn oil

I have been racing these numbers for 20 years now with execlent results

Interesting... I'm curious; also run the 3.5s? What timings do you like on them, and what other mods do you make (skirting, piston ports, "turbo" groove in crank, etc.)? I've got a few K&B 3.5s (some drum rotor intake, and some VERY old 12mm crank engines...), and want to make 'em go real fast before they go KaBoom ;) Aside from using Aeromarine or RPM rods, what helps 'em to stay together? The round beam rods in my drum rotor motors seem somewhat weak, getting bent on hydrolock, or coughing the big end bush.. I don't know how exaggerated the rpm/hp #s are on the competition (around 3 hp/40K for some), but the K&B 3.5 seems enemic and fragile in comparison. I sure wish MECOA/K&B would come out with a modern engine line for boat racing..

[jydracing]

I can build the 3.5 to run as fast as the rest but the block will split at the casting joint on the bottom with in 2 or 3 laps. if you can get the rpm or aeromarine rod that is better than the round rod for higher rpms. you can also strap the block. if you are running it in an inbord use an octura motor mount it is a craddle under the block not just supporting it on the mounting lugs.

as far as mods all the same except .008 to .010 head clearance and exaust timming at 192 degres skirt the piston, turbo the crank. sharpen the closing side of the timming disc or crankshaft, rebalance the engine. i know that you can not take all of the vibratings out of a single cyl engine but you can move where it viborates. it is better to viborate at idle than at wide open throttle, use the red or purple carb or one with an .340 bore and a good tuned pipe. Also make sure that the crank and pto turnes as free as possable