Port Timing & Duration Specifications

[1550]

Thanks for explaining. Im not expert, so that why i ask stupid questions

 

[#ZERO]

I am going to start a similar motor project. What one of the 4 port timings you listed did you end up using?

I'm using a 62T/61X 828cc engine with a 5mm stroker and the Northwest big bore sleeves with 85mm Riva flat top pistons. The pistons are flush with the deck surface and the 29cc flat top domes had to be machined with a .048" squish gap on a 1.5° radius. The cases have been heavily ported and Devcon epoxy ramps were built on top of the fingers in the reed cage area. Also case was cut a few degrees on the intake manifold side pointing the reeds more toward the transfer ports. I'm using 46mm Mikuni carbs with the stock 760 manifold with the crossover filled and stock reeds. The cylinder had to be port matched then both sleeves were removed to make the tracks wider from top to bottom on the transfer and boost ports. On the exhaust side I'm using a limited pipe with the manifold and head pipe opened up to 50mm with stinger tip size reduced and shielded from the water inlet. It will be using the stock waterbox with a custom made dual front exhaust and hopefully it won't be too loud with 190lbs compression.

Here's the port timing specifications for this engine.

87.3° Exhaust Port Opens
118.4° Main Transfer Ports Open
118.7° Auxiliary Transfer Ports Open
121.6° Boost Port Opens
185.6° Exhaust Duration
123.2° Main Transfer Duration
122.6° Auxiliary Transfer Duration
116.8° Boost Port Duration
31.1° Blowdown Time

What are good duration specs for freestyle?

Yes, I know and think also that it is Racing Superstock cylinder, and that exhaust port is like 71% of piston diameter.

That's a tough question and depends on a lot of different variables and has a lot to do with what type of setup you're running and the type of engine you're going to build with an overall package. The stock 61x cylinders run at 118° transfer duration with a 179° exhaust duration and has a blowdown time of 30.5°. It was primarily designed for good emissions and a smooth pull throughout the entire rpm range. If you're going to build a bigger engine, you can get away with raising the duration slightly to improve mid-range performance without sacrificing the bottom end too much. Increasing the blowdown time makes the emissions worse, however, it improves the performance in the mid range and top end, but the engine will sputter and pop in the lower rpm range if not set properly. This is because the blowdown time area must allow the cylinder pressure to drop below the pressure of the fuel air mixture when the transfer ports open. If the blowdown pressure is too high when transfer ports open, it will stall or reverse the incoming charge of fuel and air. Usually as a rule of thumb, the exhaust port shouldn't be more than 66% of the bore width for freestyle/freeride use, with 68% to 70% for racing only. The higher duration numbers on the exhaust side will effect your compression while giving more top-end performance. Also there's a thing called the port time area, which is the amount of time and area required for a port to flow the necessary air at a specific rpm. The higher an engine rpm and/or pressure, the more time area required. The porting of the cylinder casting can also effect how the engine is going to perform. For instance, if you change the roof angles and shape of the transfers, it can drastically effect how the port operates. A transfer port roof that's aimed upward will work better in the lower rpm range while the curved roof angle will give better top end & mid range performance. Any engine components that you choose to bolt on; such as reeds, carbs, intake, exhaust, ignition, etc., will effect how each port operates and may or may not improve the overall performance. So when you ask me "what's a good duration spec for freestyle", I'll have to say it depends on your complete setup and what components you're using to make it all work.

 

[deanz]

stinger mod

gee thanks #.0 for all your informative posts, they are very much appreciated.

is this what your stinger looks like, and if so what is the idea behind that mod ?

Dean.

 

[#ZERO]

That's Chuck's idea from X-Scream and I believe he charges around 100 bucks for that modification.

He saws the end of the stinger pipe off then welds a specific size pipe matched to the engine combo.

The shield around the outside is the same size as the waterbox hose and deflects the water inlet from going directly into the stinger tip.

 

[robertg]

Increasing the blowdown time makes the emissions worse, however, it improves the performance in the mid range and top end, but the engine will sputter and pop in the lower rpm range if not set properly. This is because the blowdown time area must allow the cylinder pressure to drop below the pressure of the fuel air mixture when the transfer ports open. If the blowdown pressure is too high when transfer ports open, it will stall or reverse the incoming charge of fuel and air.

For the couple of hours that my Vilder ignition was working I would get the sputtering and popping on the low end. I cant remember the exact curve but the max advance was around 28 deg. When it crapped out on me I switched to an enhancer and the popping stopped.

It seemed to have better power with the timing advanced but the sputtering is annoying.

 

[geraban19]

So, a ported race cyl (8 port/Lamey/std stroke) w/ 80 degree exh ports and 115 degree transfers ports will never produce a good low end power... right?

 

[jetski9010]

I'm using a 62T/61X 828cc engine with a 5mm stroker and the Northwest big bore sleeves with 85mm Riva flat top pistons. The pistons are flush with the deck surface and the 29cc flat top domes had to be machined with a .048" squish gap on a 1.5° radius. The cases have been heavily ported and Devcon epoxy ramps were built on top of the fingers in the reed cage area. Also case was cut a few degrees on the intake manifold side pointing the reeds more toward the transfer ports. I'm using 46mm Mikuni carbs with the stock 760 manifold with the crossover filled and stock reeds. The cylinder had to be port matched then both sleeves were removed to make the tracks wider from top to bottom on the transfer and boost ports. On the exhaust side I'm using a limited pipe with the manifold and head pipe opened up to 50mm with stinger tip size reduced and shielded from the water inlet. It will be using the stock waterbox with a custom made dual front exhaust and hopefully it won't be too loud with 190lbs compression.

Here's the port timing specifications for this engine.

87.3° Exhaust Port Opens
118.4° Main Transfer Ports Open
118.7° Auxiliary Transfer Ports Open
121.6° Boost Port Opens
185.6° Exhaust Duration
123.2° Main Transfer Duration
122.6° Auxiliary Transfer Duration
116.8° Boost Port Duration
31.1° Blowdown Time



That's a tough question and depends on a lot of different variables and has a lot to do with what type of setup you're running and the type of engine you're going to build with an overall package. The stock 61x cylinders run at 118° transfer duration with a 179° exhaust duration and has a blowdown time of 30.5°. It was primarily designed for good emissions and a smooth pull throughout the entire rpm range. If you're going to build a bigger engine, you can get away with raising the duration slightly to improve mid-range performance without sacrificing the bottom end too much. Increasing the blowdown time makes the emissions worse, however, it improves the performance in the mid range and top end, but the engine will sputter and pop in the lower rpm range if not set properly. This is because the blowdown time area must allow the cylinder pressure to drop below the pressure of the fuel air mixture when the transfer ports open. If the blowdown pressure is too high when transfer ports open, it will stall or reverse the incoming charge of fuel and air. Usually as a rule of thumb, the exhaust port shouldn't be more than 66% of the bore width for freestyle/freeride use, with 68% to 70% for racing only. The higher duration numbers on the exhaust side will effect your compression while giving more top-end performance. Also there's a thing called the port time area, which is the amount of time and area required for a port to flow the necessary air at a specific rpm. The higher an engine rpm and/or pressure, the more time area required. The porting of the cylinder casting can also effect how the engine is going to perform. For instance, if you change the roof angles and shape of the transfers, it can drastically effect how the port operates. A flatter roof angle will give better low-end performance, while the steeper angle will work better in the higher rpm range. Any engine components that you choose to bolt on; such as reeds, carbs, intake, exhaust, ignition, etc., will effect how each port operates and may or may not improve the overall performance. So when you ask me "what's a good duration spec for freestyle", I'll have to say it depends on your complete setup and what components you're using to make it all work.

I know this is a older post but I was wondering about the squish angle radius. Is this somthing that can be changed or does it have to be the same angle as your pistons? I see the ADA flat top domes comes with 4 degree angles and non flat top domes are 12.5 degrees. You had cut yours at 1.5 degrees is that because of the pistons you used or just a way that you set it up?

 

[SUPERTUNE]

+ 1.5 degrees over your piston angle, is suitable for all o-ringed heads.

 

[#ZERO]

I know this is a older post but I was wondering about the squish angle radius. Is this somthing that can be changed or does it have to be the same angle as your pistons? I see the ADA flat top domes comes with 4 degree angles and non flat top domes are 12.5 degrees. You had cut yours at 1.5 degrees is that because of the pistons you used or just a way that you set it up?

What Chuck said is just about perfect for the squish angle over the piston angle.

The ADA Yamaha domes use a 10.5-degree squish angle that's .015" deep with an 83mm diameter for the 701 domes & 86mm in diameter for the 760 domes for use with the 9-degree oem style pistons.

The ADA Yamaha flat top domes use a 4-degree angle with an 86mm diameter for use with the R&D or Kawasaki or Japanese flat top pistons which have a 2-degree angle on top.

The Riva Yamaha flat top domes use 1.75-degree angle with an 85.5mm diameter for use with their Riva flat top pistons which have a 0-degree angle and are completely flat on top.

This piston to dome squish angle can be altered slightly to increase or decrease the velocity time depending on a lot of other factors and the overall setup; this is why a lot of engine builders choose to cut their own or modify existing domes.

 

[masterblaster]

what does altering the velocity time with the angle make the motor do diff in performance?

 

[jetski9010]

I was wondering the same thing but I am affarid we are getting into engine builders secrets.

 

[#ZERO]

The tapered angle on the squish band is there to help the squish action; it forces the charge to where the spark plug is located and is generally one or two degrees more than the angle of the piston. A narrow squish band ratio allows for more of the total intake charge to be located in the combustion dome resulting in more power potential during spark ignition near TDC. The down side is that there is more piston/dome area that is exposed to combustion on a highly loaded engine and heat build-up can become an issue that could eventually lead to detonation. As RPM increases, there is less time for combustion and a shallow dome designs will take less time to scavenge and refill vs. a head with a deep dome. Most pump gas engines tend to like a wide squish band width and smaller diameter domes with more volume. Race gas engines like narrow squish band widths and larger diameter domes with less volume. The squish band area or ratio can vary with each engine and usually is between 30 - 60 percent of the bore size and the larger squish ratios require greater squish clearances to get equal velocities. There are many factors that come into play to get the correct maximum squish velocity or (MSV), such as; RPM, squish clearance, squish ratio, rod ratio, compression ratio, port timing, blending radius, diverging squish angles, fuel type, etc. and it can get quite complicated. You'll need a computer program such as the Bimotion advance head design software to calculate all the factors. This squish program enables you to calculate the MSV of turbulence in the combustion chamber. This is an important design tool for finely targeting the hit in the power band and to determine a link between power band and fuel. The squish ratio, dome shape, compression, MSV, etc., all work synergistically while at the same time are all a compromise. There's a fairly delicate balance that needs to be maintained and small changes are better than larger ones. Increased MSV will help speed along the flame front and complete the combustion process more efficiently, but fuel choice will limit MSV. There is a point where the friction from the squish action can be so great and happen so fast that it generates enough force/heat to ignite the charge. Some basic MSV numbers that have been around for some time range from 15 - 30 meters per second. This is divided into two groups, high MSV and low MSV. Lower MSV numbers, around 15 - 19 m/s, generally make power from peak torque to max RPM or mid-top power. Higher MSV numbers from 20 - 30 m/s generally make power up to peak torque and then start to go flat. Also MSV numbers that are too high will kill off over-rev and lead to detonation.

Here are a few things that can either raise or lower the MSV.

Factors that raise the MSV:
Lower Compression Ratio
Less Squish Clearance
Larger Squish Area Ratio
Higher RPM
Smaller Bore
Longer Stroke
Shorter Rod


Factors that lower the MSV:
Higher Compression Ratio
Greater Squish Clearance
Smaller Squish Area Ratio
Lower RPM
Larger Bore
Shorter Stroke
Longer Rod

Here's the Bimotion head software: http://www.bimotion.se/

Free squish velocity program: http://www.torqsoft.net/squish-velocity.html

 

[CARBONX2]

A correction to your post #42: flatter port roofs are better for TOP-end and angled are better for BOTTOM-end

 

[#ZERO]

That's true I was thinking flat pointing upward and not flat across. A transfer port roof that's aimed upward will work better in the lower rpm range while the curved roof angle will give better top end & mid range performance. http://www.macdizzy.com/cylinder_map6.htm

 

[the_natrix]

Hi

Can anyone tell me the specific differences in the sleeves and port timing between the 62t 760, and the 65u 1200 motors? every time i search for sleeves they are listed as different part numbers, which leads me to beleive that they have different timing/duration values.

thanks

 

[loictahiti]

Hi #ZERO thanks for this tread , and I subscribed , :biggthumpup: now, i 'm reading it all day :Banane09:

so, i'm start to build a stroker engine with +6 (stock rod lenght) crancase 62T , 62T cylinder and 85 flat top kaw piston, blowsion head with cut dome .the piston are no flush with top of cylinder , they are under with 0,6 mm

with this engine my port timing are very race oriented

36,94 mm Exhaust hight
55,40 mm Main Transfer hight
55,50 mm Auxiliary Transfer hight
54,50 mm Boost Port hight
197,02° Exhaust Duration
136,98° Main Transfer Duration
136,98° Auxiliary Transfer Duration
30,02° Blowdown Time

if I cut the cylinder base with 3,1 mm my port timing are

40,04 mm Exhaust hight
58,5 mm Main Transfer hight
57,5 mm Boost Port hight
187,86° Exhaust Duration
124,88° Main Transfer Duration
31,49° Blowdown Time

in same time the head dome will be machined to match perfecly with piston with a good squish.

what you think about that ? it will be more oriented in freestyle/freeride setting ?

or I waste my time and labor money ? :laugh2:

sorry about my bad english and not using inches size

thanks LOIC

 

[waxhead]

Are you going to run your piston 3mm positive deck, thats a lot.

 

[loictahiti]

not realy because I have a 0,6mm negative deck, so , it will be going +2,5 mm

 

[waxhead]

That port timing will work okay on a free ride boat.

 

[egbrig]

I see that most here always talk about bottom end, mid to top, and top end power rpm ranges. I'm currious as to what rpm everyone here equates these ranges to and if the ranges are tach derived or just feel. I'm just curious. WAX, ZERO this isn't for you to answer just yet.