Staggered port timing

[TIM LUTZ]

Was reading about staggering the port timing today (opening the main transfers first then the secondary’s and the boost port last. Go figure I just finished my porting last night. I went up 1.5mm on the exhaust and 1mm on the transfers (all) and left the boost at stock height.

 

So my question is, If I took my mains up another .5mm would it give me any advantage (then the ports would be staggered) or would it just kill a little more bottom end (or would it make any difference at all)

 

Also was wondering about the back wall of the secondary’s (closest to the boost port)

There seems to be a sharp turn away from the boost port.. Should I widen this back wall and make it a more of a straight shot into the cylinder? It looks like it may be like this for a reason. Maybe to direct the flow clear of the boost port, You guys that port banshee cylinders should know what I’m talking about.

[TIM LUTZ]

This is the secondary port back wall I am talking about.

[Snopczynski]

This is the secondary port back wall I am talking about.

 

There is a little bump in there on the transfers that I leave in. It helps direct the charge to the center of the chamber. Most of the hp to be had in stock cylinders is from unleashing the anemic transfers.

[mopar1rules]

When I get home in a little while, I will run your port heights in my software and see what durations you are at now. I personally like the staggered porting. Right now my main and secondarys open at the same time and my boost next. My shee is 188* exh, and 124* transfers, giving me 32* blow down and the boost I think is now at 118* duration. When I pull my cylinders off again, I'm going to raise my exh port, to give me 190* duration and I'll raise my main transfer only and enough to hold 32* blow down. That area of the secondary transfers that you are talking about, is what's called the "hook". Depending on how sharp the "hook" is, it will depend how the charge is aimed and where it will end up. Rule of thumb is that a sharp hook that aims towards the exhaust port is for top end and ones that are not so sharply hooked are more for bottom-mid.

[mopar1rules]

i ran your numbers tim lutz and here is what i got.....

 

exh 187.44*

main and sec trans 122.3*

boost 110.8*

32.57* blow down

***this is assuming a .4mm deck height***

 

it should run pretty fair/strong for you.

 

if you raise your main transfers up another .5mm, it will change the main transfer duration to 125.03* and blow down to 31.2*....IMO if you go this route, at least raise the boost port to 43.5mm from deck and that will give you 119.52* duration. i have always loved this .5mm staggered port setup.

[Snopczynski]

Tim, what pipes and compression are you gonna run?

[TIM LUTZ]

Thans Mopar1rulas for running the numbers. I think I'll go ahead and rise the mains up another .5mm and the boost just a tad from stock. I just sent my head to Mull for a 93 pump gas cut. I'm running DMC 916 pipes and I sure hope I have the same super wide power band with the new port map and new OKO 30mm.

Thanks all.

Edited August 14, 2010 by TIM LUTZ

[Snopczynski]

Thans Mopar1rulas for running the numbers. I think I'll go ahead and rise the mains up another .5mm and the boost just a tad from stock. I just sent my head to Mull for a 93 pump gas cut. I'm running DMC 916 pipes and I sure hope I have the same super wide power band with the new port map and new OKO 30mm.

Thanks all.

 

Tim can you post those pics so we can see larger ones of your stuff there? What is all that, a jig?

[mopar1rules]

IMO, i think you'll notice a bottom end loss, w/the 30mm carbs, raised exh port, and lower compression, that only requires 93 pump gas. but it will rock from mid-top.

[mopar1rules]

Tim can you post those pics so we can see larger ones of your stuff there? What is all that, a jig?

 

yeah, i would like to see those pics larger. is that some sort of jig, for your 90deg handpiece? pretty cool. looks like you got good lighting in your work area.

[TIM LUTZ]

OK Think I got er down to 50K. Open the ,PDF and use the zoom.

 

Center, bottom center and bottom right, are some ¾” cast acrylic tool I cut on our CAD/CAM router at work. The doughnut with a 320 grit DA disc (center cut out) will give your base gaskets a nice new surface in 15 seconds. The adjustable depth hand piece jig works great for getting all your transfer and exhaust ports exactly the same height. Just have to be careful with the steep angle of the secondary’s and just go in a little with a flame or cone carbide of aprox. the same angle and hand blend the rest.

 

Left center and top are my cylinders sitting on my light table, ¾” clear acrylic recessed in to the work surface (counter top) with a 150 watt metal halide below and egg crate between so I’m not looking directly at the bulb.

 

Top right is a 150 watt fiber optic setup I threw together, Just shove the ends down your transfers and you’ll be porting with sun glasses.

 

Thanks again fot the input.

shop pics.pdf

[TIM LUTZ]

IMO, i think you'll notice a bottom end loss, w/the 30mm carbs, raised exh port, and lower compression, that only requires 93 pump gas. but it will rock from mid-top.

You think I'd be better off with The OKO 28's

Oh, and on that .PDF file there are 2 pages. The first one is blank. Don't know how that happened.

Edited August 16, 2010 by TIM LUTZ

[mopar1rules]

You think I'd be better off with The OKO 28's

Oh, and on that .PDF file there are 2 pages. The first one is blank. Don't know how that happened.

 

depends on what your are doing w/this atv......woods riding, dune riding, etc. can you put up w/a little less bottom end, but way stronger top end, or would you rather keep as much of the bottom end and have a mild mid-top gain? that's up to you. i know when we put tm28 mikuni flatslides on my buds shee this summer, i noticed a bottom end loss. i kinda didn't care for it at first, but when i got used to it, then it wasn't bad.