Calculating Blowdown, Did I do it right?

So I decided to figure out what my port timing is and I am not sure I did it right.

I made a port map and used the measurements and the table in the port timing wiki page to get my numbers.

Blowdown= (Transfers - Exhaust)/2

B= (114.3-169.8)/2

B= -27.75

I wasn't expecting a negative number, what am I doing wrong?

Also will someone look at my squish and tell me if this is too big it seems too big:

Also my exhaust doesn't close all the way. This is at BDC:

Re: Calculating Blowdown, Did I do it right?

Also if someone could tell me if this timing is appropriate for my setup,

19mm Phbg carb (mixture screw 2.5 turns out, #40 slide, W7 needle @ top clip, 42 idle, 82 main jet)

70cc Hi Hi comp head (modded for less compression)

70cc Kstar Piston port (exhaust port raised 1mm)

Estoril Pipe (De-restricted)

Treatland CDI (timing 19mm BTDC)

Treatland 3-Shoe Clutch (blue springs, engage at 15lbs)

Treats Kstar aluminum stuff crank.

it would be appreciated.

Re: Calculating Blowdown, Did I do it right?

Charles Cole (OFMC) /

I'm pretty sure it can be done mathematically, however, I think it's much easier & far more accurate if you use a degree wheel. I can't remember how much I paid, on ebay, but I think it was a bargain to have such a handy tool that's spot on. A trick a euro tuner taught me is to attach it to the crank with a large washer behind the wheel using magnets. Worked for me.

Re: Calculating Blowdown, Did I do it right?

Absolutely way easier to use a degree wheel...

Degree wheel - cheesy n cheap -

http://mabecanemobylette.freeforums.org/viewtopic.php?f=24&t=930

or find another picture of one on the interweb, just print it and glue it to a old CD or DVD.

Re: Calculating Blowdown, Did I do it right?

Is this right?

BlowDown - Measured in degrees of crankshaft rotation from Exhaust Port opening to the Transfer Ports opening.

BlowDown TA - Must allow the cylinder pressure to drop below the pressure of the fuel air mixture at time of transfer ports opening. If the Blowdown pressure is to high when transfer ports open, it will stall or reverse, the incoming charge of fuel and air.

Re: Calculating Blowdown, Did I do it right?

reversing T and E in the formula gives useable numbers.

(169.8 - 114.3)/2 = 27.75

degrees of crnk rotation between exhaust opening and transfer opening.

squish looks huge, 1.2mm s max recommended, measure it.

"fixing" the squish and the exhaust / piston issue requires machining the deck height and shimming the base.

major redesign.

i don't like cutting pistons, changes swirl, if nothing else.

Re: Calculating Blowdown, Did I do it right?

Rebel said,

Absolutely way easier to use a degree wheel...

Degree wheel - cheesy n cheap -

http://mabecanemobylette.freeforums.org/viewtopic.php?f=24&t=930

or find another picture of one on the interweb, just print it and glue it to a old CD or DVD.

I did that too but I figured I wanted more accurate numbers so do both and I could really see the small notched on the degree wheel. My port map is acurate though, paid attention to detail.

Why would KStar make a kit with such a big squish, or is it my crank?

Re: Calculating Blowdown, Did I do it right?

Overpriced Parts /

Ya the kstars of late are cast as that

It's not your crank

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