DIY portmapping HOW?

[dyrberg123]

Thanks for helping out. I will try to read out numbers during the weekend..

[dyrberg123]

What i did find was:

Bore is 61,o3mm so std still
Stroke is 54mm

Ex port opens at 93 ATDC

Transfer opens at 119 ATDC

Intake opens at 113 ABDC

Exhaust port roof is 32mm Down from cylinder top.

[ja-moo]

that's 174 EX duration. 122 on the transfers, 26 degrees blowdown, and 134 on the intake. Should be a torquey motor with with that short of blowdown.

[dyrberg123]

that's 174 EX duration. 122 on the transfers, 26 degrees blowdown, and 134 on the intake. Should be a torquey motor with with that short of blowdown.

It is fully standard, and torquey. Have you got any idears?

[ja-moo]

I personally would go to 90 on the exhaust, and widen to 68% cordle with a 75mm radius on top, 24mm corner radius, clean up the intake and transfers, match the liners in the windows, and cut 2mm off the rear piston shirt. And probably remove .040" from the heads.

I'm sure TZ will pipe in with his recommendations also.

[dyrberg123]

I personally would go to 90 on the exhaust, and widen to 68% cordle with a 75mm radius on top, 24mm corner radius, clean up the intake and transfers, match the liners in the windows, and cut 2mm off the rear piston shirt. And probably remove .040" from the heads.

I'm sure TZ will pipe in with his recommendations also.

Thanks, 68% cordle Means what sorry?

Form exhaust port roof to radius 75mm, and the corners to radius 24mm, and top of radius 75mm = top of roof to open at 90 deg right?

The head milling is done to get from 1mm squish to 0,9 mm squish right? I will be using the squish heads shown of Photos previous in the thread.

BTW ex port are 36mm wide, intake 22 mm wide, 18mm high. Ex port also have two auxsillary borts attached.

Thanks Ja-moo

[Vintageman]

Wow, The intake height is narrow at 18mm and intake duration low at 134 degrees. Bell's book lowest suggestion for 7000 rpm is 150 - 155.

Here is GT250 (74) I measured
Each intake port window of a 74 gt250 is 18.5mm wide by 19.5 high.

T20 (From Suz book)
Width total 36mm - 3mm bridge (so each is 16.5mm) by 21.5mm high
Exhaust is 33.0 mm from top 33mm wide
Piston skirt from pin center to bottom of piston = 36mm

T305 from Suz book ( if I recall same as T350)
Intake width 44mm - 3mm bridge = 20.5mm by 18.4 mm height
Exhaust is 33.3 mm from top 36mm wide
Piston skirt from pin center to bottom of piston = 38mm

Note all are 54 mm stroke. Same rod length.

Not the T20 effective intake port is lower than T305 by 4mm

Know this data is why I took 2mm off skirt on my T305 made difference for me in power feel and higher RPM I can reach.

I only went 1/16" (1.6mm) on my T350 which I have not tried yet. Wish I now went 2mm now knowing intake duration you guys posted here (engine rebuilt setting on my shelf. Still time... maybe take 1mm off exhaust and head to match)

For exhaust example see Yamaha R5 - RD350 32mm - 29.5mm same stroke Not sure about rod dimension etc.

Note the 76/77 GT250 went form 32mm to 29.5mm on Ex

http://erlenbachracing.net/portmaps.htm" onclick="window.open(this.href);return false;

[dyrberg123]

SORRY GUYS, intake hight is 19mm, hit the wrong button. Why is 8 so close to 9 at the keyboard

Transfers are 29mm wide and 11mm high. Center side of cylinder transfer seems just ,5 mm wider than outside side transfer.

Auxilary exhaust ports are only 6,5mm wide. All meassures taken across the ports.

And JA-MOO
68% cordle Means what sorry?

Form exhaust port roof to radius 75mm, and the corners to radius 24mm, and top of radius 75mm = top of roof to open at 90 deg right?

The head milling is done to get from 1mm squish to 0,9 mm squish right? I will be using the squish heads shown of Photos previous in the thread.

Thanks

[ja-moo]

I personally would go to 90 on the exhaust, and widen to 68% cordle with a 75mm radius on top, 24mm corner radius, clean up the intake and transfers, match the liners in the windows, and cut 2mm off the rear piston shirt. And probably remove .040" from the heads.

I'm sure TZ will pipe in with his recommendations also.

Thanks, 68% cordle Means what sorry?

Cordle is the measurement straight across the port, (68% cordle of 61mm is 41.5mm) not taking in the curvature. A 68% cordle measured "flat" on a 61mm bore is 45mm

Form exhaust port roof to radius 75mm, and the corners to radius 24mm, and top of radius 75mm = top of roof to open at 90 deg right?


Remember, radius, so its a 150mm circle. And the corner radius is really 12mm or a 24mm circle. And yes the top of the radius is where the port opens.

The head milling is done to get from 1mm squish to 0,9 mm squish right? I will be using the squish heads shown of Photos previous in the thread.

Actually you really don't want the squish closer than 1mm. Heads are rather complicated. I'm just trying to get you some compression back from the raised exhaust.

BTW ex port are 36mm wide, intake 22 mm wide, 18mm high. Ex port also have two auxsillary borts attached.

Thanks Ja-moo

[Vintageman]

promise won't hijack just curious about this too. Couple question to clarify what others said

I personally would go to 90 on the exhaust,

What does 90 on exhaust mean?

I "prefer" lowering the port, but that is usually with bigger carbs.

Sounds like intake window area is less than the stock carb which is a 32mm Dia (relatively large for 157.5cc).
So agree 2mm off intake should be better than off piston, but you will feel it off piston too, just not as well.

Exhaust port roof is 32mm Down from cylinder top.

If stock that would be 1.3mm higher than T305 Data.
I'll add transfer port data for T305 to see how it matches your T350
Hairypickles (eBay seller) did say on the post "The ports are unchaged, but the intake and exhaust ports have been smoothed out." However, 32mm does seam to be what was also used on later 54 mm stroke engines from Suz until 76/77 Gt250 went 29.5mm.

Did you get the deck height for the T350 when piston TDC? Given all this data we can put into port timing softwar eand see how well it agrees with you findings.

I have all pistons (T305, T350, early and late GT250) and may take pin to skirt and pin to piston top edge measurements.
if different that could change timings between engines I am curious about.

Good luck

[tz375]

Daniel what size are the carbs on that bike and are you keeping the stock carbs or going larger?

[ja-moo]

promise won't hijack just curious about this too. Couple question to clarify what others said

I personally would go to 90 on the exhaust,

What does 90 on exhaust mean?

90 degrees ATDC

I "prefer" lowering the port, but that is usually with bigger carbs.

Sounds like intake window area is less than the stock carb which is a 32mm Dia (relatively large for 157.5cc).
So agree 2mm off intake should be better than off piston, but you will feel it off piston too, just not as well.

Rule of thumb, intake port window around 15-20% larger than the carb. Since I'm going "off the cuff" (being a Kawi guy) one has to figure their own window area.

[dyrberg123]

Daniel what size are the carbs on that bike and are you keeping the stock carbs or going larger?

Carbs are 28mm Keihin PWK.

Thanks for all your feedback Guys. I am gratefull.

Ja-moo - i get it now

[tz375]

Oops, I forgot that you mentioned that earlier. Thanks

[dyrberg123]

What preassure should i aim fore afterwards? PSI?