Exhaust port height stock vrs 4 mil

[4cyl h2]

I'm doing some basic porting on the engine I'm building an ( rd350) and wanting to know how the exhaust port height Compares to these two different strokes any thoughts? For now I'm planning on setting ex spec at 28 mm from top of ex to deck if I use a 4 mil crank what spec should be used to keep ex duration the same as stock stroke.
Thanks for any input in advance

[MK]

The 350YPVS has 27 mm for the '83-85 models and 26 mm for the later ones.
Haven't got the exact values in mind, but if you use a 2mm base plate and the stock head, you increase the port timing from some 192 - 196 to some insane 206 deg.
That'd be 27 mm height before and after.

The other way round (i.e. no base plate and mill the head contour 2mm, you'll be at 29 mm compared to 27 before. That's what I found to be a much better solution.
Unfortunately I don't have the angles at hand, but that'll make a nice homework for you ...

If you're at calculating anyway, check the transfer port timing. If memory serves me right around 126 deg wasn't too bad for rideability. More was not better, just peakier ....

[4cyl h2]

Thanks for the reply. Makes better sense to me now. Do you even have an estimate of how they compare? I don't have a 4 mill crank to CK degrees with or I would . does it seem like it would be close , 54 stroke 27 mill height same as 58 stroke for 29 mill height as an example?? As this will be a big cc 4 cylinder engine I'm not as worried about low end power I want it to be really strong in powerband I like the idea of a higher exhaust port but I still don't want to kill low end. I have an h2 kaw modified and even at 750 cc the low end is really weak
Also anybody know if there is a 4mill crank commonly available for the ac rd