port timings

[tea5ive]

got a sr190 cast/ally type cylinder and would like to do a bit of home tuning on it. here are the current timings as best as I can measure them and this is with a 60/107 crank with crown level with cylinder top

exhaust 161.5 deg and 42mm wide.

inlet 136.96 deg and 35.48 wide.

transfers 130.91

piston 76mm to top of dome and 69mm to crown , 39.50mm from pin centre to crown

will be using pacemaker gear box with 15/46 or what ever the tuning will allow and an ancillotti 42mm exhaust and a phbh 28 or 30 mm

can some one recommend some port timings to aim for, pm me if you don't want your tuning wisdom shared but would like to have a go myself. cheers simon

[Muppet]

175-180ex
125trans
150inlet

[camel]

Your going to need at least a 17 front sprocket with that box to stop it revving its nuts off in 4th

[tea5ive]

Your going to need at least a 17 front sprocket with that box to stop it revving its nuts off in 4th

I have 15,16,17, and a 19 front sprocket or I could swap the gearbox to li 150 or sx200/tv175 . would like to try the pacemaker gearbox though.

[camel]

Great box.I use one on a reed 200 17x46=5.0 ratio

[tea5ive]

[quote="Muppet"]175-180ex
125trans
150inlet[/quote

to get these I will need to raise the cylinder 3mm (presuming crown was level with cylinder top, have not built motor yet but have all parts to do so)

raise exhaust by 0.50mm

cut 6.50mm off inlet side of piston skirt or lower the inlet port or a bit off each. seems a lot I will re check my measuring and run the figures through the timing calculator again. measure 5 times cut once


piston weighs a lot, just compared it to a deanspeed and that seems as bad and looks worse that the piston that was supplied with the cylinder.

cheers simon

[tea5ive]

Great box.I use one on a reed 200 17x46=5.0 ratio

have an under kickstart fresco and a mbd rev-tour but would like to stick to the ancillotti, don't want to spoil the looks of my box standard li125s

cheers for the advice. simon


screen shot

[Special X]

I'd be a bit more conservative at
Exhaust 170
Transfer 125
Inlet 145

With the box pipe anything over 170/172 exhaust will kill too much bottom end and the pipe won't rev high enough to take advantage of the top end potential. At 150 inlet it'll work well but with lots of spitback 145 is a good compromise.

Just my take on it Muppets timings would give good power just beyyer suited to an expansion exhaust.

[Adam_Winstone]

You certainly don't want to go raising the cylinder as it would further extend your transfer timing, which appears to be long already (if you intend to go anywhere the inlet and exhaust durations being suggested). The fairly common 150/125/170 (all 'ish) isn't a bad range to aim at but you will need to lower your transfers as a starting point... machining the cylinder base will extend inlet timing, fitting a longer rod and thicker head gasket (or machining a step into the head) will address this but either introduces complications and cost.

If you change the conrod to give you more tuning options then you've got the cost issue and need to allow for the extra length at top or bottom of cylinder, otherwise you'll hit the head.

You need to slow down and consider options before doing anything. Seeing whether you can get a transfer timing that benefits you is the key question, then deciding if this is the right cylinder to start with. If you don't want to fit a different crank/rod or have the cylinder machined then you'll be stuck with the transfer timing that you already have, then you need to consider how best to tune the exhaust and inlet ports to suit... or just to live with the transfer timing and make the best of the exhaust/inlet ports, which are easy to extend with a little grinding.

If you look at the sort of revs that work best with 130degrees of transfer timing then this would be a pretty revvy motor!

Adam

PS - Thankfully, you asked this question on a decent tuning site so you'll get others along to help with more detail

[tea5ive]

engine stripped cleaned and top end dry built for cylinder measuring.

here are the results

piston crown is level with top of cylinder with no base gasket , so allowing for a 1mm base gasket here are my new timings

ex 165.53. raise by 1.15 mm will get me 170.09

trans 132.81 (after re measure)

inlet 133.24. clean a little off bottom of inlet and take 3mm off piston, inlet side gets me 145.46.


this seems better but as adam says the transfers may still be a little to high . what about the width of the ports ? cheers again. simon