Triton # 1 (T1) : Liquid Cooled Conversion & Updates

[2strokd]

Mar 22, 2010 11:25:21 GMT -5 190mech said:

That 90 crate motor is looking better all the time!

Sure is! I was telling the wife about that one.
Told her if i ever go over 70 some cc,s the best way to start
is with the 90cc crate Minarelli. Best bang for buck mod in the
US!

[90GTVert]

I took notes from 190mech and used a big degree wheel instead of a little one this time. I do like it better this way. It should be more accurate with a larger diameter, but with me behind the wheel... who knows.



Using a base gasket, the thick aluminum spacer, a .3mm aluminum spacer, and another base gasket the piston's edge is still about 0.1mm above deck at TDC. I'd probably still need to add another .3mm gasket plus a head gasket to get a somewhat acceptable squish clearance.



I used a flashlight shining through the exhaust port or into the reed opening to help me determine port opening and closing times.



47.6mm Airsal T6, 45mm crank, 2 base gaskets, 5.3mm spacers

Exhaust Port Begins To Open : 85° ATDC
Boost And Transfer Ports Begin To Open : 107° ATDC
All Ports Fully Open : 140° ATDC
All Ports Begin to Close : 140° BTDC
Boost And Transfer Ports Close : 107° BTDC
Exhaust Port Closes : 85° BTDC

Exhaust Duration : 190°
Boost And Transfer Duration : 146°

Transfer numbers looked a bit steep to me, so I thought I'd try out the Polini Sport using the same spacer and gasket setup. Deck height is about the same.





46mm Polini Contesta/Sport, 45mm crank, 2 base gaskets, 5.3mm spacers

Exhaust Port Begins To Open : 88° ATDC
Boost And Transfer Ports Begin To Open : 111° ATDC
Exhaust And Transfer Ports Fully Open : 146° ATDC
Boost Port Fully Open : 161° ATDC
Boost Port Begins To Close : 161° BTDC
Exhaust And Transfer Ports Begin to Close : 146° BTDC
Boost And Transfer Ports Close : 111° BTDC
Exhaust Port Closes : 88° BTDC

Exhaust Duration : 184°
Boost And Transfer Duration : 138°

The transfer durations look a bit wide to me, but I'll look up what Bell's book says to be sure. I'm thinking the Polini kit may be close enough to work alright, maybe even open the exhaust up a tad. Not sure.

[90GTVert]

Bell's notes on transfer port duration and RPM :

RPM----Transfer Duration
6500-------120-124
8000-------124-128
9000-------126-130
10000-----128-132
11000-----130-134
12000-----132-136
13000-----134-140
14000-----136-142

Based on those numbers, the Polini Sport is ready for 13,000-14,000RPM and I guess the Airsal should be for 15,000-16,000RPM.

[90GTVert]

Some note's from Bell on exhaust duration :

Engine size (cc)---Application---Engine speed (rpm)---Exhaust duration (°)
1x80--------------Moto X---------11000------------------196-198
1x80--------------Moto X---------12000------------------202-204
1x80--------------Road race------13000------------------205-207
1x100-------------Moto X---------11200------------------198-200
1x100-------------Go-kart--------10800------------------176-178
1x125-------------Moto X---------10000------------------190-192
1x125-------------Moto X---------11000------------------196-198
1x125-------------Road race------12000------------------202-204
1x125-------------Road race------12500------------------203-205

So the Polini's exhaust should be best suited for 9,000-10,000 RPM I guess, and the Airsal should be setup for around 10,000-11,000 RPM. Both severely mismatched with the transfer durations.

[90GTVert]

What do you guys think? Should I try to set the Polini up with the proper gasket and squish and then see if I could get it to somewhere around 190 degrees exhaust duration with a little port work and hopefully very close to the same transfer numbers.... or do you think I should forget the whole close-to-square bore/stroke idea and just go 100+cc with a cylinder meant for a longer stroke?

[90GTVert]

I went back out and added 0.5mm worth of spacers to the base of the Polini kit. That put the piston about 0.4mm below deck...



...which gave me 0.76mm of squish clearance.



I took new measurements to see what changed.

46mm Polini Contesta/Sport, 45mm crank, 2 base gaskets, 5.8mm spacers

Exhaust Port Begins To Open : 87° ATDC
Boost And Transfer Ports Begin To Open : 110° ATDC
Exhaust And Transfer Ports Fully Open : 146° ATDC
Boost Port Fully Open : 160° ATDC
Boost Port Begins To Close : 160° BTDC
Exhaust And Transfer Ports Begin to Close : 146° BTDC
Boost And Transfer Ports Close : 110° BTDC
Exhaust Port Closes : 87° BTDC

Exhaust Duration : 186°
Boost And Transfer Duration : 140°

I'd probably still need to add a head gasket to make it run alright on pump gas if I went with that setup. Maybe 2 head gaskets and drop back to 138° of transfer duration. I dunno quite what to think. 190+ exhaust and 138 transfer might make something nasty... but it doesn't sound that street friendly.

[190mech]

138 still is a bit high on the transfers,how much of the piston will
be 'showing' if you pull some shims to get 130-132?We could
trench the head,then raise the exhaust port to get around 192.
Remember piston speed is a factor on a stroked motor,they
always have a lower rev limit with increased stroke...

[90GTVert]

Yeah, trust me I wasn't planning on actually trying to rev to the numbers those transfer durations indicate. I'll see if I can figure out just what it would take to drop down to 130-132 or so. By "trench" the head, do you mean recess the whole combustion chamber? That doesn't sound like trenching, but I'm not seeing another way to raise the roof so to speak. That sounds like a lot of work. I'd be better off to try a different head at that rate. I think I have another around. The Airsal's is out, that bad boy looks like it's meant for some serious compression with close squish.

[90GTVert]

I tried just removing the thin spacers :

Deck : +0.7mm

Exhaust Duration : 182°
Transfer Duration : 134°

With the 5mm spacer and only 1 base gasket :

Deck : +1.1mm

Exhaust Duration : 180°
Transfer Duration : 130°

Looks like that's where I'd need to be, transfer-wise. I'd have to shave the base gasket thickness off of the spacer so I could use a gasket on each side or use a sealant.



Here are the heads I have. Left to right : Polini, MRP, Airsal



The MRP head has a 0.6mm lip to get the head up just a little. It would still take 0.5mm just to get 0 squish clearance. It'd be nice to have the big squish band of the Polini for a street motor though.

On another note, I had planned on using my 19mm Arreche carb. Not so sure that's a great choice here. Looks like this engine will breathe a little heavier than I anticipated. I found a 25mm DellOrto cheap on eBay just like the one on T2, but it's missing parts.

[190mech]

I like the last try,see how much meat will have to be removed
from the top of the exhaust port by using the degree wheel,
then scribing the cylinder using the piston top as a straight edge.
Keep the exhaust oval,but it looks like it could be a bit wider..

[90GTVert]

I was thinking of going just a bit wider on the exhaust port. I believe it's something like 70% of the bore diameter is the max safe width. That would mean I could go as far as 32.2mm. It's 30mm now.

[190mech]

We're getting some where now!!!
Here is a dirt cheap 42mm stroke crank for everyone hunting a
deal;
cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=250556000253&viewitem=&sspagename=STRK%3AMEWAX%3AIT

[90GTVert]

Holy crap. That is a heck of a deal. Nice find.

[90GTVert]

I set my degree wheel to the position that will give me 192 degrees of exhaust duration. 180 - 84 = 96, 96 + 96 = 192.



I used a pen to mark a line across the piston while it was at 84 degrees.



Then I filled in some of the area that needs to be removed with a red Sharpie. It's a very rough shape. I'm going to widen the port slightly too, so I'll round it better when I do that.



I don't have time to do it right now, but it looks like I'll be doing some serious grinding later.

[190mech]

Round out the edges and widen it to 70 percent....Double and
triple check before cutting,you cant put back that metal!