SX/SXi/SXi Pro port timing question

[jetski9010]

Have any of your 750 guys cut the bottom of the cylinder, top of the cases, or couter bored the sleeves deeper to lower the port timing of the 750 motors? Might be building a 750 motor up for a friend soon and trying to get an idea. I have seen some of the port timing specs from factory and they are really high so I am trying to lower them. Just seeing if anyone has done this type of thing yet?

 

[Crab]

Just delete the base gasket and run .020 copper head gasket to retain squish.

 

[jetski9010]

what is the squish clearance you guys get stock?

 

[kevbo]

Use an 92-95 SX cylinder.

 

[jetski9010]

Its already a 92 750sx so I am good there.

 

[Hirschfelt]

you will want to run that buy a good engine builder. I had my PJS 850 set up that way.. The entire motor was built to lower the port timing and setting up the domes for 100 octane. The pistons will be higher than the deck at TDC. The domes and head gasket need to be compensated for proper octane.

 

[chriselmore_1]

Just delete the base gasket and run .020 copper head gasket to retain squish.

wouldnt you worry about leaks without the base gasket? is 1211 enough for that spot?

 

[jetski9010]

you will want to run that buy a good engine builder. I had my PJS 850 set up that way.. The entire motor was built to lower the port timing and setting up the domes for 100 octane. The pistons will be higher than the deck at TDC. The domes and head gasket need to be compensated for proper octane.

I set a 550 up like this before and poked the pistons out the top. I am also going to set it up for 105 octane fuel. Sounds like the only way to get low end out of the 750 motor is to run monster compression and a factory pipe with water injection. How important is it on the 750 motors to run a girdled head?

 

[2XLR8]

The 750 sx cylinders have lower porting than all later 750 sxi cylinders. If you run a lot of compresion you will need a girdled head because the early 750 cylinders are not solid near the base mount holes. A good thing would be to get an 800 cylinder because the ports are similar to the old XI cylinder and you can gain displacement by boring it out to 84 MM they are also solid near the base so you should not need to use a girdled head. You could even use the stock head milled.

 

[jetski9010]

I was hoping you could get away with running 210psi on a 750sx cylinder without the girdled head but I guess not. Got to come up with the $400 to get the girdled one from ADA I guess.

 

[kevbo]

I always found a direct trade-off between power and response when going from 178-186-192 degree port height. Can you get enough power with an ultra low port?

 

[Hirschfelt]

105 octane? Why? Just go straight 110 leaded or better the C12 from VP. at 105 you wont be mixxing much 93 with 110 anyway to reduce the actuall per gallon price. JMO

 

[jetski9010]

105 octane? Why? Just go straight 110 leaded or better the C12 from VP. at 105 you wont be mixxing much 93 with 110 anyway to reduce the actuall per gallon price. JMO

Because I run my skis on E85 which is 105 octane. Keeps the price down at $2.30 a gallon rather the $9.00+ for a gallon of 110 octane.

 

[Cannibal]

Most 2 stroke folks stay away from even E10 because of the solvent characteristics of Ethanol. In fact, in some states, airports and marinas are the only place to find gasoline without ethanol added.

Do you worry about breaking down your mixed oil or have you taken steps to combat that? Still running oil injection? Found research proving this wrong? Special oil?

I don't know one way or another, just that it seems to be on people's minds at times.

 

[jetski9010]

I use klotz benol which blends with alcohol very well. The only probelm I have had with it is it will gum your carb up if you let it sit for weeks/months. The way I fixed this is I have a bottle full of marvles mystery oil with a 1/4 hose on it and when I am done riding I take the inlet side and outlet side of the carb fuel lines off and hook up my bottle. Then I squeeze the oil in it till I see it coming our the overflow. I have never seen any crazy wear from using this setup. If it did come down to me having to rebuild my motor before someone running the same setup on race gas had to rebuild there motor I am sure the money I am saving on fuel cost would be higher then the cost of rebuilding a few hours earlier. Just my testing though. I know there are tons on people on here that hate it but it has worked out great for me. And if you use enough of it to matter you can claim it on your taxes.

 

[Cannibal]

Sounds like you have it figures out. Nice tob see someone thinking outside the box and willing to take a risk where others aren't. I, personally, have been playing it safe.