Super Jet Squish opinion wanted.

[amitchell]

I just assembled my motor after a bore(61x 82.5mm), freestyle sport porting and clean up decking. I also lapped the top of the cylinder to ensure a good oring seal with my ADA head.

My cylinder measures 4.673" in height, so I lost about 0.020" from stock(seems like not the first time its been decked).

My squish measures 0.031" PTO and MAG, with newish 37cc ADA domes. Switching to 35cc when they arrive.

I run stock static timing with an MSD enhancer, B-pipe, dual 38's, 91 pump gas. I would like to be able to run WOT. Should I worry about that squish? If so should I go with a thicker base gasket or cut the domes? Would a thicker gasket affect port timing noticeably? 0.010" or 0.020" heavier on the gasket?

Thanks!

 

[Quinc]

Subscribed.

 

[Harbor]

Squish opinions wanted--- here's mine and cut the domes

 

[amitchell]

So cutting just the squish band on the domes? 0.020in at 10.5degrees I presume.

 

[Harbor]

The ADA 701 domes start @ .015 squish band with 10.5 degree.

Squish spec "if I can say that" around .045 to .050

The chart above is a dasa chart for their cylinders and domes

Yes If you went .020 you'd be at .051 then 10.5 degrees

Adding .020 to your base gasket would lower your compression in addition to changing port timing

Let's see what others post, you have your set up listed pretty well



This charts is to help show the squish band area

 

[kevbo]

ADA domes have a narrow squish with lots of taper. This makes them more forgiving with fixed timing. Raising the whole cylinder will tend to soften throttle response, sometimes by a lot.

 

[waxhead]

Set your squish so that your pistons hit the head 1000 rpm higher than your rev limit.
You don't get deto when there is nothing there

 

[amitchell]

Set your squish so that your pistons hit the head 1000 rpm higher than your rev limit.
You don't get deto when there is nothing there

That sounds destructive.

 

[LegDragger64]

One percent of stroke. Wax is right.

 

[amitchell]

How would you set squish via rpm? Whats the correlation?

 

[Harbor]

My wifes 01 RN so far is set up like youve listed yours, i can take a squish measurment off it later tonight so youll have a comparision ski. Ive run it flat wide open one time cruising with a sit down no problem. The power up top with the B-pipe was pretty flat, reminded me on a stock ski while @ cruise.

 

[amitchell]

My wifes 01 RN so far is set up like youve listed yours, i can take a squish measurment off it later tonight so youll have a comparision ski. Ive run it flat wide open one time cruising with a sit down no problem. The power up top with the B-pipe was pretty flat, reminded me on a stock ski while @ cruise.

I was suffering from the same flat top end before the rebuild. I had a type 4 drypipe that was stupid fast up top before, kind of miss that.

 

[Harbor]

I was suffering from the same flat top end before the rebuild. I had a type 4 drypipe that was stupid fast up top before, kind of miss that.

Thats funny because the type 4 was my last pipe to, now both my skis have the B-pipe, no more crazy barely controlable top end on the 701, my 865 stroker is a differant story so far. but ive never had iit wide open, it accelerats hella fast but i can tell its flat up top too. I do enjoy the bottom end of the b-pipe though, dont miss the 2 second lag and nothing on bottom with dry pipe, i had water injection and it helped a alot on getting some bottom back, needed more timing down low and a flow control valve and water restricter into the stinger and a differant prop, it was a bouy boat no wonder

 

[fastgtfairlane]

if you run a thicker base gasket you will raise the port timing.. in your case i would get a thicker headgasket which wont affect port timing...

 

[Harbor]

if you run a thicker base gasket you will raise the port timing.. in your case i would get a thicker headgasket which wont affect port timing...

The ADA used o-rings instead of a traditional head gasket

 

[fastgtfairlane]

ohh ok i missed that part.. either way the thicker base gasket will slightly raise the port timing

 

[amitchell]

I should add that my main concern is reliability. I seized two pistons last year and did not get to enjoy riding.

 

[Harbor]

Did you get the cause of the seizures isolated?
If it's already isolated never mind the rest

Was that two separate failures or both at the same time?
Same piston each time or different?
Piston domes were ok, just skirt and cylinder wall damaged?
What was the set up then and how much cranking compression/squish?
Fuel and riding style during failures?

 

[amitchell]

First failure was with the dry pipe at WOT, pulse nipple broke off... not fun.

Second was adding hand warmers, line up to the bars was too small and overheated the front cylinder. Dumb dumb dumb.

 

[waxhead]

How would you set squish via rpm? Whats the correlation?

There is a certain amount of stretch in the con rod bearing piston etc the higher you rev it the more it stretches.