Running no base gasket, 650/750 engines...

Cannibal

Cannibal

Tasty Human
Location
Summit Lake, WA
So I was talking to a guy who's been a PWC mechanic/tuner for 28ish years. He said one trick on the 650/750 engines is to remove the base basket and run a thin bead of 1211 instead. This does a couple things.

1: Moves the ports down to help with the high ports Kawis have to increase bottom end.

2: Increases compression 20ish pounds, so no need to run after market head.

Has anyone done this with any success? Anyone have problems not running a base gasket?
 
SUPERTUNE

SUPERTUNE

Race Gas Rules
Location
Clearwater Fl.
If you do the math, depending on what cylinder you have, could be about 15 lbs on a healthy bore cylinder.
Let's say Kawasaki 750 sx, bored to 1st over at 80.5mm.
Bore2 *.5 *.7854 divided by 1000 = 2.5cc's that you would raise the compression.

O.K.
I'll help you here for you to understand how I did this.
Bore X Bore X Stroke X .7854 Divided By 1000 = 2.5cc's
80.5mm X 80.5mm X .5mm (thickness of gasket) X (constant correction factor) divided BY 1000 (converts the decimal point to read in cc's)=2.5cc of piston displacement that your raising the compression by.
 
Cannibal

Cannibal

Tasty Human
Location
Summit Lake, WA
crab said:
Shan gave me that trick.
Click to expand...

That's who I got it from. He stayed with us for Surf Slam. Nice talking to him. Knowledgeable guy. And his labor is only $30/hr and he keeps quite a few parts in stock. Good resource!

SUPERTUNE said:
If you do the math, depending on what cylinder you have, could be about 15 lbs on a healthy bore cylinder.
Let's say Kawasaki 750 sx, bored to 1st over at 80.5mm.
Bore2 *.5 *.7854 divided by 1000 = 2.5cc's that you would raise the compression.

O.K.
I'll help you here for you to understand how I did this.
Bore X Bore X Stroke X .7854 Divided By 1000 = 2.5cc's
80.5mm X 80.5mm X .5mm (thickness of gasket) X (constant correction factor) divided BY 1000 (converts the decimal point to read in cc's)=2.5cc of piston displacement that your raising the compression by.
Click to expand...

Ok, so on my old 650 I'm probably only looking at 10psi at most. So not huge, but when your a broke bastard like me, it's a couple free ponies and .5mm lower port height.
 
kevbo

kevbo

Location
dfw
It will make your engine more responsive. Be very careful if you advance the ignition timing because that along with reduced squish will greatly increase the octane requirement at full throttle.
 
Cannibal

Cannibal

Tasty Human
Location
Summit Lake, WA
kevbo said:
It will make your engine more responsive. Be very careful if you advance the ignition timing because that along with reduced squish will greatly increase the octane requirement at full throttle.
Click to expand...

Ya, I'd surely want to check squish to make sure it's still in spec. Maybe if there's any more room, mill the head just a little to get the compression up to the 180ish zone if possible.

crab said:
and yes my 752 rips your arms off.
Click to expand...

I've heard that thing rips hard. No porting done on the cyl? I figured you must have had more tricks up your sleeve with that engine besides the SXR intake and the B pipe.
 
2

2XLR8

X-
On the 800 kawasaki you might have a spot that is too tight. That is because the head is machined for the 750 bore and not the 800 bore. Even with just a .010 the clearnce is around .030 to .035
 
Waternut

Waternut

Customizing addict
Location
Macon, GA
Just out of curiosity... I see that it increases compression but what about the ports? When I ported my 750 engine, I noticed that the rings were still visible in the exhaust port when the piston was at the bottom of the stroke. Is that 0.020"-0.030" removed from under the cylinder going to affect port timing in a positive or negative way?
 
Cannibal

Cannibal

Tasty Human
Location
Summit Lake, WA
From what was described to me, it was the top of the exhaust port that was the important factor here. By running no base gasket, it lowers the top of the port down a little which helps out with bottom end power.

Obviously it changes the transfer and boost ports too, but I don't know how that effects power.
 
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