KT 100 tricks

Gillies

Gillies

Member
Wanting to know if anyone has any other tricks for gaining hp on a KT100. Here's my plan?

I am going to remove about 2 cc's from the combustion chamber to increase the compression. I cut the top of the barrel, not the head. The reason for that being; the piston in the KT does not come to the top of the barrel like in euro engines. Their pistons always come to the top of the barrel. It makes sense, aluminum, in the head, transfers heat better than the steel in the barrel.
Not sure if I will add xtra counterweights in the crankshaft??
I am going to port the engine, I will start with raising the exhaust port about 4 degrees. Eyebrows on the top, out over the transfers, also. I am going to leave the transfers where they are.

I will Slot the holes in the coil so I can retard the timing. The timing I believe should be set at about 85 degrees BTDC.

Any other suggestions would be great
 
Dino crank,IAMErod, HPI ignition, forget the Burris piston they are junk any of the 135 piston will work with a little work lol. Mikuni34 on alki. 2413, 2414, Ngk10egp, 9egp plug. Been done to death lol. Like most will say not worth the money just get a reed or rotary I'm done later Chuck.
 
Murdock said:
Wanting to know if anyone has any other tricks for gaining hp on a KT100. Here's my plan?
<snip snipo>
Any other suggestions would be great
Click to expand...

Biggest tricks? --> Don't overlook the mechanics of the engine:

- main bearings aligned?
- main bearings have correct interference?
- con-rod has correct clearance on both ends, and checked for parallel ends and in twist direction as well?
- crank running *dead* true?
- cases dead square?
- bottom of cases perfectly flat? Top of motor mount perfectly flat? (Yamaha cases bend/flex easily)
- correct end play in the crank?
- bottom of cylinder dead square to the bore?
- is the piston you're using square? (wrist pin bore to the sides)
- check taper of piston (more radical tuning requires more taper, milder exhaust and lower gears less taper)
- is the cylinder deformed correctly for honing so it will be perfectly round when engine assembled?
- DON'T over-tighten the exhaust header (deforms bore) - very low torque and double-nut is best (same torque as when honing)
- does the ring *perfectly* fit the bore size? (light checking is best).
- shoot for the correct ring tension, end gap not critical as long as it has enough
- choose an assembly sequence and torque increments on every step, and try to always do it the same way

- give the top of the exhaust a slight bit of an "arc", don't make it straight across (way easier on the ring)
- when it comes to cutting cylinder or head, I'd personally cut the head if I can get to the squish I want
- combustion chamber shape can definitely change the power band:
----- small diameter deeper dome for for short/tight tracks
----- larger diameter shallower dome for tracks where a lot of time is spent at higher revs

PM
 
Pete_Muller said:
Biggest tricks? --> Don't overlook the mechanics of the engine:

- main bearings aligned?
- main bearings have correct interference?
- con-rod has correct clearance on both ends, and checked for parallel ends and in twist direction as well?
- crank running *dead* true?
- cases dead square?
- bottom of cases perfectly flat? Top of motor mount perfectly flat? (Yamaha cases bend/flex easily)
- correct end play in the crank?
- bottom of cylinder dead square to the bore?
- is the piston you're using square? (wrist pin bore to the sides)
- check taper of piston (more radical tuning requires more taper, milder exhaust and lower gears less taper)
- is the cylinder deformed correctly for honing so it will be perfectly round when engine assembled?
- DON'T over-tighten the exhaust header (deforms bore) - very low torque and double-nut is best (same torque as when honing)
- does the ring *perfectly* fit the bore size? (light checking is best).
- shoot for the correct ring tension, end gap not critical as long as it has enough
- choose an assembly sequence and torque increments on every step, and try to always do it the same way

- give the top of the exhaust a slight bit of an "arc", don't make it straight across (way easier on the ring)
- when it comes to cutting cylinder or head, I'd personally cut the head if I can get to the squish I want
- combustion chamber shape can definitely change the power band:
----- small diameter deeper dome for for short/tight tracks
----- larger diameter shallower dome for tracks where a lot of time is spent at higher revs

PM
Click to expand...
Thanks for the extra tweaks, Pete. I guess it's attention to detail when assembling hey?
 
What's at least if not more important than the number is the shape. Parallel squish? Does it have a slight taper?

If parallel, I personally would *not* run tighter than that.
 
No need to slot the coil. Just remove the rotor key, set the rotor at the desired setting & lock it down. The KT piston doesn't come to the top??? Not sure where your engine came from but all my KT pistons come right to the top of the cylinder, not below. I even have one that pokes out the top a little bit (it's stroked with a 53mm piston). Forget cutting the barrel, cut the head. Watch your blowdown. If your real creative, instead of cutting "eyebrows" in the exhaust, add a hole on each side of the exhaust. And, you could add reeds in the case. I hear that wakes up a KT. I've envisioned making the KT100 a case fed reed engine. Would be a lot of work, but just wanted to try it. No closer squish than .030". Also, better run the heavy duty rod. Do what Pete says. Make sure everything is exactly square & extremely straight. If your going to do a lot of mods, just ditch the KT ignition. Go with an updated ignition like what Chuck said, HPI. Back in the day we used the Motoplat ignition. Also, don't forget about using the correct pipe & flex length to complement your mods. Buller makes a 52mm stroker crank or go even more with the other cranks suggested above. Don't forget to cut the bottom of the piston on the intake side. About .100" should do it, give or take a little. Front transfers need a little taken off each side to make them closer to the center, pointing toward each other. The yellow KT owners manual shows these modifications.

Good Luck!

Brian #89
 
Look closely at the engine on the #79 kart

1634958719321.png
 
phantomkartracer said:
No need to slot the coil. Just remove the rotor key, set the rotor at the desired setting & lock it down. The KT piston doesn't come to the top??? Not sure where your engine came from but all my KT pistons come right to the top of the cylinder, not below. I even have one that pokes out the top a little bit (it's stroked with a 53mm piston). Forget cutting the barrel, cut the head. Watch your blowdown. If your real creative, instead of cutting "eyebrows" in the exhaust, add a hole on each side of the exhaust. And, you could add reeds in the case. I hear that wakes up a KT. I've envisioned making the KT100 a case fed reed engine. Would be a lot of work, but just wanted to try it. No closer squish than .030". Also, better run the heavy duty rod. Do what Pete says. Make sure everything is exactly square & extremely straight. If your going to do a lot of mods, just ditch the KT ignition. Go with an updated ignition like what Chuck said, HPI. Back in the day we used the Motoplat ignition. Also, don't forget about using the correct pipe & flex length to complement your mods. Buller makes a 52mm stroker crank or go even more with the other cranks suggested above. Don't forget to cut the bottom of the piston on the intake side. About .100" should do it, give or take a little. Front transfers need a little taken off each side to make them closer to the center, pointing toward each other. The yellow KT owners manual shows these modifications.

Good Luck!

Brian #89
Click to expand...
Like this :)
 

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Pete_Muller said:
Biggest tricks? --> Don't overlook the mechanics of the engine:

- main bearings aligned?
- main bearings have correct interference?
- con-rod has correct clearance on both ends, and checked for parallel ends and in twist direction as well?
- crank running *dead* true?
- cases dead square?
- bottom of cases perfectly flat? Top of motor mount perfectly flat? (Yamaha cases bend/flex easily)
- correct end play in the crank?
- bottom of cylinder dead square to the bore?
- is the piston you're using square? (wrist pin bore to the sides)
- check taper of piston (more radical tuning requires more taper, milder exhaust and lower gears less taper)
- is the cylinder deformed correctly for honing so it will be perfectly round when engine assembled?
- DON'T over-tighten the exhaust header (deforms bore) - very low torque and double-nut is best (same torque as when honing)
- does the ring *perfectly* fit the bore size? (light checking is best).
- shoot for the correct ring tension, end gap not critical as long as it has enough
- choose an assembly sequence and torque increments on every step, and try to always do it the same way

- give the top of the exhaust a slight bit of an "arc", don't make it straight across (way easier on the ring)
- when it comes to cutting cylinder or head, I'd personally cut the head if I can get to the squish I want
- combustion chamber shape can definitely change the power band:
----- small diameter deeper dome for for short/tight tracks
----- larger diameter shallower dome for tracks where a lot of time is spent at higher revs

PM
Click to expand...

Pete_Muller said:
Biggest tricks? --> Don't overlook the mechanics of the engine:

- main bearings aligned?
- main bearings have correct interference?
- con-rod has correct clearance on both ends, and checked for parallel ends and in twist direction as well?
- crank running *dead* true?
- cases dead square?
- bottom of cases perfectly flat? Top of motor mount perfectly flat? (Yamaha cases bend/flex easily)
- correct end play in the crank?
- bottom of cylinder dead square to the bore?
- is the piston you're using square? (wrist pin bore to the sides)
- check taper of piston (more radical tuning requires more taper, milder exhaust and lower gears less taper)
- is the cylinder deformed correctly for honing so it will be perfectly round when engine assembled?
- DON'T over-tighten the exhaust header (deforms bore) - very low torque and double-nut is best (same torque as when honing)
- does the ring *perfectly* fit the bore size? (light checking is best).
- shoot for the correct ring tension, end gap not critical as long as it has enough
- choose an assembly sequence and torque increments on every step, and try to always do it the same way

- give the top of the exhaust a slight bit of an "arc", don't make it straight across (way easier on the ring)
- when it comes to cutting cylinder or head, I'd personally cut the head if I can get to the squish I want
- combustion chamber shape can definitely change the power band:
----- small diameter deeper dome for for short/tight tracks
----- larger diameter shallower dome for tracks where a lot of time is spent at higher revs

PM
Click to expand...
 

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