Engine Braking: What Clutching Factors Affect This

[mountainhorse]

Some clutch setups/sleds have excellent engine braking on downhills and some dont.

What clutching factors affect weather or not the sled will "engine brake" well on downhills.

I've had a Dynamo Joe setup in a 2006 Summit that was tenacious on holding downhill braking without needing to blip the throttle and was spoiled..

Other sleds I have been on or owned have had good engine braking, but then all of a sudden let go and "free wheeled" untill you blipped the throttle.

What factors in clutch setup keeps the primary engaged while still having good, balanced cluching/performance?

 

[mountainbigbull]

I'm not sure but I ask my dealer about that he said if you change the secondary spring you can change the engine braking. I can not remember if it less or more spring gives you what result. I know from personal experience if that cutting in or out with the blimp of throttle you talk about this effected by belt tension. So the tighter the belt tension is less likely to become disengaged going down a hill.

 

[mountainbigbull]

Also the sleds that have electronic reverse have a reverse helix in them. They have more engine braking compared single helix secondary clutches. Also the team roller clutch with ramps on both sides of the rollers are similar operation.

 

[SNOW JW]

MH buy a 4-stroke no clutching is needed and the engine braking rocks!!! HAHA just kidding.

 

[mountainhorse]

Mtn bb, thanks for the input.... im looking for more of an advanced perspective...but I appreciate your time.

J dub, dont even go there!

Helix angles, secondary preload, primary spring force compared to flyweight deflecton, relationship between primary force and secondary, gearing etc all effect clutch operation and thus engine braking.

Some sleds I've been on seem to be clutched right and are rock solid performers but will not engine-brake worth a sh!t... others are clutched right and will.

?????

 

[Ron]

The primary clutch has to be the key to release of the engine braking effect. When it pops open at 4-5000R's the link between track & engine is gone. But having said that the secondary has a lot to do with the E-braking effect-maybe by keeping the primary turning above release R's.
Case in point-my 07 Summit X would throw you over the bars if you let off the gas quick with the stock clutching. Changed to a Team driven with a steeper helix & softer spring and the feel was more like my 05 Poo-engine brake was there but subdued.
Now my 800 Dragon has more EB than any Poo I've owned. The only drive train difference from my 05 is a deeper lug track, a little stiffer Driven spring and shallower initial helix angle.
So to answer your question-I Don't know $hit about engine brakes.

 

[Rixster]

Is is done in the primary clutch. Its all about spring pressure and helix. The abililty of your primary to "backshift" Is what makes what you call engine brakeing. get a steeper helix and or a stiffer spring. see what happens then. you are going to have to change more thatn once to get it to perform and backshift the way you want it to.

 

[MARCUSO]

Is is done in the primary clutch. Its all about spring pressure and helix. The abililty of your primary to "backshift" Is what makes what you call engine brakeing. get a steeper helix and or a stiffer spring. see what happens then. you are going to have to change more thatn once to get it to perform and backshift the way you want it to.

So you are saying that there is a helix in the primary?? I am not sure what you are trying to explain...

My machine has no engine brake, I run a 160/320 primary spring.
If I want engine brake, I blip the throttle. It is better that way, especially if you are flying down a real steep descent, you want that track to freewheel, and not drag. (Sometimes)
Basically, my theory is that the opening of the primary is determined by the weight of the spring. The lower the engage spec on the primary spring, the lower rpm's needed to engage, and stay engaged.
The secondary, well if you set it up to not open at all (hypothetically speaking RER).... the engine braking should not happen if the primary is fully open. If it would, your belt is too tight.

 

[Rixster]

Im sorry about that, I meant secondary. Thought one thing said something else

 

[mountainhorse]

My 2006 Summit 800 151 would engine brake downhill and not let go unless you got really slow.

It had a fairly stiff spring in it... 160-350 and it performed the best in the clutching department of any sled I've ever had... a Dynamo Joe setup with his helix, stock ramps, 17g in the flyweights, stock secondary spring and stock gearing.

It's not the primary spring aparantley... Marcuso and I have the same starting force on the primary spring.

Any input is much apreciated.

 

[geo]

Turning your idle up to a smooth 2400 ( means you may have to richen the pilot circuit) helps when you use high engagement springs.
Starts easier too.

 

[thefullmonte]

I'm not a clutching expert, but here it goes. Taking motor design out of the equation. I would think that the quicker the backshift, the more prenounced the engine braking. In the team secondary clutches, what would seem like an excessively stiff spring works extremely well. A question does arise though when you let off the throttle your primary would also backshift and loose engagement.

What sled are you running? Ski doo's are often geared very well. I believe the older summits were were like at 19/43 stock. Correct me if I'm wrong.

My 03 rmk when switched to the 19/43 gearing and a much stiffer spring in the team. It would definitally let you know when you let off the gas.
Good topic, I hope some clutching guru's chime in.

 

[winter brew]

If you're just referring to engine braking (like for going downhill without using the brake) and not backshift, this is controlled entirely by the primary spring/engagement RPM. If you have a high engagement then your engine has to be at a higher RPM to be engaged with the belt....lower engagement means you can better utilize the engine coming down hills. I noticed this alot when I went from a 200 to a 160 spring, with the 200 there is basically zero braking unless you're haulin' ***.

 

[milehighassassin]

Does a high comp head increase engine braking? Seemed like it to me, but this is a new sled for me, so I don't know what it was like without the head.

 

[mountainhorse]

Does a high comp head increase engine braking? Seemed like it to me, but this is a new sled for me, so I don't know what it was like without the head.

Only if the clutches stay engaged to each other.

TTT

 

[Dynamo^Joe]

Belt dimensions/Gearing/Secondary spring start forces are the major contributor to engine braking enhancement.

Belt: Wider belt width. Tight belt deflection. Shorter belt.
Gears: Lower gear ratio [higher secondary rpms]
Spring: Higher spring start forces.
...will enhance the engine braking before declutching occurs.

Compare a 166 belt to which is 1.375" wide.
A 377 belt which is 1.49" wide and 4mm shorter.

A 166 belt may declutch at 5000 rpms.
A 377 may declutch at 4500 rpms.

For fun I seen how far I could go with the forces and ended up installing a goodwin dark blue/red 250/345 secondary spring with 19:47 gears and deflection tight enough that the belt squeel at idle..then back off a bit.

Downright dangerous on the trail....I would get reduced throttle oversteer and the rear of the sled would come around because the track would lock up as tight as applying the handbrake. The feel was like I had a standard transmission underneath the hood.
Not changing anything other than deflection as I opened up the deflection cam from 5 to 4 to 3...etc each change would reveal declutching at a higher rpms it would be like someone slipping the transmission into neutral - but give a quick flip of the throttle and whammo....track locked up again, sled going sideways.

I ended up getting back to the stock purple 225/300 and greatly reduced the amplitude of braking force. Went to the green 180/300 and less brake reduction yet.