Maximizing Velocity in Two-Stroke Engine Intake Manifolds: Why Speed Beats Volume

[waxhead]

Consumers would have to make sense of port heights and tuned pipes before they could get much useful information from a dyno chart. I dont think this group is that sophisticated. Its like mixing letters with numbers, not many want to understand it.

I completely agree with you. Most people want their ski to hit hard the moment the throttle is cracked wide open. Big horsepower numbers mean nothing if there's no power under the curve to support it. The most fun engine to ride is one that’s responsive and torquey—it makes the ski feel alive and engaging.

That’s exactly why we designed these manifolds. No other manifold gave us the throttle response we were looking for. While making top-end power is relatively easy, creating an engine with both responsiveness and torque is a far greater challenge—and that’s what sets these manifolds apart.

 

[Sxirider44]

Sick intake WAX . Love the fit and finish look it has.

Wonder if any 2 stroke outboard gurus could chime in on the dyno talk. I guess though, a prop hp is way different than a jet. But, the engine itself can be dyno’d .
I know jet boat guys who sink 15k into the motor and hardly get much increased speed until they sink 5k into the pump.
I think that’s the thing that makes stand ups so unique . Hardly any two skis are alike there’s so many variables.
Even the same ski with two different riders with different skill sets make the ski not even look the same while watching.

 

[fastgtfairlane]

Sick intake WAX . Love the fit and finish look it has.

Wonder if any 2 stroke outboard gurus could chime in on the dyno talk. I guess though, a prop hp is way different than a jet. But, the engine itself can be dyno’d .
I know jet boat guys who sink 15k into the motor and hardly get much increased speed until they sink 5k into the pump.
I think that’s the thing that makes stand ups so unique . Hardly any two skis are alike there’s so many variables.
Even the same ski with two different riders with different skill sets make the ski not even look the same while watching.

Even the same hull with the same engine, carbs and pipe just with a different pump will act entirely different.

 

[WFO Speedracer]

When I had the 550SX engine in my ski I ran dual 38's with a Hot products manifold and the reed stuffers , I was also able to pick up a Westcoast intake that had the dual acrb bolt patterns and a set of Kehin red 38's , I installed the Westcoast intake , dual Kehins and removed the stuffer, the difference between the two setups was like night and day and made an already great running engine run even better , I attribute most of this to manifold design and removing the reed stuffers.

 

[kevbo]

Plus Keihins are very good carbs!

 

[WFO Speedracer]

Plus Keihins are very good carbs!

Yes I know that but still I can't see there being that drastic of a difference in power when both were 38 mm carbs , I attribute most of it to taking the reed stuffers out , those just don't work very well in these engines. If you have a 550 reed and want to get some more cheap power , take the reed stuffers out and throw them in the trash.

 

[waxhead]

Yes I know that but still I can't see there being that drastic of a difference in power when both were 38 mm carbs , I attribute most of it to taking the reed stuffers out , those just don't work very well in these engines. If you have a 550 reed and want to get some more cheap power , take the reed stuffers out and throw them in the trash.

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Praise the lord! Someone finally agrees with me about reed stuffers. I’ve been pushing this point for years, and everyone always thinks I’m crazy for saying it

 

[WFO Speedracer]

Here’s a more refined version of your message:

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Praise the lord! Someone finally agrees with me about reed stuffers. I’ve been pushing this point for years, and everyone always thinks I’m crazy for saying it

I try to speak on subjects that I know or have had first hand experience with, this is one of them for sure , I had one of the first 550 reed engines in the states because I ordered all new parts off the microfiche when it came out , which is before the ski actually hit the showroom floor. They didn't have the reed cages available yet so I used KDX 200 reed cages in it .

I had one of the first dual intake manifolds, as soon as Hot Products put it in their catalog I ordered it , at that point there were no SBN carbs so I used brand new 38BN's , I quickly realized the compression was high enough stock that I didn't need an aftermarket head on it but I did but a Coffman half pipe for it.

Later when I did a submarine and manage to bend both rods I rebuilt it using stock Thunderjet pistons with the boost holes in the pistons , they line up almost perfectly wit the stock transfer ports , when I pulled it apart the second time I put in another new set of pistons , ported the cylinder and installed the Westcoast dual total loss system on it , I later sold the engine to a customer and removed the total loss putting his stock ignition back on it , the last time I heard that engine was still running strong in a customers 550SX.

 

[Quinc]

Guy over seas making engine parts with a dyno:

https://www.instagram.com/jet_ski_mann?igsh=MXFiaXVoZnJuY2k0ZQ%3D%3D&fbclid=IwY2xjawFyN0VleHRuA2FlbQIxMAABHa3B8z_r1rrOy8zKSCk6c9dyWWE8mfcllHHNuqEuIUvHkzfwdtKlOclZQQ_aem_ZIPbuDhG-H4u4BVYyBXohA

 

[E350]

Should we get to know this Polska guy?

CNC-MAN-kompleksowa obróbka skrawaniem metali i tworzyw sztucznych

Firma z obróbki metali i tworzyw sztucznych. Nasze usługi: frezowanie, toczenie, cięcie laserem, druk 3D, grawerowanie, spawanie

cnc-mann.com

 

[Storbeck]

Lots of interesting stuff for sure. I'm not sure what's up with the round slides on a watercraft motor though (I think it's a watercraft motor?).

 

[E350]

Isn't it because he has changed how the intake manifold attaches to the crank case? See 2020 SJ crank case below:




biuro@cnc-mann.com

 

[Storbeck]

I'm not seeing why that would affect carb selection. Pretty easy to get any carb on there with a lot less resources than he has.

 

[E350]

Isn't that just because of the manufacturing technique?

CNC cannot make as intricate indentations as casting can?

 

[E350]

Back to the subjject of the thread.

Anyone for a Delrin intake manifold?

 

[Storbeck]

Isn't that just because of the manufacturing technique?

CNC cannot make as intricate indentations as casting can?

You lost me I don't understand what this has to do with using round slide carbs on a watercraft.

 

[bkspeedwerks]

You lost me I don't understand what this has to do with using round slide carbs on a watercraft.

there was an instagram story stating the motor and carb arrangment was for use on a boat.

 

[WFO Speedracer]

You lost me I don't understand what this has to do with using round slide carbs on a watercraft.

E350 has no idea that you are talking about round slide carburetors , it's fun to watch though !

 

[E350]

^^^ Verily, he speaks the truth.
Amen.

 

[kevbo]

A carb with a float wont work on a watercraft since the engine is soft mounted. Slide carbs meter fuel much more accurately at part throttle making them better for wheeled vehicles and dyno work. There is not much left to learn about engine and pipe development beyond the application aspect. Watercraft guys do a lot of things to make the engine work in a ski that would never be done in any other vehicle, even with the same engine.