Exhaust valves on a two stroke.

[Hillclimber]

Has anyone modified a V6 or 8 to use exhaust valves - successfully?

I would put the EFI injectors after the reed valves.

[LakeFever]

Rotax invented the R.A.V.E. Rotax automatic variable exhaust in the late 80’s which uses a gillotine to shrowd the exhaust port down with a spring until exiting gas pressure becomes high enough to push the gillotine up and open the port size. The tech works fantastic I raced many of these things and with a rotary intake valve it took a lot of reed valve cubes to compete against these systems. They have since become broadly used in many manufacturers since.

I can’t see how running a cam/follower system for a two stroke valve would do anything but add weight and complexity. Maybe a koenigsegg free valve desmo type servo fired system that replaced both the reed and gave exhaust port dimensional powers would be something worth doing. I believe Jaguar invented that tech anyways so it’s in your backyard

[Hillclimber]

Hi Lake fever - Yes I use the power valves on my 600cc Rotax triple with 6 speed gearbox, but need the expansion chambers to make everything work correctly. Three expansion chambers OK but I am looking at 8 and theres not so much room on a race car to accommodate these. Further more I run a CVT transmission on the V8 car, with tuning it I keep the engine rotating at the 5500 to 7000 RPM range, I engage the CVT at circa 4500RPM so no need for low rpm power. Currently the exhaust valve solution means a single simple exhaust and I can dyno tune the cams for max power at the operating range.

[LakeFever]

What cams? Im not sure I follow.

As for adding the valves ( OMC V8 yes? ) I imagine it could be done with some careful machining and welding but the work involved would be intense. I dont know of anyone who added power valves successfully to any two stroke it may have been done but I sure dont know for what its worth. The Volvo with the V8 OMC has pipes that look pretty tight. I think you would benefit from a phone call to Monty and see what he has in mind to help you with your power and fitment goals he knows these things best

[Hillclimber]

Lake Fever - I am already talking to Monty and we are working together on this project.

[LakeFever]

Maybe the exhaust chest could be machined flat and you could fabricate a manifold plate with exhaust valves cobbled together from a rotax that bolts on? Exit out some zoomie type exhaust snouts?

[BarryStrawn]

Your picture shows two exhaust poppet valves sort of like a Detroit Diesel two stroke. I can't imagine how this could ever work on spark ignition two stroke because of the valvetrain velocity. I guess maybe if someone had the budget like a F1 car engine with pneumatic springs etc.

I know some have experimented with systems like RAVE on two stroke outboards but not much resulted.

[powerabout]

Very short time to get the exhaust out via a poppet valve in a 2 stroke.
Better to engineer a rotary valve in the head.
Could add an inlet one too for the blower/turbo air

[LakeFever]

Your picture shows two exhaust poppet valves sort of like a Detroit Diesel two stroke. I can't imagine how this could ever work on spark ignition two stroke because of the valvetrain velocity. I guess maybe if someone had the budget like a F1 car engine with pneumatic springs etc.

I know some have experimented with systems like RAVE on two stroke outboards but not much resulted.

I have to wonder with results like this who did the work and how well was it incorporated? The rave valves sit so tightly fit into the port on the 583/617/670 twins I worked on it is essentially a port modifier which even slight port height changes make such a huge change on our outboards I’d have to think if the guillotines were machined and added in such a way to fit the port exit tightly there would be noticeable gains. The work to do all this though seems daunting to me but when racing? This may be worthwhile with enough will and determination. Might have to chew up a few blocks to realize it fully.

Then again if there’s no fuel restrictions to this class your racing it might be best to have Monty hog it out and build for methanol and stick with the omc exhaust chest architecture which I’m guessing would meet your space requirements? Not sure what the power ceiling would be with this but I would guesstimate you could possibly double the stock power levels

[FMP]

Very short time to get the exhaust out via a poppet valve in a 2 stroke.
Better to engineer a rotary valve in the head.
Could add an inlet one too for the blower/turbo air

Going against expanding cyl displacement blowdown volume by top exit, scavenging pressure drop behind blowdown pressure in opposite, working against displacement increase towards BDC. Max scavenging degrees could lag.
Assuming this won't be NA or will have CR / cranking psi high value, dynamic increase won't be available as usual.
Still interesting.

[BarryStrawn]

With that much complexity, might as well go four stroke turbocharged and make some real power. If rules allow.

[Hillclimber]

Barry - I only race two stroke engined cars - and the exhaust valve addition plus supercharging is not complex compared with the existing 3.6l - V8 installation with CVT transmission, 8 Mikuni Super BN carbs., pressure oil system for the crank main bearings, and making my own ignition system with 8 Hall sensors ans a magnet!!

[BarryStrawn]

Opening and closing poppet valves every revolution will get pretty complicated. Like turning a 4 liter 4 stroke V8 14,000rpm.

Creating an overhead cam cylinder head also seems rather complicated. I can't think of any existing auto or bike head even close to an outboard engines bore pitch. So you would be making it.

But it might be a fun experiment on a single cylinder. Adapt a four valve dirt bike head and use all four for exhaust. Cylinder with a full surround of intakes would be the easy part. But still going to be impossible to make the valvetrain keep up with the revs on an engine of any size.

[Hillclimber]

Hi Barry - I am 77 years old and retired, love building things that are different. For the Rotax engined race car , picture above, I needed a 6 speed gearbox. I bought a damaged Aprilia RSV4 engine and cut out the 6 speed gearbox and coupled it to the Rotax engine. For the new V8 project I am looking to instal 4 valves per cylinder operated by 2 cams running half engine speed. two valves are exhaust, operated alternately and the other two valves inject fresh air, from the 5 psi supercharger, into the cylinder whilst the exhaust valve is just closing ensuring that all exhaust fumes are gone out, i.e. simulating the effect of an expansion chamber. When I have decided on the final design, I have a 400cc single cylinder 2T engine for conversion as a development ready for the V8 project.

[LakeFever]

Now I understand the cams. Lobe design and spring will be critical to this. B splines, tough math