V8, 2 stroke poppet valve Lexus 1UZ engine 1

[Letlhakane]

Has any one got any experiance with two stroke poppet valve engines that they would like to share. I have built a Lexus 1uz V8 which is running as a two stroke. This project is primerily for increasing the volumetric efficiency for racing purposes. Any comments will be apreciated.

 

[BrianPetersen]

I am aware of Toyota and Kawasaki playing around with this concept. I have never seen nor heard one run. If that engine you've shown in the photo runs, show us!

I would expect efficiency to be very poor unless direct-injection was used, which the engine that you have, does not appear to have. It doesn't appear to be even remotely possible to stop a lot of the fresh charge from short-circuiting out the exhaust valves.

I would expect valvetrain acceleration to be a severe RPM-limiting issue given that the valves need to open and shut within roughly half the number of crank degrees.

 

[miningman]

Two stroke motorcycle engines in the 1970s produced very high HP but werent that easy to ride and had absolutely horrendous fuel efficiencies ie high fuel consumption. Might not be a serious objection when racing but something to be aware of.

 

[Letlhakane]

Hi Brian, the engine can be seen running on facebook. You are correct in saying that the valve timing is half the duration as it previously was but it is force feed now. The short circuiting is not an issue, this is only for racing where fuel consumption is of no consequense. I have not run the engine under load as yet but getting 7500 rpm instantly is not one of my problems.

 

[TugboatEng]

Could you share a link to a video?

 

[Letlhakane]

Engine video: ian.crawford.100 Facebook/Posts sept 2014

 

[gruntguru]

Sounds awesome - even with no load.

Can you share valve timing and/or valve lift with us?

je suis charlie

 

[TugboatEng]

Where did you see the video? I don't have a link.

Oh, I figured it out. Dang, no Facebook

 

[Letlhakane]

Ex opens 90 BBDC, Ex closes 25 ABDC, Inlet opens 25 BBDC, Inlet closes 90 BTDC. Cam and crank belt gears are 40 teeth using stock belt (stock gears are 24 for crank and 48 for cams). The engine is basicaly stock apart from the camshafts, Bullit blower manifold and the ignition and fuel ECU. The ECU is Spitronics with wasted spark for ignition and fuel triggers using batch injection. Blower overdrive is 20%.

 

[BrianPetersen]

I have facebook, but the cryptic information about the engine video leads me nowhere. Proper link to it?

From the cam timing, it looks like the idea is to let the exhaust blow down and perhaps even pull a slight vacuum on the cylinder with only relatively slight overlap between IVO and EVC, then blow in most of the fresh charge afterward, thus cutting down on the wasted scavenging. There's going to be a fair bit of residual exhaust in the cylinder; oh well.

 

[Letlhakane]

Brian, really, what part of the "cryptic" link don't you understand? Is it Facebook or is it ian.crawford.100 or is it "Posts Sept 2014"? Please let me know so that I can help you.

 

[3DDave]

Anyone not having a facebook account can hardly ever see anything posted to facebook. It's part of what makes it an effective marketing tool for advertising - users are essentially forced to opt in to see anything there. Even with a direct link the first mouse touch causes the screen to be covered with a "Sign in" pop up.

 

[Letlhakane]

Okay here it is for all that may be experiancing difficulties

 

[TugboatEng]

Thank you!

Keep us updated on this... thing you have done.

 

[BrianPetersen]

Wow - That sounds surprisingly smooth, very unlike a normal (carbureted and loop-scavenged) two-stroke! It's sure a screamer!

With a normal (4-stroke) V8 crankshaft, it's going to have a simultaneous-double-fire firing order.

Good job for making it happen!

 

[Lou Scannon]

Cool project.
You mentioned waste spark, but I don't get it, if it's double fire. Or do you have waste spark happening at BDC?
One pitfall to think about; the crank has not been validated for double fire and the rpm may be a torsional vibration challenge as well. Be prepared for some learning when you get some load behind it.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[PJGD]

There are several SAE papers on this topic and configuration. It is worth reading up on the Ricardo "Flagship" concept in papers 900802 and 920778. There is a lot of information of scavenging of such an engine in 1999-01-1250.

 

[Letlhakane]

The wasted spark is as in 4 stroke configuration but is used to fire the oposite cylinder at TDC to crate the double firing. Like wise the injectors can be set to "two stroke" to fuel the opposite cylinder. The injector setting was not intended to be used this way but rather to supply more fuel for engines that are running injectors that are too small to supply the rquired amount of fuel, for instance if you change from gasoline to methanol. I will attach the wiring diagram and ECU setup instructions. What Lou and PJGD have said is usefull information and it is this that I am looking for.
So far so good, the engine is super responsive on gasoline but what about methanol or even nitro. The purpose of this project is obviously to get more power out of the engine, but rather than going the conventional route as a 4 stroke with big cams, heads and valves, give it twice as manny power strokes in a given time without the drawbacks of of a narrow powerband.
Brian mentioned that the engine runs very smooth. This is true and supprisingly it is simmilar to a Detroit 6-71 or 8V-71 at idle.

 

[Letlhakane]

This is the user manual

 

[bradrs]

Even though the waste spark will deliver a spark to the cylinder at the right time, there is a big difference in the 2, in terms of spark requirements.
The waste spark is only firing 1 cylinder under compression at a time. The other cylinder is not, and takes a significant less amount of voltage to jump the spark gap. So you have 1 cylinder that requires high voltage, one that doesn't. This also means that most of the energy will go to the cylinder that is firing.

With the 2 stroke, they will both be in compression at the time of spark, and so you will have 2 cylinders that require high voltage each time. So you need to generate higher voltage, and the energy will be roughly split between the 2 cylinders.

If your existing system is strong enough, it's not a problem. Usually OE ignitions and coils can provide voltage well in excess of the amount they need. But if you start to experience misfires or coil failures, this could be something to look at. Especially if you crank up boost or do something that will require more spark voltage per cylinder.

Coils can be rated for 30kV-65kV(typical ranges I've seen), and this has mostly to do with epoxy, and methods of winding to limit voltage jump between turns of the coil. Running 2 single output coils in place of the dual output coil, with the primaries in series, would be a way to fix this if it seems like coils are failing

Adding a CDI could give you a bump in voltage if you start seeing misfires. Plus those use the original signal just as a trigger, so if your engine is accelerating too quickly for the ECU dwell calcs to correct, that should take care of that problem.