Has anyone run across a custom built Miller Cycle engine or considered/done it yourselves? I'm looking for any experience from race shops or other hot rodders. This is a different approach to valve timing that holds the intake open way past BDC to the point that some of the cylinder charge is actually pushed back out. This has the effect of reducing physical compression but when coupled with a high efficiency supercharger pushing a lot of boost you still get great power due to dynamic compression more than making up for it.

I know Mazda did it well with their Millinia sports sedan getting 10 HP per liter in stock trim but not everybody has their R&D capabilitys. I've done a bunch of searching but found very little. How Stuff Works goes into more detail than anyone else and that's pretty sad since it's very little information. Link: http://auto.howstuffworks.com/framed...ticleZoneID=92 There's a race engine shop in Ontario that admits they use Miller Cycle cams in their supercharged engines (the boat kind at least). But of course they don't just give out thier trade secrets. Have any of you Canadians heard of "Bullet Engines" and know anything about them? Link: http://www.bullet.on.ca/performance.html

I'm thinking of having a custom cam ground for my truck with Miller Cycle specs. This would allow me to run my Whipple with high boost levels and the existing 9.1 to 1 compression ratio and iron heads. I also have a Duramax intercooler that will be bolted on then intergated into the charge air plumbing. I'm not quite sure where it would all end up but based on Miller Cycle theory it might even improve milage under cruise due to the reduction in pumping losses on this mamoth 8100 cc V8. This in addition to the large increase in power eqivilent to a low compression motor running 10-15 lbs. of boost.

Mazda used a 10.1 static compression ratio but that was with aluminum heads. I'm not sure if by running a point under this if I should slightly shorten the intake event to capture more charge or just stick with the standard Miller Cycle intake valve closing range because of the higher combustion chamber temps and more detonation prone engine. And what about fuel octaine rating? This setup should allow for high boost with pump gas on a 9.1/1 ratio motor.

I also wonder if the delayed intake closeing to allow some charge reversion would play havoc with fuel injector timing. I surmise that with the MAF system A/F ratios will be maintained and if any fuel is pushed back out that it will be used on the next intake cycle anyways or by that of other cylinders therefore the PCM should be able to addapt to any of this quickly.

Some Japanese power plant engineers converted their large stationary turbocharged gas engines to Miller Cycle with only a year to do so. The language translation and numerous mathmatical formulas make the site hard for me to understand, but the I believe overall jist of it is that it was relatively easy to do and works well. I think only valve timing and minor tuning were required to increase power and efficiency by a viable amount. Here's the link: http://www.itepsa.com/samples/AFE199907_CH1_MAIN.PDF

I'm wondering what the rest of you forced induction guys might think on this? By the way I've way into the Thunderbird SC scene for many years now so working with forced induction is nothing new to me. This may just be a way to have cake and eat it too when bolting a big blower onto a higher compression engine than usual like most of us.

Thanks,
Vernon

 

I think you may have exceeded the intelligence of this board (and most certainly mine), but props to you for thinking outside the box. It is refreshing to hear some ideas besides the old "get a 6.0, add blower, add *******'s tune, and have a lemming hotrod truck exactly like everybody else's". Heck, if I didn't have to keep mine as a daily driver, I'd even volunteer to be a guinea pig. One possible drawback may be that such a setup might have driveability problems at low rpm's when the blower isn't making much, if any, boost. Hence it would make for a lousy street car. But maybe I'm wrong. Anyway I say go for it, you may be onto The Next Big Thing.

 

LOL, I may be the king of unanswerable questions on the net. But hey without feedback from guys like you and everyone else I won't be able to figure it all out myself. You're absolutely right about the low end. The engine won't produce much power without serious boost pressure, therefore it must also come on quickly. That's the main reason it took so long for anyone to actually build one for production. Before the Lysom Screw blower was mass produced and cost effective it just wasn't feasible. Roots can do it but the high boost pressures usually put them out of their useable efficiency range and limited RPM to stationary use. As I'm sure you know from your truck, the positive displacement supercharger will easily take care of throttle responce. From what I've read (and drove actually) the Millenia will roll out like a standard 2.3 from idle but by the time you reach 2000 RPM it's on peak torque. However long it takes your supercharging device to produce dynamic compression in excess of the lost mechanical compression is the only lag. The Millenia I drove was in bad tune and had stale gas so I wasn't impressed at the time. It made some power but it didn't have tire shreading torque off idle like a conventional cam/blower engine. But remember that is a wee 2.3 liters hauling up a good sized sedan. My truck has computer limited torque output below 45 MPH to prevent breakage, so I can always remove as much of that as needed and rely on 496 cubes for power below 2000.

One thing I'm not sure on yet is what size this Whipple Charger I have actually is. I got a used kit (complete) off Ebay and it's not listed on Whipples site. I don't actually know yet how much boost this unit is capable of producing on an 496 limited to 4800 RPM. If anyone could shead some light here I would be grateful.

Vernon

 

A miller cycle engine behaves much like a 2 stroke and would require very extensive engine modification,not just a camshaft.

 

Whitt1, can you elaborate? What else would need to be modified? What experience do you have with them?

Thanks,
Vernon

 

Would it be pushing air and fuel back out into the intake with that cam?
Or do your injectors fire as the piston is moving up into the cylinder?
Just curious.

 

You would need a redesigned crank and pistons with a different firing order to accomodate the different power strokes of a miller cycle design.

 

Well, I'm totally ignorant on the Miller Cycle, but something you posted did catch my eye. You mentioned your truck engine has 496 cubes, so that would be the 8.1L correct? If so, please be aware that the stock 8.1 pistons have very thin landings, which easily break under even a few psi of boost. Aftermarket pistons with thicker landings are available.

 

Dude, yes I'm working this out for my 2500HD with the 8.1/Allison. I know what you're talking about with the pistons but I'm from a long history of forced induction motors. I've had very good luck with them (motor parts) by avoiding detonation and excessive RPM. I think detonation and speed will kill them before power will. Actually this provides one more reason the Miller Cycle cam seems like such a good idea when supercharging this engine, added piston safety. Speaking of which, the cam and big blower are the only mandatory changes to convert a 4 stroke to Miller Cycle. Whitt1 must be confused on one or more points here. Any supercharged 4 stroke that puts out 100 HP per liter will run "like" a 2 stroke in the appropriate chassis. I know from the cars in my back yard.

Thanks,
Vernon

 

If what I understand from the howstuffworks website that the Millenia gets about 13% better gas milage than a 2.3L should (if a 2.0L gets 13% better milage because it is 13% smaller), I don't think that you should bother. Unless you would get the same power as an Otto-cycle boosted 8.1L, then just a custom grind cam to get boosted power and better gas milage would be a good idea. But of course it will be a compromise, with better fuel milage than a stock 8.1, but not as much power as a boosted 8.1. I think you should go for the power, and be happy with the increase in power with stock fuel milage. What would 13% be anyway, 1.3mpg? Stick with the attitude that you had when you bought the big block: F___ the gas milage!