Let's have everyone with a 400 HP M90 powered vehicle raise their hand here...

What, just me? That's what I thought. I've done a lot of R&D regarding roots, in the building of my roots charged GTP (and 2-3 friends with similiar cars).

The M90 peaks in effiency in the lower 60s range. It is also a positive displacement blower that compresses air AFTER the blower, or, to put it simply IN the intake manifold. This means it cannot be "intercooled" in the typical sense (A/A style). An A/W will work, but then you have to turn it harder to push through the core, making more boost, and quickly hitting diminishing returns on your boost/vs deltaT map. So you set this all up, at great expense (for a proper tune) and you still have a hairdryer stuck to your engine, pushing horribly inefficient, incredibly HOT boost into an engine that is VERY sensitive to knock.

case in point, I've watched 3 friends of mine grenade WELL tuned piston engines, with hypereutectic pistons, on 9-10 psi of boost, because they went lean in cooler temps with M90s.

If you want to spend the money to put a power adder on your engine, go turbo, it WILL save you headache in the long run, and you WILL make more power.

Now, if you really are dead set on supercharging (which does kick serious *** when done right). Put on a screwcharger (i.e. whipple, kenne belle, etc). Those blowers compress the air IN the supercharger, and exhale compressed air into your manifold. Typically these are still air/water intercooled, because of space constraints in their typical applications, but in theory a/a would work (but be less efficient in this case). These blowers have the power curve of a roots (read lots of torque, right away) and the efficiency of a turbo. The only real downside of a screwcharger is cost....

regardless, this has been discussed enough times on the forums, I'd suggest a search if you want to know more. I know SonicRat and 88IntegraLS have discussed the merits of screwcharges, and the general ***-tacular-ness of the M90 (and most if not all roots chargers).

 

Roots blowers aren't meant for rotaries. Of all engines, rotaries are the least tolerant of knock, and roots blowers discharge the hottest intake air of all superchargers. The Eaton series is more refined than old style blowers, but air is still getting punched back and fourth through the blower exit port as it flows through, which, through viscosity friction, heats it up. Furthermore, roots blowers boost to discharge temp graph goes non-linear after half a bar gauge pressure.

Let's face it, turbos heat up intake air too, but at least they can do 15 psi without turning into hair dryers.

*edit* AND YES I'm biased, haha, just look at my avatar. Evil Aviator counterpoint in 3 posts....

 

His CFM calculation is correct for the given values. You don't need to convert the 13B to 2.6L unless you use the 4-stroke piston engine formula for CFM.

I think his 88% efficiency is a reference to the supercharger's volumetric efficiency, not thermal efficiency. An M90 would have roughly 88% EV at about 10psi boost. It appears that he played a shell game with the poor thermal efficiency by hiding it with the unrealistic intercooler setup. I smell a salesman.

I think what most people on this forum don't understand is that a Roots blower is a LOW BOOST supercharger. As long as that concept remains in focus, you can find several viable applications for rotary engines.

 

Three?

 

Yeah so no one has published a boost to discharge temp graph for a roots blower. It's probably because it would show that the blower starts getting very high intake temps which rise at a non-linear rate compared to boost pressure, and I'd wager that this curve would start taking off at about 8 psi. Come on man, if it isn't obvious to you that the oscillatory nature of the airflow out the blower port is a source of extraneous friction, and that viscosity related friction is based a multiple of velocity, which must go up for a higher boost level, I'll just have to ask for your designer # and engineering license, to make sure you don't go designing front bumper "splitters" or canards for Dltreezan's next body kit.

 

Yes, I made mention that he was using VE (which is actually higher than 88%), which is a pretty useless number for the most part, it just means it doesn't 'leak air', but what's kind of more important is the temp it exits at even if it doesn't leak it.

 

I have some sitting around that are results of boost vs. temperature at a given restriction level, conducted on a custom M90 supercharger dyno, if you'd like to see them.

 

I would.

 

We all would!

 

http://www.automotive.eaton.com/prod...argers/M90.asp

I still don't know what you are talking about.

The VE is not useless because it is a very large factor in determining how much boost will be produced at a given engine and supercharger rpm.

I have some older M90 charts that do in fact show the M90 at about 88% VE @ 14,000rpm and 10psi, and that's the highest VE it achieves at 10psi. The VE goes all the way down to about 60% @ 4,000 rpm.

 

[QUOTE=Evil Aviator]http://www.automotive.eaton.com/prod...argers/M90.asp


I still don't know what you are talking about.


QUOTE]

The designer # was a joke . . . based on something you posted a long time ago, so nevermind. As for the nature of a roots and how compressed air from the intake manifold will travel into the blower for a split second before the lobes push it back out during the lobe cycle, I thought you knew about that. It's in supercharger faq's. Air inside the blower is at ambient pressure and when the lobes open up the next chamber of air being shoved in, the compressed air inside the intake manifold will meet it. Then there is a pressure differential and backflow, before the pressure equalizes inside the blower and shoves the air back out........ ? My beloved lysholm compressors wouldn't have that problem, hahahaha!

 

Yeah, I was well aware at lower RPM's the VE drops, but every chart I've found so far showing any gen of the m90 has always showed about 91-93%, while not a very big difference, that's all I've found. Also, the reason I say VE is pretty useless for the most part, is that in calculations it works well to determine CFM/etc moved, but figuring out the relative 'boost' (which I am leading to be, in terms of psi), it doesn't do much good since, obviously, the hotter it is, the higher the pressure will be. But anyway, basically we're continuing on in a part that didn't matter for what I had mentioned to begin with, due to it's poor adiabatic, it's incapable of the 300+mark. But, good information is always great! Thanks for all the comments/corrections/etc.

 

Darn, I'm too old to remember. I will need to look it up.

Ah, carryback volume. I still don't understand the "linear" reference.

The Lysholm still leaks some, but not anywhere near as much as the Roots.

At what boost pressure? My older charts show 91-93% VE at 5psi.

The resulting performance of the engine will be a function of the density ratio. Density is affected by both temperature and pressure.

 

Yes, density would involve VE (and obviously temp), but just to make sure I'm understanding right, this doesn't leave room for AE which would indicate that to compress the air to a certain level, it's going to increase it's temp by a great ammount, is there a calc that incorporates both?

 

Density Ratio = Pressure Ratio / Temperature Ratio

Pretty simple, eh?

 

Ok, I'm understanding that part, I'm just trying to figure out where in most of the calculators listed here it takes into consideration that, most of them I find just do VE and boost.

 

I guess I don't understand the question. Which of the variables are you having difficulty placing in the equation?

 

Ok, for example, most calculators that guesstimate HP based on fuel ratio, displacement, ambient temp, etc, that allow room for intercooler & turbo equations, usually just have a VE field, what I'm saying, is how would you calculate, say a VE of 88% and a AE of 52% at say 8psi, at 7500rpm (engine speed), this is what I can't seem to find very well. I've generally multiplied the VE and AE together, and used the resulting number as a 'low' estimate, which has always seemed to work well, but I know it's not right.

 

Anyone consider the M112 supercharger? I believe they come off the Mustang Cobras. Those should flow more.

 

I looked at the M112 a while back. It looked like an ideal solution for a heavily ported 13B. Lower intake temps and HP loss for anything over about 5psi. Too bad I haven't seen any for sale cheap...

 

geez. every few months someone brings this subject upa nd everyone fights about the potential/actual results members have seen. I say go for it if you want to spend more money then you would on a t2 swap but want to do something different. I feel and always will that the T2 swap is easier and much more upgradable. Where do you go after what sonicrat has??

 

on the subject of the "un-intercoolability of the m90 blower" you could try water injection. i'm not sure of how much it will lower intake temps, but it would help a bit at least.

 

you absolutely CAN intercool an M90


i had a thunderbird supercoupe... i added an IC to it ... you have to do water to air though

 

The supercoupes COME intercooled.

 

added a better one