So How Fast Can One Spin The Little M90...?

[AutoXRacer]

Looking for my next power mod, VMP gave me a couple of options; overdrive crank pulley to soin the M90 faster for more boost or long tube headers...none of which will give me results as the VMP 500HP kit, but a slight satisfying power boost without taking the engine part...

I met a fellow ROUSH owner in south FL which is pushing a little over 500HP at the wheels with an M90; he basically has the 500HP kit, overdrive crank pulley boosting the M90 to 12 PSI, plus headers and an upgraded heat exchanger; plus some nitrous, but thats one top of the 500HP.

So my question is, how fast can one spin the little M90...?
How fast can you spin it before you reduce its life or kill it...? Keep in mind this is a daily driver...

Looking at the available overdrive pulleys, Innovators has a 10%, 15%, and 18% overdrive pulleys.

According to VMP, the 10% overdrive will yield me an extra 1 PSI of boost...
Anyone know what the 15% and 18% will yield?

Any insight will be greatly appreciated!!!

[gabrieldy]

I started with JBA custom ceramic coated l/ts, BBK t/b and the Roush 12%OD balancer and was seeing about 12-13 psi. More boost = more heat so I also upgraded to an AFCO heat exchanger. The biggest diff I saw from the balancer was a nice increase in Q and it spun up a lot quicker.

[Roushinator]

http://www.fnsweet.com/forums/search.php

[0NF1R]

nice....

im also part of the blown dd groupand have had the same concerns about ideal boost range daily driving in comparison to powertrain life....

im still a noob at this type of power so i dont want to boost my beast straight to its grave :-)

also, any pics of your after market heat exchangers installed on your beasts is greatly appreciated :-)

[DiMora]

Look at the above closely. The design limits the engineers planned on the M90 were a max pressure ratio of 1.7. That is equal to about 10 PSI and just shy of 18,000 RPM - around 550 CFM or airflow (M90 displacement is 90 cubic inches, which is 1.47 liters). The problem with the M90 is that when you start spinning it that fast, you start generating a LOT of heat without a commensurate return in the form of horsepower.

Eaton only mapped it to 13,500 RPM. It's peak efficiency occurs at 6,000 RPM and 1.3-1.5 PR...around 4.0 to 7.5 PSI of boost.

[flyby763]

cams ftw

[NastyStang113]

Keep in mind that mods like cams, long tubes, heads will also reduce boost so that means you'll be actually able to spin the blower faster. Personally if it was my car I'd go with a set of longtubes and than cams, possibly heads. Pypes makes a set of headers that uses 409 stainless and is a direct copy of Kooks for $499. I'm actually thinking about throwing a set of them on my car once I spend some money on some other things.

[redfire427]

Gerald,

Your question parallels another forum topic from today. Personally, I think you would be wasting your time and money by seeking more power out of our little huffer. You would be way further ahead by selling your current blower and adding the TVS. When you add up the cost of headers, possibly cams, overdrive crank pulley, re-tuning, etc, the price becomes absurd and I am assuming you would be doing the wrenching yourself. Just wait until the Florida summer heat comes and see how hot that little M90 gets as you are new to the "overdrive". In my opinion, the extra heat generated by an overdrive crank pulley would be a problem waiting to happen.

[Avaldes]

So looking at the map that DiMora posted, it is easy to see that we are already past the peak efficiency point on our blowers. I think that spinning it any faster will put it past the point of diminishing return. That explains why everyone that is running an OD crank pulley has problems with heat. You aren't getting any more boost efficiently, just creating more friction and heat.

TVS would be the right call with an underdrive pulley set. If I had the cash, that would be my upgrade of choice too. Actually my upgrade of choice would be the full P-51 engine upgrade with long tube headers and CNC'd heads and cams, making about 700 RWHP

[DiMora]

So looking at the map that DiMora posted, it is easy to see that we are already past the peak efficiency point on our blowers. I think that spinning it any faster will put it past the point of diminishing return. That explains why everyone that is running an OD crank pulley has problems with heat. You aren't getting any more boost efficiently, just creating more friction and heat.

TVS would be the right call with an underdrive pulley set. If I had the cash, that would be my upgrade of choice too. Actually my upgrade of choice would be the full P-51 engine upgrade with long tube headers and CNC'd heads and cams, making about 700 RWHP

Indeed...now look at the TVS blower...it is much more efficient...and if you drive it with a LARGER snout pulley such as Carmen' 3.47" and keep the stock crank pulley, the TVS is just loping along...it barely even whines, is super efficient, generates very little heat, and makes more power than our non-forged engines can handle. And when you get forged, you can turn it up to 18-20 PSI with the Roush-supplied overdrive crank damper and a smaller Carmen's pulley and make 650-700 RWHP.



With Carmen's 3.47 pulley and the STOCK GT drank damper, you get a drive ratio of 1.908:1. At that ratio, I run a peak of around 12 PSI currently at redline - that is roughly 1.82 pressure ratio. At 6500 Engine RPM (the red-line I am using) my TVS is spinning at 12,402 RPM...and I am still at 67% efficiency per the chart.

- You can also see that between 8,000 and 11,000 blower RPM, the TVS 70% efficient. That correlates to an engine RPM of 4200 to 5765 where you are still in the really sweet spot!

On a stock TVS setup with the Roush supplied 7" damper and 3" snout pulley, your drive ratio is 2.333:1 So at 4,000 engine RPM our TVS blower is moving at 9332 RPM.

[gabrieldy]

I'm running the 3.25" TVS pulley from Carmen and see about 11-12 psi but that is with L/Ts.

[DiMora]

Here is an Adobe photoshop overlay I just made matching the Pressure ratio and flow rates to the same scale. You can see they are two completely different animals. The M90 is perfect for low-boost applications...up to around 8 PSI of boost and around 15,000 blower RPM.



The M90 efficiency rings are very hard to see. Moving from the M90's peak efficiency (62%) the rings are 62,60,58,56, 54, 52, 50 etc.

If you don't care to strain your eyes, here are some comparisons:

At the M90's peak efficiency of 62%, the M90 is spinning at an RPM of 6000. That gives you 5-8 PSI of boost (Pressure ratio of 1.3 to 1.5).
The TVS, when producing 5-8 PSI of boost (Same P/R as above) is at a blower RPM of 4,000 and is 68% efficient.
So the TVS is spinning 2,000 RPM SLOWER than the M90 and is 6% more efficient.

Let's start spinning the M90 faster now...

Let's go to 10,000 M90 blower RPM....with Carmen's 2.57 pulley and a 6.5" stock GT crank damper pulley, our ratio would be 2.529:1 so our engine RPM would be 3,955. At a P/R of 1.48 (roughly 7 PSI) the M90 is now 56% efficient.
To make the same boost (Same P/R) the TVS is spinning just shy of 7,000 RPM and is 71% efficient - advantage 15% in favor of the TVS.

Let's go the the end of the M90 chart now at 13,500 blower RPM. With a 2.57 pulley and stock GT damper, the engine RPM is at 5338. At a P/R of 1.5 (around 8.0 PSI) the M90 is 48% efficient.
The TVS (same boost (P/R), and flow rate) is spinning at 9,000 RPM and is 71% efficient. Advantage 23% in favor of TVS...and the TVS is spinning now at HALF of its design max RPM (18,000).

If I recall correctly from when I had my M90, a "realistic" max boost with an M90 and 2.57 pulley is right around 10 PSI. Let's go to red-line with the M90 with a 2.57" pulley. Let's call red-line 6500 RPM which should be safe for the engine, and assume we are making 10 PSI. We will say we are running a Carmen's 2.57 pulley and stock damper again...so 2.529:1 drive ratio. The M90 is now spinning at 16,439 RPM. It sounds awesome (Wheeeeeeeeeee - I do miss that M90 whine). The M90 is now off the efficiency chart. We know it's efficiency is somewhere less than 48% efficient...again boost is going to be right around 10 PSI.
The TVS to make the same 10 PSI (P/R 1.68) will be spinning at just shy of 11,000 RPM - and still be 70% efficient. So the TVS is going to be AT LEAST 22% more efficient and have lots more room to spare.

Using this chart one more time:



Let's assume as they did in the above test that we used a 1.975" M90 blower snout pulley (or an overdrive crank pulley) and spun the M90 to a screaming 19,746 RPM and made 12.6 PSI (1.85 P/R) with the M90. The drive ratio would be 3.291:1. Engine RPM would be 6,000.
What would it take of the TVS to make the same boost?
-At the same engine RPM with the Roush supplied 7" crank damper and 3" snout pulley, the ratio would be 2.333:1 At the engine RPM of 6,000, the TVS would be spinning at 13,998 RPM. It would be 64% efficient.

I'm not trying to disparage the M90 in any way; rather, I'm trying to make the point that (in my humble opinion) if you want more than about 430 RWHP and want to keep the M90 installed, you are going to need cams, longtubes, and the cost starts adding up to the point where you are better off just putting on a TVS (half day install) and selling your used M90 vs. the hassle of installing cams, longtubes, etc.

[AutoXRacer]

Wow, wasn't expecting this in depth discussion with supporting data... Great job DiMora; really appreciate it!!

So I guess at best I can spin the little M90 to 9 PSI for an extra 30HP...without any ill effects according to my tuner.
Price tag would roughly be in the $600; overdrive pulley and tuning.

Cams are out of the question as far as I'm concerned... I don't care much for a rough idle to gain more power.
Long tubes are temping depending on install difficulty and overall gains.

I was debating the super-spinning of the M90 as opposed to going all out with a TVS (and possibly) forged block...
I am really happy with the power now...ideally, I just want another 30-40 and I would be set where I would not feel the need to go TVS/build.

I don't include the long tubes into the cost of M90 vs TVS since its a mod that is independent of either...whether you have a M90 or TVS, you will probably still go with headers; that also goes for an upgraded heat exchanger and radiator.

So basically the answer to my question would be that I can probably go with the 10% overdrive crank and not cause an ill effect and make good power...and still retain that sweet whiiiiiiiiiiiiiiiiiiiiiiiiiiine.
Headers, upgraded heat exchanger, and new more efficient radiator would help in restoring some efficiency or reducing the extra heat caused by the over-spinning.

Does this rational make sense...? Is it rational...?

Also, just for a data point; anyone know what the Innovators 10%, 15%, and 18% overdrive pulleys yield as far as boost with a 2.57" pulley on a M90?

Thanks again for all the data!!!

[Wharf Rat]

That explains why everyone that is running an OD crank pulley has problems with heat.

I haven't any problems with mine and I live on the hottest place on the planet. It's almost daily driven, road raced, drag raced, and gets spun even more since it's pushing 4.10s.

After I did the longtubes I thought about going from the 10% OD up to the 12% to get some boost back but really I am done spending money on the M-90. It's gotten me were I wanted to go and will keep me entertained till the enevitable glorious day that the UPS man drops off my TVS.

[AutoXRacer]

I haven't any problems with mine and I live on the hottest place on the planet. It's almost daily driven, road raced, drag raced, and gets spun even more since it's pushing 4.10s.

After I did the longtubes I thought about going from the 10% OD up to the 12% to get some boost back but really I am done spending money on the M-90. It's gotten me were I wanted to go and will keep me entertained till the enevitable glorious day that the UPS man drops off my TVS.

So your current setup is 10% OD...? What kind of boost were you getting before the long tubes?
And after the long tubes? Did you notice a decrease in power after the installation of the headers?

[Avaldes]

DiMora, thank you again for posting some real engineering data. This is exactly how we select components in the aircraft world for propulsion systems. It's a little more complicated because of altitude and airspeed, but you are well on your way to a practical engineering degree in supercharger design

AutoX, I can't tell you that it won't hurt your SC to spin it faster, because as you can see, you would be well past the peak efficiency point. So the extra heat would have to affect the life expectancy. Does it cut into the design margin, or does it shorten the life of the blower...I don't know?

[Young Stang Owner]

Keep in mind that mods like cams, long tubes, heads will also reduce boost so that means you'll be actually able to spin the blower faster. Personally if it was my car I'd go with a set of longtubes and than cams, possibly heads. Pypes makes a set of headers that uses 409 stainless and is a direct copy of Kooks for $499. I'm actually thinking about throwing a set of them on my car once I spend some money on some other things.

Do you have a link to these headers you speak of? I have kooks O/R X-pipe ready to be paired up with kooks LT's but if what you are saying is true then i am very interested in getting a pair of these. Are they really an exact copy? Shoot me a pm Thanks.

P.S. Sorry for going off topic here

[AutoXRacer]

Not off topic... POST THE INFO NASTY!!!

[redfire427]

Jonathan,

The key word in the above quote is the "exact copy" is made from 409 stainless. These headers will develop surface "rust" ( turn somewhat orange ). The Kooks headers are made from much more expensive 300 series stainless steel which will not turn orange. They may turn somewhat purple with heat though. Either set could be ordered with a ceramic thermal barrier coating which would prevent discoloration, but add a couple of hundred dollars to the cost.

[NastyStang113]

We can look at efficiency numbers and flow data all day long but it's not so black and white in the end. A compressor map might say it's only 'good' up to 8 or 10 lbs but there are plenty of people making over that without issues. Wharf Rat has one of the fastest M90 cars that I know of so he must be doing something right.

Do you have a link to these headers you speak of? I have kooks O/R X-pipe ready to be paired up with kooks LT's but if what you are saying is true then i am very interested in getting a pair of these. Are they really an exact copy? Shoot me a pm Thanks.

P.S. Sorry for going off topic here

Not off topic... POST THE INFO NASTY!!!

Lethal Performance and a lot of others vendor sell them for $499. Pypes uses a set of Kooks for their designing and someone on S197 Forum actually bought the set of Kooks headers from Pypes at a race. It is 409 stainless like I said and Carmen mentioned. I don't see it being an issue unless you're living in a state that sees snow and salt than I wouldn't recommend anything but the absolute best and that's Kooks or American Racing. I think for both of you they would be a good mod. I thought I had heard Pypes longtubes will work with their mid pipes as well but don't quote me on that. I need to find out because if that's the case I could get a set of longtubes for $500. If you had to there are places who will ceramic coat a set of headers like this for $150.