Ok, as for the intercooler, the first year of the Super Coupe T-bird had no intercooler. Then the next year they put one on the car and it made absolutely no difference. Therefor my thoughts are that this particular S/C is resonably effecient when it comes to producing heat. SO, if the s/c doesnt produce much heat, but the air going into the engine is hot its most likely due to the S/C being mounted directly above the exhaust manifold. Thats why i think that wrapping the manifold and a heat sheild would work.

Thanks for the input on the 5/6 ports

 

i would hate to repeat myself but if you look at my privious reply. Basicly i need more measurements. i will be happy to draw anything if measurments are given Currently i do not have money for a SC. Im taking my finals next week and the week after that so most of my time will be spent studyin Advanced physics 2, cal 3, visual basic C++, and econ. But i'll be also trying to start my own car after a engine swap.

 

Hey guys,
I still dont get how cfm and psi are related. If you know the cfm required by the engine, and you know how fast you must spin the supercharger to achieve this, then how does psi come into it all? If anyone could explain this, or give a link to somewhere that does it'd be great.
Thanks

 

cfm is volume/time and psi is pressure/area. The S/C has a given PSI, either 5 or 10psi. The superchargers also have a given displacement per revolution as is on their website here

For the M90, it flows 1.5L per revolution. Therefore, at a S/C rpm of 12,000... It would be flowing 18,000L/min... this can be converted to cubic feet/min as well.. Basically what I am saying, is that your psi is given automatically on your roots style blower, and you do not have control of it. CFM however is controlled by varying the speed you spin your S/C. In the end, it means that PSI and CFM are not related with this type of blower (roots style). Centrifugal blowers, however, are like a turbocharger, and they do vary the psi, and the cfm.
Please feel free to correct any mistakes I have in here.
Daryl

 

Thanks for the reply Daryl, I think I'm getting a better grasp of the situation. So would this mean that you would have to spin the m45 twice as fast to put out the same cfm as the m90? Now if your motor only flows say 200 cfm, then using a smaller unit like the m45 would be acceptable, wouldn't it? It just means that the smaller the supercharger is the faster it must spin. One other question I have is why they refer to different pullies in psi instead of cfm...or is this just for centrifugal units? Thanks for your help, sorry I'm a little slow.

 

Of course your CFM isn't constant but but the ratio of SC CFM to engine CFM is constant for a roots type blower. That's why boost is constant for a roots style SC. If the engine is taking in 1.3 L per revolution (is that right?) and the SC takes in 1.5 L per revolution then a 1:1 pulley ratio will give you 1.5/1.3 pressure ratio and by using the equation (boost+14.7)/14.7 = pressure ratio you would get 2 psi boost.

If you run the SC redline of 12000 to match an engine redline of 7000 the boost would be 14 PSI.

Actually the boost would be higher because any heat generated would increase the air pressure. But trying to run an M90 at 14 PSI would hurt the volumetric efficiency so the boost would be lower. So anyway just use 14 PSI as a general ballpark.

Or if you want, you can convert CFM straight to HP. I seem to recall that 200CFM is about 100 HP so the max from an M90 could be something around 250 HP.

An M62 has a max CFM of about 450, it runs more efficiently at the same CFM as an M90, and it would fit in the engine bay better. Unfortunately you can't find them as cheaply in the junkyard.

I'm sure I made a couple of mistakes in there somewhere but I think those are the ballpark numbers.

ed

 

you can mount the M90 sideways cant you? I dont see any reason that you couldnt all its doing is moving air... and there are not meters or anything in it..

 

Thats already been established in this thread. You can mount in anywhere you can run a belt; upside-down, sideways and/or backwards.

 

FYI, wiring the auxiliary ports open does not reduce their restriction at all, since they're fully open at high rpm anyway. All it does is lower low-rpm port velocity, which reduces chamber filling efficiency and hence reduces power and torque at those revs.

 

yes, I am quite aware of this... however, they were seized, well.. damn near.. and I wired them open to get better higher range power rather than having them always closed.

 

Sorry, this thread is so damn long, it's easy to miss.

 

To clear up some things regarding the m90, 1) the s/c does NOT draw 50 hp. A 6-71 GMC, yes but at 42in/lbs of turning torque you are a looong way from 50hp. 2) the first year for s/c Tbird/xr7 production(1989) did use an intercooler, as a matter of fact all post 86 ford and mercury cars with either a 2.3 turbo as well as the 3.8 s/c had intercooling standard. The lone exception is the Merkur xr4ti. Great mod, zbrown. Now to decide ; turbo or s/c.

 

Because the SC is continually putting out air into a small volume between the SC and the engine, the air has no choice but to go immediately into the engine. The ports do not need to ever be closed with a roots type SC.

ed

 

thats wrong... air is already at 14.7 psi, increasing that 5 psi to 20 psi isnt going to change the fact that you need high port velocity at lower rpms for better low end power.

Just because you are increasing the pressure of the "atmosphere" the engine is running in doesnt mean all the tricks used on N/A engines wont still apply... in fact they probably will work better at higher pressure

the only thing that might work a little differently is VDI since it relys on the wave propegation rates thru the air... with higher pressure (aka) denser air the wave speed will be different... but i doubt the change will be great enough to render the system useless

so i dont see any reason not to use the 6pi and vdi systems with a boosted motor... possibly the engagement points of each system may have to be changed, but I don't see any reason why they won't benefit the boosted motor just as much as they do the N/A motor

 

Reading this is so inspirational...

 

this thread is nuts for the amount of replies and veiws for such a short period of time.....paris hilton didnt get this many veiws in the lounge when she was coming out with her vids

 

lol paris hilton really is far less interesting than an eaton SC on the stock TB...serious!!

 

What you say might be true for turbine style compressors but a positive displacement SC works differently. The SC is pumping out a specific volume per revolution and the only reason you have boost is because the engine can only take in a smaller amount of volume per revolution. With such a small volume of piping between the SC and engine any air that does not immediately go into the engine will cause a swift rise in boost pressure which will force the air into the engine quicker. As a matter of fact, boost pulsation can be a problem if the blower is mounted too close to the engine (not likely a problem in the Rx7).

Those ports are there to persuade air from the infinite plenum of outside air into the engine by creating velocity in the intake runners and letting inertia of the air "supercharge" the engine.

In general, positive displacement blowers will move the torque peak down in RPM and it's a good idea to favor the higher RPM because the low end will take care of itself.

Closing the ports may not cause any problem but they are not necessary with a roots style SC.

ed

 

assuming WOT (since at any other time the bypass valve is open) and a pully set to give 5 psi of boost

then the plenum is pressurized to 20 psi... i don't see how 14.7 psi vs 20 psi will behave any differently in regard to port area.

I agree that if the boost regulator was set to decrease boost as the rpm went up to push harder at lower rpm then what you are saying would be true... but as far as I know thats not how the bypass valve works (But I may indeed be wrong... if thats how the bypass valve works than I stand corrected... but id think it would have to be tuned to each engine then?)

 

think about it this way... with a supercharger having higher boost levels will increase parasitic loss. having larger port area will decrease boost. Thus less parasitic loss. Now, how much would we gain by having increased port velocity? would it be enough to counteract the extra parasitic loss of the supercharger?

 

so has Zbrown been around lately? I would like to see an update .. see how things have been running for him so far.
Daryl

 

Nice work! Instead of buying a new intake manifold and fmic, you can just do water injection. It lowers the intake temp buy injecting a small amount of water into your engine. You can use alcohol if you're not comfortable with injecting water. Also alcohol is fuel, 110 octane IIRC, so if you're still running the stock injectors Alcohol injection would help on that area. Most people use a 50/50 Water/Alcohol mix to get the greater cooling effect of water and added fuel/octane of alcohol, best in both worlds. This would be a cheap alternative to an IC.

Good luck. Keep up the good work! I wish my HS autoshop would do something cool like this.

 

This statement is true on many turbo systems as well. If the turbo exhaust housing is a small restriction, the more air you pump through the engine, the greater the exhaust restriction effectively becomes and the greater the loss even though power keeps rising.

The bypass valve on the supercharger actually doesn't have much flow through it. The bypass valve is really nothing more than a pressure equalization port. At low rpm's, the blowby past the rotor lobes has a bigger effect on how much air is actually getting into the engine. The supercharger is always pushing air towards the engine which is why the need for a long manifold really doesn't apply to the positive displacemtent types. The centrifugals would require a longer manifold though. Here is a quote from the article I am placing a link to talking about intake manifolds. This guy really knows his stuff and is very good at modifying superchargers for much greater efficiency. "The distribution was not as critical as originally thought, as the blower is still delivering air to the engine even in NA applications. "

Check out this website for some good supercharger tech info:

http://www.theoldone.com/articles/bl...and-howto.html

 

Thats awesome!!! I love those superchargers, because of the price. We just finished a similar project with an Eaton M90. We extended the shaft section to go in front of the engine on my friend's Probe GT (because of it being fwd). It builds 7-8 psi also. Did you use a rising rate fpr or fmu? We used a Vortech FMU to bump the fuel pressure up when there is boost present. The piping is very very tight for the intercooler. Here's a pic of our setup. The engine bay is very dirty in the pic. It was the first time we had the car started. I know it dosen't look like it, but the rad hose clears the pulley (only by like 1/2 an inch, but it clears, haha).

 

Maybe we scared zBrown off...