project FC3S 13BT-TC(twin charged)
 

long story short i recieved an eaton M90 roots supercharger about 8 years ago that i have been waiting for a project to utilize it, i had originally intended on putting it into my '74 REPU and i will probably still use an eaton supercharger for that project but for now i am allocating it to the FC.

the supercharger needs to be rebuilt before i put it to use so in the next month or two i plan to get the rebuild parts and rebuild the unit prior to making the intake and outlet adapter plates for the SC.

https://img832.imageshack.us/img832/5037/dsc00167l.jpg

end of summer before last i installed the master power T70 i had sitting on the shelf into the FC and sold the stage 2 hybrid turbo, the T70 has an upper range of ~550WHP with the .96A/R turbine as the car sits now, i'm only running it at about half capability and plan to tune it to 20PSI, until i read about the twin charging ideas on the 3rd gen section which got a wild hair up my ass to do the twin charged setup.

the plan as of now is to remove the stock throttle body and run the outlet from the supercharger to the plenum(no throttle body between), make an inlet runner up to a 90mm throttle body which is then connected to the outlet of the v-mount intercooler. before the intercooler is the standard turbo system which will draw the fresh air feeding the whole system. the idea is to have the supercharger build instantaneous positive pressure to start spooling the turbo earlier and drastically improve low end throttle response until the turbo catches up and then feeds through the supercharger, which i will port out for more airflow to match the rotary/turbo needs.

this will take a few months to accomplish and if it all goes well more time to work out the final drive gearing of the supercharger so that it is responsive enough to manage the upper power range as well without eating itself to pieces.

goal is to shift the usable power range down so that the lower RPM range is more usable versus shifting at 7.5-8k to keep the engine in the power band of the turbo, while this setup will reduce the efficiency of the turbo it should still make the engine more responsive all around with just a sacrifice with the upper power range capability of the turbocharger.

i also will be injecting alcohol after the supercharger to drop intake temperatures down to a more reasonable level.

all in all if everything goes according to plan it should make around 450WHP at 20psi and have nearly the grunt of a V8 motor.

criticisms and suggestions are welcome.

Been reading this thread, huh? https://www.rx7club.com/build-threads-292/twin-charged-fd-build-fraternal-twins-940240/

Can't let the FD guys have all the fun.

yes, in fact this may be the first twin charged rotary ever that i have heard about so far. i have seen pictures of the twin turbo/twin charged 20B FD but no one has seen any recent progress on it. i could have this done in a week if i really had a full week to devote to it. ;)

they just started the ideas rolling around in my head and it sounds like a solid idea.

of course someone will now post pics from a japanese site where there is 3 FCs lined up with exactly this... lol! i want to know where they get the time and money from!

Looking forward to more progress on this. Interesting idea.

Mmmm, twin charged.

I have been dying to do a centrifugal SC on my car for a long time, just don't have the funds. Run low boost, maybe 3-4 PSI.

This should be an interesting thread and I'll keep watch of it!

i've never been a huge fan of superchargers - and i know it's partly my close-mindedness, although i have come a long way. i remember the Koenig Competition was the first twin-charged car i ever saw/read about. however, the first car that actually made me think "hey twin-charging might be a pretty cool thing," was actually a Mark I MR2.

anyway, i think if you stay true to the goal you've stated, you'll be just fine. as long you can keep looking straight ahead when the temptation to explore the upper RPM ranges starts tapping on your shoulder, then you may even have something akin to a mildly tuned 20B when all is said and done. i think it's a pretty neat project.

Holy Hell Goodluck!!!! Im keeping an eye on this!

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This should be fun....
My friend let me borrow his supercharged miata for a while, it was a beast. I can't image an fc w/that kind of low end AND a t-70 up top! And good god, what would such a thing sound like?! ?!

May the force be with you.

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F*ckin subscribed!

Been waiting for someone to do this on a rotary.


question(already)...

In theory, would it be beneficial to have some sort of bypass around the supercharger when the turbocharger is creating higher boost pressure? I've read on other compound setups that a clutch is utilized on the supercharger pulley and disengages the supercharger at a set psi.

[QUOTE=nate91242;10460597]F*ckin subscribed!

as stated.

Check out the thread I linked to earlier. Chudsoncoupe is planning on using a clutched supercharger setup so he can prevent things like over-revving the supercharger. The alternative would be to use a larger pulley, but that would also mean the supercharger would spin up slower.

a bypass around the supercharger would be ideal but it is a little more difficult to achieve the desired results, feeding the air through the supercharger will create quite a bit higher intake temperatures and create a bottleneck for the turbo airflow. i'm trying it this way because i already have the auxiliary injection installed which should keep intake temps under control and as a premise to trying alternatives, basically to see how everything reacts.

if the supercharger eats itself apart i really am not too worried as the superchargers are easy to find, cheap and cheap to rebuild, even cheaper than small turbos. of course it will damage the engine also if that happens but the engine has 70k miles on it and the mcmaster carr/rotary aviation/and now goopy style coolant seals have already been compromised about 2 years ago due to the teflon skirt chafing through creating intermittent internal coolant leaks so the engine is on it's last legs as it is so to speak with over 150k miles on the internals now pushing ~350WHP @ 15psi with the small FMIC being the bottleneck in the system(it is going to be replaced with a v-mount and a custom radiator for the v-mount). it has been at this power level for about the past 4 years now, i kept it that way because it was a 100% reliable car at those levels and i have never worried driving it 1000 miles one way while having fun on the way that i would need a trailer to get home.

the REPU is going to replace it as my work vehicle so i won't have to be stuffing 2 short blocks into the back of the TII anymore, which also allows me to replace the old worn out original 207k mile grey interior which i have grown to despise(going to black interior with light red accents, not the ricer painted red crap dash panels, etc) as i can also tint my side windows in nevada legally to finish up the theme of the car which has a very stock-ish look but yet not very stock at all(only giveaway is the 275's in the rear and 2.5" lowering).

i really don't plan on pushing the engine further up top in the RPM range if the power band can be shifted lower, i will build safeguards into my LT8s maps to prevent it from overrunning the supercharger regardless of how much i want to push the engine deeper in the RPM range, it should have plenty of torque that i can set it safely at most to about a 7k RPM redline at which point the supercharger will be cooking if i don't set it's speed down, with the setup i really can't imagine why i would need to try and push the redline higher than 6500-7k. with the simple turbo i would have to take it to at LEAST 7.5k to keep it in the usable power range for the next shift but i could easily push it up to the end of the mapping to 9k.

this is one of the nice things about having the 8.5CR rotors, i am disgusted by how slow this turbo spools but it is the safest engine for these types of experiments.

+1

a quick teardown of the supercharger prior to cleaning and reinspection shows no drastic signs of wear, simple couple wear caused the "rod knock" noise which is typical for the eatons with over 100k miles. minor galling inside the case can be cleaned up, i don't think i will polish the surface as that will probably reduce it's efficiency. the main focus will be on porting the inlet and outlets inside the case.

the cuplrit coupler to the left of the vanes, causing about 1/4" slack in the drive gear(at the OD of the pulley which is where it is important). seems to be made of a phelonic plastic which is now pretty worn. i can't feel any significant slack between the vanes or gears after removal.
https://img831.imageshack.us/img831/5318/dsc00168fz.jpg

https://img708.imageshack.us/img708/1223/dsc00169ds.jpg

be sure not to get any of the compressor oil on you, it stinks like shit and you can't wash it off! lol

total disassembly time of the charger: ~10 minutes.

this one came from a kid who worked at the cadillac dealer with me, he was going to sell it for aluminum recycling so i gave him $20 for it, came from an early 90's thunderbird supercoupe in which the SC was making a rattling noise which is common for his 100k+ mile car. can be fixed in about 2 hours and for less than $100, mostly in cleaning time. i could probably get by with just changing the coupler in this assembly which costs about $30 and spending about 30 minutes cleaning off the oil varnish and going over the roots case surface with 800 grit sandpaper to remove any galling.

for now i just wanted to be sure everything was ok internally while i order parts for it. sometimes it is better to not mess with things if they are working properly so if everything specs out i will reuse the original bearings, clean the internals, replace the coupler, port the case and reseal it. gear lash/endplay is very critical when pressing the vanes back onto the gears, so better to leave sleeping dogs lie, as the oil came out clean telling me the bearings should be in good shape still.

total estimated cost for supercharger, rebuild parts and cleaning supplies: $60 and 2 hours labor.

of course this was an exceptional deal, usually you can find the Eaton M90's on ebay for $50-100 used in need of rebuilding.

and the case after about 30 minutes of light wetsanding with carb cleaner and 800 grit.

https://img600.imageshack.us/img600/8190/dsc00170b.jpg

now for some research on porting styles for the needs of this setup.

one issue i will have to try and sort out is lubricating the rear screw roller bearings, seems they got their lubrication from crankcase gases in stock applications through the intake manifold from underneath. maybe i'll drill some pilots through the sides and just install some grease fittings, or plumb the bottom adapter plate to run to the crankcase vent lines, hmmm. they may survive just fine packing them with grease, just not sure.

i will probably just wind up packing them with grease and sealing the bottom holes that would have gone to the crankcase on the piston motor. roller bearings usually can take a bit of abuse with minor wear with minimal lubrication required, it will see some oil from the turbo.
next step is figuring out how to ideally port the bottom case on this charger, it isn't as open as some of the other versions to open up as i have seen on other eaton chargers.

I wouldn't worry about porting it just yet. I've been reading some DIY's on modifying Eaton's, and opening up the ports can actually reduce efficiency. Some people actually reduce the opening surface area (specifically the two small holes to the side of the main triangular port). Those two holes are for sound reduction purposes on OEM applications, and can hurt the flow. You can't just weld them shut, but if you search you'll see that there are a few routes you can take.

I was not aware of the roller screw bearing lubrication, can you post some pictures of what you mean? I didn't realize this could be an issue.

My supercharger is also apart, do you have torque specs and specific end plate gaskets (are they needed? or did you use silicone) when you put it back together?

i'll check on the specific torque but i imagine it is around 17ft/lbs. the original case used anaerobic sealer, it is an aluminum gasket maker material that is red in color and has a thick glue texture which turns hard when assembled. we used it on aluminum parts such as transfer cases and transmission rebuilds. you can get it from dodge subsidiary dealerships for sure, other makes i'm not sure if they use the same thing. i recognize it because i have scraped it off many many times while rebuilding aluminum case halve assemblies.

i'll get some pictures tomorrow of the bottom of the charger to show the 2 holes leading to the back of the rear roller bearings. i could be on crack and they are just to aid in removal of the bearings and have nothing to do with lubrication as i am not using any service information regarding this specific supercharger.

one other thing i noticed while cleaning the screws is that they are coated with an epoxy to smooth out their surfaces, the carburetor cleaner i'm using to clean everything is taking the epoxy off so i will have to find an alternative way of cleaning the screws, even simply rubbing them with a shop rag seems to be removing the material... ugh.

and yeah, i have noticed various types of porting, most people leave the side vents alone and add a port towards the inlet side of the screws while only slightly modifying the triangular opening to the rear. unfortunately my case opening doesn't give me much room to do this without modifying the whole bottom side of my charger. so i may just start with real basic porting and try different things such as porting that section later on.

Well I know your probably not close to the point of trying to come up with an adapter, but this may give you some ideas. Good luck with the build.

http://www.honda-tech.com/showthread.php?t=2792652

Thats not good, might be a good idea to get new ones after your sure that your system works. I think the coating has two purposes.

1. Efficiency, without it, you won't be able to push as much air
2. Heat, without it, the heat your supercharger compresses will increase greatly.

Also not sure if the increase in heat will warp the screws at all if they don't have the coating. Probably not, but not sure. If this happens, they could clip eachother while spinning.

i'll do a little more digging because i have seen a number of rebuilt eatons with cleaned screws that looked used.

thanks for the link, though not really needing anything that drastic for a standalone setup. i plan on making my own baseplate to taper down to a pipe for connection, also don't have access to a CNC mill nor do i feel like paying $1000 to have a flashy piece made as a one off so it will be a simplified piece and probably not too flashy. it won't even hardly be visible on the side of the engine with the discharge facing down to the spark plug area, the SC will be about even with the top deck of the engine.

i would love to have a CNC mill, it would be nice to be able to do these projects more professionally looking but for my own personal car, it's more for testing now versus dumping money into for bling.

If you want to get into CNC/Mill, here are a few links you might be interested in.

CNC conversion for Sieg X2 mini mill (There are many copies of this mill, even harbor freight has one)
http://cncfusion.com/minimill1.html

Best X2 mini mill I have found. (Largest X and Y travel in its class)
http://www.littlemachineshop.com/pro...ory=1387807683

When all said and done you can have a small CNC machine for around ~$3000. It’s a decent size investment, but it’s an investment into your career, and the returns should be worth it.