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Wondering if anyone has done an e-shaft driven centrifugal supercharger as I'm interested in the idea (like a crankdrive procharger). I don't have an RX-8 but I may buy one in a couple of years, I'm just putting my ideas out for debate. Yes I know turbos are more efficient, but I believe better reliability can be obtained with a centrifugal supercharger. I also like the idea of a linear power band. Most are driven off a belt, which puts strain on the front stat bearing but with a crank driven SC it's a non issue (in my mind). Also with turbo setups if mounted low heat build up could be an issue, affecting side seal life in my mind but this is probably a non issue with the right cooling, tuning, maybe coatings etc. With an SC you can evacuate all that heat since you don't have any restriction there, helping engine life (imo). Was looking into Rotrex centrifugal SC's but don't know how to read the compressor maps yet.
The goal would be 250WHP+, if possible 300WHP tops with an engine that doesn't need to be rebuilt every 10K miles while still holding power at 8000rpm+. In my mind some things that would definitely need to be done is rebuilding the engine, blueprinting, and balancing. Maybe some exhaust port polishing/very very slight porting to help flow a little since I know porting the exhaust is a dangerous game. Light clean up on the intake manifold possibly, maybe an air to water IC to minimize intake piping (another weird idea). SOHN adapter if possible w/ premix, fully adjustable ECU, water/meth injection and lots more. Anyone think it's possible? N/A power from what I've read caps out around 220WHP and that's the best of the best. Never driven an 8 but if it could squeeze out a little more power I feel like it'd be perfect. Looking forward to hearing from y'all.
There have been a few belt driven SCs over the years. Those have worked fine up to around the 300whp level but low down power is disappointing and they never really took off because of that, IMO. Eshaft drive creates another set of issues that no-one to date (AFAIK) has attempted to overcome.
Off the top of my head :
*No room in front of the eshaft due to x-member and power steering.
*how to do the timing wheel
*How to deal with the loads on main bearing and torrington bearing.
If you have all that figured out .... be the first
There have been a few belt driven SCs over the years. Those have worked fine up to around the 300whp level but low down power is disappointing and they never really took off because of that, IMO. Eshaft drive creates another set of issues that no-one to date (AFAIK) has attempted to overcome.
Off the top of my head :
*No room in front of the eshaft due to x-member and power steering.
*how to do the timing wheel
*How to deal with the loads on main bearing and torrington bearing.
If you have all that figured out .... be the first
Not worried about the first 2 I'm sure those can be figured out quite easily, but wouldn't the loads on the main and Torrington bearing be minimal since its driven off the crank? Certainly less than a typical belt driven sc right?
Not worried about the first 2 I'm sure those can be figured out quite easily, but wouldn't the loads on the main and Torrington bearing be minimal since its driven off the crank? Certainly less than a typical belt driven sc right?
I'm no expert. You might be correct on that - or there might be detrimental loads put on the bearings in other ways.
Centrifugal compressor will not be linear, because pressure will increase with RPM. For relative flat pressure you need a screw type.
A mockup from when I played with the thought some years ago, highly theoretical, probably errors, and with "guesstimations" all over:
I'm aware of how an centrifugal SC affects the powerband with rpm, screw types could be an option but I'd have to think about how it could be done. It's all just an idea of mine, don't have an RX-8 in my driveway .. yet. What's the compressor map showing? Red line in the middle?
If I am reading this right, instead of a belt you want to directly mount the shaft of the SC to the front hub to avoid the bearing issues with belt tension? I dont know **** about SC tbh other than the basic concepts. Didn't that ball bearing front hub kit already create a solution for the belt load issue? SC pulley ratio issues, are they 1:1 with the front hub? You may worry about the engine bearings, but what about the SC being battered directly by the engine, clutch and driveline loads? In a way a belt is dampening to a degree to protect the SC axially.
I know the typical argument is that traditional rotaries have amazing exhaust potential for turbo application. However I always thought that the renesis 3(4) port exhaust leans more towards SC application since you dont need to recollect the varying ports. It probably comes down to is collecting the exhaust pulses lose more than the usefulness of the rotary exhaust potential?
For a turbo REN keeping the exhaust split for the split turbine is an issue, mainly due to the siamese. A SC can disregard this issue and just run an enlarged log manifold. (mazda not doing a collector IMO shows it is not a simple feat to deal with the siamese. Granted that could have more to do with no overlap scavenging) Really the only big REN innovation I could think of would be to make an insert that can survive and successfully split the siamese. Then maybe a turbo specific intake.
E-shaft mounted SC needs a gearbox to increase the shaft speed for the SC,
Those SC's are very big in size and used on ProMods.
You will be in a radiator by the time all items are fitted. The SC needs its mounts on the engine (like pillars to clear the belts) which the renesis doesnt really allow. As the front case is very weak compared to an engine block..
A centrifugal supercharger has a linear boost curve, not power curve. Power curve will be almost like a quadratic curve (often called exponential) . As boost rises linear with rpm and boost, creating a rpm² response..
A roots and screw type will have almost a flat boost and you can mount it top side.
Im sharing the same idea that an SC is better suited for a renesis. The Petit racing had screw type and undersized / maxed out at 298hp..
Also screw type is better for higher boost, roots is better for lower boost. This is becouse screew type compresses the air internally, thus heating it even under no boost conditions requiring huge capacity on the intercooler. Roots doesn't compress internally, but instead in the charge pipe after the air has exited, so as long as the engine is not under boost the intake air doesnt get heated by compression of the supercharger.
E-shaft mounted SC needs a gearbox to increase the shaft speed for the SC,
Those SC's are very big in size and used on ProMods.
You will be in a radiator by the time all items are fitted. The SC needs its mounts on the engine (like pillars to clear the belts) which the renesis doesnt really allow. As the front case is very weak compared to an engine block..
A centrifugal supercharger has a linear boost curve, not power curve. Power curve will be almost like a quadratic curve (often called exponential) . As boost rises linear with rpm and boost, creating a rpm² response..
A roots and screw type will have almost a flat boost and you can mount it top side.
Im sharing the same idea that an SC is better suited for a renesis. The Petit racing had screw type and undersized / maxed out at 298hp..
Also screw type is better for higher boost, roots is better for lower boost. This is becouse screew type compresses the air internally, thus heating it even under no boost conditions requiring huge capacity on the intercooler. Roots doesn't compress internally, but instead in the charge pipe after the air has exited, so as long as the engine is not under boost the intake air doesnt get heated by compression of the supercharger.
I got the superchargers characteristics mixed up, realized that. Those crank driven SC's are pretty large but I wonder if a smaller setup could be made, due to size. An SC sized for a renesis would be no where near the size those promods use. Would help space a little bit but could still be in the radiator by the time you get it setup. I also believe an SC setup is better for a renesis, mainly due to the exhaust port. I've seen and researched a fair bit on those petitt racing supercharger kits, but all the info on them is from years and years ago. They make good power but every kit I've seen doesn't rev much above 7000, unsure about the reliability aspect as well.
Last edited by s1ckksn0w; Nov 2, 2024 at 07:45 AM.
If I am reading this right, instead of a belt you want to directly mount the shaft of the SC to the front hub to avoid the bearing issues with belt tension? I dont know **** about SC tbh other than the basic concepts. Didn't that ball bearing front hub kit already create a solution for the belt load issue? SC pulley ratio issues, are they 1:1 with the front hub? You may worry about the engine bearings, but what about the SC being battered directly by the engine, clutch and driveline loads? In a way a belt is dampening to a degree to protect the SC axially.
I know the typical argument is that traditional rotaries have amazing exhaust potential for turbo application. However I always thought that the renesis 3(4) port exhaust leans more towards SC application since you dont need to recollect the varying ports. It probably comes down to is collecting the exhaust pulses lose more than the usefulness of the rotary exhaust potential?
For a turbo REN keeping the exhaust split for the split turbine is an issue, mainly due to the siamese. A SC can disregard this issue and just run an enlarged log manifold. (mazda not doing a collector IMO shows it is not a simple feat to deal with the siamese. Granted that could have more to do with no overlap scavenging) Really the only big REN innovation I could think of would be to make an insert that can survive and successfully split the siamese. Then maybe a turbo specific intake.
Could you link that ball bearing hub you're talking about? I think I might have heard of it on the RX7 forum but I don't know if what I'm thinking is what you're talking about. Never considered the belt acting as a dampener but it does make sense. But yes, I'm talking about a setup similar to what another member mentioned, promods use crank driven sc's as seen above this reply and I've wondered about using a similar setup on the renesis since belt driven SC's wear out the front bearing a lot from what I've read. I suppose with low boost it wouldn't be an issue but with a belt driven SC, more boost = more belt tension to avoid slip = more load on front bearing = more bearing wear (may be wrong but I believe that's how it is). In theory the crank driven SC would overcome that issue.
Another benefit of a supercharger on a renesis like you mentioned is not needing to collect the exhaust pulses like a turbo setup. I read a lot and TeamRX8 would often talk about the 0 overlap design of the renesis, and made an exhaust manifold to back his theory up (old thread somewhere on here). He made a simple, very free flowing log style header and it made more power than I thought it ever would. The heat extraction w/ a supercharger is a big bonus too, unlike a turbo setup where the heat could build up and hurt side seal life. It's a different rotary like he once said .. somewhere. Anyways, an insert that could split the siamese would be great for turbo setups, but I have no clue how that would pan out. The heat would be a problem for sure in my mind.
Last edited by s1ckksn0w; Nov 2, 2024 at 07:48 AM.
This is currently on my table. Same 300 whp aim
TVS-R 1320 front intake with custom snout .. uses the main drive pulley, AWIC .. at the moment making moulds for the intake manifold (on picture its just 3D printed model.
This is currently on my table. Same 300 whp aim
TVS-R 1320 front intake with custom snout .. uses the main drive pulley, AWIC .. at the moment making moulds for the intake manifold (on picture its just 3D printed model.
Yup, I've seen that bearing support. There's a long thread about it on the rx7 forum, went really in depth about the pros and cons of it but I think they settled on OEM being better (couldn't find the thread, maybe sometime I will). Supercharger looks good, should pair nicely with an AWIC. 300WHP is in the golden range imo, post updates whenever.
For the eshaft support, I would add a radial ball bearing on the front cover where the oil seal is. IMHO, removing the toringtton trust assembly on favour of this is maybe OK on an automatic, but on a fully manual .. axial load is much greater and so small radial bearing os simply not up to the task.
For the eshaft support, I would add a radial ball bearing on the front cover where the oil seal is. IMHO, removing the toringtton trust assembly on favour of this is maybe OK on an automatic, but on a fully manual .. axial load is much greater and so small radial bearing os simply not up to the task.
I'm not that knowledgeable yet, but I agree with you about keeping the Torrington assembly. It's there for a reason. If you really wanted to you could add a centre bearing support for the e-shaft in the center iron. Would help support greatly as well as reliability, but it's costly. I'd imagine it'd also help with front stat bearing wear with a typical belt driven S/C as there's 3 areas of support for the e-shaft rather than 2. Quick google search and looks like its just 4K for the e-shaft
If you add a supprt at the front case you almost completely eliminate bending on it (from accessories)
Imho the wear comes only from starting condition untill oil pressure is built up. I plan to use acusump for that purpose..
