Im in the process of building a supercharged rx7 for drag racing. Im having a hard time finding info on the subject and was wondering if anyone has or is currently racing such a vehicle, thanks.

 

First you post on a wrong section. Contact busted7, he have a supercharged FC running alcohol but he have a hard time getting it running right. I advice is to turbocharge it.

 

there is a can in NZ running a big SC and a 20B with PP's

 

there was a guy on here a while back who bough an FC already supercharged,
and a few days back there was something on sc'ing an FC too

heres that... https://www.rx7club.com/2nd-generation-specific-1986-1992-17/fc-supercharger-write-up-711116/

 

There is not really a whole lot of info out there about supercharged rotary engines- but here's a start-

http://pbgarrott.tripod.com/pgsupercharger/index.html

I have recently supercharged my 88 vert, and am in the process of adding a BOV and Microtech LT8. The Paxton kit is what I used, bought from a forum member here about 3-4 months ago.

 

www.camdensuperchagers.com is the link for a roots blower. The site pretty much sucks and has very little info, so I would call them up if thats the route you want to go. The price that is easy to find on the website is wrong now. If you go to the supercharger pricing guide (its around there somewhere) and choose your blower you will find the setup is now about $5500. It comes with an AFPR, Microtech LT-10 (IIRC), TWM ITBs, and associated hardware so thats why its so expensive. As it is ordered it appears to be a complete package.


For drag racing a roots blower with meth injection is probably a superior setup to a centrifugal blower. The paxton type set ups only see full boost at redline, whereas the roots blowers tend to see almost full boost instantly, with the meat of the powerband being mid rpm.


BC

 

camdensuperchagers? shouldn't it be superchargers?

http://camdensuperchargers.com/

 

yep, missed an r. the work keyboard sucks.

also I was informed in another thread that you can still buy the barebones kit if you wish, say you already had a standalone.


BC

 

Thanks thats alot of help. This project will take a while to complete so im trying to get the best info out there.

 

The search function will be your best friend for this project. Good luck!

 

If you intend to use a 13B, that's going to be a lot of time and effort (not to mention money) to run low 15s.

Unless you have a specific reason to supercharger, you should look at what is being done on turbo cars. You'll make far more power for a lot less money, with basically bolt on stuff.

 

I understand what your sayin about using a different engine. But i plan to build most of the parts myself. I want to see the potential of a 13B first hand, i believe with the right tuning and info i can run good times. I do have a budget and if it looks like i might go over it ill concider something else. But for the time being ill have to use the 13B.

 

Been there, done that. Supercharger=awesome for a daily driver, wonderful torque, great reliability. Turbo=more power, lower ET.

 

He's not telling you to use a different motor, just a different method of forced induction.

Turbos are much cheaper to set up for big power. Superchargers, although they don't have the lag of turbos, are much more expensive/difficult to get big horses out of.

Oh yeah, and as an SC'ed 13b driver, I concur with the above poster.

 

You have to decide what you are wanting to do.

If you are wanting a drag car then a turbo is probably the cheaper easier way to go about things. Its all been done before.

If you want more power, but want to keep the feel of an NA 13b then a centrifugal is probably your friend. Keeps the high revving nature of the car with low end power being kept down.

If you are trying to change the nature of the car, ultimate power isnt your goal, AND you are trying ot be different, then a roots blower is probably your ticket. you get low end instant torque that is now just becoming available with dual BB turbos, a strong mid rpm hump, and some increase up top. It will completely change the nature of the engine in relation to NA, turbo, or centrifugal blower. The nice thing about a roots blower is the feeling of complete connection to the engine. There is no disconnect like there is with a turbo (as imperceptable as it is), and there is no gradual rush of power that you get with a centrifugal blower. Its a very connected feeling.

That being said you can almost get the same feeling with a smaller turbo. And just like with a roots blower, your top end will suffer some in relation to a more appropriately sized turbo.

personally i would love to see someone to a full build with a roots blower. its simplier in design, and in my opinion has huge potential with such a high overlap engine like the 13b.


BC

 

I was not suggesting you change engine, but your method of forced induction. As mentioned already in this thread, the power band of a supercharger is very narrow compared to a turbocharger. You're stuck running high boost down low which overspeeds the blower up top, or running high boost up top which results in horrid low/midrange.

You will not be "seeing the potential" of the 13B with a supercharger.

I'm not against superchargers per say, but it has been tried, tried and tried again. The results are never that great when you compare with an equal turbo car.

What's nice about a properly set up turbo system is that you can basically set a boost level and have that boost level through the entire RPM range.

 

thats not totally true. A properly chosen roots blower will provide a very significant increase in low end torque, and meaty mid-rpm band, and not overspint he blower up top. Its all about choosing your blower correctly. With a centrifugal blower you get a very peaky power band, but a good roots blower can provide you with avery broad level torque curve through out the rev range.


For instance, an MP62 would give a ridiculous amount of boost down low and be severely overspun and out of breath up top. Or conversely you could underdrive the blower and get little boost down low anda peaky curve up top.

However an M(P)90 Gen 5 blower (the 9 inch on the camden site i think. THey arent clear how their blowers compare) with an appropriate pulley will give you a very broad torque curve and not be peaky at all.

just like with a turbo choosing the right blower for your application is incredibly important. Magnuson is also introducing a new 4 lobe rotor with the new vette ZR1 that is going to have adeabatic (sp?) efficiency at about 70% at operating speed. That same set of rotors is going to find itself in roots blowers all over the aftermarket very fast. Thats turbo efficiency territory. With a good A/W IC or meth injection you could see roots blowers returning power figures very similar to a turbo with a wider torque band. There will be some parasitic loses due to direct driving the blower, but there will be flow gains due to an open exhuast, scavenging from a good header, and the lack of exhaust contamination due to overlap/exhaust back pressure. So the ultimate output will be very close to that of a turbo.

But in the end a roots blower is almost always going to end up more expensive/hp than a turbo set up on an RX7. Simply because the RX7 came with a turbo so the parts are readily available.


BC

 

For reference:




100 m^3/hr = 58.857 cfm.

So the M90 equivalent of the TVS blower, the R900, will see 70% efficiency between 294cfm and 412cfm ata pressure ratio between 1.6 and 1.8.

So between roughly 9psi and roughly 12psi the blower will provide the above airflow at 70% efficiency.

At 3000rpm, assuming 90% VE a 13b at 9 psi should consume about 190cfm. That is about 65% efficient at 9 psi.

At 6000rpm, assuming 90% VE a 13b at 9psi should consume about 385cfm. That put the R900 in the meat of its 70% efficiency.

At 9000 rpm given the above variables, 9 psi, 90% VE(dont we wish we saw 90% VE at 9k rpms, but to keep things *simple*) a rotary should consume about 578.8 cfm. At this pressure and flow the R900 is at 65% efficiency.


What this means is that a TVS roots blower will provide a 13B with 9psi of boost between 3000-9000 rpm at nearly 70% efficiency. Given that the VAST majority of us wont see 90% VE at 9k rpms its likely that the blower will provide 70% efficiency the whole time. At lower rpm the efficiency is still up around 65% for the vast majority of the time.

Thats turbo territory. Thats a good turbo's territory. The TVS is going to make a big case for roots blowers in the aftermarket where turbos we're the rave for efficiency for decades. Thats a meaty torque curve everywhere you look, from throttle tip in to redline with the throttle response of a blower.

TVS is going to be sweet.

 

For reference, this is a map of the M90, or the 9in blower on the camden site.




You can see quickly that the blower, even at its most efficient is only about 62% efficient. At 9 psi with the above variables the blower is about 58% effcient at its best on a rotary. At its best. And this is the 5th gen blower, which is WAY more efficent than the 3rd gen blower found on the 1997-2002 Grand Prix GTP, and is probably the camden SC. Given the rotary's tendancy to not like hot air, I can see why few have had any luck using a roots blower in the past. Given the cost and results I would stay away from it to. Go with a TVS blower and things get a **** ton better.



BC

 

One thing I've always assumed is that if you get a good sized roots style blower on there to provide good boost down low, isn't the inertia of the blower significant to the point where it's sucking up most of power created just to spin it?

Keep in mind that I've not looked at superchargers in almost 9 years, and then only briefly.

Are there any examples of high HP 13Bs running superchargers that I could look at?

 

I was always under the impression that superchargers were better for higher displacement piston engines

 

Thats alot of info to work with, you guys know your stuff. Do you think a 13b with no modifications can handle 30lbs of boost or higher?.

 

Superchargers do have a lot of inertia.

I haven't dealt with any newer ones (M62 M90 671 is about it).
I also haven't used centrifugal type superchargers because I would sooner have a turbo than a peaky supercharger.

I never noticed the extra inertia, the throttle response is better than with an NA.

A positive-displacement supercharger makes the engine act like a higher displacement NA. In first gear, all you can do is spin the tires anyway, so it doesn't really matter if the inertia is higher. In the higher gears, the inertia makes much less difference.

Basically a .5bar supercharger setup on a 13b would act like a NA 20b. I doubt that the supercharger has any more inertia than an additional rotor. (I do not have numbers to back this up as I have no access to rotational inertia numbers for the superchargers.)

Turbochargers also have inertia, commonly called turbo lag.

The power requirement from the engine is approximately the same either way, the supercharger adds more heat to the air, limiting the boost considerably below what a turbo can give. If this TVS supercharger can really achieve 70% isentropic efficiency, then it will be equivalent to all but a very large turbo (about 80% IE).

In my opinion, more AutoXers should use superchargers, as the turbo just starts to spool up as you lift your foot for the next corner. If you want all-out power, the turbocharger is still better because you can control your boost, where on a supercharger, it is fixed.

 

This is really a very old mentality on turbos.
With the introduction of ball-bearing centers - i.e. Garrett GT-series - you can get turbos to kick into boost as low as 2,000RPM, if you want.
This has a lot to do with sizing (turbine section) also.


-Ted

 

Just to add a bit the the power/money ratio touched on earlier. The camden kit costs over $2000 and only claims to make 176 hp, my friend made more than that to the wheels with a $300 safc and a tune on stock ports with no other mods. Thats a ridiculous waste of money if you ask me.