So I blew my engine over the weekend

[Jeff20B]

Not that well. 84stock tried it and his results weren't noteworthy. He concluded the Camden SC is best as a daily driver on a nonported (stock port) engine.

You have two major choices when boosing a rotary. If you want maximum power and don't need good driveabilty, go turbo. If you want and need good drivability and want a modest noticeable power increase, get a supercharger.

[Rogue_Wulff]

In my opinion, the best match for a SC is mild streetporting of the intake, but going a bit more agressive on the exhaust. With a 12A, this is even moreso the case.
Anything beyond a streetported engine doesn't seem to work well with a roots blower, unless the blower is geared to work well at the higher RPM range needed to get the most out of the porting.

[Whizbang]

has anyone thought about using the lysolm s/c? they yeild about an 80% eff.

[85rx-7gsl-se]

Originally Posted by Jeff20B

Not that well. 84stock tried it and his results weren't noteworthy. He concluded the Camden SC is best as a daily driver on a nonported (stock port) engine.

You have two major choices when boosing a rotary. If you want maximum power and don't need good driveabilty, go turbo. If you want and need good drivability and want a modest noticeable power increase, get a supercharger.

I guess you are referring to doing both on a 12a? Because a 13BT streetport swap with mild mods (BNR Stage 1, 3" I&E, around 260-280whp on 10psi) is very driveable

[PercentSevenC]

Originally Posted by Low Impedance

has anyone thought about using the lysolm s/c? they yeild about an 80% eff.

I've definitely thought about it. The main problem is that they are very pricey.



But, I mean, just listen to that! It's a bugeye Sprite with a rotary and a Whipple supercharger.

[Whizbang]

Originally Posted by PercentSevenC

I've definitely thought about it. The main problem is that they are very pricey.



But, I mean, just listen to that! It's a bugeye Sprite with a rotary and a Whipple supercharger.

no different than the camben

[85rx-7gsl-se]

That sounds sexy

[Jeff20B]

I have an MG Midget which is similar to a bugeye sprite. It has a 13B in it, too. I don't think I'll be putting a supercharger in it, though.

[PercentSevenC]

Update time.

I switched to a Gatorback belt and tightened it down really good, and now it doesn't slip anymore. Peak boost is around 9.5 PSI, which I'm quite happy about. I wouldn't want to go any higher with the current carb setup anyway. I am toying with the idea of grabbing a TBI setup off a 454 SS and MegaSquirting it. Carbs just aren't really my thing, I guess.

[Phoenix7]

can't wait to see what gains you've made....

[PercentSevenC]

Neither can I. It feels very quick now. I'll try to get a video soon, if the weather will cooperate. The sound it makes at WOT is amazing, I hope my cheap camera will be able to capture it accurately.

[Rotarydave]

I have a couple of the Atkins Set-ups and have done quite a bit of butt-dynoing as well as some engine dynoing as well. I currently have a custom set-up that yeilded a peak Hp of 301 at the flywheel, now before anyone cries BS.... it was done with high octane racing fuel, very expensive NGK Racing plugs, Holley 650, 5 inch (fresh rebuild very tight spec) camden supercharger with a -11 pulley (not recommended for street use), the engine is a 6 port 13b s5 cast irons, new rotor housings with a monster exhaust porting, no internal intake porting but the camden intake was port "modifed" to remove restriction and the external intake ports on the cast irons were ported some. The goal was to prevent any additional overlap allow extra exhausting time and reduce the time of intake restriction(hence the expanding of the ports externally). With the -11 pulley it created a max boost of about 13.5. Now this is not an extreme increase from numbers quoted previously by Atkins in other locations but I think that the engine modifications will allow it to survive longer. Everyone told me my previous engine wouldn't last, something about a stock S4 NA rebuild with s/c and 10lbs boost continually launching at 4k rpms but not shifting until 10k... decreases engine life... don't know why not like i was abusing it or anything..... BTW old engine go BOOM but not until many passes and 10k miles, I asked Atkins to rebuild it, they said I needed another core as there was nothing left of it. Oh well....

Back on topic, I have used both the 5 inch and the 7 inch, I prefer the 5 inch although the 7 inch can rev higher it takes more engine power to do so with the smaller mass the 5 inch does it faster but can go as high, at 10k rpms with a -10 pulley the 5 inch starts to cavitate and won't push more air (as indicated by boost drop) but it does get there in really big hurry due to the dramatic increase in low end torque, plus if I leave my foot out of it I can see 30 mpg. I hope this helps and if anyone wants to verify this with Atkins go ahead, the engine was installed in 2004 and just died late last year.

[PercentSevenC]

My experience with the 5" has been rather underwhelming. Jeff's setup with the -7 pulley (and I think he'll agree) wasn't all that powerful, especially at the low end. My friend's 5" with the -10 pulley was better, but honestly I think my car has at least as much power now with the 7" and -7, and my throttle response actually seems better (granted, my flywheel is a couple of pounds lighter). The only reason I would use a 5" is if I was limited by the space in the engine bay.

[Rotarydave]

Originally Posted by PercentSevenC

My experience with the 5" has been rather underwhelming. Jeff's setup with the -7 pulley (and I think he'll agree) wasn't all that powerful, especially at the low end. My friend's 5" with the -10 pulley was better, but honestly I think my car has at least as much power now with the 7" and -7, and my throttle response actually seems better (granted, my flywheel is a couple of pounds lighter). The only reason I would use a 5" is if I was limited by the space in the engine bay.

I understand what you are saying, Jeff knows who I am we have talked this a bunch elsewhere.

IMHO I used both the 5 inch and the 7 inch on the same motor same carb on both setups, I used the 5 inch with a -10 pulley and the 7 inch with the -7 pulley they pulled nearly the same boost but on the track I was a full 0.5 seconds faster with the 5 inch at the 1/4 mile. Now I also drove several other Rx7s with blowers 5 inch and 7 inch, different setups FI/carbed 12a/13b different engines. I like the 5 inch better it has always given me faster throttle response.

I guess I can equate it this way, it seems to me that using the 7 inch blower with the -7 pulley the engine was having a hard load to turn it over. It was as if the -7 pulley on the 7 inch acted like changing the ft sproket on an bike to the larger gear (yea it dosen't spin as many times to go as fast but takes a much larger energy load to do it)

Regardless of the outcome I am very pleased with the supercharger vs the turbo for street use and you will be also once you start hitting the gas station. If you call Dave Atkins and ask him on some of this he will probably agree with me as my car was the one he did a bunch of testing with while I was stationed there. I know that he has continued testing since I left but last I knew he was recommending the 5 inch exclusively for most rotaries esp if it was a street application. If you have time try to sit down with him and explain everything you have done and what you are trying to do I can't see him not wanting to help you and share info to the same, regardless of what you may have heard.

Again my results may not be typical but I tried to keep them within a controlled standard so I could identify the parts improving or not.

[Jeff20B]

Hey Dave, thanks for your input. I have a 5" SC that has a -7 pulley and it has always sucked; takes forever to get into boost, will only boost under high load conditions like going up a steep hill etc. It came like this from Atkins during the days when they were recommending 7" SCs for everything (we had to special request the 5") so ending up with a -7 pulley where it clearly was incorrect for the application was probably an honest mistake on their part since -7 pullies works so well on 7" SCs. We also recieved the wrong length belt for the 5", sure enough. It is the correct belt for a 7" SC with a -7 pulley, but was way too long for a 5", even with a -7 pulley. I had to get a shorter gatorback, which stretched a little and caused the alt to need to be lifted to its maximum on the bracket, and it would still slip sometimes.

My friend has a 7" SC in his REPU with a -8 pulley and it seems to have problems such as belt slipping even thought it's tight as heck, even while still in vacuum before it transitions from vacuum to boost; sounds like marbles rattling around in a coffee can, belt shredding (black shavings everywhere) etc. He's been too busy to deal with it. He also has a 5" SC with a -10 pulley in a rotary converted 510. He doesn't like how quickly the boost kicks in and would like to try a -8. I'm not going to argue with that because it means I'll be able to get his -10 pulley and a good used belt.

So I suggested this:

My 5" SC will get his -10 pulley and his good used belt (nothing for me to buy, hehe)
His 7" SC will get my -7 pulley and the new belt that Atkins supplied with my 5" SC which was too long to fit a 5", but fits a 7" with a -7 pulley perfectly.
His 5" will get his -8 pulley and he will have to buy one new belt.