Your RPM of power depends on a few variables. It depends on what you are looking for. I do not like the peeky HP crap. I would rather have a nice curve (like my dyno!) that allows for continious usage of power if needed.

If you want higher RPM, besides doing internal tricks to withstand the constant rotation, you need air to feed it. You need a good port of the engine, and a turbo to match. A turbo too small will not be efficient, and will have a difficult time.

Get an engine that can breathe mated to a turbo to allow it not to choke, and you can run your high rpm range. I guess for peek horsepower you should setup this way.. but until you have the power, it is just a numbers game vs. practicality.

What is your objective? All out drag? Otherwise, not sure of the power curve you are looking for.

 

you know frankly i never thought about why they loose power up there. i was always assuming that it was due to the twins running out of breath.

now there could only be a few reasons that this would occur if there is not a set of stock twins on there. there are (if i remember correctly) smaller exhaust sleeves on the 20b (it was not nessisary to rev that high cause the car is a large automatic cruiser). they can be ported (or possibly replaced with FD sleeves i think). everything else in the motor should be about the same. all the internals are the same.

the only other limitations (compared with the 13b) you are faced with is the weight of the extra rotor (so more rotating mass) and maybe for some reason its not balanced as well???? (it very well may be, thats just a thought). The last thing is the eccentric shaft as im sure you know is a 2 piece assembaly, and may be more prone to flex at higher RPM's. oh yeah, the motor is also longer so the studs that hold it together (since they are the same width as the 13b studs but much longer ) may be more likely to twist.

but really as far as working operation goes the 20b is just a 13b with more rotating mass, and smaller exhaust sleeves (which can be enlarged, or possibly swapped for larger ones)

there are only a few possiblilties of why we would loose power higher up... anyone know the cause? id be happy if i could rev my stock motor to 8K. i wouldnt want/need to go any higher than that (i never have w/ my 13b).... with the stock ports on the 13b i can feel power start to taper off at ~7.5K so thats when i normally shift, but id like to be "able" to take her to 8K safely if im not staring at the tach.

 

Red, my car will mostly be street driven with occasional strip use.

I feel the same way you do about peaky hp. This is one of the reasons why I'm going with a 20b. The torque alone will make the car more drivable down low for the street as compared to a 13b. Overall I just don't want my hp to fall well short of red line. This way I could use the entire rev range if need be. I'm hoping to build my setup so the hp levels off in the upper rpm's and doesn't fall drastically like what I've seen in the past. Hp wise, I'm only looking to make no more than 600 at the wheels.

 

Thats what I always thought. My engine will be rebuilt with new 13b housings. I'm also planning on using the 2mm rotary aviation seals with doweling of the block. As far as the turbo....I'm still not sure whats best for my needs. I was considering a GT42r. I know that turbo may be more than I would need for my hp request but, it shouldn't run out of flow at only 600rwhp.



I think you understand my point

 

A stockish redline should be excellent for your setup (and 98% of 20B owners!). A GT42r is an excellent choice for the 20B in my opinion. If I were building a 20B today that would be one of my top choices.
Do some mild porting to the engine, both intake and exhaust and you shouldn't have to worry about losing any HP towards redline.

Red-RX7, you have an amazing car! I saw the dyno in another post, looks great.

 

I wouldn't suggest just swapping the sleeves. I was warned about this from every builder whom I talked to when I researched my engine build. The sleeves have to be drilled out of the aluminum housing. Not easy but can and has been done. We just took apart a 20b that had the sleeves swapped with 30K or so on the rebuild. What a friggin hack job. All the sleeves were WAY loose and the front sleeve you could move back and forth almost 3/8 of an inch. It's not like the rotor will suck them in since they only see pressure, but I wouldn't want loose parts floating around in my engine, maybe that's just me.

Btw, we're slapping it back together like that (not my engine).

 

You have no clue what you're talking about...

1) If you're drag racing, it has NOTHING to do with (horse) power.  It's all about torque.  Look where the torque peaks, not where the horsepower peaks.  The name of the game is to be able to up-shift and hit the meat of your torque band (which typically is slightly prior to your torque peak).  STRIKE ONE.

2) If you're a serious drag racer, you build the engine, then you build the drivetrain to accomodate the engine's powerband - not the other way around.  STRIKE TWO.

3) If you're a serious drag racer, you adjust other components to match the engine powerband.  You can adjust (rear) tire diameters pretty easily.  More expensive is a rear end ratio swap.  And, even more expensive is a quick change ratio transmission.  STRIKE 3.

You should've known all of that, and you didn't mention any of those points.

This pegs you either as a totally ignorant newbie, or you're lying out your behind about this project.

Now before you go all ballistic on me (and I know you will), you might want to try and ask a little nicer and drop the attitude like you know what you're doing.  Clearly you haven't mentioned any of the above option, and this paints an ignorant picture of yourself.


-Ted

 

Ted your still assuming things. Just because I didn't mention anything about my drivetrain doesn't mean it won't be properly upgradeded as well. I don't need to explain every single detail about my set-up. All I needed was for someone to provide me with the info I reguested. For your infomation I asked another person on another forum and I got my answers without all the hoopla. However; I really do appreciate some of the responses I've gotten in this thread. FWIW with all your post, you still haven't answered any of my questions. Please stop trying to analize what I'm trying to do. If you can't answer my simple question, then please go elsewhere. Overall it's my money that will be spent.


By the way, my attitude came from you "assuming" it was all about bragging rights. Also I have more important things to do than to go"ballistic" on someone over the internet.

 

whoa now boys... simmer down. when did this get all confrontational.

t-von... is you intention to DRAG this car? building a car for drag racing is a whole different soup than street. for my own 20b swap i am not planning on taking it to the dragstrip... it will be a street car. i have no desire to break expensive parts doing some amature drag racing... i cant afford it, and frankly i dont think of the 7 as a drag car. im building mine to be streetable (as in i could throw my friend the keys and he'd be able to take it out like any other car... or i could hand the keys to my sister to move the car to the other side of the street for street sweeping). im going for some amount of practicality... like AC, power steering, cruise, and yes being able to use those red marks on that tach as a gauge of where not to rev past... thats just me. id like this to be a street car that could handle the track if nessesary.

why dont you tell us the planned useage for this car so we can get a better idea of your intentions.

 

well we've been playing with stock turbo 20b's and by 6200 (power peak) they are making about 3-5psi of boost. or even simpler the turbo is too small.

the next restriction would prolly be the exhaust sleeves, then the intake manifold, ports etc etc

 

Heath, above in my reply to Red Rx7 I said my car will be street driven with occasional strip use. For me that ratio would be about 95% street vs 5% strip.

Upgrades for the drivetrain will be a turbo II diff and chrome molly axles & E/T streets on my stock 16 rims. This setup "similar to Boosted7's" should provide overall added strength. His car with 400 rwhp is a high 10 sec car. With the additional hp my car would produce, I would easily hit the 10 sec range with ease. I also would have the boost turned down to a specific level to achieve my goals. This would keep me from really abusing my drive train with max hp at the wheels. Another thing, if my car performs as expected overall strip useage would really be minimal because of me being banned for not having a roll cage. LOL Overall I'm trying to build what I call the "perfect Rx7" that does everything exceptionally well.

 

Thx This info pretty much confirms my suspicions. My engine will be rebuilt w/ brand new 13b housings, the necessary port work, rotary avaiation apex seals, and doweling. Overall thx for the info guys I really appreciate it.

 

ask todd, he built a motor for the its car and it sucked a sleeve in. granted he is a wmd, but still

 

loose sleeves are a really bad thing after time the steel
sleeve will wear the aluminum housing and the hole
the sleeve fits into will get bigger and bigger until
it can turn, then there is a chance that the sleeve can
reach into the port and hit the rotor, i have seen this
only once, and since i make sure that the sleeves are
tight in the hole!
how hard is it to tap the hole the pin goes into and
thread in a set screw to hold the sleeve in place, only
takes a minute and makes it much easier to remove the
sleeve in the future.
matt

 

You still don't get it...

Shifting at 9kRPM will probably drop the revs down to 6k...maybe 5,xxx.
Most 20B torque peaks around 3k to 5k, so you insisting revving that high means you're running slower.  Unless you're running a BP motor or turbo(s) with a very large turbine A/R (1.3 or larger), you gain nothing by shifting that high except unnecessary wear & tear.

You just don't get it.


-Ted

 

I appreciate the advice your trying to give me but it still doesn't change the fact that in the end the car will be built the way I want.

Since when did torque play such a huge roll in dragracing? From what I understood torque is what gets you moving. Hp is what makes you go faster? Thats why the torqueless Rx8 can nearly hang with a stock Fd from a roll. Also if torque was such a big advantage, why is it that the S2000 is able to run similar times in the 1/4 mile as the Fd? Both cars weigh the same yet the Fd has more Hp and alot more torque?

 

Clueless...

The answers can be found on this forum - do a search.


-Ted

 

not to instigate anything, but im going to have to agree with Ted... you need to do a little more research on dragracing. yes torque gets you going... so to shift high in low gears just gives you a disadvantage if you are at the track (because of the losses at low speeds)... now when you get the car moving i think we have a different situation (correct me if im wrong Ted... im not too knowledgable about dragging)

 

Horsepower is a function of torque. If you can keep a constant torque output as the engine speed increases you'll make more and more power. However, all engines will sooner or later fall out of their efficency range and start making less torque as the engine speed increases, resulting in either no gain in horsepower or a decrease in horsepower in the upper ranges. The S2000's usable torque curve is in realtivly high rpms, as is the RX-8's, but they both follow these principals and its though careful design of the power output and transmission together that they do what they do so well. That said, if you were to go above or below their powerbands, you'd run into the same problem and wind up with a much slower, much less efficent car.

What everyone is saying is that if run a car outside of its useable powerband you're going to lose a lot performance wise. The name of the game isn't how high can you rev. The name of the game is how much area's under your torque curve. If you want to arbituarily rev higher just for the sake of reving higher then fine, go for it, but without designing the entire powertrain and drivetrain around that you're only going to suffer performance wise.

 

Thx for the detailed explanation John. Now it all makes since So basically when it comes to dragracing, I can't compare the 13b's hp and torque curve to a 20b because there power band is so differant?

 

I'd like to dig up this old thread,

My setup continues to produce power past the rev limiter. We don't know how far, as the tuner decided it was his safest bet to let out around 7200rpm, since he did not build the engine. I've since raised the limiter to around 7500, and the car continues to pull hard.

This is a D series, ra seals, twin plate clutch, no pins/studs or balancing.

What do you guys now-a-days, with 20b's, agree the physical limitations are to revving this motor?

I believe it would gain HP even up to 8k-9k given the size of the turbo/ AR, it pulls progressively harder as the RPM's climb, the tuner believed the power band would continue well past 7.5k but do not want to push this block too far

 

my opinion is that the physical limit is firstly the balancing of the assembly. if you have a factory set of rotors and weights, or had the whole thing balanced this is good. second limit is probably the oil supply, as the same oil pump needs to oil 2 more bearings.

since the 2 rotor also redlined at 7000, but actually works ok up to about 9k, i think 7500 is probably safe with the 20B, maybe a little higher. ultimately it is a "how lucky do you feel" question.

 

My opinion is if you really feel you need more power you should carefully consider which will impact reliability less and provide more usable power.

Raising the redline?

Increasing the boost?

Obviously, raising the boost will provide more power usable power as it raise power everywhere the turbo can achieve full boost and often improve spool.

When do you need the power? If you can plan ahead on needing the power the answer is obvious- 116 leaded and much more boost.

If you want to "plan ahead" on higher redline instead of more boost you have a rebuild ahead of you and lots of $$ into machine work.

You have a turbo, use it.

As a bonus, once you start working your compressor wheel out you will peak power much earlier and it will drop off so you can feel like you are maxing your set-up.

Anyways, it was fun to read this old thread and see how racers and enthusiast shop owners like Logan at Defined have re-defined what a 20B can and can't do.

Projay semi p-port 20B manifold is an over the counter solution to the flow problem! I wish the machine work were that easy.

 

my main reason for posting after reading this thread was simply to say ... look at T-von now.

however, to stay on the actual topic ... i guess i have more of a question than a comment. i would imagine the 20B would behave similar to a 13B at increased RPM in that the front and rear rotors would want to crash into the housings as the shaft start bowing.

1. does it happen at roughly the same RPM?
2. does the center rotor do anything weird?

 

i would imagine the 20B would behave similar to a 13B at increased RPM in that the front and rear rotors would want to crash into the housings as the shaft start bowing.

1. does it happen at roughly the same RPM?
2. does the center rotor do anything weird?

1) It is the rear 2 rotors that share the common shaft/2 bearings like a 13B on the 20B and yes, they have e-shaft whip like 13B plus more from loads from the added front rotor/e-shaft extension coupled to the front of it so if anything it happens at a lower rpm.

2) Its the front rotor e-shaft extension has 2 bearings to itself not the middle as mentioned above. A 20B is a 13B +1 rotor tacked on the front. Note an R26B 4 rotor is a 13B +1 rotor tacked on the front and + 1 rotor tacked on the back.

You could build a full 3 bearing 13B from a 20B front rotor/shaft/housing assembly and a 20B e-shaft rear section cut down to 1 rotor and the 20B rear rotor/housing assemblies. Might rev higher than regular 13B, might have problems with the e-shaft coupling and self destruct.

Probably better to go aftermarket 2 piece with full length rear and slip on front e-shaft extension and line bore your housings for 3 bearings perfectly lined up.

Mazda's 20B method was so they could have "production tolerances" so you can replace parts with parts off the shelf without re-machining your side housing bearing centers.