Say you build a 13B with all of the trimmings and it blows up eventually. Would you not have been better off, financially, just building a 20B in the first place and running less boost to make the same horsepower? Ignoring the possibility of getting boost greedy with the 20B.

 

Usually, it depends on how 'trimmed' your car is to begin with. As we all know, only certain items will transfer over to a 20B. So if you're planning on going standalone anyway, my opinion would be to spend the extra $200 or so and go straight for a Haltech PS2K instead of the PS1K. In addition to the cost of the engine, a proper EMS capable of handing the 20B is the #1 expense that gives the conversion its sticker shock. The #2 high-ticket item outside of the engine depends on the vehicle. For FDs, it's the mounting kit (either from Hinson or Defined Autoworks), whereas the FC usually needs a T2 drivetrain and cooling upgrade. Beyond those items, it all depends on how you want to approach it.

My 20B conversion is being chronicled in itemized in my build "The 12 Days of Rotormas", to put everything in perspective from a 'ground-up' perspective since my car started out as a sickly S4 GXL Automatic. A lot of people would say it's not worth doing to my car, but I'm gonna show them all that it is worth the effort if you're creative like me. After all, who better to talk about dollars and cents when it comes to mods than a broke S4NA owner

 

It all depends on the hp level. I consider the safe limit at pump gas only and a perfect tune. No aux-injection!

I know of a sequential twin turbo 13b with 3mm apex seals that has over 100k on it's rebuild and making 340rwhp that whole entire time. This is the most reliable modified 13b that I know of and is driven dailey. 20b equivalent would make 510rwhp. Remember boost is only a measure of how well the engine is breathing. In my above example, both engines will have the same internal combustion pressures/temps but completely boost levels to make the power.


Here's some thing people keep getting confused about when it comes to turbos, boost, and efficiency.

Take two stock 13brews. One engine your going to do a bridge port while the other stays stock. Lets say were gonna run 14psi boost pressure on both with the factory twins. The stock engine will make about 340rwhp. The bridge will make more at 14psi but the turbos will be spooling much harder to generate the same boost pressure because the engine breathes far better than the stock unit. The higher spooling bridge port engines turbo will run way out of it efficiency range trying to keep up. Now to make the same power as the stock engine, the bridge port engine will maybe only need 10psi. Now this is where some of the confusion comes from. Most people think that because the bridge port engine is making the same power at a lower boost, that is must be more efficient. Well yes and no! Just because the engine itself is more efficient in breathing, doesn't make the turbos themselves MORE efficient in moving air through it. The turbos on both engines still have to spool X amount of air volume to make X amount of power. If you have a turbo tachometer, both turbos should be spooling at roughly the same rpms. That means the turbo charge temps are going to be the same on both even though, the bridge engine shows less boost because it breaths better. Make since?


Now as far as your question about which engine, make sure you run a turbo that the most efficient for whatever power goals you want. Keeping the charge air cool is very important to long term reliability of any turbo rotary.

 

I guess you and me are one in the same (broke fd owner). LOL! Yes you do have to be VERY creative to do thousands of dollars worth of work for pennys.

 

Yes, I understand that. But this is more of a $ vs benefits question. "IF" a 13b pops from trying too hard to make X hp, would it have been less expensive to just bite the bullet and invest in a 20b?

As long as we're on that subject though, how much hp is safe on a 13B assuming everything is built properly and the turbo is not being overworked and combustion temps are in the safe zone?

 

See my second paragraph above. I have never heard of a 400rwhp 13b engine lasting that long. If you stay with-in the above power levels, you can reach seasonable service life. All things being equal, 20b is gonna cost more, because more torque will have a more impact on the drive train related items (tranny, rear end) over time. It really is hard to answer your question because there are too many factors. That's why I based everything on power levels.

 

Banzai posted a while back with a price breakdown of a 20b (done as if it came from Mazda).... and if i remember correctly a comparison to what it would cost to to make X hp on a 13b. Search.

Personally, i don't believe you should even compare cost in a 13b vs 20b desicion.

 

Engine rebuilds should NOT be your only concern when considering 500whp.

Technically this would be a hard question to answer as I and I'm sure others would like to factor in build quality, tune, driving habbits, and anything other than the engine that breaks.... Tranny, axles, diff issues.

Sure, the 3 rotor will make the power you want and carry more torque and the engine may even last longer at those power levels but now that I think about it the amount of money spent on both a 2 rotor turbo or 3 rotor turbo build might actually end up costing the same when it is all said and done. Over time of course.

 

It really depends on the goals you have for your car. If it is currently bone stock and you are in the process of making the decision to go single turbo with all the supporting mods for 500+ hp, then it is a great time to consider a 20B. One of drawback is that you have to complete the entire conversion before you can enjoy the car, where as most people go single turbo over a period of time (some many years). This allows the owner the luxury of spreading out the costs and still being able to enjoy driving the car. For example the twins can be used on the 13b while the cooling, fuel, ignition, EMS systems are all being upgraded independently.

With the 20B, you really just have to upgrade everything all at once. This is where the sticker shock comes in. Technically you could run the twins in the interim, but this would require custom fabrication that would later be wasted money. A well sorted out 450-500hp 13b single turbo, with all the supporting mods will run upward of $20k-$25k (excluding Ebay cheapos, used parts and hack jobs) over the life of the project.

A 20B will cost more, as there are more parts to buy and everything is bigger (= more expensive) and/or custom fabricated. Most 13B single turbo builds require much less custom work as parts are readily available to bolt on. Costs go up from the very beginning with the 20B core itself, typically costing from $3K-$4500, the standard J-spec 13b-rew core engine is $1K-$1500, besides the fact that the car already has a 13b in it bringing that cost down to $0.

Yes, there are always deals to be had, the rare story of the "guy that bought a 20B long block for $500" etc, this is not the norm and can not be considered as a budgetary price when considering cost comparisons.

One of the drawbacks of going from bone stock 13b-rew to a single turbo 20B, if you are doing the work yourself, is that it will be a very steep learning curve. There are not any instruction manuals for this conversion.

All that being said, none of that means you will not blow up the 20B just as fast as the 13b, it is all in the tuning and build quality. We have customers with 500-600whp 13b's, pushing 23+ psi for years (obviously not their DDs). These levels of power can be achieved at lower levels of boost with the 20B, but they can/do blow and the cost to repair are much higher, e-shafts are very expensive, as well as the thick center iron. You are almost better off buying another complete core if you break either of these parts.

 

Thanks Banzai. So either way, it will cost a lot. Sticking with the 13B allows you to "finance" it slowly and pay as you go. 20B means you need a second mortgage on your house or a fat piggy bank. And if you blow up the 20B, it just means its even more expensive to fix.

 

It really does depend on what you want in hp..but so many people will mod their car, like it and enjoy it then want a little more.....spend more money on mods, like and enjoy it then want a little more...it is a vicious cycle. At the end of the day, you've spent a lot of money and you have a 500hp car that is close to maxed out for the street...or spend the about the same amount of money on a 20b and have a 500+hp car that is running low boost and not on the ragged edge..plus it sounds really cool and there is a lot of upside on the hp side.
I've talked to many many people that have had that experience. But, be prepared to spend some money either way....hp is not cheap.

 

After owning a few 20B's and building quite a few I chose to stick with the 13b in my car. The cars we've built were no doubt fun and no doubt made power easily, but the cost and availability of parts made me think otherwise. Try hunting down a e-shaft if and when needed, and when you do find it not only will it cost you a 13b but you better hope it passes a good solid inspection. There are ways I would do it for my car but initial cost is even more, so that is out of the question for this thread. If you're doing it simply because you want it to be more power with more reliability, 13B's can be built pretty darn reliable by a few people on here at power levels you would be hard pressed to believe depending on your goals and use of the car. I'd say if your concerned about blowing a 13B you don't want to pay for repairs on a 20b. A well sorted 450whp 13B FD can give you a good amount of fun and be pretty solid with the right build and tune. Don't get caught up in the HP mess, 450whp 2800lbs can kill you just as quickly as 500 or 600whp.

~S~

 

The real question is what power levels do you currently have? and what is your goal with the car..street/strip, etc?

I have had several single turbo setups(t-88, s372) with the 13b and different ported motors (street, half bridge, full bridge, cosmo) I drove my car between 425whp and 655whp over the last 7 years, but in the end I wanted a motor that could produce more tourque and be in the 600whp range @ 15 psi or less and not be heard 3 blocks over ;-)

To me the 20b made sense, it gives me bottom end tourque and gets me to the power level that makes me smile on 94 octane which was a must for me....... for others its 375whp with a 20b and thats fine everyone has different wants and needs with there car.

The point is that with enough seat time everyone can make a decision as to which direction they want to see there car go......going 20b has been an awesome experience and one that I personally love but for others its all about 13b

20b = $$$$$$
13b= $$$

End Result:

 

The car will be used for street on curvy mountain roads and road racing in HPDE events. I have no idea how much power would be ideal and I've never been in a 20B car. So I'm kind of clueless as to how much power would be ideal right now. I just want to make the big decisions right the first time.

 

I'm planning on going to DGRR this year. It helps that I live 2hrs away from there also!

 

i agree. i really liked my 20B FC but if i had to do it again, i'd be NA. the 20B SOUNDS and FEELS great.... and if you want HP the 13B makes enough to make the car stupid fast.

if you're headed in the racetrack direction do yourself a favor and start with a stock car.

learning how to drive is VERY IMPORTANT.

driving on the track is a skill, and as such needs to be learned. its easier to learn in a car that isn't fast.

 

Yup, I agree. I have track experience in my old 350Z. It had enough power to go fast, but not enough power to break traction at will unless I as doing something stupid. Plus I have uncountable miles driving on the back roads here. Given, though, that the race track is completely different.

 

Comparing the 13B to the 20B is an apples-to-oranges comparison. I have both. Here's how they compare:

-----Boost rwhp rw torque
------------ ------ -------------
20B 12____368___425 lb./ft.
13B 14____390___301 lb./ft.

That torque makes a world of difference. As one NASCAR-type once said, "Horsepower sells cars; torque wins races."

As for being "better off, financially," you best bet is to buy my car:

http://www.cris.com/~Asam/20B.html

 

I'm planning to be there as well. Gordon, I look forward to meeting you. The number of 20b's attending is certainly growing. I understand your car is well done and I'm looking forward to seeing it. I was extremely impressed with David's car......well that might be an understatement. So, there should be a wide variety of 20b's to have a look at.

 

Yeah, I broke an e-shaft and couldn't make it.

Should be a good year.......I'm sure I won't even make the podium at the car show.

 

N/A 20Bs have about 250 hp. How did you mod the engine to get at 350-375? Port?

 

I think the real benefit of the 3 rotor is driveability.

The reliability and big power is nice, but honestly not necessary. A 4xx rwhp rx7 is FAST, and you can do that easily enough with a 13b.

The nice thing with the 3 rotor is that it gets better fuel economy, cruises better, and has that available torque that in town driving is a breeze. I was surprised how much of a pain in the *** my new FD was to drive around vs my 20B car. You have to pay a lot more attention to what gear you are in and to how you take off. The 20B just goes. To me that is the biggest benefit

 

I really think is about your budget 13b are really fun but the 20b brings the fun to a new level but also your budget. if you have the MONEY, good TUNER, and ENGINE BUILDER (that is the most important part of the conversion.) go with the 20b if not then go with the 13b. I love every sound, and every minute i drive my car everybody stops me and ask what kind of engine i have in there. You can make some pretty sick power in 93 pump gas and run it very reliably every day. I was able to make 610hp with 16psi very safe on the rich side. and with race gas 831hp c16 but its all about the budget. One thing i will suggest plan accordingly because when you go 20b it gets expensive depending on the power level. I always say over build it and under use it. so it will last long time.

 

Here's a look into some of the things he's done to his motor.
https://www.rx7club.com/showthread.p...ighlight=rotor