red xeven

I know a lot of people have done it, but it seems that it would just be easier to buy a turbo engine than to turo an NA. So i suppose that trying to lower the compression, as well as getting stronger apex seals, new rotors, etc, is all pointless?

rico05

Yes. Yes it is. Why spend 10x as much and ahve 10x the headache tryin to be able to get as much boost as you can get for $2000 and a weekend. Remember, a turboed N/A will never handle as much boost as a TII engine can, without stuffing turbo internals into the engine.

red xeven

how about instead of a turbo II engine, i ship a j spec 13b REW because they are stronger than the turbo II, would that be an even better solution, an how much would that cost?

j9fd3s

iTrader: (3)

a lot they dont fit. the jc cosmo 13b's will fit, or there are mounts available to make them fit in the car (www.k2rd.com and www.fc3s.org). the good part about the jc motor is that it looks cool, fits in the car, they are not expensive, and they have huge ports.
the bad part is its not a bolt in deal like the turbo 2 motors, the t2 motor swap can be done in a weekend a jc swap takes a couple of months. oh and either one is capablie of making more power than you need

mike

rico05

Where do you get the idea that they are stronger? Same block, ya know? Notice it is called the "13B"-REW. Just twin sequential turbos, different intake, different ECU, and a few other small details, but internally, the same rotors and housings. Yeah, you can get FD apex seals and corner seals installed during a rebuild, but the 13BT is just as good as the 13B-REW. Plus, the REW dosen't just drop right in. New mounts are needed, a whole new cooling system (ever cooled twin turbos on a stock N/A cooling system?), new transmission, new tranny mounts, the n/a differential can handle the 13BT for a while, but it will explode with the power of the REW. Got $6k to spend and a long time and lots of Excedrin? Go for it!! Want a turbo car in a weekend? Get a J-Spec BT. But then, this is just my opnion, this plus $.50 will get you a Snickers...

Aaron Cake

iTrader: (1)

A "lot" of people have not done it. I can count 5 off hand, so I assume there are probably 10 or 20 in the world. I'm just guessing here, though.

Second, the turbo apex seals are the same as the NA seals.

And you're basing this on?

j9fd3s

iTrader: (3)

hey rico, you have an 89+ right? just get a 13bt for it you dont even have the change the wiring harness

mike

rico05

So a car with that high compression can handle as much boost as a car with lower compression can? How do you expect to run 10+ psi on the stock N/A block? I am actually not being an ***, I am truly wondering!!

And I never said that BT apex seals are differnt from n/a, but taht REW are different than BT ones.

j9fd3s

iTrader: (3)

the 13b 2mm apex seals are all the same until 96ish, then they changed the part #, i'm not sure what they changed though

mike

Aaron Cake

iTrader: (1)

I'm running 10 PSI right now...It's all about fuel and timing. With the higher compression rotors, you just have MUCH less of a safety margin. Though I got a few good pings on Monday, my engine doesn't show any wear so far associated with the boost...

It was not you mentioning the apex seals, it was the other guy. I just didn't see the point of replying twice.

j9fd3s

iTrader: (3)

hey aaron did you back the timing off? or is it fine the way it is?

mike

busy13b

iTrader: (5)

Same block my arese.

Read this [then read it again], then tell me if you think a 13b turbo and 13b-REW are the "same block."

reprinted from: http://my.engr.ucdavis.edu/~pko/13BTvs13BREW.html

13BT vs. 13B-REW: (Last revised Aug. 14, 1997)
There are two types of 13BT blocks, one from the 87-88 Turbo RX7 (FC3S GTR) and one from the 89-91 Turbo RX7 (FC3S GTX). While the older 13BT GTR block differs a lot from the 13B-REW block, the GTX block is some what a compromise in between. Most of the changes made by Mazda engineers are refinements to address the problem areas of the previous designs. For comparision purposes, the 13B-REW motor described in this article is the one from the FD3S, not one from the Japan-only Mazda Cosmo.

One significant difference on the 13B-REW is the areas around the dowel pins on the side housings. They are reinforced and ribbed with thicker castings. This is a major problem area on high output 13BT engines, as they tend to crack at high power levels and is the main reason that the 13BT blocks are not reliable beyond 400HP. Most competent rotary rebuilders will look for this before rebuilding a 13BT motor. The 13BT GTX blocks are said to be more reinforced than the earlier motors but not as significantly as the newer 13B-REW designs. Before the introduction of the 13B-REW motors, some engine builders experimented with brazing extra metal around the dowel pins area on the side housings of the 13BT motors.

The port sizes on the 13B-REW are extremely larger than the 13BT's, especially the primary ports on the intermediate housings. This is accomplished by increasing the height of the side and intermediate housing where the ports are located and relocating some of the coolant passages inside the housings. The larger ports increase the duration and "lift" of the intake stroke, allowing more air to be ingested into the combustion chamber. While the intake ports are larger, the intake runners of these motors are still about the same size. The 13BT intake manifold has a surge tank plenum which is found to create too much pumping losses because of its large volume. The 13B-REW intake manifold is a "Dynamic Pressure Intake System" which eliminated the surge plenum tank and has opposed-facing secondary intake runners. This new design enhances intake flow by taking advantage of the strong pressure waves inherant in rotary engines. The throttle bodies on the 13BT are 3x45mm, while the 13B-REW are 1x45mm + 2x50mm.

Contrary to popular beliefs, the 13BT's and 13B-REW share many internal components. The 13B-REW rotors are interchangable with the 13BT GTX rotors, although they don't have the same part number and thus are not the same part. But they do have the same compression ratios of 9.0:1 and they weigh the same. The CR of the 13BT GTR rotors are 8.5:1. I believe the later model rotors are manufactured from a more accurate milling technique while the older ones are left partly casted. This is evident in the bathtub faces of the rotors.

Almost all the internal seals and springs are the same parts in the 13BT and 13B-REW. This includes the 3-piece cast-iron 2mm apex seals which are found on all post '86 rotary motors, both turbo and non-turbo. With the exception of the side seals and corner seal springs, all the other rotor parts of the two motors such as oil seals, rings, springs, side seal springs, and corner seals, are the same parts. The newer design corner seal springs are reccommended for use in all rotary rebuilds.

The eccentric shafts for these motor seem to all look the same, but the 13B-REW shaft has a larger oil bypass/crank pulley bolt. The newer motor surprisingly maintains the same warm-up oil-bypass pellet as the older motors. The 13B-REW motors does have larger front-end thrust bearings than the 13BT motors. These larger bearing components require the use of a different front counterweight. The larger thrust bearings allow better loading and thus a tighter torque setting of the pulley bolt. This design will reduce the chance of the eccentric shaft bending at the front section, which is sometimes a problem on high-output 13BT motors. The large thrust bearing is probably also designed for use with the pull type clutch assemblies found in the FD3S.

The front cover of the 13B-REW has one more attachment bolt which prevents the gasket from blowing out, which is a problem on the 13BT motors. These front covers are interchangable between the two motors as the bolt patterns are the same (except for the one extra bolt on the 13B-REW). The 13B-REW motors uses crank trigger sensors mounted on the crank instead of the crank angle sensor (CAS) on the 13BT. The crank trigger sensors allows a better accuracy resolution because of its wider teeth spacing. Also, torsional flex on the crank angle sensor shaft causes inaccurate readings. The two triggering systems has similarities in the numbers of triggering teeth. The 13B-REW's crank trigger has 12 syncro teeth and 1 home tooth, while the 13BT's CAS which spins at half speed, has 24 syncro teeths and 2 home teeth.

The rotor housings on the 13B-REW motors are refined for reliability. Since the motor is designed for higher standard output, the wear surface on these housings has a carbon-graphite coating which is said to exhibit 32% less friction than the 13BT motor's fluorocarbon resin coating. The new coating actually allows less oil to be injected into the combustion chambers, thus the 13B-REW requires only two oil injectors instead of four. In addition to this coating, these rotor housings has the water passage machined around the spark plug areas to increase cooling at the spark plug tips. This modification is similar to the ones done on race motors.

The stationary gears on the 13B-REW are factory hardened. They are interchangable with the 13BT's, provided that the 13B-REW's thrust bearings and front counter weight be used. Inside the stationary gears, the standard main bearings on the 13B-REW motors are the multi-holes type and are locked into place by an anti-rotation set screw. This design, similar to the "3 window-type" bearing is pioneered in the earlier LeMans and IMSA motors. The holes allow extra oil to flow around the oil groove thus providing a thicker oil film for the eccentric shaft to ride on. The 13BT has standard bearings with no oil holes. Oil pump capacity and pressure are also increased in the 13B-REW motors. The oil pumps are not interchangable. The 13B-REW oil pressure regulator is interchangable with the 13BT motors and is a reccommended upgrade when power output is increased. Also, a new oil pan design on the 13B-REW motors helps to minimize air induction into the oil strainger. A thinner pan with a inner bulge maintains oil level to keep the oil strainer submerged in oil. The 13BT GTR blocks use mechanical oil metering pumps, while the 13BT GTX and 13B-REW blocks use electronic oil metering pumps.

The water pump of the 13B-REW is probably the only reverse rotation water pump assembly found on any Mazda rotary engine. It is driven by the back of the serpentine belt. The water pump housing assembly on all the rotary engines are interchangable, but the appropriate front cover/pulleys/etc... must be used.

Fuel injectors used in the 13BT motors are 4 standard Nippondenso top feed rail injectors rated at 550cc. Depending on production dates, the 13BT motors had both low and high impendance ratings. The 13B-REW motors has 2x550cc injectors for primary and 2x850cc injectors for secondaries. This higher fuel capacity is for higher power levels. These injectors are side-feed rail types with high impedance so it can operate cooler. They are not interchangable with the 13BT injectors.

The engine mounts locations of the 13B-REW are under the rear side housing, while the mounts on the 13BT are located on the intermediate housing. Because of this, interchanging the motors between the FC3S and FD3S chassis is a very involved project.

The tranny bellhousing bolt patterns are the same on the 13B-REW and 13BT motors, thus the trannies are interchangable with the appropriate clutch/flywheel assemblies.

In summary, because of these and many other refinements, the 13B-REW is a much more potent powerplant which can easily handle high HP output beyond for which it is originally designed for. Many of these refinements are shared in the designs of the 20B-REW and 13B-REW of the Mazda Cosmo.

Any questions or comments? Please send email to pko@mindspring.com

Green

yea, was looking for that post...
13B and 13B-REW have big differences...
Some people need to start putting this in front of their posts "I think..." or "correct me if I'm wrong but ..."
, or " I may be a moron but ..." Starts less fights

rico05

Learn something new everyday. Thanks Busy13b. That is a REALLY informative article!! Hey Green, some of us do not know when we are wrong. I was just goin by what I have read around. Sorry to **** your highness off. Allow me to humbly apologize for any inconvinence.


Cool Aaron, thanks for the good info and being polite!!! Other people should learn these people skills!!

red xeven

i dont mean to say i told you so rico, but thanks to busy13b. I knew i read it somewhere. the REW IS stronger than the BT.

rico05

Well, if you read, yes and no. The stationary gears are stronger, but other than that, nothing is "stronger". Just better designed. By you saying stronger, I assumed you meant seals, rotors, and eccenctric shaft. Pick your words better, and we can help ya better!!

busy13b

iTrader: (5)

"I really am an armchair quarterback, but...."

the big one should be, "I read somone else's post that said..."

Much love to the guys and gals actually out therer turning the wrenches, getting the hands-on experience, not always believing what they read, and not looking to be spoon-fed.

Green - I think I live about two blocks away from you [for the next two days anyway]. Off 120th and L?? Ever see/hear a loud series 5 N/A buzz down your street??

rico05

Ok, so I never work on my car? Right. Sorry I don't have a 13B-REW to rip apart and compare as you obviously do. And as for spoon fed? You can take that spoon and eat my ***.....

NO ONE touches my car be me.

Aaron Cake

iTrader: (1)

The timing is stock, but that's not fine as far as I am concerned. It's on my list of things to change.

busy13b

iTrader: (5)

Odd, you should take that comment to heart.

Cheer up, fellow FC'er. I was just making a general comment, just happened to be in the spirit of the thread.

we are ALL continuously learning about what makes our cars tick. Some have more **experience** than others, but not to say we can't all help each other learn a bit more.

But some people don't like feel comfortable when others try to come off as an expert and sound like they know something as being nothing but **fact** especially in regards to two compex powerplants, whereas a few days prior, they were polling the list to see how much coolant an RX-7 takes....

We're here to help each other, certainly, and we share a common interest, the beloved rotary engine, and the cars they go into. No hard feelings, brotha.

2ndGen.rocket

so is it that hard to drop a j-spec turbo in my 86 N/A GXL? i assumed that i had to replace the ECU, but does the engine bolt right in? would i have to replace the transmission? what else would i need to do?

the only reason im asking is because thats what i want to do as soon as my engine goes. if it ever does go.

NZConvertible

I’ve corrected you a couple of times on this compression issue, but you keep bringing it up! Comparing S5 engines, running 10psi boost on a 9.7:1 NA engine is exactly the same as running 12psi boost on a 9.0:1 Turbo engine. The effective compression ratio is the same. The Turbo engines run fine on 12psi, so an NA will be fine on 10psi, as long as the tuning is right. Engine strength is not the issue.