I'm going to my rotary mechanic next week to get pricing for putting a 20B into my S4 NA. My car is in immactulate shape which makes it a prime candidate for the swap.

But is it realistic to use a 20B as a semi daily driver. I'll be making it an NA 20B so that I can run 87 octane. I'm going to look into getting renesis rotors put in (10:1) or S5 rotors to replace the stock 9:1's and a modest streetport.

Can I reuse the stock 20B ECU? I figure I should be able to get away with a TII transmission.

I'm shooting for 300Hp and 300ftlbs is this realistic?

Oh yeah, my main concern is emissions testing. Can a 20B pass emissions with a huge airpump and cat?

looking for some tips or hints from the 20B gurus, this will be a street car. thanks guys.

 

Correct me if I'm wrong, but don't higher compression ratio cars tend to use higher octane? I don't think it would be wise to run 87 in it.

If your shooting for 300HP, then get a TII swap or 13B-Cosmo. Cheaper, easier intall, less problems, etc.

 

I would but I'm not a turbo fan, not as reliable.

yes higher compression needs higher octane
but all the guys i know with 9.7:1 compression NA's run 87 octane....the 10:1 would be iffy but still not nearly as bad as with a turbo, I'd probably end up going with 9.7:1 rotors cuz renesis rotors are expensive, for not much more of a gain in Hp.

up in canada 94 octane is over 1$ per liter now(4$ CDN per gallon) and 87 is about 79cents per liter. also, considering the higher torque of the 20B, my fuel cost's shouldn't go up that much more than with a tII swap because I could shift lower.

Plus 20B's are just cool!
This is going to be my graduation present to myself when I finish my degree. I also might just leave in the 9:1 rotors until I have the cash to run a good turbo setup.

 

Almost anything can be a daily driver. From a semi tractor trailor, to an ATV. My REPU is a semi daily driver, and it gets like 10MPG highway with a heavy foot and the tail gate up. Fortunately, I don't need to drive it on the highway to get to where I need to go. Anyway, yes, a 20B is very streetable due to its higher torque.

Renesis rotors probably wouldn't be a very good idea, but NA 6 port (high compression) S5 rotors could work. I'm not sure if you could use 87 octane with them. Personally, I'm keeping the 9.0:1 rotors in mine. It's actually pretty close in ratio to my stock REPU rotors at 9.2:1. I'll be able to run 87 octane with no trouble at all.

You won't want to use the stock 20B ECU once you learn how hard it will be to make it work without the rest of the Cosmo sitting there. Evil Aviator and/or j9fd3s etc will know of some good ECUs to check out.

300/300 is doable for a price. Anything is, really.

If all you have is a sniffer test, then yes it should pass, as long as it's not burning oil like a minivan.

 

I started with an S4 NA and have regretted it during the whole conversion process. However, if you really like your car, then I guess it may be worth adding all of the TII parts to it. You will probably want to buy an entire TII because it would be cheaper than buying all of the parts, such as the transmission, starter, clutch, driveshaft, LSD, halfshafts, and you may also want the hood, brakes, and suspension, depending on what is currently on your NA. I'm not sure which flywheel will work, but my guess is the S5 TII flywheel, although you should check with your mechanic to make sure that it will balance properly on the 20B. I would also recommend swapping out the S4 front end for an S5 or custom front end with a larger radiator inlet, so basically an S5 TII donor would be preferable to an S4 TII.

Yes, the 20B-REW originally came in the Mazda JC Cosmo luxury car, which was... a daily driver.

I don't understand that statement at all. Why would you want to rip a perfectly good twin turbo unit off the engine, replace it with an expensive custom header, and port the engine so that you end up making basically the same horsepower as stock but with twice the noise? Also, you can run 87 octane in a stock 20B-REW. What is so great about 87 octane anyway?

Yes, if you buy an entire Cosmo front clip, you run the engine in its stock form, and you have enough electrical engineering knowledge to modify it to work without the other Cosmo components. Otherwise, you will need a standalone EMS.

Only if you can somehow manage to shift the peak torque from 3,000rpm up to 5,250rpm, and the peak horsepower from 6,500rpm down to 5,250rpm.

A stock 20B-REW with split ignition timing and 10psi boost or less can pass US emissions. A ported non-turbo 300hp 20B is going to be much more difficult. If you have a visual inspection, that may also pose problems.

 

All of the production 86-92 13B and 13BT engines were rated for 87 octane, so IMO that pretty much lets you know that those respective rotor/boost combinations are OK with 87 octane. Other factors may change that, such as modifications, advanced timing, poor engine condition, etc., but I think the stock specs make a good reference point.

IMO emissions testing means split timing. Therefore, listed from lowest to highest price... Microtech LTX12, Wolf3D 4.0 Plus, Haltech E11, Electromotive TEC3, and Motec M8 series.

 

since i live in california ive had a chance to play with the emissions systems a bit. on a s5/s6 with a stock based emissions system and a port IT WILL NOT PASS AT IDLE, the port adds too much overlap and it will fail at idle by a couple hundred ppm of hc. the s5 and s6 ecu's are not adjustable enough to compensate. it might be possible to pass with a port and an aftermarket ecu

mike

 

i didn't know that the 13bTII was ok with 87 octane!
i am only putting 6 psi boost to the vert so i think i
will start to save a couple dollars and go with the
low cost stuff, which only remains low cost if
the motor doesn't blow up.

matt

 

Same here. I didn't know you could use 87 octane. That's pretty cool!

 

LOL, I live in S4 world, so I didn't know that the S5 could work on 87 either until two owners quoted the owner's manual in the below thread. About a year ago somebody on the forum quoted 89 octane for the S5, which must have been a RON rather than PON rating. For those who don't know, the US uses a different octane rating than most other countries, so 87 PON in the US is around 90 (+/-) RON in other countries.
https://www.rx7club.com/forum/showth...hreadid=192537

As always, you need to take the stock fuel ratings with a grain of salt because these engines are old now and most likely have a lot of detonation-inducing deposits, and that new oxygenated fuel seems to not perform as well as its PON rating suggests.

All I can find on the JC Cosmo is that "premium unleaded" is recommended. However, the search goes on for the official Mazda minimum octane rating.

For those who have a fetish for 87 octane, you can always retard the timing, upgrade the intercooler, install a water injection system, reduce the boost, etc., in order to run 87 on an engine that would otherwise require a higher octane fuel.

As for the emissions issue, this car passes emissions testing in its area, and it's still for sale as far as I know:
http://www.cris.com/~Asam/20B.html

 

wow, thanks for all the replies guys.

I've been pricing out how much changing the rotors would cost and I don't think it's worth it to swap them anymore. I'll be keeping the 9:1's unless i find some S5 rotors for cheap(not gonna happen)

Also, it depends on the condition of the engine my mechanic has. If it's low mileage I'll leave the turbo on and won't rebuild it.

It's just that I'm expecting them to be blown or in need of a rebuild anyways. In which case I don't want to deal with setting up the Turbo.

My mechanic quoted me a minimum of 280-320Hp on a streetported NA 20B.

I'm in British columbia, Canada. For emissions we have to go to "Air Care" where they check for cats and hook the exhaust up to a machine that reads NOx, HC and CO levels.

 

thats what we had too, we're moving on to the dyno testing, which is easier to pass because they dont check idle anymore

mike