Ive been kickin this idea of putting a N/A 20b in my 86NA. Im not concerned about the driveline, Ill get TII parts. Anyways. Ive talked to reted, but Id like some other opinions for a broader view. I was thinkin NA because I already have a turbo car, a 13b but the capablity is there. So I dont want crazy HP just over 250 rwhp. Say I run it with a haltech 11, build the header, and use the stock intake mani. do you guys think 250 would be achieveable. I would like to street port it and make a custom intake manifold later but I would really like to get a decient engine in to my NA. Think it can be done for under $8g excluding the header and motor mounts. Any input would be greatly appreciated.
Sky

 

oops Im sorry I didnt scroll down. Lazy, tired.
I still would like opinions.

 

i think its doable, if you street port the motor 250-300rwhp is doable, if you leave the motor stock it might do 200, but it has lots of torque so even though your dyno numbers are not so hot, it would still be quick on the street.

mike

 

Find 3 S5 N/A 9.7:1 rotors to help every bit you can.
I'm not sure about what to do with the exhaust sleeves as the cosmos have odd sleeves pointed towards teh stock turbines to help spooling.
Cosmos have large ports. So porting might be alright. A little intake manifold porting would help. I'm not sure how much it could improve as I see it mostly done to FC intake manfiolds.
Redline would probably be around 8,000-8,500 which is good for a non pport/non bridgeport engine.
Other than that I don't see much else to worry about.
I don't really have any suggestions about headers other than find someone who makes good headers for 2 rotors and just ask for a custom.
If you're worried about noise then just carefully think over your Header, Exhaust porting, and exhaust (including silencers/catalytic convertors).
The Haltech E11 would be perfect for making a N/A emissions legal 20b. Although I'm not sure how much a highflow cat would hurt the horsepower. I don't think it would be too bad. It will quiet it down a bit too
As you can see I've given this lots of thought

 

the 20b has enough torque that a cat prolly wouldnt be that noticeable of a power difference.

mike

 

the 20b will make that kind of power easy with the
9.7:1 rotors and some porting, the funny looking
exhaust sleeves in 20b were more for noise reduction,
this is what I was told by a person who was working
for mazda during the design of the 20b for the Cosmo.
so removing the sleeves and putting in TII or rew
sleeves helps as well.
I think I am going to build my 2nd 20b in this way for
another project.

matt

 

I think that's a great idea. It would be a quick enough car (14's) and yet be nicer on the street than most RX-7's on the road. I think you can do it for $8k also. Especially if you pick up used TII drivetrain for cheap.

200 rwhp doable on stock internal 20B in my opinion. I'd put in the 9.7:1 rotors and maybe do a bit on the porting (maybe) and easily have 250 rwhp.

 

I cant think of any way to use a s5 rotors. The counter weight wont work. It was designed for 2 rotors. The 20bs counter weight isnt the same as the 13rew or 13bt s5 right?

 

the rotors from 13B N/T 89-92 are the same weight as the rotors in the 20b as far as i know.

matt

 

hmmm. thats right...duh... and actually i have a pair.

 

ha but a pair wont work! you need three!

mike

 

hehe mike, I was going to say that to but refrained,
besides he has two more than I have

matt

 

Well I could always run blown. I saw one at atkins shop. I think it was a 12" roots blower. Wouldnt be the best for HP but it still would make the set up simple and my torque would be rediculous. I could brobally burn all the way though 3rd gear. Hmm.... Step by setp though. NA will be the goal first. Thanks the help guys. The piecxes are coming together. Im picking up the rest of the TII drive line today.
Sky

 

In dealing with naturally aspirated engines, you have to consider back pressure. I have no clue what you have to consider, but I know it is a big player in most NA applications. I kind of skipped the whole NA thing and went straight to turbocharged power... I feel I'm missing some things. I would like to do an NA project in the near future... but the desire for boost is a HARD one to turn away.... I think Peter Egan put it nearly had it perfect when he said "Racing makes Heroin addiction look like a vague wish for something salty." The only change I'd make would be replacing his word "racing" with my word "boost"

 

I have a TII already so boost need is satisfied. I will eventaully get to a major turbo swap on the thing. Your right though, boost is very addicting. So is the sound of a blow off valve =)

 

soo, uh anyone have any more to add to N/A 20b. Think daily driver, and emissions legal

 

How about a header? I think the best starting point would be the header plate from Racing Beat. Last I checked it was $42. Just get it and a couple of U bend pipes and maybe you could fabricate something that will have equal length primaries. Has anyone tried equal length short primaries on a 20B before? Is it even possible in an FC (or my Cosmo hehe) engine bay?

 

Is it SS?
If you can fit a 20b w/ turbos sticking on the side of it you should have room for some headers.

 

well the header collector is one half of a v6, that should be easy to find, and it looks like theres plenty of room for headers in an fc, i looked at my 1st gen for something else and thers about 4-5" between the rb headers and the chassis rail, the fc should be similar

mike

 

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