Ok so I have read just about every thread on turbos for the 20b and it looks like the preferred size is a gt42r with a .95 to 1.15 hot a/r. I just got a 20b and the guy didnt know really anything about it so I am just going to assume that it is stock. I cant afford to have it built right now so would that turbo be best for me or would a gt4094 be more suitable? I would like to attain close to 500-550 rwhp with methanol. Also I have read that a BB turbo doesnt really make that much of a difference until you get into the bigger turbos. So what is the cut-off size to where it starts making a difference?

 

I would say if you are not porting it, and just want 500whp and not spend a fortune, go with a Garrett GT4202 journal bearing turbo and a 1.01-1.15A/R. I have seen about 500whp easily with relatively good spool on stock port 20B. I can't remember the name of the forum member but he is on here.

Chris

 

If that's all you're shooting for, and the turbos on there are still stockers, I'd personally go the BNR route. Maximum simplicity, keep cost low, get the power you want, and have great response.

 

http://www.catenet.net/dyno.php

This might help and even if it doesn't it's still interesting.

 

Thats kind of the way I was leaning, but unsure. So should I see full good boost around 3500 with this on street port. Also I read that torque starts to fall off around 5500 is this typicall of all turbos on the stock port 20b?

 

gt4202 is too big for that power level, you will be much better off with something like a gt40r or a Borg Warner s370.

20b stock exhaust ports are terrible, so yes you will start to lose boost very early, which is all the more reason not to get a turbo that is way too big.

 

So you think a GT4094 would be better? If so I have a buddy with one I can get fairly cheap. I read the posts on turbo sizing and though they have a lot of information it is just that. I am not sure how the stock 20b will flow and exactly what turbo and trim to use. The only reason I was thinking a 42 is that just about every post asking about what turbo for a 20b ends up with a gt42 answer. Its funny how confusing this can get.

 

Thanks patman and chris for your inputs.

 

A GT4202 is the smallest single I would put on any 20B. And yes you should see boost from that rpm even without a streetport. Here is a stock port 20B with a GT4202:

http://i244.photobucket.com/albums/g...8corrected.jpg

Looks good to me. BTW a GT4094 is a GT4294 stuffed into a GT40 compressor housing so its still a GT42. If you get a T4 flanged Gt4294 you will essentially have the same turbo and spool but more HP capability if you want more later on...and a GT4202 is only slightly bigger on the front end.

Chris

 

At what boost did that hp occur? Since I will be using Methanol I was thinking of running around 20 psi. Any idea what type of power I should expect with the 4202 with basically a stock motor better inj/ignition/ecu?

 

The boost in that dyno plot was somewhere between 9 and 7 psi. The WG was a V44 with a 0.5-bar spring in it. No boost controller. The boost spiked to ~9psi, and then dropped to ~7psi.

 

Oh very nice. It looks like it started building boost around 3800. Thats pretty good. So with a 7.5 hp increase per every psi of boost would mean that at 15 psi I would be making roughly 498-500 hp. Which would make the 20b fairly durable. Does that sound about right?

 

The AFR trace could serve as a rudimentary trace of engine load (though not exactly).

It began building boost before that, ~3300RPM, and was at ~9psi about ~4000RPM.

 

I am getting really excited and cant wait to start putting it in. I have to finish stipping the engine bay down for repaint first. I figured since its out I might as well repaint it since it has been scratched up. Plus the car had some weird black graphic on it that didnt look right. So I am repainting the whole car back to the original J9 CYM. I am going to have Steve Kan do the tuning since he is only about 2.5 hour drive from me. I think I am going to go with the gt4202. So my next question to Calculon or Chris is how much sooner would a BB spool up vs the JB on this turbo. If it isnt 500 rpm or better I wont waste my money.

 

1.0 A/R Vband gt42r bb. Lighter and will spool better.

 

I think you would be pretty welll off if you used the s475, with a divided 1.10 a/r, and of course, the divided mani. the BW is proven to outspool the gt42r, its a ton more reliable being a journal bearing, and its MUCH cheaper! you can get a race compressor housing for it as well, which will increase that spool time just a bit more, with another couple dozen ponies on top.

 

Kind of but not really, the moment you stuff that compressor into a smaller comp housing it effectively reduces the A/r meaning more boost required for a given amount most often. Also a 4094 runs a slightly different wheel than the 4294 that isn't quite as efficient. Not harping just clarifying.


dreed7235

Here is a dyno of a essentially a stock ported 3 rotor. I say 3 rotor because it uses FD housings not 20B housings.

https://www.rx7club.com/showthread.p...light=20B+TiAL

This car ran FD rotor housing that were only port matched to the sleeves nothing more, wouldn't even classify it as a mild street port. This was also with a somewhat restrictive exhaust as the owner wanted quiet and smooth running since he was near 60. That was on 10psi with pump gas.



~S~