turbo choice s4/s5

[sil80drifter]

I am planning on turboing an SOHC block this summer. Now because my budget is somewhat low, and I am not expecting any humongous power gains, I will not get a t3/t4 turbo because I doubt I can get one for 300 bucks (even if used). My friend suggested that I get a used RX-7 2nd gen turbo, either the older s4 or the somewhat newer s5. Accompanying that wil be a some kind of weird-frakenstein weld of the FC (2nd gen) turbo manifold and an 240 SOHC header exhaust flange (the welding will be done by me and him, it IS possible, it has been done, and can work out quite well if you knwo how to weld, so please don't flame this part too bad). I know it doesn't sound very safe, and extremely bootleg and ghetto, but the real question is; how much power can I expect out of a s4/s5 turbo, at up to 10lbs of boost. Also if anyone has any info on those turbos (I've looked in search and overall in google about this kind of setup, it seems it's quite an uncommon idea), please share it with me so I can make an "informed" decision. Also if you maybe know of a t3/t4 or t4 which are being sold for not over 400 bucks (new) or 300(used), then please let me know. Another reason for not getting a t3/t4 is because of my low boost plans (i will not boost over 10psi, this is just a learning project), a t3/t4 will be over-kill to a degree, because I won't be using its full potential. Hence a smaller turbo, for little money is a very good choice for me. Any input on turbo choice would be appreciated, keeping in mind that this project is more lesson oriented than max. performance gain oriented.

Thanks in advance guys,

sil80

[C-Kwik]

Choosing turbo size is not limited to boost. I don't have compressor maps for the turbos you describe, but keep this in mind. Compressor efficiences are different at different flow rates even at the same boost. Smaller compressors will hit their peak efficiencies sooner. If the peak efficiency comes in quite early, you will get to more inefficient areas for the compressor as you rev higher. This means less power. Keep in mind Turbine flow is also crucial to making power. Too small a turbine will restrict flow and make your motor feel like a dog at higher revs. T3/T4 combos are actually a good compromise between good response and high-end power. Personally, I'm more of a big turbo person myself. What I would look at more when choosing a turbo is how much power you want, how much fuel do you want to have to supply, and if you run a small turbo for response but you want big power, how much more boost are you willing to run to make up for the compressor inefficiencies at higher flowrates. Me? I'll take a little bit of lag anyday to get more power. Trust me, lag really occurs only in 1st gear, as you should be in your powerband in everyother gear if you size your turbo properly. Drifting is one of the only things I would think you would want more response over sheer HP.

[sil80drifter]

Although only a "practice run" I hope to achieve 300HP at the crank with this setup, and I will not skimp much on the parts that will keep it from blowing up, like injectors/fuel rail/fuel pump/fuel management, IC/IC-piping, and oil/oil-routing/cooling.I guess I should rephrase my question in this form: Can I achieve 300HP with the FC turbo? And where would I be able to get flow-charts for this or other turbos. Is there a program (software) that accepts different turbo parameters/engine parameters and then pops out a flow chart?Thanks for your answer C-Qwik, it already pointed me into the right direction of thinking about this whole thing.More knowledge is always welcome.

sil80

[ziggy682]

For information on the s4/s5 turbochargers, search here.

http://www.rx7club.com/forum/

I know the s5 turbochargers were less reliable, because they used either a dual stage turbine or dual stage compressor. I think it has some kind of gate that opens after a certain rpm to make the turbo act like it's bigger. I know that a lot of RX-7 guys have problems with this system.

Why are you planning on using an s4/s5 turbocharger anyway? I think you would be better off using a z31 turbo. Their's less guess work involved because we already have the flow maps, and it is a good size for <10psi setups.

Anyway, good luck with whatever you decide to do.

[sil80drifter]

You are a little misinformed. The SETUP of the double turboes on the 3rd gen rx-7 was not very good for high HP applications, because of boost/torque spikes it provided, since the second turbo would violently kick in after a certain RPM. The turboes themselves are as reliable as any other turbo out there that is used and (hopefully) not beaten on. Now another question; can the z31/z32 turbo make 300hp (at crank) at 10 psi? Is it hard to obtain one? How much would it cost? How much would the stock manifold for either turbo cost? Where do you have the flow charts for the z31 turbo? Could you link/post/email them to me, please?Thanks,

sil80

[oi138]

You are a little misinformed. The SETUP of the double turboes on the 3rd gen rx-7 was not very good for high HP applications, because of boost/torque spikes it provided, since the second turbo would violently kick in after a certain RPM. The turboes themselves are as reliable as any other turbo out there that is used and (hopefully) not beaten on. Now another question; can the z31/z32 turbo make 300hp (at crank) at 10 psi? Is it hard to obtain one? How much would it cost? How much would the stock manifold for either turbo cost? Where do you have the flow charts for the z31 turbo? Could you link/post/email them to me, please?Thanks,

sil80

Nothing short of a bigger t3/t4 or equivelant will make 300 hp at 10 p.s.i.

And that would have to be tuned almost perfectly to make that much on a t3/t4 at that amount of boost

James Poe

[sil80drifter]

Anyone who can back that up? Dynos/someone's car? I don't wanna be judgmental but from someone with 15 posts, I don't quite have complete faith in that statement. You know what I mean, no hard feelings. The thing is that I've seen someone run 280 HP, almost completely untuned (and not professionally tuned at all) turbo the SOHC with a t3/t4. At 7.5 psi. Hence, I think at 10psi, the very well tuned t3/t4 should be around 350 HP at the crank. Which is why I'm wondering if a very well tuned smaller turbo can make 300. Btw, flowcharts anyone? Any kind of flowcharts. T3 or t4 or t3/t4 or z31/z32, anything?

sil80

[ziggy682]

You are a little misinformed. The SETUP of the double turboes on the 3rd gen rx-7 was not very good for high HP applications, because of boost/torque spikes it provided, since the second turbo would violently kick in after a certain RPM. The turboes themselves are as reliable as any other turbo out there that is used and (hopefully) not beaten on. Now another question; can the z31/z32 turbo make 300hp (at crank) at 10 psi? Is it hard to obtain one? How much would it cost? How much would the stock manifold for either turbo cost? Where do you have the flow charts for the z31 turbo? Could you link/post/email them to me, please?Thanks,

sil80

Nope, I'm not misinformed. I wasn't refering to 3rd gen twin turbo setups, I was refering to 2nd gen twin scroll turbochargers. Scroll down to 1987 and read about the twin scroll turbocharger here http://home.earthlink.net/~icemark/FCseries4.htm

I think the z31 turbocharger could make 300hp, which would be about 240rwhp, if the system was designed properly. The z32 turbo is a T25, and is too small for our cars. The turbo should run $100-$200, and you should be able to find one at a junk yard. Not sure about the stock manifold, because I haven't ever seen one.

Here's a compressor map for a 60 series T3 like the z31 turbocharger.

http://208.55.223.137/comp_maps/fig4.html

Also, check out this link for some really cool turbo-related java apps.

http://www.turbofast.com.au/javacalc.html

[C-Kwik]

http://www.turboneticsinc.com has flow charts for Garrett/Turbonetics compressors.

At 7.5 psi, 280 Crank HP would be a high estimate for a T3/T4. 280 WHP would be very difficult to obtain. Considering that a guy I know ran 278 WHP at 11 psi with a T3/T4.

[WDRacing]

Well we're obviously looking for a real good used turbine. Size should be T3 or better. I have no personal data on any RX7 turbo's other then all my friends swap them out fairly early in the mod process. But The Wankel makes silly amounts of exhaust volume and can run extremely large turbines with considerably less lag.

You should take into consideration what the stock crank HP is. Then assume that the average gain is 8-10 hp per psi of boost.That will help out with the amount of boost you'll need to run to achieve your goals. The 8-10 also assumes your using a fairly efficient turbo. Again anything T3 or greater.

I have quite a few friends in the Skyline world who have swapped in the Z31 turbo with fantastic results. This is with the RB20 as well as the RB25. They've found the Z31 turbine to run out around 14 to 16 psi. After that it tends to become a heat pump.

With a really good fuel system and I/C I don't see any reasons you couldn't run 12 psi. Of course assuming you know what your doing and have some type of knock indication.

Best of luck, keep us posted. Not that many KA24ET's running around.

WD

[sil80drifter]

ziggy682, sorry I misinterpreted you, you are correct in the fact that the design of their turbo manifold was somewhat odd, QUOTE: "At low engine RPM's, the smaller primary chamber concentrated the exhaust gases, increasing their velocity. Above 2500 RPM, the larger secondary chamber opened, directing additional exhaust gases across the full face of the turbo blades providing further increased horsepower at high engine RPM's." This does not make the turbo bad, only their twin chamber manifold setup, but I will not be using the whole thing, just the turbo flange.

Thanks a lot for the links and info on the z31 turbo, they've helped quite a bit.

http://www.turboneticsinc.com has flow charts for Garrett/Turbonetics compressors.

At 7.5 psi, 280 Crank HP would be a high estimate for a T3/T4. 280 WHP would be very difficult to obtain. Considering that a guy I know ran 278 WHP at 11 psi with a T3/T4.

C-Qwik! 278WHP is 347.5HP AT CRANK AT 11PSI! (considering 20% drivetrain loss) I only want 300 at crank at 10psi, only 1 psi less. Why is it a high estimate?Great link on the turbo charts, thank you.

WDRacing, your info has been most uplifting. Now I am eager to find a z31 or t3 and find out as much as I can about it.

If anyone else wants to share anything related to this, feel free

sil80

[oi138]

Anyone who can back that up? Dynos/someone's car? I don't wanna be judgmental but from someone with 15 posts, I don't quite have complete faith in that statement. You know what I mean, no hard feelings. The thing is that I've seen someone run 280 HP, almost completely untuned (and not professionally tuned at all) turbo the SOHC with a t3/t4. At 7.5 psi. Hence, I think at 10psi, the very well tuned t3/t4 should be around 350 HP at the crank. Which is why I'm wondering if a very well tuned smaller turbo can make 300. Btw, flowcharts anyone? Any kind of flowcharts. T3 or t4 or t3/t4 or z31/z32, anything?

sil80

Well I have completely built my own turbo kit. welded the manifold and all. I have had my 240 for about 5 years and have put 4 motors in it all by myself. transmissions swaps. Harness swaps. Not to mention this is the 4th car I've turboed from the ground up (not using turbo kits). I would definatly consider myself qualified.

James Poe

[sil80drifter]

James, still I will have to disagree (perhaps temporarily) with you that nothing short of a t3/t4 will make 300HP (crank) at 10 psi. Until I do it myself and find out that it;s true Trial and error, hmm? Have you put a t3 or similar turbo (smaller than t3/t4) cranked it up to 10 psi, tuned it well and saw that it didn't make 300hp? If yes, then maybe it is harder than I think it is...if not then I don't think you can 100% be sure of it. I do respect your opinion however and am willing to go as far as lower my goals, but...I really wanna try it first. Btw, maybe u can give me some tips when I am in the middle of building my turbo kit, cuz I sure as heck will need some advice

sil80

[WDRacing]

What is your motor putting out at the crank right now in NA form?? Take that # and add 80 assuming you stick with 10 psi. That will give you a close approximation to what you'll be running with a T3. The Hybrid T3/T4 will generate slightly higher figures do to the volumetric efficiency being better. But the boost level is to low(10psi) to make a huge difference.

WD

[sil80drifter]

Then can someone explain to me how C-Qwiks friend is running 347.5HP at crank with only 11 psi and (the slightly better) t3/t4?How is the guy on the other thread running 285WHP (which is like 536HP at crank) on a T3, if it is supposed to crap out around 14-16 psi, so he can't be boosting TOO high (http://www.nissaninfiniticlub....ber=2). And how did the first maker of the SOHC turbo kit with a t3/t4 at 7.5 psi make 280HP at crank? I can't post the link right now, but it's the guy on the 240sx.org forum, in the section of all the mods done to the 240s, actually there are two guys, the one I just mentioned and another running 230WHP at similar boost levels using same type of turbo. Are all these people lying? Is their tuning THAT good? It doesn't seem to take much to achieve those numbers. And the 10hp per psi seems to be a bit of an underestimate. This is just what it seems like from my side of things.Could there be different reasons?

sil80

[oi138]

Then can someone explain to me how C-Qwiks friend is running 347.5HP at crank with only 11 psi and (the slightly better) t3/t4?How is the guy on the other thread running 285WHP (which is like 536HP at crank) on a T3, if it is supposed to crap out around 14-16 psi, so he can't be boostign TOO high (http://www.nissaninfiniticlub....ber=2). And how did the first maker of the SOHC turbo kit with a t3/t4 at 7.5 psi make 280HP at crank? I can't post the link right now, but it's the guy on the 240sx.org forum, in the section of all the mods done to the 240s, actually there are two guys, the one I just mentioned and another running 230WHP at similar boost levels using same type of turbo. Are all these people lying? Is their tuning THAT good? It doesn't seem to take much to achieve those numbers. And the 10hp per psi seems to be a bit of an underestimate. This is just what it seems like from my side of things.Could there be different reasons?

sil80

ummm. well maybe it could be done. but 536 hp at the flywheel = about 429 to the wheels assuming 20% drivetrain loss.

[oi138]

James, still I will have to disagree (perhaps temporarily) with you that nothing short of a t3/t4 will make 300HP (crank) at 10 psi. Until I do it myself and find out that it;s true Trial and error, hmm? Have you put a t3 or similar turbo (smaller than t3/t4) cranked it up to 10 psi, tuned it well and saw that it didn't make 300hp? If yes, then maybe it is harder than I think it is...if not then I don't think you can 100% be sure of it. I do respect your opinion however and am willing to go as far as lower my goals, but...I really wanna try it first. Btw, maybe u can give me some tips when I am in the middle of building my turbo kit, cuz I sure as heck will need some advice

sil80

Hell go for it. If you do it then more power to ya. I will be glad to help during your process of trial and error

James Poe

[sil80drifter]

Sorry I meant 285WHP = 356 crank HP. I hate typoes.Thanks for being supportive, James, I really appreciate it.You just watch, in two months form now u won't know what to do with all the little detail questions I'll be asking

sil80

[WDRacing]

Then can someone explain to me how C-Qwiks friend is running 347.5HP at crank with only 11 psi and (the slightly better) t3/t4?How is the guy on the other thread running 285WHP (which is like 536HP at crank) on a T3, if it is supposed to crap out around 14-16 psi, so he can't be boosting TOO high (http://www.nissaninfiniticlub....ber=2). And how did the first maker of the SOHC turbo kit with a t3/t4 at 7.5 psi make 280HP at crank? I can't post the link right now, but it's the guy on the 240sx.org forum, in the section of all the mods done to the 240s, actually there are two guys, the one I just mentioned and another running 230WHP at similar boost levels using same type of turbo. Are all these people lying? Is their tuning THAT good? It doesn't seem to take much to achieve those numbers. And the 10hp per psi seems to be a bit of an underestimate. This is just what it seems like from my side of things.Could there be different reasons?

sil80

The 8-10 psi is an average gain. I'm not about to quote exact numbers, its not my motor. I don't have any data on C-qwiks buddies car. Again, I didn't build it or tune it.

My friend has a GT30 on his RB20 putting out 28psi, who said T3's are only good for 15 psi??

I guess I'm not understanding what your looking for here.Each motor you refer to isn't built the same, the ECU's aren't the same, the injectors aren't the same the intakes aren't the same...

WD

[sil80drifter]

WD, it's ok, I already got the answers that I wanted, sorry to have confused you/not expressed myself clear enough. I am going to build an SOHC turbo, with a t3 or similar turbine, and custom manifold/intake. Injectors will be 440cc or equivalent.No ECU mods, just piggyback. All I wanted to know is whether I would be able to achieve 300HP at around 10psi with this setup. It seems feasible, but probably only with good tuning. Thanks for everyones input,

sil80

[C-Kwik]

C-Qwik! 278WHP is 347.5HP AT CRANK AT 11PSI! (considering 20% drivetrain loss) I only want 300 at crank at 10psi, only 1 psi less. Why is it a high estimate?

I actually confused myself a bit on this one. I usually refer mostly to wheel HP. I was meaning to say 280 Crank HP would be high at 7.5 psi.

I roughly mapped out the T3 turbos in the Turbonetics Catalog, and most of the T3's are off the compressor map at 10 psi at redline. The T3 super-60 seems to be just off the map at or near redline. While it may still provide some boost, you're talking about compressor efficiencies of less than 65%. The higher efficiencies will occur much lower depending on what T3 trim you get. A T04E - 50 Trim is dramatically more efficient throughout the range where it would hit max boost up to redline. Pretty much puts it at 78% most of the way and doesn't look like it will be below 76% at anytime. You might be able to do it at a higher boost level than 10 psi.

[C-Kwik]

Oh, and just to add onto this, keep in mind that more torque made at a higher RPM will raise the max HP much easier than raising it at low and mid RPM's. With too low an efficiency at higher RPM's, the torque will drop off and won't make the same HP that a more efficient compressor will at the higher RPM's.

[sil80drifter]

I'm gonna shoot for the best with a t3 or whatever I can afford then

thanks again for so much good info.

sil80

[JESTER]

Try looking into getting a T3 off one of the old body style 300zx.

you can find one in the junk yards for $300. Check here http://car-part.com/

I dont think the turbo off the ReX-7 is gonna be what you want. Like WD said, T3 or bigger.

[JESTER]

Also, http://WWW.RX7club.com.

They have all the specs on the Turbo II's.

That is if you are still thinking that way......