I'm an "old" RX7 R1 owner (bought it 3/92) and am finally modifying it. I'm new to modifying and kind of learning on the fly. Started out simply enough with a few "bolt on mods" which rapidly got out of hand to an engine rebuild (street porting), full exhaust, ignition, fuel, IC/radiator, water/meth etc. all by the RX7 Store. Just found out that my stock turbos are leaking oil. I have always liked the twin's and had planned on keeping them. Even had the vacuum lines replaced. Zavier is recommending a single GT35R for the power, simplicity, and savings in engine bay heat. I was originally looking at the BNR's as I like the early spool in the power band from the twins but it seems that the GT35R spool early.

For DD and possible the occasional road course would you recommend an A/R of 0.82 vs 1.06 if I'm interesting in most approximating the early spool of the twins rather than having more power at the top?

How is the low end response of the GT35R compared to the twins?

 

Well, I think the .82 would be good for the street, but the 1.06 for the roadcourse. ;-) I'd worry about too much heat with the .82 if you are spending alot of time in the revs.

You're never going to get the real low end response of the twins, but by 3500rpm up a gt35R should be better from there on out. Much better.

IMO,

Andy

 

Thanks for the answer..... To many choices. I would love to be able to side by side test a GT35R and a pair of BNR's with similar setups. The car is still set up for TT (new vacuum lines, Pettit down pipe). Going to single removes all of that. I may have some stuff to sell with only about 400 miles on it.

 

Yeah styx, I know what you mean, I was considering twins for a while, but I mean if I can get the spool I'm looking for with a 35R setup designed for quick spool I'd be down.

How much would having 9.7 rotors help with spool? I'm also going to be running a small core FMIC I believe with small/short piping.

 

Styx,
I have bnr's with many mods as you can see in my signature. I just purchased a car with a gtr35 tonight. There is no comparison, you need to decide what you want more, and how it is useful to your style of driving. Bnr's are the same as stock twins for response, and very close to the same level of HP given the same boost. Where bnr's excel over stockers is they can safely handle higher boost levels.

Single turbos will not give you the same low end response but will certainly have more ooomph once they get spinning. As you can see depending on your setup most ppl would peg the gtr35 around low to mid 3000 range.

My fear was that a single was like non sequential, and based on my limited drive time of non sequential ( a friends fd ) and a single ( the one I just bought ) a single is better.

I am not looking to turn this in to a debate, as this was not a thread for single vs twins - just trying to give my input.

 

I have similar mods to yours. I will be running either the BNR's or the GT35R at 15psi with water/meth @10psi. For a street car 350-400 rwhp would be possible and ideal with either. For reliability a single is probably better.... Likewise for heat. What I can't wrap my head around is how much different will the car ride with a single - how noticeable is the lag.

When you said "no comparison" what were you referring to and which do you prefer?

 

I do not have much drive time with the single so it is not a fair comparison. The difference in response is significant. Twins hit fast and it is pretty steady to red line. The single builds much slower but when it hits it feels harder. For cruising around town the twins would be more fun. I had to concentrate not to build boost. They are just so quick.

I can live with either.

 

Thanks again.... Still undecided. Unfortunately I think I am leaning to the twins for everyday driving. On the expressway it is easy to downshift and take off. On the streets the lag/ zoom effect may become annoying.

I'll sleep on it and call the RX7 store in the AM.

 

Let me get this straight: Because "jobro" said something that opposed my post, you are now satisfied with this and are talking in as fact?

I suggest you go do a little reading on what a "twin scroll" is vs. what a "divided" housing is before you have the int0r-webz make your mind up.

-J

 

Something I found the other day

http://www.freshalloy.com/forums/arc.../t-171744.html
Directly mid page.

"Full_Race_Geoff
07-23-2007, 11:03 AM
Geoff, do they make that T-67/T3 HO in a twin scroll version or is that just to over kill? I'm curious after looking at that turbo on your website. I guess the real question is, does anything have the "response" of the .63 a/r GT35R but make more power at the top on a 2.0Liter SR?

The t3/t67 HO is available in twinscroll, but only on a T4 footprint. I think the T3 might be possible but have not tried it yet.

turbonetics developed their new F1-35R turbo becuase a twinscroll gt35R is almost impossible to make. we are going to test them on some stock evo motors in a cpl weeks, will be interesting to compare them to a 35R. The f1-35R is basically a t4 frame with a twinscroll t4 housing and gt35R turbine/compressor wheels.

I think a good setup that almost has the power of a 35R but better response is the twinscroll 3076R. its a t3 so its easy to work with and vband outlet is nice. TS4L (jason) on fresh-alloy is a good person to ask, he is running that setup now. hope this helps"


As for specifics on my setup;
9.7 Rotors
Streetport
Small FMIC or Air-Water IC
Full racing beat exhaust
some sort of electric boost controller (for multiple settings)
HKS Twin Power
Lighter flywheel
Light WI
94 oct fuel

What I'm REALLY trying to ask is what turbo will get me 15 psi around 2700-3300 rpms, make 350rwhp on that tune and maybe 400+ on a separate tune with higher boost?
Rez's old FC made 1.3 bar @ 2700 but with a .84 hotside. He claims to make ~350 but would it?
http://www.youtube.com/watch?v=Ty85qzSQKcE

Here are some specifics of his setup:
Garrett GT35R .84 hotside
FMIC
Greddy BOV Race with soft spring
SS Autocrhome manifold / wastegate
550 primaries
1600 bosch secondaries
haltech e6x
stock coils/wires/plugs
turboxs manual boost controller
rx7.com in tank upgraded fuel pump
3" exahust all the way back strigh piped to dual racing beat mufflers.
streetported Series 5 motor.

 

instead of being a dick about it why don't you educate the community? obviously it's not very common information because I couldn't find anything about it.

 

After "sleeping on it" I called the RX7 store and am going with the GT35R with the 0.82 exhaust.... opting for more early spool and less top end. Should be better as a DD and is easy enough to change later If I want more.

 

Did they tell you roughly how much whp it'll make with that turbo and at what revs you'll be seeing full boost?

 

Well is a square not a special type of rectangle or did you skip that class in grade 2? Unless people are SPECIFICALLY talking about using a series 4 RX-7 turbo then we can safely assume all twin/split/divided turbine talk is talking about typical divided exhaust housing volutes with matched A/R's.

If you want to get all technical the twin scroll gets better response by making the turbine A/R appear smaller by blocking one turbine runner. Split pulse/divided turbos get better response by keeping the rotors or pistons correctly grouped to space each exhaust port pulse as far from the preceding and following pulses, in order to reduce the negative downsides of overlap via intake cycle charge dilution.

 

^^^ someone who actually knows the difference that's a bit refreshing.

~S~

 

How much boost are you planning to run? What is full boost?

If you're referring to typical 15-16psi that most here refer to. Then figure your going to hit that number (15-16psi) in the 3500rpm area on most cars some do better some do worse. As for HP at that boost level anywhere from 330-400 on that housing is a safe bet with most falling in the 350-380whp range. A lot has to do with WG routing, IC routing, port work.

~S~

 

so what was gorilla ranting about?

 

Basically what he says here, explains it.

Twin scrolls basically were a divided housing that had a flapper in it that would open up to allow a secondary volute to flow more air at higher RPM thus effectively having both a smaller and a larger A/r. Think of it as a poor mans VATN. Divided and or split pulse housings are just that, divided and they split the exhaust pulses for better efficiency allowing you to run a larger A/r with better low end response. I honestly believe people starting confusing the terms once APS starting marketing their stuff "twin scroll" but that's just my opinion.

~S~

 

thank you, I was unsure of how they blocked one turbine runner, but that explains it.

 

The problem arises from people using a term/word improperly, and after a while the wrong usage is accepted.

The technical differences between an engine and motor is know by many people.
But "motor cycles" and "motor boats" are accepted as correct now.

The term automobile is equally used for cars and trucks, and has been that way for many years.
But a car was a small personal use people moving vehicle while a truck was a vehicle to carry heavy loads.
With the advent of SUVs, vans, etc.; the line is now very blurred. Today people call small trucks cars.

What should we call cars like ours?

 

awesome!
how about personal entertainment high performance automobiles?

 

Sorry for the newbee questions:

Are all T4's divided?

I understand the physics behind why 0.82 A/R will spool up faster than a 1.06 ... What will street porting do to the spool up time - will it help make it faster? How about a straight through exhaust?

Short vs long manifolds - which will spool faster (and why... If it's not too much of an answer to post).

Thanks!

 

One more question....

Stock twins spool up at about what RPM's for comparison. If the GT35R is 3000-3500 rpm's ... Where do the twins kick in?

 

Sequential turbos kick in almost instantly. In 5th gear I can hit MAX boost near 300 RPM after hitting the pedal. I don't think I've ever timed it but its not long.

 

Thanks.... 300 or 3000 rpm?