I have a new (to me) 1995 R2 that I'll be bringing back to life very soon. Needs a rebuild and a variety of other things. Very exciting times.

I'm starting to put together a plan of attack for what I'd like to do with the vehicle. Obviously, a full rebuild is on the list and that will be done by Rotary Performance since they are about 8 miles from my house. My vision for the car and it's power plant is I want the absolute best engine response possible while still maxing out what I can get on 93 octane fuel since that's readily available in my area. I'd like to daily around 400whp if possible, with the option for more on E85 which I also have locally. I am willing to run a flex map, but not E85 exclusively. I have a feeling the stock twins are shot so they will not be going back on the car. Thus, I'm trying to make up my mind between 3 potential options....BNR Stage3, EFR7670, or EFR8374.

Questions: How do each of these setups responsiveness compare with regards to each other? Logic tells us the 7670 is going to spool better than the 8374...but does it spool better than the stock twins or the BNR Stage 3 twins? Do the BNR Stage 3 twins spool better than stock? I can't find compressor maps for the BNR Stage 3 setup so it's also unclear if the 7670 will have more top end or not. And lastly, the 8374 will obviously make more power than the 7670, but how bad is the added lag? And how does the lag of an 8374 compare to stock twins?

I suspect the "order of responsiveness" may go something like this... Stock Twins > BNR Stage 3 > 7670 > 8374. Anyone have a different opinion? It's also occurred to me that with the advances in turbo technology over the years, the EFR turbos might actually be more responsive than the stock twins. I've owned a low mileage stock twin FD so I know what that's like but I've not driven any of the other 3 setups.

And yes, I realize this thread is worthless without pictures. You know I'd never do that to y'all.

 

7670 IWG on our cast short manifold does out response the stock twins( and every variant on the market). Generally the bigger twins slow spooler in my experience, its just basic physics( bigger wheels have more mass).

The 8374 EWG is slower than the OEM twins noticeably( assuming twins are on a full 3" exhaust). The 8374 IWG with a 3" exhaust is a tick slower than the OEM twins, but as soon as you move up in exhaust size its about the same as the OEM twins. Be aware that 3.5" or bigger leads to boost creep( as it does on the OEM twins also) on the IWG large B2 frame turbos( 8374 or bigger, not an issue on the 7670).

I've never had a soul complain about the response on the 8374 FYI.

 

Thank you Sir. I was hoping you'd chime in since you guys have a lot of experience with those turbos. I didn't realize the IWG EFR turbos spooled quicker than the EWG variants but it makes sense.

What's the most you'll get out of a 7670 on 93? And I don't mean the ragged edge for dyno queen purposes, I mean for daily use. And what's achievable on E85? I saw the EFR8474 has replaced the 8374 boasting a larger compressor wheel and I was REALLY hoping the 7670 would get a similar treatment. Kinda hoping for 400whp on 93 and 450 on E85. Is that possible with a 7670?

 

I haven't had direct experience with the new IWG turbos, but in general a single turbo car is going to be louder than a sequential twin car. The stock turbo control door on the twins quiets things down at idle/cruise/low RPM and gets louder when you are at full throttle with the secondary turbo online.

Another option is 99 twins. They will probably be closer to 350 but you have fantastic spool and response. I've been running 99's for ages and the response is fantastic.

You won't make as much top end power, but the low end power that you use all the time is so much better. Pair it with 4.44 rear gears from an RX-8 and the car just leaps off the line.

Dale

 

 

The 7670 is at its limit to make 450 peak rwhp, as the compressor runs out of steam in the high rpms( at higher boost pressures). The low end and mid-range will make a ton of power however, as you can see in this video; This car on the 7670 will eat a 450rwhp Rx7 with a standard turbo kit alive.

 

IMO, don't rule out the newer twin stock-like Hitachi SP or KAI's. They spool like stock twins(faster than anything else if you redo your intakes and exhaust as I did), put out 12% more air, and are designed by Hitachi to take more boost and to last longer at higher boost. Ari has them at RX7.com, your neighbor too, right next to Chris at Rotary Performance. Look at some of my previous posts about these turbos as well as the intake and exhaust mods that really helped.
Mike

 

I'm very happy with the 8374 IWG spool, with a 3" open exhaust, and a ported housing to help with boost control. I can't imagine going through all the work/expense for a single turbo for anything smaller, unless you've got a really specific application. And, I had an extremely strong TT car w/ '99 twins.

 

To elevate the boost creep, get an external wast gate version as boost is easier to control - that is what a few have told me.

 

I will agree with ptrhahn. With the added cost of going single, I don't think I could justify the 7670 unless you were just hell bent on that particular setup. I was looking at the 7670 myself, and while it is a phenominal turbo, my "advisor" noticed a drop-off in boost in the upper rev-range that was echoed from a few different people I asked for advice, leading me to go with the 8374.

 

One thing to keep in mind about the stockers and BNR's: If you want that quick spool then you have to be sequential and deal with the complexity of the 72 vacuum hoses. With that said, looking at your power goals while taking into account the pros/cons of your options the EFR 8374 IWG is the top contender.

 

Yeah, I think once you choke off the $6-10k it really will cost you to go single, getting 10 extra rwhp would really kill your wood.

 

+1

If the car is stock, and even if you can do the work yourself, you are looking at a lot of money to upgrade supporting systems to push BNRs or 99 spec twins. Going single is almost a no brained unless you want a stock looking engine bay.

$1000 fuel system
$500-$1000 intercooler (if vmount add more)
$2,300+ new twins (used knightsports on eBay right now for less but I wouldn't recommend it)
$600-$1000 downpipe and exhaust
$1500-$3000 Ecu and tune
$1000 of random other things while you are at it (wideband, gauges, fluids, gaskets, etc).

That is without labor, assuming you do the work yourself. You will have to do all of this (maybe you can save a couple hundred on a fuel system with less capacity) for the upgraded twins. Swap out the cost of the twins above for an EFR 8374 turbo kit (which includes the downpipe), and you are within $1k-$2k in terms of total cost, but way more potential for power.

 

I've heard about the boost drop off in higher RPMs too. I'm told it's the wastegate basically gets forced open? I think I remember seeing it can be remedied though.
I think that if your pricing estimate is for "straying from stock and going single" then it's probably accurate. However, if you're already doing a variety of other upgrades that would need to be done regardless of whether you're going BNR twins or single, then I think the price difference is MUCH less than what you've stated.

 

No, it's a flow limitation. On these engines at higher RPM ranges, that turbo begins to run out of steam. Large ported motors can get more out of it, but a crude analogy would be to say that this is like squeezing juice from an orange; squeeze harder if you want but eventually you're just going to run out.

You're not entirely wrong but that shouldn't suggest switching from BNR3 to EFR8374 (for example) would be inexpensive; the EFR kit alone is 4k+ and that's before any inconel shielding (if you elected to buy it). This is especially true if RP is doing the work. They're great but are by no means a value option for service.

I think you're guiding star for these decisions, though, should be how you intend to use the car. If you're aim involves regular track time at either MSR, Eagles Canyon or elsewhere, that should weigh heavily on your decision here. And if you do indeed plan on getting out to the local tracks with any frequency; 8374 all day long..

 

I did the EFR 7670 with bigger 1.05AR external wastegate housing on my FC with 3.5" turbo back exhaust.

When I was on my high boost race map on the EFR 7670 it hit 26psi a bit faster than my stock twins can hit 10psi (creeping to 17psi) now on my FD.

My FD was running dual 60mm style downpipe (bigger area than 3", less than 3.5") to 4" downpipe back exhaust.

I was just looking at dyno graphs of the two set-ups myself because although the stock twins can hit 10psi by 2,000rpm I was curious why it didn't feel more powerful 2,000rpm to 2,500rpm than my EFR 7670.
You see, my EFR only has ~4psi at 2,000rpm and didn't hit 10psi till 2,500rpm or so.
Still the EFR 7670 made 125ftlbs at 2,000rpm and 170ftlbs torque at 2,500rpm which is also what a really good sequential twins plus bolt-ons set-up will do.

I think the high overlap rotary just doesn't like the restrictive exhaust side of the primary turbo operation.

I would actually advise that you do the EFR 8374 though since I don't think you need the response of the EFR 7670 if you are only spooling it up to low psi on 93 octane tune.

My EFR 7670 response.
On my Greddy gauge (lower one to Right of stock gauges) when it is peaking at 1.75 (x100kPa) that is 26psi. That is how fast EFR 7670 hits 26psi.

 

That is absolutely mind blowingly fast!!!

 

Holy ****....yeah, that's unimaginably fast! I'd love to have that sort of boost response. That video is exactly what I'm looking for to see how the car actually behaves. I'd be interested to see a similar video of a car with the 8374.

 

In Armen's videos of his Turblown EFR 8374 kit you can see tach and boost gauge to the right on the speaker cover gauge pod.

Straight up is 13psi (which is more the range you would want).

EFR 8374 is no slouch!

 

Me playing around on practice laps feeling out new powerband.

Note how throttle looks directly tied to boost gauge needle. Incredible response.