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Single Turbo conversion versus stock 3d Gen.

Old 03-18-18, 10:54 PM
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OK Single Turbo conversion versus stock 3d Gen.

My son and I are having a generational discussion about the stock twin turbo set up of the 3d Gen RX7 versus the single turbo conversion we are seeing on many after market modifications offered in used cars. I prefer the factory, original twin turbo setup. My son said that there is no reason to do a single turbo conversion, as the factory twin is road tested, factory engineered and gives the most consistent and reliable engine performance over the single turbo. What do you think? I would pay more for a factory stock car over a modified single turbo conversion car, regardless of the quoted horsepower increase. What do you think? Thank you. Respectfully, John J. Garvey
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Old 03-20-18, 09:20 AM
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Modern singles will easily outpace the OEM system in response and output (simultaneously!) & be more reliable from a lack of vacuum lines standpoint.

That being said, well maintained stock examples will always be worth more.
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Old 03-20-18, 01:00 PM
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Most people go single turbo on the FD because they can't figure out how to keep the sequential twins working (it is complex) or they want more than the 350-400rwhp the stock twins can provide.

Not many single turbos can match the stock sequential response.
Most quality ball bearing single turbos (GT3576R, Apex RX6, etc) of the same 350-400rwhp range as stock twins will be as responsive above 3,000rpm.
A very few (I have experience with EFR 7670) can be as responsive as the stock twins with bolt ons from 2,500rpm on.

For the Gunsai Touge competition in Hot Version videos RE Amemiya has stuck with stock twins for response while Feed (both have been "Touge Monsters"/winners) uses small singles (T04S or the new Garret GTW they put on).
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Old 03-20-18, 01:11 PM
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Originally Posted by BLUE TII View Post
Most people go single turbo on the FD because they can't figure out how to keep the sequential twins working (it is complex) or they want more than the 350-400rwhp the stock twins can provide.

Not many single turbos can match the stock sequential response.
Most quality ball bearing single turbos (GT3576R, Apex RX6, etc) of the same 350-400rwhp range as stock twins will be as responsive above 3,000rpm.
A very few (I have experience with EFR 7670) can be as responsive as the stock twins with bolt ons from 2,500rpm on.

For the Gunsai Touge competition in Hot Version videos RE Amemiya has stuck with stock twins for response while Feed (both have been "Touge Monsters"/winners) uses small singles (T04S or the new Garret GTW they put on).
I think the 7670 is slightly oversized if 400whp is the ticket. a 6758 is good for 450whp and would likely provide the response the OP is looking for. You certainly have a lot more headroom with the 7670 though! If you were just looking to match the stock twin performance, I'd even consider a 6258 for ~325whp.

On the other hand.. if you're booking it, you'd never be at 2500-3000 rpm anyway

edit: disregard this! I am in piston engine land when it comes to turbo sizing..

Last edited by colditz_II; 03-20-18 at 08:50 PM.
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Old 03-20-18, 02:41 PM
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I may be biased as I just made the switch, but I would vote single turbo all day long. But your end goal will greatly influence which turbo to run. I had sequential twins with bolt-ons up until I chewed up an apex seal. During the rebuild decided to go with the Turblown 7670 kit. Still breaking the set-up in so i can't give a true apples to apples comparison yet but given the choice I would pick the single turbo.

The sequential twins are very complicated as everyone has said. They are a massive hunk of castiron that pukes out heat. Beyond the headaches of the miles of vacuum lines, multiple solenoids that can fail, countless gaskets and potential leak points, they run much hotter than the newer single turbos. I made no changes to my oil cooler, radiator, intercooler set-up when going single, but I did switch to an electric waterpump. With the twins, I regularly sat at 190-200F idling and it wasn't uncommon to see 210+ driving around. With the single set-up I have yet to go over my set temperature of 185. And after driving around for an hour I can open the hood and grab the hot side piping of the intercooler. I could barely touch the cold side before.

The only upsides I really see sticking with the OEM set-up is if you live in a place that is very strict about modifying a street car, you're a collector and want a piece of late 90's engineering, or you want to keep the car as quiet as possible. The 7670 is a very quiet single turbo but it make more noise (Turbo whistle, BOV, etc...) all of which enhance the experience IMO, but aren't for everyone.
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Old 03-20-18, 08:45 PM
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I think the 7670 is slightly oversized if 400whp is the ticket. a 6758 is good for 450whp and would likely provide the response the OP is looking for. You certainly have a lot more headroom with the 7670 though! If you were just looking to match the stock twin performance, I'd even consider a 6258 for ~325whp.

On the other hand.. if you're booking it, you'd never be at 2500-3000 rpm anyway
The EFR 6758 compressor is good for 52lbs/min or ~ 350rwhp on a rotary engine maxed out.
The exhaust wheel is really small and will choke performance on the rotary. EFR 6758 58mm exhaust wheel is bigger than 51mm FD stock primary turbo exhaust wheel, but smaller than FC stock 64mm turbo exhaust wheel.

EFR 7163 is the smallest EFR I would think of using on a single turbo rotary.

EFR 7670 compressor is good for 64lbs/min. Mine maxed out at 420rwhp on the dyno I was on (will vary). I was running 26psi and it would fade to 21psi at peak power and "recover" to 23psi after the engine VE dropped. Even the EFR 7670 exhaust side is on the small side for a single turbo on the rotary depending on how much power you want to make. I really saw this when I did a run with the dual 44mm external wastegates closed and boost/torque peaked early and fell like a rock- much less power than with wastegates letting engine breathe and a lower boost.

On the other hand.. if you're booking it, you'd never be at 2500-3000 rpm anyway
Yup, unless you really pooch a shift or launch- in which case I found even the 7670 recovers really fast. Above 2,500rpm or so the EFR 7670 was more responsive than the primary on my sequential FD with bolt ons. Pretty twitchy even- always spooling on the freeway for instance.
I think if you did a variable volume "quick spool" valve on the EFR 7670 it would be just as responsive as the stock sequential's primary below 2,500rpm.
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Old 03-20-18, 08:49 PM
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Thanks for the corrections! I am thinking of piston engines when I think about turbo sizing. Didn't realize the VE differed so much on a rotary.
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Old 03-20-18, 08:49 PM
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I may be biased as I just made the switch, but I would vote single turbo all day long. But your end goal will greatly influence which turbo to run. I had sequential twins with bolt-ons up until I chewed up an apex seal. During the rebuild decided to go with the Turblown 7670 kit. Still breaking the set-up in so i can't give a true apples to apples comparison yet but given the choice I would pick the single turbo.
Just remember the EFR 7670 isn't anything like other single turbo swaps available.
It is worlds apart. The bigger EFR 8374 is the closest single turbo in terms of response that can meet the stock twins power- that is how far in front of other single turbos the EFR turbos are...
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