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Car is a long way from doing the engine work, but trying to plan out my build. I’ve done a ton of reading on the forum and have learned a lot, but still have some questions. I’m looking to go single turbo to clean up the engine bay and get rid of as munch of the old stuff as I can. Build goals are to keep the car as Mazda would have intended it, but update and improve a bit with current technology for the most part. Would be happy with 350 hp. I’ve been looking at the BW7670 and BW8374. Seems like 7670 might run out of steam a bit toward redline and have read that it is always spooling, so sounds like the 8374 may be a better choice, but is that to much turbo for my hp goals? I have a power FC and currently tuned using FC tweak and really like it, plus new upgrades coming out now make it even better. I would also prefer not to have to run AI and keep things as simple as possible. Really looking for a good sports car and don’t intend to do any racing with it, just a good street/windy road car, that has a bit of reliability. What are your thoughts?
Going single for a 350hp goal is not worth it at all. Keep the sequential turbos and your PFC, and keep the car how Mazda intended, your words. Downpipe, v mount, keep it easy. If you want a single, go 450+ so it’s more worth the trouble and cost
Yes 8374 is massively oversized for your goals. Yes the 7670 is always boosting, just like the primary turbo will always been spooling, that’s the point you want the best response possible, that’s why Mazda used a sequential system.
… good luck being between the rock and the hard spot
once you get a taste of the ol’ razzle dazzle though, then wanting a mouthful from the 7670 will be like trying to squeeze dew from out a piece of quartz. You might as well go for the 8374 0.92 IWG that won’t even be breaking a sweat doing that all day and all night long.
If you were competing in autox and accepted dealing with nervous nancy continuously and the cost/maintenance of keeping a turbo wound out to it’s design limit for the few extra rpm here or there, then the 7670 could do that. That’s maybe a reason for dumping the twins.
I haven’t seen a single person on here with an 8374 street car that ever pined over not having a 7670 instead; not even one.
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Car is a long way from doing the engine work, but trying to plan out my build. I’ve done a ton of reading on the forum and have learned a lot, but still have some questions. I’m looking to go single turbo to clean up the engine bay and get rid of as munch of the old stuff as I can. Build goals are to keep the car as Mazda would have intended it, but update and improve a bit with current technology for the most part. Would be happy with 350 hp. I’ve been looking at the BW7670 and BW8374. Seems like 7670 might run out of steam a bit toward redline and have read that it is always spooling, so sounds like the 8374 may be a better choice, but is that to much turbo for my hp goals? I have a power FC and currently tuned using FC tweak and really like it, plus new upgrades coming out now make it even better. I would also prefer not to have to run AI and keep things as simple as possible. Really looking for a good sports car and don’t intend to do any racing with it, just a good street/windy road car, that has a bit of reliability. What are your thoughts?
This is twins territory with not much effort and saves you a ton of money. Single turbo is not a cheap adventure.
Use the money you'll save to do cooling upgrades and such.
G/L
Good info, thanks for the responses. With the 8374 what kind of boost can I run without having to worry about knock and not having to run AI assuming v-mount, down pipe, good tune etc. Sticking with twins is still a possibility, but what I have is an unknown as far as condition etc, so looking to replace with new as part of the build, so feel the cost to go either single or new twins are probably in similar ball park and I like how the single simplifies the whole engine compartment.
… good luck being between the rock and the hard spot
once you get a taste of the ol’ razzle dazzle though, then wanting a mouthful from the 7670 will be like trying to squeeze dew from out a piece of quartz. You might as well go for the 8374 0.92 IWG that won’t even be breaking a sweat doing that all day and all night long.
If you were competing in autox and accepted dealing with nervous nancy continuously and the cost/maintenance of keeping a turbo wound out to it’s design limit for the few extra rpm here or there, then the 7670 could do that. That’s maybe a reason for dumping the twins.
I haven’t seen a single person on here with an 8374 street car that ever pined over not having a 7670 instead; not even one.
.
Plenty of people blowing engines after going for more power that the 8374 can provide, I'd say that's large turbo regret. The 'ol razzle dazzle of big boost will always be there no matter what, it's OPs self control of wanting 350 that should keep it in check. Should be tons of fun, but the twins will be just as good, cheaper, easier, pass state inspections, more future buyers, and probably retain more value vs a single conversion.
OP is about to fall into the "just get a big turbo" hole and grossly overspend for a 350 goal. And a 350hp FD is plenty quick, the internet just fetishizes high power builds.
But RX8 is right. If you go single, go bigger and upgrade the fuel system and coils and get ready to keep spending.
Im in the same boat as you OP (except rest of car is ready and waiting).
I just couldnt bear to put the twins back on despite having a nicely developed simplified sequential set-up as my last engine.
I went with EFR 8374 having previously had EFR 7670 on my FC. I do have a new EFR 7670 as back-up if I dont like the bigger turbo.
I am planning 10psi and let it creep to a cap of 12psi (tuned with exhaust restriction) for ~350rwhp and hopefully usable power to 9,000rpm (no reliability issues with previous twins engine at that rpm).
I bought 5.86:1 rear gears for some torque at the wheels and driving engagement (lots of shifting) despite low boost/torque.
With stock 4:10 rear the 9,000rpm is a bit of a wait at 300-350rwhp. Almost all fun windy roads I drive are all 2nd gear with no shifts since 2nd gets you to 80mph.
I will create a build thread when its done and tuned. Shooting for an October 2024 race event.
I would say if a single is your end goal and only 350 HP is what you are shooting for, working on all the supporting mods for that while keeping the twins and not worry about the single at the moment, by the time you are done with the supporting mods, there may be a new "latest and greatest" single that works better than what is currently offered. We saw this happen with the GT, GTX and G-series turbos with Garret. The twins can make the kind of power you want and you can tackle the supporting mods piece by piece. This is currently what I am doing but I am not planning on going single, I'm keeping the twins. Either way, you will need the same supporting mods for the HP whether you are single or twins. Get your fuel set up to handle that HP (which isn't that hard, factory stuff can support this, just make sure everything is in prime condition and do a drop in pump like a Walbro 255.) Work on your cooling system which just should be standard for any of these cars but a simple radiator update and fan mod with everything working as intended will support your goals. Figure out what kind of intercooler you plan to run (you can make pretty much any intercooler setup work with twins or single.)
My thought process is, if you build everything up and do the single last, you may just end up liking the twins at the HP and save a few thousand dollars, if not, its really not much work to pull the twins off and drop in a single once you have the rest of the support completed on the car.
After decades loving the twins, I am also considering single turbo. Mostly to preserve my sanity and simplify troubleshooting and working on the car and keeping it running. In my case, the car was working well for years and then was suddenly plagued with secondary boost issues that I no longer have the time and patience to relearn how to troubleshoot and execute on it. In short, I empathize with OP.
The concerns that I have is boost control - which seems to be a function of turbo size, exhaust manifold design, wastegate design and an actual boost controller. Seems like the smaller turbo would be easier to control and run less boost. Still researching. Response is more important to me than big numbers. YMMV
You know I actually regretted going 8374 instead of 7670 on my fb. Lost response on the previous t04 hybrid set up and had to spend money on a bigger, heavier diff. Admittedly it was the largest ewg housing , not the. 9 iwg. Fuel system was up for an update anyway so that wasnt a problem
All really good feedback, and I have probably been reading for the last 3-6 months on the forum, which drove me to post my questions as this topic seems to be as concrete as the AST delete or what oil to run. Just a bit of background to share where I'm coming from. I was a Mazda tech when these cars were new and though we didn't sell many of them I did have a chance to work on and drive a few back then. I also owned a 79' and 86' and were my daily drivers for years, and had well over 100k on them with little to no issues albeit they were not turbo cars. This car will be a ground up rebuild to bring it back to like new or better. Photo below, the Datsun 260Z project I just did, so plan for this build is to be on the same level as that. I'm not committed one way or the other, but here are some of my thoughts. I generally like the idea of the twins, and I have done a lot of work going through the twin setup I have that has a Trust/Greddy intercooler, Apexi intakes, HKS down pipe and HKS carbon canister exhaust and I have tuned it with FC teak and it runs pretty decent. My goal was to understand what I have as it came with the car and know the condition of all of it before taking it apart to help with build decisions. Motor will be rebuilt as part of the project as compression hot is around 75psi and I'm refreshing everything on the car as this is a ground up rebuild. The car will be a bare metal engine out repaint (haven't decided on color yet), so if I'm going that far then want to put it back together with everything as new as possible. What I like about the single is that it gets rid of a lot of stuff from a troubleshooting standpoint and a visual cleanliness perspective. But don't want to go that route if it is going to mean I'm running a turbo that is too large and turns it into a drag car, but if I can run an 8374 IWG at say 16psi boost and make 350-400 HP and it is reliable without having to run AI and drives similar to a twins setup i.e. not to laggy and has drivable power delivery i.e. not an on/off switch then may be the way I go. Not chasing HP numbers, just looking to build something with appropriate power for chassis and a bit of a boost over the original stuff is good if i'm putting money into it anyway. Would love to ride in a few cars with the 7670, 8374 and a good twins setup, anyone have any of these in NC? Keep the comments coming :-)
You know I actually regretted going 8374 instead of 7670 on my fb. Lost response on the previous t04 hybrid set up and had to spend money on a bigger, heavier diff. Admittedly it was the largest ewg housing , not the. 9 iwg. Fuel system was up for an update anyway so that wasnt a problem
It was an engine swap. Built and extend ported s4 s5 hybrid. Prerty much same turbo requirement as a rew with the same port
yeah all the same arguments on here are what swayed me. In the end, a 7670 is a touch small for 400hp and 8374 a touch big. I guess the .9 iwg vs the 1.05 ewg housing is what makes the difference. Everyone was osing their **** about overboosting at the time so I went ewg
Im in the same boat as you OP (except rest of car is ready and waiting).
I just couldnt bear to put the twins back on despite having a nicely developed simplified sequential set-up as my last engine.
I went with EFR 8374 having previously had EFR 7670 on my FC. I do have a new EFR 7670 as back-up if I dont like the bigger turbo.
I am planning 10psi and let it creep to a cap of 12psi (tuned with exhaust restriction) for ~350rwhp and hopefully usable power to 9,000rpm (no reliability issues with previous twins engine at that rpm).
I bought 5.86:1 rear gears for some torque at the wheels and driving engagement (lots of shifting) despite low boost/torque.
With stock 4:10 rear the 9,000rpm is a bit of a wait at 300-350rwhp. Almost all fun windy roads I drive are all 2nd gear with no shifts since 2nd gets you to 80mph.
I will create a build thread when it’s done and tuned. Shooting for an October 2024 race event.
Will be interested to see your impressions once you get it on the road.
No doubt you have an eye for details. It sounds like if you are ripping everything out, a single turbo is in your future. I imagine money isn't an issue if you are doing a full engine out repaint. I'd also recommend the 8374 as my research throughout time has swayed me away from the 7670 since the twins can do what a 7670 does all day. Ultimately, how much boost and what fuel you run will dictate how your engine holds up. Rotaries aren't super sensitive to timing to make power as they are AFR. You can even watch some free HP Academy tuning videos when it comes to making rotary power. Having a mild goal of 350-400 rwhp is achievable safely.
Personally, I plan to keep my stock twins until they die. I enjoy the response too much. My other car, is a 600rwhp Supra, so if I want the old razzle dazzle and open dual wastegates, I can have it.
No doubt you have an eye for details. It sounds like if you are ripping everything out, a single turbo is in your future. I imagine money isn't an issue if you are doing a full engine out repaint. I'd also recommend the 8374 as my research throughout time has swayed me away from the 7670 since the twins can do what a 7670 does all day. Ultimately, how much boost and what fuel you run will dictate how your engine holds up. Rotaries aren't super sensitive to timing to make power as they are AFR. You can even watch some free HP Academy tuning videos when it comes to making rotary power. Having a mild goal of 350-400 rwhp is achievable safely.
Personally, I plan to keep my stock twins until they die. I enjoy the response too much. My other car, is a 600rwhp Supra, so if I want the old razzle dazzle and open dual wastegates, I can have it.
Thanks for the feedback. I have an HP academy membership, so have watched their videos. Seems most on here are leaning towards the 8374 as a better single option. Will do some more research on that. Is anyone running that in the 350-400hp range with good results, or are most in the higher HP ranges with it?
For a 'do all' turbo, it's tough to beat the 8374 at the moment. Sub 400 it will still be fantastic and you'd be able to run a smaller .92 IWG setup with room to grow into an EWG 1.02 with relative ease (I'm playing with turbine housing mounted wastegates for this reason).
Yes an 8374 will do 350, but remember it can also do 540whp EWG, so you're running way too large a turbo for your goals. Other Garretts, T04, 7670 are all better 350 choices. A 7670 will be a killer 350hp turbo. It's done 420ish whp before so you're hardly riding the line there. Look at what it's designed to do. You can always run it EWG as well, you don't need to use the iwg 7670. BW says it's a 375-650 piston turbo, that's 260-455 rotary you're exactly in the middle of that, if you want whp you're still very comfortably in the zone, and the response will be way better than an 8374.
If you want to make more, then make more. But for your goal of 350, an 8374 is a bad choice.
There are some nice aftermarket twins. Honestly that would be a more unique setup, everyone is going single these days.
Seems like this convo is already giving you power creep. You want 350, build it for 350. Don't built it for 500 because a bunch of forum guys said you should.
02-03-24, 01:06 PM
