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Because it is so small, the 7670 builds boost at very low RPMs. Does this affect highway cruising? like is it always going to max boost everytime you hit a slight incline or wiggle your foot? How is it compared the twins or larger turbos on the freeway?
Im looking for a turbo kit that I can bolt on myself. Power goals are ~300hp. The turblown 7670 iwg kit appeals to me for that reason. Of course I'll get the car tuned afterwords. People don't really talk about drivability on these forums, so any other insight people have on the matter would be appreciated.
On a highway going say around 65mph and on 5th gear I see 3-4psi on my 8374, I assume you'll see more on 7670. And generally I think 7670 is one of the most street-able/easier-to-drive turbos for rotaries.
Going into boost does not automatically mean dumping in fuel and having your fuel economy go out the window. Even the stock ECU goes into some boost and stays in closed loop. It's all in the tune.
My experience with the EFR 7670 is compared to the same size T04B 60-1 turbo on my FC.
With the EFR 7670 the turbo response was much more twitchy. Cruising on the freeway the 7670 always made the spooling noise unless going down hill and when you touch the throttle the boost jumped up.
I had my tuning run rich on load, very little TPS deadband and open loop only (no o2 feedback) as my car was primarily a race car and this tuning provided the best throttle/torque response and feel. But it meant going from 60-1 to EFR 7670 my road trip gas mileage (out of state races) went from 22-26mpg down to 17-20mpg. This was using the shortest 0.82:1 5th, 4.10 rear and the usual 5-10mph over the speed limit. Gas mileage from tanks of gas burnt racing did not noticeably change.
You can keep the AFRs reasonable on light throttle/boost and run O2 feeback into light throttle like a modern car, but the throttle/torque response will suffer and you will feel it surge into power a bit when you "pop" out of closed loop.
Well, you have driven a modern car- you know how it feels. Not like a race car.
This is part of why modern "sports" cars have different ECU modes like "economy", "performance", "track" where it actually changes the ECU mapping for different applications. You could do the same thing with an advanced aftermarket ECU if you wanted.
One of the reasons I went to the EFR over my old same size T04 turbo was I wanted the best engine feels- not going to kill that with economy tuning and I didn't have a super fancy ECU.
I have various videos of both EFR and 60-1 where I am just cruising on the freeway for a comparison- I will upload those to YouTube. Never did before because I figured most people would just find it boring, but I recorded them because like you it matters to me.
I have been running the turblown 7670 iwg kit on my car for the past 2 years and have put a lot of free way mileage on it (Including a long road trip when I moved from Minneapolis to Seattle).
In my opinion, the 7670 is great on the freeway. At freeway speeds you don't need to down shift out of 5th to make full boost. Since everything happens really slow in 5th gear, turbo lag is pretty much negligible and all you are contending with is boost threshold. The my car can make full boost (15psi) at about 2700 RPM in 5th gear. Yes, you will go into boost with only a little bit of throttle, but it is easy to modulate and not sensitive enough to be anywhere close to a driveability issue in my opinion.
Here is my EFR 7670 cruising on the freeway ~65mph.
Its a straight through turbo back 3.5" exhaust with just 1 Vibrant Streetpower muffler, so turn up the volume till you hear the exhaust (for some reason camera always recorded quiet in the TII).
Turning the volume way up is the only way you are going to get an idea of the constant whirrr from the turbo.
Believe it or not the couple trips to 20psi there are gentle roll-ons into/out of the throttle (wastegate opens at 26psi). Well, you can watch my other vids to see the response with stabs of the throttle.
-edit- Oh yeah, the lower 60mm gauge is boost and the upper AFRs. 9 O'clock on the boost gauge is 0psi, straight up is 14.7psi.
My experience with the EFR 7670 is compared to the same size T04B 60-1 turbo on my FC.
With the EFR 7670 the turbo response was much more twitchy. Cruising on the freeway the 7670 always made the spooling noise unless going down hill and when you touch the throttle the boost jumped up.
I had my tuning run rich on load, very little TPS deadband and open loop only (no o2 feedback) as my car was primarily a race car and this tuning provided the best throttle/torque response and feel. But it meant going from 60-1 to EFR 7670 my road trip gas mileage (out of state races) went from 22-26mpg down to 17-20mpg. This was using the shortest 0.82:1 5th, 4.10 rear and the usual 5-10mph over the speed limit. Gas mileage from tanks of gas burnt racing did not noticeably change.
You can keep the AFRs reasonable on light throttle/boost and run O2 feeback into light throttle like a modern car, but the throttle/torque response will suffer and you will feel it surge into power a bit when you "pop" out of closed loop.
Well, you have driven a modern car- you know how it feels. Not like a race car.
This is part of why modern "sports" cars have different ECU modes like "economy", "performance", "track" where it actually changes the ECU mapping for different applications. You could do the same thing with an advanced aftermarket ECU if you wanted.
One of the reasons I went to the EFR over my old same size T04 turbo was I wanted the best engine feels- not going to kill that with economy tuning and I didn't have a super fancy ECU.
I have various videos of both EFR and 60-1 where I am just cruising on the freeway for a comparison- I will upload those to YouTube. Never did before because I figured most people would just find it boring, but I recorded them because like you it matters to me.
Blue_T2, you're running custom exhaust manifold right? How does a Turblown cast manifold compare to yours? I'm deciding between 8374 and 7670 because of this and compressor map. 7670 fits my power goal, but the compressor is really small, and I'm not looking for bad highway gas mileage...
There is potentially another way around it. If you've got a decent ECU with electronic boost control, couldn't you set boost by gear or rpm and limit boost in 5th gear.
There is potentially another way around it. If you've got a decent ECU with electronic boost control, couldn't you set boost by gear or rpm and limit boost in 5th gear.
with a soft as possible spring, 4 port or a couple of 3 port solenoids and either 4d or additional tps logic/tps scaled WG duty you could certainly limit boost to a few PSI at low throttle %s (while still being avle to sruve to 40psi at WOT) so the engine isn't fighting itself. This is where VVT and electric/vac operated wastegates makes it easy for modern cars. They run really late intake close and force the wastegates open at cruise to reduce pumping losses.
Blue_T2, you're running custom exhaust manifold right? How does a Turblown cast manifold compare to yours? I'm deciding between 8374 and 7670 because of this and compressor map. 7670 fits my power goal, but the compressor is really small, and I'm not looking for bad highway gas mileage...
Yes, I ran the FD RX-7 HKS T04Z stainless tubular manifold on my FC and modified it by changing to two 44mm wasteates instead of the single WG arrangement.
Both the Turblown cast manifolds should have better response than the manifold I was using because I believe they are 1.5" diameter runners whereas the HKS T04Z manifold is 2" diameter runners. Made a big difference in response with my 60-1 when I ported out my manifold/turbo runners trying to fix a boost creep issue.
The 7670 isn't very small for a two rotor. The T04 60-1, the T04S and the GT3576R are all the same size and have been the go to turbos for ~400rwhp on the 2 rotor for the last 20 years.
You can map an ECU to help kill the response of the turbo while cruising, I didn't have a way to do that with my ancient ECU and still have it be responsive when I was racing.
KYPREO-
There is potentially another way around it. If you've got a decent ECU with electronic boost control, couldn't you set boost by gear or rpm and limit boost in 5th gear.
You could do that, but the response will still be there so if your ECU is mapped like mine where it goes rich when you get into any boost to help spool it into more boost you are still wasting gas. Like I say above, you can tune for stoich in low boost for good gas mileage which will help kill the response and use less gas. Cruising on the freeway I could easily prevent it from accidentally hitting 26psi boost, but not 15psi. Sneeze or pull a hill and you were at 15psi.
Slides-
with a soft as possible spring, 4 port or a couple of 3 port solenoids and either 4d or additional tps logic/tps scaled WG duty you could certainly limit boost to a few PSI at low throttle %s (while still being avle to sruve to 40psi at WOT) so the engine isn't fighting itself. This is where VVT and electric/vac operated wastegates makes it easy for modern cars. They run really late intake close and force the wastegates open at cruise to reduce pumping losses.
When I first put the 7670 in I accidentally used the wrong WG springs an was running 6psi springs. Car drove like an NA car as far as power production, just the turbo sounds giving it away.
Problem I had with soft WG springs is with using just the bottom WG port and a simple MBC the weak springs did not keep the WG shut against exhaust manifold pressure so I couldn't appreciably raise the boost over spring pressure and boost dropped more in the high rpm.
As you say, you can counter that by using the top ports on the WG to feed boost to hold the WG shut using a 4 port boost solenoid or even a simple old school bleed MBC (who doesn't want the giant boost **** in the cabin like in the '90s?). This is a more complex arrangement than most people do, but should provide the great boost control and boost options you indicate.
Yes, I ran the FD RX-7 HKS T04Z stainless tubular manifold on my FC and modified it by changing to two 44mm wasteates instead of the single WG arrangement.
Both the Turblown cast manifolds should have better response than the manifold I was using because I believe they are 1.5" diameter runners whereas the HKS T04Z manifold is 2" diameter runners. Made a big difference in response with my 60-1 when I ported out my manifold/turbo runners trying to fix a boost creep issue.
The 7670 isn't very small for a two rotor. The T04 60-1, the T04S and the GT3576R are all the same size and have been the go to turbos for ~400rwhp on the 2 rotor for the last 20 years.
You can map an ECU to help kill the response of the turbo while cruising, I didn't have a way to do that with my ancient ECU and still have it be responsive when I was racing.
What I did with my Power FC was use the accelerator enrichment tables. At low TPS (cruising), I was stoic (or at least closer to it), and at higher TPS I would get extra fuel dumped in to help spool and create power (since I was actively accelerating)
Yes, I ran the FD RX-7 HKS T04Z stainless tubular manifold on my FC and modified it by changing to two 44mm wasteates instead of the single WG arrangement.
Both the Turblown cast manifolds should have better response than the manifold I was using because I believe they are 1.5" diameter runners whereas the HKS T04Z manifold is 2" diameter runners. Made a big difference in response with my 60-1 when I ported out my manifold/turbo runners trying to fix a boost creep issue.
The 7670 isn't very small for a two rotor. The T04 60-1, the T04S and the GT3576R are all the same size and have been the go to turbos for ~400rwhp on the 2 rotor for the last 20 years.
You can map an ECU to help kill the response of the turbo while cruising, I didn't have a way to do that with my ancient ECU and still have it be responsive when I was racing.
You could do that, but the response will still be there so if your ECU is mapped like mine where it goes rich when you get into any boost to help spool it into more boost you are still wasting gas. Like I say above, you can tune for stoich in low boost for good gas mileage which will help kill the response and use less gas. Cruising on the freeway I could easily prevent it from accidentally hitting 26psi boost, but not 15psi. Sneeze or pull a hill and you were at 15psi.
When I first put the 7670 in I accidentally used the wrong WG springs an was running 6psi springs. Car drove like an NA car as far as power production, just the turbo sounds giving it away.
Problem I had with soft WG springs is with using just the bottom WG port and a simple MBC the weak springs did not keep the WG shut against exhaust manifold pressure so I couldn't appreciably raise the boost over spring pressure and boost dropped more in the high rpm.
As you say, you can counter that by using the top ports on the WG to feed boost to hold the WG shut using a 4 port boost solenoid or even a simple old school bleed MBC (who doesn't want the giant boost **** in the cabin like in the '90s?). This is a more complex arrangement than most people do, but should provide the great boost control and boost options you indicate.
Given 350whp goal, would you recommend 8374? I really don't want torque to fall off after 7000 rpm
Quote:
Originally Posted by Han_5010
Given 350whp goal, would you recommend 8374? I really don't want torque to fall off after 7000 rpm
Torque falling off is not just the compressor. Its the port, and how much of the compressor you are using.
At 350rwhp level you could easily have a 7670 set-up that kept the torque strong in the high rpm because the compressor can do ~450rwhp.
Its when you max the compressor flow early running high boost and then the boost drops in the high rpms that you really see torque drop in the high rpm.
If you really want strong high rpm torque you can set the car up with some boost creep in the high rpm, you can make it so torque basically keeps climbing if you like the way that feels. That is why you can pull like 180mph in a stock port, stock '87 turbo TII with bolt-ons. The boost and torque just keep climbing through 5th gear.
At 350rwhp level you could easily have a 7670 set-up that kept the torque strong in the high rpm because the compressor can do ~450rwhp.
Its when you max the compressor flow early running high boost and then the boost drops in the high rpms that you really see torque drop in the high rpm.
If you really want strong high rpm torque you can set the car up with some boost creep in the high rpm, you can make it so torque basically keeps climbing if you like the way that feels. That is why you can pull like 180mph in a stock port, stock '87 turbo TII with bolt-ons. The boost and torque just keep climbing through 5th gear.
My theory is that, the torque dropped off because the car is operating outside of compressor's efficiency range. More heat - less power. Port work and high boost go hand in hand as the combo shifts the mass flow curve to the upper-right hand corner of the compressor map.
Nope, if that was the case positive displacement superchargers wouldn't make any torque because their adiabatic efficiency sucks and high compression pistons wouldn't make torque because their adiabatic efficiency is even worse than a positive displacement supercharger.
Nope, if that was the case positive displacement superchargers wouldn't make any torque because their adiabatic efficiency sucks and high compression pistons wouldn't make torque because their adiabatic efficiency is even worse than a positive displacement supercharger.
So are you suggesting that, on a stock port engine, with either 7670 or 8374, the torque curve will drop after 7k? If not, what is causing the power discrepancies? Thx
I don't see a discrepancy in top end power between EFR 7670 and EFR 8374 at ~350rwhp level. I don't see the EFR 7670 dropping torque faster after peak hp.
But maybe we just don't have enough samples of EFR 8374 at the ~350rwhp level.
EFR 8374 making 340rwhp ~13psi boost- street port, pump gas
Note you can see on the boost trace that the EFR 8374 is actually boost creeping in the high rpm so you would expect torque to stay high, but it actually drops fairly fast.
EFR 7670 making 377rwhp ~13psi boost- street port, pump gas HP = Torque x RPM ÷ 5252
So, you can see that the turbo that allows you to hit your 350rwhp goal and hold that peak hp the longest has the least torque drop off at high rpm. Right?
Now to totally blow your mind.
Even my EFR 7670 operating at 420rwhp/420rwhtq at 26psi till ~5,000rpm and then boost dying down to 21psi at peak HP couldn't have made much more high rpm torque without breaking out of the 420rwhp.
Yes, torque drops hard in the high rpm. If it didn't HP would keep climbing...
If you want to concentrate on making the most torque in the 7,000rpm+ range of your power band the stock twins are the best because compared to the available compressor they have lots of exhaust wheel area with 51mm exhaust wheels x2 and a loose turbo A/R with 0.6AR x2 (effective 1.2A/R).
Turblown, Blue_TII, thank you for your explanations! Twin's larger A/R and graph scaling makes a lot of sense.
One question directed to Turblown - on your website, the 8374 was advertised as having a broader powerband than 7670. How would you define a broader powerband (just literally averaged power is higher across a certain RPM range)?
Turblown, Blue_TII, thank you for your explanations! Twin's larger A/R and graph scaling makes a lot of sense.
One question directed to Turblown - on your website, the 8374 was advertised as having a broader powerband than 7670. How would you define a broader powerband (just literally averaged power is higher across a certain RPM range)?
The above statement takes into consideration that most people moving to single turbo want above 400rwhp. Above 400rwhp the 8374 provides more power per RPM in the 3500 to 8000 rpm range.
12-07-17, 11:12 PM
HP = Torque x RPM ÷ 5252
