I'm really curious on minimum boost if someone had 9.4:1 or 9.7:1 rotors. I really like these powerband results on these bw efr turbos.
I don't want to run e85, and all i have here is 91 octane and 50/50 water/meth.

Hopefully I will know in a year. 9.7 rotors here.

I ran my 7670 on a 7 psi turbosmart spring and couldn't get it past 8 psi on a 4th gear redline pull.

that's with a 3.5" downpipe, and a small shorty filter. stock port with 9.7 rotors.

7670 with a 3.5 inch full exhaust on E85 held 8 psi to redline with 9.4 rotors..

Any idea what power it made?

Around 300rwhp I believe.

For those not aware we make a top mount IWG EFR system for the REW swaps in the Rx8. These are very popular.

Here is one that made 330rwhp @ 11psi on pump gas. Full 3" exhaust.

https://www.instagram.com/p/BDIuOoUQ...en-by=turblown

What's the power potential difference between the 7670 and 8374 on 91 octane, all else equal? You said the 7670 can hit 440whp on 91, haven't seen a max effort 8374 on 91.

I think it's safe to say around the same combustion chamber pressures regardless of which turbo is making the positive pressure when speaking in terms of equal Intake temps, 91 octane etc. pressure is pressure.

I wouldn't engineer a set up for the ragged edge of 91 Octane anyway. Seems like a recipe for a short lived motor. For the cost of water injection kits these days it seems somewhat a ridiculous notion to push the envelop on just straight pump without some form of AI.

Cost of a broken motor > Cost of an AI setup.

Does full exhaust like midpipe or resonated midpipe really makes that much of hp difference than hi flow cat? i need some help with my numbers to figure out if it's my exhaust or something else? I have ur mani & downpipe, 8374 turbo iwg, SMB hi flow cat with muffer and RB catback, i only made 356 rwhp with 17 psi. stock ports, no ignition break up, and 9's sparkplug with hks twin power plus running meth injection, and power fc.

Khris, who was tuning the car? I'd actually love to check your car out and get a ride this weekend or next, would be pretty cool to compare power bands and setups :nod:

To answer your question, a HFC will certainly hurt power, as will certain restrictive catbacks.

Hell, I recently switched out from a resonated MP and RE-A dolphin catback to a different larger diameter resonated MP and freer-flowing catback and picked up boost and power, a fair amount from the feel of it :D

What dyno? You have been around long enough to know Dyno's all read differently. Also a better indication of power would be a trap speed. You could always take it to the track and get a 1/4 mile MPH or if that's not your thing get a Vbox and use that. You can compare notes with other owners and slips and see where you are.
It's quite possible you can was tuned extremely conservatively. Or God forbid your motor is low on compression. You can get a compression test, buy your own tester or take it to IR Performance and have them use their rotary compression tester.

As mentioned what brand of dyno? A dyno dynamics in standard mode reads %15 lower than a dynojet.


I did a back to back on a 7670 with and without the cat, and it was 33rwhp on the top end.

There are a ton of variables, but lets see the dyno chart.

^Elliot, what boost level was that back to back at?

here a snap shot of the dyno
 

I will need to go back to finalize more tuning, if i decide to removed the cat smell like fumes!

The torque curve is nice and flat at least, but I always hate seeing a dyno graph with different scales for HP and TQ. makes it appear that the torque is higher than it is.

The dyno sheet says 15psi for each run? Is this wrong?

I assume this is wrong. pull 15 in green is at 15psi and runs 21/22 are 17 psi?

Based on the difference in AFR between the pulls( low to mid 11s for run 15, and 10.6 to 10.3 for runs 21/22) I assume this is because of the increased boost pressure.

Notice pull 22 is pretty wavy up top, and this is with smoothing set to the 5( MAX).

Also notice how close the torque and HP on pull 22( 356rwhp to 313rwtq). This indicates a flow issue in the higher rpms.

I am sure you are aware Peter Hahn made 430rwhp on this same turbo kit, and same dyno at 15psi( pump gas). So we can rule out the dyno reading low completely.

Take the cat off, and while you are it throw some real plugs in there( NGK R7420-9s).

Tune seems awfully on the safe side with meth injection( 10.6 and lower)

When I swapped from a GT3574R to an EFR 8374 IWG, I gained power down low and up top at max rpm. the car feels a lot better. it also delivers power more smoothly. I have a 3.5" downpipe, 3" magnaflow resonated midpipe and 3" amuse R1 exhaust.

I also notice the car likes richer fuel mixture, leaving the boost controller (powerfc) at the same level if I add a little more fuel 11.5 afr vrs. 10.5 afr, the 10.5 has lower knock, more boost (slightly) and overall feels better and healthier. so I left the tune on the rich side as it seems to like it.

Peak power wise the two turbo's are close at 15PSI. the 8374 makes more above this, 6,000ft above sea level.

I think the GT3574R feels faster, but the efr 8374 is faster. the turbo delivers power soo smoothly and easily, the only thing I do notice is the 8374 does not like to go to redline under partial boost levels, seems like the turbo surges or kicks you out of that area. not really a big downfall as you would rarely be doing this but something I noticed, didn't do this with the GT3574R.

I think that is because the EFR turbo is so much lighter and more efficient that part throttle boost becomes an issue. I know for a fact that on my Dodge SRT-4, if I run a MBC then it surges like crazy and spools at part throttle. Even as low as 2000 rpm. It's because the turbo is so darn tiny, so Dodge used a 3 port solenoid to keep the turbo offline to avoid surging unless you are at or near WOT. Even still, I get 18 psi at 2000 rpm with the stock turbo, so the response is amazing, but it shows how tiny it is with the surging. I took the MBC off and kept it at factory control

ACR_RX-7


I think that is because the EFR turbo is so much lighter and more efficient that part throttle boost becomes an issue.

If this part throttle issue is with all EFR 8374 it could be compressor surge I guess.

I'm thinking it is a tuning issue. If you can get to a loading dyno like a Dyno Dynamics or Dyna Pack you can set the RPM hold and work through all load ranges to get clean AFRs in each RPM range.

This really helped my TII back when I had the old 60-1. I used to have to short shift 1st and 2nd or it would spin or buck at high rpm like you are describing, but once I got a good tune it was smooth.

------------

I didn't have that bucking at all with my EFR 7670 and it had crazy response.

In fact, I was super impressed with the EFR 7670 because I could really dial in whatever torque/boost I wanted with the throttle pedal. It was like there was a direct connection between the throttle pedal and the boost gauge needle.

With EFR 7670 I could just give it baby throttle and drive around smoothly at any rpm/boost. If I got a little randy with the throttle it would instantly spin the tires.

Less-gradual(narrow) power delivery does indeed 'feel' faster.
https://en.wikipedia.org/wiki/Jerk_(physics)
It's why turbo's are so much fun, in general, compared to N/A engines.

^ I disagree with that. To me the big downfall of a turbo engine is the nothing nothing wham thing.
Which is a novelty at first maybe but after that its a pain in the arse and a hindrance.

as if all turbo engines are created equally.. sounds like you only have experiences with shitty turbo setups and never a proper one. like a journal bearing gt45 on a 2 rotor.

lag depends on the turbo the engine and the desired goal.
wanting to use a 2.0 4 cyl to make 900hp is unrealistic, yes people still do it but then you get no power until 6k rpm with the turbo finally spools
on the other hand you could use a boosted ls1 to make 900 and IF proparely sized will spool low in the rpm for a broad power band.

the simple fact is going from our 1.3 rotary to any thing bigger is outside most peoples budget as the only thing bigger is the 3 or 4 rotor. this means we get pushed in to a state of putting too big of turbos on too small of en engine...

that's why sequential 7670 is the hot ticket.

I'm still waiting for someone to get around to a twin EFR setup. The idea has been thrown around for awhile, but alas, I am unable to afford such adventures.

Thanks for that professor.

But its true, most people really love the no power then boost and big power feel of a laggy turbo. I mean, how else do they know the turbo is doing anything?

Honda used to tune its VTEC so torque dropped off on the primary cam before the VTEC cam comes on (too late of switchover) so you can feel that VTEC kick. How else does the consumer know they are getting anything with VTEC?

I had plenty of years driving a TURBO car (lag) so I really appreciate an engine that has a broad torque band that includes the rpm range I cruise in (2,500rpm-3,500rpm in RX-7 gearing).

I don't care it it doesn't have 300ftbs torque from idle-2,000rpm like an LS V8 since you can't put that through the tires anyways in 1st gear.

As long as it has enough torque to spin drag radials on a prepped track through 1st without having to abuse the clutch by revving the engine up much over 2,000rpm I am happy.

Oh, and I want to be able to granny shift and still be fast. I am over the whole having to get everything perfect on launch and power shifting each gear to get a decent time.

Ideally you fix this by using a decent BOV, like the synapse item for example. ideally one dials it in so it just not open at maximum airflow under wot conditions. , lets say 100 mbar delta which you could or not get with a littlebit restictive throttle

then if you cruise with lets say atm pressure in intake, the bov will open at approx 1.5 psi boost upstream throttle and avoid turbo from surging.

even if zou generally increae load the bov will adjust the boost upstream throttle plate to a fixed value ( +- 100mbar) and avoid surging and unneccesary pumping losses and thus also improves mileage

That is one way of doing it, absolutely. I will say that I was amazed at how fast my Dodge spooled with an MBC. I was totally unaware that the PCM was overriding it that much to prevent that. My BOV is built into the compressor cover, much like an EFR. It opens at the slightest lift of throttle, even when around town. My fix for it, in the future, is to upgrade the turbo. Bigger turbo has less surge, but I am far away from that.

I should clarify what I meant above.

So both the GT3574R and EFR 8374 surge at partial throttle. so when I am driving hard and I am in the middle of a long sweeper, I don't hold the throttle partially open, you sometimes modulate the throttle more/less/more/less with your foot. both turbos would surge doing this, perhaps its at altitude that makes the turbo's do this at part throttle. What I think is happening is when looking at vacuum at altitude the turbo still boosts 3PSI to get to "positive pressure on the MAP" or the zero line in the powerfc or to get to 14.7 Absolute pressure. Most of the BOV springs probably are meant for sea level, so when I part throttle at a few PSI or so and the throttle closes some but the turbo is still feeding the intercooler tract, I don't think the BOV can open at such small pressures, so the turbo surges as the throttle body plates are closed and the BOV doesn't relieve the pressure, on my old turbo is made all sorts of noises but "fought" through it so to speak, the efr wants to kick me out of that region back into vacuum cells more easily at these partial throttle positions when modulating the throttle.

Another thing I noticed is with the GT3574R I could more easily control the throttle at partial boost levels...although it still isn't super refined like an N/A machine, the efr wants to go to upper boost levels so easily with the lightweight turbine wheel.

I still need more seat time and see how it performs outside of mostly tuning the car on straights and playing around.

I need to take it on the turns now that it is tuned.

and don't mistaken what I wrote as bad against either turbo. the efr 8374 just gave me a whole lot of low end power I didn't have, the car is easier to drive fast.

That's exactly what my Dodge did on a MBC. I don't think that altitude should make a difference, since the reference stays the same, regardless of atmospheric pressure. Are you using the PFC for wastegate control? or are you using an MBC? You may want to consider changing your low end boost curve to avoid part throttle boost, or adjust your BOV, if you can to be softer.

My fix for it, in the future, is to upgrade the turbo. Bigger turbo has less surge, but I am far away from that.

That is exactly wrong. The smaller turbo is less likely to have compressor surge.

Most likely your dodge was just tuned to run stoich and no boost at low loads for fuel economy and now it is trying to run stoich and boost or possibly going wonky trying to correct the AFRs for boost at low loads since you took away its turbo control.

On paper, or proven? Would love to see a sequential 7670 dyno :nod:

Wish there was a 7683 EFR option, I guess beggars can't be choosers :(

from what blue was saying the compressor side is the bottle neck on a 7670, not the turbine...

also i'll post up the 7670 SEQ dyno as soon as a build it. :P

Wish there was a 7683 EFR option, I guess beggars can't be choosers

lastphaseofthis

from what blue was saying the compressor side is the bottle neck on a 7670, not the turbine...

Yeah, I was able to make peak hp ~6,000rpm on the 7670 and then hold that till just past 7,000rpm where my near near stock closing ports crap out on VE.

I think it is my ports because it was the same time hp started dropping on my same size compressor but larger exhaust wheel 60-1 and no matter what boost I run (meaning at lower boost the compressor would have more flow available if the ports were still in there VE range and flowing.)


The 7670 compressor is "bottle-necked" at 64lbsmin flow which is ~450rwhp rotary.

I still think an EFR 7683 would be bad ass.

I think it would actually spool faster on a rotary with the right exhaust housing and exhaust than the 7670 (from my experience going up turbine wheel sizes on my 60-1) and offer lower exhaust manifold pressures for a happier engine.

You are probably exactly correct. I have not touched the PCM in any way. I just tossed a MBC on because I had one, then went back to stock.

If you are running an EBC that activates at around 1psi of positive boost (like my greddy profec does) and you put the signal line to the EBC into the manifold AFTER the throttle, you will get surge as you describe above .
If you put the signal line to the EBC PRE throttle , that surge will disappear and throttle control will improve greatly.

The reason for this is that the EBC needs 1psi of boost before it will activate the 'start boost' function which closes off the wastegate and spools up your turbo . With signal post throttle and at light throttle you are hovering around that trigger point and the wastegate is opening and closing as you modulate the throttle causing surge . With the signal pre throttle any throttle at all will yield more than 1psi and therefore the wastegate stays closed allowing full control via the throttle.

sure but without good BOV this still means closed wastegate an turbo pushing against a near closed throttle possibly causing surge.

I connected my BOV line between the engine and throttle body. So when the throttle gets cut the BOV opens. this is supposed to be how its installed. If you put it on the intercooler side of the throttle body it won't open the BOV.


At altitude the turbo can boost 3-4PSI depending on elevation to get to a sea level pressure state. Our atmospheric pressure at certain altitudes is between 11.7-10. so I can boost a good 3-4PSI to get to a sea level atmospheric pressure of 14.5ish.


I am guessing the spring on the BOV, and this would include both set ups, could possibly be too strong? Or the engine moves a lot less air flow and I am moving the turbo into its surge line?


I haven't ridden in another rx7 under the same conditions. it basically using high rpms with low boost at part throttle under modulation. its something you would do around long sweepers at high speeds.


I used an HKS SSQV on my first set up and the second I am using the stock BW BOV on the turbo. The tune in this area is around a 13.5 to 12.5AFR depending on the boost pressure. I target 13.0 for a 14.5PSI atmospheric pressure and ramp down in boost.


The turbo definitely wants to boost to max pressure pretty easily, it does not like hanging around part boost level.


Perhaps it could be a TPS issue? I will see how other cars respond before doing anything on my car with the same turbo up here.

Didn't mention the BOV. Although adjusting the BOV or using a synapse (like Rub20B mentioned) can help with the severity your problem ,but not solve it.

I'm talking about the line that goes from your manifold to the electronic boost controller .I'm assuming you do have one ?

yes, the powerfc is controlling my boost and the controller is on the face of the BW turbo using the stock solenoid that came with the BW kit.

The BOV is not tweakable to my understanding. perhaps a different spring is needed? I know BW offers a stiffer spring but not a softer one.

And the signal line to the powerfc is coming from the manifold ?

Actually ........... I just realised the powerfc is controlling your tune as well as your boost so you can't do what i suggested . You would need a separate boost controller.

The boost pressure source for the controller and wasteaget is connected to the turbo itself. the boost controller is in between the turbo and wastegate solenoid. obviously it bleeds some air to control boost higher than the wastegate spring.

I have a separate line running from the UIM between the throttle body and engine to the BOV.

You input a boost number and a wasetagate duty cycle along with it. the duty cycle is how it controls boost, the boost pressure is when the duty cycle "kicks on". the boost controller controls boost by modulating the grounding of the solenoid. so if you don't have 12V going to the solenoid the solenoid is going off spring pressure, the 12V closes the solenoid till the boost setting is reached and the duty cycle modulates from there, the computer tries to keep it as close to the desired setting as possible and this is where you might need to play with duty cycle. If the boost exceeds more than .25 KG/CM^2 (I think that is the units) the computer will do a fuel cut.

I am sure everything is connected correctly and I am sure I am using the powerfc correctly to control boost. This has happened on both of my set ups now using different boost controllers (Blitz spec S and powerFC) but this has nothing to do with it as these aren't doing anything at this low boost level (both are shut).

OK ..got it . If you just run on WG spring pressure (boost controller is off)does it still do it ?

Also : is there a pressure line going from the manifold to the powerfc ?There has to be (assuming you are map tuning). If so , this is also acting as the signal line for boost control .

I too am having surge issues at partial throttle lower rpms.

I am considering buying the Turbosmart BOV replacement for the standard BW unit. Anyone have any experience with this in terms of solving the partial throttle surge?

Yes ...I have . Which is why i mentioned it above.
I'm not running an efr but the principle is the same for any fast spooling turbo using an EBC.


Boost controllers typically supply power to the solenoid once pressure in the signal line reaches 1 psi . The problem is, at part throttle , you don't get to 1psi in the manifold even though there can be significant boost pre throttle. So the solenoid isn't switched and the WG can open .
At this point there is no power so you open the throttle a little bit more . By opening the throttle you now get 1psi in the manifold but there can be up to 20psi pre throttle and the WG is now closed by the solenoid. This is when you get that sudden uncontrollable surge in power from the accumulated boost reservoir pre throttle plus the activation of the turbo.

Changing the source of the signal line to pre throttle eliminates this as the EBC sees that 1psi much earlier and keeps the wg shut .

This in turn means you don't need to open the throttle as far to get any power , making throttle control much more precise.

The MAP sensor (GM 3 bar) is the sensor I am using for boost control/engine control tuning.

It's located in the stock location.

The wastegate controls boost and shouldn't have any effect on this. The BOV should be relieving the pressure but its tough because its right at the threshold of boost/no boost. so you have slight boost getting jammed up in the intercooler piping backing up to the turbo and surging/fluttering it. I don't think there is anything you can do about it.

My set up is set up exactly the way you describe. my boost controller is connected to boost pressure at the turbo itself. The BOV is connected in the right spot so when the throttle shuts it immedietly sees vacuum, but the pressure is super low so the spring on the BOV might not open.

My old turbo had more rotational mass so it fought through it better then the lightweight turbine wheel. not that its bad or anything...just what it is.

This above tells me that it isn't the way I described .
The map sensor is what is giving the signal to the boost controller which in turns sends voltage to the boost control solenoid.
The problem is that the map sensor will be plumbed into the manifold (as it should be).
This is why i suggested you need a separate EBC that you can plumb pre throttle.

they don't have likes here, so we go with +1

that's some real good info, that i was following and then getting lost in his reply...

My turbosmart EBC also has its boost source right off the turbo. The BOV has its source off the UIM.

The turbo flutters like mad between ~0-5psi partial throttle acceleration. After 5psi its smooth. Its not tuning, its my BOV going nuts it seems. I assumed the turbosmart EFR BOV has a stiffer spring which might help?

So the line going to the boost controller on your dashboard (not the solenoid) ....... that is coming from right off the turbo ?

Sorry to labor the point but there seems to be some miscommunication on what is a boost controller and what is a boost control solenoid.