Man, that almost looks like a Diesel Dyno with the high Torque. What RPM does this come online and reach full boost?

 

I'm guessing you had to ramp boost up quite a bit after 6800-7000 to get a curve like that, if you had flat boost curve I bet it was dropping off quite a bit after say 6600-7000.

 

That is not my dyno! Just an example I found of a fat flat HP curve. Pretty sure it’s a boosted V8 tuned to fit a race class.

But this is your goal. Power everywhere. Sometimes playing inside the rules is fun

 

I predict the opposite.

Like 30psi boost 3,500rpm tapering to 14psi.

dyno chart looks to be zoomed to 3,000 rpm to 6,000rpm and its still not even a full sweep through that plotted.

 

Oh, looks like my efr 7670 at 30psi.

 

Yup will take hard early boost, and taper off a lot by redline. It’s a 400whp capable turbo, it will flow just fine at 300whp at redline, and at 300whp at all the points between. Get to max boost asap, hit 306, then taper off to maintain 306.

 

So there is a couple of ways to get the max allowed HP over the broadest vehicle speed.

On my FC I did efr 7670 on high boost (final tune 26psi dropping to 21 psi). Charting rear wheel torque per vehicle speed it was the same torque in 3rd, 4th or 5th at 65mph because like the chart above it made so much more torque at low rpm (420rwtq/420rwhp).

On my FD I want a more reliable, cheaper fueled track focused low boost build so Im trying the bigger efr 8374 and 9,000rpm redline- with rear end gearing to get the torque at the wheels up (instead of relying on engine torque.)



4.10 rear gear at 8,000rpm is same vehicle speed per rpm as 4.77 rear gear and 9,000rpm.


I wanted more shifting for driver engagement so I went with 5.86 rear. 2nd gear from 20mph to 80mph is boring.

At 12psi boost and ~300ftlbs torque 5.86 rear is more torque at wheels than my 26psi and 420ftlbs with the 4.10 rear and has the max torque pitched up to the higher rpms so its more rotary fun feeling instead of v8 feeling.

Rotaries are more reliable with rpm than boost.

 

https://x-engineer.org/calculate-wheel-torque-engine/

 

The regulations will definitely make it feel like a V8 in power delivery. But it will still be rotary silky smooth and revvy so the character won’t be completely gone.

Extending the redline and gearing down is infinitely more fun. 7670 will make 306 at 10,000rpm if you play with the boost.

8374 vs 7670 for your legal goals, 7670 all day long. 8374 if you’re going to have a different map for off road / private property use and intend to go beyond 350hp on pump gas

 

Don't forget about the newer 8370! I've shipped about 50 8370 IWG turbo kits out, just waiting on people to finish their installs & dyno.

 

We need iwg efr 7674 with sxe compressor housing.

 

That dyno graph is exactly what you want if you are circuit racing or similar. The timing will say you're fast. However, if your intent is a streetcar for fun to be had, that is not what you want. You feel torque, not HP. A descending torque figure like that will make the car feel so sluggish. I'd prefer a torque curve that remains flat or slightly ascends as you increase in RPM. 8370 results might be worth waiting for.

Initially my car had a boost taper from 16 to 12psi at redline and it sucked. I never drove it above 6000 rpm because it felt like it was dying. Now it peaks at 16psi and drops to 14 at redline. The sluggish feel above 5500 rpm is significantly better.

 

To some extent, it seems mostly an artifice produced by equivalency rules.

Improved production turbo cars over here, certain rally classes and I think FSAE suffer under the same dreaded intake requirement that produces that type of curve. If you could replicate it in one of these somehow, you'd better become adept at changing gearboxes, diffs, CVs and axles!

 

I will take this into consideration as i was not aware it was such a thing. Also, thanks for making so much awesome stuff for our cars @Turblown

 

Im bumping this again to ask if there is any big downsides to using the EFR 7670 IWG on the 13B-REW (except the lower top end power). Both if trying to maintain 360 crank HP and if its given free reign. Is it "too small" for the enigne?

Backpreassure, overboost, heat management (exhaust/intake) and detonations?
Would it at all be viable with E85?

 

EMAP doesn't get high until above 6500 rpms on this turbo, and it makes a difference how much boost you are running. I know guys who have been racing our 7670 turbo kit for years without engine problems FYI( on E85 at 20+ psi)
360hp crank is very low, no issues what so ever. Its basically the same size as bigger twins. This size turbo never overboosts. I would do E85 if you have it regardless of turbo size, even if you were on stock twins.

 

PLENTY of cons with E85 depending on where u live in the world. Especially for cars only used occasionally.
For a low power weekend car I wouldn't recommend it personally..
But when everything is working well, yes its a great engine protector.

 

Another factor to consider is boost creep. Where are we at in 2024 in the discussions on the tendency of 8374s to boost creep? I recall that 8374, at least the IWG models, that you were basically having to run a minimum of 15-20psi boost. That would put you well over the power limit.

Has there been any changes on that front now that these turbos are so widely used in the rotary world?

If so, 7670 would seem to be much better if, as I suspect, the authorities will want you to use an IWG turbo.

Or is the 8370 an improvement in the boost creep department for someone wanting an IWG setup?

 

It depends on the car, some creep, some don't. I've seen 3 customer 8374 in the last week that held 10 psi( 3" free flow exhaust too).
Its very rare for a 3" exhaust 8374 to be past 16 psi.

The only way to ensure low boost with a free flow exhaust is to port the turbine housing, the more you port the lower the boost( IE removing the T4 divider, and WG divider).

The new 8370 doesn't creep, its like the 7670, just a little bit more top end.

 

There is nothing worse than a blown engine, and turbo thats not rebuildable IMO. But you are probably correct if you mean sub 350rwhp, that is not track driven that should live a very long time on pump gas only.

 

haha yup agreed!

Yeh just seen sooooo many issues with all sorts of vehicles, stuck injectors, water absorption issues, no flex sensor so leans out, very quick oil contamination etc. Not to mention having to run alcohol friendly premix if its a rotary. So yeh E85 is fine, PROVIDED you have all the safeguards and everything done right.
Else just pump fuel and everything just works. There is a boost, temp knock limit of course.

(Also in NZ we can't get E85 at the pump so the whole idea is just a no go now, water meth is easier)

I view E85 as a high maintenance fuel, not a 'normal street car' fuel.

 

Again, thanks for the valuable insight

The authorities don't care what turbo i put on, they only care about the advertised maximum power.
Then i am trying to argue that the top numbers are specced out for piston engines, and that rotaries are a different thing all together when it comes to air requirements for the same power figures. I got a lot of help in this thread to formulate something that explains the differences.
As it looks now i have a pretty solid argument (i think at least) for why rotaries should be treated different. For instance looking at the HT12 vs CT20A (2JZ-GTE stock twins) i show that the HT12 is much larger that the CT20A on both hot and cold side, but the CT20A deliver almost 90hp more on the 2JZ in europe (240 vs 330). This is pretty conclusive evidence that the rotary require a lot bigger turbo than pistons. I also have found quotes from both Rob Dahm and Howard Coleman stating a that their experience is that you can estimate 70% of piston power rating to be the max on rotaries.


But for my case specifically, i am aiming at the 7670 package since it looks possible to approve and it also seems like its a decent choice that retain much of the OEM characteristics of the car. I will run with a flex-fuel sensor, and most probably be using 98 RON gasoline. Tho there is a ongoing issue with more and more fuel having ethanol mixed in. Our regular pump gas (95 RON) is now E10, and they are also talking about mixing that so either E5 or E10. The time i will spend above 6500RPM will be minimal, as i dont track the car, and only use it for cruising and some spirited driving on mountian roads.
I enjoy the building and tinkering much more than the actual driving

 

Thats funny that all they car about is peak power, so set ecu rev limiter to 6000, and run a 7670 at 30 psi. Will be stupid fast IRL, just won't look it on paper.

 

If you're writing something formal to present by all means have real world comparisons on hand however I'd probably attack the problem from the perspective of BSFC on a rotary being lower, rather than turbo A makes less power than turbo B. If I recall correctly there are more than one SAE papers that reference BSFC of a rotary, not the least of which may be the paper(s) referencing the S8 FD. I haven't glanced at them in a while though so I may be conflating which papers reference what - I'd go read a few.

 

I have tried adding a chapter about BSFC but i struggle to find good comparisons. I have some SAE papers, mainly from the FC and one for the 3-rotor twins, but nothing on the FD. If you have S8 spesific ones it would be ace if you could share! My googling and a lot of chatgpt prompts put the differnece at 25% ish. But agian i lack exact sources for this.