So what part do you bevel - this part?



iSP33D-for-J3SUS

 

Great info BLUE TII. Figuring out new ways to make power usually comes from 2 things: Imagination and limits. Kinda like a screw charged 7 making 300hp from less dough than the cost of the average used RX-7.

Go figure.

 

Where is there a twin-screw charger making 300hp for less than a used RX7? (Considering the average used cost is like $1500)

 

Sorry, I'm using my personal experience in used RX-7 2nd gens. I've seen some crazy people ask for upwards of 7k for an NA vert with over 100k miles. I payed a pretty penny for mine, as have many of the 7's in this area. But, IIRC, the thread starter, even though he hasn't posted a price list, hasn't spent more than a couple of k.

Either way, it was an example.

 

lol, well where's one for $5k then? I love twin-screw 7's, I've built a couple myself and haven't seen very many (only two others)

 

Increasing overlap will kill low end power in the extreme.


-Ted

 

I have kinda suspected what BlueTII said. Thanks for the re-enforcement.

Ted, with all due respect, think about the rotor and plexi check. Even with a radical street port( on a turbo) the port doesn,t show past the edge of the rotor till the rotor is almost at TDC. At that point there is nothing to overlap into even though the apex seal hasn't closed the exaust. Kinda like the motor with no side seals. The rotor face is so close. What is it? Like 1mm?

 

If it's 1mm you might have some problems

--Gary

 

Reread what I said...

This is the argument I used with all the BP turbos running around.
I even made an Excel graph of Tony Farkas' 499hp BP turbo versus my lowly 253hp SP turbo.
I made more hp up to 4kRPM.
This is all the evidence I need to tell me low end power is reduced, period.
You can argue all you want, but I have proof it doesn't work.

Increase overlap kills low end power, period.
It's been proven with piston motors, and there's no reason why a rotary engine won't do the same.
No what these other BP guys argue, the dyno graphs don't lie.

Why increase overlap when you have very little to gain?
Why is the 1mm increase necessary?
Are you racing in some spec class with restrictions?
I'd rather lose the 10hp and gain a little more in reliability than start to compromise it.
My motors make great streetable power, from off-idle to redline.
None of those BP motors can claim that - all owners claim is how fast the car is from their butt dyno, but their dyno graphs all tell a different tale.


-Ted

 

I was just thinking that the combustion chamber is past the port at TDC. The rotor face is very close. Even though the intake port may be begining to open, there is not a free path.


The timing of the engine. I rotary dream about this often. I have a turbo, therefore, the subject of my dreams. I have come up with some ideas.


Keep overlap to a min. (later)
Extend intake timing.
Dont go crazy, like so many, with exaust. Mainly by earlier opening. Keep overlap down by not raising to much.
Open exaust a little out, a little up, and a little down. Keep radiused and smooth. After all, volume is limited by portability of the sleeve and port timing by shape. Right?
After looking at the beveled rotors and dreaming. I believe that earlier intake may not be as detrimental as believed.
Just wonder if there is real benifits.

I meant the rotor face runs close to the housing at TDC. Maybe 1mm.
This was a complete guess. I do not have the stuff in front of me. But when I was using the set-up with the plexi, I remember how close the trochoid shape of the rotor fit the housing at TDC. Thats all.

 

Dude, you have no idea what "overlap" means...


-Ted

 

i would say that 88integrals's beveling job is much more for flow than timing, as he only beveled a little bit, and therefore wouldnt hurt low end noticably, but might help high end quite a bit. there is a very big difference from laminar to turbulent flow. the more laminar you cna keep the intake the better, no matter what. as far as sureshot and his huge bevels, that is a different story, but as with most mods, if youre shooting for area under the curve rather than streetability, then its not a bad deal. if you want a super streetable car, why the hell would you drive an rx7? get a civic or a corolla or even a miata, something that will run for years without ever breaking down.

 

Well, Ithought it meant the time both ports are exposed to the face of the rotor at the same time. I know that at speed, there are engine dynamics that come into play.


I,m willing to concede if you can help me understand.

But, I was hoping for more insight.

 

Didn't see Patmans reply.

EMISSIONS DOG! I have the man on my back.

 

Yes, it's the time / duration in which both the intake and exhaust ports are exposed.
So what does that have to do with the "combustion chamber"?
What you say "combustion chamber", I'm assuming the rotor position where the spark plugs fire?


-Ted

 

Extreme overlap will definitely kill low end power.

There are ways to have good overlap for top end power without killing low end grunt!

I am breaking in my engine now and I added a bit more overlap than the Pineapple port had by raising my exhaust port more to add a bevel for flow and apex seal happiness. The intake ports have the same early opening as Pineapple but primaries have a smaller volume at port exit. A bit later closing all the way around over the Pineapple.

It revs faster, can run leaner and has better low end power because of the higher velocity primaries despite the added overlap. Doesn't hurt it has boost at 1,300rpm and full boost at 3,000rpm in 4th gear on my small 3" exhaust. Hopefully I will have the 3 1/2" exhaust on it next week for better boost response.

I am posting pics of my engine build up now- check out the new primary port style.

 

I thought TDC was rotor face against in/out side of rotor housing?

 

Do you have dyno graphs by any chance?


-Ted

 

Rotor face against the spark plugs holes?
Yes.
But the ports have nothing to do with the rotor (face) in that position, right?


-Ted

 

a rotary has 2 TDCs and 2 BDCs, it could be consufing to use these terms. there is a TDC when the rotor face is flat agains teh spark plugs, then there is the other tdc when one rotor face shares both the intake and exhaust port openings aka overlap. then there is a BDC on the intake side and the BDC on the exhaust side.
when reffering to TDC or BDC you also need to say which one of the 2.

 

better low end compared to what? what boost pressure do you refer to when you say full boost? and what turbine are you using?

i doubt you will get any better boost responce with the 3.5 inch exhaust as boost responce is usually better with smaller volume, higher velocity tubing. if anythign you might notice peak power increase if you are near the limits of 3 inch piping flow. its been asked but any dyno sheets from 2k rpm and up?

 

TDC is when the volume of the chamber is smallest, aka when the rotor is flat against the housing. it has nothing to do with overlap. TDC and BDC are just the times of maximum and minumum volume.

 

better low end compared to what? what boost pressure do you refer to when you say full boost? and what turbine are you using?


Better low end compared to the previous rebuild that did not have the exhaust port raised, but had a larger primary port hurting velocity.

This full boost is only wastegated at 10psi right now as I it is still being broken in. The boost curve from 10psi to the 17psi I will be running is VERY steep though looking at my past data logs, so it should hit 17psi before 3,500rpm. It hit 17psi at 4,000rpm on the last rebuild with this smaller 3" exhaust.

I am using a BNR stage 4 S5 stock hybrid w/ 60-1 Hi Fi compressor and clipped "P' trim exhaust wheel. Turbo housing has been modded for flow (doubled width of turbine scroll slots etc).

It is a ~400RWHP turbo. It would lose traction in a straight line ~6,000rpm in 3rd gear with 225/50 A520 (200 treadwear) on 8" rim.

i doubt you will get any better boost responce with the 3.5 inch exhaust as boost responce is usually better with smaller volume, higher velocity tubing. if anythign you might notice peak power increase if you are near the limits of 3 inch piping flow. its been asked but any dyno sheets from 2k rpm and up?

Nope. it does get much better boost response with the 3.5" system as I found on my previous engine. Much faster spool down low (boost off idle cruising in 5th) and ful 17psi was 3,500rpm. It just drove like a bigger engine w/ the 3.5" exhaust on it.

Spool up is all about having the highest pressure differential on the inlet and outlet of the exhaust turbine and still having enough flow it doesn't choke.

Peak power felt about the same with the 2.5" exhaust, the 3" exhaust and the 3.5" exhaust (except it couldn't even hit full boost with the 2.5" exhaust- felt the same per boost level achieved).

Here is a thread with my engine work and most recent turbo work.

https://www.rx7club.com/rotary-car-performance-77/pics-blue-tiis-engine-build-new-type-primary-port-489429/

 

So far, so good.
Break in is done, boost at 11, fuel & timing are very conservative until I get it tuned.
VERY streetable.
No idle lope unless I turn it down to 650 RPM.
Low end grunt is solid.
Nailing 2nd at ~5K really spins the 225's.

2 weeks ago at 8PSI & 6K RPM the G-tech showed 217 net HP.
rev up video at 8PSI

I plan to take the G-tech for a ride when the weather gets better to get some 0-60 & Qtr mile numbers.