SiRkid

Ive been thinking about this lately and Arts post about 6000000000000 Hp made me remember it.
Why is it that RX-'s put extremely large turbo's on their cars?
I dont know howmany things Ive read or videos Ive seen where the turbos will get fully spooled..then they have 500 rpm left and they have to shift.
They are putting on turbos that supra's use. I just dont get it.
IF they are going to rev higher than I understand but I see far to many guys with turbos that are way too big. even if a 1.3 L rotary is the equivalent to a 2. whatever 4..They are still to big.
any thoughts?

b18bturbo

Just look at greddy and many other manufactures. They been working with rx-7 and many other cars for the longest time. They seem ot use the large turbos for top end power. I think rotary guys can fly up on the top. Look at ari or steven kan from rx-7.com or many others they all using large greddy setups with nitrous off the line works perfect. not saying everyong is going all out large but some kinds just like the stg1 type upgrade like td06 or something in that form... compared to a t88 t78

spike

one rotor is equal to 3 cylinders actually if you think about it.. there are 3 combution chambers per rotor. They flow a LOT of air and can spool these larger turbos. Their 1.3 liters are equal that of a 3.9 block/piston motor in reality.

Brandon

I'd like to see somthing a little more interesting, like someone taking advantage of the rotary's best feature, ability to rev past conventional piston engines. A well balanced motor could easily see 20krpm.

johnisenglish

Good point Brandon, but there's really huge lack of people who have the know how to do something like that, at least domestically. Maybe the Renisis Engine in the 8 will change that...

boosted hybrid

The rotary engine also produces an extreme amount of energy in the form of heat. They run much hotter than piston engines. They waste alot of their energy in the form of heat. For turbo purposes heat carries the engines energy out of the combustion chamber, and the greater amount of energy will allow the spool up of some very large turbo's that honda could only dream of. You can compare the heat energy of the rotary to the heat energy of a high compression piston engine. The high compression carries more energy into the turbo, allowing you to spool up a larger turbo easier than a lower compression engine. My friend has a 1st gen with a 3 gen engine, 2nd gen turbo II trans and runs a t78 on the street. He claims to make full boost by 5,500rpm and redlines at 10,000rpm with ease.

BlueShadow

Errr...all the guys on the RX7 forums would probably pass out if I showed them all that stuff you just posted. You're trying to explain rotaries in terms of piston engine combustion cycles but you're doing it wrong and I think it's gonna cause a lot of confusion.

As we all know, a piston engine has 4 cycles (intake, compression, power and exhaust). FWIK a common 4 banger will have all all stages of the cycle going on at all times in the different cylinders. IE. cyl 1 will be on intake, cyl 2 will be on
compression, cyl 3 will be on power, and cyl 4 will be on exhaust. On rotary engines though, only three of those four cycles will be happening at any one time...but the fourth one will be coming up in rapid sequence.

The thing that has a lot of people say that a 1.3L rotary equals a 2.6L V-6 is because of the number of strokes each side of the rotor housing gives you. This whole "1.3L = 2.6L V-6" all came into play way back when the first rotaries were racing and they needed to classify the engine.

This is from page 96 of Mike Ancas "Mazda RX7 performance handbook"

...So as the rotor revolves around the housing, three different things happening in the three different chambers. It is hard to think in terms of "three" if you are used to dealing with a piston engine which does things in "four". But those same "four strokes" are present in a rotary engine ...It's just that only three of those four strokes are happening at one time, as opposed to a piston engine in which you can find all four things happening simultaneously somewhere in the engine.

But technically, with three strokes happening in each rotor, it is essentially equivalent to a three cylinder engine. Put two rotors (rotor housings) together and you have a six banger

I think if you break it down by combustion cycles you'll find that it is very tricky convert a piston engine to rotary terms and the other way around.
Look at it this way:

ROTARY:
1 combustion cycle (360 degree rotation of rotor) makes the eccentric shaft.rotate three times. So if the RPM guage moitors the eccentric shaft rotation what does that mean? 3 revolutions = 1 combustion cycle.

PISTON:
1 combustion cycle makes the crankshaft rotate half a revolution. So in order for the crankshaft to rotate 3 times the engine has to complete 6 combustion cycles.

what does that tell me? I dont know, but Im too tired to type anymore...I'm going to bed now, maybe I'll pick this discusion up later. Or show it to the guys on http://www.RX7club.com

Before I go though I will answer the original question...the RX7 is able to use a big turbo because it can flow enough exhaust to spin one of em...if you want a more technical answer....I can ask the RX7 guys, but I'm, pretty sure I'm correct (or close).

SiRkid

i know they flow a lot of air but from what ive seen(mostly japanese stuff) they reach full boost and then in a second or less they have(or choose ) to shift.
and seeing some dynos confirms this.
i wouldnt mind having a few rx-7 techies come in and explain it
as i dont know much about them really(just some basic stuff ) that i forget half the time cause i should be concentrating on my honda stuff

BlueShadow

Well besides the obvious answer that they have the capabilities to flow engouh air for a large turbo, the other obvious answer woul be because that turbo can also give them the high HP numbers they seek with less strain on the turbo and engine (turbine backpressure & IAT). It doesn't take a RX7 or Supra guru to figure out why they chose bigger turbos over smaller ones. (It's for the same reasons we do it)

GZERO

another good point is that rotary engines work at about 50% of efficiency, meaning that they still have some development to do. this have been something that always make me think.

BlueShadow

I think one of the reasons Rotaries are at "50% efficiency" as you put it is to meet EPA standards. Take the ports for example, by enlarging the ports (street port bridge port etc) you can get some decent gains, but IIRC you also raise emmisions.

JDM92CX

Good point BlueShadow...

SiRkid

no need to be mean
well with the improved rotary coming out I wonder how well a boost prepped one would do.

GZERO

you're wrong, rotaries doesn't produce their full potential, they are between 50%-60%, one of my friends knows a **** load of rotaries, and he told me that one of the greatest thing about it is that is an engine that hasn't been exploided to his full potential, you are right that they lower power numbers and efficiency of the engine to meet with emmisions, but that wasn't my point.

BlueShadow

How am I wrong? did you read what I said? I myself am saying that rotaries ARE NOT seeing their full potential because of all the emmisions controls they put on their. (cats, air pumps, port sizing etc)


[Modified by BlueShadow, 1:02 AM 2/5/2003]

pissedoffsol

the biggest problems with rotaries and revving is the seals go, and suppliying enough spark after 8k rpms is tough.

remember- the 3-stage as stated above. although it seems like its a 3-stage, it CONSTANTLY repeats- so at any one time, each of the chambers is doing its thing.

in all reality, the rotary spinning at 8k rpms is seeing 24,000 rpms to the spark plugs. as you can see- its fast as hell, and even with 2 plugs per combustion process, it still is the down fall.

Jacobs ignition packs help out a lot, but like all things, there are limits.

BudaKai

Blah bunch of gibberish. Rotaries produce more torque than a piston engine of comparable size. The entire combustion chamber is the rotating assembly. Slap a big turbo on to really get it spinning and watch out. Rotaries rock.


[Modified by tzsir, 1:45 PM 2/5/2003]

SiRkid

hmm..
i think most know the rotary is nowhere near its best performance..
isnt there some sort of conspiracy(sp) about the motor and other manufacturers not wanting it to be develped?(i read that somewhere)

ill_take_one

I wonder how many changes were made on the new Rx8 rotary engine then? Must be plenty of changes due to the fact its NA now? right?
peace

BlueShadow

The same thing could be said about a lot of stuff that you post.

BlueShadow

The previous generation of rotaries also had NA versions available. One of the many improvements I can think of is the intake and exhaust port design. As I mentioned above significant gains can be made with the right port job on a rotary (NA or turbo). I cant recall all the improvements off the top of my head but I think the RX8 also has higher compression rotors.

For comparison, the older 1.3L NA motors found in the 2nd gen RX7 had around 160 HP while the new Renesis 1.3L NA rotary had 250 HP.

BudaKai

I don't care if you listen or not Blueshadow. It's what my times compared to your's are in the end that will tell you how much I know. It sounds like gibberish because it's over your head. If it bother's you that much maybe you should listen for once to better understand from other's experiences instead of assuming you know the 'right' way. You can't know everything because I can admit that I don't.

Anyways the Renesis benefits from moving the ports from the previously employed side intake ports and peripheral exhaust ports to having them in the side housings. Which in turn almost totally eliminates overlap, and improve combustion efficiency and stability. Intake ports are about 30% larger,and they have been moved to have them open sooner increasing power stroke and providing greatly improved heat efficiency. They have sic ports (as opposed to the old 13b with 4) with a variable timing mechanism that opens the high horsepower ports when it reaches a specific RPM. (OOOooo VTEC on a rotary.) On the exhaust side there's now two ports as opposed to the one like in the Turbo II's and twin turbo model's. The rotors are also appriximately 15% lighter than the ones in the third gen Rx-7. All this (plus a little more that doesn't really matter to any of you) adds up to the new higher power and efficiency.

All of this I got off the information packet I received on the Renesis four monthes ago. I'm a rotor head that's into Honda's.

ill_take_one

My bad, i should have been more specific. I knew the second gen. had NA rotories as well at FI.

So how were the NA rotary engines as far as reliability? Just through reasoning, could one assume they arent as reliable, due for the fact that they are very rare in new cars? Which probably could lead to an assumption that they arent in many cars because there hasnt been much research and develpment put in to these. Just a guess.

Maybe i answered my own question?

BudaKai

Wrong, there are more NA rotaries in cars than there are turbo ones. My first RX-7 had an NA, but like many NA RX-7 owners I turbo'd it. To really find out about rotary performance you need to look for the first gens. The first gens are the real monsters when it comes to performance with engine swaps. Old school 510's are popular too. Most rotor heads like the old school imports. I love those R100's and Cosmos. The best was the third gen RX-7 because it was the most advanced, but had a lot of reliabilty issues with the sequential turbo system. The RX-8 should change all that. Especially when they start slapping turbo's on to them

BlueShadow

I dont care if you're right or wrong, it's your **** poor attitude and the way you answer some peoples questions that I dont like. But dont worry I'm pretty sure I speak for a lot of people on here when I say that you aren't very well liked on H-T.


[Modified by BlueShadow, 12:02 PM 2/5/2003]