? RX7 2nd gen Bottom end

[dj10]

I was wondering how the RX7's bottom end was set up? If you have a BMW you could use a 328 crank and rods (stroke it) and no one would ever know because as far as I know no one has ever checked the bottom ends at any tear down I know. My question is can the RX7 be stroked or displacement increased with out detection.

I know that a southeast team was running my car (when they had it) as a 2.5l but was actually a 2.8l.

Thanks, just curious

[Marcus Miller]

Originally posted by dj10@Dec 26 2005, 03:39 PM
I was wondering how the RX7's bottom end was set up? If you have a BMW you could use a 328 crank and rods (stroke it) and no one would ever know because as far as I know no one has ever checked the bottom ends at any tear down I know. My question is can the RX7 be stroked or displacement increased with out detection.

I know that a southeast team was running my car (when they had it) as a 2.5l but was actually a 2.8l.

Thanks, just curious

69225


Yow. :blink: :blink: :blink:

The short anwer would be no, the easy answer is not a chance. the long answer would be that a displacement increase of a meaningful (anything more than a CC or two) amount is not possible, but if you want power, port it. Its amazing what a well placed swipe with a dremel will do...

Marcus, who wishes he was that unscrupulous

[JeffYoung]

Um...there is a car in the SEDiv running a 2.8 in a 325? Geez....that's like Superman ...never mind.

[ddewhurst]

bj10, ya need to search under "How stuff works"'rotary motor & you'll learn in a hurry the long answer about why stroken or displacen a rotor motor ain't going to work.

[lateapex911]

Good points on the concept, but the displacement increase from a 12A (70 cubic inches) to a 13B (90 ci) is due to a wider rotor and rotor housing. Unless you are able to roduce those you are out of luck...and nobody would ever try, because detection is is easy as measuring the outside of the engine with a tape measure!

As MM points out, porting is the ticket. The ports, at the point where they enter the rotor chamber, can be "eased"...very little...and the gains can be significant. I know that the 12As are "checked" with a "go/no go" guage called a lolipop at certain SE races, such as the ARRCs, and that a probe with a finger is done as well, but my research indicates that significant gains are possible even with those checks being performed.

I also understand that the 13B (ITS) motors can not be checked with the guage, as none exist.

Recent "rumours" are about that suggest that "new" hp has been found in ITS using a tricky method of increasing breathing. It's not legal of course, but tough to prove, even if you know what you are looking for. Of course, that's all rumours and innuendo, nothing has been proven much less protested. So, I don't put much stock in those....not yet at least, LOL.

So, to answer your question, yes, there are gians possible, and a teardown is needed to find them, but it is very invasive...much more than checking a cam for instance, on most piston engines.

[JeffYoung]

Truly amazing the power those motors make out of that displacement.

[ddewhurst]

Jake or anyone else, did you or have you reviewed the porting rules for rotary motors which IIRC Dave Lemon & Jesse Prather did & presented to the SCCA to define & control ports. These written rules might be in a rules review process. Dave showed many methods that a lolly pop would not even come close to detecting intake ports. Exhaust is a littler simpler to check. Under the HOW COME column is the question of why isn't some sort of what I'll call a protoscope :119: used. With all the technolgy in the medical field & other places today it seems there should be an economical devise to stick in the exhaust port for checking the intake ports.

[lateapex911]

Dave...did you read my post a year or so back called "A Protest Story"?

Lots of reasons embedded in that treatise...

Ignoring those, lets just think this thru. IF a protest lists porting, what happens next? (Here come the assumptions, LOL)

I would think the Tech Steward would go to the protestee and eventually an agreement would be forged which would detail the place and time and money required to open the engine up.

Then what... How do the techs KNOW what they NEED to see???? One way is to get an independent supplu of stock components....in this case, a side housing. Gulp....but, lets say they did...then they would make a comparison between the two and make a call.

But..how would they make the comparison? Well, they could make templates and cast radius molds, then see if the protested one matched.

Now, how can that be done with a "protoscope"?
Sure, the obvious ones would be easy to see, but it doesn't take much, and while I like and applaud your ideas. I need to be convinced.

No, I haven't seen the items you refer to. I assume they are for Prod motors?

[ddewhurst]

Jake, yes I read your protest story a year ago. After I posted last p.m. I searched scopes including bore scopes which get pretty costly. Sometime today I'll go look in intake ports openings finish at both ends, look at the intake internal surface finish & also look through the exhaust port at the side plate intake opening. Will return with more details & then launch into if pistons can overbore, increase compression ratio increase by .5, port match & ECU management we should be allowed to port enough to get back to the front of the ITA game on tracks other than momentum tracks. I now that no one on the ITAC wants to hear my launch. To bad................. ;)

[dj10]

Originally posted by ddewhurst@Dec 26 2005, 09:44 PM
bj10, ya need to search under "How stuff works"'rotary motor & you'll learn in a hurry the long answer about why stroken or displacen a rotor motor ain't going to work.

69243


Dave,
This site usually provides much more info & BS :D than a search site. What you get here are different perspectives.

BTW, I'm pretty sure that a volume gauge screwed into the spark plug hole would detect any stroked 4 stroke engine.....if the scca had them or would use them.

Dan

[ddewhurst]

***My question is can the RX7 be stroked or displacement increased with out detection.***

Dan, check my member number & that should tell you that I pretty well understand the workings of this site. Hey, you asked a question when you started this thread. I responded that by searching howstuff works.com you'll learn in a hurry the long answer about why stroken or displacen a rotor motor ain't going to work. When looking at a working rotoary engine please take the time to understand the ecentric shaft, the two gears & the path the rotor follows.

Not trying to be a dick head but I do like to provide direction & information to those who ask. If I wanted to be a dick head I When I read your question my first thought was/is you don't have a clue about the parts/workings of a rotary engine & I would have said so. But, I didn't. :)

[ddewhurst]

Jake, I looked at an assembled motor through the exhaust & at some housings & side irons. It had been a while because I was thinking that the 12A OEM exhaust port was a big old round hole (ya see what I was thinking about keepen up with the CRX's) which was much closer to the intake port. The OEM exhaust port is this tiney little rectangular opening with 4 round corners & it is a long way from the intake ports. As you well know checking the exhaust port is a no brainer. The intake ports in the side irons are cnc milled with the side of the mill, the length of the side iron intake runner is cast & rough. I am going to presume that when a lolly pop is used it's used after the intake mainfold is taken off & the lolly pop is inserted through the side iron intake manifold end of the intake runner which is a much shorter distance & ya can see part of the intake port looking through the side iron intake track from the intake manifold mount surface. Is that correct folks ?

I will continue to do some research towards using a loll pop/template which would be inserted through the manifold end of the side iron intake runner after the intake mainfold is removed. If someone started grinding the cast surface it would get costly in a hurry to redo the grind surfaces with a cast look. (People did it in Karting in the cast alum areas of the intake ports but the wise old tech owls gotem most the time.) The intake shape at the manifold end of the side iron is pretty distinct. A plane template for the side & the top surfaces would do the check. Now the side iron intake port where the rotor side seals is another story. But being that it's opening is mill machined from an unknown place by me at this time I'll need to do some research. I'm thinking a lolly pop & bore scope/small mechanics mirror/hollow tube with a side hole at the far end with a mirror inside the hollow tube at the far end will be a good method to check. Might be how they check now............ ;)

Tune in in a couple days for research/check test results.

Rick, HELP.................. :023: