Greetings,
I recently dropped Racing Beat a line re: the operation of the 6PI system found on the 13b 86-91.
By my account, with the current gearing, it does not make sense to have the ports open only past 5000rpm because when you shift at 6300rpm (the stock peak operating zone for a n/a '89+) the revs drop below 5000 in the next gear. Hence you are out of the 6PI area or for those Honda fools, the VTEC range. Little do they know Mazda was in production with an aggressive intake system well before they were.I was wondering if there was a way to fool the actuators into a hightened sensitivity to the pressure and open earlier.
Jim Mereder (may have been ignorant with the spelling, sorry) the co-founder of the whole RB org. e~mailed me back personally and explained how they did testing on this exact theory a few years back. Under 5000 rpm the hp climb was actually compromised with a slight loss in power! He did not explain why (I figure that's all he needed to know), but I figure that the engineers at Dept 5 in Hiroshima knew the dynamic effect plenum's behaviour would negate any way to coax any more power out of the ports down low, so they designed it to operate as a compromise (like just about anything else to go fast). Wiring your port actuators or butterfly valves is not the answer! As far as modded cars go, the only way to get answers is to put them on the chassis dyno and get your wallet out to determine if the wired approach works with increased breathing mods etc. Any thoughts or experiences?

 

wow, what a nice little post. Thanks for all the info to chow down on.
Gotta love this factual info and history
Got any more goodies for us?

 

well if i was racing i wuold never shift at just 6300 and if i was driving normaly i would never shift at 6300...

 

In re: to never shift at 6300 period... The key disclaimer here is that the dyno graph doesn't lie. If you want to go shifting at 8000 rpm that's dandy, but hp, has long since started to decline, you may pick up higher after the upshift, but any advantage will just cancel out, and the extra abuse on the engine will send you to rebuild land sooner. With a race prepped vehicle things are different, as the power band shifts due to gutted smog equip etc, etc. Ie. there is something to be said for higher revs.

 

6ports open around 3600-3800 IIRC, about the same time as the secondary injectors open. However, the 89-91 VDI comes open around 5 grand I believe.

So in essence, you've got a decent theory, but also keep in mind that shifting at 7 grand may net you less power than shifting at 6300, because, while you are correct, at HP peak, no more power is being made, it all depends on the curve.. If HP peaks but doesn't fall off dramatically, reving to 7-7500 and shifting will plop you right back into the HP peak area. However, if HP dramatically falls off after 6300 in your example, then you would be right, shifting near 6300 will help keep you in the power band longer. But you can't make general statements like this without a dyno graph.

PaulC

 

also the 6 port valves wont close that fast, so even on a stock car they may be open

mike

 

6-ports open at 3800rpms, VDI opens 5.5k rpms. Even shifting at 6300rpms you shouldn't drop below 3800 rpms. Also, show me a graph showing peak power at 6300 rpms. That MAY be so, but power doesn't drop off quickly after 6300 rpms. There is NO way even on a stock 89+ that shifting at 6300rpms, will yield faster 1/4 miles time then shifting at 7500-8000. The powerband doesn't even start until around 5500rpms. So your saying there is less than a 1000 usable rpm range to be used for racing on a stock RX-7?

 

Of all the different sources i've read about the 89+ Rx-7s, they made peak hp at 7,000 rpms. Stock, anyways. CJ

 

I think Mazdatrix may have dyno chart for stock 2G. I know one existed in the catalogue, they were doing a comparo between stock exhaust and RB gutted set up for racing, said 30% increase in pwr, even though this has nothing to do with anything. And yes, power decline is sharp, not plateaued. Then you must take into account the actual power loss due to the permanent open nature of the ports on your 0-60's. The fact is, engineers design each part to interact with eachother in stock trim for a reason. They never seem to count on shadetrees messing with their masterpiece. The baseline hp peak is around 6000 and the surge tank and VDI are designed around this fact. Couldn't find visual rep of my claim but found literature. Sorry that's the best I can do right now. I am going to consult J.Yamaguchi's 2G book on definitive answers for the opening rpms, and see what else I can find. I have always found this an absolutely crazy topic for getting proper answers, and even if I prove my opinion wrong I will be satisfied that the truth will come to bare anyway. It may be a wk or so, but we'll get to the bottom of this.

Except from Mazdatrix website "Racing Section"
This system is the culmination of considerable testing time here at Mazdatrix, using many different designs and pipe sizes. The result is by far the best HP from a bone-stock 86-92 13B non-turbo we have seen. We showed a 28% increase in rear wheel HP on a chassis dyno with this system. Torque is increased greatly from 2000 RPM on up, with the power peaking at 7000 RPM. Peak on straightpipes is 7000, shifted from 6300rpm.


Note: All pollution emissions altering parts are not legal for use on public road driven vehicles - for off road and closed circuit racing only.

 

Absolutely the most respect intended here, but- WHAT THE F*CK???
Maybe I'm misinterpreting this, and if I am, oops, sorry.

Ok, I have a challenge for someone here.
I can't do this because my car is way to modified, and my porting completely changes the dynamics of the power curve.
Someone with a stock car (funtional 6 ports) needs to do this.
Someone take a rolling start, 1st gear at idle.. (rolling start to eliminate launching variables)
Time how fast it takes to get to 60 mph, shifting at redline.
Then do at again, shifting at 2000 rpms before redline!
See which run will be faster.
I don't even have to see the results.

On a stock car, the transition point is just about perfect- assuming you shift where you are supposed to, at around redline.
If I shift at 6000, that's right at the START the power peak, not allowing the power to get transferred to the wheels... and that shift would put me at about 3800 rpms or so in next gear (gear dependant)... that SUCKS!!
By your theory, you only get peak power for a split second at the top of the shift... I really hope I'm misunderstanding this!! (My car has a high peak, but this is just an example)

Ok, I think I see whats going on.... he's saying the power drops off so much after the 6300 peak that's it's not worth it to stay in gear....
Ok, first off, really don't think it drops off that quickly after 6300 at all, but rather keeps increasing untill about 7500 (stock)
THE MAIN point here is that holding on to you shift point higher will put the bottom of your shift into a higher, more powerfull RPM range in next gear. The reduction in power at redline still MUCH offsets short-shifting and getting bogged on your face at 3500 rpms!!
Even by ballpark in-head figures There is a much higher absolute HP/Sec total while shifting at redline than at 7000 (on a 89+)


Anyways, the stock rx-7's power curve is moderate- not too flat, but not a spike either. All the smog equipment, and restrictive exhaust keeps the upper end down. Change all that, and the torque curve will keep climbing till redline.

Anyways, lets clear this up, I hope I don't sound harsh, no flaming implied!!!
Cya

 

we g-teched one of the parts trucks once, and it was like 1 second faster on the 1/4 if you shifted at 4.500 instead of the 6,500 red line.
it depends on the torque curve, and the gearing. i bet the optimum shift point is different in each gear

mike

 

Mr ECCENTRIC........I agree with the fellows on the opening of the aux actuators. It happens b/t 3500 to 3800. I've put a spare lower manifold in my wifes bone stock 86 front seat, and tee'd into the servo line for the actuators. Drove and watched them start opening around 3500 and fully open by 4000. If you want them to open at some other rpm, the Team fc3s site has an electronicaly controled one. Don't know nothing about VD.I never had it. Been careful. humor

 

great topic.. Here some STOCK 86 & 89 powerbands
6300rpm?------>

 

89

 

intresting the stock HP and torque differences.




It appears (and maybe I am reading it wrong, but it appears) that the series 4 motor is much more torquey than the series 5 motor

 

Looks that way to me too.

 

Ok...according to the book Mazda Rx-7 by John Matras the 86-88 n/a Rx-7 146bhp (net) @ 6,500rpms and 138lb-ft @ 3,500rpm

The 89-91 Rx-7 made 160bhp (net) @7000rpm and 140lb-ft@4000.

I have no idea where you're getting your info from but shifting your car at 6,300 you're going to get beat by just about everything on the road. Some good info in your post, but i don't think you know what you're talking about. CJ

 

Youre missing an important point here though. NOBODY shifts at the power peak. The optimum shift point is above the power peak, where drive power falls below what it would be in the next gear after the shift.

CJ, correct me if Im wrong here, but PP engines have a power peak around 8500 rpm, but the optimum shift point is closer to 10K rpm due to the power barely falling off. It has more drive power at 9500 rpm than it does where the RPM's would be after the shift. This takes into effect gearing, raw torque numbers have little to say about shift point without gear ratios.

 

VERY GOOD POINT i even forgot to say that one,
FYI i got the graphs from MD RACE

 

So exactly how do u shift 1revin

 

well revving past 6300 would be key to land the next gear higher than 5, I can take my meter to 7500 and hit the next gear at 5 and a half everytime, at least in 2nd and third.

 

i usually shift just above 7G, after i hear buzzer. Need to keep eyes on road. My peak horespower is about 7G, i can feel it. little after my peak.
Where did they guy go who started this topic? ppl have lots of Q's for him....

 

All this information and so little time. Wow

 

How about we test it and i will post the results You guys exsplain the perameters and i will tell you if i can do it.

If this would help to see thing tryed

89GXl Stock other then thottle body mod and filter.

 

Exactly