adidas_720

I gotta 85 RX7 carb and I can take it to 7500 or 8000 in 1st n 2nd, when i get to 3rd it sputters out like its gettin too much fuel??? bad carb? or emissions messin it up??

Rx-7Doctor

iTrader: (13)

You are running the motor past it's limits and the fuel pump can't keep up that demand.

nopistons3

iTrader: (1)

so would a new fuel pump or fuel filter help that?

Rx-7Doctor

iTrader: (13)

Maybe but their is no power band at that level in stock form and all you will do is retire the motor early. It is not made to run at those levels.

rx-7 obsessed

trust me dont do it. I was showing off one night 2 a friend and yes the motor can rev that high and docs right there is no power there. And POP there goes a seal dont kill the 7 man shift when u hear the buzzer it will last much longer

nopistons3

iTrader: (1)

the buzzer is broken, and from 6 to 7500 it has the most power i think.

trochoid

iTrader: (6)

It doesn't, what you think is more power is the engine telling you to back off. Peak hp has droped off by 6800/7200 rpm on a stock engine. The more miles on the engine, the lower the peak is.

nopistons3

iTrader: (1)

Well by putting a new fuel filter on it, it has no problem revving to 8000rpm. sputtering problems gone. And call me stupid but my car right now has more power from 6500 to 7500 than from 5000 to 6500. I know peak hp is at 6800 or the buzzer. But I have removed the cats and strait piped it with 2in back, and also removed the clutch fan and installed a electric fan. It has no problem winding like its supposed to. Double clutch into 3rd and it kicks sideways.

Rx-7Doctor

iTrader: (13)

Ok Stupid. Chime back in when you need the link to, "How do I rebuild my motor because I did not listen to those who know"!

OnlyOnThurs

the cold hard truth lol

DriftFB

+1

and can you explain how your double clutching into 3rd?

Shadow2

Is double clutching short for double de-clutching?

My book gave de-clutching for a tranny that is grinding. I find it makes mine grind less while it is warming up. 24 year old tranny, and it only unhappy when cold. No complains.

Haynes Pg. 21 (1986) - Book is almost as old as me. Car is older

It's not fast, but i guess you could just let it rev out to 6k and drop the clutch, might rip the tires out. Good hard power shift mine would chirp 2nd. I'm not very fast at hitting 3rd. (Ever wonder why my car broke?)

So any ways, is this the same thing?

nopistons3

iTrader: (1)

is everybody a genius on this website or something? I double clutch to get the rev's back up. Btw, Were is it writing that reving the engine to that speed is going to harm it? Is there a starvation problem with oil or somthing? I got the carb thing sorted out with a fuel filter that you said wouldnt help.If you know how to drive you know what double clutching is.

mazda6guy

iTrader: (1)

There is oil starvation with the rotor bearings at those high rpms that your are producing. Take it from me I have an extra engine that needs a rebuild in my shed from doing the exact things that you are doing to your running engine.

Rx-7Doctor

iTrader: (13)

I guess your the Astute one here. From now on we will just pm you if we have any trouble at all with our cars.

bliffle

Use Redline MTF in your transmission and only double-clutch in extreme circumstances, not rourinely. You'll save clutches, transmissions, and maybe some other things.

Kentetsu

If you're not getting peak power until that late in the rpms, then I would suggest that you check your timing. You are probably actually down on peak horsepower because the ignition isn't set to the correct advance at high rpms. Get it set correctly, and you should have better overall power throughout the rpm range.

Where in Michigan are you?

bliffle

Overrevving is unwise, not necessarily because of oil starvation, but because at higher frequencies additional vibration modes are excited that would otherwise be absent or subdued. As frequency increases wavelength decreases and smaller dimensions become eligible for vibration. Some of those modes may be unstable and the vibration increases until structural failure occurs from repetitive stress or even from a forced rupture when components crash together.

Piston engines often fail in overrev from a forced rupture in the valve head as the head crashes against the valve seat because the overrev produces acceleration rates of the cam follower greater than the ability of the valve spring to follow the easement ramps on the cam. Often, valve crash is accompanied by cam galling. Sometimes a camshaft will actually break.

Rotary engines have fewer occasions for such valvetrain crashes, but they have failure modes similar to piston rings, where the ring vibrates in a mode that causes it to repeatedly crash against its confines until it fails. Something similar happens to apex seals.

It's a nonlinear process. The structural strain is NOT proportional to the applied stress forces. At some point there is a crisis as vibration modes increase in number, not just excursion, and peaks coincide and re-enforce each other. Boom.

Sometimes you find a broken engine part whose two mating surfaces exhibit a gleaming multi-faceted granular appearance and someone announces "oh, it crystalized, that's why it failed". As if it were a fabrication defect. But it is not a material defect, it is a Repetitive Stress fracture just like what you get when you keep bending a paperclip back and forth until it breaks.

Machines don't mend themselves, unlike biological organisms such as people. When abused they just break and quit working.

One may get away with beating a person, who may subsequently mend, but a machine will not. But why abuse either one? No good can come of it. "Trial and error" is an even worse way to learn about machines than it is to learn about people. When I hear someone say "drive it like you hate it" I cringe much as I do when I hear a parent say "you've got to beat children into submission".

Rx-7Doctor

iTrader: (13)

What bliffle is stating in layman terms is that because of the close tolearance between rotating parts. The further you push them the less clearance there is and therfore failure begins.

Kentetsu

Another reason not to over rev is apex seal chatter...

trochoid

iTrader: (6)

For a rotary engine to sustain 8k rpms, it needs to be built to handle it. They are not built for that from the factory. For continuous or sustained revs above 8k, the rotors need to be lightened and clearenced, the entire rotating assembly needs to be balanced as a unit, the stationary gears need to be replaced with hardened ones, the bearings need clearenced and replaced with the 3 window style, the e-shaft needs the oil jet mod, the oil pump needs to be upgraded to the 17.5 mm one and the oil pressure regulator needs upgraded to the higher pressure one.

You can rev your engine as high as you want, until it blows, but it's still not making more power above the levels I stated earlier, even with your exhaust mods. The only way you're going to raise the useable powerband above what it is is with some serious porting, i.e. a bridgeport or larger.

Fwiw, double clutching to bring the revs back is actually slowing your et's down because the time takes you to bring the revs up, you could instead be applying power to the wheels and maintaining your rate of acceleration. From what I see, your little trick is nothing more than showing off so you can say you get scratch in 3rd gear. Funny thing is, on my stock engine with headers and a Mikuni, I did too and all I needed to do was flat shift at the track. No fancy Steve McQueen "Bullit" double clutching needed.

Genius, well I can't speak for the others here, but the last time I was tested, I was 12 points shy of that designation, which puts me somewhere in the 95th percentile of the general population. Since you seem to feel you know more than the rest of the 'experienced' members, care to share your IQ numbers with the rest of us?

If you want to over rev your engine, with the false assumption that it's faster, well, it's your engine. Keep in mind that wear does not increase on a 1:1 basis as engine speed increases. As Biffle was trying to explain, wear increases at an exponential rate If you don't understand that concept, you will soon learn it, the hard way, when your engines says "I've had enough of this idiot and I quit".

Kentetsu

To the original poster: Since you are a fellow Michigan resident, I have the impulse to defend you to my fellow members. However, some of your comments have been pretty inflammatory.

If you didn't think that this forum was full of "experts" when it comes to these cars, then why did you come here? And if you did think we were "experts", then why would you argue with the most highly informed members when it comes to some of the information that they are trying to give you?

Do you tell your Doctor how to do his job? Or a lawyer? You go to experts to get expert opinions, not to argue with them (unless you are also an expert with a differing view).

Anyway, please be polite to those that are trying to educate you. We only have the best of intentions, we care about these cars in general, and we are always willing to help new people learn about their cars.

And by the way, Trochoid is one of the most highly informed members of this forum, and definitely the hardest working member. If you doubt his knowledge, then you should take a look at his thread on the building of his car. I assure you that you will be impressed. Take care, and good luck with your car...

Kentetsu

What you described is not double clutching. All you are doing is pushing in the clutch, revving the engine up, then dumping the clutch. Have I got that right?

Double clutching is a technique used to match the engine rpms to the speed of the tranny when changing gears. Modern trannys have synchros, so that is totally unneeded unless you have a bad clutch or a worn tranny.

Double Clutching = aproach turn and start decelerating> clutch goes in > stick goes into nuetral > clutch goes out > rev engine to appropriate speed (to match gearing that you are going in to) > clutch goes back in, and gear lever moves to appropriate gear > clutch goes out. Done.

About the only people who really have to do this any more would be some of the drivers of 18 wheelers, if their trannys are unsynchronized models. Not much use to an rx7 driver.

Now, heel and toe shifting on the other hand is a very useful technique for performance driving....

Also, if you're not a member yet then check in with www.mirotory.net That's the Michigan forum. Not a whole lot of action there right now, but that's where you'll find out about local meets and races etc.

trochoid

iTrader: (6)

Kentetsu, good point on the double clutching. What nopistons3 is describing sounds more like a clutch kick to initiate a drift in an underpowered car. If that's what he's doing, and doing it at redline in 3rd gear on curves, someone is going to be scraping him and his 7 off the pavement, wall, tree or whatever he eventually runs into when the snap oversteer catches him by suprise.

nopistons3

iTrader: (1)

I do appreciate the help but I do not like being criticized for something that I am in the learning process of. and im not redlining in 3rd and dumping the clutch, I dont take my car to 8g everytime i drive it. but somedays it seems to go to 7500 quicker than reaching for the next gear at 7g. I do understand the real concept of double clutching compared to just shifting to keep more power to the wheels for better acceleration.
Im from lansing area and I do intend to keep my RX7 in great running condition and building is the next step. I am a extreme Mazda fan especially with the RX7, this is my 1st rx7 and I am glad that it is a 1st gen with carb 12A. I get to learn from the bottom. I also have a 2nd gen that I will slowly build up. I came to this website to get some possible suggestions. Some of the problems with my car i didnt pay real close attention to, so i just asked instead of diagnosing the problem. and i should have payed more attention to my car then posted comments. But like I said I dont like being criticized for something I am learning. Im from the lansing area and hope to meet new ppl and get more into what the rx7 really is built for. So apologies if I sounded like an ***, but like someone said expressions arent easily taken in writing. Im just here to learn and have fun.