rev limiter 1991 protege dirt track car

[Liquid_Ag]

you have no back pressure or exhaust velocity going on, both of which you need, causing power to taper out up top, and the engine to struggle to breathe. put a side exit exhaust or something - 2-2.25in with a resonator, and it should help

[Gen1GT]

you have no back pressure or exhaust velocity going on, both of which you need, causing power to taper out up top, and the engine to struggle to breathe. put a side exit exhaust or something - 2-2.25in with a resonator, and it should help

Come on man, let the backpressure myth die. You do not need backpressure. None, zero, ziltch. The less, the better. Your second part is correct. You need velocity.

Anyways, you can change the rev-limit by changing the clock speed of your ECU by installing a different Crystal. Everything you need to know is here.

http://forum.miata.net/vb/showthread.php?t=145076

[Liquid_Ag]

Come on man, let the backpressure myth die. You do not need backpressure. None, zero, ziltch. The less, the better. Your second part is correct. You need velocity.

Anyways, you can change the rev-limit by changing the clock speed of your ECU by installing a different Crystal. Everything you need to know is here.

http://forum.miata.net/vb/showthread.php?t=145076 with low displacement engines with low output , like a 1.8 sohc, no backpressure = no velocity. while in theory you are correct, without power mods and/or displacement, his motor will die with no back pressure. even my lx sometimes struggled to breathe with the gutted cat and stock exhaust mani, as the exhaust was to large to maintain proper pressure and velocity

[Liquid_Ag]

The rev limit is not at all based on airflow. it's totally RPM based. No question on that. If it were based upon airflow you would get different rev limits based upon altitude and free-breathing mods.

On pre-99 cars the RPM is sensed by the Cam Angle Sensor. 96/97 cars have a crank sensor, but it's only OBD2 misfire detection. It doesn't have anything to do with the rev limit, tach signal, etc.

By the way, I don't know that upping the processor clock speed will accomplish what you want. It would seem to me that the potential downside is much greater if the ECU does rely purely on that clock speed to time events. If that were the case, I would imagine that changing the overall speed would alter fuel, timing, idle, etc. That can't be good.
-Chuck


i read the whole thread, and without access to dyno time and professional tuning, this is a potentially dangerous mod. and all of these people that did it were with the b6/bp - who knows if itll even work with the b8

[tritonheat1]

What your problem is, that you have A DX which= to No RPM Tachometer, so yes u r hitting the Rev limiter! And to answer your other question at high speed's? What speed's are you doing when this occurs, b/c the DX top's out at 108-110mph seeing you have a Automatic! I had a 94 LX 5speed had quite a few mod's and it had no problem getting to 135mph. :)

[Gen1GT]

Are you kidding me? I'm not just some chump who decided to pop in on a random thread and make some point.

silver03p5: Let me say this again. I want you to listen, and listen tight. YOU NEVER, EVER, EVER, EVER want back pressure. When? Never. Why? Because it chokes off power. What do we want? Velocity.

You want as much velocity as possible, with as LITTLE backpressure as possible. This is sometimes a dichotomy, because when you make exhaust system piping small enough to aid in VELOCITY, a SIDE EFFECT is backpressure.

And if he's in a racing car, he doesn't need velocity, because he's constantly at WOT. If he's running around a track at 6500RPM plus, low RPM scavaging is not his concern, and the lowest restriction exhaust possible will be to his benefit.


and BTW, upper the clock speed WILL raise the rev limit, and with no side effect. It's been done many times. Do you really think you know more than all the genuinely well-informed car guys over at miata.net? The very same guys who are electronic engineers and who racing automobiles?

In the mean time, stop spreading mind viruses and misinforming everyone. If you don't know what you're talking about, say nothing, instead of making it up.

[Liquid_Ag]

wth man, look on the fucking last page of that thread you posted. changing the crystal bumped the dudes timing to 26 degrees, and changed the injector pulse. the man who went to the dyno is talking about having to change his timing etc and having to add more fuel. plus you have the added danger of valve float and serious engine damage if you change the limit to high. and with his car, with unknown mods, we know he doesnt have a header, and he just has the exhaust cut off at the manifold so he has no back pressure atm, i.e. no scavenging, i.e. no velocity, i.e. he is losing power. he needs enough back pressure to create proper velocity.

[anarchistchiken]

Dude Rob dont argue with him. The dude clearly knows wht he's talking about. I mean come on, he runs a 15.5!! Not many people can claim those kind of numbers from an NA car!

[Liquid_Ag]

i will. i will show better than that after i have my tranny mount fixed

[TampaSport20]

gen1gt is right...and you do NOT need backpressure to maintain velocity

....backpressure is a nasty side effect of the pipe size being small enough to maintain optimum flow without losing velocity

[Liquid_Ag]

http://www.miata.net/garage/KnowYourCar/S4_Back.html

So when taken to its extremes we can see that a too narrow pipe will create backpressure (restrictions to positive flow) problems and a too wide pipe will cause a very slow flow with no backpressure...This situation will arise when the pipe is wide enough so that there is the least level of positive backpressure possible whilst achieving the highest exhaust gas velocity.

omghi2u what ive been saying

[TampaSport20]

http://www.miata.net/garage/KnowYourCar/S4_Back.html

So when taken to its extremes we can see that a too narrow pipe will create backpressure (restrictions to positive flow) problems and a too wide pipe will cause a very slow flow with no backpressure...This situation will arise when the pipe is wide enough so that there is the least level of positive backpressure possible whilst achieving the highest exhaust gas velocity.

omghi2u what ive been saying





So instead of going for the widest pipe possible we should be looking for the combination of the narrowest pipe that produces the least backpressure possible. In this scenario we achieve the least restriction on positive flow and the highest gas travel speed.


I can copy and paste too....

here's another good read...

http://www.genmay.com/showthread.php?p=8442876

[Liquid_Ag]

The larger the exhaust diameter, the slower the exhaust gasses end up going for a given amount of airflow. Now the ***** of all this tech is that one exhaust size will not work over a large RPM range, so we are left with trying to find the best compromise in sizing for good low RPM velocity without hindering higher RPM flow ability. It doesn't take a rocket scientist to understand that an engine flows a whole lot more air at 6000 RPM than at 1000 RPM, and so it also makes sense that one single pipe diameter isn't going to acheive optiaml gas velocity and pressure at both these RPM points, given the need to flow such varying volumes.

again, this validates what im saying, pulled directly from your link. what im saying is, you want the largest piping with the most exhaust velocity

[TampaSport20]

again, this validates what im saying, pulled directly from your link. what im saying is, you want the largest piping with the most exhaust velocity

exactly, but you WANT AS LITTLE BACKPRESSURE POSSIBLE, you do NOT need backpressure


no backpressure = no velocity

The whole point Gen1gt was trying to point out is THAT is incorrect

[anarchistchiken]

Back pressure is not something you want a lot of, but if the objective was simply to have the largest possible pipes, then professional racing teams wouldn't spend tens of thousands of dollars developing exhaust systems to optimize flow and pressure.

[Liquid_Ag]

im sorry, what i meant was no back pressure = insufficent velocity to maintain or increase power in most cars

[TampaSport20]

im sorry, what i meant was no back pressure = insufficent velocity to maintain or increase power

I'm afraid that is still too all inclusive a statement to be correct....I know what you mean, but the fact is backpressure doesnt come into the equation.....you want optimal velocity with maximum flow, period...backpressure is simply a side effect

by definition, backpressure is a restriction in flow...and as I previousy stated you want MAXIMUM flow, without losing velocity ... Is there a strong possibility that you will start losing velocity before you eliminate all back pressure, especially with most standard pipe sizes, YES !! At some point you end up having to make a sacrifice. Backpressure is and old school idea instilled by muscle car guys....it dies hard

When I took my MX-6 GT to an exhaust shop to get 3" cat back installed, the owner didnt want to do it...He was trying to tell me a 4 cylinder shouldnt be using 3", I will just lose power....The younger guy working there tried telling him it's a turbo, and he just didnt get it....finally he agreed to do it, and he would guarantee the work, but not the performance of the vehicle...I just laughed and said ok

[Gen1GT]

Ok, I think it's safe to say we have the backpressure issue out of the way. Backpressure is a side-effect of velocity in most circumstances.

In regards to the raised rev limit: Since his SOHC B8 has a distributor, initial advance can be adjusted to compensate for any additional timing the ECU may add. My point with this information is that THERE IS a cheap and easy way to do it. The guy's doing circle track for god's sake, drivability isn't his number one priority.

[Liquid_Ag]

true that, i just dont know his technical ability/if he as access to see what settings were changed/if hes running the car safely

[slayer4u]

Alright let me lay a few things out that I noticed.

Back pressure is not a myth and is common knowledge among ANY profesional mechanic. I doubt most people go to mecanic skool so they assume it's a myth. It's a simple law of physics. take a garden hose for instance. I larger hose will alow more flow but what it gains in flow it loses in the force in which it is expelled. A smaller hose flows less but expells water with a greater force than a larger one at the same pressure. The reason for this is backpressure. you are trying to force the same amout of air through a smaller hole.(kind of like sticking a square peg in a round hole if you catch my drift) The amout of backpressure is diferant in all cars because diverant engines move air faster or slower than others. The key is to find a combination of intake flow and exaust flow to alow the optimum power throughout the RPM range. The best combination without extensive modification.is a stock setup. Automotive designers base there design on the optimum performance while stayng within the restrictions of production costs. Any modification to the factory setings can go to loss or gain. We must also remember that power is both a combination of HP and torque. The optimum power is gained buy an engine producing equal amounts of torque and HP throughout the RPM range. THis is next to imposiible without extencive modification and extensive knowledge of what the fuck one is doing.
I mus also mention a forced induction engine is a totaly differant story. on a turbo engine you want absolutely no backpressure if that is posible. The more flow the faster the turbo spools up.



ALL revlimiters that came on the B series engines were set at 6400 RPMs. Do not rely on a stock tachometer to find this as the stock tach is VERY inaccurate. The ECU used diferant means to limit teh enginse RPMs . teh BP B8, B6e, B6ME,B6DE,B6ZE and B3 were limited by means of a timing cut. the same found in most after market rev limiters. The B6, B6T, and all carberated B series used a fuel cut.

[slayer4u]

at stand still in park, it idles ok, but when I stand on the gas, and once it reaches top rpm's, it does the same thing, kind of like a skip rather than sputtering. probably because more gas is needed while driving than reving it up. I'm at a loss, and this is all I can think of.


What you are describing is exactly what a funtioning rev limiter is suposed to do. These are not reving engines. You want a good reving engine then buy a honda.

[Liquid_Ag]

mine goes to 7200 on the dyno O.o

[slayer4u]

mine goes to 7200 on the dyno O.o
yours is probably caliberated wrong that happens somtimes at the factory.

[anarchistchiken]

Was the 1.5 liter engine a b-series?

[Liquid_Ag]

josh dyno'd up to 7200 iirc

[MazKid]

Was the 1.5 liter engine a b-series?

Depends, in the US 1995-1998 Protege, the 1.5L was the Z5 engine.

Other countries got 1.5L 1990-1994 "Proteges"(323, Familia) and they used the B5 engine.

[Gen1GT]

Alright let me lay a few things out that I noticed.

Back pressure is not a myth and is common knowledge among ANY profesional mechanic. I doubt most people go to mecanic skool so they assume it's a myth. It's a simple law of physics. take a garden hose for instance. I larger hose will alow more flow but what it gains in flow it loses in the force in which it is expelled. A smaller hose flows less but expells water with a greater force than a larger one at the same pressure. The reason for this is backpressure. you are trying to force the same amout of air through a smaller hole.(kind of like sticking a square peg in a round hole if you catch my drift) The amout of backpressure is diferant in all cars because diverant engines move air faster or slower than others. The key is to find a combination of intake flow and exaust flow to alow the optimum power throughout the RPM range. The best combination without extensive modification.is a stock setup. Automotive designers base there design on the optimum performance while stayng within the restrictions of production costs. Any modification to the factory setings can go to loss or gain. We must also remember that power is both a combination of HP and torque. The optimum power is gained buy an engine producing equal amounts of torque and HP throughout the RPM range. THis is next to imposiible without extencive modification and extensive knowledge of what the fuck one is doing.
I mus also mention a forced induction engine is a totaly differant story. on a turbo engine you want absolutely no backpressure if that is posible. The more flow the faster the turbo spools up.



ALL revlimiters that came on the B series engines were set at 6400 RPMs. Do not rely on a stock tachometer to find this as the stock tach is VERY inaccurate. The ECU used diferant means to limit teh enginse RPMs . teh BP B8, B6e, B6ME,B6DE,B6ZE and B3 were limited by means of a timing cut. the same found in most after market rev limiters. The B6, B6T, and all carberated B series used a fuel cut.

You are wrong on TWO points. First, and still most obvious, YOU DO NOT NEED BACKPRESSURE!! Holy shit, I'm getting tired of saying it. Any 'professional mechanic' can kiss my hairy ass if they believe this. Your hose theory is so flawed, it's not even funny. First of all, water is not elastic like air. But when you make a smaller orifice for the water to exit, the same amount of water has to exit at the same rate(this is a generalization assuming the water is being pushed by a positive displacement pump), so it has to move faster.

Once again, it is VELOCITY that you aim for, not friggen backpressure. Piping must be small enough to aid in velocity, and it has nothing to do with the need for backpressure. Backpressure is a SIDE EFFECT of smaller piping. You want the most velocity at all RPM as possible, but with the least amount of backpressure. This is impossible to do of course, since there has to be a compromise somewhere.

Your second error is that all B-series engines were 'set' to 6400 RPM. BP-ZE Proteges and Miatas has a 7000RPM redline with a 7300RPM fuel cut. My car has hit 7400RPM on the dyno, and I trust the Dynojet pickup more than the tack in my car, which showed 7600RPM on that run.

Please let the backpressure myth die...please

[TampaSport20]

Please let the backpressure myth die...please


(deadhorse (deadhorse (deadhorse (deadhorse

[slayer4u]

You are wrong on TWO points. First, and still most obvious, YOU DO NOT NEED BACKPRESSURE!! Holy shit, I'm getting tired of saying it. Any 'professional mechanic' can kiss my hairy ass if they believe this. Your hose theory is so flawed, it's not even funny. First of all, water is not elastic like air. But when you make a smaller orifice for the water to exit, the same amount of water has to exit at the same rate(this is a generalization assuming the water is being pushed by a positive displacement pump), so it has to move faster.

Once again, it is VELOCITY that you aim for, not friggen backpressure. Piping must be small enough to aid in velocity, and it has nothing to do with the need for backpressure. Backpressure is a SIDE EFFECT of smaller piping. You want the most velocity at all RPM as possible, but with the least amount of backpressure. This is impossible to do of course, since there has to be a compromise somewhere.

Your second error is that all B-series engines were 'set' to 6400 RPM. BP-ZE Proteges and Miatas has a 7000RPM redline with a 7300RPM fuel cut. My car has hit 7400RPM on the dyno, and I trust the Dynojet pickup more than the tack in my car, which showed 7600RPM on that run.

Please let the backpressure myth die...please

Do yourself a fucking favor and take a physics class before you go throwing around words like side effects. Ther are no "side effects". Actions and reactions. You would not have any fucking velosity of anything without force behind it. Backpressure causes an equal and opisite reaction of forward pressure. (if any of this is confusing you please let me know)


You are however correct about the ZE engines. The ZE were performance engines and were set higher than others. however You could rev any Bseries that high as long as the stock rev limiter was disabled.


And on a last note. DO NOT RED LINE UNDER SQUARE MOTORS> IT MAY BE TRILLING FOR THE FIRST FEW HUNDRED MILES BUT YOU WILL NOT BE HAPPY WITH THE END RESULT AND NEITHER WILL YOUR WALLET!!!!!!!!!!!!!!!!!!!1111111111ELEVENTY


That being said (or rather screamed at the top of my lungs for which my parents were not pleased.) The factory rev limiter is completely useless as you are already doing serious damage to your engine at redline. btw Redline buy automotive definition is the point at witch rour engine will not rev any higher. Usually you wil not have a properly funtioning engine when you reach that point. The little red line on your tachometer is just a way of saying your engine is about ready to give tou the ass fucking of a lifetime.

You want a goot reving motor go with an over squar motor such as honda. Wankels are a fine choice as well. you could redline one all day long. they are not however the most relyable chois so honda has them beat on that point.

[Liquid_Ag]

no more