And the original poster probably doesn't have the car anymore. This was all from
6 years ago.

I think CharlieBrownRacing is a troll of some kind. Stirred us all up real, he did.

 

For the record: Cats do create back pressure and reduce HP. Replace them with a race pipe if you're cheap or better a full RB system if you can afford it.

The shutter valve, however, has nothing to do with performance. It's just there to reduce the amount of unburnt fuel being dumped in the atmosphere. Which is probably a very good idea, but that said, I disabled mine after spending way to much time trying to get it to work.

Now, to call that electronic logicon that functions as the rat's brain a computer? Well I never really thought about it that way. Semantics, I suppose.

But Sam, I agree with you completely on one point: I don't have a clue how all that stuff works, including the rat's brain.

All I know is that when I took the rat's nest one summer, I got no improvement in power and a big loss in performance in the form of much lower gas mileage (5-6 mpg less) and a very squirrelly throttle response. So I put it back in and immediately got back my old GSL responsiveness, performance and just plain fun.

What more do you need to know?

 

Then we all agree, I'm working on the other problem in another thread, I believe the coast/shutter valve removal is what results in loss of mpg...

 

23.239 KPH faster.

 

"I believe the coast/shutter valve removal is what results in loss of mpg... "

I don't think that could be the case, since I didn't notice any change in fuel mileage when I disabled mine.

I know it sounds like that, in principle at least, there should be a loss in mpg when you disable the shutter valve, because it stops gas from getting into the rear rotor on deaccelertation.

But I think the actual amount of fuel that gets sucked into that rear rotor when you are off the gas is probably not very much (if, of course, the rest of your rat's nest is working properly).

However just a little raw gas pumped into the exhaust could make a big difference with pollution standards.

I mean, think about it. You are pumping pure gas into the atmosphere. Even a little of that stuff hurts with Global Warming.

Hmmmmmm...... I think I'll put a shutter valve in the White One II project, thanks for bringing this to my attention.

 

The 1984/1985 have 3 converter-esque devices. I don't claim to know their individual functions, but if you look at the parts fiche for a 1984 or 1985 they have Pre Converter #1, Pre Converter #2, and finally the Monolith Converter. They are in section 4000A-1

 

What else can the loss of mpg with the rats nest removal be attributed to? Mazda claims it helps by 20% and in 1981 when it was introduced MPG did rise significantly... The only other thing I can see that might help is that in 81 mazda positioned the spark plug closer to the combustion chamber... but even so, Why do we lose mpg when emissions components are removed?

 

Because the first thing we do after clearing out the rat's nest is throw on a Sterling carb, freeflowing exhaust, and run the hell out of them...

 

When I did it on my first RX7, it was hard to start when cold, and I lost 3-4 mpg, that one was a beat to hell 84 gsl... Sold it with 96k on it, Now I have an 85 gs(less features, but less to go wrong...but it looks like new) with 80k on the odo and want good mpg, good performance, and good cold starts... I beleive the cold starting issues have to do with the fact that the nest removal has vacuum advance running to manifold air cause a lean at idle which does not matter when warm, but when cold caused it to stall... The mpg I think I can blame on the shutter valve... Thee freeflowing exhaust as well as the other mods (efan, direct fire ignition) did seem to increase performance aswell as mpg and made it about the same as with a rats nest... Removing the richer valve should also help with mpg since it richens the mixture after deceling to help control cat temps...

 

The 79-80 rats nest is different from the later cars but when I removed all that from my 79 there was no drop in fuel mileage. I still get on average 24-25mpg out of the old 12a even if I dont keep my right foot real light. The 79 does have a richer valve to my knowledge that keeps thermal reactor temps up, similar to the later cars, but has a couple fewer controls otherwise and no shutter valve.

 

I suspect the real reason mpg went up in 81 was because they implemented a much
better ignition solution than the initial electronic ignition that came on the 80s. Also
they went to catyltic converters which operate more efficiently than the old thermal
reactor (which requried a rich mixture to keep it from disintegrating). The combine
mpg saving from both those changes would be significant I think.

 

You were responding in a 5-year-old question posted by a member from Australia with 8 posts total, and whose last activity on-site dates from 2007.

Your response, however, did not specify that you were responding only to the initial poster (five years too late to do him any good) with regard to his model year - - you made blanket statements and you specified only "emissions stuff in a first gen rx7". Some of which statements are true, some are only true for specific years/models you did not mention, and some of which are not true.

Example of true: removing cats from cars that have them will increase exhaust flow & reduce back pressure, which up to a point is generally good for performance. It is also illegal some places.

Example of sometimes-true: "most of the emissions stuff on a first gen rx7 is for those three cats." This is opinion at best, and depends upon the very 'semantics' that you disparaged any point of arguing about in your reply to me. "Most of" by what measure? Weight? Parts Count? Complexity?

Depending on year and model, zero percent of the emcon parts serve the cats - - as there are no cats.

Example of not true: "Many remove or disable the coast/shutter valve only to be disappointed with the loss of mpg."

"Many" are disappointed? Really? Who? How many? What is your source for this statement? Clearly NOT the "Mazda service manuals" you later said your statements are based on - - Mazda FSMs never discuss disabling emissions control equipment.

This statement cannot be considered 'true' until you provide some sort of support for your opinion.

But then, you went on to claim "truth" for your insult against Ray. So maybe assertions of 'truth' on your part need to be taken with a grain of salt.

It works the other way around, friend... you need to be right, or smart, or both, to earn reputation.

Leastwise, a positive one.

What 'era' is it you claim to come from, exactly? Might shock you to know which 'era' some of the members here come from.

Don't make the mistake of assuming every member here fits some age, education, or other template you may have in your head... this is a surprisingly diverse group.

The ECU in most first gens is no more a computer than is a lamp dimmer; they are dedicated analog control devices: they are not general-purpose devices, cannot be reprogrammed without modifying their circuitry, and they do not operate arithmetically.

According to Korzybski, there is little else worth arguing about, because without agreement over meaning of terms, there is no communication.

When you choose to make assertions of truth, you are arguing semantics whether you want to or not.

But you didn't "question," did you? You chose to insult the man instead, disparaging both his knowledge and his courage, without knowing the first thing about him or his level of experience or knowledge, or of the community's generally high opinion of him.

Now, you're attempting to argue your way out from under that rather obvious blunder, rather than simply manning up and admitting that you were out of line & shot your mouth off without thinking.

Embarrassing.

I'm glad to see that you later amended your "...many have reported..." 'statement' about the shutter valve to say instead "I believe...", and then later revised it further to actually questioning your assumption.

That's a positive trend.


End of rant.

 

I've never owned a car with a thermal reator... Anyhow... I'll work on said Ideas and report my findings...

 

Early RX7s had Thermal reactors instead of headers...

You should see the look on the autoparts store guy's faces when you ask about a thermal reactor!!!

 

So DD, I take it from your very elegantly composed rant that we have concluded once and for all and forever more that tearing out your rat's nest will do nothing to make your RX-7 go faster, right?

 

Yet another rats nest removal war going on here. I have seen no improvement in performance since removing mine, and gas mileage hasn't necessarily gone down either. We will see when I clean her off and reinstall her

 

Full removal of the emissions results in a nearly unbelievable reduction in weight. Any reduction in weight will result in a performance increase. I do not believe that any supposed downside to the removal can overcome the advantage of sheer weight reduction.

 

How much does the whole thing way. 50 pounds? My pump is (PO did this, not me) disconnected, but I doubt he did it intentionally and I would guess the belt just broke. Trying to decide if I should remove the pump and do a dual alt pulley, or tinker with it till it's back in working condition. If I removed the pump entirely, I would not be reworking exhaust, not enough cash at this point. I am under the impression that no pump/not running pump and old exhaust system (83 gsl) is bad for the exhaust components. Am I mistaken in this regard?

 

If you include the stock exhaust manifold, it's a lot more than 50 Lbs. I would guess it is over 100. I think Glazedham weighed everything when he stripped his car, so he might know the exact weight.

If your car has a stock cat, then you need the air pump to keep from melting it.

 

Yes of course removing emissions related stuff from the exhaust side of the engine does give a big boost in power and large reduction in weight, as Kentetsu suggests.

This certainly helps quite a bit with performance, including more power and better gas mileage. So much so that I would argue that a well tuned engine and efficient free flowing exhaust system actually can reduce emissions over a typical half clogged cat system.

On the other hand, the rat's nest consists of just those brightly colored solenoids that sit on top of the engine and their associated plumbing and wires. The rat's nest doesn't help to remove emissions per se, as the stock exhaust component are designed to do.

Instead it works with the Nikki to help it live up to it's full potential to avoid the production of emissions in the first place.

Keep the rat's, get rid of the dogs and cats.

 

Let me put it this way, Ray...

Based on personal experience and my understanding of the systems on the SA, removal of the Rat's Nest alone does not provide any benefit that would "make your RX-7 go faster." In fact, removing it without making other compensating modifications would make an SA pretty much not run at all!

Hopefully, I can avoid being accused of arguing semantics (wink) but some definition of terms might be in order in this thread, including;

"Rat's nest" versus "emissions system". Not the same thing at all.

Removing the rat's nest alone only saves about 2 pounds of weight, and disables several systems that are beneficial. Removing it requires that alternate provisions have to be made for crankcase ventilation, bowl ventilation, tank ventilation, & vacuum advance - - all of which plumb through the rat's nest. Loss of the vacuum control and coasting valves requires further mods & adjustments to compensate.

If you lump the Vacuum Switch in with the rat's nest (it mounts on the fire wall rather than the block, but it's connected to the rat's nest) then removing it forces you to make some mods to systems controlled by the ECU, because it is a primary input to the ECU.

Removing the Exhaust Emission Control system, on the other hand, including the stock Manifold/Thermal Reactor, Cats/Heat Exchanger, Air Pump ACV, EGR, and associated tubing, saves a tremendous amount of weight as Kentetsu pointed out, as well as recovering lost HP used to run the pump, and the significant efficiency loss that the restrictive stock exhaust imposes.

But you can remove the exhaust EmCon without having to sacrifice the rat's nest. Very little of the actual rat's nest functions have anything to do with the exhaust emcon, with the notable exception of the EGR control solenoid and some peripheral effects of the vacuum control valve.

"Faster." This term without a referent is meaningless. Are we talking better acceleration, higher top end, faster slalom times, or what?

"Performance." Same problem. Could be talking about torque, horsepower, fuel efficiency, power/weight ratio...