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Old 05-21-2011, 02:17 PM
Ted Johnson Ted Johnson is offline
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Default Single Inlet Restrictors/ Rev limiters

Our dog ring transmission thread is getting muddied by engine discussions mixed in. I thought I would bring the engine discussion to a new thread.

Kyle has brought this idea of a "single inlet air restrictor" to the table as used in prod and GT classes..

http://www.raetech.com/Restrictors/R...r_Function.php

Our current engines have good parts in them and the build sheets are a good compromise on availability and parity with our edlebrock heads. I would not want to look at a rewrite of our engine rules as they seem fine in my opinion.

It seems like the best ideas to help keep our transmissions alive are 6500 rpms and lowered torque/ hp numbers.

In my opinion, a rev limiter at 6500 rpm with a properly designed SIR would help our situation to help our engines and transmissions last for a reasonable amount of time.

Obviously, more research needs to be done, but ideas I think warrant a closer look.

Thoughts?
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Old 05-21-2011, 02:30 PM
Walther
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Since I am still occasionally wrenching on a few AS cars (not mine), my thoughts are; How does one adapt a SIR to a 4776 carb body that is slightly over 5"? It looks like it is designed for throttle bodies on fuel injected cars.

I honestly believe these types of ideas will tighten the fields and increase participation. However, there are a few ways to defeat the SIR. Most sanctioning bodies have a rule that "all air entering the engine must pass through the carb". To keep everybody honest, there would have to be a way to police the SIR's to ensure air is not entering the engine from other areas.

Past that, I too think this subject is worth further discussion.
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Old 05-21-2011, 04:05 PM
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DBailey DBailey is offline
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I think the carb was supposed to be our inlet restrictor and as long as the main body and lower plate stay "as cast" it should do it's job. The Rev limit
plan is very do-able and would accomplish the goal at a very low cost, and is relatively easy to tech. Most of us are already using an MSD box. (mine has a 7K chip) and the Limited prep cars have them built into the ECU.
Other series' use rev limits and weight to equalize cars in a class and it seems
to work well.

Dean
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Old 05-21-2011, 05:34 PM
KW78
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Ted - Probably a good idea to start this thread.

I want to stress I am just brainstorming here. I don't know enough to be for or against this, or even if it is a viable suggestion to consider. But, if reliability problems are cropping up from too much HP and RPM, and participation problems are cropping up from too much HP and RPM, and new AS efforts are discouraged by too much HP and RPM, and Limited Prep Crossovers are discouraged by too much HP and RPM, then I thought about the restictor and rev limiter as a multi facet possible solution.

My experience with them is limited to helping others in my region with a few of their race cars.

Walther, the issues you bring up and many others in fact, have been tackled by the classes that have used them for awhile, so one merit of this idea is it is not re-inventing the wheel for the purposes of a club racing application.

Dean - I don't think our current carbs are the limit at all, as the rumors of 8600 rpm and high 4 to low 5 hp numbers are out there with the current carb. In fact, a 390 carb still can deliver 600+ hp in a nascar application, so we aren't using all of our carb.

It was believed by many the edelbrock flow numbers would be the limit.

In fact, I would hope that the restrictor would not slow down the average of the top 5 lets say.

Many have invested in a nice piece that would race reliably at 7000-7500. I would advocate a RPM limit in that range. Further, I would advocate a restrictor that is invisible to say Wheel's motor or Chuck's. The first step up from the iron heads has not been a problem, its just seems that the newest horizons are.

Anyway, to answer Walther - In the other classes the SIR feeds and airbox, and the carbs (and their float boal vents/emulsion tubes) are exposed to or even completely housed in the airbox. I believe that the tech procedure as it drives into impound is to hold the car at 2000 rpm and put a rubber ball in the SIR as a plug and the car has to die within 20 seconds. The airbox and tubing has to hold up to that, so that seems like a solid idea.

There may be complex ways to cheat that, but that is true with any of our rules.

All of our cars have the same holley carb and the same 14x3 aircleaner that fits under the hood and has the holley air bleeds and bowl vents seeing filtered air. So, I think it would be a natural to spec the airbox as that 14x3 round housing, with hard sides and a "snorkel" heading for a headlight, with the SIR at or near the headlight. Put a smaller around filter like a 12", in the air box behind the strip of aluminum making the filter housing hard sided.

Developing a true airbox like these side draft GT cars for example is an added complexity and expense that I don't think we need to mess with, so I would suggest a simple spec airbox.

To me, there is one critical key about this idea would have to prove true with a bank of good evidence. That is, that the SIR is really an absolute limit (Vs. a relative limit), and it is invisible to the motor until that limit is reached. This is key.

Another key is that we don't change the engine build to allow messing around with high compression or low compression with porting etc etc etc... Just make this is nearly as simple as an electronic rev limit.

If an SIR doesn't really work this way, then I wouldn't be for it.

Anyway, curious about the discussion on it.

Kyle
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Old 05-21-2011, 05:41 PM
jimwheeler jimwheeler is offline
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Carb, intake manifold, air cleaner size, cam lift, valve size and no cold air induction, all act the same way an SIR would, to limit the power. The SIRs, in most cases, are used to equalize cars that all have completely different engine types and specifications.
NASCAR gets more hp with a little carb because they are not limited on all of the things that are limited on our cars, so NASCAR numbers are not important to our class.

wheel
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Old 05-21-2011, 06:09 PM
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DBailey DBailey is offline
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Kyle--I see where your coming from and agree more can be gotten from these carbs, but to get more hp from the fixed size of the throttle butterflies you need to increase the velocity of the airflow pulled through the carb. This is where engine RPM comes in and why some are turning 8,000+ rpm--spin the pump faster--move more air and fuel. a Rev limiter would have all the "pumps"
losing efficiency at the same (or near same point). The drivers would then have to make up for the fact that at a point on the straight they will run out of revs and make up for this in corner speed. We did use Rev limiters in 4cycle karting with great sucess--also made for some great racing. The SIR's are great for the new injected engines and would be perfect for the new crop of pony cars to come into the class.

Dean
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Old 05-21-2011, 06:27 PM
Walther
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I read the links about SIR's and it seemed intriguing.

My only "experience" in this particular arena was when circle trackers were facing similar obstacles 30+ years ago, and "limited" late models were born. 500 CFM 2-barrels were mandated and it worked to slow the cars down..for a while. But eventually intake manifolds were developed for those carbs and the HP numbers began to climb again. I dyno'd one of my 351's years and years ago, and it made nearly 450 HP at the flywheel. You can go on racingjunk.com and find "limited" engines claiming 500+ today. Anyway....

I understand nobody in particular is advocating SIR's, spec airboxes, or rev lmiters (yet), but I still think the topic is worthy of further discussion. I think it would be a HUGE step towards closing the gap between regional and national level AS cars, as others have stated. Realistically, I could assemble an engine myself that could compete at a national level if there was something that would could limit the HP. In other words, if an SIR limited the engine to 400 at the flywheel, I am confident I could build one that would last for under (say) $7000. I feel certain there are others that could as well.

Seriously, without delving into another of my long diatribes, I had no desire to load up everything (including a spare engines/trannys I didn't have) to make the trek to Wisconsin just to be a back marker. I knew what it would take to have a chance of running up front, but chose not to spend that kind of money. That's why I never bothered running my AS at a National. But that's just me.

If (BIG "IF") something like this were to pass, I strongly feel the Andys, Jeffs, Jims, and Toms of the class would still be at the front, but the Walthers of the class could stay within reach, and to me that would be worth the trip.

My .02
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Old 05-21-2011, 07:04 PM
Ken Felice Ken Felice is offline
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Default Hp? Sir

As you know our shop builds a lot of different types and kinds of eng.We are very happy to be able to build AS engines for a lot of you racers.I am concerned with some of the TRQ&HP&RPMs that people are posting.We use a Supper Flow 902,our numbers are not inflated or pumped.I do not want to start ping match but some of these figures are high, our dyno may be a little on the conservative side but I do know it is very occur. As for Chassis dynos they are for tuning or comparison not an accurate HP figure.
We seem to be our own worst enemies when it comes to changes.I may make a few people angry even some of our own engine customers but lets not change for a while,you have an RPM limited the trans.if I hear you all.If you spin it you will have to pay the price,why do you want to change trans. then install a rule to limit RPM.
I am not good at typing or expressing my self but I hope that this made some sense.Please NO ONE take this as an insult or that I am saying any thing against any one.This is only my perception


Ken Felice
PERSONAL OPINION ONLY NOT THE BUSINESSES!!!
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  #9  
Old 05-21-2011, 07:15 PM
KW78
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Hey Dean,

From what I've seen on rev limiters only controlled classes is that you re-focus the engine build on Torque. The example that the GT and prod classes have lived thru the use of the SIR is to have a high spinning twin cam 1.6, and a torque monster 2.4L and a ridiculously high spinning torqueless rotary all competing really well with each other.

And, while our class doesn't have that much latitude, you can field from 260 to 350 cubes. Curran was quick with his 350 thru the same carb that gets a 308 to 8000+. I would think a rev limit would affect one of them much more than the other.

But, it was HP and RPM that the trans guys were talking about. Maybe a rev limiter only would work...???

Quote:
Originally Posted by Wheel
Carb, intake manifold, air cleaner size, cam lift, valve size and no cold air induction, all act the same way an SIR would, to limit the power.
True, we don't have unlimited power here. But, that limit seems to be up there to the point of needing more investment in other places. As we go faster the widget that needs the upgrades next seems to be a moving target...

And, as a sidebar, the limit from this collection of parts seems to have a really wide window. Wider than the iron heads?? If an SIR can narrow that window for a rotary vs. a 14:1 2.4 litre, then would it work here? Or is it bad to have a narrow window?

Quote:
Originally Posted by Wheel
NASCAR gets more hp with a little carb because they are not limited on all of the things that are limited on our cars, so NASCAR numbers are not important to our class.
Yeah- but the concept is! So, if (within what we can do) you want to get that lifter that lets you have a steeper ramp, and that 15th manifold port job that finds a few more CFM, or that lightest rod that lets you need a few more CFM from a few more RPM, then the carb will support it. That was my point.

Quote:
Originally Posted by Walther
I read the links about SIR's and it seemed intriguing.

My only "experience" in this particular arena was when circle trackers were facing similar obstacles 30+ years ago, and "limited" late models were born. 500 CFM 2-barrels were mandated and it worked to slow the cars down..for a while. But eventually intake manifolds were developed for those carbs and the HP numbers began to climb again.
I agree. Technology marches on. The interesting thing to me about the Prod and GT classes is the SIR seems to be the newest better mousetrap on this concept, and at least in the GT club racing context, the SIR has the mix of race efforts still co-existing, or co-existing again maybe. We could learn from them how they are still increasing the envelope with this newest "limiter", but I've heard that it is running up and down the compression scale and playing with trick airboxes. I've also heard that moves the target around on a really small scale relatively, also.

Dunno, this is the aspect of it that I personally would want good evidence about before I would be on board.

Well, If I am going to make our first Double "Rational", I better get off the computer.

Good discussions

Kyle
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Old 05-21-2011, 07:16 PM
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DBailey DBailey is offline
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Ken, I have built Racing engines for the past 40 years and agree with you.
The rev limit idea could be more to make the class a bit more cost effective
and equalize the competition. Not to counter the gearbox improvement.

Dean
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