What carb?

lateapex911

lateapex911

Super Moderator
Ok, some of us RX-7 guys think we are underdogs in a major way in ITA. But the writing on the wall says we're here to stay.

PCAs may add weight to some front runners, but adding weight to ALL the frontrunners AND the new cars coming from ITS isn't very likely.

And while we might get a weight break, I doubt it could be enough. We can't get that much more out of them legally.

So, just a wild thought here...I notice all cars have alternate carbs listed. (for example, the Weber 32/36 DGV, etc.) My understanding is that the allowable carbs are rarely a better choice.

IF we were to be allowed an alternate carb, to even things up, what would be the right choice? Not too much, not too little.

(And this is just blue sky crazy talk, nothing more....)

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Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]
 
Jake, I don't know what carb would be a better choice than the stock carb. But what I've heard from numerous experienced IT7 campaigners is that the stock carb flows more than any of the currently allowed alternates. The only IT7 cars I've been up close and personal with had stock carbs. I'm probably not telling you anything you don't already know, though. :-)

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Doug "Lefty" Franklin
NutDriver Racing
 
***And while we might get a weight break, I doubt it could be enough. We can't get that much more out of them legally.***

Jake, maybe they will work around the word legally. As in whatever the rule says for 2005 is legal. Weight, clutch, flywheel, porting ?????????? Brainstorm & let's see who comes up with what ?

With the carb, it's my understanding that the blueprinted OEM carb will more than do the trick. How about at the other end. EXHAUST ??????? There are two main issues with breathing.

Have Fun
wink.gif

David
 
Within the rules as they are now, neither the Nikki 4bbl or the permitted exhaust systems are limiting the HP of the 12A. There are 12A's making lots more than ITA-level HP with a Nikki, so clearly the carb is capable of more. And if we are only talking about another 20HP being required, porting is going to allow much more than that.

If you spec the amount of porting that can be done you are going to have an expensive teardown bond, and very few people will ever get protested.

I'd prefer that they spec a minimum weight and not limit what can and cannot be removed so that weights that will allow the cars to be competitive can be met.

Limit the number of diagonals in a cage and the amount of ballast and get the car down to a spec weight of 2050 and they'll be fine.
biggrin.gif
 
well if they were to give us something porting is viewed as a pandora's box and i disagree that we can get much more weight out so back to jake's question, would a different optional carb help. what size holley or webber would be right for a unported 12a with the stock intake. does anyone know what kind of power increase we could expect.
dick patullo
ita rx7 ner
 
lemon used a 48 IDA on his pro7 car in cal clup to run in EP, I think he said it was a 20 HP increase. he won a couple too.
 
Daryl, help me out here. Let's say a Pro-7 car is 120/125 hp (IT motor correct)& then I bolt on a 48 IDA & whan-o I have a 17% hp increase.

????????
David
 
I've got to disagree. An IT level 12A is not being restricted by the stock Nikki. Throwing a bigger carb on it, alone, is not going to do anything to make more power.

The weight argument might be a mute point because I doubt they would ever allow us to remove any components we want to make weight. But I can speak from experiance, since I have raced 12A rx7's where there isn't a minimum weight spec'd. No fiberglass body panels and windshield still glass, the car weighed 1880#, less than 2100# with me and a full tank. And at that weight I could hang with/beat a very fast ITA legal CRXSi.



[This message has been edited by Quickshoe (edited June 19, 2004).]
 
Originally posted by Quickshoe:
I've got to disagree. An IT level 12A is not being restricted by the stock Nikki. Throwing a bigger carb on it, alone, is not going to do anything to make more power.

this suprises me. you would think that the stock carb was properly sized by mazda to work with the very restrictive stock exhaust manifold. with a more open exhaust flow I assume we are pumping more air. why is it that we would not benifit from a larger carb. how many cfm will the stock carb flow anyway.
dick
Click to expand...
 
Originally posted by dickita15:
how many cfm will the stock carb flow anyway?
Click to expand...

According to Yaw's site 325 cfm.

Added on edit.

..it requires between 1.5 and 1.6 CFM of air in a gasoline engine and 100% Volumetric Efficiency to produce 1 HP.

That would equate to a HP peak between 203 and 216. (The most that could be theroetically made with that carb on gasoline, naturally aspirated).

A 12A is roughly 72 CI or .0416 CFeet. Which means that a stock carb is only capable of completely filling that chamber 7812 times per minute. Anything over 7812RPMS and the carb can not completely fill that chamber, no matter how optimized everything else is.

In real life those chambers aren't anywhere near full at 7812 rpms or we would have somewhere north of 200HP. Generally speaking the peak Volumetric Efficiency occurs at the peak torque rpm, from that point on we are only trying to get the rpms to rise faster than the torque falls.



[This message has been edited by Quickshoe (edited June 22, 2004).]
 
Originally posted by Quickshoe:
Perhaps the 20HP addition with a 48 Weber is because of a different intake manifold?
Click to expand...

A Bingo there brother Daryl, its the combo although Dave L could pinpoint it to the number as to which he thinks added more. I know he tuned the weber to his pro7 motor on his dyno so if he says 20 he means something very close to that. Did I mention he won races with that setup with slicks in the rear and toyo 185's up front.

a side note D is that the rotary recycles a quarter of its spent exhaust gas which allows that carb to more than keep up.



[This message has been edited by 7'sRracing (edited June 22, 2004).]
 
About the only "competition adjustment" that makes sense for the rx-7 is to allow alternate mazda transmissions and lower weight.
Like computers, the tranny gear ratios are difficult for tech to measure w/o tearing the thing down. Mazda has several tranny's that bolt right up to the rotary engine and have much better gearing. It would also mean we can stop wondering if competitors have illegal gears. (racing crashboxes will give themselves away with gear wine and gear change crunch).
The weight is also a no brainer. I've built 3 ITA rx-7's (79, 82, 84). All were under weight.
Allowing port matching by modifying the manifold only is a dubious option IMHO. Lots of work, questionable gains.
Tak
#29 ITA
SFR
 
I seem to recall that the old style RX3 12A had bigger ports didn't it? Maybe making those housings (if I am right) legal for the RX7 would work. But I don't think 120 rwhp is going to do it in ITA. I remember a dicussion here that indicated the CRX Si is capable of 120+ fwhp and the weight is like 150 less?
 
Like computers, the tranny gear ratios are difficult for tech to measure w/o tearing the thing down

Not always. Our Tech crew has developed a device, using a MyChron AIM3, that measures transmission gear ratios accurately enough to spot illegal gears easily. With the transmission still in the car. Takes about 15 minutes to do a car, including jacking it up.

[This message has been edited by pgipson (edited June 22, 2004).]
 
Originally posted by pgipson:
I seem to recall that the old style RX3 12A had bigger ports didn't it? Maybe making those housings (if I am right) legal for the RX7 would work. But I don't think 120 rwhp is going to do it in ITA. I remember a dicussion here that indicated the CRX Si is capable of 120+ fwhp and the weight is like 150 less?
Click to expand...


Well,you might want to sit down before you read this pgibson....CRXs are putting down closer to 130, (127 IIRC) and weigh 240 pounds less.

You can make your own handling comparisons....


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Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]
 
Originally posted by Tak:
The weight is also a no brainer. I've built 3 ITA rx-7's (79, 82, 84). All were under weight.

Tak
#29 ITA
SFR
Click to expand...

Tak, I too have found that I can get an RX-7 under weight...(others, though, have not) ....how much under do you think it can go legally?



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Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]
 
My car with 200 lbs of me in it is 20 lbs light so I have to add ballast. My car is a 1980 with heavy bumpers and a 3 row radiator (not aluminum). If I went on a diet I could get the car to 50 under and I don't know how much difference an aluminum radiator would make. I can't think of legal ways to reuce the weight much below where it is now.
#99 IT7
 
I'm currently driving an 84 chassis (Heavy, but free). I have NOT peeled the undercoating off. I still run all the stock heat shields. I still have a passenger seat, and a lot of components on the right side of the car that can be legally removed. And I have to carry 20 pounds of ballast. Mind you, that's on Hoosiers and Panasports. If I were to run other tires, I lose the ballast. My cage is 8 points, triangulated, double door bars both sides (not nascar). If I were anal, I'd add 3 more bars to the cage and it would be perfect. IMHO, the real weight savings on these cars comes from removing the stock gas tank and replacing it with a fuel cell. Oh, and I tip the scales at 170lbs. If pushed, I think I could get another 50-100 lbs out.

So to answer your question Jake, I think 2300 w/ driver is achievable (but difficult).

Tak
#29 ITA
SFR SCCA
 
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