jutny

advantages/disadvantages of both

basically looking at an IDA or DCOE... or their Dellorto Counterparts.

so, drop some knowledge.

also, post some pics of IDA/DCOE/DHLA setups if you can.

Logo

I always hear people claiming that the sidedrafts make better torque down low while the downdrafts make better peak horsepower. This may be true for the most part but I don't think it's due to the design of the carb itself. It has more to do with the fact that most of the sidedrafts utilize wrap around manifolds with long intake runners. In most cases long intake runners give better air velocity at low rpms while short runners flow more air in general.

Project84

Why does faster moving air increase torque? Once the air reaches the rotor, the rotor moves it from the intake port to the side of the housings where the compression takes place. The faster air doesn't speed up the rotor. Does the faster air fill up the rotor pocket faster? Thats the only way I can see it working. If the rotor opens the port for 1 second, faster air/fuel will fill up the space faster than slower moving air. Someone enlighten me.

racermike

Turbulence? How about the longer the runner, the larger the air mass in motion within the runner, which tends to stay in motion??

Project84

Understood. However, the opening at the end of the runner, whether the runner be a shorter downdraft, or a longer sidedraft, is the same. So reguardless of the carb and intake track length, the smaller mass has the same opening to pass through as the larger mass. If the masses are moving the same speed, then the size of the mass doesn't matter because at a given speed, only X amount of volume will fit through the intake port before the rotor closes it off. What accelerates the air mass as it passes through the intake manifold? The speed of the mass, not the size, seems to be the important variable. Thats why forced induction from a supercharger gives you more torque than a normal N/A intake. The mass is moving faster, forcing more into the rotor before the rotor closes the port.

REVHED

Velocity definately plays an important part whether it's down-draft or side-draft. But, I don't see why a longer intake tract would increase velocity provided the runner diameter is the same.

In fact, the reason longer runners increase low rpm horsepower is because of pressure wave tuning. Timing the pulse to arrive back at the intake port just before it closes maximises the pressure differential which improves chamber filling.

It's the same concept as exhaust tuning. Longer runners in effect delay the pulse to arrive back at the intake port at the correct time for a lower rpm while shorter runners tune for higher rpm. The only difference is, intake runners are a lot shorter than exhaust headers so it's usually tuned for the 3rd or 4th harmonic.

REVHED

Just on the subject of IDA vs DCOE etc. I've yet see any evidence of DCOE's making the same sort of power as an IDA on larger ported engines like bridge or PP (on stock or street-ported ported it probably won't make too much difference). Plus the fact that the IDA has been almost the sole carb used in serious road-racing Mazda's speaks for itself. But, I am slightly biased though.

REVHED

Other side...

onepointone

dude, i LOVE how clean your engine bay is.. there is almsot nothing in there...

jutny

what about dhla vs dcoe?

because of cost issues, an IDA seems to be out of the question because the carbs are ******* expensive.

IDAs do look cool as hell sitting there, but there's something cool all in itself about a sideways carb when all you've ever known is holley double pumpers and 750 q-jets.

Project84

very nice

What temprature paint did you use on the engine?

REVHED

Just regular engine enamel. It was almost two years ago so I can't remember which exactly... I think it was either VHT or Motospray.

jutny

well, i think i just bought a 48 dhla and rb intake for $300.

so yay

diabolical1

iTrader: (3)

congratulations! when you put it on and start to use it, keep me posted on your thoughts of it. i'm curious ...

jutny

yeah, only thing is i wont have a before and after, cause now that i'm getting this, i'm not even gonna bother getting the car to run with the Nikki, just take it off and wait for my new loot to get here. I've never driven this car, only worked on it... a lot.

hopefully by then i'll have my coolant system hooked up and can let the car run and possibly even drive it *gasp*

and i gotta get some ******* insurance too... bastard insurance company not responding to me, i hate that ****.

diabolical1

iTrader: (3)

yeah ... i hate them, too!

anyway, it's a shame you didn't get it running with the Nikki. i was just curious to see how another person new to Dell'Orto's feels about them compared to the Nikki. i bought mine brand new in 1994 and i never got a real chance to use it until last year when i got this car and put the 13B in it. it took me a while to get it dialed in this far ... and as good as it feels, i'm still not THAT impressed by it. i mean, i know i have some tuning left to do on the engine (hell, i still need to get an exhaust system - i have my header sitting here, waiting until i can afford to get the RB S/P system ) - but even knowing that the motor's not breathing as well as it should, i still don't expect my opinion of the Dell'Orto to change much.

i've given it a lot of thought, that the manifold shape SUCKS! then i saw my thoughts echoed on a website, where this guy changed to a Lake Cities Rotary manifold with his Dell'Orto, and he said that it's a totally different animal.

anyway, it doesn't matter. right now i just need the car for transport, not fun. i'll just wait 'til i get my life together and build my EFI system. actually, that was my initial interest in this thread because i'm trying to decide if it should be IDA-based or DCOE-based. so far, it looks like IDA is better (in no small part to Revhed's sinister, telepathic messages no doubt. )

jutny

well, way to make me feel better about my purchase

but anyway, i'm gonna get the exhaust with my next paycheck, and possibly a holley blue and regulator to go with the Dell'Orto, and then i should be making considerably more power than stock, and at least it will be running, and this is also my daily driving car (or it will be) and i just want it to be a little less anemic than 100hp stock allows it to be. What would be a power estimate for a properly dialed in 48 DHLA with a full racing beat exhaust and an upgraded fuel system?

it also makes life much easier with vacuum lines and all the leftover emissions **** on the nikki that i dont feel like deciphering. Eventually, i'll go turbo and efi on it, so i'm not too worried about the manifold. Do you have the 2 piece or the one piece manifold?

i'm also hoping that the dhla will be easier to adjust than the nikki, in terms of idle and things like that.

diabolical1

iTrader: (3)

LOL ... dude, i'm sorry. i totally didn't mean to cast doubt into your head. don't get me wrong, they are good carbies! it's just for my particular taste, i expected more from them. i think my biggest deal is that i'm used to a progressive/staged intake system ... like the Nikki (and it's probably the reason why i seem to be in the minority of people that love rotaries with Holley systems) ... but the Dell'Orto WILL give you a noticeable increase. it's just that to me, it feels a little understated. it doesn't scream! does that make sense?

all said an done, you should be able to clear 145 HP with it, and your upgraded fuel system and exhaust system. since you've never driven the Nikki, this probably won't mean a great deal, but the Dell'Orto definately has midrange punch to it. you may shift a lot, but with a Dell'Orto as a daily driver, it won't be because you HAVE to - it'll be only if you want to. to me, it seems to pull from as low as 2,000 RPM and it starts to feel a bit winded at 6,000 RPM. however, someone with a Dell'Orto in better tune can probably get good power to 7,000 RPM out of it. from what i've read, the manifold won't really let you make anything much over 7,000, though.

EDIT: and yes, i do think it's a lot easier to work on than the Nikki.

jutny

allright, all i want is a car that is very driveable, and VERY clear of the 100hp mark.

there will be NONE of my friends 94 civic dx HB beating me (102 hp, lighter car)... that certianly would not be acceptable.

diabolical1

iTrader: (3)

well, rest assured, you'll get a car that's very driveable and VERY capable of gang-raping stock Civics ... however, modified Civics are not cars that you should sleep on. chances are that you'll beat all but the most seriously modded Civics (like the heavy cams, Integra-swaps or forced fed ones) but don't get too cocky ...

I admit that I've gotten beat in the past because I drove a "real" sports car, and was challenged by something lesser ... don't let it happen to you. just do me a favor though, and think "safety" before you race.

racermike

Qualifier #1. I am NOT an engineer!! So I will try to remember how it was explained to me some years ago. More qualified people are invited to better educate me where neccesary!

Assume all other parameters are equal, size of openings, venturies, shape, and directions of flow. The only difference then is the length. If you have a certain flow at say 4k rpm, in a runner that is X long, you will have a certain "mass" of air moving within that length. Mass in motion tends to stay in motion. (some physics law about conservation of energy, I think) Mass times velocity = force. Now concider that the length is 2X, or twice as long. Average density (not concidering pressure waves or harmonics) being the same between the two examples, means there is now twice the mass, in motion. Because that mass in motion WANTS to stay in motion, you now have more "force" available at the end of the tube. (this by no means says that you get twice the air flow, only that you have more force to overcome the restriction) At the input to the engine, both the flow and the pressure would be plotted as a "sine wave" (~). As the "opening" appears, the "pressure" will begin to decrease (I know, we are really talking the inverse, and it is a "vacumn", but I'm speaking relativity) while the "flow" or volume will begin to increase. After the ~midpoint as the opening begins to "close", the flow will decrease and the "pressure" will increase, to the point that the next cycle would begin. During the time that the pressure is rising and flow is diminishing, the "mass" of air in the runner will WANT to stay in motion and thus expend its "force". Therefore, if there is more "mass", because the runner is larger (longer), there will be more "force", and contribute to an even higher "pressure". This higher pressure then, is what allows more of the mass through the opening in a shorter time.

Now for trubulence, although by itself it actually causes less flow (by increasing resistance), it also contributes to a better "mix" of gas and air. This better "mix" promotes better combustion and therefore more power.

To be sure these effects are NOT massive, but rather subtle. Some years ago (like 15 or 16) I was running a Holley 650 on a RB manifold. Although the competition rules said I could "match the ports" within 1 inch of the surface (this would be either side of the intake to engine gasket), I was advised NOT to. Matching the ports would have enhanced the "flow" because it was a cleaner path (particulary at the upper range of rpm). But it was said that the extra turbulence caused by NOT matching them would increase the HP at the lower end, by a better "mix" of air and gas.

Ok, I think I got through all that right. Now a question for you guys on carbs. Back then I was running a Holley 650 on a completely stock 12A. I liked it alot and NEVER thought I was running out of legs at the top end, going to 8,000+, as routinely as shifting gears. (this was in autocross) The only help I was getting to "tune" the carb was from 2,000 miles away, and so I am not an expert of doing that. So for you Holley enthusiests, what would be the hot set-up now?? Keep in mind that I may need to run the engine that fast or even more in the next project. What is out there now that you would recommend. Exhaust is RB long tube header for "ported" engines (2 "power pulses", no cats. The engine is once again a stock 12A, and I use the "tach buzzer" as a shift indicator. When the buzzer goes off---I count to 4 and then shift. I have not dabled in aftermarket carbs for over a decade, so what's out there???

Directfreak

iTrader: (2)

Diabolical, you got the Dell because you got the 13B, that's understandable. Without the exhaust, you are really, really holding the power back.

I had an 81 GSL with a 13B 6 port, Dellorto, and a good exhaust. That car, would go like a raped aped, and really scream to redline. That seven was really ugly too, so it was quite the sleeper.

That little car would beat stock TII's, 300zx's in the 1/4 mile, and almost any other "sports" car from the 80's.

Get the full exhaust, and you should see a huge increase in power, - I promise

diabolical1

iTrader: (3)

F=ma (Force = mass x acceleration)

Body in motion, tends to stay in motion ... yes that's one of Newton's laws - conservation of energy, if I remember correctly.

Anyway, I'm not an engineer either, so I may be wrong, myself ... but I think you have it all a bit backwards, and you, yourself, duely noted that "... (I know, we are really talking the inverse, and it is a "vacumn", but I'm speaking relativity)"

To me, it would seem that the engine itself will be creating the airflow, by virtue of it's internal motion. As the rotor moves around it's axis (or piston moves in it's cylinder) the vacuum created will start the air at it's leakpoint (the intake). The reversion waves (turbulence) you speak of, are caused by the closing of the port (or intake valve) because of the air being reflected by the solid object (the rotor or valve) blocking it's way into the combustion chamber.

That does it for the parts I'm pretty sure about.

Now, on to the parts that I'm taking a guess:
It would seem to me that longer intake runners would have to be thinner than shorter runners. Here's my thinking ...

An engine has a "relatively" fixed volume, like your lungs. I said relatively, simply because you always have the option of increasing the diplacement on some of them. However, not taking into consideration the variables like temperature and pressure, air doesn't change either.

Think of the vaccum you create when you suck through a straw. Stop it with a pith ball or your finger. Now think of what happens when you extend the length of the straw. I think you'd be able to hold the pith ball in the straw a lot longer and with greater vacuum on the regular length, as opposed to the extended one. You'd basically have to move air over a longer distance with a fixed vaccum source (the size of your lungs, the engine or each chamber). At some point, you're going to be using some of the power you make, to keep it breathing.

Think of the same analogy now, only this time, instead of a straw, use a piece of 2 inch PVC pipe. There's no way you'd be able to reproduce the same vacuum, unless you had lungs the size of an elephant.

This is where I believe the wave tuning that Revhed mentioned comes into play. They have to tailor the sizes and lengths to work with the engine so it will use the least amount of power just trying to breathe, and therefore yield more power for driving the wheels. It also has to be a diameter and length that will promote a progressive effect as RPM increases - so it will breathe better and better within driveable RPM ranges.

Anyway ... that was my attempt. I'm not sure how well I did. It makes sense in my head, but I'm not sure how well I did in transferring it to the keyboard. Who's got next?

EDIT: oh ... also, with all the stuff that's happened lately, i just wanted to make sure that i made it clear that i'm not picking on racermike i just wanted to try to see if i could help out a bit.
1

diabolical1

iTrader: (3)

man, that's what i like to hear!

Wankelguy

What about provisions for a choke between the different aftermarket carbs? Anyone have any info on that? -WG