j9fd3s

iTrader: (3)

i think you're in the ballpark with the runner lengths, the GSL-SE and S4 are 500mm long, and the fixed length EFI P port intakes are 370mm long.

the IDA on the P port intake is 400mm long, so its right in the happy place.

i bought my IDA used, for like $450, like 6 months before RB started offering new ones. $500 for a new one seems fine to me, although you still need to buy jets and venturi's and stuff as they come built for some random car.

t_g_farrell

iTrader: (1)

I've dynoed my stock port 12A with the mods in my signature at 134 whp about 124 for torque.
The sheet is in the 1st gen non-tech dyno sticky thread if you want to see it.

rx7freak13v

oh wow, ok that is good to hear about the runner length! but what about a 48mm ida on a bridge port 13b?

i am going to go looking for that dyno chart, im interested in seeing the powerband. i know its a stock 12a vs. a bp 13 but im curious. thanks guys

rx7freak13v

t g farrell, i searched all the posts you have made by searching through your profile and cannot find you dyno post if you have the link for it could you please post

j_tso

iTrader: (2)

Here's one guy's impression on straight side draft. Cliff's Notes: It gives better response over the wrap around for a street ported engine.
Makes sense to me because just about every other application for DCOE Webers has them coming straight out of the engine.

Here's another thread about the Atkins side draft manifold, a couple of people say the quality of the casting isn't that good. If you can find one, Lake Cities is the brand/company you're looking for.

rx7freak13v

alright j tso, thank you so much for posting that. i had no idea how bad the casting was on the atkins manifolds. also, i didn't realize how many people actually want the true side draft style manifold. i think i would love to have it now, too bad LC doesn't still make them. hmm. anyone know another source that sells the same style manifold for a 4 port (turbo II) 13b? also, longer ram stacks would be desired, but wouldn't fit.....maybe cut a hole and run ducting through the fender lol. would be worth it.

so i have learn how much the wrap around manifold sucks, yet sooo many people still use them.

i have read somewhere that an ida setup doesn't clear the hood on an fc, any pics of this? i couldn't find any but i keep reading it. (i know i know, first gen section)

you guys really are great for helping me through such a difficult decision. really thanks a lot guys, sincerely.

j9fd3s

iTrader: (3)

the length of the intake = the rpm you get peak power at. so the longer intakes like the wrap around and the stock EFI ones are good for a stock engine, but would be a bad choice for an engine like a bridge that is setup to make power @ higher rpm.

i don't know about an IDA in an FC, but an IDA in a 1st gen with the stock air cleaner on it, is really close to the hood. mine does rub a little, but i used a piece of metal that was too thin to bolt the air cleaner to the carb, so it flops around more than it should.

rx7freak13v

i understand how how the wrap around intake would be better for a stock engine or even one with a mild extend port. but when used for something like im building, it won't be sufficient. that all makes sense.

just wish i could find someone replicating the lake city side draft manifold that is actually worth owning unlike the atkins one. that with a 55mm dco sp would be siiick! i'll probably end up with the 48 ida though since i don't know another company that makes a good true side draft manifold and the lake city one has been out of production for some time now.

i can manage out any kind of hood clearance if necessary, no big deal. i had actually though of adding some kind of functional scoop for better air, or even just stick the stacks out of the hood and make some kind of rain guard for them on bad weather days. <--it would look badass and should perform well too. just an idea. or build a cold air intake to it, but i really don't want to hide that induction noise, although it MAY be too loud anyhow lol.

opinions on a 48 ida with a bridgey? or know anyone else who replicates the LC manifold better?

Siraniko

iTrader: (13)

I dont like the new IDA. It has a push-in squirter that is held by an viton o-ring that can go bad after x # of use.

I just picked up my new 51. Its an old school IDA that cost me $350 to convert with new shaft, 46 venturies, butterflies and such. Its actually a 52mm, not 51.5. Its going to a newly built old school 13-B full bridge but i ran out of time to install this new motor on my RX-3

rx7freak13v

however the new ida has the third progression hole already drilled where the older models you have to have it drilled (or at least thats what i have gathered from the interwebz)

i would love to use a lake city true side draft style if anyone makes such a thing anymore other than atkins....maybe i will build one. hmm....found a website that sells an intake manifold flange so would just need some pipe and a welder. then weld on some weber flanges. could work, hopefully i can buy one but if not i may attempt to find someone to weld one for me.

Siraniko

iTrader: (13)

However, adding a 3rd progression is a piece of cake

j9fd3s

iTrader: (3)

granted i've only tuned a PP engine, but i don't think its really needed

peejay

Street ports are peaky. Bridge ports are not.

Powerband is a two dimensional plot, RPM vs. loading. Street ports don't make much power at low or mid RPM, so you need to use more RPM. Bridge ports don't make much power at low loading, so you need to use more throttle.

That's why bridges aren't the best street engines - you can't drive them lightly. In 5th gear, the minimum speed where there's enough load on the engine for it to run smoothly is about 70-75mph.

I can sort-of see why people say they have no low end power, because on mine there is a definite torque surge at 7500 and it goes from "pulling hard" to "WARPSPEED". But street ports do that too, and the difference is, a bridge at lower RPM is still a lot more torque than a street port at max potential.

Also: Carbs suck. EFI is cheaper and better. I have a carburetor, in that my throttle cable is connected to a Holley 750 that mates the gap between air filter and intake manifold, but all fuel goes through fuel injectors controlled by a computer.

rx7freak13v

hmm, i thought the 3rd progression hole was "really a big deal".

Peejay, i thought bridge ports were supposed to be peaky also, that's what everything on the interwebz says about them. im not that concerned about having to keep speed up to drive in 5th gear, i will just cruise around in 4th instead. yea less mpg but if that was what was important to me i would be driving a corolla instead of a rotary. the reason why a carb actually came up for me is because i may want to try out different kinds of intake setups until i find one im really happy with. i know how to tune a carb, i have no idea how to tune an ecu . so if i change up the intake then i can simply retune it instead of needing to pay someone else to tune it for me. also, eventually i want to move up from autocross to road racing, and scca says either factory efi intake manifold, or weber style carb. im not the most knowledged but i would rather have a fine tuned weber over a factory intake setup.

this is all still trying to work out what is in my head. i know what i want, but all comes down to what would be easier, and i think the weber would be the easier option. then again, i live in fl where the humidity is always changing through out the day, thats what scared me away from a carb setup in the first place, until i found some people that run webers on their cars and trucks and swear by them.

i don't know. thanks a lot guys, and i will see what used ida's are going for. might find a deal, my luck probably not. we'll see. i have other ideas kicking around in my head too, but for now. im still learning more about the tuning differences between dco sp and ida webers. wish i knew more peopleusing them on rotary engines.....

j9fd3s

iTrader: (3)

the webers have two circuits in them, they have the idle circuit, and the main circuit.

the idle circuit works from throttle position (it needs to sit over the idle hole), while the main circuit works from airflow.

the transition between the two is where the "art" part of tuning comes from, as there are a couple ways to do it, and it depends on the engine somewhat.

i think most people try to run a slow/lean/wrong emulsion tube (F11), and so the main circuit can't come on fast enough and you get the lean stumble. you can fix this with the 3rd hole because the transition circuit works to a higher rpm.

i run an F7 tube (13B should have an F8), i almost have the opposite problem, the main circuit can come on so early it causes a rich stumble.

how early the mains come on is partly the Etubes, partly the engine and partly the air corrector.

peejay

4th is even worse. Less load on the engine means it runs rough more.

The trick is to load the engine down. Again, it's NOT an RPM problem, it's a load problem, the engine (well, mine anyway) seems like it needs to make a minimum of 60-80 ft-lb before it will run smoothly. Less load means unstable running, meaning buckbuckbuckbuck which sounds nice on a YouTube video but sucks in the car, especially when you think about what all of that constant jackhammering is doing to your drivetrain. Running richer helps to a point. At the load cell for 60mph on flat ground, I'm running close to 12:1, but you can't let off the throttle or it'll buck. At the load cell for 60mph going uphill, I've got it at about 15:1 and it runs fine, looks like about the same amount of fuel actually (~16-18% duty cycle with 2x680s) My fuel maps end up looking bizarre, with weird holes where the engine is loaded and peaks where it's lightly loaded, then falls off at loads lower than that. But it drives fantastic. Try getting a fuel curve like that with a carb.

I run an FC trans and 205/70-15 tires to knock the highway RPM down (and therefore increase engine load) as much as possible. I'm only turning 2700 or so at 60mph, not 4000 like with an FB trans and stock size tires. It takes X amount of power to push the car through the air at a given speed, so less RPM means more engine torque needed means the engine's happier.

Be a great truck engine, though. It loves being loaded.

j9fd3s

iTrader: (3)

i keep saying i could tow with mine.

its not really load, its more like intake vacuum vs rpm. intake vacuum = exhaust gas sucked into the intake = buck buck buck.

i reduced the intake vacuum (holes in the throttle plates) and its almost brap free from idle to about 2500. over 2500 i need to open the throttle more, but hey on the track i need to open the throttle more.

my fuel "map" is totally normal, although finer fuel control would only improve things

rx7freak13v

hmm i didn't realize how complicated it is.

driveability isn't the most important thing to me, as it's primary build purpose is to be a track car, though still be driven on the streets. i understand what you mean though, i know what the bucking issue is all about.

i've never owned a bridge port engine. everything i've read says to keep on the throttle and should be relatively tame. but if you come off the throttle it will start bucking again. Peejay, you explain that it's load based, that changes a lot of things! it's hard to keep a good load in a flat state at cruising speeds. how do others tolerate it? or maybe they just don't care? i was planning to change to a fb trans for the closer ratio's and then change to smaller tires which is the exact opposite of what you did. what final gear are you running? does that impact load as much also, because im planning a miata rear end swap so i can run cheap R&P gear swaps. i was planning to start with like a 4.77 and move shorter or longer depending on how it feels. but it sounds like that would make low cruising worse. hmm.....

a lot of people run carbs in race cars and dd car and dd race cars, is the rotary that much more delicate with load/vacuum than other engines?

im really glad i started this thread. a lot of good info in here. even if i do decide to follow Peejays advice and stick with a efi setup, im glad i got the chance to broaden my knowledge.

btw, Peejay. how are you liking the efi 4 holley? i would love to see a vid of it idling and such. just saying

peejay

FC trans are closer ratio than FB, although the difference is minimal. Not counting 5th.

Smaller tires aren't really available to me. 65cm tires are very easy to find used, while wide 58-60cm tires exist but they require 13" wheels, which would be very expensive to find aluminum 13x7 wheels that fit GSL-SE brakes. Plus I'd have to buy new, and with shipping it works out to about $500 a pair, before I get wheels for them...

Tuning is a LOT easier. Carbs are a lot more time- and money-intensive to tune. As an example, with the new engine, it took me about 5 minutes to get the tune 95% there, starting with a map that was 100% wrong.

rx7freak13v

whaaaaaaaaa?????!!! people keep telling me the first gen trans has a shorter ratio. alright, thank you for that piece of info sir. that saves me from having to swap out the tail shaft housing.

and i guess also, most people who are running carbs are using them on street ports, not bridgey's which have better vacuum and are probably easier to tune.

i gues for the ease of tuning efficiency, i should probably stick with efi then. it would change my class, but then again i will probably be autocrossing for a while anyhow sincing it's cheaper and easier on the car. i the next 2-3 years or so im hoping to move out of fl up to nc and run hill climb events which would be difficult witha carb i think. tuning efi to compensate for elevation changes would be much easier then doing so with a carb.

thanks Peejay for explaining that to me in a way that actually makes since to me.

im running a 15" rim and am using 225/55r15 now, i was planning to swith to a 225/50r15. both of these tire sizes are pretty common around here for H-Z ratings and can be found used in almost new condition for relatively cheap. like $150 bones for all 4 mounted and balanced with almost 90% tread left.

thanks guys for all the help. i have a much clearer picture now.

peejay

1st-gen transmissions DO have shorter ratios. That is why the spacing is wider.

4th gear is always 1:1 since it's not a gear, just a direct connection between the input and output shafts. Therefore, if 1st gear is lower, then the gaps between gears must be wider.

That's exactly it. Engines with a nicer vacuum curve are much more friendly to carburetor tuning. The more electronic controls we're utilizing, the more "radical" the engines can be.

Even so, the last of the carbureted RX-7s had a funky valve in the intake port that would cut off airflow from the carburetor to the rear rotor under deceleration, and dump a bunch of air in there instead. All to eliminate a tiny bit of buck-buck-buck. (It was done in software on the EFI cars) That's with tiny stock ports. As you go larger on ports, the bucking takes less and less load to produce until it's doing it at idle, and even under cruise and some times...

j9fd3s

iTrader: (3)

i spent a LOT of time tuning the carb, however if you gave me a car with a weber on in and a bag of jets, its only a 1-2 hour deal.

i will grant you you can hit a key on the keyboard, and sometimes i have to wait for a part from italy...

peejay

What kind of fuel economy are you getting? I'm knocking down 23-24mpg.

(Yeah, that's a loaded question, I know )

peejay

HOLY CRAP!!

All of the old Anniversary Racing Factory videos are on YouTube now!

P-port on Weber IDA:


P-port on EFI:

Siraniko

iTrader: (13)

Yup, i dont use any technology to tune, just a.simple common sense and a former motorcycle canyon racer who drives my car to the limit. Then he reports back with his unbiased opinion on what changes or improvement can be made to reach its full potential