rx7freak13v

hey guys, im a second gen guy here but have some questions about weber carbs and autocross. everything i read says carbs and autocross don't match well, but i have seen some vids of some fast first gens that are carb'd and am curious.

the reason for my curiosity, im building a 4 port bridge port motor for my 86 fc for autocross use. i had originally planned to run efi itb's but i don't plan to stay in autocross. i plan to move up to road racing and in scca my 13b is limited to either side/down draft weber carbs or factory manifold. no efi itb's. i would hate to spend that much money on a efi itb intake with a standalone to run it just to later have to switch to a carb intake.

so i figure i would ask the guys that probably have the most real world experience autocrossing with carbs, the first gen section so please tell what you guys think aout useing weber ida downdraft or side draft carbs in a autocross chassis.

is the fuel slosh really as bad as people say it is or are they talking about something they don't know about?

any info you gurus have to share would be appreciated. please only "advice" from someone who's actually ran some autocross on carbs. thanks guys!

Sgt.Stinkfist

iTrader: (6)

IDA/downdraft hands down

82FanTC

iTrader: (9)

never run a down draft but I have zero issues with fuel slosh on my side draft

t_g_farrell

iTrader: (1)

Sidedraft will give you a better power curve for autox and fuel slosh is a small issue but easily
reduce through proper tuning and smooth driving. Thats using a wrap around intake.

Since your running bridge ports, I would go with a downdraft. A bridge probably won't be very
good for autox unless you really know how to drive it and are a smooth driver. I say this
because the power curve is so much higher in the rpm range and tend to be peaky.

Also you may want to look into the rules for autox and scca roadracing as your building a
motor that will automatically restrict the classes you can enter in. I don't know the specifics
but I'm pretty sure that will be the case.

rx7freak13v

thanks for the responses already. i understand suspension loading for smooth driving and have gotten pretty good at heel toe braking. im pretty good in that area, i can drive my buddys holley 4 bbl equiped fc through the corners better then he can (it stalls easily if you don't roll the throttle). that kind of stuff isn't really the issue. i know that with efi you can tune out a lot of the bucking and rooting that the bridge port has, but im unsure that you can do as well with a carb. i've always been a fan but understand that efi has better tuning capabilities. i was planning to run 2 50mm efi itb's on a wrap around style manifold for better tq. it's not a drag car so peak power isn't really my interest.

i would have thought to go with a wrap around style carb for the same longer primary runner effect, why dyou guys recommend the ide downdraft instead? (please im not trying to sound like any kind of smart ***, just asking a good question). if im not mistaking, adding longer ram stacks could give the same increased tq effect as longer runners correct?

this is one subject i really lack knowledge on, i've done a lot of reading but until you talk to someone who has personal experience it just isn't the same. thanks for the help guys!

t_g_farrell

iTrader: (1)

My thoughts were that a bridge won't run well below 4K so the wrap around might not yield
the torque at lower rpms and will definitely not deliver at the higher rpms >8K that bridgeys
like to run at. So not using a wrap around would put the sidedraft sticking out the side and
you would have clearance issues with your filter, so thats why I'm suggesting an IDA.

j9fd3s

iTrader: (3)

i've had no trouble with the IDA at the road race track, not that i'm going race speed though, needs more driver.

i do notice the fast guys with IDA's get a stumble when they hit the bumps in turn 15, i'm not sure there is a way around that, its physics.

rx7freak13v

interesting you state about bridgey's not wanting to run under 4k. i've seen a few on efi first hand that make tremendous power over a stock motor at 3k rpm. i guess, what i mean is, a bridge port should make more power everywhere even though it doesn't really hit its power band until up high. thats a highly argumented topic though.

any of you guys autocross? road racing carbs aren't known for any real issues, because the turns are a little longer and not so close together, but in autoctoss the entire course is basically switchbacks. that's where carbs are known for having issues. thats why i ask specifically in autocross. again, i was originally planning to run efi itb's but i am thinking about carb so i don't have to spend more money later. but maybe i should just stick with the itbs....hmm. i have always likes the simplicity of a carb vs. efi and that carb raw gas smell... it's too bad we can't run efi itb's in scca road racing, they are legal in autocross.

rwatson5651

iTrader: (5)

I autocrossed a sidedraft (Mikuni 44 pph) for several years w/o any problems at all. Pulled hard through the corners with nary a cough or sputter!

rx7freak13v

^-----that's what i have been waiting to hear, personal experience. i just found webercarbsdirect.com which is webers official sight. when i was on racingbeats site and read that the 48ida is exactly the same as weber sells it, not modified i started searching. racingbeat has a +$220 mark up on the 48 ida carb (weber direct has it for $329! they also have a 44 ida for only $250). also, i found a 55 dco side draft carb for just $490. they offer free ground shipping too.

im going to be running a street bridge, so a larger street port on the primary with the eyebrow cut in only to the edge of the rotor housing,not beyond it. i was originally wanting to run the wrap around style manifold. racingbeats 51 ida is more than twice what a 48 ida is from weber direct. do you guys think that a 48 ida would be enough? honestly, im not going for peak power. im really leaning towards the 55dco carb.

anyone using a wrap around manifold on a bridge port? atkins sells a one peice wrap around side draft manifold for a 4 port 13b. will a older model 4 port 13b intake manifold fit a turbo 2 4 port 13b? <---that's something i have been meaning to ask you guys. lemme know what you guys think.

j_tso

iTrader: (2)

I think you're looking at IDF carbs. They won't bolt to an IDA manifold because the barrels are closer together.

Main differences between the carbs themselves is the IDF has more progression holes and a diaphragm for the accelerator pump, IDA has a meal plunger.

clubber

My autocross experience with my Dell is, when it's running good, no bog going left but a huge bog going right. When it's running bad, bog both ways. I Hate it and I'm going fuel injected over winter break.
Also having run 3 12A's, my two street port engines have had really rotten bottom end power and ok power at top end. My stock port was really fun (with a stock nikki) all over the power band. It was no major powermaker but it was fun. I've read in other posts that a small bridge four port can make good bottom end power but I have no experience on them yet. I hope to soon though.

rx7freak13v

^----and the controversial begins! or maybe the problem is your Dell'Orto. i used to have a Dell 48dhla and no matter what i did, it just wouldn't run right and would randomly flood down the front throat. i even ordered a rebuild kit for $45 bucks and payed an extra $55 for fastest delivery which took 3 weeks out of small really tiny town in Italy. finally someone offered me what i had invested in it knowing the problems i was having and i sold it. i've heard that Dell's can make great power but they never hold a tune and have more problems than Weber on small technical courses. my Dell, i could tune it. take off from one stop light and walk on anything. take off at the next stop light and get beat by kids on skateboards lol. who knows.

Clubber, you said your stock port motors made more power than your street ports?

J Tso, your right i am looking at idf carbs. that's a shame because of the price. the 48 ida isn't even listed on the site . can you tell me the difference between the dco sp carb and the dco 1 sp carb? lol they are both 55mm side drafts.

anyone else with autocross and carb experience?

t_g_farrell

iTrader: (1)

Neither of you appear to have had the patience to deal with tuning a carb. Its not digital, its fully
analog and its unforgiving and theres no magic programmer or tools that fix it for you. You have
to know the theory of operation of your carb and then deal with its issues. Each and every carb
is different even if they are the same model etc.

clubber

rx freak, I don't think my stock port engine made more power but I gave up WAY more bottom end than I gained on top and keeping it wound out and in the power band gets old. As a drag race engine it's probably better but in autocross, I miss the bottom end power often.
t g ; Yea, I freely admit I suck at carbs but I even bought the weber dellorto book and although I can tune it better, it seems like keeping it running right is like balancing ball on a knife edge and is just more work than it's worth. Maybe if I had someone local to show me some stuff it would go better but I do feel that rx freak should know about this stuff before comitting to a very finiky learning curve. Fuel injection is much easier, for me anyway, to keep in tune.

j_tso

iTrader: (2)

I've no idea, never heard of a DCO 1.
There's little rhyme and reason on Weber part numbers.

rx7freak13v

Clubber, yea i didn't mean that the way it seemed. i know obviously the stock port didn't make more power, but more usable power for your set up. mind me asking what rear gear your running?

im not new to carbs, i've been tuning on them for a while on differen't applications, mostly holley's and old toyota 2 barrels (i grew up working on toyota 22r type engines, have friends with holley carbs that don't understand tuning and used to have an ae86 with a single cam engine in it carb'd) but none of those were autocrossed. i know how the carb works, how it atomizes fuel into the air and things, just hear so much about fuel slosh from the switchbacks causing hesitations, choking and stalling on occasion and am a little discouraged. that's why i came to the first gen section. the first gen cars came carb'd and i have seen some awesome autocross videos of first gens, but no idea if they are still carb'd or if they are 13b swapped on efi. i thought i would post in here to see what the guys that use side draft/down draft carbs think with using them while autocrossing.

but i think i have my answer, i should just stick with an efi setup and change it later when time is needed to. thanks guys for all of your input

clubber

I'm using stock gearing and for me this is working quite well. I get to use thrid on about half the events and occasionally get to the top of third. I don't think lower gears would help much but maybe I'll give them a try when I get that far along in the mod list.

Kentetsu

Stockport 12a with a Sterling carb:





.

jgrewe

iTrader: (1)

I didn't see any acknowledgement from the OP on the engine choice for road racing so I'll re-state it. Going with a 4 port engine in an FC will put you into a class that is wide open for EFI or carb. Pretty sure you'll end up in at least GT, not EP that the stock manifold EFI or carb option comes from. You have to keep the 6 port to run in EP. That said you can run EFI if you want.

You'll be up against tube frame, purpose built cars and being in Florida you will get to see the back end of my friend Bill McGavic's car more than you'll want to. Maybe even a couple times in one race as he goes by you.

There is a catch-all class called SP that they pretty much let you run what you brung as long as it has all the proper safety equipment and just about anything goes.

edit: For the carb, the only other carb besides a Nikki that belongs on a rotary is a Weber IDA.

rx7freak13v

hmm yea gt classes are not what i had in mind. maybe i need to reconsider. unfortunately that video will not load for me . im planning a miata rear end swap so i can have easy access to rear gear ratios.

im pretty certain im going to go with efi. the roughness of teh bridge port alone may be more than what the carb can handle while autocrossing.

im really not interested in running in gt classes so i might just stick with autocross for a while. maybe find someone running crooked drags (for those who aren't sure, crooked drags are 2 autocross tracks side by side and mirrored of each other and ran drag race style) it looks like a lot of fun. i really want to get involved. maybe int he future i'll build a 6 port engine to road race with. thanks a lot guys for all of your input.

clubber

Yea, I tried to get one of them too.

rx7freak13v

hey guys im back. after doing a bit of learning, i found a lot of people on ausrotary that are autocrossing with carbs and even rally'ing with them, which means these things can definitely be tuned for what i want. very excited. the reason im so intrigued and really want to go a carb route is the fact that i can get the whole set up cheaper for one, i can tune a carb and in the future if i make changes to the engine setup i can retune it instead of paying someone else to do so.

im definitely game for a good carb setup. i was debating between a holly 650 double pumper with center pivot float bowls and mechanical secondaries that are modified so that all 4 throttle plates open together or a set of weber's either true side draft or wrap around style, i've decided against the ida. the engine is a racing beat bridge port with a modified racingbeat exhaust port, for better flow.

have any of you ran the true side draft manifold from atkins? i cannot find much info on it, but looks amazing lol. i think it should give more peak power, though sacrifice a bit of low range tq. but thats why were raising eyebrows so guys, tell me holley about your experiences with either of these carb set ups (im really hopeing someone has dyno'd on a true side draft set up that can share some info) hopefully someone with racing experience too.

j9fd3s

iTrader: (3)

my friend had a holley on his BP Rx3. he spent a LOT of time tuning it, and on the street except for the brap brap idle, it basically ran like a stock car.

at the track, turning one way = smoke screen from all the fuel dumping in and the other way it would just stop running cause there was no fuel at all.

so for a street car the holley is ok, if you turn its junk, and there isn't much you can do about it.

rx7freak13v

^----- smokescreen muahahahaha! <--- yeah thats what i fiigured, i have read about people using them in road racing with some success but i assumed a weber would be better.

ok so i gave some thought and i think a true side draft over trhe exhaust would probably be a bad thing. not because of heat soak (had already thought about that and was planning to build a heat shield) but because of how much of a pain in the *** it would be to install and remove and service, but more importantly, no lower mid range tq because of the super short runners. which is why the ida has success. it has longer runners and makes ok tq with great top end. the wrap around manifold looses top end but gets better tq. the bridgey will make tq.....hmm

the big difference is guess is size and cost the 48 ida from racingbeat for $556 plus shipping or from webercarbsdirect $489 shipped for a 55dco side draft. that's even larger than racingbeats 51 ida.

i couldn't imagine paying $900 for a 51 ida, so either the 48 ida or the 55 dco with a wrap around. which would you guys prefer and why?

and sorry for the long posts and the inability to make a decision on my own. that's why you guys are great