ive been reading a lot of the carb threads on here, but i still cant decide what to get for my vette. i hear that demon carbs are best for modded engines, which mine is, but im really not much of an engine guy yet, mostly just an electrical, interior, paint guy. havent got to the motor yet. i bought my 79 in october and have restored the interior, fixed all the electrical problems, and just got done restoring the paint. this engine sounds like it has some good stuff in it, but i dont think the carb is doing it any justice. it gets up and goes, but runs really rich. for the guys that know what this stuff means, here is the build sheet
corvette 350, 4 bolt main
4 bold main w/#2482 main caps, bore = +030
#450 heads w/1-94 intake, 1-5 exh. 3 andle grind, posi seals
cast crank, ground .010-.010
pink rods w/arp rod bolts
h345 p pistons = hyper +.030 (flat top)
sealed power rings +.030
engine is balanced by equipoise
cam = comp cam #cca122112 = 270-270 dur., .470-.470 lift
lifters = johnson flat tappet hyd.
time chain set = comp cam true roller
cam bearings = clevite, std.
rod bearings = clevite +010
main bearings = clevite +010
torque converter = boss hoee 1800 stall

the handwriting of whoever wrote this isnt the greatest, so im hoping that stuff makes sense or u can atleast get the idea from it. oh, and right now it has the quadrajet on it. i dont know if they did anything to it when they built up the engine, i cant find any paperwork on it, so im assuming its stock still. thanks for any suggestions that u might have.

 

looks like you got a pretty big cam and with an automatic..if you want to go with Demon...i'd probably recommend a Speed Demon 750 with Vacuum Secondaries. they are hard to tune in my opinion...but once you get it...they're great! call they're tec line or e-mail them...give your specs and they can be the ones to tell you what you really need.

 

What kind of carb is it? If you're running a stock Q-jet you may be able to have it rebuilt, especially by Lars, and have a nice running carb. On the other hand I've never had much luck with Q-jets and I'm happy with the Edelbrock Thunder series 650 that I installed a few months ago. It was basically a bolt on and go situation. If you like to tinker with carbs and don't mind the tear down and rebuild you could go with a Holley/Demon carb. You can adjust them to take care of just about any fuel need and there is a lot of knowledge about them. Be advised that when you have to change jets or adjust floats you will have to drain them to remove the fuel reservoirs and quite possibly have to replace gaskets at the same time. Just some food for thought.

 

im not sure what the previous owner had in mind when he was building this car up. it also turns about 5500 rpm goign 75 down the interstate, ive only had it on the interstate once, that was when i was driving it home. anybody else turn this fast? im thinking he put some low gears in the rear. will the 750 be too big for my engine? ive heard of a lot of people going with the 650 and being happy with them, do i need to go bigger because of the big cam?

 

Holley 750 vacuum secondary.

Brett :thumbs:

 

The valves are small for serious flow. I don't know much about the head casting #. The cam looks to be 270 adv dur w/.470 lift. I would say you will be all in by 5500. Either your gears are real low or your stuck in 2nd. Demon carbs seem to be rated by "wet" flow. That makes them flow about 10% more than a dry rated carb. I found this out the hard way. Most mags use a 750 to get big HP. I don't think for day to day that is the answer. Personally I would let Lars mess w/q jet. Also w/o duals the intake changes won't help very much! JMHO
Rick

 

The Demon 650 is a good carb but they are not just drop on and forget about it kind of carburetors...they do require alittle tinkering...but they do come with lots of info on maintenance, including a video. I've heard the new Edelbrock is a nice choice. :thumbs:

 

the gears are low, it goes through all three gears, i checked that. this is my daily driver when the weather is nice, but if there are any clouds that might turn into rain, it stays in the garage, but i would like it to have a lot of power so i can burn the local rice. its got some big exhaust on it, duals out the back, and rumbles the houses i pull up to, which is ok cause the horn doesnt work. what are the advantages and disadvantages with a 750 cfm on a 350 rather than a 650 cfm?

 

The advantages and disadvantages of any CFM rating is directly related to the setup you have, not the amount of HP you want....adding a bigger carb doesn't mean more HP.

You need to find out what max RPM you are getting, what intake manifold, and what carb you have. With your setup, a dual plane intake may require a 750 CFM , but a single plane may be happy with 600-650CFM.

At any rate, your complaint about the carb is only that it's running rich, so maybe all you need to do is tune it?????

I'll point out that street driving and drag racing are two different things. For the street, you need a setup that maximizes low to mid range RPM and torque. But if you want to burn ricers at the drag strip, then you need a totally different set up.....one that won't be economical or practical for the street.......

 

my engine turns a lot of rpm's right now, it will max out the tach and then some, but im not sure if that is right or not. doesnt seem like it should be reving that high, so my tach might be off. there is a wire coming out of the cap under the hood that looks like it could just be hooked up to a seperate tach for tuning purposes, i havent tried it yet. how do i tell if my intake is a dual plane or single plane? the carb just seems like it is old and isnt doing the car the justice it deserves. the tires dont even break loose very often when i floor it. i know traction is good, but with a built engine and low gears, breaking the tires loose shouldnt be very hard right? there arent any drag strips around here, i live in a small town, but for some reason my fellow highschoolers seem to think they are all in the fast and the furious, even though nobody really has anything that great. there are a few kids that got there licenses recently that have rich parents that bought them ricers that are built up a little. and a few of them think they are all big and bad, and i want to shut them up once and for all. so it would need to be set up for the street yet still have some major power. when the car is in park and i rev it up, the car also backfires when the rpms are coming back down. could the rich mixture and backfiring be cured by advancing the timing? if that is the problem, would that also help the power and eliminate the need for a new carb?

 

What rear gears are you running? 5500 RPM & 75 MPH sounds like 4:11 or better. Not good for milage or daily driver/street car. Just curious.

 

Couple points of advice from someone not too much older, but perhaps with a bit of wisdom...

1) DO NOT RACE ON THE STREET.

2) SEE ITEM 1.

Seriosly though, if you've followed any of the recent postings by norvall, you'd know that street racing can by very serious business. A recent race resulted in the death of a very young man who was racing, a couple of others who got hit head on, and the man in the Corvette who killed himself, presumably due to guilt, leaving behind a wife and two kids.

Now that I'm done with the runnon sentence lecture, here's some advice about your setup... Backfiring usually means you're running too lean, not too rich. You may be looking in the wrong place for a solution given that knowledge...

If you want to burn 'em, you may just need a torque converter with a higher stall speed, or perhaps you're running highway gears (3.08) or both? Also remember that just because you can break the tires loose doesn't mean you're going anywhere fast...

You should find a track, even if it's a long drive, make a weekend of it.

 

Speed Demon 650 would work well on your set-up

 

i havent checked the gears yet, but it doesnt get out on the highway or interstate ever. it turns just under 2000 going 30, but that might be high because i think my tach is off. when i start it up in the morning, it has to warm up, i usually have to two foot it out of the garage, just so it doesnt die, it likes to die when it is cold and u put it into gear. the exhaust really smells like it is running rich, any racing that goes on in this town is done out on old highways at night, where no other cars are, i havent raced anyone yet, and dont really want to unless it is on a track. i hear about a quarter mile a couple small towns away from here, but nothing but talk so far, im thinking about looking into it when i get the vette running right. im perty sure the car maxes out in the quarter though, cause it will only hit about 95. oh, and the tires are almost 10 years old and only have like 5000 miles on them. is this good or bad as far as traction?

 

Holley 650 double pumper mech. secondaries (HLY-4777)

 

To find what gearing you have go to http://www.smokemup.com/

You will need to know what size your tires are and there is a calculator that give you the hieght of them.

Then there is another calculator to determine your gear by RPM, it will also ask for type of transmission. I guess you have a th350 ot 400 someone may be able to tell by the year of your car.

Also with your cam it won't have much power (tire spinning) at take off but over 2300 it should come to life. I'm guessing your cam is around 222@50, if that's the case get a higher stall convertor like around 2500 stall and it should spin all you want.

 

While warming up the exhaust will smell very rich, that's because your choke is set and you are indeed running rich. Once the choke unsets (your idle comes back down after revving the engine a bit once it's warmed up), you'll have a better idea...

As for your tires, there's a lot more to a tire than it's age and use. What is the brand and model of your tires? The rating will tell you a lot about the traction. I've got Pirelli Scorpion Zero 255/60R15s that are Traction A Temp A V-rated tires. They stick really well and don't like to spin out like my old crappy Goodyear Eagle GT IIs did...

I don't like to sound too much like an old crab or something when I say things about street racing, heck I am not perfect, but just know the seriousness of what can happen and think twice before you do something you may regret. Just because you race at night doesn't mean that you're not endangering anyone, an animal in the road at 50 MPH can change your life forever, think about what could happen at even faster speeds. Good natured fun is one thing, racing is another. See if you can get to the track, you're sure to meet some cool people and have a really good time. I haven't been myself yet, but I'm planning on going to one of my local tracks (I'm more fortunate in that I have two nearby strips to choose from) this summer.

 

when i pull into the garage after ive been driving a while, it still smells rich, not just when it is warming up

 

There should be some identifiable mark on the intake, e.g. "Edelbrock Torker" or a casting number. Otherwise, you'll have to remove the carb. Single plane manifolds have an open plenum, and a dual plane will have a divided plenum.

BTW.....people here are happy to give advice to help you get your car running right or so you can learn about different parts, but your not going to get much support in your quest to be the fastest street racer......

 

i know people here dont support street racing, and neither do i really. ive never raced on the street. last night i took the vette out cruising and pulled up to a stoplight next to a older mustang witha 5.0 that sounded built and had street slicks on it. he started reving it a little and wanted to race, so i reved mine up and acted like i was gonna go. then when the light turned green i took off like a 90 year old man, it was really funny, the mustang squealed its tires, and took off, not nearly as fast as i expected it would go, but i guess loudness doesnt always mean fast. then he slowed down a lot and i caught up with him again, he was pissed. ive never street raced and dont plan on it unless some ricer really pisses me off and i have to put him in his place. i keep telling people that if they want to race, find a track and tell me when. im 18 and a half and have only been pulled over once, for "swerving", but i didnt get anything for it, she just thought i was drunk like all the other highshoolers that night. never got a speeding ticket, though i have got a few parking tickets. sorry if i gave the impression that i wanted to build it up so i could go tear up the streets with it. im too scared of what my parents would do to me if i did that to even try it.