Would like to get just a tad more performance out of my streetrod (39 Chev---weighing around 3,100 lbs)....with its fairly tame 350 Chevy engine/350 T tranny. Other than headers and and a hot ignition...the Edelbrock Performer intake and a 600 CFM Edelbrock 4 barrel are about the only performance boosts. My carb...a 1406 Edelbrock...is said to be calibrated for fuel economy. I surely believe that a 750 CFM carb would be too much carb for this setup, for mostly street use....but my question is....Does anyone think that getting a calibration kit and enlarging the specs slightly would be a good fit for this carb?
If the car starts, idles, and drives out well and gets acceptable gas mileage, increasing jet sizes may be a bit over the top. You might feel a performance increase but the bigger jets may also richen up the mixture at light and medium throttle and cost you some fuel mileage. Unless you're also really increasing the amount of air flow thru the engine you probably won't need to richen up the mixture very much. The beauty of these Carter AFB style carbs is their easily replaceable metering rods and power piston springs. The old Carter Strip Kits used to give you an assortment of different rods and springs to experiment with. The metering rods tips fit loosely into the jets and have a two or three step tapered end. Depending on how deeply they sit in the jet, they vary the amount of fuel that's allowed to pass thru the jet. The metering rod's position is variable and determined by the power pistons and springs working against manifold vacuum when the engine is running. Now this is the part where I tell you to go get a vacuum gauge and install it in the cab connected to a source of manifold vacuum and keep an eye on it while driving. Idling and steady cruising should provide high vacuum keeping the power pistons pulled down, putting the largest diameter of the metering rods into the jets restricting fuel flow and leaning thing out. Medium throttle or an uphill climb should drop the vacuum some allowing the metering rods to rise a bit putting a slightly smaller diameter section of the rod in the jet allowing more fuel to pass and richen the mixture a bit. Under heavy acceleration or wide open throttle the vacuum drops even further raising the power pistons fully and leaving only the smallest part of the metering rod tip in the jet allowing maximun enrichment. This is not just to bore you with details, but to show how just a jet change affects mixture across the board at light, medium or full throttle. Metering rod only changes can be made that will only affect the mixture under heavy throttle conditions. Specs for the metering rods should show the diameters of the individual steps and you may only want to change to something with a slightly smaller power tip. Changing the power piston springs alters when and how far the piston moves based on the vacuum curve of your engine. And you can make all these changes without removing the carb or even taking off the bowl cover! And don't forget to make sure that your distributor is working properly too, especially the mechanical and vacuum advances. Adjustments here can also make big changes in manifold vacuum readings and overall performance.
What is your timing set at? What is the stall of your tourque convertor? Gears in the rearend? What cam and compression are you running? What heads do you have? You should be able to kick ass in a car the weighs 3100 pounds with a 350 with a 600 carb. A 600 is just about all you need for a mild 350. How mild or wild is your motor? How does it perform now? If your motor is all stock right now I bet a cam and convertor change would wake it right up.
Find the book that came with the carb. If you dont have one, get one off the internet. You will need a vacuum gauge to properly tune the carb. Playing with the springs and the distributor at the same time can be very rewarding.
You can download a pdf file of the book right off Edelbrocks site, metering rods and spring change but not jets right away. I just changed rods in my pair of carbs in about 15 minutes, it's pretty easy. Keep a record of your changes so you know which way to go and also you can put a piece of numbered fine line tape on the matching pair of rods you're storing away.
is the car in good tune now. not pointing fingers but a tune up might do wonders. also could you try a lower profile set of tires. they would change your rear end ratio with out tearing anything apart. also is it truly slow, you might already be driving a rocket and are just gettin used to it
As already stated, in different words, jet size should be that which gives the best air-fuel mixture. The best mixture is slightly to the rich side of peak EGT, where all of the available oxygen and fuel is burned. That is true no matter whether you are going to the candy store or the drag races.
I think the advice about leaving the jets alone and just tuning a bit with the metering rods and springs is the way to go here. Thanks very much ClayMart, for the tips on those items....and thanks to all the folks who listed suggestions....I'm off and runnin......
a fairly easy/inexpensive route to is to add a 1" aluminum spacer with swirl markings in each of the four holes. I think Trans Dapt makes one of several on market. I have used this add on with Chevy small block mild motors and it adds a good amount of bottom end for off the line throttle. I also have basicly the same type of set up on my '94 GMC PU with a Throttle Body 5.7 and mild cam-works good. Worth a try.
Yes I did download the Edelbrock specs/calibration book and there are plenty of settings I can try...just using the rods and/or the springs. Thanks again all you guys!
Yeah, I was also thinking of checking out a carb spacer....and then alot of the info I read about them seemed to lean toward them making things a little sluggish on the bottom end and really kind of "kicking in" and providing the biggest improvements towards the mid and high end. I'm glad to hear of your experience with an improved lower end.....maybe I'll end up tryiny one.
Should I take the yellow pill or the green pill to fix my medical problem ? You cannot fix something until you know what the problem is. Stick it on a chassis dyno, run it up under load and and see what happens. Only then can you find and fix any problems with fuel or ignition.
a chassis dyno session would be cool, but is not always practical or affordable. Seat of the pants road tesing can be used effectively. Drag strip time is one preferred method running rich is a loss of power, and running lean invites detonation. if you can afford it, and you're a tool or tech junkie, an AFR monitor is a great tuning aid.
I'll throw in my 2 cents. I own a dyno and have tuned dozens of mild 350s on it. The 600 Edlebrock carb is always dangerously lean out of the box if you're gonna run the car hard even on a stock small block. You can make it work well and probably get an additional 5-10 horses out of it with rod and spring changes. Make sure the ignition is in good shape and total timing is around 34 degrees before you start screwing with the carb. Holleys always make 8 to 10 more horses than an edelbrock. The 3310 works great on just about anything. If it's only 8.2 to 1 compression flat tappet engine like most smog era small blocks don't waste your time. Tune all you want and it'll never make more than about 260hp. Even with a performance cam. A little rich is better than a little lean if you don't want to break something. Get some literature from the 70's that'll teach you how to read plugs and tune by sound and feel. To tell you the truth those old farts that didn't have access to modern equipment back in the 60's and 70's were pretty sharp fellas. I've had as much success tuning with tips I've pulled from old hot rod magazines as I have with the wideband. And there was this time a 60yr old made me look pretty dumb tuning a 401 AMC that I though was spot on but he said "doesn't sound right to me". A story for another time.... If you do want to cam it up. Give me a call. I'll hook you up with a cheapo grind that sounds wicked, works with any combination, and has no ill side effects on the street. Don't spend big bucks on a comp or lunati or something for an otherwise stock small block. We use good stuff in high horsepower applications but you cant beat this generic grind for the average street rod motor. Well that was just a few random musings. I'm not a highly educated high tech kind of guy, but we've been able find a whole lot of hidden horsepower for alot of local rodders and racers with our crude little dyno cell. Contact me through my website if you like http://ncperformanceinc.com/ Later, Greg
Hey Greg....thanks so much for the suggestions....yeah, I know just by driving the rod that I'm running a little lean....I think what I'll do is tune it first....new plugs...check wires for wear (they do get "lit up" and I have about 10,000 miles on this mild crate engine, alot of it in very hot conditions).....check my timing, clean and/or replace filters, etc....then try a couple of Edelbrock's suggestions on richening it just a bit with rods and springs only. And...possibly I might try a Trans-Dapt Swirl-Torque carb spacer.... the one inch one....I think that can't hurt and for not much more money it may help a little. Jalopy Joker on here seemed to have a good low end result out of that particular spacer. I've thought about another cam but think this one's okay for now....and eventually I wanna put a mild 383 stroker in here anyway so I'd just as soon leave most of this engine alone before sticking in the stroker engine. Thanks to all you guys...and especially you, ClayMart, and Jalopy Joker for your feedback.
I dont know to much about Edelbrock carbs ,But I had a buddy play with a calibration kit and it did wonders ,After you do that install different weights on your distributor ........
Greg...might rethink that cheapo grind cam....what would the specs on a cam like that be? (that wouldn't create any ill effects on the street)....
It's 230 @ .050 with a 108 lsa and about .480 lift. The 108 lsa is what makes it sound so sweet. I've used probably 6 of them so far and they work awesome. Heres a link so you can hear one. http://www.youtube.com/watch?v=Vq29mGCrnJg
I'm surprised that nobody, including myself, thought to ask if you were running a stock torque converter and what kind of axle ratio you had. Tinkering with the carb can still make some real improvements but you can only hope for so much if you're lugging around some tall "highway" gears. If you really want to "see" how these things work here's an experiment you might try. Drive the thing for a while with the vacuum gauge installed and watch how it responds at idle, cruising speed, pulling away from a stoplight, going uphill or downhill, carrying a load or towing, passing a car on the highway, kicking it down into passing gear, etc.. Now, in your driveway, hook up the vac gauge so you can watch it under the hood. Now get a volunteer behind the wheel to hold the brake and watch the vacuum at idle in park, at idle in "Drive", and then slowly give it bit more gas, still in gear with the brakes set, and see what the vacuum does. Any increase in the load on the engine should show a drop in manifold vacuum. Let it idle back down and put it in park. Loosen the distributor hold down a bit and slightly advance and retard the timing a little and watch the vacuum gauge. Advance should increase vacuum, up to a point, and retarding the timing should decrease it. Unplug the hose from the distr. vacuum advance if you've got one and watch for a drop in vacuum. Assuming it's connected to a manifold vacuum source and not ported vacuum. The reason to go thru all this horsing around is to help you see that anything that affects manifold vacuum also affects the operation of the power pistons and metering rods. Now if you're feeling really brave you can run the engine with the truck parked and take the little cover off of at least one of the metering rod assemblies. You may want to remove the screw and cover with the engine off the first time. With the cover off the piston spring should lift the metering rod fully out of the jet. DO NOT FORCIBLY PUSH THE METERING RODS BACK DOWN INTO THE CARB OR YOU'LL DAMAGE THE TIPS!!! OK, no more shouting. Gently tap the piston down with light finger pressure a few times till the power rod tip "finds" the center of the jet below it and allows everything to drop back into position. While still holding things in place with your finger, start the engine and manifold vacuum should pull the piston down fully into the carb. This should put the largest diameter section of the metering rod into the jet and restrict fuel flow to keep the main fuel circuit as lean as possible. With your finger still in place of the metering rod cover, blip the throttle a few times to quickly drop the manifold vacuum. You should see, or even feel, the power piston come up momentarily as the spring pressure overcomes the low vacuum condition. Sensing the increased load on the engine, the rod will raise leaving only the smaller power tip of the rod in the jet allowing more fuel to pass and richening the mixture to meet the demand. If you really want to be fanatical about it you can watch the vacuum gauge and note how much vacuum it takes to get the power piston to move and when it's fully raised. This can help you decide if a lighter or heavier piston spring is called for. Or as simple as it is, just swap in some different springs and see if you can feel a change in how it drives. Just try not to change both rods and springs at the same time or the results may just confuse you more than I probably have!
Am in the process of several of the above pieces of advice from different readers.....from what I can tell, the totally "open" centers on the carb spacers are a little better for high end....while the spacers with the 4 holes (ie "swirl-torque style) seem to get better low end results. I'm thinking about doing a 1 inch alum swirl-torque with my 600 Edelbrock but.... anybody have any personal experience with a 2 inch carb spacer? (ie. better at low end or mid to high end?)
Had a seat of the pants kick this week....just put a 2 inch phenolic carb spacer from Jegs under my #1406 Edelbrock....and changed out the metering rods and springs....(put in the smallest rods and the strongest spring)....and the difference in throttle response is VERY noticeable! Also, since my 350 has around 20K miles on it by now, I figured it was seated in well enough to go to synthetic oil.....don't know if that also helps but...has to be a little less friction. Anyway....for a small $ outlay, I'm mighty happy with the performance results!
Thanks for the update, you don't see that often enough in these forums. It's nice to hear the results of experimenting with some of the suggestions posted here.
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