Cam specs for dual carb SBC?

OK, before any of ya'll call me a kook, I'm trying to build a low budget rod thingy using what I have lying around. Right now I have a fresh late '60s SBC that casting #'s tell me is a 307. It has no cam or rocker arms. I also have a Weiand tunnel ram with two Edelbrock 600 carbs of unknown jetting with a progressive linkage.
I plan to mate the two and am wondering what sorta cam I should be looking into spec wise as well as what I should jet the carbs at. I'm not gonna race but I want it all to work and be driveable and have a lopey idle. I realize that I'm throwing way too much carb at the poor little motor but that's rock and roll. Any advice would be appreciated aside from telling me to go by a Performer manifold and stick with one carb.

Thanks

 

I've got a dual plane weiand highrise with a 650 holley on it I'd swap you

 

Get a CS186R Speed Pro camshaft and a set of HT817 lifters for it, you can get a deal from www.northernauto.com if you like. The cam has .480 lift and 230 degrees @ .50 duration. I run one in my SBC w/twin Carter 500 cfms.
On a tunnelram, you need to run both carbs at the same time linkage wise.
GLenn

 

Thanks for that useful information, AHotRod, but another question, why no progressive linkage on the tunnel ram? It was run like that on a guys 355 in a '56 chebby and he never got it right, maybe that's why. I'm somewhat ignorant on the setup. If I link 'em what do I jet them at?

 

On "Low-Riser" designed intake manifolds, you can use a "Progressive" linkage because the carbs are so close to the intake valve.

On tunnel rams, you need to run both carbs at the same time as the distance is so much greater. In other words, if you were to try and run off the rear carb progressivly(?) the front 4 cylinders will receive EXTREMELY LEAN Air/Fuel mixtures, and the engine will stumble, puck and fart!

As for jetting, the AFB by design is rich on the primary side and lean on the secoundary. So, proper "Syncronizing(sp?) is very important and easy to do.

When you get to that point, email me...and if nothing else, I can call you and walk you through it.

Don't fear it, tunnel rams are WAY COOL

Glenn

 

the 650's should be too much for your 307 even with a manual trans. on the street. if you wre to go with 488 rear gear and a stall high enough it would work on the track.I am saying you need a pair of downjetted 500's at the most and recommend a manual tranny. if gooing with an automatic for street use I recommend a 2800 stall and a 373 rear gear at the highest. as to camshaft the above came will work or even a stock early LT1 [350 HP 350]with 450" /460" lift hydraulic cam.-If you get too much cam then you'll have to have a lower gear or higher stall or both to render it useful- then it may be a miserable peice of shit on the road.

 

Thanks again, Brother. Pmed ya with some of my info.

 

The gears are 4:10 and the tranny is an old Powerglide.

The carbs are 600s.

It will not be a daily driver but a Friday night tire burner, I expect it to be a miserable piece of shit on the road.

 

CROW,

Did you say what this engine combo is going in?

 

AHotRod, I have not for fear of mockery. It is an experiment, Frankensteinian if I may. I am making a bucket roadster out of an old Willys Jeep. Refer to my introduction thread, "Another dang ole Texan" for eyesearing mock up picks and please don't hold it against me.

 

A while back, I asked Fat Hack about running a 2x4 tunnel ram on an engine that didn't need it. Here's his response:




How do ya make it work?

(What motor is it for?)

Duddn't REALLY matter.

Lefty loosey, righty tighty...off with old manifold, on with the new!

Holley 390 cfm's...yeah, okay...they WILL work...although they are overpriced fu-fu carburetors...but since he HAS them already...no reason NOT to use 'em!

Throttle linkage is important...you want both carbs working TOGETHER...it ain't a race to see which one opens up first...it's a TEAMWORK deal! Okay? Get that ironed out before worrying about too much else.

(Yes, you CAN run progressive linkage and open one carb faster than the other...but that's RETARDED on an intake with as much plenum area as a typical tunnel ram, and with carbs as dinky as 390s...make it simple and run straight linkage).

Running a tunnel ram on the street can be a kick ass deal...or a piss poor nightmare...depending on how you do it. Tuning is of the utmost importance, but once you're set...you're Disco for a good long time!

Do all of your settings and carb changes SYMETRICALLY...if you run Number X jets in the front carb...run the same jets in the rear (at first...precise tuning can have four to eight different jet sizes on the same engine at once...but forget that for now unless you have a dyno, O2 readings, and other fancy stuff). If you set the idle mixture screws out a given number of turns in the front carb...do the same out back. Same with accelerator pump adjustments and cams, secondary springs, discharge nozzles, power valves, etc. You CAN eek out minor performance improvements ONCE YOU'VE MAXIMIZED A SYMETRICAL COMBINATION by tweaking each carb differently, but don't do that at first...you'll end up all over the place and never get anywhere performance wise unless you work at it systematically.

Remember that those 390 carbs are vacuum secondaries carbs...that means that their TOTAL COMBINED CFM RATING is only 780cfm. Now, in the real world, no engine or carb is 100% efficient, so those carbs may only deliver a MAXIMUM flow of maybe 680-720 cfm at WOT if you're lucky.

That is NOT too much carb for anything but a lawnmower engine...and most of the time you're only gonna be driving around on 390cfm rated venturis.

Two stock 390 Holleys right out of the box should work fairly well on a street small block...and you can tune them from there. With all of your linkage and settings in sync, drive the car and see what you've got. Take a plug reading and see if you're too rich or too lean. Does it bog, or is throttle response crisp? Does it 'surge' at cruise? How does it idle? Think about these things on your initial test drive.

As far as what you should have in addition to your tunnel ram, it's pretty obvious...headers and a good exhaust system, a decent ignition system properly timed, an engine in good mechanical condition with decent compression across all cylinders, and a hotter cam won't hurt.

I could write a BOOK on setting up a tunnel ram for the street, but I'll sum it up here by saying that the myths about them NOT being streetable are just old wive's tales! In every modern head-to-head comparrison, a wisely selected and properly tuned tunnel ram set-up makes MORE LOW END AND MID RANGE POWER than single 4v set-ups! Throttle response is incredible and the top end charge is unbeatable!

Like any other performance modification though...you have to optimize THE ENTIRE VEHICLE PACKAGE! Throwing a pro stock tunnel ram with two 1050 Dominators onto a stock 289 with single exhaust and 2.73 gears is exactly what you DON'T want to do! A street-oriented tunnel ram with smaller carbs on a warmed over motor with decent gearing is gonna rock and roll, though...and it'll make a believer outta the skeptic once they take it for a spin or go for a ride!

(The scariest ride I was ever in was a tunnel rammed V8 Vega...even though the car was TUBBED, I still shit my pants when my buddy nailed the throttle FROM A 45MPH ROLL on the freeway and the car was all over two lanes and accelerating like a rocket with two long wide black strips behind us! And that was 'just' a 331 small block!)


You watch the details and take your time...that tunnel ram will work out well for you!

 

Here's part two of his reply:


The tunnel ram and 390s should work well on the 350 crate motor..but I'd look into a hotter hydraulic cam grind for it...the Edelbrock Performer Plus cam or Torker series cams work well, as do many of Crane's offerings. You can save a few pennies with a cheap-o single pattern cam, but I hate 'em myself...too generic and I've seen none that truly work well in a STREET motor.

In general, you'll want a duration @ .050" on the intake side of somewhere in the 222 to 228 degree range or so. Get springs and lifters matched to the cam, and a new timing set. (If you run one of the Edelbrock cam kits, their timing set will work perfectly).

For an automatic, I'd go for at LEAST a 2000rpm stall converter...2500-3000 would work better if you want to get it off the line a little harder, but a milder one will work better if the car is going to be mainly a cruiser.

Rear gears oughtta be 3.55 to 4.10 for a stout street car...I like 3.90 gears as a good compromise, but you can go a little bit higher or lower to suit you.

You're not talking about a very light vehicle...a tunnel rammed 350 is an odd choice for it...but with a little planning and carefull tuning, you should be able to make a decent runner out of it!

 

Good luck Crow- I have had some of those myself is how I remember............I didnt mean it in a mean spirit/just a guess of the end results

 

Thanks for the info, guys. Getting me off to a decent start.

It's all cool, choprods, I actually also have an old Performer and a medium sized Holley if I can't make it work, just have to give it a shot, ya know, staring at that big evil monstrousity sittin' on the bench with its two shiny carbs...it's just calling my name.

 

it aint gonna run worth a shit and will cause you lots of problems just to warn you.... camshaft is only part of the equation compression heads that breath are the others motors that could handle it were a pain in the ass .

maybe youll figure out something i dont know.good luck.!!!!!!