I run both carbs together. It was my hope to use one or the other as a primary carb but it didn't like it at all. Couldn't get rpm's to come up and labored real hard. Together they respond real quick as I'm sure you've seen.
IMHO progressive is more likely to work when the manifold is very tall with large volume, so that the distance from the primary carb to any cylinder is closer to equal. Just watch your plugs for lean mixture at the cylinders opposite the working carb. You can also use a plenum divider (same as a single plane) to increase response.
Blackmopar, if this is the one you are contemplating http://store.summitracing.com/partdetail.asp?part=SUM-CWND310&autoview=sku DON"T do it! Those are the mechanical secondary carbs without squirters. They will bog, run like sheep chit, require you to drill to make changes on the secondary side and be unsaleable to anyone with knowledge. They are very cheap carbs, that's why they are in the package deal. Order a good set of carbs from them or someone else. They do mention that they will package the kit with 600s. I'd go that way if you want a package.
The guy you bought the tunnel ram from has a PAIR of 600cfm Holleys that are MATCHED and TUNED FOR THAT INTAKE??? And he wants $300 for them??? Dude...GO BUY THOSE CARBS!!!!!!! Problem solved!
Panic, The cfm formula is for total cfm the engine needs, not per carb. I got that equation from earlier in this thread. Fat Hack, Most people are saying that 390's or 450's will work better for my application. Blackmopar, Someone is selling a pair of 450 mechanical secondary carbs in the classifieds. I was surprised nobody mentioned it, which is why I asked about running mech. secondaries.
I am selling the 2 450 holleys in the classifieds. one guy offered me $300 shipped but dose not know if he wants them yet or not. the first $300 plus shipping takes them.
The cfm formula is for total cfm the engine needs, not per carb. I got that equation from earlier in this thread. Yes, and it still doesn't apply.
yea, that was the one I was considering - but I do get what youre saying - thanks for warning Merckid I agree with fathack again, buy the set the guy has for sale
Is it possible to swap in 390 or 450 vaccum mainbodies in regards to the 600 T-ram carbs? I know some Holleys can swap parts, but I'm still a big noob when it comes to all the different types. I've gotten quite a bit of contradicting information as far as all this carb sizing business is concerned, which is why I started the thread. It all comes back to the original post about two schools of thought.
I have ran tunnel ram setups on the street and track for over 25 years with great results. The 390's (Holley 8007) work great, but are getting pricey. The 450's (Holley 9776) work very well even though they have mechanical secondaries. I have run the 450's on small blocks from 283 to 406 with only minor accelerator pump and power valve tuning. While the 450's can be run on a big block, they are best used on smaller engines and they do generally require some re-jetting. There are many factors that go into putting together a good running multi carb set up. The "trick" is to have good velocity through the entire intake system from the carb venturi past the intake valve. All to often, people put a tunnel ram on an engine with huge intake ports and a huge cam designed to operate above 4000 rpm, then they blame the tunnel ram for streetability and drivability issues. Almost any carb and manifold set up can be MADE to work on the street. Here is a picture of the set up I run. Yes, it took quite a bit of work and the throttle response isn't what anyone would call "crisp", but it is streetable and it does get the looks. By the way, that's a 433 in. engine. I feel fortunate that I have been able to help many people run multi carb set ups when eveyone else told them it was impossible. Carb tuning is getting to be a lost art. I do more than my fair share at my shop and am glad to do it. If anyone has any questions, please feel free to PM or email me. I'll be glad to help.
Re: "The "trick" is to have good velocity through the entire intake system from the carb venturi past the intake valve." I know what you mean, but with your permission, I'll insert an exception? The velocity almost dies after it leaves the throttle blades, because the area of 8 bores (estimating 1-3/4" ID) is 19.2" expands instantly to (example only) 112" (plenum is a 7" wide by 16" long box) or 580%. The velocity is only sustained for a few inches, then drops to 17% of the original, and picks up again as it nears the intake port on vacuum. Nothing except an IR sustains discharge velocity into the port, and the tunnel ram is among the worst. The "trick" is to have good velocity through the entire intake system from the carb venturi past the intake valve, including minimal plenum cross-section consistent with your carburetor size and power requirements. This is one reason why tunnel rams are sometimes taller than the best "package" size - the height retains volume for good power while keeping velo as high as possible. A wider plenum with the same volume will be shorter top to bottom (more hood clearance) and have lower velo.
Looks to me like anyone setting sail with a tunnel ram is headed for a good learning experience or total frustration. Just depends on what kind of person you are I suppose. Anyhoo . . . I was wondering how big your cam is?
I found a pair of 390's for 300 bucks. In the latest issue of car craft there is an article about tuning a tunnel ram, they say a lot of the same things you guys have. You guys have given a lot of great advice.
The specs are: In. 246° @ .050, Ex. 254° @ .050. In. Lift .615, Ex. Lift .636 Lobe sep. 114° for the nitrous. MK, that's a good buy on those carbs. Are they list# 8007's? By the way, if anyone is looking for a tunnel ram for a big block chev, I have one in the classifieds for oval port heads.
Panic, you are correct about the velocity. That is the reason you want to find a manifold with the longest runners(not the largest) and the smallest plenum. It will help keep the velocity drop to a minimum. We could go into quite a discussion at length about this subject regarding ignition, rod length, compression ratio, cam timing and cylinder heads in regards to optimizing a street engine for use with a tunnel ram, but that could take years and cost thousands of lives.
I'd go with the school #1 Having once installed dual 500 cfm's on a rather healthy 289. The heads were 2.02/ 1.60 valves 7 angle valve job with a very heavy port job. Port matching to the gnats ass. Compression 11.0 :1 Key to making a small block Ford run is porting. The car a 67 fastback with 4.11 gears and 4 speed. The engine ran great warmed up. Streetable on days with temps or 60 to 90 degrees. yeah it was ove kill. When warmed and runinng 110 this car pulled like a jet on 3k and above.
Don't run the 600's. I had them on my car-they were too big for the street. I was more interested in show than go. I wanted an engine that started up easily and ran without sputtering etc. I put together a set of the early Holley 390's # 6299 carbs-no longer made but they are on ebay on a regular basis. They have the vacuum secondaries and don't have all the emissions crap on them like the 390 #8007's have. I would run the 450's as a second choice. Also run the mildest cam that makes the most vacuum you can find. A rumpity rump cam will make the car run very bad on the street. My comp ratio is 9.5:1 and works great. If you are running a 4 speed find the heaviest steel flywheel you can find-really help on low rpm torque. Run an electric fuel pump to prime the carbs. Makes staring must more easily.
That depends on the shape of the screen. If it's flat, yes it will reduce the flow area of the runner. In my brothers design the surface area of hte screen is so much larger than the opening is sits in that the net available flow cross section was not negitivly effective. ie... the open area of the screen was larger than the opening it was inserted intotdue to it's pyramidal shape.
I went with the #8007 390 cfm vaccum secondaries. The guy I bought them from is a friend and he told me if they don't work out I can get my money back. My heads are Edelbrock RPM with the 1.9/1.6 valves in order to work with my stock pistons. When it gets rebuilt it will get the 2.02 intake valves, along with at least 10:1 pistons and a cam that has yet to be determined. I'm building this motor as I get the money, or if good deal comes along. It isn't the "ideal" in any sense of the word, but the plan is for it to be someday down the road.
Agreed. Also keep the cam duration on the smaller side. Something with an operating range of 2-6000 rpm with around 110-112° of lobe sep.
The cam in it right now has 224/234 @ .050 with .496/.520 lift. I can't remember the lobe angle. It's the Edelbrock RPM grind. When it gets rebuilt the cam will be tailored to the motor combination.
Whatever you do, whatever size, the most important thing is getting GOOD carbs. If you get 2 crappy 600's and can't make them work, then you get 2 GOOD 390's you'll always think that the 600 size was the problem. The money back guarantee is a great deal for you. It's like a free trial. I run 2 660's on a 440 dodge and It is a kick to drive. 5 pumps on the pedal and it fires and idles with no chokes or pumping. Of course, this is cause the idle circuits are huge in a 660. I am going to put wire in my circuit. Otherwise, they work awesome. I think I have all the low end I need. You can see it operate on you-tube by searching 46 dodge. There's 2 vids of burnouts. Also, just as important as getting GOOD carbs is when you tune, don't change a bunch of things at once. You'll never know what did what to your tune up. Remember, carb sizes are based on max flow, not the cfm's you are driving around with and just as easy as you can flood with a ram, you can lean out!!
Should I gasket match the plenum where it bolts to the top of the runners? What about where the runners meet the heads? I've always been told that it's free power, but it seems that in this case leaving it alone would give a little more vaccum, and thus better signal to the carbs.
If it makes you have better peace of mind, do it. There's 1/8 inch steps in my ram and never checked the head/intake mate and I'll bet if I ground on the setup all thru November I'd never feel the difference. Full race motor looking for 2 hp, yes. Street 6000 rpm occasionally, no. Not trying to be mean, but this usually works best, Quit worrying about every little thing, just bolt the shit together and flog it and then try to make it better.
I run 2 450's on a old edelbrock trx on a 355 sbc.I run a .575 lift solid cam.12:1 compression,power pac heads with 2.02 vavles and 58cc chambers on pump gas.I run 4.88 gears.M22 4 speed.I never really did alot to the carbs.They work great
Lots of good info on this thread .I see alot of people had some major tunning issues with the T-rams ,but i must have got lucky.My 302 held a steady 19.5 lbs of vacume at an idle with the Torker on it and it holds the same 19.5 with the T-ram on it.The only real tuning i had was the jetting in the primaries and a went to a biiger shooter size on the 600 .It runs great in all weather from 20 degrees to 105 .The dead spot was minimal from the get go ,but the jetting it up a few #'s and the bigger shooter cured it.As a few people have mention my 600 does kinda have a flat spot in it when i hang right hand turns hard.I never thought about the side hung float causing it ,but it makes sense .It doesnt happen often enough to worry about.The only problem mine has is sometimes it will caugh through the carb when i kill it and then start it hot after its been driven hard .Anyone know whats causing this? The timing is right .I have a blow proof power valve so it isnt hurting nothin ,but im still curious .Not trying to hyjack the thread but while you guys are on the subject...
Doubt it ,unless aTunnel Ram can make a double roller chain with 5k miles on it stretch ,just by bolting it on the motor.It never did this with the low rise on it...
The Jalopy Journal
