Multiple Carb Question

[CobraMan]

I am interested in dual carbs for my 427so. It is strictly street and highway and will not see a track. How streetable is a tunnelport intake and heads? When I switch manifolds, have a single 4, I will be switching most likely to Edelbrock heads.

Opinions please.

[bmalone]

I can answer the streetability of TP in general, but you might consider how your existing setup will match the TP heads and intake. For instance, what cam are you running? What CR? WHat rear-end gear? WHat type of transmission?

I run TP w/ 2x4 mech. sec. 750 Holleys. Cam is .580 lift w/ a lot of duration. 9.6 CR. 3.54 rear w/ CR top-loader. IMHO, car is quite streetable running this setup. It will never idle at 800 rpm or sit in traffic all day, but that is OK w/ me.

THe single-plane TP intake is not going to give you alot of low-end power, but the torque of the engine and light weight of the car makes up for it.

[Mr.Fixit]

Streetability has no agreed upon meaning. I know guys who think that their 10 second, 14:1 compression drag cars are streetable because they have license plates. Some guys think any roadster is non-streetable because there is no roof. For me, if I can fill the gas tank at the gas station, and drive it without overheating, loading up real bad, or breaking anything, than it's ready for the street. Depends on if you want to drive a race car on the street, or race a street car. Dual 4bbls are definately more of a handfull to drive, but they are workable on the public highways.

[CobraMan]

Thanks. Streetable to me is that it can be driven easy on local roads or at highway plus speeds on the interstate without any problems. The looks are a different story.

I'll have to get the specs on my cam and solicit more advice.

[6T5 Cbra]

I've already been that route. My setup was similar to bmalone's above. I have a 390 and was running dual 500 Webers, .572 lift w/296° duration on the cam, 9.5 CR and 3.50:1 gearing w/tremec 3550. I agree with the above posts that the duals are 'streetable' but I decided to swap out to a single (Holley 770) as it is much easier to keep up with (maintenance/tuning).

Of course, I gave up a noticable bit of HP in the process, but in reality, the car still screams with more power than I'll probably ever use. Also with the single, no more 'loading up' at idle (read - 'eye burning').





Gene

[Michael C Henry]

Did Elderbrock start making tunnelport heads.The way I understood it tunnelport heads(round intake ports) go with a tunnelport intake manifolds.The Elderbrock heads are a version of the lowriser or Cobrajet.Maybe he is talking about a tunnel wedge intake w/ rectanglular intake ports.From my veiw a single four and a large air cleaner is the way to go.After the tunnel wedge intake height and the closenes of the dual carbs there isn't much of a place for an aircleaner under the hood of a Cobra replica.I have the twin 8 1/2" Stelling and Helling. they are altered w/the foam elements. I have the K&N elements in hand but alterations like milling carb flanges may make it possible to fit.Otherwise the hood will not close.The new carbs these days go beyond dual fours fuel control and adjustability. Then you have the secondaries to consider .Vacum secondaries will hardly open w/2 600cfm's.I ve already got them. If I had it to do over I'd go with a larger single four like a BG or an EFI setup and a large air cleaner up in the larger than traditional hood scoop to catch the cool air.

[SCOBRAC]

Edelbrock ONLY does Low- rise to Med-rise heads and the valve sizes to match.. Here is a tunnel port manifold for sale if you really.. I mean really.. want one.

http://cgi.ebay.com/ebaymotors/ws/eB...tem=1852547276

[CobraMan]

Well I guess with all the remarks, I think I'll stay with the single four. Dual quads really do look nice.

Thanks for all the input.

[Dennis Mosley]

I love my multi carb setup...some would say I'm nuts about it. I started my 428 as a 2x4 set up using Holley 600's that I had done at a local carb shop for the car.....Then I started thinking, if 2 is good wouldn't one or 2 more be better . Now my Cobra runs a 428 with edelbrock aluminum heads and a 6 duce set up....that's right folks 6 duces!

The car is very streetable and the people here in Texas will tell you, I drive it everywhere. This baby ain't no trailer queen. A 200-300 mile day trip is nothing for me and it never misses a beat. Does great around town as well.

The first comment out of someones mouth when I open the hood (after they catch their breath) is "I bet that thing is hard to tune with all those carbs"...answer....no! (it runs a tiny bit rich but so does my friends 428 running a single 4) OR " I bet you pass everything but a gas station"....answer no! The 300 mile trip I took this weekend had the cobra averaging 16 mpg maybe could have gotten better with reduced speeds but who wants to do that.

[6T5 Cbra]

The 300 mile trip I took this weekend had the cobra averaging 16 mph maybe could have gotten better with ......

Wow, just think about what 6 quads could do!......



Sorry, couldn't resist.

Gene

[CobraMan]

A veritable speed demon.

Here is what happened after my last post. I came across a brand new dual quad setup. The price was right. It is on its way to me. I will bring everyone up to date after I install it and drive with it for a few months.

[Dennis Mosley]

I guess that should have been "MPG" I will change the mph to mpg just to confuse everyone else

[6T5 Cbra]

Dennis,

What cfm were you running on the dual quads and now what are you running with the 6 duals? Any difference in performance?

I was running dual quads (500 cfm/ea) on my 390 and never could get more than 10 hwy/6 city. Always ran a bit rich though.

Gene

[Excaliber]

No doubt about it. A single four will give better over all performance and is much easier to "dial in" and maintain. MOST of the time it will provide as much HP\Torque as two fours will provide (often it will provide MORE). To much CFM on carbs is a VERY common problem, more\bigger is NOT better! You have to have a pretty radical motor to gain any HP advantage from two fours over a single four.

That said: Two four barrels look WAY cooler than a single four! And a set of Webers look even cooler than that.

Ernie

[Dennis Mosley]

6T5 Cobra,

I was running 600 cfm Holleys with my 2x4 set up. The Carb shop I used did a great job on the build and the linking of the vacume secondarys. Of course it was mathmaticly over carbed so it ran a bit rich but it wasn't too bad. Throttle response was great and the car was fun to drive.

The 6 duce set up uses a progressive linkage so that at low throttle I am only using 2 of the 6. You do notice when the others come in . each carb is about 275 cfm so at low throttle it's like running on one 600. The car is quick and has great performance on the street and hiway. I'm not a track guy so I don't have a point of reference there. It this point I do not see any reason I would go back to the 2x4.

[Mr.Fixit]

Three two barrel holleys are fun. The middle one is mechanical, the other two are vacuum driven. If you can feel the other barrels (or carbs) coming in, what you are feeling is the motor recovering from the bog it was in due to overcarburation. It is finally pulling enough air to get the velocity through the venturis high enough to work properly.

[Dennis Mosley]

My other carbs are not vacume activated....they are all mechanical. What you feel is me pushing my foot down and opening the other carbs. When I stomp on the gas and the other 4 2barrel carbs open your hinny gets pushed back into the seat had you feel it!

[edwhite7]

I have a 427 medium riser and have a dual quad setup. The carb size is related to whether the manifold is single or dual plane. A dual plane needs a bigger carb than a single plane. My current tunnel wedge (single plane) with two 450's works better than my Ford dual quad dual plane with two 650's. Both run a little rich at idle but the dual 450's have much better throttle response.

[snake farmer]

T.P.'s were designed to operate in a very narrow band @ high RPM. That was when cubic inches were limited by santioning bodies. Now cubic inches are only limited by dollors. A stroked big inch T.P. with dual quads works well with the right cam and tune. Edelbrock does not make tunnel port heads. A T.P. manifold can only mate with T.P. heads. Hold on , If you want the look, consider a Tunnel wedge intake 2x4, mated to med riser heads. Much more streetable with non stroker (427cid). I have a set of Holley 660 cfm carbs with center squirters on my T.P. Dove reproduces the Tunnel wedge intake as did Ford originally.

[edwhite7]

Dove does reproduce the tunnel wedge but I had to return mine three times before I got ont that holes in it that could at least be sealed. The first three were so porous as to be completely unuseable. One actually had a hole at the base of the plenum that I could pass my finger through. It was very hard to believe that anyone could have looked at this before it shipped. The manifold that I finally decided to keep has a hole between one of the pushrod channels and an intake port. This I could seal with epoxy. I also had to open up one side of the distributer hole because I could not get the manifold bolts to line up. As sone as I can find a replacement this will come off. I would stay away from Dove unless I could see the product first.