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  #16 (permalink)  
Old 07-10-2004, 01:59 PM
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The 390s are going to run too lean. 450s just barely cut it on my 5.0 that I had the tunnel ram on. The idle circuits are just too lean on the 390s.

Musky2,
There was ice on your Offy because you had a fuel leak in one or both of your carbs. Fuel is a coolant. With a tunnel ram, the cooling effect is greatly increased. You were running rich.

If you want show without go, then run a tunnel ram on the street. I think it is cooler to have a faster car than it is to have a poser car.

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Old 07-10-2004, 05:00 PM
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390 vacuum sec carbs will work on a tunnelram setup . After i had built my set up ,I was in the process of tuning my carbs,and i asked if any one on here had experience with a tunnelram set up,with tuning the carbs.. One of the moderaters on here(Willys36} helped me tune my set up along with camaroman,and 1bad80.. but at first Willys36 told me i would be better of running a set of 390 vac-sec carbs,cause the sec-plates wouldnt come into play until they was needed..NOW his advice was only for street use driving,not drag racing. But i already had what i had,so they helped me tune them.. I went to a local car show and there was a truck that was running a set of 390 carbs on his 350.. so yes i know they will work.

Quote:
Originally posted by lluciano77
The 390s are going to run too lean. 450s just barely cut it on my 5.0 that I had the tunnel ram on. The idle circuits are just too lean on the 390s.

Musky2,
There was ice on your Offy because you had a fuel leak in one or both of your carbs. Fuel is a coolant. With a tunnel ram, the cooling effect is greatly increased. You were running rich.

If you want show without go, then run a tunnel ram on the street. I think it is cooler to have a faster car than it is to have a poser car.


Just because your 5.0 was slow ,doesnt mean everyones else's is.. I have a fast car,and believe me,its not a poser..To bad you dont live close to silverdollar raceway here in georgia,cause I would show you.
He** i would even let you drive it, and feel the power.
Im not saying a tunnelram setup is better then a single carb setup,but what i have now is badddddddddddddd. period..

Last edited by Robbie; 07-10-2004 at 05:00 PM.
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Old 07-10-2004, 05:01 PM
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I'll stick by my two vac secondary 390's recommendation for a street engine. After all, that gives a healthy 780cfm potential which will serve a small V8 very well thank you! Just take your time and tune them properly. Any carb is a good carb, problems come when someone who doesn't know what they are doing tunes them improperly. Holleys, Carters, Edelbrocks can be dreams or nightmares, just depends on if you know what you are doing. Avoid the siren's song of bigger is better for carbs. Sure you can run two 1000cfm Dominators on the street but why? If for looks then by all means go ahead. I run a Holley 950cfm 3-bbl on my 354 for the look but I modified it so it runs more like a 650cfm @ part throttle (see inserts I made for the primary throttle bores in photo). Yes it is a racing carb but notice that Holley designed it w/ vacuum secondary. Wonder what they knew? However if you are after performance and economy (a well designed hot rod engine), then go with a properly sized vacuum secondary carb setup.
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Old 07-10-2004, 07:56 PM
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CFMs are one thing. Metering is another.

Changing airflow ratings without changing the air bleeds and fuel restrictions is lame. You end up with a carb that never quite works right. Like I said you need a flow bench and a dyno to properly adjust thes parameters. Experience helps too.

Again, the 390s are to lean. The airflow totals may be good, but the metering is way too lean. Take a look at your exhaust valves. They either are or will be white as a ghost.

A sleeved 950? Did you adjust anything to compensate? Did you enlarge the air bleeds, PVCR restrictions, idle restrictions, change jetting, anything? If not, I can tell you right now for sure your carb isn't metering right.

Vacuum secondaries? I know what they knew. They knew if people had a carb that was too big, it would be a lot more forgiving with a vac. secondary. You get better customer response, and can sell a lot more carbs that way. I'm not saying they don't have their place. I have one on my SBC 400 right now.

A 1 barrel carb might "work" for your engine, but would it work best? A tunnel ram and two fours might work for your engine. Show or go that is the question.

Oh yeah, and was my 5.0 fast?

The front wheels came off the ground.

It beat my friends GTO by a few car lengths. The next day his car ran low 12s all day long.

Last edited by lluciano77; 07-10-2004 at 07:56 PM.
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Old 07-10-2004, 08:50 PM
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Small carbs tuned for small engines can and do work well on 2X4 applications. The 390's being discussed are such carbs. When you double them up on a tunnel ram you're also doubling the fuel area. That's why they work. Holley recommends them for that particular usage because of the fuel curve.

When any carb builder specs a part number for a 2X4 application the air bleeds, emulsion circuits and supplied jets are downsized considerably.

The whole reason behind using multiple strombergs in the old days wasn't for the extra airflow, it was for the fuel curve. One or two of them wasn't enough for a 327, it ran too lean no matter what. Four or six of them was just right, together they would allow anough fuel to pass to keep it from running lean.

Take a pro stock engine in a fine state of tune and remove the tunnel ram, use one of the carbs by itself, with no changes, on a 1X4 intake and it will be too lean to work because you just cut the fuel in half.

The 390's in question will work on a tunnel ram because one of them would be too lean to use by itself.


I disagree with you on Musky2's icy manifold. Fuel may cool to a degree but only fuel changing from liquid to a gaseous state could form ice on an intake. If anything the carbs were slightly lean and only fuel that was atomizing well enough to cause a temp drop of that magnitude.

Not try to insult or bust anyones chops here. Please don't get mad.

Larry
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  #21 (permalink)  
Old 07-10-2004, 09:25 PM
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That is true, you are doubling the fuel area. But the flow isn't exactly double for each carb.

Holley most definetly does not recommend using two 390s on a V8. The 390 is recommended for single carb applications on small dispalcement V8s and performance 6 cylinder engines with aftermarket intakes.

If you ever get the chance, take the powervalve gasket out of one carb on a dual carb setup. Let the engine run for a little bit. There will be dew and ice forming. It is because of the over rich condition. The excess fuel does evaporate inside the tunnel ram plenum.

Running lean will not cool things down. Think about it.
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Old 07-10-2004, 10:23 PM
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http://www.holley.com/HiOctn/ProdLin...SC/0-8007.html

Third line down under Features.

A lean burn most definately causes higher combustion temp. A liquid converting to a gas will reduce ambient temps in the immediate area, hence the ice on the intake.

Larry
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Old 07-10-2004, 10:23 PM
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A well thought out tunnel ram intake and corresponding two four barrel carbs will out perform a single four barrel system hands down. The trick on the street is to keep runner size long and narrow, to help with low speed operation. Tuning for driveability is the issue and requires some work. However, you cannot beat a tunnel ram for high speed operation.

I will say this, however. I do, however feel it's a waste of time to use one for performance if you don't intend to twist it over 6500 RPM. If your intended RPM range is under this, I would probably stick with a single four barrel.

On drag engines that I have dyno'd, I have seen as much as 75 or more horsepower increases with a tunnel ram vs. a single four barrel system. They just work that much better over 7000 RPM, and even though they seem "old school" they are still the ultimate carburetion system. I firmly believe that the atomization capability produced by the large plenum of a tunnel ram offers better top end horsepower over injection.
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Old 07-11-2004, 12:29 AM
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Quote:
Originally posted by coldknock
http://www.holley.com/HiOctn/ProdLin...SC/0-8007.html

Third line down under Features.

A lean burn most definately causes higher combustion temp. A liquid converting to a gas will reduce ambient temps in the immediate area, hence the ice on the intake.

Larry
That is a new description they added recently. I have a few older Holley books in my bookshelf and none of them recommend 390s for 2x4s.

I have used two 450s, two 600s, and two 750s. The 600s were about right for my 5.0.. The 750s were a bit too much. When I used the 450s, the mixture was lean all around. The idle circuit was insufficient, and the top end (PVCR area) was inadequate.
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Old 07-11-2004, 12:40 AM
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tunnel ram

LLuciano 77 ; you might be right about the carbs were running rich or leaking on my old Offenhauser because : that was the first tunnel ram I ever tried out , I brought it from Calif. around 1972 in the back of my 64 327 , 365 horse Jeep . I was young and dreamed of running this polished ram , especially in L A my original home . I sold the 327 and replaced it with a stock 327 in the jeep and believe it or not it ran pretty good , but yes it was well over carbureted with two 600 Holleys ; so you were right about that point . Now I dont understand what you are saying about show and no go ! Seems to me if I am running the well set up tunnel ram on my highly modified 350 Chevy 55 that I would be show and go not just one or the other . Do you really believe that the same two cars with the same engines but one with a single 4 barrel and the other with the tunnel and two 4 s that the single 4 car would win ? Im not brilliant but ! Ill leave it to the experts so youll carry on so I can learn . never too late they say !
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Old 07-11-2004, 01:08 AM
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Quote:
Originally posted by lluciano77
That is a new description they added recently. I have a few older Holley books in my bookshelf and none of them recommend 390s for 2x4s.

I have used two 450s, two 600s, and two 750s. The 600s were about right for my 5.0.. The 750s were a bit too much. When I used the 450s, the mixture was lean all around. The idle circuit was insufficient, and the top end (PVCR area) was inadequate.
That's the very reason my next carb purchase will be a Race Demon RS. Adjustable everything. No tiny drills or impossibly small chunks of brass needed. One carb does it all.

This was all so simple when I didn't give a hoot about the last hundredth of a second.

Larry
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Old 07-11-2004, 01:10 AM
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Quote:
Originally posted by lluciano77
A sleeved 950? Did you adjust anything to compensate? Did you enlarge the air bleeds, PVCR restrictions, idle restrictions, change jetting, anything? If not, I can tell you right now for sure your carb isn't metering right.

Vacuum secondaries? I know what they knew. They knew if people had a carb that was too big, it would be a lot more forgiving with a vac. secondary. You get better customer response, and can sell a lot more carbs that way. I'm not saying they don't have their place. I have one on my SBC 400 right now.
That's bad news! I have only gotten 15 years of trouble free daily driving out of this setup @ 15mpg. I was hoping for 30 years but I guess it will blow up B4 then? Of course I changed the metering with the new barrels, like I said these carbs are great if tuned properly. I set up all my custom carb installations w/ an Edelbrock O2 sensor so they are optimal at all driving conditions.

And the 950 and 1050 Holley 3-bbls were designed for NASCAR, not the street market. You had to special order one and the box said "not for street use". And they came race ready as vacuum secondaries. They were never made as mechanical secondaries. Couldn't have been too bad, NASCAR banned them after less than 2 seasons for being too good!

Again, I have seen and installed many dual 390s on medium sized engines and they work marvelously if tuned properly. They are no different than 650s or 750s etc. as far as metering tuning goes. Jet, secondary spring, power valve, and accelerator pump them correctly and they purr! And some of the cars can lift the front wheels too. One thing they do provide is better off idle response which is preferable for the street. For sure if you want WOT performance at the drag strip @ 8,000rpm, go for the 750 or 850.
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Old 07-11-2004, 02:15 AM
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A tunnel ram with dual carbs should give an easier time of equalizing the mixture to all cylinders shouldn't it? -that way if you have 1 cylinder rich or lean, you can change the jet on the corresponding barrel...
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Old 07-11-2004, 02:33 AM
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I am realy likeing this info guys, keep it comeing.
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Old 07-11-2004, 05:01 AM
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im loving it
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