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confusion. Copied from "other" forum is this a correct statement/observation?? I would rather have verification from this forum. Have been reading all I can on Holley's and ordering all books on the subject. What say 'yall.
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Yhey aren't talking about main jet, if that is what you are asking.

They are referring to some metering blocks that have the idle feed restriction jet(more commonly referred to as the Idle Feed Restriction or IFR and not as a "jet") buried in the metering block rather than exposed at the face. These are typically OEM spec or emission spec metering blocks, and not used on any of the carbs considered Performance carbs by Holley and most others. Most common on Chrysler and Ford OEM application from the smog 1970's years.
 

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IIRC, the IFR 's in my list 9776 450 cfm mech sec carbs are " buried" . Since these carbs are marketed as a tunnel ram / dual 4 bbl carb , I'd consider them "performance" ??
 

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IIRC, the IFR 's in my list 9776 450 cfm mech sec carbs are " buried" . Since these carbs are marketed as a tunnel ram / dual 4 bbl carb , I'd consider them "performance" ??
The original application was for large 4 cylinder and small V-6 application....they have been "bastardized" into tunnel ram service because of their cfm rating, same with guys using two of the 390cfm Vac Secondary because of it's size....the450's actually make terrible TR carbs to tell the truth, if you are using the TR to actually make power. Street poser/street rod cruiser TR carbs at best. They weren't actually designed to be tunnel ram carbs.

Two 450's wil not flow 450 cfm each when the airflow demand is split between two of them, actual flow maxes out in most cases at about 370 cfm each.

Places like Summit, and even Holley has now started calling them TR carbs, but that don't make them great choices.

The 660cfm centersquirter L-4224 that Holley recently discontinued was the good TR carb for small blocks and smaller size big blocks, along with the L-6709 750cfm near 1:1 linkage double pump and the long discontinued 830cfm centersquirt L-4223.
Most serious guys now just rework regular double pumpers with 1:1 linkage links.
 

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So , with all that said , it boils down to your definition of " performance,, " all out track performance or street performance . If those of us who are street guys don't measure up to your definition , there's really no reason for you to be demeaning , its two different pursuits , that's all .. FWIW , I'm well aware that 2-450 don't make 900 , more like 7+ which is more than enough on a mild small block..
 

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Sorry, didn't realize it came across that way. I'll try to keep that in mind.

You are right, my thinking is why run a Tunnel Ram if you aren't really going to use it.

The 450 mechanical with no rear accelerator pump is difficult to make work in a more serious performance application due to that lack of rear pump and somewhat odd, hard to alter meterng.
 

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" why run a tunnel ram if you aren't really going to use it " You just can't help yourself ....:sneaky:
Something in your craw?

Some blocks have the IFR's moved to the bottom of that same channel as a popular upgrade change. Usually on aftermarket blocks.
 

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Something in your craw?

Some blocks have the IFR's moved to the bottom of that same channel as a popular upgrade change. Usually on aftermarket blocks.
Yes , folks who make blanket suppositions & folks who are foolish enough to think their way is the only /best / worthwhile way ........among other things :rolleyes:
 

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You are right, my thinking is why run a Tunnel Ram if you aren't really going to use it.
Eric admitted wrong, then corrected it to an opinion piece yet your still not okay with it?
This is Bonecutters post and seems to me it's his place to take it how he wants to read it. I personally agree with Eric but I also don't go for show, I go to win.
In any case, some carb retuning is likely gonna be needed to make it all work the best it will. Especially to the idle metering.
 

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Discussion Starter #12
HEY, GUYS, easy, I gained insight from everyone. I respect any of you on this post that have an opinion whether or not I agree at the moment🤐
 

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Discussion Starter #13
Next Q, e72, IF 450's only yield 700 I have seen 454s and bigger with T'ram with 390's. What is there yield??:unsure:
 

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Hrd to say exactly. Carbs are flowed at a specific vacuum for easy comparison. A larger engine might pull on the carb harder and result in flowing more than a smaller engine so a hard number isn't always telling you anything. I'm not qualified enough to take any guesses worth anything but I'd say 2 390's at around 550cfm each are somewhere about 750-800 total.
 

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............"but I'd say 2 390's at around 550cfm each are somewhere about 750-800 total"
It might just be me, but the math does not add. I think the formula for CFM flow is that it is reduced by, I think 1.5
correct me please if I am not understanding, am I reading this all wrong?
 

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It will be less than their rating due to the engine's vacuum signal being spread across 8 barrels rather than 4. A big engne like a 454 could get them to flow their rated amount, or even more, but it will be a rather severe restriction to peak power if you are looking to make the amount of power the tunnel ram could be capable of making.

Putting these small carbs that together only flow what a single carb could is just a way or crutching a tunnel ram to try to force it to do something it isn't designed for really. It's just an attempt to try to make it more low rpm freindly.
Not a whole lot different than guys running the 750cfm Dominator on a mild engine just for the looks. You could easily get a more common and better venturi sized 750 Vacuum Secondary to do the job and run better, but they want "the look" and are willing to sacrifice potental power for the look.
 

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Discussion Starter #17
I was questioning johnsongrass1' last sentence
I'm not qualified enough to take any guesses worth anything but I'd say 2 390's at around 550cfm each are somewhere about 750-800 total. Math ?
 

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I was questioning johnsongrass1' last sentence
I'm not qualified enough to take any guesses worth anything but I'd say 2 390's at around 550cfm each are somewhere about 750-800 total. Math ?
Maybe a typo and he meant to type 350 cfm?

Or he may be more familar with the "390 Nascar" spec mechanical secondary carb, i thnk I recall that tuned up and blueprinted for them it will flow close to 550 cfm as the restricted engine pulls 3-4" vacuum at peak rpm..
It's not the same carb as the 390 Vacuum Secondary you see some TR with.
 
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