Smallblock 2x4 setups

[Captainkirk]

Hmmm....TQ's are rated at 850 cfm. x2 would be 1700 cfm. Little overkill for a small block don't you think? I would imagine that once the secondarys opened the venturi velocity would drop like a rock, which would as result in a severe lean condition.

The TQ's primaries are rated at 283 cfm. The secondaries' airflow is controlled by engine demand, much like a vacuum secondary Holley. Primary airflow on both carbs is a mere 566 cfm with the carbs at WOT until the engine demands more. Even though the secondaries are open, air and fuel flow are controlled via the secondary air valve. Sure, you've got 1700 cfm available, but doubtfull a smallblock would ever demand that much. The small, torquey primaries and close air valves would keep the engine vacuum (or manifold pressure) up; much more so than a pair of Holley double pumpers or AFB/Performers with their manual secondaries I think it would make an intriguing setup for a strip motor on a tunnel ram, or a nice street/strip setup on a dual=plane street manifold due to the spreadbore design.

 

[longarm]

do you know the i.d. numbers on the
big port 2x4 manifolds from offy and weind?
did any body else make a 340-360 2x4.
i've researched and not come up with any numbers.

 

[rumblefish360]

Longarm, Edelbrock used to make a 2 X 4 dual plane intake for the small block.
I do not have the larger port part numbers for the Offy's. I do not know if you have enuff material to port match the Offy small intake to a larger port window.
If you went this route anyway, I'd port it to it's max. height and not worry about it. Better to have an intake window to small or smaller than a heads intake port window to large.

 

[ramcharger]

No, because you would tune the carb for such use. YES, velocity would drop, but then again on a race intake and numericaly really high gears, it will not matter much.
You can also tune when the door opens and how much it opens alittle bit.
The smaller T-Q's are said rated @ 800. The primarys are smaller.

I don't know squat about TQ's, thanks for the info! I guess I'm just a dyed-in-the-wool Holley guy. And yes I agree, on a race intake at the strip with a high stall/high gears and WFO it wouldn't matter that much, but I thought "The Captain" was considering this for the street?

I have noriced that cfm formulas are not on line with what the car will do at the track.

I always thought it was was odd that a small block (of any make) would make more peak hp on the dyno with an 850 than a 750, which would be completely out of line with conventionally accepted formulas. Then again, no one drives a dyno and a dyno can't give you a reading of throttle response or idle quality, street manners in other words

Don't get to caught up in formulas, equations and dynos (both computer program & mechanical) etc. These are just tools and guidelines after all we race and drive cars not formulas, etc.

I agree, and I wonder if Smokey Yunic ever even used a calculator! I just can't help it sometimes, being an engineer by trade. Sometimes I forget that I had started building engines as a mechanic before I got my degree and real world experimentation and results is where it's at.

Buick did this on their 2x4 setup on their nailhead 401 and 425. These engines ran off the back carb during part throttle cruise because the primaries on that carb are closest to the middle of the intake. When you got to about half throttle the front carb started to open up and of course if you mashed the throttle both carbs were open fully. Being the carbs have different opening rates the front carb had the linkage mounted closer the throttle shaft than the back carb because it needed to open at a faster rate than the back carb.

Neat Idea! I would think that for this to work and allow fuel/air to all cylinders, the the carbs would have to share a common plenum. I'm not sure if the tall Offy top shown here http://www.offyparts.com/product_in...d/247?osCsid=eb79eb72db384df7161ee4f72e4bd1d5
or the low-rise version shares a common plenum. Hard to tell with just a picture.

When you run dual 4's you don't add up both carbs to determine the cfm of the carbs to use, it does not work that way.

Why is this the case?

I think it would make an intriguing setup for a strip motor on a tunnel ram, or a nice street/strip setup on a dual=plane street manifold due to the spreadbore design.

I've always thought that speadbore designs lead to fuel distribution problems? What's your thoughts on this Captain?

To all,

Please don't think I'm being a smart ***, I'm here to learn, and the only way to do that is to ask questions (and admit I dont know!).

 

[JR]

Edelbrock started making a air gap duel 4 intake for the smallblock chevy and fords, I wonder if enough people bug the hell outta them if they would tool up for a small mopar version. I would love to get one.

 

[rumblefish360]

Edelbrock started making a air gap duel 4 intake for the smallblock chevy and fords, I wonder if enough people bug the hell outta them if they would tool up for a small mopar version. I would love to get one.

It's just a matter of time. Ol'Vic Jr. over there does think of just about everyone. Even the big old Cad-do's have a performer. Granted, not everyone has what the Chevy camp has, but he does do a great job in surplies to the hot rod crowd.

ramcharger

Neat Idea! I would think that for this to work and allow fuel/air to all cylinders, the the carbs would have to share a common plenum. I'm not sure if the tall Offy top shown here http://www.offyparts.com/product_in...61ee4f72e4bd1d5
or the low-rise version shares a common plenum. Hard to tell with just a picture.

That intake is a tunnel ram. The Offy's have the low rise (pictured) in line dual quads and then a high rise in line dual quad. It's about, not that I've seen one up close, this is from memory, and old pictures, about 3 inchs taller, but looks very very similar. Instead of short runners and 2 -3 inchs in intake height, the taller versions runners were approx. something like 4-5 inchs long.

ramcharger

I've always thought that speadbore designs lead to fuel distribution problems? What's your thoughts on this Captain?

This is true. You have to overcome these problems or look past them to a degree. It's even more problematic on a intake like the MoPar M-1 single plane. There not easy to deal with on several levels. Perfect never enters the picture. Only good enuff. Run like hell it will, but with intake mods and a Holley/Demon, it'll run better down the track.