Thinking about a new intake manifold for a SBC

[Xnke]

I have a decent 1970s 350 that I picked up for 50$ last week in the corner of the shop, that is going to be the "putter around" toy for a bit. I was planning a 377 build, as the bores are practically perfect, using the 062 vortec heads instead of the 2.02/1.60 valved 624 castings that were on it. Appears to have been rebuilt, chewed a lifter, and was plonked on the floor. Had an iron 4-barrel dual plane intake on it.

The 624s aren't cracked yet, but the have a reputation for cracking and the 76cc chambers aren't going to help anything. A set of junkyard vortec heads is under 90 bucks, even new ones are under 600.

Since I will need a carb and an intake, (I do mostly 6 cylinder stuff so I don't normally have that kind of thing around) I am looking at using 3 weber 38DGES carbs on a "not quite a tunnel ram" intake. I've got stacks of weber DG/DF carbs collected so making a set of 40DFAV or 38DGES or 32/36DGAV carbs is nothing difficult.

I'm going for the Cool Stuff factor over the all-out power factor, but I don't want to throw 100hp away for some shine. The engine will be "show and go" type deal, I'll try to find an old pickup to build into a "muscle truck" toy.

So, 3.75 stroke, 4.000 inch bore, vortec 175cc heads that will get some bowl work and pushrod area work, with headers and intake built to suit. What size throttles do I need to be looking at here? 36, 38, 40mm? Long, crossed-up pairs of Intake runners or try to pair them in the firing order? Water jacket crossovers done differently?

What does speed talk think?

[Carnut1]

IMG_7595_2.jpg

At the last DV seminar I did a quick cleanup on these EQ vortecs. Very heavy and clean casting. These were cut for 2.02"/1.6" valves and pulled 275 cfm after 45 min. porting. They beat the stage 2 034 iron bowties I did the same night by a large margin. I would not hesitate using these on a street 383. Thanks, Charlie

[Xnke]

Can those EQ vortecs handle bigger springs and lift or are they like the summit racing vortecs that can't have bigger springs or more than .450ish lift?

[Carnut1]

I didn't check so I can't give an answer. Sorry, they are machined for studs and guide plates so that is a plus.

[MadBill]

...What size throttles do I need to be looking at here? 36, 38, 40mm? Long, crossed-up pairs of Intake runners or try to pair them in the firing order? Water jacket crossovers done differently?

What does speed talk think?

If the Weber 2 bbls flow the same CFM per square inch of butterfly area as an 850 CFM Holley, then 3x38 mm would be ~ 940 CFM and 40 mm would be a bit over 1,000. The 32/36 would be ~ 675. I'd say any of the three would be fine, but with all that effort to build a manifold, it would be a shame to choke it down with the 32/36s.

EDIT: I've just read that the 38 mm Weber is rated at 390 CFM, but at 2.5" Hg., and thus ~ 300 @ 1.5"hg, so 3x38 = 900 CFM.

[Xnke]

Fun part with the webers, I can start with 32/36 progressives and move to the 38/38s with zero changes-they only differ in throttle plate size and synchronous vs progressive throttle linkage.

I am toying with the idea of using the stock vortec lower manifold as a starting point, the spider-injection manifold. That would give a nice runner length to work with, a fairly large plenum area, and other than the ugliness of the EGR boss and some of the other protrusions and warts it looks like a quick way to get the project rolling. Other starting points include the Edelbrock triple-deuce manifold with a cut-and-shut for each of the carbs, the weber base is a bit wider than the Holley two barrels.

I think at this point it's time to find a vortec in the yard for parts.

[F-BIRD'88]

I would use the Edelbrock Dual quad RPM air gap dual plane hi rise intake manifold for the vortec heads and make up 2 bolt on carb adapters to mount 4 weber 2bbls on it. Be sure the adapters keeps the 180deg split plenum of the dual plane intake manifold.

It will look boss and run great.

[Keith Morganstein]

I would <snip> mount 4 weber 2bbls on it.
It will look boss and run great.

The 4 webers for sure! Especially if you already have them...


How about on a tunnel ram?

[Xnke]

Eventually it'll be a new casting, but the first will be a fabricated manifold. I've been doodling this afternoon, looking at the old IDA/IDF style manifolds, that Edelbrock Air gap mini-ram, and the holley hi-ram for the LS-all look pretty awesome.

Having never built anything other than a few blower manifolds and a single-plane sheetmetal manifold for V-8's, I'm getting hung up on things like runner length, packaging, etc. If I were to switch to DCNF's, this would be easy-they are more compact front-to-back than the DGAV/DFAV style carbs...and Ingalese did cast a few manifolds back in the day for the SBC, but it was an IR setup.

Weber DCNF's (I think theses were really made for the job, and were used a lot for just this sort of thing)





Vs the Weber DGAV, which is what I have a lot of, and am very familiar with.



The DGAV takes up a lot of room with the float being hung out the front of the carb like it is, so I could only fit 3 of them in there-maybe. At this point I need to figure up if I can run a single-plane style, with the progressive linkage on the 38/38 body, (which works fine) or a dual-plane, with the synchronous linkage on the 38/38 body.

[F-BIRD'88]

Another option is to run 3 of those webers on a carb adapter, on a single 4bbl dual plane or single plane vortec intake manifold.
Another way to skin the cat is to run 3 or 4 of your webers on a custom manifold plenum top, on the Vortec version Weiand/Holley Stealth Ram efi intake lower
manifold. Like a tunnel ram.

There is a Mercury marine Vortec EFI intake manifold Ram style that also could be run with a custom carb top. It is OEM on the Mercruiser Scorpion/Black Scorpion
5.7L and 6 L ski boat motors. These are all existing intake manifolds for the vortec heads.
If the manifold is a dual plane design than make the carb adapters split plenum design too.

[ptuomov]

How about this one, except with a modification: make the middle two runners on both sides cross the banks like in a cross ram:

F989BEFB-B474-47CD-86BB-435D5EED6A42.jpeg

[Xnke]

Doing this as a ITB setup is so tempting. I love the sound of ITB's. Especially on alcohol, but it would be difficult to get these jetted proper on alcohol. (jets and circuits too small) I could do 38DGES on one side of the engine and 38DFES (not a weber produced carb, I'd be building it out of weber parts) on the other side to get the throttles to all pull the same direction. (DG and DF are the same carb, just mirrored)

Better to just do the tri-power setup and have something neat that fuels fairly well. To this end, I'm thinking longish runners, bringing them up under the plenum, and I could run a single-plane style plenum, OR split the runners into a complicated dual-plane style plenum. This is a decision to make after I figure out the RPM range. Personally I've never seen the benefit to dual-plane manifolds except on rather sedate street engines, when compared to a properly sized single-plane. I'll have 900CFM of carb on tap, so I should figure on building an engine that can use that much carb, eh?

[MadBill]

Because the flow through an IR throttle occurs in less than 40% of the full engine cycle, it must be much larger than for a plenum system, so even 40 mm ones would be restrictive for a 377". (Not to mention needing very different calibration due to the pulsating flow.)

[ptuomov]

If one crosses over the center runners, one can put plenums in both sides. It’ll create a quite nice torque curve if the plenum volume is picked correctly.