Shear Plates

[frnkeore]

What is the best type of shear plate?

Pictured are two types of about 4 variations that I found. One has a extension of 1/2" and a 7° taper (2"x2 1/4" exit), the other has just a radial groove around each throttle. The extensions vary, in length on others, 1/2" being the longest I found. Some have almost sharp corners at the bottom of the extension.

What's story, on what type works best or is it application derived?

[BOOT]

From what I understand shear plates have a Lip/edge to shear fuel from and a lot of times are also like a reversion plate. I would call the red one picture a Reversion and the clear a Shear but they basically do both somewhat. Technically a 4 hole spacer could be considered a shear plate if the edges are sharp-ish. But a shear plate that goes into the plenum doesn't add as much volume while adding velocity and shear if IE you have a tall single plane.

One of the Tapered spacers instructions I saw told not to polish/blend the tool marks(burr finish), I assume because it would loose what little shear it had and as mentioned in an old post that I like on here, "wet likes to stick to smooth". Honestly I'm not a fan of tapered spacers unless your just looking for WOT.

Some people cut/mill the carb pad opening larger to make the throttle plate kinda like one n help with shear/reversion. Many people bolt on large carbs w/o checking the plenum opening, EFI guys usually check to make sure their BIG TB isn't obstructed LOL

As with any spacer, each app is different and much be tested to see if it compliments yours.

Oddly enough I used a shear plate on a modded open spacer with a dual plane that had the divider cut-out, was the best setup out of what I tried on that combo.

[juuhanaa]

"wet likes to stick to smooth"

No,

What i see daily, but not when developing an engine.. wet/substance heavier than air tends to stick to the low static pressure/high speed area, but thats not necessarily an area we should be concerned about with wet flow. In other words, if you see raw fuel traces in the high static pressure/low speed area, and assuming its not a puddle you spilled on the table from a milk can, it won't stick.

So how much do we shear fuel by using a different shape at the spacer exit? And what percentage of the fuel do we divert to another area?



-juhana

[BOOT]

Fuel will puddle and run down a sheet glass A LOT better than a sheet of sandpaper or other rough surface. Sand and smooth parts of a block and oil will drain back faster.

The purpose of the saying is a general guide and works well as a simple reference.

It's like the Lefty Loosey argument, at some point the hand is going left tightening or loosening. Why I prefer clockwise or counterclockwise.

Ideally you wouldn't need to shear anything and the fuel would be perfectly atomized from start to combustion But we live in the real world were things are often not perfect.

[BOOT]

Oh and surface texture turbulent layer or blah blah blah w/e

[Lloyd klem]

I have dozens and dozens of variation s of both those pics.I call them bandaids for hatchet wounds.90 percent of the manifolds that come to me with plate in top pic ,it won't work correctly because they didn't allow enough area around it too.No stock plenum manifold will work without opening it a ton.The lower pic I have used several variation of to direct fuel.But they are never all 4 holes same length ,shape etc.With today's way over sized carbs being used allot of things come into play.What works on the Dyno normally doesn't work at track with a hood scoop.I have yet to meet anyone that has a complete handle on this.Many guys think they do!!I have come across some variation of design that work on split doms but in certain rpm areas only.I have learned through trial and error that anti reversion grooves can be more of use in the tops we make for our manifolds.You could literally go broke trying to r&d several designs and never have a handle on something that works well through the rpm spectrum you are trying.If you need every last hp ,have at it but most would be better off playing with open and 4 hole spacers that fit std plenum and be happy.Its another one of those people think they have a fix but truly are just lucky if they found something that works.I have had or worked on manifolds from damn near everyone that does performance engines.I have looked or tried their bandaid of the day and normally have to mod it to work at track or throw it in junk drawer with all the rest.Im not saying I know any more or less about allot of them.These high end race engs are one huge compramise.What helps cover csa needed does not help signal etc.You just work on area or span of rpm you need and forget the rest.Guys say to me well this builds torque.I don't care about that in my builds.Im never clear down range near peak torque but ?

[Walter R. Malik]

Anyone ever used a "Jenkins" plate...? In later years, Moroso used to sell them.
It was just a flat carb plate with tubes extending down into the plenum to contain some reversion.

Bill Jenkins used them in his tunnel ram manifolds and some NASCAR people used them in restrictor situations before they got revolutionary.

[steve cowan]

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Refer and Morrison shear plate I have had for years,used on a couple of 500hp sbc.
The tapered spacer is to fit standard carb pad size.
In this photo the tapered spacer is smaller than carb pad as it was a look and see.
A friend ran super stock gas class here in Australia with a 358sbc pro - stock truck engine 970hp and they turn around 9600rpm this was 15 years ago.
It had shear plates very similar, so my opinion is the reversion pulse is there no matter what rpm .

[steve cowan]

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This spacer made the best torque, hp and evened out lambda on the dyno on a 383sbc I dynoed in may this year.
A perfect matching 2" open spacer was down 15 hp with variety of afr in each hole.
Erland Cox opinion says the 4 hole helped speed up the air and fuel,dyno guys say the mis- match on the spacer perimeter helps knock down reversion pulse, for me it was just a shock as the engine sounded better from idle right up to 7000rpm.

[frnkeore]

This is what I'm working with. It's a Weiand TR, made for the 351C 4v and 8896, 4500, 1050 cfm carbs. Engine is 412 ci FE.

The 3/4" thick solid spacer will be mounted to the lower manifold, to make a IR system. The pic with the lower gasket is how it fits the lower, the black circle is a very rough indicator of how the reversion under cuts will fit the lower manifold.

The other 2 pics are with a upside down super sucker, 2" tall and will guild the flow, into the D shaped ports, creating a short, small volume (can be extended if needed), TR. Here those same reversion under cuts, will be fully exposed to the plenum.

What I'm after, in both cases, is to minimize the reversion, to the boosters.

What are your thoughts?

[1980RS]

Every time I used my 4 holed tapered spacer on a single plane intake my car picks up at the track. When I use that very same spacer on a dual plane intake my car slowed down big time, for me the open spacers work the best with my dual planes.

[Lloyd klem]

This seems common for what works in mountain motor world with split doms.Its something I'm gona work with this winter at track.We have whole different setup we use on the Dyno.

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[frnkeore]

Is there any consensus on which of the two shear plate types, I pictured, work best at protecting the boosters?