Shear Plates

[mr348-409]

Has anyone used Shear Plates under the carburetor to help with the bog and backfire problem that comes with a tunnel ram type intake? Any ideas or input is appreciated. Thanks.

 

[61-63]

Shear plates help with atomizing the fuel as it leaves the base of the carburetor I'm not sure how much they help with bog or backfire. But I'm not the expert here so will be interested in what others have to say.

 

[La Hot Rods]

Shear plates are to help settel the pulse in the intake and increase the signal to the carburetors.
If you are stomping the throttle from idle and have a stumble you need to get a bigger accelerator pump shot to cover the slow moving air through the carburetors until the air speeds up. Or you need to be leaving at a higher RPM.

 

[MRHP]

I have tuned many dual quad/tunnel ram set ups. Shear plates won’t help your symptoms. You need more tuning. Either carbs, timing, or ignition issues in my opinion. Tunnel rams are a different animal altogether, as you are finding out.

 

[Ishiftem]

Shear plates or anti reversion plates are meant to help isolate the carb from pulses in the intake. Like others said, they won't fix your problem. You have other issues.

 

[wristpin]

What carbs are on it? Newer Holley acc pump squirters that have longer style nozzles will help with initial atomization as will blocking the lower 3 levels of idle fuel holes in metering blocks. The rest is as the other guys said

 

[mr348-409]

The car has dual quick 850s on it now have tried 650 750 and800 edelbrocks over the years ,different intakes higher stall motor has this bog and backfire just bringing it up on the 2 step unless I have it running at 1800 rpm at idle and leave then at 5500 then it will go Even changed the cam timing from 109 to 112 which is straight up on the marks this made it worse Open for new ideas for the winter

 

[MRHP]

What does the timing curve look like?

 

[mr348-409]

run the timing locked at 37degrees

 

[La Hot Rods]

Set your cam timing to the best cranking compression.

 

[Barry Taylor]

What size squirters do they have!

 

[Ishiftem]

Backfire through the carb or exhaust? Does it only backfire on the two step or when you come off of it? When on the two step do you have the throttle all the way open?

 

[mr348-409]

The backfire is like a huge bog when you just step on the motor when you bring it up on the 3 step or it even hesitates real bad when you just open the throttle with no load

 

[mr348-409]

will check the size on the squiters on the 850s

 

[MRHP]

What ignition system do you have, and what is your plug gap? Do you know what number power valve you have, or are they plugged?

 

[Tooth]

Ralph, we talked about rotor phasing, excellorator pumps. Has it back- fired sense you had a valve job? You put it through a leak down test and it was blowing back up through the intake and carbs. Valves were not seating. It's my personal opinion that the heads are very large!!!! 400cc intake runners, and large intake plenum, fuel isn't atomizing at low r p m. 482 cid and 11.0 compression will require you to leave at higher rpm not off idol. Leave at 5500 and shift at 7500 and see how that works. BIG HEADS REQUIRE MORE AIR AND FUEL.... How many people are running Z-12 heads on less than 500 cid engines. Call Carl he would know. Example: Dart BBC 360cc heads are too big for a 396/427. Referring to intake runner volume.

 

[scott hall]

I’m not a smart guy but when I had this trouble I changed to an annular booster and the problem almost completely went away even from an idle. If your carbs are dog leg the signal with low vacuum will not pull enough fuel. The annular will help. At least it did for me.

 

[Iowa 409 Guy]

Cut the crap about not being the smart guy Scott. Your experience on roundy track and at the strip is invaluable.... I can look stuff up but don't know sheet...
Well, just enough to be dangerous.

https://www.motortrend.com/how-to/best-carburetor-booster-design-racing-carburetors/#:~:text=Additionally%2C%20while%20annular%20boosters%20do,see%20on%20the%20race%20track

 

[scott hall]

Dave there's many to argue that. I met up with a smart guy Sunday. He was kind and didn't make me feel to not smart but it was obvious i was.

 

[blkblk63ss]

when I had this trouble I changed to an annular booster and the problem almost completely went away even from an idle. If your carbs are dog leg the signal with low vacuum will not pull enough fuel. The annular will help. At least it did for me.

I'd say you are correct.