Has any one used a "powerblast plate"

http://www.thompsonperformance.com/shop_products.html

A friend sent me a link to this and I thought it looked interesting. I was curious if any one had any experience with it?

 

interesting....

 

I found this page with a 10 min. video. At the 7:15 mark they have some dyno graphs. Not sure on the motor used for the test but the numbers looked good. For 40 bucks it might be worth a try. http://www.thompsonperformance.com/

 

No experience with the device but I've learned enough studying airflow at the various points throughout an engine in my lifetime to understand how such a protrusion could affect airflow around the booster. In fact, some older engine/intake manifold designs required staggered jetting and booster tabs or spivots to correct fuel distribution issues. Here's a factory installed version to give an idea of the concept.

http://image.superchevy.com/f/21311...barrell-carburetor-fuel-distribution-tabs.jpg

Is there really a definitive problem with improper atomization during the pump shot on partially opened throttle plates? Especially considering that fuel will just recollect/bunch it back up before slipping through the cracked throttle opening? If you look at the fuel coming into the manifolds plenum you will see fuel shearing past the edge of the partially opened throttle plates. IOW, turn the pump shot into foggy ultra fine mist up near the entry of the carb and it still regathers and blobs back together to get past the throttle plates anyways. TBI and many of the newer EFI throttle bodies will have similar fuel puddling effect because they too release fuel above the partially opened throttle plates.

The other thing to consider is that many/most intake manifold designs, even the newer ones, do not allow a fully homogeneous fuel mixture(even if it was attainable with gas/has to be REALLY hot and detonation resistance goes down the tubes) to make it all the way from the carbs accelerator pump and booster to the combustion chamber. The valve seat and the perimeter of the valve are the final venturi in the overall equation and have far more to do with atomization than any carb or EFI will probably ever offer. Even direct injection into the chamber at ultra high pressures has a hard time competing with the homogenous mixture that a well tuned venturi design can allow. At least until the partially atomized fuel mass moves too quickly and fails to stay attached to the short side radius of the traditionally dog legged shaped intake port.

Something else to ponder here as well. Why did Holley move the vent tubes, pump squirter and even those seemingly insignificant little air bleeds out away from the throttle bores of their newest ultra XP designs?

Because every little bit helps when it comes to airflow and mixture stability. Also the same reason a Dominator of same size venturi and throttle bore will flow more air than its smaller footprint 4150 series counterpart.

IMHO, there is usually far more to be gained in the way of throttle response and AFR consistency with a properly tuned carb(fuel and ignition curve) than expecting some simple bolt on device to "fix" those shortcomings.

 

I decided to gamble and try it. Holy crap it helps with the throttle response. The difference is definitely noticeable.

 

Expensive solution for the wrong squirter size . The pump shot is done in what a second or less at WOT, or when the blades stop. After the transition there is no fuel from the squirters.

 

hmmm....now when i was 16 (1991) i tried something an older guy told me. he gave me a piece of copper screen and told me to put it under my carb on my mustang and make sure to use gasket maker to seal it good. i actually could tell a big difference in the response and power in that little 171 v6. (74 mustang 2). so a year later when i got a 70f100 pickup with a 302 i tried the same thing, but it killed the power. i always wondered if that screen on the 302 killed the air flow to much.

 

very interested.

 

I have not been in the classic car game very long and I am a novice when it comes to carburetors. I do not have the experience that some have of knowing how to fine tune them. In the future I will have that knowledge for sure as I experiment more. But right for right now I am limited in what I can do. There was a noticible increase in pedal response and Now my WOT response is almost instantaneous. So with fine tuning and experience this plate might not be necessary for some, but for others like me that are still learning I would definitely recommend it.

 

Just ordered one for a friend's 670 Street Avenger, supposed to be here tomorrow. Local guy that builds race and high performance street engines says it cured a stumble that he's been trying too get rid of for some time. We'll see...

 

Keep us posted on how it goes.

As an FYI, and you may already know this, but even the newer/smaller Holley's respond to this mod when the engine size is smaller. Smaller'ish cylinder volume displacement engines reaction to even a 600cfm rated carb tends to be more similar to a bigger carb installed on a medium or larger engine. I do it to all my own personal carbs and it seemingly helps the secondary opening transition phasing to become more tuneable. Kinda like adjusting the IFR sizing to allow the adjustment screws to be dialed in closer to ideal. Ideally you use the secondaries to fine tune idle rpm after the primaries have been properly adjusted to the t-slots. Every little bit helps and adds up.

http://racingfuelsystems.myfunforum.org/Vacuum_Secondary_Diaphragm_Signal_Tube_about205.html

The other thing I come across as one of the more consistently seen rookie carb tuning mistakes is the front throttle plates adjustment on the t-slot. Get that relationship closer to wrong, often just for the sake of taming idle rpm down, and you will be chasing your tail round and round with one form of compromise after another. Most try to semi-successfully cover the tip-in stumble with more pump cam/squirter size.

And base timing is usually way too low as well, some people even adjust their idle speed by reducing it which is downright silly from a power and efficiency standpoint. Then add another fatal blow of not having full manifold vacuum running to the distributors vac advance pot.. which just adds insult to injury when trying to tune for maximum manifold vacuum. People seem to either not understand or quickly forget that it's the higher manifold vacuum that makes the carb feel smaller and more responsive to tuning changes. Carb's are pressure differential devices and very forgiving even when the calibration is pretty well off the mark. That's the main reason why we can put a big Dominator on a small block and little 2bbl on a big block and they still make more power with steadier AFR's than anticipated. But if you allow the idle/part throttle ignition advance to become too far retarded from what it wants for best t-slot/booster transitions.. then the carb goes even further outside its available self-compensating abilities.

Sorry to ramble.. just trying to help anyone who will possibly understand the words. That and I seem to be running from work today. I'm getting soooooo sick of grinding on parts!

 

My friend installed his power blast plate last week. Says it got rid of an off idle stumble and a stumble when accelerating from cruise. Didn't notice any other differences. This is on a goofy 670 Street Avenger on an NA 347 that we've done a lot of work to to try and get it to run right; QF metering block with replaceable IFR and PVCR jets, much bigger jets front and rear. Out of the box the carb was very rich at idle and lean at WOT.

 

Is he happy with the result?

 

I think he's satisfied, it seems to have taken care of the problem he was having.

 

Most people don;t run sufficient base timing to maximize manifold vacuum levels(you know, the part that stays with you when the vac advance pot suddenly drops away during abrupt heavy throttle). This weaker signal to the carb causes the transition and metering issues and most just toss more fuel at it, usually in the form of a bigger more immediate pump shot, to minimize the perception of the issue. The initial should be set to whatever number makes the most manifold vacuum.

If you ever want to blow his mind on how that carb could act 1 size smaller, be more responsive with improved metering consistency?.. help him "test lock" the timing to around 36° and retune the mixture screws. Then tell him to drive down to the end of the street or driveway to test out all the extra torque. If it starts breaking up or lean surging at steady state cruise then you'll either have to break out the airbleeds(small wire stuffed into the air bleeds works pretty well for quick testing) and/or get back into the IFR circuit sizing. Or pull timing back out till it better matches the carb's current existing calibration. Ideally you give it more timing and then it will want more fuel as the cylinder pressure/manifold vacuum and rises.