Engine Power valve

Treneth · Apr 13, 2020

Do you guys think my power valve is shot? And is there any other ways to test to see if its shot?

So I have a holley 4150 800cfm carb, car was running rich I confirmed that by installing AFR gauge. Getting like 10s 11s partial throttle, idle was low 12s WOT seemed pretty good. So I jetted primaries to #68. Then started messing around (not actually knowing what im doing) with the idle set screws and actually had the best vac with them turned all the way in which from what I understand if it does not kill the engine its blown.

Now when I hammer on throttle it goes sluggish and leans right out. I've got a 6.5 power valve right now I get 13inch vacuum in park and 10 in drive with brakes applied. Thinking my power valve is shot and is likely to big anyways?

General karthief · Apr 13, 2020

That's a big carburetor, I take it this engine is putting out big hp numbers.

Treneth · Apr 13, 2020

Lol no it's not maybe 370 tops?, it's how I purchased this car from a guy who I think had the mentality bigger is better. Im not about to go and purchase a new one at the moment so I'm trying to make it work.

General karthief · Apr 13, 2020

From my limited memory of carburetors it is going to take some tuning to get it to work unless the previous owner did it already, go to the holley website and see the tech pages.
That's what I would do, actually I would buy a 600 cfm carb and go from there, not knowing what the previous owner has done to it you may be chasing your tail.

Treneth · Apr 13, 2020

General karthief said:
From my limited memory of carburetors it is going to take some tuning to get it to work unless the previous owner did it already, go to the holley website and see the tech pages.
That's what I would do, actually I would buy a 600 cfm carb and go from there, not knowing what the previous owner has done to it you may be chasing your tail.

If I'm to be honest from what i can see I dont think he did anything, just plunked it on and used it as is, he thought it was a 750cfm but when I looked at the list number it says its 800cfm. He's only ever used it on track WOT few times a year, where I'm trying to use it street/strip and be all street this year due to this virus and closing the nearest track.

JD1964 · Apr 14, 2020

Unless you have a high rpm big cubic inch engine, 800cfm is too much. The result is reduced velocity at the venturies and that makes it difficult to dial it in correctly.

Monkeybutt2000 · Apr 14, 2020

Isn't this s 351w? This kind of info ALWAYS helps.

Treneth · Apr 15, 2020

Monkeybutt2000 said:
Isn't this s 351w? This kind of info ALWAYS helps.

Yes 351w.

junkyardwarrior · Apr 15, 2020

John Dirks Jr said:
Unless you have a high rpm big cubic inch engine, 800cfm is too much. The result is reduced velocity at the venturies and that makes it difficult to dial it in correctly.

Depends on the boosters, blocks, baseplates, throttle bores, shafts, and a bunch of other things. There are more than one style of each.

"too big" is meaningless. Too big for the tuner? That happens sometimes.

JD1964 · Apr 15, 2020

junkyardwarrior said:
Depends on the boosters, blocks, baseplates, throttle bores, shafts, and a bunch of other things. There are more than one style of each.

"too big" is meaningless. Too big for the tuner? That happens sometimes.

800 cfm is just that. How are the throttle bores (carb body) changeable? I suppose you could put a base with smaller blades but how is that going to work with a body designed to flow 800cfm. You gonna run the air through a larger body bores and try and neck it down past a smaller base plate opening? I can’t imagine how that would

Considering a naturally aspirated engine is basically a mechanical pump that will pull a fixed amount of air related to the crank rpm. There’s rarely any measurable benefit from an oversized carb.

General karthief · Apr 15, 2020

It would be possible to 'de' tune a big carburetor for a mild build but you need extensive experience with doing this, is it worth the trouble, no.
On top of that you have no idea what has already been done to this one and if it was done right, it may work fine at wot but it is going to be a turd every place else.

2000xp8 · Apr 16, 2020

I'm no carb expert that's for sure.
But I would think we are missing the most relevant information about engine, the heads...

Treneth · Apr 16, 2020

2000xp8 said:
I'm no carb expert that's for sure.
But I would think we are missing the most relevant information about engine, the heads...

Stock.

2000xp8 · Apr 16, 2020

Treneth said:
Stock.

Stock from what vehicle?
Cam?

Treneth · Apr 16, 2020

2000xp8 said:
Stock from what vehicle?
Cam?

79 block I beleive, D9ae-6015-ed-21

It's a street/strip cam I'll get you the cam specs within a week when i return home from work.

2000xp8 · Apr 16, 2020

Treneth said:
79 block I beleive, D9ae-6015-ed-21

It's a street/strip cam I'll get you the cam specs within a week when i return home from work.

You should do some research on that engine.
Some of the history guru's may be able to figure it.
But i'm thinking right now you could be significantly off on the horsepower.
If it's the 79-83 era there wasn't a whole lot of power in any 351.
It's also not a roller block.

IMO, the same rules apply to carbs as EFI intakes, you use as close as possible to what you actually need and things always run better.

Treneth · Apr 24, 2020

2000xp8 said:
You should do some research on that engine.
Some of the history guru's may be able to figure it.
But i'm thinking right now you could be significantly off on the horsepower.
If it's the 79-83 era there wasn't a whole lot of power in any 351.
It's also not a roller block.

IMO, the same rules apply to carbs as EFI intakes, you use as close as possible to what you actually need and things always run better.

I very well could be way out on numbers, that's based off dyno 2000 program which I realize aren't all that accurate.

I did however change power valves and played some more with idle mixture screws and I'm not saying it's as efficient as it could be but its ways better with a much more solid AFR reading.

Treneth · Apr 24, 2020

2000xp8 said:
Stock from what vehicle?
Cam?

This is the only info I have on the cam

Engine Power valve

Treneth

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General karthief

wonder how much it would cost to ship you a pair

Treneth

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General karthief

wonder how much it would cost to ship you a pair

Treneth

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JD1964

there is enough sticking out to grab on to

Monkeybutt2000

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Treneth

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junkyardwarrior

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JD1964

there is enough sticking out to grab on to

General karthief

wonder how much it would cost to ship you a pair

2000xp8

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2000xp8

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Engine Power valve

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wonder how much it would cost to ship you a pair

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wonder how much it would cost to ship you a pair

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there is enough sticking out to grab on to

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there is enough sticking out to grab on to

wonder how much it would cost to ship you a pair

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