1.8 inches of vacuum at wot

[raynman1969]

On the dyno it showed 1.8 inches of vacuum at wot. BLP 950 carb. 421 sbc afr 220 heads cnc super victor. Does this mean thecarb is too small or maybe it didn’t flow 950.

[CGT]

On the dyno it showed 1.8 inches of vacuum at wot. BLP 950 carb. 421 sbc afr 220 heads cnc super victor. Does this mean thecarb is too small or maybe it didn’t flow 950.

Possibly both. Regardless, a bigger carb would be worth a try for sure.

[F-BIRD'88]

Check throttle linkage for full throttle.

Most "950" holleys flow less than a 850 holley does.
They are a 750HP body with a 850 throttleBase.

Get 2 of them and your problem will be solved.

[statsystems]

Carb CFM is almost meaningless. At 421 inches you need a dominator. That carb is too small for a well built 350 Chevy.

[raynman1969]

Since I just spent big dollars on a cnc super victor for a 4150 their must be another option

[F-BIRD'88]

Since I just spent big dollars on a cnc super victor for a 4150 their must be another option

There is... make or buy a 2x4 carb adapter and bolt it on the intake with 2 "950" carbs.

[oldjohnno]

At the risk of stating the obvious, it can be difficult to accurately measure the pressure of a flowing airstream. Depending on the location of the point of measurement you might be getting a good pressure reading but you might also be getting an indication of flow velocity. It can be hard to eliminate pitot or velocity probe effects.

[randy331]

http://braswell-com.3dcartstores.com/Co ... ep_42.html

One of the 4825 series carbs Braswell sells would be an option if you don't want to, or don't have room for a carb adapter to run a 4500. They will bolt to a 4150 intake, but the intake may need some grinding.

Randy

[randy331]

There is... make or buy a 2x4 carb adapter and bolt it on the intake with 2 "950" carbs.

The technical info available on speed talk is outstanding. LOL

Randy

[rustbucket79]

My somewhat limited experience thus far trying adapters and dominators on a 4150 flange at best was a wash. Of course most adapters like this are fairly short so the transition from throttle bore to runner is harsh. I suspect if the adapter was 6" or taller the results would be more favourable.

You could always save the intake and carb upgrade for a later date.

[raynman1969]

I wonder how much difference it would make to get it down to 1.0 or 1.2

[cardo0]

To find a restriction a vacuum gauge is a useful tool. I measure 0"Hg on my '94 LT1 Camaro at WOT. But it's gauge and not as highly accurate as the MAP sensor which measures absolute press instead of vacuum. Most likely the MAP would show some amount of pressure in the intake manifold at WOT. It could be a very accurate sensor as gauges will show near zero vacuum while a complete vacuum is nearly possible to create. Not to make a science lecture here but complete vacuum means there no gas molecules in that space - think about what that would take. But either one can be/could be used to find restrictions in the intake track.

Well you should verify you have a restriction by measuring vacuum on both sides of the throttle blades. If you have 1.8" Hg behind the throttle blades but less than 1.8" Hg before the throttle blades then yes the carb is the restriction. If both sides of the the throttle blades read 1.8"Hg then the throttle blades aren't creating a pressure drop.

Since in front of the throttle blades it should be close to atmospheric which is 0"Hg when we talk as vacuum or less than atmospheric pressure. Using a vacuum gauge (or MAP) to find restrictions in the intake is fairly easy. Outside the air cleaner is atmospheric or zero vacuum (or 29.92"Hg from the MAP). At idle your intake has highest vacuum but a race motor will be less than 12"Hg while a street motor will have like 18"Hg vacuum in the intake behind the throttle blades. Everywhere in between the air cleaner and the throttle blades should be atmospheric or 0"Hg vacuum (29.92"Hg absolute) unless there is a restriction. A restriction will create a pressure drop and increase the vacuum reading - but never more than the intake vacuum reading.
Same thing for part throttle or WOT but the intake vacuum becomes much lower (closer to atmospheric) and difficult to see the difference in vacuum reading from a restriction.

Hope this helps more than confuses.

[F-BIRD'88]

Some things are just not that complicated or need be that expensive to fix.

[user-23911]

If a 950 CFM carburettor is rated at 950 CFM then what is the pressure drop that it's rated at?


edit, found it, 20.8 inches (water) on a SF1200 flow bench.
So if it's only dropping 1.8 inches (Hg), it's about 24 inches water. so actual flow is a bit less than 950 CFM.

[steve316]

Borrow 1050 dominator; use a adapter check what you have. It will give you the answer your looking for. I have ran a 1050 dom. on a 326 cu.in. to 434 with good results.