1.8 inches of vacuum at wot

[427dart]

I switched over to a dual Holley 650 setup be cause I just like the look of a hot 427 Ford type engine with the two Holley carbs....like a FE 427!
I found the throttle response and mid range is great but the manifold I use lacks the ALL OUT top end over the 950 and Super Vic manifold I built the engine with.
However my grudge racing with my buddy is over and at 64,I just enjoy crusing around with an occasional blast thru the gears....too much traffic for anything else!

[roc]

...I found the throttle response and mid range is great but the manifold I use lacks the ALL OUT top end over the 950 and Super Vic manifold I built the engine with. ...

Are you saying that one Holley 950 and Super Vic manifold flows more than a dual Holley 650? Could it be that the lower top end power is because of fuel curve?

[andyf]

Thanks for all the replies. I spoke to BLP carbs and the venturi size is 1.375 but they can bore it to 1.450 and recalibrate the carb so I am going to send it out to try this, i should be close after this. The vacuum was measured off the engine builders dyno not on the vehicle itself.

I was wondering about that. The 1.375 venturi size is typically called a 750 cfm carb not a 950 cfm so that is probably part of the issue. BLP is a good shop so talk to them about what you are trying to do and show them your test data. You might not need to go all the way to a 1.450 to get the performance that you are looking for. We run 420 inch SB dirt track engines with 1.41 or 1.42 carbs and they typically make 720 to 730 hp with excellent throttle response. Those are high compression race engines with roller cams so not apples to apples, but it just shows that you might not want the biggest venturi size that is physically possible.

[statsystems]

Thanks for all the replies. I spoke to BLP carbs and the venturi size is 1.375 but they can bore it to 1.450 and recalibrate the carb so I am going to send it out to try this, i should be close after this. The vacuum was measured off the engine builders dyno not on the vehicle itself.

I have a question? How did you end up with that 1.375 Venturi carb? I called BLP to buy that exact carb, and BLP talked me OUT OF IT. Said it was on the ragged edge of being too small for what I was doing.

So they sent me the 1.450 Venturi B4X. I have a 340 inch street strip car.

I'm just wondering how you ended up with what you have.

[F-BIRD'88]

This is why I build my own carbs.

[F-BIRD'88]

I switched over to a dual Holley 650 setup be cause I just like the look of a hot 427 Ford type engine with the two Holley carbs....like a FE 427!
I found the throttle response and mid range is great but the manifold I use lacks the ALL OUT top end over the 950 and Super Vic manifold I built the engine with.
However my grudge racing with my buddy is over and at 64,I just enjoy crusing around with an occasional blast thru the gears....too much traffic for anything else!

You could have your cake and eat it too by putting 2 4bbl carbs on your super VIC intake.
And so could the poster here. Both are also prime candidates for the "Six Shooter" scheme induction.

[randy331]

If we get the vacuum down to .8 or 1.0 what will happen to the performance?

There is no set answer to that. I've seen 15-18 HP going from 1.4"-1.5" area down to .9"-1", but I've seen the same drop net nothing.

Got a big block here we were getting 1.9"-2" with a modified 850 that they claim flows 1000 cfm now. It's headed back to the dyno shortly and we have a 1150 4500 carb to try this time. Guess we will see what it does.

Randy

[raynman1969]

Thanks for all the replies. I spoke to BLP carbs and the venturi size is 1.375 but they can bore it to 1.450 and recalibrate the carb so I am going to send it out to try this, i should be close after this. The vacuum was measured off the engine builders dyno not on the vehicle itself.

I have a question? How did you end up with that 1.375 Venturi carb? I called BLP to buy that exact carb, and BLP talked me OUT OF IT. Said it was on the ragged edge of being too small for what I was doing.

So they sent me the 1.450 Venturi B4X. I have a 340 inch street strip car.

I'm just wondering how you ended up with what you have.

I purchased the carb used from a guy who went to injection. It was on a 454 street car. I was afraid it might be too small but it flowed 950 according to the spec sheet. My engine made good hp just want to fix the vacuum issue at wot.

[statsystems]

Thanks for all the replies. I spoke to BLP carbs and the venturi size is 1.375 but they can bore it to 1.450 and recalibrate the carb so I am going to send it out to try this, i should be close after this. The vacuum was measured off the engine builders dyno not on the vehicle itself.

I have a question? How did you end up with that 1.375 Venturi carb? I called BLP to buy that exact carb, and BLP talked me OUT OF IT. Said it was on the ragged edge of being too small for what I was doing.

So they sent me the 1.450 Venturi B4X. I have a 340 inch street strip car.

I'm just wondering how you ended up with what you have.

I purchased the carb used from a guy who went to injection. It was on a 454 street car. I was afraid it might be too small but it flowed 950 according to the spec sheet. My engine made good hp just want to fix the vacuum issue at wot.

Thanks. I was trying to figure out how you ended up with what you did. Makes sense now.

[Casper393W]

Making blanket statements regarding CFM vs CID is not an accurate way of thinking...

Here is how I come to this...
Just because a carb has say a 750cfm rating is it flowing 750 cfm on your engine?
When I built what was one of the first Carbed Ford 4.6 2V engines back in late '07 ish everyone said " You need a 650 CFM carb" makes sense right? After all it's only 281 CI. When I first made the change I was shocked by the power it made but as time went on I thought I would do a set of Chassis Dyno tests on different carbs. What I found was the Engine made most power and Torque with a AED 950 HO.... Now this had everyone stumped of how well this way too big carb did on only 281ci... The key is in the boosters! Having a booster that can atomize the fuel properly can and will make more power as long as the manifold design lends itself to that type of booster...
A heated manifold will lose power if you try to use a High gain booster!

On the 4.6 Ford the intake is in open air...the intake runs cool when the engine is running due to it's design..I first got the idea to test carbs with different boosters when I had my temp gun pointed on the engine while it was running and I had intake runners that was 60 degs vs 180 degs engine temp! When I witnessed this it told me that the fuel couldn't be atomizing like it should with regular straight leg boosters that come stock on a 650HP Holley DP...

So to me it is about giving the engine what it wants vs what people think it should be...because sometimes there are differences

[427dart]

...I found the throttle response and mid range is great but the manifold I use lacks the ALL OUT top end over the 950 and Super Vic manifold I built the engine with. ...

Are you saying that one Holley 950 and Super Vic manifold flows more than a dual Holley 650? Could it be that the lower top end power is because of fuel curve?

Well first it is a custom built carb that actually flows more air than the old HP series 950.

As compared to the Super Victor intake the runner size of the PME dual quad intake is smaller thus on this 427 sized engine it has a bit less top end power than the race type Super Vic. Still performs well in the 2000-5500 RPM range though.
I built the carbs from the best 1850 parts I had and added the larger 750 base plates for a 650 type carb. They are in great tune!


Note: don't get excited as that is NOT the fuel filter in low left of picture...it's a PCV filter.

[andyf]

Thanks for all the replies. I spoke to BLP carbs and the venturi size is 1.375 but they can bore it to 1.450 and recalibrate the carb so I am going to send it out to try this, i should be close after this. The vacuum was measured off the engine builders dyno not on the vehicle itself.

I have a question? How did you end up with that 1.375 Venturi carb? I called BLP to buy that exact carb, and BLP talked me OUT OF IT. Said it was on the ragged edge of being too small for what I was doing.

So they sent me the 1.450 Venturi B4X. I have a 340 inch street strip car.

I'm just wondering how you ended up with what you have.

I purchased the carb used from a guy who went to injection. It was on a 454 street car. I was afraid it might be too small but it flowed 950 according to the spec sheet. My engine made good hp just want to fix the vacuum issue at wot.

Just don't go crazy opening up that carb. You might gain 10 to 15 hp on the very top end of the power curve and pay for it down low with sluggish performance. On a drag car that leaves off the brake at 5000 rpm that is a good trade off. For a street car that spends 90% of its life below 3500 rpm it is not a good deal.

[Stan Weiss]

In theory going from 1.8 in hg @ wot to 0.8 in hg @ wot should be about a 3.5% HP increase. If the weather is close to STP.

Stan

[user-17438]

I have a question? How did you end up with that 1.375 Venturi carb? I called BLP to buy that exact carb, and BLP talked me OUT OF IT. Said it was on the ragged edge of being too small for what I was doing.

So they sent me the 1.450 Venturi B4X. I have a 340 inch street strip car.

I'm just wondering how you ended up with what you have.

I purchased the carb used from a guy who went to injection. It was on a 454 street car. I was afraid it might be too small but it flowed 950 according to the spec sheet. My engine made good hp just want to fix the vacuum issue at wot.

Just don't go crazy opening up that carb. You might gain 10 to 15 hp on the very top end of the power curve and pay for it down low with sluggish performance. On a drag car that leaves off the brake at 5000 rpm that is a good trade off. For a street car that spends 90% of its life below 3500 rpm it is not a good deal.

A good carb is a good carb. I completely disagree with your statement. I have customers with 1400+cfm carbs driving in stop and go traffic during cruises and car shows. A BLP carb is not a PROFORM kit off ebay.

He might gain 10-15hp and it drive like it was fuel injected.

[77cruiser]

This is why I build my own carbs.

What do you build them from?