Posts: 77
From:Amherst, WI, USA
Registered: Aug 2000

posted 10-01-2000 11:37 AM               

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In reading some of the posts about these heads, somebody mentioned that to make up for a lack of low end torque, a higher gear ratio numerically (4:10) would make up for a lack of torque on 4V Cleveland heads. For 2V Cleveland heads, does it hold true that because of good low end torque, a lower gear ratio numerically (3:25 to 3:55) would be sufficient for good acceleration while still allowing driveability on the street, such as on the freeway? I know that tranny type comes into play, but everything being equal, does this sound right?

IP: 207.227.51.158

Posts: 7360
From:Saco, Maine USA '72 Mustang Sprint 351C '94 F-150 XL 5.8L and a '97 Probe GTS 2.5L DOHC
Registered: May 99

posted 10-01-2000 05:29 PM               

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While the 2V heads are a lot better for low end torque, I still think you want 3.50s and lower {numerically higher} ratio to take advantage of the potential of these heads.

The 2V still has some large ports and valves.

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SteveLaRiviere/Webmaster -- MCA # 47773

IP: 208.51.216.238

Posts: 197
From:Walnut Creek, CA USA
Registered: Jun 99

posted 10-01-2000 11:54 PM               

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While we're on the topic, I was messing around with flow vs valve lift numbers for the 2V and 4V heads. What I found was 2V and 4V intakes flowed the same total volume of air at 0.5 inches of total lift. If the lift is increased to 0.55", then the 4V heads outflowed the 2V heads by almost 11% and at 0.6" outflowed by over 15%. Again, this is total air flowed for a given valve cycle. More air flowed per cycle is more torque and horsepower. I also plotted exhaust air flow and the 4V heads outflow the 2V heads by 10% to 15% across the lift range.

Most of us are running at least 0.5" cam lift and many are probably over 0.55" regardless of whether we are running 2V or 4V heads. Therefore, the 4V heads really ought to make more torque and horsepower than the 2V heads at all rpms.

I'm guessing that the 2V heads have higher air velocities and better carb metering at lower rpms and, therefore, will make a little more torque down low. However, if we're running a decent cam, the 4V heads will turn on a few hundred rpm after the 2V heads and blow it away after leaving the line. My guess is that the 2V head advantage lasts for only a few car lengths off the line before the 4V heads leave them in the dust.

Therefore, I guess my question is: Are the 2V heads really better for the street??? Or do they lose there advantage too quickly off the line?

I'd post the charts I created, but couldn't figure out how.

[This message has been edited by Scott (69Mach) (edited 10-02-2000).]

IP: 207.172.166.120

Posts: 77
From:Amherst, WI, USA
Registered: Aug 2000

posted 10-02-2000 10:36 AM               

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This is also a pretty good time to talk about the difference between street and track racing. When I think of street, and the typical drag race that occurs, what comes to mind is something that will be less than a 1/4 mile in most instances, and more often than not speeds of less than 70 mph. As we know, every situation is different, but for the most part it seems like this is the case unless you can get someone to follow you to some safe back road where you can go a long distance. Also, if you can smoke someone before you get to 70, they usually give up by then anyhow because of the doughnut patrol looking to hand out tax increases. As for the track, the distance is already determined and there is no punishment for getting it up to 100 mph. Does this make sense? Does this explain why someone who doesn't go to the track and just gets into shoot outs on the way home from work might be better served with heads that take advantage of lower torque because they won't go over 70? If someone does do a lot of track racing, doesn't it make sense that they should go with something like 4V heads because in the last 1/8th or 1/16th of a mile they want to be still pulling hard for the finish? A million other factors come into play here, but in general is this what everyone means when they talk about the difference between 2V and 4V heads, and taking advantage of their characteristics?

IP: 207.227.51.179

Posts: 197
From:Walnut Creek, CA USA
Registered: Jun 99

posted 10-02-2000 12:04 PM               

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Yep, you hit on some key stuff. I'm building mine to run at the strip on grudge night. I'm too mature to mash the peddle on the street (no, really I am). I'll let the look and sound of the car speak on the street. If they want to get serious, we need to go elsewhere.

IP: 157.22.247.18

Posts: 7360
From:Saco, Maine USA '72 Mustang Sprint 351C '94 F-150 XL 5.8L and a '97 Probe GTS 2.5L DOHC
Registered: May 99

posted 10-02-2000 05:22 PM               

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This chart from our Tech Articles section shows the difference between the 2V and 4V heads.

There are several errors in this chart, {i.e. the 2V intake valve is 2.04", not 2.03" and the 4V exhaust valve is 1.71", not 1.67"}

But this chart shows a significant difference at all lifts.

You have different figures, Scott?

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SteveLaRiviere/Webmaster -- MCA # 47773

[This message has been edited by SteveLaRiviere (edited 10-02-2000).]

IP: 64.208.65.201

Posts: 1002
From:Rohnert Park, CA USA
Registered: Jul 2000

posted 10-02-2000 05:51 PM               

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There is a similar chart at ww.waldens.com with figures very close to that also.

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Marcus
Fast, Reliable, Cheap.... Pick any TWO of these words.
68 Mustang, still in purgatory.
BOYCOTT EXCESSIVE MOTORSPORTS

IP: 63.203.204.165

Posts: 197
From:Walnut Creek, CA USA
Registered: Jun 99

posted 10-02-2000 06:40 PM               

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That's the one. I took those lifts, assumed a sine wave approximated a lift vs time profile and got relative amounts flowed for each lift increment. Since the cam stays at max lift longer than it does at a transitional lift, there is more time to flow at max lift.

What I did wasn't necessarily good engineering, just an easy way to recreate flow under the curve that used to be posted on the web at a now defunct site.

IP: 157.22.247.18