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> Head question, Port size vs valve size
VaccaRabite
post Oct 24 2011, 08:12 AM
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In a recent thread I noted that the ports on my 1.7 turned 2056 heads are 47x37.5mm. I don't know what the valve size is.
Is the valve size usually the same size as the port, or smaller?
The heads are installed and I don't want to remove them unless I need to, but the engine is about to come out for conversion to EFI. The engines PO had the headwork done and I don't have all his notes.
If the valves are the same size as the ports I am going to pull the heads to have proper fitted valves for my engine.

Would too large a valve size lead to higher head temps? The PO said when I bought the motor that it ran warm and I have noted this myself even after rebuilding the bottom end in 2009. Its manageable but I do have to take care climbing hills on the freeway.
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HAM Inc
post Oct 24 2011, 08:31 AM
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Hi Zach, just got back to the computer and got your PM.

QUOTE
Is the valve size usually the same size as the port, or smaller?


A properly sized intake port will be ~ 85% of the diameter of the valve.

Those port sizes sound extremely large, and very unlikely to me. They are probably valve sizes. A 47mm intake port would be appropriate for feeding a 55mm valve.
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jsayre914
post Oct 24 2011, 12:53 PM
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Hey Zach,

Did you get your car back from Tony yet??
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VaccaRabite
post Oct 24 2011, 01:21 PM
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Its in my garage.
I need to get the engine dropped.

Zach
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r_towle
post Oct 24 2011, 01:40 PM
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Not to make you roll your eyes....
BUT

47mm intakes may explain many of your issues.
The heads and 2056 displacement cant support that....and it will make tuning it very hard.
You may really want to look for the notes, or pull a head and take a look.

I thought you rebuilt this at some point in time???


Rich
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jsayre914
post Oct 24 2011, 01:44 PM
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QUOTE(Vacca Rabite @ Oct 24 2011, 03:21 PM) *

I need to get the engine dropped.

Zach


You and me both, I need to get the 2056 put togeather before I try to drop mine. Im running out of room in there (IMG:style_emoticons/default/unsure.gif)
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McMark
post Oct 24 2011, 05:14 PM
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Take a picture and show us where you're measuring. (IMG:style_emoticons/default/wink.gif)
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VaccaRabite
post Oct 24 2011, 05:21 PM
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QUOTE(r_towle @ Oct 24 2011, 02:40 PM) *

Not to make you roll your eyes....
BUT

47mm intakes may explain many of your issues.
The heads and 2056 displacement cant support that....and it will make tuning it very hard.
You may really want to look for the notes, or pull a head and take a look.

I thought you rebuilt this at some point in time???

Rich, I rebuilt the entire bottom end in 2009. I did not touch the heads as the PO had them done not long ago at a shop in VA. I SHOULD have rebuilt them at the same time. I agree, if the valves are as big as my notes seem to indicate that could be a key to the running issues I have been having.

QUOTE

Take a picture and show us where you're measuring.

I will. Is it not obvious where I should measure the valve diameter?

Zach
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McMark
post Oct 25 2011, 09:49 AM
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QUOTE
I will. Is it not obvious where I should measure the valve diameter?

Nah, just one of those, checking the basics first things.
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Mike Bellis
post Oct 25 2011, 09:54 AM
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Theory...

n/a engine: ports should taper down from the port opening to the valve. This increases velocity as the air travels into the cylinder. Added velocity helps the mixture and speeds up the intake process.

Forced Induction: Ports do not need to taper. Ports should be as large as possibe to help flow the forced air into the cylinder.
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HAM Inc
post Oct 25 2011, 10:37 AM
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QUOTE
n/a engine: ports should taper down from the port opening to the valve. This increases velocity as the air travels into the cylinder. Added velocity helps the mixture and speeds up the intake process.


True; til you get to the short turn radius and bowl area beneath the valve. 1.8 & 2.0 914 intake ports twist rather than taper as a way of enhancing mixture quality. That is a method that has gained much popularity with the high-end V8 race head crowd.

QUOTE
Forced Induction: Ports do not need to taper. Ports should be as large as possibe to help flow the forced air into the cylinder.


That is a popular misconception. The dimensional relationship between port and valve is still critical. The intake/exhaust flow ratio needs to be increased to around 85% for turbo engines as compared to around 75% for NA engines.
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Jake Raby
post Oct 25 2011, 11:37 AM
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And....
Bigger is far from better. Finding "just right" takes about a decade.
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VaccaRabite
post Jan 8 2012, 09:34 AM
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I finally pulled the heads off the motor yesterday.the intake valve measure at 45mm. Looks like I need to rebuild them.

*grumble*
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