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Flat Flow Curve

General engine tech -- Drag Racing to Circle Track

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fordified
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Flat Flow Curve

Post by fordified » Mon Aug 12, 2019 6:03 pm

I have a set of C3 Yates heads that have a flat flow curve from .600 lift up. Is it valve limited or something else thats causing it? The valve is 2.150. I was thinking about putting a 2.180 in them.

Here are the numbers.

Lift Intake
0.100 73
0.200 145
0.300 216.4
0.400 293.2
0.500 346.9
0.600 380.2
0.700 382
0.800 381.1
0.900 384.7

Racer71
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Re: Flat Flow Curve

Post by Racer71 » Mon Aug 12, 2019 7:16 pm

Are the floors filled up with epoxy? I used to have 5 or 6 sets of them and no two were alike all nascar leftovers, some worked well and some didn’t, they tried lots of different things with them through the years.

fordified
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Re: Flat Flow Curve

Post by fordified » Mon Aug 12, 2019 7:22 pm

They're a later casting ported for drag racing by a well known shop. There's no epoxy.

mag2555
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Re: Flat Flow Curve

Post by mag2555 » Tue Aug 13, 2019 7:22 am

First off what percentage is the Throat size right now?

Flow test them without a Intake valve in them.

If the flow picks up above .600" lift then you have found out 2 things.

1) the valve size is a restriction.

2) there may not be much shrouding to deal with if you go up to a bigger valve size and the mess that can make with compression.

Will the OD of the current valve seat accept a 2.180" valve?

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Re: Flat Flow Curve

Post by mag2555 » Tue Aug 13, 2019 8:27 am

mag2555 wrote:
Tue Aug 13, 2019 7:22 am
First off what percentage is the Throat size right now?

Flow test them without a Intake valve in them.

If the flow picks up above .600" lift then you have found out 2 things.

1) the valve size is a restriction.

2) there may not be much shrouding to deal with if you go up to a bigger valve size and the mess that can make with compression.

The good news is that atleast the high lift flow numbers are not regressing as they could if the short turn apex was not tall enough, or if the short turn was not shaped right.

Does this head use a 50 or 55 degree seat?
Will the OD of the current valve seat accept a 2.180" valve?

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Re: Flat Flow Curve

Post by Elroy » Tue Aug 13, 2019 8:56 am

Is there a reason that the flow curve doesn't suit you as it is? Im just curious if its something you've encountered or something you've read?

fordified
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Re: Flat Flow Curve

Post by fordified » Tue Aug 13, 2019 9:03 am

Thanks for the post.

I see your reasoning for flowing the heads without valves to see the maximum flow potential. The throat is at 91% and the seat is 52 degrees I believe.

There "should" be room on the seat for the bigger valve but I would have to replace the exhaust seats anyway to put in a 1.550" valve and could put a bigger seat on the intake side if needed. I also need to check how much material is left in the bowl to see if I can put the larger valve in.

fordified
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Re: Flat Flow Curve

Post by fordified » Tue Aug 13, 2019 9:12 am

Elroy wrote:
Tue Aug 13, 2019 8:56 am
Is there a reason that the flow curve doesn't suit you as it is? Im just curious if its something you've encountered or something you've read?
I had a new cam ground and the guy I talked to said he was baffled that the head went flat. He's done a lot of cams for small block chevys that run in my class and said that none of them do that. I should be able to run with a 15 degree chevy but can't seem to get there.

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Re: Flat Flow Curve

Post by pcnsd » Tue Aug 13, 2019 9:36 am

I had anything even close to what your heads do I would think I had died and gone to heaven. I guess it is all in expectation.
In round numbers, your valve throat area and valve curtain area are about equal at a bit less than .5" lift. That you gain flow above that number indicates the increasing curtain area is improving the valve throat CD at least initially. It does not appear to me that you are yet limited by throat area. (I assumed a 91% throat and 50* angles.) I will try to post a spread sheet that looks at valve throat and curtain areas and the effect on velocity for a given flow rate when I get off work today. The stalling of flow, could be any number of things from valve or seat shape to shrouding. It could also be something up stream of the valve. If you are chasing flow improvement, you will need to engage with a head porter. Only further testing can find a solution. Anything here will be conjecture.
If you could answer the questions on seat angle and throat percentage, it will help to finalize the spreadsheet.
- Paul

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Re: Flat Flow Curve

Post by Elroy » Tue Aug 13, 2019 9:37 am

It may be fun to dissect your combination on here. Maybe something beneficial will come from it for you or not. :D

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Re: Flat Flow Curve

Post by Joe-71 » Tue Aug 13, 2019 9:53 am

As suggested above, I always take the valve out and turn it upside down and insert it back in the guide, then flow the head at 28" to see what the flow does. 380 cfm through a 2.150" valve is fairly decent flow, but I have seen as much as 410 cfm with that size in the D3 head. Joe-JDC
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fordified
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Re: Flat Flow Curve

Post by fordified » Tue Aug 13, 2019 9:54 am

Joe-71 wrote:
Tue Aug 13, 2019 9:53 am
As suggested above, I always take the valve out and turn it upside down and insert it back in the guide, then flow the head at 28" to see what the flow does. 380 cfm through a 2.150" valve is fairly decent flow, but I have seen as much as 410 cfm with that size in the D3 head. Joe-JDC
The problem is that the D3 is a way better head than the C3. It has a .400" taller intake port and a canted intake valve. It also has a lot more material for porting. I doubt I can get to 400 cfm with a set of C3's.
pcnsd wrote:
Tue Aug 13, 2019 9:36 am
I had anything even close to what your heads do I would think I had died and gone to heaven. I guess it is all in expectation.
In round numbers, your valve throat area and valve curtain area are about equal at a bit less than .5" lift. That you gain flow above that number indicates the increasing curtain area is improving the valve throat CD at least initially. It does not appear to me that you are yet limited by throat area. (I assumed a 91% throat and 50* angles.) I will try to post a spread sheet that looks at valve throat and curtain areas and the effect on velocity for a given flow rate when I get off work today. The stalling of flow, could be any number of things from valve or seat shape to shrouding. It could also be something up stream of the valve. If you are chasing flow improvement, you will need to engage with a head porter. Only further testing can find a solution. Anything here will be conjecture.
If you could answer the questions on seat angle and throat percentage, it will help to finalize the spreadsheet.
Thanks,

The seat is 52 degrees I was told and the throat is 91%. I don't know the chamber volume.

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Re: Flat Flow Curve

Post by fordified » Tue Aug 13, 2019 10:15 am

Elroy wrote:
Tue Aug 13, 2019 9:37 am
It may be fun to dissect your combination on here. Maybe something beneficial will come from it for you or not. :D
It's kind of a messed up situation.

The engine is an 8.2 deck with a 4.110 bore and a 3.00" stroke. It has a custom manifold and a 750 dp specified for the class.

The original builder really screwed up the build. It only had about 11:1 compression and made 715 HP at 8600 rpm. It got hurt on the dyno before the pulls but he ran it anyway after changing a bad lifter. Being hurt may have caused the low hp numbers. It also has low peak RPM for such a small engine with decent heads and a giant cam.

I tore down the engine when I got it and the piston skirts were full of metal and the rings were shot. My new builder made chamber molds and had new pistons made with thinner rings. The engine is now a little over 14:1 and is where it should be.

I had a second cam ground for the dyno session and that's when I was told that the lift curve was strange compared to a 15 degree SBC head. He also said the dyno numbers were off. The fresh engine should be on the dyno in early September.

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Re: Flat Flow Curve

Post by pcnsd » Tue Aug 13, 2019 10:36 pm

I found an error in my first spreadsheet adaptation, so I will hedge my opinion with this post. These heads are very high in performance. There is perhaps a bit more that could be had, but you are close with the current valve size and flow rates to what Don Terrill and Patrick Hale described as the "World Class" flow performance maximum for a single intake valve design.
The red line on the chart is velocity, the blue is CFM. Both are referenced to lift. This sheet looks only at the valve threshold. It is adapted from the Horsepower Chain. It looks to me like the valve can expect to top out at about 390 cfm. (132 cfm per square inch of flow path).

I found an discussion of the Yates C3 at YB. There are some flow numbers given that align closely with what you are seeing. One poster says 390 cfm at .7" through .9" another says 398 @ .8". both with a 2.15" valve. Don't know what bench you are using but I assume you know that orifice type benches skew their output depending on what cfm you calibrate at within the flow range unless you have a correction table. Just saying a few CFM discussed on one side or another may be the same in reality. If high end flow accuracy is most important to you, that is where your calibration should focus.

https://www.yellowbullet.com/forum/show ... p?t=534179
Valve flow velocity ST test Ford C3.xls
You do not have the required permissions to view the files attached to this post.
- Paul

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Re: Flat Flow Curve

Post by fordified » Wed Aug 14, 2019 3:11 pm

pcnsd wrote:
Tue Aug 13, 2019 10:36 pm
I found an error in my first spreadsheet adaptation, so I will hedge my opinion with this post. These heads are very high in performance. There is perhaps a bit more that could be had, but you are close with the current valve size and flow rates to what Don Terrill and Patrick Hale described as the "World Class" flow performance maximum for a single intake valve design.
The red line on the chart is velocity, the blue is CFM. Both are referenced to lift. This sheet looks only at the valve threshold. It is adapted from the Horsepower Chain. It looks to me like the valve can expect to top out at about 390 cfm. (132 cfm per square inch of flow path).

I found an discussion of the Yates C3 at YB. There are some flow numbers given that align closely with what you are seeing. One poster says 390 cfm at .7" through .9" another says 398 @ .8". both with a 2.15" valve. Don't know what bench you are using but I assume you know that orifice type benches skew their output depending on what cfm you calibrate at within the flow range unless you have a correction table. Just saying a few CFM discussed on one side or another may be the same in reality. If high end flow accuracy is most important to you, that is where your calibration should focus.

https://www.yellowbullet.com/forum/show ... p?t=534179

Valve flow velocity ST test Ford C3.xls
Thanks a lot for taking the time to do all that.

The bench is a superflow 600. The guy I bought the heads from said they flowed over 380, and I confirmed it on the bench.

I still wonder why the head just stays flat. I understand that they are a good flowing head and your charts confirmed it. I'm wondering with a 2.180" if the same thing will happen. The short turn on the C3 is low compared to the D3 head and the D3 has a lot of material on the roof around the short turn. When I got the heads the porter said that the short turn limits the head. Not sure if that's why they go flat or if it just limits how much flow you can get out of them.

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