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 Post subject: Re: New Type 4 VW build
PostPosted: Fri Feb 08, 2019 2:41 pm 
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I am not locked on any valve sizes. My research shows that the exhaust port is the weak point. If I get the exhaust port optimized then I can match the intake port to the percentage that works best. I have run a few different cam profiles that have more exhaust lobe, but that really didn't help any. That's really why I wanted new heads. I want to work out the issues over the summer and be ready when I take it apart. 36mm is the big exhaust valve. I am sure I could get bigger custom exhaust valves but I don't want to.

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 Post subject: Re: New Type 4 VW build
PostPosted: Fri Feb 08, 2019 2:53 pm 
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Sounds like a fine plan.

A 36mm valve should flow about 95@10" which is about 163@28". It wants a seat ID of no more than 31.32mm...that gets you a velocity of 191ft/s @10" or 329@28". That's what you want to target for a 36mm valve.

I did 911 heads some time back, my 1st real porting attempt. I'd heard the exhaust was the issue so I started there and got all I could....then found it nearly impossible to get the intake high enough to match :oops:

on the ferrari I KNEW the exhaust port as plenty big and spent all my time on the intake....and had to live with less exhaust flow than optimal. :oops: :oops:

I guess my point it is its always a good idea to work in steps going back and forth intake to exhaust to make sure you end up with a matched result....not that i do that but someday I many learn from my mistakes......


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 Post subject: Re: New Type 4 VW build
PostPosted: Fri Feb 08, 2019 2:57 pm 
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Good to know. I will be working back and forth trying to make sure I get what I need. I like giving you info, you bang out calculations like breathing. I have to sit and smoke my brain to get that stuff right. :?

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 Post subject: Re: New Type 4 VW build
PostPosted: Fri Feb 08, 2019 3:08 pm 
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The exhaust numbers I have found shows max exhaust flow is 140. That is actually flow data I have found. That may be a more realistic number target. :)

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 Post subject: Re: New Type 4 VW build
PostPosted: Fri Feb 08, 2019 3:16 pm 
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I can use 38 mm exhaust valves too. Found some that size.

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 Post subject: Re: New Type 4 VW build
PostPosted: Fri Feb 08, 2019 4:54 pm 
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FoaTech wrote:
The exhaust numbers I have found shows max exhaust flow is 140. That is actually flow data I have found. That may be a more realistic number target. :)


That might be the port limit for some reason, but that is much to low to be efficient with a 36mm valve. If its due to a choke location near the valve that's ok...but it you're making the port big and not getting the flow then you are losing velocity and that is bad.


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 Post subject: Re: New Type 4 VW build
PostPosted: Mon Feb 11, 2019 8:30 am 
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mk e wrote:
FoaTech wrote:
The exhaust numbers I have found shows max exhaust flow is 140. That is actually flow data I have found. That may be a more realistic number target. :)


That might be the port limit for some reason, but that is much to low to be efficient with a 36mm valve. If its due to a choke location near the valve that's ok...but it you're making the port big and not getting the flow then you are losing velocity and that is bad.


As I understand it, the design of the port is pretty bad. It has a nasty turn right at the valve and it limits the flow quite a bit. Haven't actually seen them yet, but that is the word on the street. The square port is said to be better than the round, I have square and will buy square castings as well. What my research has found is the intakes can flow 200 and the exhaust can flow in the 150 ish range or 75-77% of the intake. I think that is the target percentage for intake/exhaust.

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 Post subject: Re: New Type 4 VW build
PostPosted: Mon Feb 11, 2019 9:03 am 
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When I was googling a couple weeks ago I stumbled on a guy moving the exhaust ports to be more like the type I ;)

Just be careful about hogging them out to get flow....less flow at a higher velocity usually makes more hp. 150cfm@28 only needs a 26 or maybe 27mm valve and may 23mm min area (seat or guide)...that is WAY south of a 36mm valve. Big valves expose more seat area faster so they can be a help but big slow ports don't help. You can see the effect of slow ports by increasing the min area, that doesn't change flow but it usually makes a pretty big difference in predicted output....it also tend to move the peak torque rpm higher so you get a peakier engine.

What the right intake/exhaust ratio is I don't know. It kind of seems like the higher the VE number you're after the higher the exhaust flow you need. I see flow numbers on high reving 4v stuff at 85% and my engine at like 77% because that's all the exhaust flow I could get needs more duration on the exhaust. But a buddy of mine used to swear by 65%...but he flowed with the pipes in place so I suspect the stack numbers would have been more like 75%...just a guess.....and this is the value of dynomation. It will help get everything matched.

One thing to really watch as you get into the final details is that the valve size in the engine setup matched the valve size in the head flow....the software will scale the port flow in the head file when you change the valve in the engine setup. This is really helpful to quickly check stuff like % I/E ratio to see what works best, but you have to remember to get the 2 matched back up and matching reality.


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 Post subject: Re: New Type 4 VW build
PostPosted: Fri Feb 15, 2019 8:00 am 
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So I ordered the new seat cutting set up today. Profile seat cutter, seat insert cutter, & spring seat/guide cutter.
I have a few sets of heads coming from another shop that needs the seats replaced and I am going to do that for them. They had a shop that put in seats and then staked them for good measure. On a Ferrari head, staked them, WTH? I would not stake my lawn mower seat must less a classic 275 Ferrari head.
Oh well, I guess that is why I will be doing it now.

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 Post subject: Re: New Type 4 VW build
PostPosted: Fri Feb 15, 2019 8:37 am 
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I'm not even sure know what "staked them" means? A pin in sideways?

What profile did you order? This is the one I use, a buddy pointed me to it and it seems to work very well for flow as he said it would. Its from Goodson Its got the standard 3 angles but with radius blends. bore the seat ID to whatever number the math says, like 85-87% the valve OD, then cut the seats to get a nice contact patch nears the center of the seat on the valve, then there is usually a sharp transition to the 75egree cut the I blend in, and there may be something up in the chamber that wants to be blended depending how big the valves are and how close they get to the sides of the combustion chamber. There is always a magic seat cut depth...this profile like the valve sitting a bit deeper than a normal 3 angle...go in about .005" steps..flow goes up, goes up...unchanged...drops...you don't want to get to drops :) I make test seats (steel or alum) that that are a very light press of just loctited in for the development work so I know how to do the real seats with little risk of screwing them up.


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