# CFM rate 16v vs. 20v



## gigmatt16v (Feb 10, 2004)

what has a better cfm after a full race P&P and resized valves.


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## PowerDubs (Jul 22, 2001)

*Re: CFM rate 16v vs. 20v (gigmatt16v)*

In this case, a flowbench will not show real world results.... a 16v head should outperform a 20v due to the larger lifter diameter allowing bigger cams.


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## mrkrad (Nov 9, 2000)

*Re: CFM rate 16v vs. 20v (PowerDubs)*

need to flow bench with intake manifold etc on tool. the weakest link will bring a ported head to its knees.


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## bobqzzi (Sep 24, 2003)

*Re: CFM rate 16v vs. 20v (gigmatt16v)*


_Quote, originally posted by *gigmatt16v* »_what has a better cfm after a full race P&P and resized valves.

Not even close..the large port 20V flows WAY more, and has a vast;y superior combustion chamber.


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## PowerDubs (Jul 22, 2001)

*Re: CFM rate 16v vs. 20v (bobqzzi)*


_Quote, originally posted by *Dave Baker* »_The diameter of the lifter (or bucket) directly limits the speed with which the valve can be opened and therefore the amount of valve lift that the cam lobe can produce for a given opening duration. The maths behind this premise is far too complex to go into here but is something which any cam designer needs to take into account when designing a profile. The faster and higher a valve can be opened, the more airflow potential the valve is going to have and the better its ability to fill the cylinder. Some engines are so severely limited in their power potential by having small diameter lifters that it can outweigh any consideration of their power potential based solely on valve area. 
For example the Ford 1800 Zetec and the VW Golf 1800 16 valve engine are the same capacity and have identical valve sizes. Both have twin overhead cams acting directly on buckets and similar bore and stroke sizes. An initial view might be that, baring any major problem with port shape and size, that both engines would have similar power potential when fully modified. The Ford though only has 28mm lifters and the VW has 35mm ones. This allows the VW to run much more radical cam profiles and achieve more "flow area" from its valve lift curve. 
By contrast the VW 5 valve per cylinder engine has plenty of inlet valve area from its 3 inlet valves per cylinder but space constraints mean the lifters are only 24mm diameter. This limits the design of the cam profile so badly that the power potential of the engine is reduced below that of the much simpler 4 valve per cylinder design. In effect, this engine ended up as nothing more than a very complex and expensive marketing exercise.


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## bobqzzi (Sep 24, 2003)

*Re: CFM rate 16v vs. 20v (PowerDubs)*

The 1.8T is turbocharged, and thus requires much less cam than a N/A engine. Cams are available in sufficient size to make at least a 1000HP. 
In anything that could remotely be described as street trim, cams are not an issue at all, and the AEB 5v head flows much, much better, and has has a much better chamber. Even the small port head offers better overall flow characteristics.


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## PowerDubs (Jul 22, 2001)

*Re: CFM rate 16v vs. 20v (bobqzzi)*

Nobody mentioned anything about a turbo...the 20v was (is?) available in some markets NA...and is a slug.


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## rracerguy717 (Apr 8, 2003)

*Re: CFM rate 16v vs. 20v (PowerDubs)*


_Quote, originally posted by *PowerDubs* »_Nobody mentioned anything about a turbo...the 20v was (is?) available in some markets NA...and is a slug.








 I do believe Prof NATE has the worlds fastest NA VW is on 20V head , not a 16V. i wonder why ?







Bob.G


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## TBT-Syncro (Apr 28, 2001)

*Re: CFM rate 16v vs. 20v (bobqzzi)*


_Quote, originally posted by *bobqzzi* »_The 1.8T is turbocharged, and thus requires much less cam than a N/A engine. Cams are available in sufficient size to make at least a 1000HP. 

lol, got some 1000HP cams sitting around do you?

_Quote, originally posted by *bobqzzi* »_
In anything that could remotely be described as street trim, cams are not an issue at all, and the AEB 5v head flows much, much better, and has has a much better chamber. Even the small port head offers better overall flow characteristics.

do you just make this stuff up on your own?
so you don't think cams will help a street trim car? thats funny.
a 20v head in stock form is better than a 2.0 16v, which is better than a 1.8 16v head. However, the head with the biggest MAX flow is an old 1.8 16v.
-combustion chamber is better on the 20V, true.


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## matsad (Dec 22, 2003)

*Re: CFM rate 16v vs. 20v (TBT-PassatG60)*

What exactly gives the 20v head a better chamber than the 16v? Also, did any US-market cars come with the big valve version of the 20v head? 
Thanks, just trying to get edumicated.


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## bobqzzi (Sep 24, 2003)

*Re: CFM rate 16v vs. 20v (matsad)*


_Quote, originally posted by *matsad* »_What exactly gives the 20v head a better chamber than the 16v? Also, did any US-market cars come with the big valve version of the 20v head? 
Thanks, just trying to get edumicated.









The 16V head has an odd tilted chamber with the exhaust valves straight up and down. This was done for emissions purposes, but has the unfortunate side effect of making the chamber more prone to detonation.
The VALVE size on all 1.8T heads is the same. The intake ports come in 2 sizes, small and large. The large port head came on AEB engines in Passats and A4s. The exhaust ports are all the same.


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## bobqzzi (Sep 24, 2003)

*Re: CFM rate 16v vs. 20v (TBT-PassatG60)*

There are solid lifter cams available for the 1.8T that would be suitable for an engine that was making 1000HP, for instance Cat Cams offers this grind:
clearance [cl] 0.20mm 0.25mm 
duration [0.1mm+cl] 285° 286° 
duration [1.0mm+cl] 256° 252° 
valve lift [cl=0] 11.00mm 11.65mm REQUIRED PARTS 
cam lift - - 
peak angle 110° 110° followers: info 
timing [1.0mm+cl] 18/58° 56/16° retainers: info 
lift at TDC [cl=0] 3.00mm 3.25mm 
Given te need for far less camshft in a turbocharged application, this should be sufficient to turn the engine 10,000-11,000 RPM, and with sufficient boost and support systems 1000HP should be obtainable. 80's F1 cars made 1400 HP from 1.5 liters. The BMW entry was based on the production car engine. Making 1000 from 1.8l is certainly possible, especially given the tremendous advances in engine management. So, do I have a set of 1000HP cams lying around? I reckon I could get some pretty quick.
No where did I say cams would not help a street trim car. The other poster stated the 16V head was superior because it had larger lifters,allowing more total flow. I was simply pointing out that the smaller lifters of the 1.8T aren't a limiting factor on a street engine. There are cams available for the 1.8T that are much larger than anything anyone would run on the street.
As far as head flow: your statement - 20v head in stock form is better than a 2.0 16v, which is better than a 1.8 16v head. However, the head with the biggest MAX flow is an old 1.8 16v.
- doesn't make any sense at all. What do you mean the 'old 1.8 16v head"?
Here is the relevant flow chart. As you can see the large port 20v head is by far the best,and while the 1.8 16V head has better max flow than the small port 20v, the total area under the curve favors the 20v.









_Quote, originally posted by *TBT-PassatG60* »_
lol, got some 1000HP cams sitting around do you?
do you just make this stuff up on your own?
so you don't think cams will help a street trim car? thats funny.
a 20v head in stock form is better than a 2.0 16v, which is better than a 1.8 16v head. However, the head with the biggest MAX flow is an old 1.8 16v.
-combustion chamber is better on the 20V, true.




_Modified by bobqzzi at 4:56 AM 10-28-2004_


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## TBT-Syncro (Apr 28, 2001)

*Re: CFM rate 16v vs. 20v (bobqzzi)*

lol, those numbers are what i said.
The 16v has most port potential once ported. Those are all stock numbers. Hell my 8v head has more flow than that.


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## bobqzzi (Sep 24, 2003)

*Re: CFM rate 16v vs. 20v (TBT-PassatG60)*


_Quote, originally posted by *TBT-PassatG60* »_lol, those numbers are what i said.
The 16v has most port potential once ported. Those are all stock numbers. Hell my 8v head has more flow than that.

Those numbers are not what you said. 
Don't be a total ass. Your 8V doesn't have anywhere near the flow of any of those heads.
Here is a representative flowchart for a (street) ported 8V head. I've certainly seen better, but this is pretty good








Do you have a flow chart? No, of course not.


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## TBT-Syncro (Apr 28, 2001)

*Re: CFM rate 16v vs. 20v (bobqzzi)*

i'll send you my flow chart once it's back from the machine shop. Its there being reworked a bit.








my intake is around 180, and my exhaust is around 155








and as i've said twice already on this thread.
stock 20v head outflows a STOCK 16v head.
a max ported 16V outflows a max ported 20V head.
check the 16v and 20v forums and FI forums. This topic has been covered numberous times, with numberous flow benchs.


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## TBT-Syncro (Apr 28, 2001)

*Re: CFM rate 16v vs. 20v (bobqzzi)*


_Quote, originally posted by *bobqzzi* »_Do you have a flow chart? No, of course not.

why don't you post yours, or one supporting your claims?
i'd love to be proven wrong


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## bobqzzi (Sep 24, 2003)

*Re: CFM rate 16v vs. 20v (TBT-PassatG60)*


_Quote, originally posted by *TBT-PassatG60* »_i'll send you my flow chart once it's back from the machine shop. Its there being reworked a bit.








my intake is around 180, and my exhaust is around 155








and as i've said twice already on this thread.
stock 20v head outflows a STOCK 16v head.
a max ported 16V outflows a max ported 20V head.
check the 16v and 20v forums and FI forums. This topic has been covered numberous times, with numberous flow benchs.

What in God's name makes you think a port job could possibly make up the GIGANTIC difference in flow on the stock heads? If you knew absolutely anything at all about cylinder heads you would know that it is completly impossible. How much do you think porting improves flow anyway? Have you ever ported a head? Been to a flow bench? In fact, a heavily race ported 16v head is unlikely to even flow as much as a stock large port 20V
Even if your ludicrous claim that your 8V head flowed 180cfm was even remotely true (which it's not) that would only be a peak flow number, and the area under the curve would be much, much smaller.
Heres a ported AEB head. This chart is at 25", so multiply it by 1.12.








In 1997 when the first 20vs came out, I had a stock head flowed, and compared it to ported 16v data I had from some of our projects, and also with some data Techtonics was kind enough to share with me.

You're right, this has been kicked around many times, and the conclusion is that the 20V head flows better. Period No data to contradict that statement has ever been offered.
So far you haven't offered ANY proof of anything at all, just stupid claims based on nothing more than your say so. Balls in your court- show me a flow sheet from a ported 16v VW


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## rracerguy717 (Apr 8, 2003)

*Re: CFM rate 16v vs. 20v (TBT-PassatG60)*


_Quote, originally posted by *TBT-PassatG60* »_lol, those numbers are what i said.
The 16v has most port potential once ported. Those are all stock numbers. Hell my 8v head has more flow than that.
 Thats not happening , stock AEB ( large port ) 20v head flow around 220 cfm intake , ive seen numbers as high as 280cfm in a full race head. Bob.G


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## TBT-Syncro (Apr 28, 2001)

*Re: CFM rate 16v vs. 20v (bobqzzi)*

hey Bob,
overkill performance stage 4 g60 head flows 190cfm @0.426. If anything, my head will flow a tad more then that. But like I said, its at the machine shop and i'll send you my flow bench numbers when it's back. I lowballed my flow data, as most people on here always over estimate and i'd sooner be conservative until i have real world proof.
I had flow benchs from one of those heads. But i can't find it right now. Neal's (SUV_etr) rocco put down 233 Whp with one of these heads and moderate boost ( i believe he was making 14psi with his lysholm).








As for your rant questions
how much does porting improve the head - well that depends on what's done.
have i ever ported a head - yes. ( i have 2 beside me right now that i'm working on).
been to a flow bench - yes 1000s of times, it was in the garage in the house i grew up in.
I'd search around for the 16v vs 20v flow data, but i've got work to do (i'll have time next weekend for this e-battle). Maybe you should try to back up some of your claims with flow data (since you claim to have so much of it), instead of just calling me on it.


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## rracerguy717 (Apr 8, 2003)

*Re: CFM rate 16v vs. 20v (autorotor1)*


_Quote, originally posted by *autorotor1* »_i'm scene an aeb head flow 300 cfm, and a race only 16v head flow up to 260 cfm, but thats it. the 20 valve wins all day long.
 Another BIG reason that the 20V head is superior is the CC design . That why you see the 20V motors are very good / easy, with high boost on stock pistons compared to the 16V even with good after market pistons







Bob.G


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## andrew1984 (Jun 24, 2002)

*Re: CFM rate 16v vs. 20v (rracerguy717)*

taken from porttuning.com


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