Bigger valves is better? Maybe not

karmannghia60 · 2004-01-19T06:03:46+00:00

I am getting my 1835 heads rebuilt. I spoke to couple of people about the advantages of having bigger valves put in. As you expect, nearly everyone had a different opinion. One said its not recommended because most likely they don't get the seats right. One said there is no point unless you go with a mild/wild cam. One said no point at all, he is running 2.1 stroker using standard valves and he loves it. But he also mentioned something quite interesting. He reckons that the drag guys are now experementing with smaller valves not bigger ones. Apparentley smaller ones create better airflow (kind of a compressed airflow aka turbo) and create more power. I thought that is quite a different view from the norm Raf

Bizarre Moderator The artist formerly known as blue74l

12,789 posts · joined Aug 2002 · 29 Jan 2004, 3:09 pm

#133443

But it is not a stock head.
Raf said they are 40/32 valves.

Why do it?
1) hopefully to have a better breathing head and a few more ponies to boot.

2) to have an opinion as to whether or not any one else should do it.

This way when i finally get around to doing mine Raf will post and say "yes - do it. My motor happily sings up to 6500 and feels like it can go some more!"

Futue te ipsum!!!

63dub Learner Dubber

11 posts · joined Jan 2004 · 29 Jan 2004, 3:34 pm

#133458

Barry

I think Craig is puzzled by the use of a stock cam with the new heads and ratio rockers.

I'd be interested to hear your thoughts.

Cheers

Bizarre Moderator The artist formerly known as blue74l

12,789 posts · joined Aug 2002 · 29 Jan 2004, 3:49 pm

#133461

Craig is just confused.
Last time he asked a question he wanted to know why his motor blew up cause he put water in the radiator tank in the front boot!!!

It is a discussion we are having as to the benefit of running 1.4's on a stock cam/heads.

Craig thinks there is no benefit.
I believe there is a breathing benefit.

Dunno.
Never done it. Want too. Just short of $$$$

Do you have one???

Just at $750 a set of 1.4's here i aint gunna race out and but a set.

Might consider a set from AC.net at $190US though if i can find some one to bring em back for me :bounce

Futue te ipsum!!!

Craig Torrens 6 times Australian, 7 times State Hillclimb Class Champion

8,040 posts · joined Jan 2003 · 29 Jan 2004, 3:55 pm

#133464

63dub wrote:Barry

I think Craig is puzzled by the use of a stock cam with the new heads and ratio rockers.

I'd be interested to hear your thoughts.

Cheers

ummm not puzzled, I just know it doesn't work.

Craig Torrens 6 times Australian, 7 times State Hillclimb Class Champion

8,040 posts · joined Jan 2003 · 29 Jan 2004, 4:03 pm

#133468

blue74l wrote:Craig is just confused.
Last time he asked a question he wanted to know why his motor blew up cause he put water in the radiator tank in the front boot!!!

It is a discussion we are having as to the benefit of running 1.4's on a stock cam/heads.

Craig thinks there is no benefit.
I believe there is a breathing benefit.

Dunno.
Never done it. Want too. Just short of $$$$

Do you have one???

Just at $750 a set of 1.4's here i aint gunna race out and but a set.

Might consider a set from AC.net at $190US though if i can find some one to bring em back for me :bounce

So tell us the benefits Barry, you still haven't answered my other questions ???

I don't "think" there's no benefit, I know there's no benefit !!!

As for your first sentence in your post :jesus, ?????

Craig Torrens 6 times Australian, 7 times State Hillclimb Class Champion

8,040 posts · joined Jan 2003 · 29 Jan 2004, 4:09 pm

#133471

blue74l wrote:Why do it?
1) hopefully to have a better breathing head and a few more ponies to boot.

2) to have an opinion as to whether or not any one else should do it.

This way when i finally get around to doing mine Raf will post and say "yes - do it. My motor happily sings up to 6500 and feels like it can go some more!"

mmm Barry you need to change the Duration of the cam not just the lift to increase overall engine RPM. If you think that bigger valve heads with ratio rockers and a stock cam will give you 6500rpm then you better brace yourself for a steep learning curve !!

Now I know why "Stans the Man", and my engine happily out performs others !!

Anyway each to their own, you can lead a horse to water.......................

Craig Torrens 6 times Australian, 7 times State Hillclimb Class Champion

8,040 posts · joined Jan 2003 · 29 Jan 2004, 7:34 pm

#133541

mmm so no 1.4's on a stock cam, stock head combo 😀 bummer

I have 1.1 ratio rockers (standard) on a mild 1916cc😀 and have 111hp@wheels 😉

So verdict: Go a mild cam, slightly bigger heads with some 1.25 rockers:thumb

70AutoStik Insano Dub Head

730 posts · joined Aug 2002 · 30 Jan 2004, 12:01 am

#133661

karmannghia60 wrote:Last question, promise. I can get the heads I have now reco (ie replace guides) for between $200 & $240. While I can get full reco ones from the US (I will be there next week) including new 40x32 valves, new 3 angle seats and new silicon bronze valve guides for about $300. The later option looks better value, what do you think?
Thanks a lot

Don't do it!!!

The 041s were originally produced by VW, but after their wins in the 60s had caused the authorities to limit them to a 28mm carb in order to give the competition a chance.

If I catch you before you hit 'merica, try aircooled.net's ported heads on special, also for US$300. You'll get more power, more torque, and they won't crack between 5&15k miles (unless you go for too high a compression ratio.)

Sorry to sound like a bit of an ad (but I will say that aircooled, while a bit more expensive than some, have always treated me well,) but I wouldn't like to see anyone waste their money on 041-style heads.

70AutoStik Insano Dub Head

730 posts · joined Aug 2002 · 30 Jan 2004, 12:08 am

#133663

And Craig:

I agree with you on most things, but I think you oughta rethink the ratio rockers on a stock cam bit...

Grab a stock head and your caliper and think about the flow at various lifts. I think very soon you're gonna realise why the Engle W100 and a stock cam with 1.4's have about .417" lift...

Do some sensible porting and lift a little farther and you'll start to see why some of us are a little partial to stroking...

karmannghia60 Karmann Ghia Sucker

1,459 posts · joined Aug 2002 · 30 Jan 2004, 4:33 am

#133683

Where is the reply from Jak gone? Disappeared!
Hey Jak, would the cam I bought off you work with this? I am getting too confused with all this (but learning a lot). To summarise, this will be a daily driven engine in the KG. What I have so far is:
- new heads bored for 92mm with 40x32.5
- new 92mm P&C
- dual 40 IDFs or Kads (I am tosing which set to use)
- Extractors
- 009
- 200mm clutch/6v flywheel
- standard everything else
Under consideration, 1.4 ratios, swivel feet rockers & Jak's cam. Although I'd rather not split the case but I will if I have to. I am not about to drag race it. Now make it simple for my little mind
And thanks a lot

Craig Torrens 6 times Australian, 7 times State Hillclimb Class Champion

8,040 posts · joined Jan 2003 · 30 Jan 2004, 11:41 am

#133794

70AutoStik wrote:And Craig:

I agree with you on most things, but I think you oughta rethink the ratio rockers on a stock cam bit...

Grab a stock head and your caliper and think about the flow at various lifts. I think very soon you're gonna realise why the Engle W100 and a stock cam with 1.4's have about .417" lift...

Do some sensible porting and lift a little farther and you'll start to see why some of us are a little partial to stroking...

Some understanding of cams maybe needed, its not all about the lift !

duration and overlap ???

And yes I know all the various measurement etc.

Doug I have no problems with the benefits of "lift", just with the right sized valve.

So what do you think is the maximun lift a valve should be opened to , proportionate to the diameter ?

Just wandering what everybody thinks it should be ? regardless of cams and rockers etc
Happy for someone to tell me 🙂

70AutoStik Insano Dub Head

730 posts · joined Aug 2002 · 1 Feb 2004, 12:36 am

#134364

If you can find some flow figures for a stock 1600 head you will find the flow incrases quite steadily up to about .400" before the rate of increase starts to drop off. Increases remain useful up to nearly .500", in fact. This means some rather useful increases in flow, therefore HP (especially top-end) can be gained by increasing the lift of the valve while retaining the same theoretical duaration (the actual useful duration actually increases slightly with ratio rockers.)

I can't quite remember where the 1.4 ratio comes from, I think it was Mopar, but it just happened to be just right for VW heads and led to the lifts you'll find on the old-fashioned cams... The other end to the mild cam lift figure is .476"; which is the maximum theoretically possible lift that can be used with a stock head and springs.

Craig Torrens 6 times Australian, 7 times State Hillclimb Class Champion

8,040 posts · joined Jan 2003 · 1 Feb 2004, 8:02 am

#134393

So do you believe that you can open a valve to 35% of its Diameter ?

70AutoStik Insano Dub Head

730 posts · joined Aug 2002 · 1 Feb 2004, 10:23 pm

#134636

I don't see why you are hung up on this ratio bit. I do know that if you stick larger valves in a stock head without re-shaping the combustion chambers properly you will have to lift them a lot further to get close to a stock flow (hence power.) In fact, stock heads fitted with 40x35.5 valves in general need more lift to get them flowing properly. This is not due to any magical ratio of lift to valve head diameter, simply shrouding and the need for the gasses to turn further around the valve head.

Craig Torrens 6 times Australian, 7 times State Hillclimb Class Champion

8,040 posts · joined Jan 2003 · 1 Feb 2004, 10:42 pm

#134644

70AutoStik wrote:I don't see why you are hung up on this ratio bit. I do know that if you stick larger valves in a stock head without re-shaping the combustion chambers properly you will have to lift them a lot further to get close to a stock flow (hence power.) In fact, stock heads fitted with 40x35.5 valves in general need more lift to get them flowing properly. This is not due to any magical ratio of lift to valve head diameter, simply shrouding and the need for the gasses to turn further around the valve head.

Its not magical, but it is a ratio or proportionate to the valve size. The fact that you have just said that a larger valve needs to open more confirms that each valve needs to be opened to a certain point in relation to its size. You have just proven my point that I'm trying to make, lift has a direct relation to the size of the valve. The lift should equal to about 25- 28%of the valve diameter. Any more and its not really doing anything.
So a 35.5mm valve max lift=9.94mm or .390"approx.
And without changing any other characteristics of the cam except lift with the rockers, max power will still be at the same rev ranges as before.

So in my opinion I wouldn't bother opening a standard valve any more than this. Larger valve then a different lift etc etc

Anyhow I'm sure we all have different ideas, and that's cool:thumb
But at least we agree the bigger the valve the more lift it needs to achieve the same end results 😀

Peter Leonard Moderator Volatile

1,456 posts · joined Apr 2003 · 1 Feb 2004, 11:02 pm

#134657

what's all this high liftin doing momentum-wise? revs go up... flow goes up... valvetrain load compensates the blue thingy starts talking to the red blob... left hand starts talkin to the right hand...:alien

let sleeping dubs lie

70AutoStik Insano Dub Head

730 posts · joined Aug 2002 · 2 Feb 2004, 12:59 am

#134688

What you been smokin', Craig? You're trying to tell us that all VW aftermarket cam manufacturers (and VW's own racing division) don't have a clue?. Ever heard of Super V? Ever done the maths on 99.9% of performance engines?

In fact, the early 1200 and the 13 & 1500 engines (and the 1600 on the exhaust valve) exceed your recommendation!