Im running a stage 3 head on my ZVH and im going to re-build it with new seals, gaskets and get it welded so i can use the zetec gasket ect. Are there any other worth while mods i can do whilst the head is stripped? I read somewhere that you can open up the oil return holes to help the flow back?

 

Have the head put on a proper flow bench to see if it is any better than a standard head.
Who did the "stage 3" work?

A bit of grinding here and there and bigger valves doesn't mean anything in terms of performance gains - many times the
head will make less power.

 

Hi perry,
The head was done by power engineering and origionally it was fitted to a 1900cc tall block. Im pretty confident the head is good and i was going to upgrade my inlet manifold to suit the stage 3 head.

As i was taking the head off it was just a thought that i would see if any other worth while mods could be done.

 

I would still have it flow tested - did power engineering flow test it after they "modified" it?
Many shops put larger valves in and call it stage 3 to make extra $$$.
Who would know if it was good or bad?

Larger valves are not required on a cvh anyhow. They actually impede flow.

 

how much would you head be perry?

mine wasnt flow tested but has seen many years r+d on the dyno

would be iteresting to see how well mine works in comparisson to one that has been worked as yours has

 

originally i assume they did flow test it as it was part of a system 2 ebgine package they used to sell. Im now using it on my ZVH so im guessing the big valves would help. Would you know if opening up the oil ways in the head help?

Here are a few pics perry, not that you would be able to say if its good or bad without a flow test.

 

you are quite correct - can't really tell without a test.
One test is a flow bench - with and without inlet manifold attached.

Another test is an engine dyno or even quarter mile drag test.
A good head/inlet and mapping will make great power at low boost.
No need for 20+ psi to make 200 hp.

 

ooo

mine was runing 2bar lol

guess that might say something

 

boost is good tho , cant wait to get sum proper boost in mine

 

If you want to keep the head there are still simple mods that most definitely help.

Cutting back valve guides, cut back valves and 3 angle valve seats all help. Perry is very correct in what he is saying, sadly access to a flow bench is limited so lots of people though. But if you make a noticeable gain in power at the same boost post head VE has been improved.

Rob,

 

PS, your inlet and exhaust ports do look fairly massive... which isn't always best.

 

I think i might take it to cylinder head developments about half hours drive from me and see if they can improve on it? I bet having the valve guides cut back would improve the flow quite a bit. would 3 angle valve seats make much of a diffenece? I always thought a larger valve seat for turbo aplication was better?

 

iirc the std valves are quite big already

 

All valve jobs should already be 3 angle
That is how one sets up the valve seat width and placement. You can't do that without 3 angles.

That is another term used to get extra $$$ from your wallet.

 

perry - how much would a similar head be to yours then?

 

give nms a bell

remember karl saying not to long ago he is developing a head to floe 500 bhp still on a cvh too

 

True, but the top and bottom angles are usually changed (i should have been more specific).

My seats were cut using info from the pumaracing site and the linked site.

http://www.pugheaven.co.uk/CYLINDER%...IFICATIONS.htm

My inlet valves were back cut, i didn't want to reduce the thickness of the exhaust valves. Supposedly these both improve flow at low to mid valve lift.

My guides were ground flush with the ports again this is supposed to make a good improvement to flow. These are fairly standard things to have done, all showing documented improvements to flow.

Rob,

 

Makes a good read that... Nice 1 Rob!

 

Juffer is you go cylinder head developments tell him i sent you Russell and he will look after you good bloke used work for Autosprint when they was the big name in the 80s and 90s

 

Cheers for the link rob. Makes a good read

Thanks russ i will p[ay them a visit

 

I agree that specific seat angles of the top and lower cuts (and their width) are very important to flow.
However, these angles depend on the specific valve shape, port geometry, etc....
Without a flow bench choosing angles based on what someone else has done is folly. Your flow will probably be lower than optimum. No reason to change from the 75/45/30 degree factory angles.
Only a flow bench will tell you what angles to use.

My God, does no one in the UK have a flow bench? They really aren't all that costly?
Every good shop here has a flow bench - to verify head work. Can be used more to show % gain instead of a "cfm" value too.

In a city of 700,00 there are well over 6 shops with flow benches.

 

Im sure plenty of places have flow benches, I just don't know any of them Still hasn't stopped plenty of people on this side of the pond making decent power.

I also didn't mind basing my valve angles on tried and tested results from a well known authority, i don't really have the time (or cash) to try various angles on various heads etc, and who's to say the stock angles were optimum for my ports anyhow?

Im sure my head is less than optimal, but im very sure its better than standard I also disagree that peak port flow is always the answer to a good all round head.

Maybe one day when i have too much time on my hands i'll buy a flow bench Alternatively i could just post you a head for you to work some magic on

Rob,

 

I was not saying anything about peak port flow. I could care less about peak "big flow" numbers. Head work is all about maximizing flow through a certain port cross sectional area. Of course massive ports can flow lots of air - but the engine will make no power.

Valve seat angles can hurt the mid-lift flow numbers - or increase them.
If you chose angles that were tried and tested on a cvh then great!!
Hopefully you are using the same valves (valve size and underside shape) that they were using too.
Anyhow the flow gains from "custom" seat angles is minimal. Seat widths make more difference than the actual angles do anyhow.


Cheers

Not sure why we argue?

 

time of month

 

Your knowledge is second to none perry and it's a great read. It seems that over here in the UK you cant just walk into a machine shop and ask for a flow bench test. It's not a machine that is used often for us and may take up a lot of space in there shop ??

Do you have any information of specific angles or pictures of moddified CVH heads with or without large valves?

 

I can't see any thing in the post i made that would make you think we are having an argument, but im sorry if it came across that way. As you know this is a subject im fairly interested in, im keen to learn as much as i can but im hampered due to not having access to a flow bench.

Im using the same size valves, and i believe valve shapes.

Would the seat widths you use show a gain across the board, on any cvh head? Or are they very specific to your head?


Any ho, im thinking of making up something similar to this before my next head, what sort of flow bench do you use? and what do you think of this?

http://www.diyporting.com/flowbench.html

Rob,

 

Oi don't you bloody stir the pot

I know what you mean mate, its a shame they don't!

 

http://www.pumaracing.co.uk/CVH.htm

Another interesting read. Some interesting points in there that my head doesn't have. Im actually wondering what my head flows and is it any better than standard? Again the flow bench would help lol

 

The pictures of them ports look aweful.

What power are you making and or expecting?

 

Im making 248bhp @ 18psi. im happy with my power and not looking for any more but If i can make a diffence or improve the head whilst im giving it a overhaull then its worth while. The head is fitted to a ZVH now ( 1600 cvh in photo) and the head is the key to the ZVH engine and got to be right IMO.

 

IMHO, if your looking for no more power then ports are far too big, I've got a much much smaller head than that on the ports and it gave 303bhp on a 1600cvh

Id say that head is your weak point, also standard valves are fine for 300bhp on a 1600 obviously the 2.0l zvh will need more flow but the head looks poor, I can't get over the sizeof the port at the start its huge!

 

They are fairly big. Im thinkig of grinding back the valve guide and looking at the throat behing the valve.

 

Heres a link to a thread i started when i did my head, theres loads of good advice on there from Perry and others.

My inlets are pretty much standard size and shape with casting marks removed and valve guide cut back, gentle reshaping behind the valves to get rid of any nasty steps. My exhaust ports IMO are far too big, they were opened up at the manifold end to match to my exhaust manifold, the size right by the valve is still too big but not too far from standard, the port roof was raised, Perry tells me this didn't improve flow in his head so it was probably a waste of time. The pics aren't too clear but the throat is a similar square shape to Karls NMS head and others.

https://passionford.com/forum/ford-e...started-2.html

Rob,

 

My EFI head. With original valves and new (radius shape) valve seats.
Sadly i didn't take head to flow bench. Inlet slightly ported, exhaust side only skimmed to flow properly.

 

Greetings Bomsch,

The head looks good to the naked eye.
The radiused valve seats should be used for the exhaust side only.
The inlet side needs sharp edges on the valve seat angles - this helps the
air turn. Radiused seats on the inlet will reduce air flow at all lifts - not just peak flow.
I hope the shop put the radiused seats on the exhaust side only.


One other note : The largest single increase in airflow we saw was removing the inlet valve guide protrusion. The valve guides are plenty long enough and making them flush with the port roof makes a very substantial difference (increase) in port efficiency. The air speed is very high right where the valve guide is located.
Leave the valve guide longer in the exhaust port. Shortening has no effect.


Cheers

 

Perry, any comment on the DIY style flow benches in the links above?

 

What links?
Some of the DIY flow benches are quite good.
The small ones that use a single vacuum cleaner don't really tell much.
they test at very low depressions (10" or lower) and convert to higher depressions 28", 48" etc.
The best flow test devices have several vacuum motors (6 to 10). There are some internet plans for those out there.

Cheers

Perry

 

These guys seem to show a bench type with one vacuum cleaner and others with several vac motors...

I've been having a look around at others and they give a comparison between this type and a proper bench. The difference in readings was less than 2 CFM.

Rob,

 

Hello Rob,

Flowing cylinder heads at low vacuum levels does not give good results.
An engine experiences very high vacuum levels during an intake cycle.

Sure the sellers try to show a specific test case where readings are similar.
However, this is just not the case in real life situations.
Many cylinder heads only show port turbulence at higher vacuum levels - 20", 28. or even 48".
Port turbulence is a power killer. (as you probably already know)
Some experienced porters listen to the ports (when flow testing) and can tell if they require more work.

For a very low budget, the example you provided is far better than no testing at all.

Cheers.

 

Thanks Perry, perhaps it could be a route to investigate in the future (with several vac motors).

Rob,