Vauxhall C20XE head porting queries

[alex new]

Hello,

My ported head and Iis with +1mm valves 34mm / 30mm. The inlets are wasted stem.
I opened a lot the port inside thru the splitters giving a oval shape of 27,7mm from bottom to top and 26,5mm from left to right.
Although in the beginning of the head I opened less the port and my current dimensions are 47mm x 28mm. I did that because I wanted to move the venturi of cylinder port more outside. So the minimum area of the port to be in the beginning of the cylinder port and not in the splitters. I think this shape is better when engine flows an high rpm. Although my head in Superflow sf120 that I tested at 10" of drop pressure of water flows only 140cfm.

The engine had a good performance. I had a output of 235PS(DIN) at 7950rpm with hydraulic lifters and a camshaft of 283/279 duration with 11.5max lift and opened at tdc only 3mm at 108 peak lift and 2.40mm the exhaust at 111 peak lift. Also this was with a single body plenum inlet custom design that was a combined mix with the Jenvey tapered inlet manifold.

Now I am moving at a 2300cc project. Y22XE engine block and 88mm pistons so I need more air capability from the head.
So I am thimking that the head must be opening more to see more flow and that will maybe destroy the effect of the venturi as I thought maybe to move it further from the chamber.

So I want to ask the above.
1.What do you think for the venturi shape design to be more further from the std position that is thru the splitters?

How much can someone port the dimensions of the head port?

I am thinking to opening the port from my current 47mm x 28mm to 49mm x 29mm, to give my extra 300cc more area to breathing because I think 140cfm is not enough for the spec I want. Is this dangerous for cracking with water passage canals or is it safe on that dimensions?

The head is a Coscast early type.

Thanks

[Guy Croft]

You're going way too big thru the splitter, you are definitely borderline breakthru, and you can get over 280bhp with a 35/30 valve spec even with only 26.8mm thru as my data shows below - check it carefully.

You may be losing flow because your short-side radius is wrong, those heads don't hardly need any at all and the region from the contact face of the seat (in my view) has to be raked right back to produce a relatively short and small diameter curve.

Most likely (I suggest!) there are 4 things actually holding you back, you need:

1. Jenvey Taper ITBS (individual throttle bodies) with 45mm throttle plate
2. Your CR may be too low, you need to run 11.5 or higher to get the best out of a 34/29mm valve combo and the best I've had is about =/> 275bhp
3. Solid lifters, no way will a hydraulic follow the cam profile at the kind of speeds you need to run to to get high bhp (8000 +) speeds, they might be locking up much over 7800
4. More powerful cams, I strongly recommend the Piper range with springs to match.

Hope this helps some,

G

[alex new]

Thanks for your reply, and for your advice.

You're going way too big thru the splitter, you are definitely borderline breakthru, and you can get over 280bhp with a 35/30 valve spec even with only 26.8mm thru as my data shows below - check it carefully.

You may be losing flow because your short-side radius is wrong, those heads don't hardly need any at all and the region from the contact face of the seat (in my view) has to be raked right back to produce a relatively short and small diameter curve.

When I have time I will take some pictures of my head and the porting from different angles to give you better way to see where is the problem.

Most likely (I suggest!) there are 4 things actually holding you back, you need:

1. Jenvey Taper ITBS (individual throttle bodies) with 45mm throttle plate

I made myself a custom intake that flows very well ( when install the intake in the head) it flows about 4-5 cfm more!
Here is some pictures of the intake in primary version. In my current setup I did better the angle of my oversized throttle body and also I shortened the runners about 3,5cm from the pictures that you see.


2. Your CR may be too low, you need to run 11.5 or higher to get the best out of a 34/29mm valve combo and the best I've had is about =/> 275bhp

In my old setup I had 11.6:1 CR. Now with the 2.300cc version the CR will be about 12.2:1 - 12.5:1. My valves unhapily is 34mm / 30mm (and not 34 /29) so I need a strong intake camshaft and a smaller at exhaust side.

3. Solid lifters, no way will a hydraulic follow the cam profile at the kind of speeds you need to run to to get high bhp (8000 +) speeds, they might be locking up much over 7800

For my new specs I moved to solid lifters so I think to see a gain in high rpms.

4. More powerful cams, I strongly recommend the Piper range with springs to match.

The newncamshafts I choosed is from catcams and a lot wilder from my old setup.
Inlet 293 advertised duration, 262" at 1mm 13mm max lift, TDC 4,50mm at 106" timing flat nose
Exhaust 285 advertised duration, 254" at 1mm 12,25mm max lift, TDC 3,95mm at 106" timing


Hope this helps some,

G

Thanks again dor your advice. I will post soon my jead with pictures and dimensions to see if it have some problem with the current porting.


Alex

[Guy Croft]

Quite a simple procedure to add photos.

Click on 'edit' (top right of your post)
scroll down to 'upload attachment' - click that and then 'browse'
find the photo in your folder that you want to upload (needs to be jpeg format) and click on it
click on 'add the file' and write your caption
do the same with the next photo
when you've finished putting your photos in - click on 'submit' to upload to the web

GC

[alex new]

Hello again,
I taken the pictures and I leaved also some comments in every picture so it's better to understand someone what I show in every pic.
I am waiting for your thoughts and comments for the porting of my head.

Thanks, Alex

[Guy Croft]

Looks good to me Alex, I would not go any bigger!

Cannot comment on the inlet setup, sorry.

I recommend that you do NOT shave guides, yes I used to do this 16 years ago for flow on Fiat type 8v heads but have not since this new firm was formed some 8 years back because, with good lubrication, it was clear to me that they would last for 10 years or more but shaved, well you can't overhaul the seats and so they have to go, bit of a waste of a good set of guides really.
Aerodynamic shape guides are a much better bet. The loss on little guides especially like these is minimal. 'Shaving them' (grind off) drastically reduces stem support and thus degrades valve-seat life and makes it almost impossible to get an accurate 45 deg contact face.
You should fit new ones really. I do stock them. I pull the guides before porting on almost every head and fit new only when the porting is fully complete.

Hope_this_helps some,

G