Twin cam head design

[mikuni]

Thinking about building a race engine using an Opel motor as the base.

Essentially there are two head designs.

One is called a C20XE, shortened to XE or Red top and is very hard to find here in New Zealand but is renowned for its tunability and is used extensively in the UK and throughout Europe. On any vauxhall/opel forums the love for these engines seems a little blind because they have been proven to be such good engines and 300hp and achievable with off the shelf items and a bit of know how with the headwork. This engine was used throughout the supertouring years and is apparently still used in the WTCC and BTCC cars of today (Chevrolet).

The other engine is the X20XEV ecotec which is the one I have in the Chevette. It hasn't had much, if any race developement and is severly underpowered in its factory guise. The fact it arrived later than the XE meant that it was required to meet certain emissions regulations and powering a larger, more refined vehicle it needed to be smooth and torquey low down, rather than the limited production sports oriented cars that the XE was released in.

The XE is a wide head, with a high included valve angle, making the intake and exhaust ports quite a low angle, where as the XEV has steeper angle ports with a very narrow head design. The ports of the XEV are naturally much smaller also, to increase intake velocity at low rpm and thus torque. The EGR ports make the exhaust ports much smaller and more restrictive but these are easy to remove.

What I would like to know is which head has the most potential? I'm looking at different head designs and early higher horsepower twincam designs had a very wide head. Think Toyota 2T-G (more so the race engines) or the early gen 3S-GE engines. Later engines seem to have a narrower head design, still with quite large ports but with a steep valve angle. BEAMS 3S-GE and Honda's F20C and K20A spring to mind. Any other examples?

Does chamber and piston design effect performance hugely or are these more to accomodate that particular head design?

I would like to work with the narrow head design of the XEV ecotec and open the ports right up to the size of the XE then clean them up and do some volve around the valves to see if it has the potential of other later model high horse power engines, but I have the opportunity now to aquire a couple of XE heads, which would offer a tried and true method of achieving the power I'm after.

Any links etc would be awesome. In the next few months I might be able to get pics of both heads if I do end up going down this path.

[Unclejake]

Oh dear. I sense a detailed argument in the wind so i will try to only post once.

Anyway - first off I think you need to decide what RPM range you want to work in. This will be influenced by your gerarbox ratios and what the selection of final drive ratios is like for you.

Big ports flow like the Missisippi up high but as you know have crap air speed and reduced tourque. Opening standard ports up is hard work and time consuming but the real catch is the proximity of the water jacket. A donor head to cut into bits helps here a lot.

Valves high in the head (in relation to the ports) is not desirable due to the tight short turn radius.

Swirl patterns in the combustion chamber are important too but I do not understand that art.

I have been told (but do not actually know) that the majority of UK tracks are long and very fast. The dudes over there build their Mk1 Cortina engines to sing at 9,000rpm all day. Here in the North Island we want between 4,500 and 7,500rpm to get around the three tracks in operation (HD to come of course).

Perhaps spend a few hour planning what you need and then a few dollars flow benching the available heads

[mikuni]

Oh dear. I sense a detailed argument in the wind so i will try to only post once.

Post as much as you like mate. Your opinion is always very relavant and welcome, I will try to keep the thread heading in a good direction too. My one gripe is tech yarns heading down the toilet.

You make a valid point here too. The typical 6000-8500rpm screamer that is required off shore is not necersarily applicable to our tracks in NZ. Taupo for instance, has most cars holding a single gear right through the central section, depending on ratios and engine ofcourse.

In reality the gearbox ration and the likely large wheels that we will be using will mean starting off with a torquey engine in the midrange would be most desirable, ending up with a more peaky engine once the final drive can be reduced enough to make it all work together.

[rollaholic]

im not really in a position to comment on the viability of either head, but i would have thought that if you were primarily interested in building a race car, then the tried and true method has got to be a winner. experimenting with something and being a bit different is all well and good, not to mention fun and interesting, but you've got no guarantees of a quick car - which the XE head would appear to promise.

as for powerbands, presumably the XE head still came in a viable street 'sports oriented' car - hence i have no doubt that an appropriate selection of cams and headwork you would net whatever result you desired in this respect.

[BobbyBreeze]

Quite interested in this sort of stuff too. Plan on doing some extreme headwork within the next couple years and reckon this topic could be good discussion.

Anyways, i reckon a homemade flowbench, and a shit load of heads to play around with is the way to go. Massive ports don't mean massive power and i think this is the trap people tend to fall in to. Shape is more important, especially around the valve throat. Seems kind of silly to make these massive ports which have a large taper down in area where the valve is. Yes you want a slight taper, but there is no point in making the outer section huge when you cant really increase the size of the valve/throat etc. In one of David vizards books he explains this with a diagram - basically shows the flow potential for different parts of the port.

I haven't really had a good look at race heads, but one would assume the most direct shot onto the back of the valve would be best - so moving the port further up in the head and filling the floor should be a good mod. Also, a good valve job (3 or 5 angle etc) would help.

What sort of rpm do you want to run?

[Unclejake]

moving the port further up in the head and filling the floor should be a good mod.

QFT

[Spencer]

Steep ports are where every manufacturer has gone and f1 heads have been like this for years, eliminates flow problems with tight short turn radius and gives a better combustion chamber shape.

Steep ports = win

ls1 square ports = fail

As for which head has more potential it does depend on how far your going to go? you may not be able to take the ecotec inlet ports out any more and they may become a choke point later on? we need to cut one and check it out, should ask they guy who does my cousins bike engines which he prefers has done alot of race car heads

Didnt you once tell me that you had to open these up and do pistons and rods to go anywhere anyway? whats the costs like for internals between the two?

[mikuni]

Didnt you once tell me that you had to open these up and do pistons and rods to go anywhere anyway? whats the costs like for internals between the two?

Thats right. Internals in ecotec are gay but can use all the XE stuff, which I can get with that shell, so that doesn't matter either way.

rollaholic does make a lot of sense though. As much as I would love to have a play with an XEV the tried and true XE path makes a lot more sense and rather than get a long way down a dead end path, it would be better to just get the XE from the start and go with that.

I'm dealing with a guy at the moment who has a couple of stripped down XE's and I still have a spare XEV (I hope) so I guess I will get hold of these, pull the valve train and guides out and throw them at a band saw to see exactly what we're dealing with. Even if I don't end up doing any port work at all, atleast it will provide some awesome pictures!

Continue yarns about head design with pics and links please. Very interesting stuff I reckon.

[Spencer]

I think ive shown you these but more f1 stuff, i have a few more around

I do like the ecotec head better i dont think its going to hold you back, guess im lucky with the beams heads realy only needs a clean up and go

[Yowzer]

Got a book here about head porting, Practical Gas Flow by John Dalton, it's more aimed at older head designs (and was published in '89 anyway) but still makes for a good read none the less.

Has a lot of flow bench experiments (made from a vacuum cleaner) to measure flow at different speeds etc

[twosmoke]

.

[mikuni]

Managed to find this cut-away picture of an XE. It doesn't look to bad, not a steep valve angle but doesn't have a bad short turn radius on the intake side, which is probably most important.

[Unclejake]

^ No wonder they go like snot

[mikuni]

I guess so aye. I will have a look at one more in depth in the next week or two and will decide from there. The aftermarket parts availabilty of the shelf means that it will be the best engine to work with for a race car I think.

Still have I went with the ecotec for the shove, as they are just so much easier to get hold of over here. Finding an XE seems to be very difficult but if I ever get seriously into racing and have a bit of a budget to back me up then that should be too much of a problem.

[fuel]

it would be interesting to see what the differences between an XE and XEV are placing them side by side, and what exactly are the advantages and disadvantages of each motor, and then way up the advantages vs the extra cost of the XE - but then I guess the XEV will be disadvantaged by lack of off the shelf performance parts.

[mikuni]

Thats pretty much it. For the Chevette, I just wanted a cheap, reliable (haha) engine that is easy to get hold of, parts aren't an issue, and will make good power once opened up with slight head work.

But for a race engine, where you actually have the option of a few, I think getting something that is tried and tested, has a large scope for performance and readily available performance parts would be by far the best option in the end.

[Unclejake]

^ Which is why you really want a Honda S2000 motor and transmission

[FLAWLES]

this may be pointless but i will post it any way

few years ago i was reading something somewere about port velocity ( sp check ??? ) on suzuki switf gti's in oz that were pulling 11 sec 1/4 mile out of a 1300cc n/a engine ( and i know its drag racing but thats what that article was about ) and what they were doing was making the ports smaller in size now i should say i cant remember at what end of the port they were doing this, but it worked

i cant remember all the fine points and im trying to find the web site as i write this but i am having no luck

they also seam to do it motorcycle engines

[FLAWLES]

here are some links

not the one i was looking for tho

http://www.popularhotrodding.com/tech/0 ... ocity.html

http://www.eng-tips.com/viewthread.cfm? ... 416&page=1

here is a calculator for working it out too

http://www.wallaceracing.com/lpv.php

[cute wee gem]

I was reading a thing a while back about making the choke point of the port 65% of the valve size using epoxy, they were getting 6-8% gains on pretty much all the superbike engines they did it to. The epoxy was on the port floor and ended up going from round to more of a D shape.

Can't say I've seen a car engine's ports that are round like motorcycle ones though, but the theory could still be worth a shot.