i dont know if this has been said before , but is there any real power differance in the 2mm bigger exhaust valve as i am going to port /polish , shave and better spring either a std or xr6 head .
hopping someone will know thanks

If you've got a stock exhaust & cam, then the difference in hp is going to be small. Most people would probably say fit the XR6 head if you're planning to mod the engine.

The XR6 valve springs are marginally better than the stock springs.

JMM told me years ago a std 94' head is best to work on when porting.

Apparently the XR head have slightly narrower ports but with bigger valves to create more turbulance.

But at the end of the day, there is no big 'T' on the front so its not as good.

Yeah, go the Tickford 'T'! +1 It makes the car go so much faster - like racing stripes.

Its not turbulence it creates, its increased port velocity. Also enhanses scavening too. in all leads to a more efficient burn or higher volumetric efficiency.

thanks for the replies, i already have peacemaker extractors high flow cat and 2.5" exhaust , larger airintake with air ram, custom j3 chip , au injectors, 300kpa fuel reg and wade 977b12 cam
so i guess the 2mm bigger valves would be better

Aren't JMM the mob that usually shave too much off the bottom of the head to raise compression, then have slack timing chain issues leading to engine failure?

well i would like to know if that is true, as after i do some more mods i was going to get them to dyno the car, but if they cant get that rite dont think ill trust them

As much as I think the guys are tossers thats a bit harsh.
Considering most of the engines have less then 10:1 there isn't much being taken off the heads.
I have heard reports of their larger cams causing timing chain rattle though.

have you heard any good reports

I've had a JMM cam for over 10 years and been extremely happy with it.

Have also come across lots of positive feedback on their stuff - and can't say I've definitely come across clear evidence of anything bad - even chain rattling etc. all sounds more like mechanical issues or stuffups - and I've come across exactly the same sort of thing reported about the odd cam from both Wade and Crow - and again I personally think those cases are due to some other issue such as an underlying defect that wasn't spotted - or simply installation stuffups.

Setting aside the power claims that JMM have made, there's nothing outlandish or controversial about what they do - it's all straight forward sound mechanical practice. The contentious things are their results claims and the cost - not the quality / standard of what they offer or advise as such.

I have to say that I DO think JMM stuff is very fiercely priced...

On the subject of EFXR6 head: I fitted a brand new EF XR6 head to my ED many years ago. The difference between before the new head and after was absolutely zilch according to seat of the pants o meter - but I never dyno'd it. I pretty much feel it was a complete waste of money.

Physically the EFXR6 head had no built up "boss" around the guides inside the runners - the guides just came out of smooth wall. I noticed this in comparison to my removed ED head at the time - and then more recently confirmed the same in comparison to my EF Gli head.

I have noticed a definite improvement in performance with my current std EF head after tidying it up and doing some porting and chamber work - which is quite significant when as I said: I noticed NO difference before and after when replacing a std ED head with the EFXR6 one.

ok thanks for the info, i thought that would be the case with the head, if i can get an xr6 one for under 150 ill do that, other wise i think ill just do the work to a std head, after all i was going to do the same work to either head so the only diff would be the exhaust valves being 2mm bigger so ill prob loss say 2kw or so would only notice on dyno i think, could not justify the price difference

For what it's worth, here's my personal porting philosophy / guide:

When / if you do any porting, make sure to pretty much just concentrate on removing sharp edges from factory milling in the Intake ports - and remove as little material as possible. DON'T smooth the insides of the intake runners or throats - just remove any casting dags and smooth out milling edges - leave the worked areas with similar roughness to the original walls - ie. "scribbling" with the die grinder should do the trick. On the small radius of each intake port, roughen up the surface even more from maybe an inch along the port floor before the curve and right round the curve - ie. making "scribbly" marks with the die grinder should do the trick - but transverse grooves, dimples etc. will all do the trick. You can first try to take a little off the top of the small radius to "unmask" the body of the runner to the valve as much as possible - but remember that any material removed - ie. any widening of the passage - causes a slowdown. I think std heads with guide bosses allow more latitiude for this - so try to take the material from that sectional "zone" only. Keep in mind you're not so much trying to enlarge the radius of or flatten the curve as such (roughening does more to keep flow attached than making a gentler curve ever will - short of making it virtually straight) but you're trying to increase the line of sight area in the main passage of the port that's exposed to the valve (ie. SAME effect as making the port straight).

In the bottom end, having the cylinders able to pull air as straight as possible with minimal obstacles to pull it around is the go - and then at higher revs the surface finish, and absence of "shelves" is what will help maintain flow.

On the exhaust side make the whole inside of the ports as smooth as you can - if you can manage a mirror finish that would be ideal - but just making it somewhat smoother than it is (and of course removing any dags and smoothing milling edges) will do - EXCEPT on the small radius - which you leave as close to original finish as you can - even rough it up again if you work it and it ends up a bit smooth - this is to keep gas flow attached around the curve and fast along the floor of the port. The guide bosses in the exhaust ports can be tapered - think making a deep chamfer on the existing shoulders to end up with maybe half the width of shoulder left - and round the remainder of the shoulders. Also try to bring smooth grooves around the back of the bosses from each side. The thing you're trying to do is not give any flat face for exhaust pulses to bounce off perpendicularly back toward the valves - reflecting away out the ports is ideal and deflecting away sideways along the walls is next best thing (that's what the grooves coming in from the sides of the bosses are about as you can't taper that side of the bosses as such).

On the exhaust side you can remove as much material as you like - short of cutting into the water passages. This applies to the short radiuses - or "floors" of the ports - ie. if you have a good look you'll very likely notice that at least one short radius is not as "high" as the others and you can see more of the opening on the outsdie of the head - ie. at the gasket flange - try to make them all as good as the best one. What you want is to get a situation where you can see the most area possible of the opening at the exhaust flange face if that makes sense.

Do be careful of going thru the port walls tho.

thank alot for the info much appreciated

just got a tickford head 94dt, the info i got for the exhaust and intake ports was great and was just wanting to know, if there is any advice on the chambers or should i just leave them alone thanks