RB25DET Head porting info

[Bl4cK32]

yeah steve. I told u b4 its Chris Miltons. You got a qoute from them by memory, but it was too much? Interesting though - I have heard (on good authority) that the same work I'm getting done would've costed anywhere up to $1100 from another engine developers. Chris is pretty cheap - but it does save u to take the head off yourself

[Steve]

Wish I had the tools/know how - otherwise I would take it off myself:) Cheers.

[mambastu]

Hi All,

Head portings going well if slowly

I've been told that you should use an 80 grit sander for the final finish on the inlet port to promote fuel/air mixing but it looks a bit rough to me. Does anyone know if thats the correct finish for aluminium ?

[T0nyGTSt]

Do you know what the problem is???

Good labour is expensive.

Look at the head. It's 24 valves. I'm getting charged a fair rate IMO because my head (metaphorically speaking) is a bit farked.

I've got some higher quotes for a simple four cylinder 16v head.

T.

[EnricoPalazzo]

I remember a while back i wanted to do this to my car. Basically i found out alot of good info on techniques and such. What i would personally do is go to some place which has old engine heads for scrap, and use it to practice the correct techniques. That way when it come to ur real head, u shouldnt have too much trouble.

Also A dremel i find is the perfect tool for this.

[gtrhybrid]

Funny you guys are on the subject cuz Im in the process of redoing my rb26 head. Im going through the head and porting and cleaning up the combustion chamber for better burn. Now, for the humps on the exhaust side, my theory on those is smooth them out as much as you can. If you were to run into a stud the worst that could happen is that you would have a very small exhaust leak through the stud itself (very unlikely). But it will pay nicely with power increased and better spool up too.

[Cubes]

Chris milton ported and polished up both the inlet and exhaust ports. He said some thing about concentrating on the bowl area.

He also cleaned up the combustion chamber so that the air was able to flow in to the cyclinder a little easier hence removed material and then polished that up also. On the Inlet valves he did a 3 angle valve job I think it was and on the exhaust he did a different valve job which made everything really round. I'll find out the exact terminology.

It ended up costing a little more than anticipated as he forgot to mention that its extra to shim the valves when setting up the hydraulics, not sure exactly but u get the idea.

[mambastu]

Finished the head now and pictures will follow shortly.

The porting was all done using a cheap air powered die grinder and a Standard Abrasives porting kit. Took me 3 days to do it but I reckon I could do one in 1.5 days now I know the areas to concentrate on. Hope this information is useful to everybody

[Cubes]

damn.. My camera won't take pics that clear..

What camera are u using?

[mambastu]

Originally posted by -Joel-

damn.. My camera won't take pics that clear..

What camera are u using?

Its a Fuji S602 camera I think, its not mine its a mates.

I just edited the thread with a load of pictures and a description of what I did but its been rejected .......I'll do them as seperate posts.

[mambastu]

The original exhaust port showing the intrusive port bumps

The finished exhaust ports....

From the combustion chamber side....

All of the intrusive exhaust port bumps were removed the ports were enlarged to the exhaust manifold gasket.

All casting marks were removed.

The divider was knife edged and the valve seat area was blended into the bowl.

The 'short' side of the port was radiused as there is a fairly sharp edge where the port turns into the bowl area.

The exhaust ports were finished with a finely polished shiney surface to slow carbon build up.

[mambastu]

Standard inlet port....

Finished inlet ports....

From the combustion chamber side....

The inlet ports are very well shaped in standard form and have 3 angle seats as standard.

Inlet ports were all enlarged to the inlet gasket.

The area where the valve seat meets the bowl was blended smoothly and all port casting marks were removed.

The divider was knife edged and the ports were finished using an 80 grit sanding roll to promote good fuel/air mixing.

[mambastu]

Combustion chambers......

All combustion chambers were smoothed and polished thoroughly to reduce the likelihood of detonation and also to slow carbon buildup.

The combustion chamber shape has not been changed at all so compression ratio should be unnaffected.

[warrick]

here's a couple of pics from my sons vl turbo.

cheers

warrick

[warrick]

pic number 2

[dkonig]

Does anyone know what sort of power a head porting job like this would make on its own? everyone I have spoken to has always done it in conjuction with other work... (this is on an RB25)

[Mick]

If you didnt have to buy a new head gasket when you remove the head i would grind and polish it all up myself... bit of a pain .. maybe one day when i need to rip the head ill do it ...

I got a question, ive got my exhaust manifold off at the moment and i was wondering if its a good idea to grind and smooth the inside of the manifold since its off anyways?

Another question i got is on the manifolds turbo outlet there is a divider in the middle that seperates the pipes - OOO|OOO -

anyone know if i can play around with that ? eg. like make it a knife edge or totaly remove it ... It has a slot in the middle of the divider as well ...

[BOOSTD]

I ported my manifold, seems to make a difference- couldn't really tell because i changed the turbo as well. Also removed the intrusive port bumps on the exhaust side of the head while it was still on the car. Making nice power for a T3/T4 hybrid. 266rwkw.

[BOOSTD]

oh and make sure you don't go to thin as it will crack. Get a pinch measuring tool to check wall thickness. don't go under 2.5mm.

Also some of the bumps near the outlet are purposeful to direct the airflow around a the bend, these need to be smoothed rather than removed.

Be carefull knife-edging the outlet as a heat fatigued piece of broken metal will kill your turbo in a second.

[Sydneykid]

Hi mambastu, did you equalise the capacity of the combustion chambers?