Street porting a 1.9 big valve head

[Vagos]

sorry here is the pic

[RallyBob]

Originally Posted by Vagos Plus the valves were stock ones.With venturi like shaped.Is it possible to give the stock valves an under cut stem to make them look like chevy valves??here is a pic of a stock opel(from Bamotec valve)next to a chevy one.

Stock Opel valves are two-piece, fusion welded together. The stem is welded to the head of the valve. If they are made too thin here, the head may come apart from the stem of the valve...not good!

Bob

[Vagos]

Realy???Didnt notice that before.It doesnt matter though as my nesxt head will be defenetly a chevy one for my future stroker motor.I have also ported a 2,4 head as BAMOTEC desing as best i could for a friend of mine.And when he tried on his 2,4block on an opel ascona b he was amazed with the results!!!HE said the car has 100% better thant before.Hope this help the german friends here.Cheers

[GTJIM]

Originally Posted by Vagos I have a BAMOTEC head ... But what i DIDNT like on this head is that the ports both the exhaust and the intake wasnt polish and rough as they should be for optimum perfomance they were just left as they were after the porting work.

The ports are supposed to be left ROUGH!

Polished ports 'look' good - and may even flow a little more DRY air on a flow bench - BUT when fuel droplets are added to the flow in the inlet port they produce LESS power and have to be run much richer to compensate for the liquid fuel which spreads out over the polished surface. This also leads to un-mixed lumps of fuel arriving at the valve without the necessary air to burn it!
The fuel film is thought to re-enter the air flow by being re-united with the air flow by being stripped off the little peaks of the rough finish by the boundary air turbulence.

The exhaust port very soon gets coated with a thin layer of carbon - which helps as an insulating layer to stop extra heat being transferred to the coolant through the port wall. A rough surface in the exhaust port helps this carbon film form and stay in place.

So polishing is not only a waste of time - it is detrimental to performance!

[Vagos]

Helpfull info Jim.I have the intake ports rough with 40 grit.And i find that it works fine.But didnt know that polish the exhuast ports has so much difreence over rough ones.Cheers

[yellaopelgt]

Originally Posted by GTJIM The ports are supposed to be left ROUGH! Polished ports 'look' good - and may even flow a little more DRY air on a flow bench - BUT when fuel droplets are added to the flow in the inlet port they produce LESS power and have to be run much richer to compensate for the liquid fuel which spreads out over the polished surface. This also leads to un-mixed lumps of fuel arriving at the valve without the necessary air to burn it! The fuel film is thought to re-enter the air flow by being re-united with the air flow by being stripped off the little peaks of the rough finish by the boundary air turbulence. The exhaust port very soon gets coated with a thin layer of carbon - which helps as an insulating layer to stop extra heat being transferred to the coolant through the port wall. A rough surface in the exhaust port helps this carbon film form and stay in place. So polishing is not only a waste of time - it is detrimental to performance!

Here's a quick question....I understand the "rough" porting in the head area to suspend air/gas mixtures. BUT.....does this also apply to a street ported intake manifold? as-per R-Bobs thread? If the intake base is matched to the carb,and the plenum rounded out a bit and even if the "tent" was in there,does this defeat the purpose of suspension a bit? The intakes shown on that thread appear to be as smooth as a babies bottom.I'm confused....again....
Joe

[RallyBob]

Originally Posted by yellaopelgt Here's a quick question....I understand the "rough" porting in the head area to suspend air/gas mixtures. BUT.....does this also apply to a street ported intake manifold? as-per R-Bobs thread? If the intake base is matched to the carb,and the plenum rounded out a bit and even if the "tent" was in there,does this defeat the purpose of suspension a bit? The intakes shown on that thread appear to be as smooth as a babies bottom.I'm confused....again.... Joe

I can't account for what everyone else is doing to their intakes, but on my own intakes, I leave the intake runners 'as cast'. And the plenum area that is reworked is polished to no finer than a 36 grit finish, so it is rather rough and matches the finish on my intake ports on a ported head.

The plenum 'tent' is rather smooth, but by virtue of the reduction in plenum volume as well as the directional control offered by the 'tent', the air/fuel stays suspended better than with a stock unmodified intake. A stock intake tends to have lower operating vacuum as well as a 'dropped' plenum floor where fuel settles out of the incoming air/fuel mix.

Bob