Exhaust porting advice

[Dragun]

Quick one guys, thinking of goin half bridge soon but I have a question about the exhaust ports. I know for street ported engines it\'s usually preferred to grind down so exhaust port opens earlier, would you guys say for half bridge it\'s the same? Or shud I open it upwards, bit of both?? Will Prob end up using templates but just need to satisfy my curiousity.

Thanks gents.

[Grant Monkhouse]

Go full bridge, half bridge is for pussies. Lol

With a bridge you will be getting major overlap so porting the exhaust up isnt the best I think.

Opening the port outwards too the sides may be a better idea??

Are you wanting to do it yourself? Getting ports ported by someone else and paying them to do is probably the best idea, as not a lot of people that do it and know what works are open to telling everyone what to do, when essentially ports are ports IMO.

Not much help was I? Ha

[Grant Monkhouse]

Infact iv just looked at  my full bridge exhaust port from the outside looking in......

They\'re not gaping holes....

They\'re real smooth....

That\'s all I can say really, nothing distinguishable about them...

Give Carl a ring and he will point you in the right direction;)

He did with the porting my dad did on my FD:) and they ended being very huge street ports:D even by Carl\'s standards

[Dragun]

Thanks grant, well I want to become self sufficient In the rotary world, I\'ve got a few damaged irons and housings I picked up on flea bay to practice on. Haha xD yeah full bridge would be awesome but I want atleast a lil dignity driving at lower revs, keep a bit of vaccume going through. I have been looking at lots of sites and documents and people say go lower, higher exhaust ports with a bigger over lap are for race engines, while a lower opening port will aid in spooling turbo etc.....others say concentrate on smooth transitions when porting which is a given.

I\'m so tempted to take them to a shop but if I don\'t do them myself I\'ll never learn.

What\'s ur view on the intake runners? I read on a site that the open area of the exhaust port should be atleast 80% of the size of the runners. Never heard this before :/ what\'s ur take?

Also does anyone know anywhere in the uk that do templates? Or will I have to order from us? Don\'t want to print any out from the net, want physical metal ones

[Grant Monkhouse]

Racing beat is your best port of call;) speak too Clive at MRP and he will be able too get them for you. They do a few different sets. Street bridge monster port.

Port match I take runners and smooth them out as it\'s a turbo motor, NA motors need a slightly rough runner, not sure why.

The exhaust port acts so of like a Venturi, by going from a smaller opening too a bigger one, which helps with spool etc this is just stuff iv picked up off Many people

[Grant Monkhouse]

Apparently stock port timing gives best spool and low end torque, so if you could bridge port small and keep the timing the same you should get
More air flow and max torque and spool, in theory.

Would be something I personally would like to
Try

[Dragun]

Thanks man,

Yeah it would make sense to keep them smaller and not go too mental. I think the rough runners in a NA car is something to do with the turbulence mixing the air/fuel better? Pretty sure I read that somewhere.

Sweet I\'ll get in touch with Clive. Be nice to have them incase. So port match runners and try keep the overlap to a minimum.

Thanks for your help dude. Hope the family is well and your keeping that rx4 out of this crazy weather

[Grant Monkhouse]

Family is good and rx4 is in the garage all nice and dry. Overlap can be a good thing as it helps spool too. But too much on a road car will be a waste of fuel.

You woo get overlap by just going too a bridge I think, you need to lay a plate down with a housing and a rotor in there and rotate it with the eshaft and you will see when the port opens. A bit hard to describe it without showing you physically.

[re japi]

Yeah it would make sense to keep them smaller and not go too mental. I think the rough runners in a NA car is something to do with the turbulence mixing the air/fuel better? Pretty sure I read that somewhere.

Yes, that is true. In 1980´ every body here made them like "mirrors", very smooth and polished. Later they realized that it isnt the best way. Now it is quite common to actually made ports smaller. When port narrows towards cylinder, it actually flows faster. So flow mass of the mixture is bigger. Also trying to create pulse effect is important

[Dragun]

Yeah I know what you mean about spinning the rotors to check overlap, maybe an idea to ink them in first and spin the rotors round to check overlap. That made me laugh about the overlap being a bit hefty on fuel yet your like "go full Bridgeport, half is for pussies) xD made me laugh.

So on the subject re jap is talking about, what are the effects of narrowing exhaust ports for improved flow on a rotary?. Also anyway to modify the exhaust collars ( that protect the irons from excess heat) to improve performance?

Also one last thing. Has anyone lightened their own rotors with a dremel and a set of scales?? Is it worth doing whilst the engine is apart? Looking at examples it can\'t be that difficult to take off material to get the rotors identical and lighter. With this would the rotor, eccentric shaft and counterweights need to be balanced as a unit too?

[Grant Monkhouse]

Don\'t lighten your rotors with a dremmel!! Lol. They need to be balanced at the same time as being lightened and clearence along with the counter weight:)

I see Colum viewing the thread so hopefully he can offer some better advice than I can.

Yeh I did laugh to myself when I wrote about excess fuel, but you got to make compromises for things

[BlitzBoy]

Haha xD yeah full bridge would be awesome but I want atleast a lil dignity driving at lower revs, keep a bit of vaccume going through.

you may as well go full bridge, I have had both,very little difference  they both idle at the same speed and made the same noise and vacuum IMO

[matt p]

You\'re only down the road from me, if you ever want to see a Halfbridge up close pop up to where I\'m building my fd. Only 20-25mins away I leighton buzzard

[Dragun]

Ah dude sounds like a nice lil trip. When I get some time off work I\'ll drop you a pm thanks

[Dragun]

Thanks blitz between u and grant I think I\'ll go full xD. Is it worth notching out the housings? Or not really worth it for a street car?