HI All,

I have a smog head, 12g1316.

Just trying to work out what the best combination of valves to use.

I already have 1.44 inlets and 1.16 exhaust valves, both rimflo.

My concern is based on Vizards manual the ratio of flow might be affected with the standard size exhuast valve. The exhaust already has hardened seats which im wondering if they can be removed to achieve better exhaust flow?

I would prefer not to offset the valves, so would it be better to swap the inlet to say 1.4 and get a slightly larger exhaust (1.21)?

Has anyone used the 1.44's with out cutting into the divider section?

I'm hoping the store i bought the valves from will swap the 1.44 for something smaller if needed.

cheers for any help.

_________________
1275LS nugget gold
GSX-R1000 K5
Ducati panigale s (carlos checa replica)

For N/A applications, a very general rule of thumb is exhaust valve area = Inlet valve area x 0.7. And I do stress this is a general rule of thumb.

Personally, I would suggest you not go too big on the exhaust valve for reliability.

Rimflow type valve on the Inlet are a good idea and work well here, but they are a backward step to use on the exhaust. Think about how they (are intended) to work and you'll see why.

I would go for the smaller valve and if I was worried about insufficient exhaust valve area then I would choose a cam with extended exhaust timing and/or lift to compensate (a bit).

cheers,

Jacob

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'72 Clubman Van - 1022cc, 295 head, 731 cam - Daily Driver
'69 Morris 1100 S - Dinged by a bus, in shed under repair
'64 Morris 1100 - Early 1100, long term project

Mate, what are you trying to achieve? Think you are are complicating this situation way too much.

Have a look at real examples of the race Nb & Nc guys, most run Mk2 S size valves, some run Mk1 S size exhaust valves. Mk2 S size valves are good for 140 - 150 hp without resorting to offseting the exhaust valve, which is not necessary. And in your case, not possible due to the hardened seat installed already. You might be able to open up the hardened seat to 1.2 (Mk1 S size), but really not necessary.

And as Jacob says, there are other combinations to consider also.

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Steve

Mate, if you read my post you would realise i already have rimflo valves. So i'm not looking for different types of valves, im happy with what rimflo claim to do.

It may be me but i don't think im complicating this at all, my question is fair for my situation.

1. will the flow ratio between the two be ok (1.44 vs 1.16)?
2. Should i exchange any?
3...

The decision to have optimum flow and a well tuned engine is entirely mine, it has nothing to do with hoping to get more horse power, hell if i was after HP i'd just jump on my 168bhp gixxer.

_________________
1275LS nugget gold
GSX-R1000 K5
Ducati panigale s (carlos checa replica)

1. will the flow ratio between the two be ok (1.44 vs 1.16)?
Probably. But because you have hardened seats on the exhaust, likely to have difficulty installing them. Not saying impossible, I wouldn't do it.

2. Should I exchange any?
Yes, your 1.44" inlet valves for 1.4" inlet valves.

_________________
Steve