Intake Ports On 16V 1100?

[mark m]

I've seen some intake runners that were hogged out and looked to be paper thin too. I guess it all depends on what your trying to do and at what rpm too.

But if I owned a flow bench I'd be given it a good workout.

Hey Jake,

I've been crunching some more numbers and it looks like 35-36mm would be more appropriate to the GS valves. Does it look like there is room for that on your 1100 Head?

Second, can you measure your 1150 head (or anyone else) and let me know what size the inlet is?

Don't those MotoGP motors spend all their time between 11-17k RPM?
Does that translate to a 30yr old hunk of iron with a 9k redline?
I'd love to know more about MotoGP bikes!

Yup, they run high rpm. But the inlet area is based on the valve area, not the rpm range. If you start looking at 4 valve engines, they almost all have the same size valves compared to their bore (around 40% of the bore diameter) because you can only physically fit so much in and all the designers (our GS's included) made the valves as big as possible in the first place. The rpm range is more based on the inlet and exhaust lengths and cam details (specifically, time-area of the valves) than port size. The inlet is sized to provide a smooth, mostly constant area duct to allow for the optimal pulse tuning effects. Flow is a detail issue that is achieved with careful design of the correct size duct.

I think it translates to all high performance 4 valve engines myself.

To know more, start reading. If anybody wants a copy of the article I mentioned, PM me and I will mail it to you.


Mark

[Big Jay]

I just check my 82 1100 16V head and at Horizontal I get 1.285 but at Vertical I was getting 1.300. Must be alittle egg shaped

This was right at the tip of the intake if I went in farther the hole is getting smaller.

For 27.5mm valves, this gives me a inlet diameter of 38mm, so the GS is quite a lot smaller than that. There isn't any room to change that, either, is there? Not 5mm worth of diameter anyways...


Mark

It is being done, but it is very expensive. The intake ports are machined off and new large billet ones are installed.

Jay

[RacingJake]

The 1150 head is still at the machine shop, but when it gets back I'll measure the intake's. I do know that they are bigger than the 1100 head.

There's alot of material you can still remove from the 1100 intake's, I'd say between 1/16 to 1/8 all the way around.

Here's a pic of both heads, can you tell which one is which

[mark m]

The 1150 head is still at the machine shop, but when it gets back I'll measure the intake's. I do know that they are bigger than the 1100 head.

There's alot of material you can still remove from the 1100 intake's, I'd say between 1/16 to 1/8 all the way around.

Here's a pic of both heads, can you tell which one is which

Thanks for the help, Jake. There does appear to be enough material on the 1100 to get near where Blair says it should be. I re-did my calculations using the ID of the seats instead of the valve head OD and that gives me about a 35.5mm port inlet diameter, which looks to be easy to get to in your pics.

The second part of the job is sticking the head on a flow bench and playing with modelling clay to see where the dead flow areas are and how to increase flow without hogging things out to a ridiculous size. I have been talking to a very knowledgable tuner who uses filled ports extensively and he has mentioned that he generally sees more flow increases (yes, he INCREASES flow by making the ports smaller) from filling the exhaust port than the intake port, but that both produce significant power gains.

Related question - is it cheaper to take an 1100 head and install 1150 size valves and seats or just find an 1150 head and run that? Given that it looks like I can get the "correct" inlet port area from either one, that is.


Mark

[RacingJake]

I'd go with the 1150 head if you had a choice and just run it stock.

By the time you buy new valve's around $300 and pay for the work $300 plus you might be able to find(may take alittle time) a good 1150 head for around $400.

Or maybe just go for a good port job on the 1100 head $300-$400.

Or even go for carbs and cams and a good exhaust. Don't you just hate the power drug. I know I do.

[mark m]

I'd go with the 1150 head if you had a choice and just run it stock.

Well, I would feel the need to work it over, too. But it has the bigger valves to start with and they are the limiting point for flow.

By the time you buy new valve's around $300 and pay for the work $300 plus you might be able to find(may take alittle time) a good 1150 head for around $400.

Good to know. I will just keep my eyes open.

Or maybe just go for a good port job on the 1100 head $300-$400.

The porting I want to do myself, it's the bigger valves I would like to have. But it is always cheaper to start with what I have...

Or even go for carbs and cams and a good exhaust. Don't you just hate the power drug. I know I do.

No, you LOVE the power drug, not hate.

Remember, MORE = BETTER

Thanks,
Mark

[RacingJake]

Got the 1150 head back and measured it. Intake from left to right was 1.402 and up and down was 1.387. How this head has been clean up some so I don't know how far from stock it really is???