Bonneville head cylinder

[KL.KL]

Hi all,

I've been searching info about motorcycle head porting as I looking to do headwork for my Triumph Bonneville -04.

The bike is for street use and most of the time I ride low and mid-range rpm's. I'm also doing big bore kit that raises cc form 790 to 904cc. What steps I should take to increase power and torque on low and mid-range rpm's?

There is a ton of information and different theories about head porting, what I have gathered of this subject:

-Bonnevilles cylinders are big and therefore big valves and large intake/outtake ports are essential for optimal function
-Small and reshaped ports for good air/fuel velocity

Any tips and comments are welcome!

thanks in advance.

[Rubin215]

Porting a cylinder head really isn't something you want to try yourself if you've never done it before, it's not a simple process.

Better to look online for performance engine workshops, give them a call and ask their advice.

[tezzer]

Sell it any buy a T120, the 1200cc motor in mine gives it a whole load of grunt.

[tvrolet]

I can't decide is this is a wind-up or not. Who decides to embark on DIY porting without a deep knowledge of the subject, probably without access to all the tools (inc flow bench) and having not seen it done before. But hey, I'll bite.

But first, remember power is just torque x revs. So if you make, say, 50 torques at 4000RPM and you can make the motor spin to 8000RPM and still make exactly the same 50 torques you've doubled the power. And this is the basis of all race/performance tuning - get the torque higher up the rev range and get the motor revving higher since you will be gearing it down anyway. But for a road bike where you want to feel low-down grunt conventional tuning to raise the 'top end' power will often reduce torque (and hence power) lower down the range. This is particularly the case with big cams with lots of overlap which run great at high revs when the intake air is barrelling down the ports with lots of momentum and similarly the exhaust is wooshing out the exhausts...but big cams at low revs turn the engine into a right dog. And so with porting - if you optimise the flow for high-speed airflow and scavenging, slower airflow at lower revs doesn't 'suck' or 'blow' as well - hence the well worn (but usually true) tale of smaller ports/carbs/intakes giving more torque at low revs.

So the sure-fire way to get more torque at lower revs is to increase the capacity. Anything you do to the heads will make very little difference in comparison; you'd probably get more impact from a decent tuned exhaust as opposed to head work. Look at different cams maybe, but don't automatically choose the cams that make the most power, as typically that's as a result of moving the torque higher up the rev range. Is an 04 Bonnie fuel injected? If so, look at a remap - factory maps are usually pretty conservative to get through emissions etc. ...or just buy a bigger bike

[cock waving]

KL.KL said:

Bonnevilles cylinders are big and therefore big valves and large intake/outtake ports are essential for optimal function

call that big? I've more capacity in one cylinder than the pair of yours If you want torque at low revs, go big.
[/cock waving]

[black-k1]

tvrolet said:

call that big? I've more capacity in one cylinder than the pair of yours If you want torque at low revs, go big.
[/cock waving]

There ain't no substitute for cubes!

[ash reynolds]

The older T100 has cams available now which give power gains. A custom map with the obligatory de-cat is always a good idea.
Have a look here: https://www.youtube.com/watch?v=hRk6x_u3mBI

[Tango13]

KL.KL said:

Hi all,

I've been searching info about motorcycle head porting as I looking to do headwork for my Triumph Bonneville -04.

The bike is for street use and most of the time I ride low and mid-range rpm's. I'm also doing big bore kit that raises cc form 790 to 904cc. What steps I should take to increase power and torque on low and mid-range rpm's?

There is a ton of information and different theories about head porting, what I have gathered of this subject:

-Bonnevilles cylinders are big and therefore big valves and large intake/outtake ports are essential for optimal function
-Small and reshaped ports for good air/fuel velocity

Any tips and comments are welcome!

thanks in advance.

To be honest you're probably wasting your time trying to improve the standard ports. Triumph would've spent a shed load of time and money getting the porting just right. You're not going to gain much with a bit of diy dremmel action in your garden shed and there's a good chance you would make things worse.

A well set up Wiseco 904cc kit should give 85bhp & 66lbs/ft of torque, if you go for the big valves and hotter cams you'll see a bit more but I've heard they can be a bit of a pig for road use.

Have a look on some of the Triumph specific websites for more information.

[Wacky Racer]

I can't see why you are bothering tbh, unless you just enjoy tinkering, any power gains will be minimal and you MAY make things worse if you don't know what you are doing.

Good luck anyway.

[catso]

A good head gasflow can make a significant difference. I had the heads on my 916 ported/flowed by CJS racing; http://www.cjsracing.co.uk/ and it gained around 15hp at the top end and with significant extra surge through the entire range.

However, you need to know what you're doing as just opening things up or polishing ports may actually make things worse and I have no idea how responsive a Bonneville engine is to tuning?