Fast Road Use - What Improvements can I make?

[Dag-Henning]

Dave, - you are right, - a lightened flywheel will definately make your engine respond quicker in neutral. The positive effect on your car's acceleration however, will be near zero.

Dag

[bill308]

I believe Dave is correct in his assessment. Power no longer needed to accelerate the flywheel becomes immediately availble to the rear wheels. Ultimate top speed will not be affected, because at this point, one is no longer accelerating, merely overcoming drag and rolling losses.

The other thing is that the flywheel represents only a fraction of the rotating inertia. The clutch itself is also a significant inertia load. The key is not to go too exteme as some total flywheel effect is still desireable. Having said this, most twinks will have more that enough low end torque to react favorably to a low inertia flywheel. If the engine is tuned expressly for high end horse power, the car is particularly heavy, the gearing is particularly tall, and the engine has poor low end torque, then perhaps a low inertia fly wheel doesn't make sense. Typically, a race engine will give up a good deal of low end torque for ultimate high rpm horse power. If used on the street, with a low inertia drive train, I can see where there could be an issue. On the race track, this combination can be tolerated, because you are not likely to accelerate from a stop, except at the start or when leaving pit lane.

My experience has shown positive results. I do not suffer from excessive clutch wear nor is undue skill required. Starting from a stop gong uphill needs to be approached with a little more skill, but should be within the realm of a rasonably competant driver. When I build up my next engine, with a 6-bolt lip seal crank, I plan to go to a higher lift cam with modest duration, that may sacrifice some low end torque, but I feel that I will still have more than enough low end torque to accomodate the low inertia flywheel under all conditions. I think this is not a high risk modification for most Lotus owners. Consider your particular situation and if it makes sense, go for it.

Bill

[steveww]

All this tolk of engine modification but no one has mentioned brakes, suspension etc.

A good mod for the brakes is to remove the servo and fit +2 front disks and calipers. Adjustable dampers and springs are also a good idea.

Back to the engine. Flowing the head is a great way of getting some extra power and can be done for little cost if you do it yourself. All you need is an electric drill and a couple of tungsten carbide burrs. For a bigger improvement use a tall block and increase the capacity.

[carrierdave]

Thanks for all of your comments. I was thinking about opening up the exhaust side of the head myself! Any comments? What things should I avoid (or is this one of them?).
What about the proximity of the waterways, how much can I take out without compromising them.

Any thoughts?

Dave

[rgh0]

On my competition heads the exhaust ports and exhaust valve throats are both opened out to 1.26 inch (32mm) with 1.4 exhaust valve head. The Dave Bean catalogue provides similar values for its developed stage 3 and stage 4 heads. The exhaust side needs much less port work to retain the appropriate flow balance with the inlet as you develop the head.

Rohan

[steveww]

You should also fit larger diameter headers (manifold) to maximise the exhaust flow. There is quite a bit of torque lost in the standard headers. The TTR system is good if a bit pricey. I am looking to see if I can get one custom made for less.

There is a lot of scope for improvement of flow on the inlet side although the long ports make it a bit more difficult to work on. The area behind the valve seat can be opened up and the radius improved. Pay particular attention to the short radius.

If you are in the UK and do not fancy doing the head work yourself and you want a proper job done then contact http://www.dvapower.com/

[carrierdave]

Thanks Rohan and Steve; I am in the UK (Kent) so Milton Keynes is not that far from me.
One other question ? What is the largest diameter inlet valve I could use without changing the valve seat. (I have a standard valves at the moment). Someone told me that I could use the big valve valves without changing the seats just by re-cutting the seats! Is this true?

Finally on the intake side would you keep the surface finish as smooth as possible or would you leave it rough to create turbulence?

Thanks

David

[steveww]

There is only 1mm difference between the standard and the big valves. I just recut the standard seats.

After reshaping the inlet/echaust tracts with the burr you need to smooth things out with a spirawrap. Best to leave the surface rough as this helps with reversion. You need to pay a lot of attention to the area around the valve seat in the combustion chamber. It is worth polishing up the combustion chamber with a cross buff.

If you want to have a chat about this PM me and we can arrange a call.

[john.p.clegg]

You can fit 1.625 valves in the original seats(I have)
John

[rgh0]

David

As John said you can normally fit 1.625 inlets on the standard inlet valve seats. I have 3 heads set up that way.

Rohan

[carrierdave]

Thanks John & Rohen,

Looking at the head today, the valves are very close to the edge of the head cavity, if you enlarge the valves do you need to remove some on the material either side of the valve to maintain the shape or would you just cut the seat and leave it?
Obviously you can see from the head gasket the actual compression area, which some distance away from this.

Thanks

Dave

[steveww]

Depends how much the head has been skimmed. The current head on my twinc has had its last skim now. With big valves installed the seat is with in a whisker of the head surface. You can measure the thickness of the head and compare it to the standard specs.

[john.p.clegg]

Dave
Two ways to do this,you can get new seats,drop them in a lathe and take some meat off the inside diameter,and then install them,blending the ali into them or if you are really handy make up a tool with a cutter of whatever diameter you want the seats to be with a centre using the valve guide.....
The seat contact on the inlet does not have to be as wide as the exhaust as there is less heat to dissipate....just so long as it seals

John

[forfenderjazz]

When you lighten a flywheel you gain in terms of quick acceleration, however you are losing torque as your rotating mass is reduced. Torque is what gets the job done for the street. If you lighten too much you will have a fast revving engine that can't even climb a slight hill without downshifting. Race cars and street cars are two different animals. For road use you may want to be careful about lightening too much, I think this is what Dag is pointing out. Roy

[rgh0]

Steve / Dave

It is quite practical to have the valve seat overlap the head face and have the lip of the valve protruding above the head face. I have a very successful race head that does this.

I would not throw a head away because you have machined a little of the edge of the valve seat when you mill the head.

Rohan