Lemans 1 Head Specs

[eether54]

OK, I am building a t3 based cafe bike and was wondering if anyone out there has the specs on the Lemans 1 combustion chamber. I have pretty much given up on finding Lemans heads so am left with modifying the t3 heads I have. Any help in this area would be greatly appreciated. I am thinking about going with the x8 cam, bored to 950,with dellorto 40's.
Thanks!

 

[Chris R]

The lemans head uses the same casting as the T3. Same part number on the casting.
Easy if you have a CNC mill with a modern controller.

The combustion chamber is perfectly hemispherical and is the same radius just machined 3mm deeper. The seats are marginally bigger - in fact a modified T3 inlet will flow better than a lemans. THe lemans performance IMO mainly comes from increased compression and the 36mm carbs. Also the spacing for the intake is slightly different. The T3 head is IMO a better starting point if you want to develop a racing head as it allows you to modify the short turn radius more easily. Big is not alway better.

Ta,

Chris R

 

[eether54]

Thanks for the reply! So, you are basically saying that it would be just as well to stay with the small valves, and pay more attention to the ports? C/R will be about as high as you can go on pump gas, in addition to dual plugging it.
Thanks

 

[Chris R]

What it boils down to is what pistons you are going to use - if you go for the lemans pistons then you have to sink the combustion chamber a little bit deeper to accomodate the higher dome. The compression you choose depends on the fuel that is available.

The guzzi really responds to having a tight squish - like 30 thou. Tight squish greatly reduces detonation which is a problem. Twin plugging IMO also greatly helps with curing detonation on the round heads when you push the compression envelope. You do have to modify the curve to suit. In my experience you can retard the timing by 6 or so degrees which indicates it is helpful (I did check this on a dyno so it is not a seat of the pants opinion)! Fuel quality will only go down in the near future so making an engine that doesn't detonate is a great advantage.

I highly recommend you use nicasils if available - Gilardoni lemans kits have become somewhat short in supply of late. If it is a choice between a T3 with nicasils or a lemans with iron bores I would pick the nicasils every time. The nicasils run a lot tighter and will outlast you!

As to valve sizes - the extra 2mm of the lemans does not produce more flow with the stock inlets! So yes stick with the small valves! And yes if it is your fancy do port work - a crude flow bench with just a manometer and vacuum cleaner (it is critical that the head be mounted on the cylinder) can tell you an awful lot. You do not need a calibrated flow bench as you are looking for improvements not comparing your results with other people. Otherwise just taper the inlets to fit the 40mm dellortos. 40 is workable but maybe pushing it a little from the part throttle perspective. I would probably go with 36s.

I think the X8 is really not the best pick for a street bike - it won't idle sweetly and will drive you nuts when you are forced to toddle around town in traffic. it will require sinking valve cutouts into the piston. The x10 is probably the most livable. The megacycle is the best bet - it is billet not a regrind. I have not seen a lot of success with welded on and reground cams. Do replace the followers or have them reground - they all seem to pit (albeit without causing damage).
I think Todd does resell megacycle and DLC coated followers so you might contact him and ask him his thoughts. IMO timing gear do not produce any measurable improvement in performance and sometimes self-destruct (no flame wars here please). The aftermarket tensioners work fine.

All the other trick parts - steel pushrods, titanium valve retainers, etc. do produce marginal improvements but at significant cost.

Replacing the starter with a valeo or mitsubishi and fitting a smaller battery can drop 30-40 pounds which will have more effect in performance, handling and reliability IMO.

Clay everything and check tolerances before you run the engine.

The other major mod is to lighten the flywheel as much as possible. I find this is the single greatest improvement to the guzzi after fitting nicasils. Do not reuse the bolts attaching the flywheel to the crank. Again if you are local Todd and his merry men do seem to do a nice job and given that they can be a bear to machine (I ate a number of cutters doing mine) not a bad price at all!