Advices to rebuilt engine

[Olympicblue]

Hello to every body,

I am actually rebuilding my Twincam.

The cylinder head is an early type with weber and the bottom end is a genuine bottom with 6bots crankshaft. It is to fit in an road Elan S2.

I want to obtain a good torque at low rev and around 135bhp as power peak.

Some people advise me a QED Q420 camshaft.

Could you advise me what kind of valve, seat, valve guide and spring will match with my configuration ? Do I need to enlarge ports ?

Thank you in advance for your advices.

Damien

[rgh0]

The QED 420 cam will give you the sort of power you are looking for and is a good choice. You want a cam with around 0.42 lift and 280 degrees seat to seat duration which is what the Q420 is. If you look through the cam suppliers catalogues you will see other cams of similar specifications.

QED can also supply the spring pack to suit this cam in road use (Q55 springs).

There is no need for extensive porting or larger valves if your target is 135 hp. The standard big valve spec inlet and exhaust valve size is sufficient. Keeping the valves and ports relatively small will improve low end torque at the expense of a little top end power. The Q420 will produce around 150 hp in a well ported head with 1.625 inch inlet and 1.4 inch exhaust valves at 6500 rpm. The only port work really needed for your 135 hp specification is to clean up any obviously excessively rough bits of the original casting in the ports and to ensure the carb and exhaust ports match properly.

When installing the higher valve lift set up such as the Q420 you need be careful to ensure the valve spring install height is correct otherwise you get insufficient load on the seat ( you want around 70lb) or you risk coil binding on full lift. This means the valves need to be correctly positioned in the head. If the valve seats have been excessively cut or incorrectly positioned they may need replacing.

You want around 10.5 to 1 compression ratio. You probably have that already as most heads have had enough machining over the years already to reduce their thickness down to around 4.60 inches that produces this compression ratio with standard block / crank / rods and pistons. You want to check that the valve cut outs in the pistons are sufficient size that the valves don't touch the pistons near top dead centre.

A good large bore road exhaust system, 34 mm chokes in the Webers and a Dyno run to set up the carbs right will also be needed. You also may need to change the ignition advance curve depending on what you have now.

cheers
Rohan