engine upgrade

[hansaxl]

Hi!

As I will have to take the engine out this winter, I am considering an upgrade. The engine is a normal spec S/E one, in good state, with +60 standard cast pistons fitted a few months ago.

I think I want to go the "420" route, so that requires the cams, springs, followers and longer valves (is that correct?) and porting of the head, of course. Then, CR has to be increased to about 10.5:1. Here's the question: If I want to achieve this by skimming the head, as it is done in the big valve engines, do I not run into the risk of the valves touching the (still standard) pistons with the higher lift?? I would certainly like to keep the bottom end as it is, as it runs very nicely, is quite freshly done, well balanced, and I do not intend to use more revs than, say, 6000.

I would appreciate any advice on this matter very much.

Cheers, Hans

[billwill]

My pistons have notches for valve clearance.

My engine was converted to big valve from standard many years ago.

[rgh0]

The cutouts in the piston will need to be deep enough and big enough in diameter to accomodate the larger valves and higher lift on overllap of the QED 420 style head.

The standard pistons cutouts size varres depending on the source of your current pistons. They may be deep enough but are unlikely to be big enough in diameter to accomodate the bigger valves

I am sure QED could advise you of their specific requirements.

I would not skim the head before measuring up the actual compression ratio you have with the pistons you plan using and the bigger valves fitted in the head and combustion chamber sioze measured and a head gasket of known thickness selected. You may want to consider new pistons with a small intruder if needed versus skimming the head. I try to not take metal off the head if I can avoid it.

regards
Rohan

[Foxie]

I want to go the "420" route, so that requires the cams, springs, followers and longer valves (is that correct?)

The valve length will depend on the cam base circle, not on the lift. You will need to check with the cam suppliers.

CR has to be increased to about 10.5:1. Here's the question: If I want to achieve this by skimming the head, as it is done in the big valve engines, do I not run into the risk of the valves touching the (still standard) pistons with the higher lift??

It's possible, that's why you should do a test assembly with plasticene on the piston tops to measure the clearance. You might need to deepen/widen the valve pockets.

You might only intend to use 6000rpm, but whatever limit you set, use a rev limiter

[rgh0]

I want to go the "420" route, so that requires the cams, springs, followers and longer valves (is that correct?)

The valve length will depend on the cam base circle, not on the lift. You will need to check with the cam suppliers.[quote]

Valve stem length is generally set by the spring pack and valve spring retainer detail design. In general a 0.420 lift cam like the QED 420 will need a longer valve spring to achieve the required lift and thus a longer valve stem. This in turn requires a smaller cam base circle and thinner bucket to fit the taller valve into the head

regards
Rohan

[hansaxl]

Hi all.

Thanks for the suggestions. The pistons are Paul Matty "standard" ones. I am sure QED will be able to advise on that. It is also a good point to leave as much metal with the head as possible, you are absolutely right, Rohan. I will certainly test the clearence with plastilin before putting it all together again. May take some time, though.

I actually tested what is called "Kompression" in German, the English expression for which is 'dynamic compression" (?), as I think (the method with the device in the spark plug hole and then turning the engine with the starter at full throttle.) . That was allright, a value of 13 on all cylinders. Is that a specifically good value for an S/E engine, by the way?

Anyway, I will ask QED about this matter soon, and the best advice is always to talk to the community here and then to the dealers, correct?

Cheers, and thanks again, Hans