Biggets possible inlet valve in Nord 1600 head?

[rogga2]

Hi

I have a Nord 1600 engine. I need to renovate the engine head. I am planing to change valve guides and to modern valve seats.

I read at some place that its possible to put in inlet valves from a 2000 engine where the diameter is 44 mm (41mm original on 1600)?

Does someone have that answer? Is it possible or what is biggest possible diameter?

Best Regards / Roger
Sweden

[Gordon Raymond]

Hello Roger,
The port, valve pocket design and many other factors conspire to make the biggest valve, not the best. While it is, in theory, possible to get a 44 mm valve in there, the seat must be made 44 mm od. as well, this puts you close to a water passage, and the edge of the chamber, (not good). Also, now the pocket needs to be made larger as well. Same problems here. Finally the runner needs to be re profiled with a more upward slant. This is the least of the problems. Now you need custom, forged pistons, to clear these valves, and a 1 mm overbore to 79 mm gets the valve away from the edge of the piston. The design of this head, because of the angle of the runner, and the turn at the pocket, has proven, over the years, that 41+, 42- mm, with a proper racing design seat, can flow all the mixture the bowl, port, cam and displacement can deliver, without going to turbos or supercharging. Moreover, a 44 mm stainless valve is heavy. I have gone to titanium valves for all these engines. The cam, follower and seat wear with heavy valves, like the 44 / 45 mm in GTA's at high rpm quickly educate one to the advantages of light valve gear, or smaller, multi valve designs.
Rather than go big, use a well designed seat, bowl, combination with 41 mm valves. Spend your money on good cam design for the engines application, (street, race, high rpm Hp. or low end torque) and you will be much happier. Just my opinion. Gordon Raymond

[rogga2]

Thanks Gordon for your great answer. I have decided to go for 42,5 mm inlet valves with modern 45 deg seats and opened ports.

I have a follow up question when I am continuing to the bottom of the engine. I have posted a new thread for this question. “ Biggest possible overbore in a 1600 Nord engine ?”

Best Regards / Roger
Sweden

[Gordon Raymond]

Hi Roger,
You will discover there is much to be gained by a racing type seat, either triple angle, 30 / 45 /60 or carried further to almost a radius type. The idea is to shape the seat like a funnel, with a fairly narrow contact area. If you PM Alfar7, here on the BB, he may have a photograph of this type seat. I have one cut 40+ years ago I will try to post here. Wish me luck! Gordon Raymond

[rogga2]

Quote:

Originally Posted by Gordon Raymond Hi Roger, You will discover there is much to be gained by a racing type seat, either triple angle, 30 / 45 /60 or carried further to almost a radius type. The idea is to shape the seat like a funnel, with a fairly narrow contact area. If you PM Alfar7, here on the BB, he may have a photograph of this type seat. I have one cut 40+ years ago I will try to post here. Wish me luck! Gordon Raymond

[Alex]

Gordon,

Some great posts this evening both here and in the other thread, thanks for sharing your wisdom! And photos too! Worth a thousand words

Interestingly, you seem to have a regular single electrode spark plug in that big valve engine you show above. A couple of quick queries - I would guess that you index your plugs as a matter of course with carefully ground washers? Assuming that that plug has been fully screwed in my intuition tells me that, with the plug orientated this way so that the inlet charge doesn't clearly 'meet' the electrode spark. Has this been done on purpose for flame front or potential valve lip contact issues? And I'm guessing there's a good reason why you didn't use a Lodge-style plug ...?

Cheers,

Alex.