400 Darts

Jem · Post by **Jem** » 02 Jun 2009 20:37

MY understanding is that most 400cc Darts were aimed at the German market and although bigger capacity had smaller valves to limit the power as well as a softer cam. What size are the valves?
I have a 400cc engine with standard Sport/Strada bottom end and 66mm bore Gilardoni barrels. I don't know where the heads came from. The inlet valve is 30mm and the exhaust valve is 23mm. Are these the small valve 400 german heads or standard 350 heads?

corsaro chris · Post by **corsaro chris** » 03 Jun 2009 15:30

I thought that it was the Japanese market as the headlight dips to the left...

The 350 Dart certainly revs better than the 400, although the latter has one extra claimed BHP...

CC

EVguru · Post by **EVguru** » 04 Jun 2009 09:36

It's a little hard to get to the bottom of the 400 engine details (even worse for the AMEX version!). The valve sizes for the stock 350 are quoted at 30.5mm inlet and 22.5mm exhaust on the www.morinispecial.it site.

I recall Alex saying that the 400 had a bigger exhaust valve, but a more restrictive port. I thought they might have achieved this by using the 250 exhaust port core, but I recently took measurements off a 250 head and the ports are the same. Even the valve seat insert is the same, but a smaller seat machined in.

A German article describing a 400 converion using machined VW Lupo pistons listed the 400 valves as 31mm and 25.5mm, but those are the 500 (478cc) sizes and 500 Heads would probably make a good upgrade for a tuned 400. Valves and ports that are too big will rob you of low and mid range torque and won't give you better top end if the cam doesn't match.

At some stage I'll have my gas flow bench up and running and I'll be able to do some proper cylinder head testing.

mantaray · Post by **mantaray** » 16 Jun 2009 10:30

A few days ago exhaust-nut of the Dart destroyed the head.

The engine was never opened before and this is what i found

Valvesizes Dart 400

Jem · Post by **Jem** » 28 Jun 2009 19:16

My rough measurements of the valve sizes for my 350 heads is 31mm inlet and 23 mm exhaust which suggests that the 400 had the same heads & valves as 350s.

In addition, the 400cc pistons have a full circle top rim unlike the 350 pistons with their cutaways. Bigger valves would need the pistons machining which would reduce the compression ratio although omitting the 1mm thick base gasket might bring compression back up.

EVguru · Post by **EVguru** » 28 Jun 2009 20:58

I don't remember my 400 pistons having a different valve cut-out design.

Are you sure yours are 400 pistons, not 375, Jem?

350 is 62mm bore.
375 is 64mm bore (special oversize available from Vertex).
400 is 66mm bore.

All of the factory 400 barrels were Gilardoni (Nickel/Silicon Carbide plated Aluminium). I think all the factory 400 barrels were square finned too.

Jem · Post by **Jem** » 28 Jun 2009 21:20

definitely 400cc.

Bore is 66mm, barrels have Gilardoni cast on them, and they're square finned, matching the finning on the heads (had to take the engine out to fit the barrels).
The pistons have a complete perimeter with a circular combustion chamber casting; into this there are two machined cutaways for the valves but they don't break the perimeter (I should have taken photos but I'm not lifting the heads now!). 350 pistons, in contrast, are cast with breaks in the perimeter so that the edge of the piston crown is lower where the valves operate and is not continuous.

Tomorrow's run to Cassington will prove how good the motor is.