Hi all,

I've been doing some research on a proposed engine spec and wondered if anyone had and information on valve to valve contact with +1 valves in a VVT or MK2 head.

FM seem to say fitting +1 inlets is a bad move on VVT (I assume due to the valve swing allowing valve/piston or valve/valve contact).

I'm keen to run +1 inlets and + 1 exhausts with some custom cam profiles, but before I order valves any info would be great.

If not then any insight into possible issues with VVT and +1's would be great!

Thanks,

Daniel

 

in for results.

 

Depends on piston dome profile, how much the head has been shaved over the course of its life, and the exact cam profile. If your cams are custom, nobody will be able to answer these questions except you.

 

Whilst I get what you're saying Sav based on a stock head valve to valve clearance/contact data will be the same. Piston top clearance is another issue.
Just looking to get rough ball park so I can start working some camshaft profiles.

I want to find if having +1 inlets and big cams will cause too much of a compromise to make the VVT worth while running or if it will need some limit stops adding to the actuator. From memory the VVT has a 40degree swing on it and looking over some profiles, I'd usually look at a 264 @ 0.1mm / 232 @ 1mm inlet cam. Running the VVT should help with drivability but I'm sure you can understand that a 40 deg swing could come into some valve/valve interface issues!

Having valve to valve contact data will allow me to model things better rather than running on "theory".

Take care,

Dan

 

No valve to valve contact on my setup over the whole VVT range, but not more than 24 degrees of advance before the valve-piston get too close for comfort.

Build the engine you want and restrict the VVT movement at the end, after measuring a huge number of times...

Just one note; Stock VVT intake springs are soft, so there are more to do than just cams and valves.

 

I build and tune MX5 engines here in the UK but not touched the VVT stuff yet, most customers preferring to stay with a stock MK2 head.

+ 1 valves it is then for a measure up, I'll post all my findings when done for future reference.

Dan

 

Dan, ill be interested in what you find.

When I eventually build the vvt I have in the garage, I'll be popping down to you for the mapping.

 

Any further info if +1intake valve would have valve to valve clearance issues with vvt full advance?

 

Lots of factors to consider, most of which were covered by Savington above ^^^

I'm running Flyin Miata +1 inconel valves with Supertech 8.7:1 comp pistons, stock cams and my engine is now interference. My block was decked a small amount by my machine shop, can't remember how much though. Head was never shaved/decked.

I read about a test on here where a user timed the engine with the intake cam advanced three teeth to simulate full VVT advance, then rotated it through two cycles to check for interference. My engine had no piston to valve contact while doing this test and my max advance is 30* (out of max 47* available by the phaser) so I ran it and haven't had any problems.

Obviously take this test with a grain of salt as your rods are going to be stretching while the engine is running and there's a slew of other factors involved versus testing for clearance on a cold, not running motor.

 

Valve to valve there really arent that many factors. just Degree of advance. I guess yeah ill cut and clamp a belt and test three teeth of advance.

 

Yes. I was just saying that you're probably going to have a little less p2v clearance on a hot, running engine than you will while hand rotating it on the stand.