Retard Intake/Advance Exhaust Timing

1969 Views 1 Reply 2 Participants Last post by Alfar7, Oct 23, 2007

Ish-Man

Discussion Starter · Oct 18, 2007

Well, completed the swap of my "skimmed to the valve seats" head with a near stock unit (thanks to Alfa Parts, San Francisco for sourcing a great 1300 head and factory sodium filled exhaust valves), and a bunch of nettlesome issues simply went away! I've lost a bit of power with lower compression, but the driveability is worth the exchange.

To give you an idea of how close the tolerances were, there were places on the 1400cc wiseco pistons in the shape of each valve, where no carbon formed at all. No nicks present on the surface, but there was no room for error to be sure. Talk about tight squish areas.

The new head was chamferred for clearance of the pistons at the edges, and at the advice of my engine guru, Tom Turner in JAX, we retarded the intake slightly, and similarly advanced the exhaust... to provide a bit of further comfort with the domed, higher compression, wiseco pistons. A bit more clearance with a bit more overlap.

I'm interested in racers impressions about this technique, as I remember this effective increase in overlap as a method of motor set up for road racing. Probably not better for emissions, but possibly a means of increasing gas flow?

It's great to be driving the little Nuova Super around with a smooth idle, better gas mileage, and a more melodic exhaust note.

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Alfar7

· #2 · Oct 23, 2007 (Edited)

Cam timing

To give you an idea of how close the tolerances were, there were places on the 1400cc wiseco pistons in the shape of each valve, where no carbon formed at all. No nicks present on the surface, but there was no room for error to be sure. Talk about tight squish areas.

The new head was chamferred for clearance of the pistons at the edges, and at the advice of my engine guru, Tom Turner in JAX, we retarded the intake slightly, and similarly advanced the exhaust... to provide a bit of further comfort with the domed, higher compression, wiseco pistons. A bit more clearance with a bit more overlap.
I'm interested in racers impressions about this technique, as I remember this effective increase in overlap as a method of motor set up for road racing. Probably not better for emissions, but possibly a means of increasing gas flow

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The outline of the valve on the piston is really not uncommon.
The cam movement (retard Intake/advancing the exhaust) that Tom ("Don`t call me Dickie") Turner did on your motor did not create more overlap, but less. However it does increase valve to piston clearance if close, and it will increase the length of the power stroke improving torque.
Because of the slow ramp design on stock & typical aftermarket street cam, advancing more than a couple of degrees usually results in more loss from overlap than gain.
Ask "your Guru" Turner about his "electrical problem" with the EP car at Roebling Rd. (the #4 rod knocked the starter off!

)

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