TheSamba.com :: View topic - 1972 VW Bus

Sat Jun 22, 2024 3:01 pm

I'm in the process of setting my valve geometry now, starting on intake side. 1972 VW Bus, 1.7L Type 4 Engine.

I know these things vary based on everything in the engine and the case etc etc. But was hoping to run my numbers by someone to see if it seems reasonable.

I've got 1.05" shims under my rockers (running swivel adjusters) and getting exactly 0.455" lift and decent geometry at 1/2 lift on the intake.

When I jump to exhaust side, best i can get is 0.423" lift. Wondering if that would be acceptable? Its about 7-8% off of what Scat defines as max lift (0.455").

If not, would the next move would be to adjust the shims again? Seemingly increase them yet further. And restart at intake and then exhaust.

Thanks

Sat Jun 22, 2024 3:47 pm

not a Scat Camshaft expert, but if the limit is .455", you will also be working with the clearance, or growth, of each valve. Intake & exhaust.
The intake & exhaust clearance is different, seeing as the intakes are exposed to fresh charge of air & fuel. Whereas the exhausts get bathed in heat & grow a bit further when at operating temps.
This stuff won't show up during a static check with valves at room temperature.
But it will once the engine is fully warmed.
Max lift is important on the intake charge, not so much on the scavenged exhaust cycle, with valve overlap helping to evacuate the chamber.
I recall seeing matched lift camshafts somewhere, but most are biased to higher lift on the intake, less on exhaust.

Sat Jun 22, 2024 5:19 pm

Hey Tim,

Thanks for the reply. Yeah i am aware of that expansion, hence why i aim for the specs. I do anticipate exhaust to be lower then the max lift, just mostly concerned with the allowable Delta.

Worth noting, on Scat website (link below) the indicated lift for the C25 mentions 0.455".

The same, apparently, cam elsewhere seems to call for 0.430" (for example on ACN). Anyone have experience with this particular camshaft and can confirm one or the other.

Given that i do achieve 0.455 so I'm guessing that's the correct one, but i guess its worth bringing up.

https://scatvw.com/product/type-iv-camshaft/ ---> 0.455"

https://www2.cip1.com/c15-20086/ ---> 0.430"
https://vwparts.aircooled.net/SCAT-C25-Type-4-Camshaft-1-3-1-Rockers-20086-p/20086.htm ---> 0.430"