1835 speculation

[Flyguyeddy]

Ok lets pretend for a minute that im considering building an 1835.

If i were to build such a thing, it would be a press fit job and id probably use a skat crankshaft. I dont have a factory crankshaft and i like the large radius fillets on the scat cranks.

The 044 heads available are somewhat large valve heads. Id like to retain the 3/4” deep spark plug threads. Is the size of the valves a problem for the smaller engine?

 

[Chucker]

Big valves work best at high flow rates... which equates to high RPM (5000+). Smaller valves keep the port velocity higher at lower RPM (in the region we operate). I don't have a flow bench but there are online calculators that will give you the optimum port diameter for your displacement and peak RPM. You can do some arithmetic (and geometry) to compare the area of that port size to the area of the open valve. I chose to stay with the stock valve size because I believe it provides better port velocity at 3000-3400 RPM. The VW engine builder I used for my machine work agreed. I have an 1835 sitting in the corner of my shop. It has single-port heads. When I build that engine I intend to retain those heads for both reliability and performance. For an efficient intake system, keep the mixture moving as fast as possible without creating excess drag and pressure loss.

My 2 cents. Talk to someone who builds VW engines for sand rails. They use a similar power band.

All the best,
Chucker

 

[Flyguyeddy]

The problem with using single port heads is you wont buy any good ones that are new, and ive been told they will not take a 92mm cylinder without becoming very weak. The 40x35 valves on the 044 heads are about as small as i can find to use with a new head that will take a 92mm bore AND has 3/4 reach plugs.

 

[Flyguyeddy]

https://vwparts.aircooled.net/ACN-Stocker-Plus-Dual-Port-Cylinder-Heads-35-X-32-p/l3-heads-pair.htm

These might do. Stock size valves